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Article

Embracing [XY3]m– and [XY4]m– Anions in Salts of [M(bpy)3]q+

by
Edwin C. Constable
* and
Catherine E. Housecroft
Department of Chemistry, University of Basel, BPR 1096, Mattenstrasse 22, Postfach, 4002 Basel, Switzerland
*
Author to whom correspondence should be addressed.
Crystals 2023, 13(1), 97; https://doi.org/10.3390/cryst13010097
Submission received: 24 December 2022 / Revised: 2 January 2023 / Accepted: 3 January 2023 / Published: 5 January 2023
(This article belongs to the Special Issue Feature Papers on "Hybrid and Composite Crystalline Materials" 2023–2024)
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Abstract

:
[M(bpy)3]q+ cations (bpy = 2,2′-bipyridine) are archetypical coordination entities containing chelating bidentate N,N′-donor ligands. Each propeller-shaped cation is chiral, existing as a Δ or Λ enantiomer. The supramolecular chemistry of [M(bpy)3]q+ cations in the crystal is dominated by cation-anion interactions and, to a lesser extent, weaker non-covalent interactions. Analysis of the data for [M(bpy)3]q+ salts in the Cambridge Structural Database (CSD) reveals a ubiquitous motif in which homochiral sheets of cations generate cavities for the accommodation of anions. A series of related and common motifs in the solid-state structures of [M(bpy)3]q+ salts has been identified. One of the commonest motifs comprises a hexagon of six cations with anions either in the center or lying above and/or below the centroid.

Graphical Abstract

1. Introduction

One hundred and thirty-five years after its birth [1,2], 2,2′-bipyridine (Scheme 1, bpy), the “most widely used ligand” [3], remains a key weapon in the arsenal of the coordination chemist [4,5,6,7,8,9,10,11,12]. Although best known as a chelating, bidentate N,N′-donor, bpy continues to delight and intrigue us with new twists and turns in its chemistry. Unusual bonding modes include monodentate, bridging and cyclometallated coordination and the established reactivity patterns include ligand-centered as well as metal-centered processes [13,14]. Furthermore, many “simple” compounds containing bpy and related ligands have been shown to be comprised of coordination polymers or networks in the solid state [15]. 2,2′-Bipyridine and related metal-binding domains have played a key role in the development of supramolecular and metallosupramolecular chemistry.
Although the use of the bpy metal-binding domains in supramolecular chemistry is well-established, the supramolecular chemistry of simple complexes containing bpy and related ligands is less studied. Dance has established the importance of “embraces” involving interactions between aromatic rings in the packing of complexes containing bpy ligands [16,17,18,19]. Although multifold van der Waals interactions and weak hydrogen bonding can result in dominant packing forces in the assembly of crystalline solids, electrostatic interactions are expected to be an order of magnitude stronger.
We have recently shown that a dominant motif in the solid-state structures of [M(bpy)3]q+ salts containing halide anions is the “halide embrace” (Figure 1) in which six homochiral [M(bpy)3]q+ cations surround a halide anion [20]. Our initial studies were predicated upon the importance of short contacts with H3 and H3′ of the bpy ligands; however, we subsequently recognized that these interactions were part of a broader supramolecular chemistry in the crystals containing [M(bpy)3]q+ cations. In this paper, we describe further studies on the influence of cation…anion interactions on the solid-state packing of [M(bpy)3]q+ salts and identify a number of common embraces involving polyatomic anions [XYn]m–. The structural data for this article were retrieved from the Cambridge Structural Database (CSD) [21] (see Section 2).

2. Methods

Conquest (version 2022.3.0 including November 2022 updates) [23] was used to search the CSD [21] for the [M(bpy)3] motif (M = any transition metal; substituted bpy ligands were excluded by explicit inclusion of C-bonded hydrogen atoms) combined with XY3, XY4 or XY5 units in which X and Y are any atom, and the X–Y bond was of ‘any type’. The connectivities of the X atoms were constrained to three, four or five respectively, and the number of bonded atoms for Y was constrained to one.
Analysis of structures was carried out using the program Mercury (version 2022.3.0) [24]. In cases where H atom coordinates were not available, H positions were added in Mercury [24]. All H positions were normalized within Mercury, such that all C–H bond lengths were 1.089 Å. The settings in Mercury for a ‘short contact’ (sum of the van der Waals radii + 0.1 Å) were applied to locate H…Y interactions.
Disordered structures were retained in the analysis. Since disorders often involve the [XYn]m– anions, the contact distances in the discussion are given as ranges for individual compounds, and C–H…X distances are also given since the position of the central atom X is typically unambiguously defined.

3. Defining the Sets of Structures for Analysis

An initial search for the [M(bpy)3] motif with no constraints on charge or counterion yielded 701 hits. Adding a separate XY3 motif gave 25 hits, six of which contained the [H3O]+ ion as the XY3 species (CSD refcodes CINYUV, DIFYUO, JARWOP, QUMCIM, QUMCOS, and TIMYEW). These were excluded from further analysis. Of the 19 remaining, three contained additional molecular motifs which impacted significantly on the crystal packing: [Ni(bpy)3][UO2(H2L)(H2O)]2[NO3]2·3H2O (refcode CUFPUO, H4L = 1,1′-biphenyl-2,2′,6,6′-tetracarboxylic acid) [25], a guanidinium organosulfonate host containing [Ru(bpy)3]2+ with formate ions as the [XY3]– species (refcode RUPGAN) [26], [Rh(bpy)3][Pt(NO3)6][NO3].Me2CO.MeCN.H2O (refcode QUDXIZ) [27]. Two structures from the XY3 search contain both [NO3]– and [CrO4]2– ions (refcodes EHIHUY [28] and XUJDEL [29]) and fall into the discussion of [XY4]m– ions in terms of packing motifs. For [Ni(bpy)3][NO3]2.5H2O (refcode ZZZVRW), no atomic coordinates are available in the CSD [30]. This gave a data set for [M(bpy)3] with [XY3]m– of 13 entries for detailed discussion (see Section 5), which reduces to 12 structures as one hit corresponded to a space group correction for the CSD entry VATHIJ [31].
A search which combined the [M(bpy)3] motif with an XY4 unit resulted in 82 hits. Five contained [NH4]+ as the XY4 motif (refcodes ELIXOP, OMUHIP, QEKCUH, QEKDAO, QEKDES), and three contained either CHCl3 or CH2Cl2 as XY4 (refcodes MOMXAO, SACDOQ, SACDIK). These were omitted from further analysis. Eleven structures were excluded based on the fact that additional molecular entities appreciably affected the crystal packing, or that the [M(bpy)3]2+ ions were embedded in an [M2(ox)3]nn– metal-organic framework: [Fe(bpy)3][SO4⊂L]·9H2O, in which the sulfate ion is encapsulated in a tris(3-pyridylurea) receptor, L (refcode BULLEA) [32], [Co(bpy)3]2[L′][ClO4]·4H2O where [L′]5– is a 4-sulfonatothiacalix [4]arene derivative (refcode NARWEJ) [33], Na[Fe(bpy)3]2[Fe2Sr2Mo12O24(OH)6(H2O)8(H2PO4)2(HPO4)2(PO4)4][PO4]·9H2O (refcode RAXBAV) [34], [Mn32(thme)16(bpy)24(N3)12(OAc)12][Mn(bpy)3]1.5[ClO4]11.11.5MeCN.12H2O (H3thme = 1,1,1-tris(hydroxymethyl)ethane, TAXHEG) [35], (n{[Ru(bpy)3][ClO4]})[MnCr(ox)3]n (refcodes GUNFAW, GUNFAW01) [36,37], (n{[Co(bpy)3][ClO4]})[Co2(ox)3]n (refcode PIMYUF) [38], (n{[Cr(bpy)3][ClO4]})[NaCr(ox)3]n (refcode ZUQVAI), (n{[Cr(bpy)3][ClO4]})[Mn2(ox)3]n (refcode ZUQVEM) and (n{[Cr(bpy)3][BF4]})[Mn2(ox)3]n (refcode ZUQVIQ) [39]. For [Re(bpy)3][ReO4]2 (refcode FEZLOL [40]), atomic coordinates for the Re and O atoms are not available in the CSD, and no coordinates can be accessed for the structure with refcode OFAYIF, although clearly, the [PO4]-unit is part of a Keggin-polyoxomolybdate cage and is therefore not relevant to the present study [41]. Coordinates for [Ni(bpy)3][SO4].7H2O (refcode ZZZKFE) [42] are also not available. The final data set for structural analysis of [M(bpy)3]q+ combined with [XY4]m– was comprised of 61 structures, including several redeterminations (see Section 6).
We note that a search for the [M(bpy)3] motif with an XY5 unit revealed no examples of this combination.

4. An Aside on Chirality

Chirality in inorganic systems is a topic dividing the community between those for whom it is a nightmare and those who embrace its elegance and beauty. Unfortunately for the former group, discussions of the spatial properties of [M(bpy)3]q+ must also consider their inherent chirality. An object is chiral if the object and its mirror image are not identical and cannot be superposed (the IUPAC uses the word superpose rather than the more familiar English word superimpose) [43]. To be chiral, a molecule must have no mirror planes, no centers of inversion or rotation–reflection axes. Any one of these symmetry elements present in a molecule will preclude chirality and achiral objects possess a mirror plane, a center of inversion, or a rotation–reflection axis [44].
[M(bpy)3] coordination entities are chiral and may exist as one of two enantiomers (mirror images). The absolute configuration may be denoted by the stereochemical descriptors ∆ and Λ (Figure 2) [45]. These descriptors are more convenient and easier to visualise than the more general configuration index [45] and refer to a readily identifiable screw axis (Figure 2).

5. [M(bpy)3]q+ Combined with [XY3]m–

Of the 13 structures in the data set of [M(bpy)3]q+ combined with [XY3]m–, 12 involve nitrate ions and one features a sulfite ion. The latter appears in [Fe(bpy)3]2[SO3][OH]4.14H2O (refcode YAWWAY) [46] and provides our first example of an [XY3]m– ion interacting with six [M(bpy)3]q+ cations in the hexagonal motif shown in Figure 3. This defines what we call the Type 1 structural motif. The solid-state structure of [Fe(bpy)3]2[SO3][OH]4.14H2O comprises [Fe(bpy)3]3+ cations assembled into layers separated by sheets of hydrogen-bonded [OH]– ions and H2O molecules. The monoclinic space group C2/c requires that equal numbers of (Δ)- and (Λ)-[Fe(bpy)3]3+ are present, and they assemble into alternating homochiral sheets. Just as in the halide embraces that we have previously described [20], this results in each Type I motif consisting of six (Λ)-[Fe(bpy)3]3+ or six (Δ)-[Fe(bpy)3]3+ cations. Figure 3a,b show orthogonal views of the Type I motif. The twelve bpy H3 and H3′ atoms point towards the [SO3]2– ion, and the CH…O and C…S metrics are given in Table 1. As noted in Section 2, we have chosen to include the distance from the C to the central atom of the [XYn]m– ion because, in many cases, the anions discussed in this article suffer from a disorder of the Y atoms about common X positions.
The motif shown in Figure 3b extends into the 2D sheet displayed in Figure 4, such that all H3 and H3′ atoms (shown in red in Figure 4) of the three bpy ligands in an [Fe(bpy)3]2+ cation are directed into a ‘hole’ in the sheet (Figure 4a) and are available to interact with a hosted anion. The side view of part of one sheet in Figure 4b illustrates that the H3 and H3′ atoms lie within the sheet while the H4, H5, H6, H4′, H5′ and H6′ atoms are located on the top and bottom surfaces of the sheet.
The compound [Zn(bpy)3][NO3][azt]0.5.6H2O ([azt]2– = 5,5′-(diazene-1,2-diyl)bis(tetrazol-2-ide)) crystallizes in a sheet structure (refcode OLOCOI) with hydrogen-bonded [azt]2– and H2O molecules forming layers between the sheets [47]. The [Zn(bpy)3]2+ ions in [Zn(bpy)3][NO3][azt]0.5.6H2O assemble into a homochiral sheet, analogous to that in [Fe(bpy)3]2[SO3][OH]4.14H2O, and alternating sheets contain (Δ)- or (Λ)-[Zn(bpy)3]2+ ions, respectively, consistent with the space group (Table 1). The [NO3]– ions are located in pockets within the top and bottom surfaces of each sheet (Figure 5a). The range of CH…O, C…O and C…N distances and C–H…O angles, and the mean values are given in Table 1. We define this motif (Figure 5b) as Type II. It is also observed in the isostructural compounds [Co(bpy)3][NO3]2.H2O.MeCN (XARPEN, Table 1) [48] and [Ni(bpy)3][NO3]2.H2O.MeCN (YEJKOP, Table 1) [49]. In these Type II motifs, each [NO3]– exhibits short contacts to H3 and H3′ atoms of six [M(bpy)3]2+ cations in addition to three O…H4 contacts (Figure 6).
The crystal structure of [Co(bpy)3]2[Co(OH2)6][NO3]8.7H2O (refcode VATHIJ and a later entry VATHIJ01 which gives a revised space group of P2/c) also reveals the encapsulation of [NO3]– ions within [Co(bpy)3]n2n+ sheets [31,50]. However, in this case, each sheet is heterochiral, and the hexagonal motifs are absent.
The structure of [Ni(bpy)3]2[NO3]3[1-CO2H-2-CO2C6H4].4H2O (refcode PUGTEQ, monoclinic space group Cc) [51] also consists of alternating (Δ)- and (Λ)-homochiral sheets of [Ni(bpy)3]2+ cations, assembled with the hexagonal motifs described in Figure 4. However, the cavities in these sheets remain vacant. Instead, the [NO3]– ions are involved in hydrogen-bonded networks with hydrogen phthalate ions and water molecules, each 2D network being sandwiched between the [Ni(bpy)3]n2n+ sheets. We attribute this structural preference to the presence of the hydrogen phthalate ion which can act as both a strong hydrogen-bond donor and acceptor. [Ni(bpy)3]2[NO3]3[1-CO2H-2-SO3C6H4].9H2O (refcode OGUNAG [52]) is related to [Ni(bpy)3]2[NO3]3[1-CO2H-2-CO2C6H4].4H2O, and also exhibits hexagonal motifs of [Ni(bpy)3]2+ cations forming (Δ)- and (Λ)-homochiral sheets separated by 2D-hydrogen bonded nets comprising 3-carboxybenzenesulfonate anions, nitrate ions and water molecules. However, in this case, [NO3]– ions are also hosted within the [Ni(bpy)3]n2n+ sheets (Figure 7), but only half the number as seen in the Type II motif. The [NO3]– ion engages in six short contacts with H3 and H3′ of four bpy ligands and two short O…H4 contacts, and we designate this as a Type III structure. Metrics for the contacts are given in Table 2. The location of the nitrate ions in the crystal lattice of [Ni(bpy)3]2[NO3]3[1-CO2H-2-SO3C6H4].9H2O again suggests that the presence of a strong hydrogen bond donor/acceptor can redirect the assembly of the Type II assembly, effectively ‘pulling’ the nitrate ion out of the [Ni(bpy)3]n2n+ sheet into the hydrogen-bonded network.
The preference for the nitrate ion to be involved in a hydrogen-bonded assembly rather than be hosted within or adjacent to the {[M(bpy)3]2+}6 motifs is also observed in the series of compounds [Cu(bpy)3]2[Cr(ox)3][NO3].9H2O (refcode MELMUM, ox2– = oxalate) [53], [Ni(bpy)3]2[Cr(ox)3][NO3].10H2O (refcode QOYDEO) [54], [Fe(bpy)3]2[Fe(ox)3][NO3].10H2O (refcodes WOMNIY, WOMNIY01) [55], and [Cu(bpy)3]2[Fe(ox)3][NO3].10H2O (refcode WOMNUK) [55]. All feature layer structures with alternating homochiral-[M(bpy)3]n2n+ layers (as shown in Figure 4) and hydrogen-bonded sheets comprising nitrate and [M(ox)3]3– ions and water molecules. These were described by Jurić et al. as ‘honeycomb like hydrophobic layers’ with ‘each hydrophobic layer sandwiched between two hydrophilic layers’ [53]. Jurić et al. also point to the extensive C–H…O interactions at the interfaces of the sheets. Among these, the interactions between the O atoms of the [M(ox)3]3– ion and the bpy H3, H3′ and H4 atoms, as well as to one H5 and one H6, are of note.

6. [M(bpy)3]q+ Combined with [XY4]m–

The 61 hits in the CSD with [M(bpy)3]q+ combined with [XY4]m– reduced to 50 different structures, once structural redeterminations were accounted for. Analysis of the structural data showed that, with two exceptions, sulfate, thiosulfate, chromate, and molybdate salts (14 structures) conformed to a common pattern which resembled the Type II assembly described above for the nitrate salts (Figure 5 and Table 1). The exceptions, [Zn(bpy)3][CrO4]0.5[NO3].6.5H2O [29] and [Co(bpy)3][CrO4]0.5[NO3].7H2O [28] (refcodes XUJDEL and EHIHUY, respectively) adopt a Type I assembly. Thus, all 14 structures comprise alternating homochiral layers of (Δ)- or (Λ)-[M(bpy)3]2+ cations arranged in hexagonal motifs. These sheets are interleaved with hydrogen-bonded networks involving water molecules, and, in two cases, nitrate ions (refcodes EHIHUY [28] and XUJDEL [29]). Figure 8a,b display the Type I motif in [Zn(bpy)3][CrO4]0.5[NO3].6.5H2O [29]. There are 14 C–H…O contacts involving bpy H3 and H3′ atoms, and metrics for these interactions are given in Table 3, along with those for [Co(bpy)3][CrO4]0.5[NO3].7H2O. Figure 8c,d show the Type II motif in [Cu(bpy)3][SO4].7.5H2O (refcode ROLLOU) [56]. The Type II motif also appears in [Fe(bpy)3][SO4].7.5H2O (refcode MOSHUZ) [57], [Co(bpy)3][SO4].7.5H2O (refcode KOKDUM) [58], [Ni(bpy)3][SO4].7.5H2O (refcode BPYNIS) [59], [Zn(bpy)3][SO4].7.5H2O (refcode OREHEZ) [60], [Co(bpy)3][SO4].8.5H2O (refcode LIFDOV) [61], [Ni(bpy)3][SSO3].7H2O (refcode KOLXOY) [62], [Zn(bpy)3][SSO3].7H2O (refcode ROKHII) [63], [Cu(bpy)3][CrO4].7.5H2O (refcode RUYYIU) [64], [Zn(bpy)3][CrO4].7.5H2O (refcode NEMPAW) [65], [Ni(bpy)3][CrO4].7.5H2O (refcode VADPUM) [66], and [Ni(bpy)3][MoO4].7.5H2O (refcode ELIMUH) [67]. As with the Type II nitrate salts described in Section 5, the Type II [XY4]2– anions show short contacts with bpy H3 and H4 atoms, with a dominance of H4 contacts; relevant distances and angles are summarized in Table 3. In the thiosulfate salts [Ni(bpy)3][SSO3].7H2O and [Zn(bpy)3][SSO3].7H2O, the [SSO3]2– ions are oriented with the O3S–S vector pointing directly into the {[M(bpy)3]}6-motif (Figure 9). This facilitates six S…H3 contacts which are augmented by six O…H4 interactions (Table 3). Salts of [M(bpy)3]2+ containing [SO4]2–, [SSO3]2–, [CrO4]2–, and [MoO4]2– anions, are therefore all classified into Type I or Type II structures, and it is interesting to note that the Type I structures also contain a nitrate ion accommodated in the hydrogen-bonded water layer. Wojciechowska et al. [29] commented that the presence of the [NO3]– ion appears to be important for the stabilization of the crystal structure. Our survey of the Type I structures here and in the previous section shows that there is a tendency for [NO3]– to prefer stronger hydrogen-bonded interactions with H2O molecules in preference to multiple CHbpy…O contacts.
While the hexagonal {[M(bpy)3]}6 motif is ubiquitous in the [SO4]2–, [SSO3]2–, [CrO4]2–, and [MoO4]2– salts, the same is not true of perchlorate and tetrafluoridoborate salts. None of the three [BF4]– salts (refcodes JIWTOZ, PAHNUI and RIGTEH) exhibits homochiral layers and hence lacks a packing motif that embraces the anion. Perchlorate salts account for 25 of the 51 structures containing [M(bpy)3]q+ cations combined with [XY4]m– anions. A number of these compounds crystallize with additional molecular anions or cations (refcodes CEDXUG, BPBPFE, KIFWIF, QITBUT, VABJIU) or free bpy (refcodes DEZPII, ROJQAI) and, in each case, these additional species disrupt the assembly of {[M(bpy)3]}6 motifs. Although enantiomerically pure, (Λ)-[Ru(bpy)3][ClO4]2 (refcode EWOTEQ, space group P212121) [68] does not form {[Ru(bpy)3]}6 motifs and lacks the hydrogen-bonded sheets that typically separate homochiral layers in Type I, Type II and Type III classes. Other structures which do not exhibit homochiral layer structures of Types I, II and III are those with refcodes CEZMAV, FIXKUT, CUHVUW, JAQDIR, POMJUX, TBPYCU, TIBMAU, YOWHEX, and ZAMGAV03; the latter (crystallizing in space group P 1 ¯ ) is a polymorph of ZAMGAV (space group C2/c, see below). This leaves eight structures (32% of the perchlorate salts analyzed) with structural motifs of interest that are described below.
The compound (Λ)-[Mn(bpy)3][ClO4]2.0.5C6H4-1,2-(COOEt)2.0.5H2O (refcode RAHRUO) [69] crystallizes in one of the Sohncke Space Groups [70], and (Λ)-[Mn(bpy)3]2+ cations assemble into sheets containing hexagonal motifs, not commented upon by the original authors [69]. In contrast to the crystal structures described earlier, this structure contains only (Λ)-sheets, and adjacent sheets are separated by a hydrogen-bonded network of water and diethyl phthalate molecules, as well as half of the perchlorate ions. The other half of the [ClO4]– ions are accommodated within {[MnII(bpy)3]}6 motifs in a Type II arrangement. Each [ClO4]– interacts with seven H3/H3′ atoms as well as four H4 atoms from six bpy ligands, and the metrics for the contacts are given in Table 4. The enantiomerically pure compounds (Λ)-[Zn(bpy)3][ClO4]2.H2O (refcode YUMJIZ) and (Λ)-[Ru(bpy)3][ClO4]2.H2O (refcode YUMJOF) are isomorphous, crystallizing in the Sohncke C2 space group [71]. The two independent (Λ)-[M(bpy)3]2+ cations form two crystallographically independent 2D-sheets that alternate through the lattice. The first comprises hexagonal {[M(bpy)3]}6 motifs and is a Type II structure with [ClO4]– ions in pockets in the upper and lower surfaces of each sheet. Short CHbpy…O contacts involving H3 and H4 are detailed in Table 4. In the Type II structural motif, the metal atoms of the [M(bpy)3]2+ cations are coplanar (or closely so). This is illustrated for (Λ)-[Zn(bpy)3][ClO4]2.H2O in Figure 10a. In the second independent sheet in (Λ)-[Zn(bpy)3][ClO4]2.H2O and (Λ)-[Ru(bpy)3][ClO4]2.H2O, the M atoms are not coplanar (Figure 10b), and disordered [ClO4]– ions occupy partial occupancy sites above and below the sheet with extensive CHbpy…O contacts.
Krausz et al. [71] have noted that the crystal packing in (Λ)-[Zn(bpy)3][ClO4]2.H2O and (Λ)-[Ru(bpy)3][ClO4]2.H2O is “nowhere near as efficient” as in rac-[Zn(bpy)3][ClO4]2 and rac-[Ru(bpy)3][ClO4]2. These two compounds (refcodes HEGMIP/01/02 [71,72,73] and ZAMGAV/01/02 [71,74,75]), along with [Co(bpy)3][ClO4]2 (refcode MEFCEG [76]), [Fe(bpy)3][ClO4]2 (refcode WOBTIQ [77]), and [Ni(bpy)3][ClO4]2 (refcodes WADBOT/01/02 [78,79,80]) possess the same 2D-sheet structure with ordered perchlorate ions (Figure 11a). Note that in rac-[Zn(bpy)3][ClO4]2 with refcode ZAMGAV01, about 8% of the metal sites are occupied by Ru [74]. Each sheet is homochiral, and alternating sheets contain (Λ)- or (Δ)-[M(bpy)3]2+ ions. Within a single sheet, [M(bpy)3]2+ cations form centered, hexagonal motifs as displayed in Figure 11b, and we label this motif a Type IV structure. Unlike the Type I, II and III structure types, each [ClO4]– ion in the Type IV motif is not fully embraced by [M(bpy)3]2+ cations within a single sheet, but rather has short contacts to three cations in one sheet and three cations in an adjacent sheet; these involve H3, H4, H5 and H6 atoms of the bpy ligands and metric parameters for the C–Hbpy…Operchlorate interactions are given in Table 5. A comparison of these data confirms the similarity of the structures of this series of anhydrous [M(bpy)3][ClO4]2 salts.
The final group of salts containing [M(bpy)3]q+ cations and [XY4]m– ions features [MCl4]2– (M = Fe, Zn, Cd, Pd) and [MBr4]2– (M = Mn, Fe) ions. Of the eight salts in this group, five exhibit Type I or II structures. The [PdCl4]2– salt is unique in the series because it contains a square-planar [XY4]m– ion, and [Ru(bpy)3]2[PdCl4][Pd(ox)2].11H2O (refcode TEXDAC) [81] has a Type I structure. The [PdCl4]2– ions are embedded within homochiral sheets of (Λ)- or (Δ)-[Ru(bpy)3]2+ cations (Figure 12a), and the 2D-sheets are separated by hydrogen-bonded layers comprising [Pd(ox)2]2– ions and water molecules. A comparison of Figure 12b with Figure 3b and Figure 8b shows the similarity of the hexagonal motifs in the Type I structures. In [Ru(bpy)3]2[PdCl4][Pd(ox)2].11H2O, the CH…Cl contacts primarily involve H3 and H3′ atoms with additional contacts to H4. Contact distances and angles are summarized in Table 6.
The packing in [Ni(bpy)3][CdCl4] (refcode BINZON) [82], [Ni(bpy)3][ZnCl4] (refcode XEQCUR) [83] and [Fe(bpy)3][FeCl4] (refcode NALSUQ) [84] is reminiscent of that in [Zn(bpy)3][SSO3].7H2O [63] and [Ni(bpy)3][SSO3].7H2O [62] with a Type II motif (compare Figure 13a with Figure 9). Each [CdCl4]2– exhibits short contacts to H3 and H4 atoms. [Ni(bpy)3][CdCl4], [Ni(bpy)3][ZnCl4] and [Fe(bpy)3][FeCl4] crystallize in the trigonal space group R 3 ¯ c and each hexagonal motif, therefore, has 3-fold symmetry (Figure 13b). Distance and angle parameters for the embraces are given in Table 6. In contrast, [M(bpy)3][SSO3].7H2O (M = Ni, Zn), [Ni(bpy)3][CdCl4], [Ni(bpy)3][ZnCl4] and [Fe(bpy)3][FeCl4] are anhydrous and there are no hydrogen-bonded layers interleaved between the sheets of [M(bpy)3]2+ cations. The mixed oxidation state compound [CoI(bpy)3]3[CoII(bpy)3][MnBr4]2Br.2DMF (refcode SABGOV, DMF = N,N-dimethylformamide) crystallizes in the hexagonal Sohncke space group P6322 [85]. The structure contains three independent Co atoms, and the Co(I) and Co(II) centers are distinguished by the Co–N bond lengths (average 2.095(2) Å for Co(I) and 2.124 Å for Co(II)). Although the packing was not described in detail in the original publication [85], we can use the reported Co–N bond length data to describe the structure in terms of alternating homochiral sheets containing (i) (Δ)-[CoI(bpy)3]+ and [MnBr4]2– ions (lower sheet in Figure 14a) and (ii) (Λ)-[CoI(bpy)3]+, (Λ)-[CoII(bpy)3]+ and Br– ions (upper sheet in Figure 14a). The DMF solvent molecules were disordered, and detailed positions are not available. The 2D-sheet containing (Δ)-[CoI(bpy)3]+ and [MnBr4]2– ions adopts a Type II structure (Figure 14b and Table 6) while the Br– ion is at the center of a {Co(bpy)3}6-motif (a Type I structure [20]).
The crystal structure of [Fe(bpy)3][FeCl4]2 (refcode HUMGEB) [86] comprises heterochiral sheets of [M(bpy)3]2+ cations and this precludes the appearance of the hexagonal motifs, and neither of the remaining two compounds in the tetrahalidometallate series (refcodes YAVCIL and PABRUJ) exhibits a homochiral layer structure. Thus, of the eight tetrahalidometallate salts, five exhibit Type I and II anion embraces, representing 62.5% of this set of structures.

7. Conclusions

We have used Conquest (version 2022.3.0) [23] to search the CSD [21] for the [M(bpy)3] motif (M = any transition metal) combined with XY3, XY4 or XY5 units in which X and Y are any atom; no structures containing [XY5]m– anions were found. After reducing the structures to those with [XY3]m– and [XY4]m– anions, two sets, respectively, of 12 and 50 structures, remained for detailed analysis.
Of the 12 structures which contain [XY3]m– anions, all are layer assemblies and all but one possess homochiral sheets containing (Λ)- or (Δ)-[M(bpy)3]q+ cations in hexagonal motifs. The doubly charged sulfite ion is accommodated in the center of the motif (Type I structure, Table 1) while singly-charged nitrate ions tend to reside in pockets in the top and bottom surfaces of each sheet (Types II and III, Table 1 and Table 2). However, when strong hydrogen bond donors or acceptors, such as the hydrogen phthalate ion, are introduced into the assembly, a preference for the nitrate ion to be involved in a hydrogen-bonded network is observed.
The 50 structures with [XY4]m– anions fall into four groups. The first group comprises [SO4]2–, [SSO3]2–, [CrO4]2–, and [MoO4]2– salts, and all exhibit homochiral sheet structures with hexagonal {M(bpy)3}6 motifs embracing the tetrahedral anions in either a Type I or II structure (Table 3). In the second group comprising 25 perchlorate salts, three structures exhibit the Type II motif (Table 4), while five exhibit a centered hexagonal motif (Type IV, Table 5). Most salts containing [ClO4]– do not conform to the patterns established for the [SO4]2–, [SSO3]2–, [CrO4]2–, and [MoO4]2– salts. Similarly, homochiral layers are not found in any of the three [BF4]– salts (the third group of structures). The fourth group contains eight tetrahalidometallate salts, and 62.5% of these exhibit Type I and II anion embraces.
The identification of a series of related and ubiquitous motifs in the solid-state structures of [M(bpy)3]q+ salts provides a new and alternative approach to considering their crystal supramolecular chemistry. The results of our analysis complement the discussion by Breu et al. regarding packing interactions in [Cr(bpy)3]n+[PF6]n (n = 0–3) [87].

Author Contributions

The authors contributed equally to the writing of this work. Conceptualization, E.C.C.; data mining and evaluation, E.C.C. and C.E.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Not applicable.

Acknowledgments

We thank the University of Basel for support.

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 13 00097 sch001 550
Scheme 1. Structure of bpy showing the change in conformation upon metal coordination. The atom numbering is also defined.
Scheme 1. Structure of bpy showing the change in conformation upon metal coordination. The atom numbering is also defined.
Crystals 13 00097 sch001
Crystals 13 00097 g001 550
Figure 1. The halide embrace exemplified with the motif observed in [Ni(bpy)3]Cl2·5.5H2O, CSD refcode EGOVEB [22]. (a) The Cl– ion at the center of a motif of six homochiral [Ni(bpy)3]2+ cations, and (b) a side view of the same motif; this unit is part of a 2D-sheet.
Figure 1. The halide embrace exemplified with the motif observed in [Ni(bpy)3]Cl2·5.5H2O, CSD refcode EGOVEB [22]. (a) The Cl– ion at the center of a motif of six homochiral [Ni(bpy)3]2+ cations, and (b) a side view of the same motif; this unit is part of a 2D-sheet.
Crystals 13 00097 g001
Crystals 13 00097 g002 550
Figure 2. The absolute configuration of the enantiomers of an [M(bpy)3] coordination moiety is conveniently denoted by the stereochemical descriptors Δ and Λ. In each bpy ligand, the green atoms are further away from the observer and the blue atoms are closer and can be related to an axis orthogonal to the plane of the paper and running through the metal center. An anti-clockwise rotation of the right-hand structure about this axis will “dig” the propeller into the page and this is described as the Λ-enantiomer. The mirror-image propeller on the left must be rotated clockwise about the axis to screw into the page and is denoted as the Δ-enantiomer.
Figure 2. The absolute configuration of the enantiomers of an [M(bpy)3] coordination moiety is conveniently denoted by the stereochemical descriptors Δ and Λ. In each bpy ligand, the green atoms are further away from the observer and the blue atoms are closer and can be related to an axis orthogonal to the plane of the paper and running through the metal center. An anti-clockwise rotation of the right-hand structure about this axis will “dig” the propeller into the page and this is described as the Λ-enantiomer. The mirror-image propeller on the left must be rotated clockwise about the axis to screw into the page and is denoted as the Δ-enantiomer.
Crystals 13 00097 g002
Crystals 13 00097 g003 550
Figure 3. Structure Type I illustrated with the motif found in [Fe(bpy)3]2[SO3][OH]4.14H2O which possesses a sheet structure (refcode YAWWAY) [46]. (a) One hexagonal motif within one sheet viewed down the crystallographic a-axis, and (b) the same unit viewed from above showing the twelve bpy H3 and H3′ atoms oriented towards the [SO3]2– ion.
Figure 3. Structure Type I illustrated with the motif found in [Fe(bpy)3]2[SO3][OH]4.14H2O which possesses a sheet structure (refcode YAWWAY) [46]. (a) One hexagonal motif within one sheet viewed down the crystallographic a-axis, and (b) the same unit viewed from above showing the twelve bpy H3 and H3′ atoms oriented towards the [SO3]2– ion.
Crystals 13 00097 g003
Crystals 13 00097 g004 550
Figure 4. (a) Part of one sheet comprising (Δ)-[Fe(bpy)3]2+ cations in [Fe(bpy)3]2[SO3][OH]4.14H2O (refcode YAWWAY [46]) with [SO3]2–, [OH]– and H2O omitted. (b) The same sheet section viewed from the side. The H3 and H3′ atoms are shown in red.
Figure 4. (a) Part of one sheet comprising (Δ)-[Fe(bpy)3]2+ cations in [Fe(bpy)3]2[SO3][OH]4.14H2O (refcode YAWWAY [46]) with [SO3]2–, [OH]– and H2O omitted. (b) The same sheet section viewed from the side. The H3 and H3′ atoms are shown in red.
Crystals 13 00097 g004
Crystals 13 00097 g005 550
Figure 5. Structure Type II illustrated with the motif found in [Zn(bpy)3][NO3][azt]0.5.6H2O which possesses a sheet structure (refcode OLOCOI) [47]. (a) One hexagonal motif which hosts two [NO3]– ions, and (b) the same unit viewed from above.
Figure 5. Structure Type II illustrated with the motif found in [Zn(bpy)3][NO3][azt]0.5.6H2O which possesses a sheet structure (refcode OLOCOI) [47]. (a) One hexagonal motif which hosts two [NO3]– ions, and (b) the same unit viewed from above.
Crystals 13 00097 g005
Crystals 13 00097 g006 550
Figure 6. Packing motif in [Co(bpy)3][NO3]2.H2O.MeCN (CSD refcode XARPEN [48]); the second symmetry-related [NO3]– is omitted for clarity. The H3 and H3′ atoms in the bpy ligand which show short contacts to the [NO3]– ion are shown in pink and H4 atoms in green.
Figure 6. Packing motif in [Co(bpy)3][NO3]2.H2O.MeCN (CSD refcode XARPEN [48]); the second symmetry-related [NO3]– is omitted for clarity. The H3 and H3′ atoms in the bpy ligand which show short contacts to the [NO3]– ion are shown in pink and H4 atoms in green.
Crystals 13 00097 g006
Crystals 13 00097 g007 550
Figure 7. Structure Type III: A side view of part of one [Ni(bpy)3]n2n+ sheet hosting [NO3]– anions in [Ni(bpy)3]2[NO3]3[1-CO2H-2-SO3C6H4].9H2O (refcode OGUNAG [52]). H2O molecules, which also contact CH units in the sheet, are omitted for clarity.
Figure 7. Structure Type III: A side view of part of one [Ni(bpy)3]n2n+ sheet hosting [NO3]– anions in [Ni(bpy)3]2[NO3]3[1-CO2H-2-SO3C6H4].9H2O (refcode OGUNAG [52]). H2O molecules, which also contact CH units in the sheet, are omitted for clarity.
Crystals 13 00097 g007
Crystals 13 00097 g008 550
Figure 8. Structure Types I and II for [XY4]2– containing compounds: (a,b) Structure Type I with the motif found in [Zn(bpy)3][CrO4]0.5[NO3].6.5H2O (refcode XUJDEL) [29], and (c,d) structure Type II illustrated with the motif in [Cu(bpy)3][SO4].7.5H2O (refcode ROLLOU) [56].
Figure 8. Structure Types I and II for [XY4]2– containing compounds: (a,b) Structure Type I with the motif found in [Zn(bpy)3][CrO4]0.5[NO3].6.5H2O (refcode XUJDEL) [29], and (c,d) structure Type II illustrated with the motif in [Cu(bpy)3][SO4].7.5H2O (refcode ROLLOU) [56].
Crystals 13 00097 g008
Crystals 13 00097 g009 550
Figure 9. Arrangement of the thiosulfate ions within a {[Ni(bpy)3]}6-motif in [Ni(bpy)3][SSO3].7H2O (refcode KOLXOY) [62].
Figure 9. Arrangement of the thiosulfate ions within a {[Ni(bpy)3]}6-motif in [Ni(bpy)3][SSO3].7H2O (refcode KOLXOY) [62].
Crystals 13 00097 g009
Crystals 13 00097 g010 550
Figure 10. (a) Type II sheet of (Λ)-[Zn(bpy)3]2+ cations in (Λ)-[Zn(bpy)3][ClO4]2.H2O emphasizing the near coplanarity of the Zn(II) centers. (b) The second independent sheet of (Λ)-[Zn(bpy)3]2+ cations which has a ‘ruffled’ profile (CSD refcode YUMJIZ [71]). Both sheets are viewed along the crystallographic b-axis and perchlorate ions and water molecules are omitted.
Figure 10. (a) Type II sheet of (Λ)-[Zn(bpy)3]2+ cations in (Λ)-[Zn(bpy)3][ClO4]2.H2O emphasizing the near coplanarity of the Zn(II) centers. (b) The second independent sheet of (Λ)-[Zn(bpy)3]2+ cations which has a ‘ruffled’ profile (CSD refcode YUMJIZ [71]). Both sheets are viewed along the crystallographic b-axis and perchlorate ions and water molecules are omitted.
Crystals 13 00097 g010
Crystals 13 00097 g011 550
Figure 11. The structure of [Co(bpy)3][ClO4]2 (refcode MEFCEG [76]). (a) Parts of three adjacent sheets viewed down the crystallographic a-axis; H atoms are omitted for clarity. (b) Part of one sheet viewed down the c-axis with anions in space-filling representation.
Figure 11. The structure of [Co(bpy)3][ClO4]2 (refcode MEFCEG [76]). (a) Parts of three adjacent sheets viewed down the crystallographic a-axis; H atoms are omitted for clarity. (b) Part of one sheet viewed down the c-axis with anions in space-filling representation.
Crystals 13 00097 g011
Crystals 13 00097 g012 550
Figure 12. Structure Type I motif in [Ru(bpy)3]2[PdCl4][Pd(ox)2].11H2O (CSD refcode TEXDAC) [81]. (a) One hexagonal motif within one sheet viewed down the crystallographic b-axis, and (b) the same unit viewed from above showing the bpy H3 and H3′ atoms directed towards the [PdCl4]2– ion.
Figure 12. Structure Type I motif in [Ru(bpy)3]2[PdCl4][Pd(ox)2].11H2O (CSD refcode TEXDAC) [81]. (a) One hexagonal motif within one sheet viewed down the crystallographic b-axis, and (b) the same unit viewed from above showing the bpy H3 and H3′ atoms directed towards the [PdCl4]2– ion.
Crystals 13 00097 g012
Crystals 13 00097 g013 550
Figure 13. Structure Type II motif in [Ni(bpy)3][CdCl4] (refcode BINZON) [82] viewed (a) from the side and (b) from above.
Figure 13. Structure Type II motif in [Ni(bpy)3][CdCl4] (refcode BINZON) [82] viewed (a) from the side and (b) from above.
Crystals 13 00097 g013
Crystals 13 00097 g014 550
Figure 14. The structure of [CoI(bpy)3]3[CoII(bpy)3][MnBr4]2Br.2DMF (refcode SABGOV [85]). (a) Parts of adjacent homochiral 2D-sheets viewed down the crystallographic a-axis; the Br– ions in the top layer are shown in ball-and-stick representation for clarity. All [MnBr4]2–-containing sheets have (Δ)-[CoI(bpy)3]+ ions and all Br–-containing sheets include equal numbers of (Λ)-[CoI(bpy)3]+ and (Λ)-[CoII(bpy)3]+ ions. (b) The Type II motif from the lower layer in diagram (a) viewed down the c-axis. (c) The Type I motif from the upper layer in diagram (a) viewed down the c-axis.
Figure 14. The structure of [CoI(bpy)3]3[CoII(bpy)3][MnBr4]2Br.2DMF (refcode SABGOV [85]). (a) Parts of adjacent homochiral 2D-sheets viewed down the crystallographic a-axis; the Br– ions in the top layer are shown in ball-and-stick representation for clarity. All [MnBr4]2–-containing sheets have (Δ)-[CoI(bpy)3]+ ions and all Br–-containing sheets include equal numbers of (Λ)-[CoI(bpy)3]+ and (Λ)-[CoII(bpy)3]+ ions. (b) The Type II motif from the lower layer in diagram (a) viewed down the c-axis. (c) The Type I motif from the upper layer in diagram (a) viewed down the c-axis.
Crystals 13 00097 g014
Table
Table 1. Structure Type I and II complexes with [XY3]m– anions.
Table 1. Structure Type I and II complexes with [XY3]m– anions.
REFCODE
Space Group		X
Y		Structure TypeRange H…Y/Å
(Mean H…Y/Å)		Range
C…Y/Å
(Mean C…Y/Å)		Range
∠ C–H…Y/°
(Mean
∠ C–H…Y/°) 		Range
C…X/Å
(Mean C…X/Å)		Refs.
YAWWAY
C2/c		S
O		I2.182–2.442
(2.296)		3.243–3.529
(3.370)		163.0–175.3
(169.2)		4.051–4.487
(4.270)		[46]
OLOCOI
C2/c		N
O		II2.136–2.815
(2.477)		3.141–3.432
(3.286)		110.8–160.6
(133.0)		3.930–4.573
(4.158)		[47]
XARPEN
C2/c		N
O		II2.230–2.786
(2.491)		3.247–3.534
(3.402)		117.6–160.1
(143.2)		3.836–4.532
(4.215)		[48]
YEJKOP
C2/c		N
O		II2.212–2.781
(2.470)		3.234–3.518
(3.378)		117.6–159.2
(142.8)		3.818–4.598
(4.185)		[49]
Table
Table 2. Structure Type III complex with [NO3]– anions.
Table 2. Structure Type III complex with [NO3]– anions.
REFCODE
Space Group		X
Y		Structure TypeRange H…Y/Å
(Mean H…Y/Å)		Range
C…Y/Å
(Mean C…Y/Å)		Range
∠ C–H…Y/°
(Mean
∠ C–H…Y/°) 		Range
C…X/Å
(Mean C…X/Å)		Ref.
OGUNAG
P21/n		N
O		III2.369–2.813
(2.639)		3.418–3.766
(3.602)		127.0–174.9
(150.8)		3.631–4.851
(4.102)		[52]
Table
Table 3. Structure Type I and II complexes with [XY4]m– anions.
Table 3. Structure Type I and II complexes with [XY4]m– anions.
REFCODE
Space Group		X
Y		Structure TypeRange H…Y/Å
(Mean H…Y/Å)		Range
C…Y/Å
(Mean C…Y/Å)		Range
∠ C–H…Y/°
(Mean
∠ C–H…Y/°) 		Range
C…X/Å
(Mean C…X/Å)		Refs.
XUJDEL
Ccc2		Cr
O		I2.097–2.673
(2.347)		3.153–3.675
(3.373)		142.6–177.9
(160.1)		4.106–4.737
(4.339)		[29]
ELIHUY
C2/c		Cr
O		I2.087–2.671
(2.319)		3.160–3.567
(3.354)		139.2–173.3
(161.4)		4.080–4.723
(4.333)		[28]
ROLLOU
C2/c		S
O		II2.290–2.722
(2.566)		3.170–3.780
(3.464)		127.6–163.8
(141.0)		3.965–4.400
(4.227)		[56]
MOSHUZ
C2/c		S
O		II2.287–2.786
(2.540)		3.087–3.701
(3.388)		116.2–158.5
(135.9)		3.860–4.430
(4.189)		[57]
KOKDUM
C2/c		S
O		II2.323–2.736
(2.539)		3.082–3.679
(3.371)		115.9–157.9
(134.4)		3.791–4.421
(4.146)		[58]
BPYNIS a
C2/c		S
O		II2.261–2.658
(2.518)		3.106–3.716
(3.407)		125.8–163.8
(140.2)		3.896–4.385
(4.189)		[59]
OREHEZ
C2/c		S
O		II2.308–2.769
(2.551)		3.090–3.696
(3.388)		116.3–157.3
(134.8)		3.816–4.416
(4.157)		[60]
LIFDOV
C2/c		S
O		II2.300–2.741
(2.554)		3.160–3.633
(3.445)		124.8–163.9
(140.6)		3.965–4.397
(4.217)		[61]
KOLXOY
C2/c		S
O/S		IIY = S
2.814–2.999
(2.901)
Y = O
2.299–2.763
(2.556)		Y = S
3.735–3.895
(3.821)
Y = O
3.187–3.756
(3.490)		Y = S
131.1–156.1
(143.5)
Y = O
124.4–166.2
(145.4)		4.113–4.595
(4.323)		[62]
ROKHII
C2/c		S
O/S		IIY = S
2.774–3.010
(2.891)
Y = O
2.320–2.785
(2.563) 		Y = S
3.711–3.866
(3.798)
Y = O
3.161–3.850
(3.502) 		Y = S
127.7–155.7
(142.3)
Y = O
124.3–167.4
(146.1) 		4.090–4.637
(4.319) 		[63]
RUYYIU b
C2/c		Cr
O		II2.257–2.778
(2.576)		3.185–3.685
(3.381)		113.9–169.9
(132.7)		4.016–4.697
(4.313)		[64]
NEMPAW b
C2/c		Cr
O		II2.198–2.816
(2.602)		3.197–3.779
(3.408)		115.0–172.1
(133.1)		4.078–4.700
(4.333)		[65]
VADPUM b
C2/c		Cr
O		II2.147–2.789
(2.587)		3.203–3.732
(3.394)		116.8–166.1
(133.0)		4.034–4.691
(4.327)		[66]
ELIMUH a
C2/c		Mo
O		II2.297–2.804
(2.588)		3.120–3.882
(3.419)		110.4–170.3
(135.6)		3.982–5.100
(4.350)		[67]
a H atom coordinates were not available in the CSD and were added in Mercury (see Section 2). b Disordered anion with common Cr position; all O sites were used in the analysis.
Table
Table 4. Structure Type II motifs with [ClO4]– anions.
Table 4. Structure Type II motifs with [ClO4]– anions.
REFCODE
Space Group		X
Y		Structure TypeRange H…Y/Å
(Mean H…Y/Å)		Range
C…Y/Å
(Mean C…Y/Å)		Range
∠ C–H…Y/°
(Mean
∠ C–H…Y/°) 		Range
C…X/Å
(Mean C…X/Å)		Refs.
RAHRUO a
C2221		Cl
O		II2.010–2.805
(2.569)		2.979–3.750
(3.419)		107.5–169.8
(137.8)		3.870–4.878
(4.369)		[69]
YUMJIZ a
C2 		Cl
O		II2.12–2.79
(2.52)		3.04–3.66
(3.31)		111.8–150.4
(130.1)		4.07–4.55
(4.27)		[71]
YUMJOF a
C2 		Cl
O		II2.19–2.82
(2.53)		3.07–3.61
(3.32)		107.0–148.4
(130.4)		4.05–4.64
(4.26)		[71]
a Disordered anion; all O sites used in the analysis.
Table
Table 5. Structure Type IV motifs with [ClO4]– anions.
Table 5. Structure Type IV motifs with [ClO4]– anions.
REFCODE
Space Group		X
Y		Structure TypeRange H…Y/Å
(Mean H…Y/Å)		Range
C…Y/Å
(Mean C…Y/Å)		Range
∠ C–H…Y/°
(Mean
∠ C–H…Y/°) 		Range
C…X/Å
(Mean C…X/Å)		Refs.
MEFCEG
C2/c		Cl
O		IV2.575–2.779
(2.688)		3.226–3.716
(3.419)		110.8–146.5
(125.2)		3.801–4.717
(4.304)		[76]
WADBOT
C2/c		Cl
O		IV2.534–2.807
(2.692)		3.200–3.713
(3.417)		114.0–147.5
(124.7)		3.810–4.672
(4.279)		[78]
WADBOT01
C2/c		Cl
O		IV2.513–2.808
(2.694)		3.182–3.682
(3.409)		109.4–147.3
(123.8)		3.796–4.666
(4.252)		[79]
WADBOT02
C2/c		Cl
O		IV2.512–2.754
(2.625)		3.150–3.595
(3.335)		109.0–147.4
(123.3)		3.677–4.578
(4.183)		[80]
HEGMIP
C2/c		Cl
O		IV2.411–2.794
(2.698)		3.151–3.706
(3.417)		105.9–151.1
(124.6)		3.873–4.668
(4.279)		[72]
HEGMIP01
C2/c		Cl
O		IV2.466–2.754
(2.688)		3.141–3.691
(3.409)		109.5–150.3
(124.6)		3.873–4.664
(4.273)		[71]
HEGMIP02
C2/c		Cl
O		IV2.526–2.726
(2.642)		3.140–3.698
(3.369)		109.1–147.8
(124.9)		3.732–4.565
(4.148)		[73]
ZAMGAV
C2/c		Cl
O		IV2.522–2.790
(2.693)		3.216–3.521
(3.390)		107.4–145.6
(123.9)		3.776–4.593
(4.201)		[75]
ZAMGAV01 a
C2/c		Cl
O		IV2.541–2.738
(2.642)		3.183–3.680
(3.372)		110.0–147.3
(125.1)		3.760–4.695
(4.263)		[74]
ZAMGAV02
C2/c		Cl
O		IV2.581–2.774
(2.675)		3.213–3.712
(3.405)		111.2–145.1
(125.1)		3.746–4.737
(4.285)		[71]
WOBTIQ
C2/c		Cl
O		IV2.507–2.812
(2.664)		3.084–3.603
(3.366)		107.4–149.5
(122.8)		3.749–4.541
(4.207)		[77]
a H atom coordinates were not available in the CSD and were added in Mercury (see Section 2).
Table
Table 6. Metrics for Type I and II motifs in salts containing [MCl4]2– anions.
Table 6. Metrics for Type I and II motifs in salts containing [MCl4]2– anions.
REFCODE
Space Group		X
Y		Structure TypeRange H…Y/Å
(Mean H…Y/Å)		Range
C…Y/Å
(Mean C…Y/Å)		Range
∠ C–H…Y/°
(Mean
∠ C–H…Y/°) 		Range
C…X/Å
(Mean C…X/Å)		Refs.
TEXDAC
P21		Pd
Cl		I2.582–3.030
(2.809)		3.460–3.980
(3.642)		117.6–176.5
(147.6)		3.762–5.770
(4.733)		[81]
BINZON
R 3 ¯ c		Cd
Cl		II2.609–3.037
(2.827)		3.490–3.856
(3.713)		127.0–156.2
(141.9)		4.41–5.04
(4.65)		[82]
XEQCUR a
R 3 ¯ c		Zn
Cl		II2.588–2.841 b
(2.715)		3.508–3.861
(3.685)		141.6–155.8
(148.7)		4.390–4.458
(4.424)		[83]
NALSUQ
R 3 ¯ c		Fe
Cl		II2.551–2.816
(2.683)		3.472–3.840
(3.656)		141.7–156.6
(149.1)		4.387–4.455
(4.421)		[84]
SABGOV
P6322		Mn
Br		II2.863–2.979
(2.950)		3.802–4.012
(3.887)		136.3–158.6
(146.0)		4.335–4.730
(4.483)		[85]
a H atom coordinates were not available in the CSD and were added in Mercury (see Section 2). b There are also three contact distances of 3.090 Å, which are longer than the sum of the van der Waals radii + 0.1 Å (3.05 Å) which are analogous to the 3.037 Å contacts in BINZON.
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Constable, E.C.; Housecroft, C.E. Embracing [XY3]m– and [XY4]m– Anions in Salts of [M(bpy)3]q+. Crystals 2023, 13, 97. https://doi.org/10.3390/cryst13010097

AMA Style

Constable EC, Housecroft CE. Embracing [XY3]m– and [XY4]m– Anions in Salts of [M(bpy)3]q+. Crystals. 2023; 13(1):97. https://doi.org/10.3390/cryst13010097

Chicago/Turabian Style

Constable, Edwin C., and Catherine E. Housecroft. 2023. "Embracing [XY3]m– and [XY4]m– Anions in Salts of [M(bpy)3]q+" Crystals 13, no. 1: 97. https://doi.org/10.3390/cryst13010097

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