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Article

Heterometallic Chain Compounds of Tetrakis(µ-carboxylato)diruthenium and Tetracyanidoaurate

1
School of Biological and Environmental Sciences, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan
2
Department of Chemistry, Graduate School of Natural Science and Technology, Shimane University, Matsue 690-8504, Japan
*
Authors to whom correspondence should be addressed.
Magnetochemistry 2022, 8(5), 48; https://doi.org/10.3390/magnetochemistry8050048
Submission received: 15 March 2022 / Revised: 18 April 2022 / Accepted: 20 April 2022 / Published: 2 May 2022
(This article belongs to the Special Issue Characterization of Coordination Compounds)

Abstract

:
Heterometallic complexes of tetrakis(µ-carboxylato)diruthenium(II,III) with tetracyanidoaurate(III) [Ru2(RCOO)4Au(CN)4]n (R = CH3 (1), C2H5 (2), i-C3H7 (3), and t-C4H9 (4)) were synthesized and characterized by C,H,N-elemental analysis and infrared spectroscopy and diffuse reflectance spectroscopy. The molecular structures were determined by a single-crystal X-ray diffraction method. A polymeric arrangement with the Ru2(RCOO)4+ units alternately linked by Au(CN)4 units is formed in these complexes. The trans-bridging mode of the Au(CN)4 unit for connecting the two Ru2(RCOO)4+ units was observed for 1 and 4, while the cis-bridging mode of the Au(CN)4 unit was observed for 2 and 3. Magnetic susceptibility data with variable temperature were modeled with a zero-field splitting model (D = 75 cm−1) and the presence of weak antiferromagnetic coupling between the RuIIRuIII units (zJ = −0.15~−0.10 cm−1) was estimated. N2-adsorption isotherms showed Type II curves with SBET of 0.728–2.91 m2 g−1.

1. Introduction

Dinuclear clusters of ruthenium carboxylates have attracted much attention as spin sources for constructing molecular magnetic materials, because these molecules have S = 1 or 3/2 spins within the dinuclear core depending on the oxidation state of the Ru2 core. Usually, these ruthenium carboxylates exist as ruthenium(II)-ruthenium(II) and ruthenium(II)-ruthenium(III) oxidation states in the dinuclear units. In the case of the RuII-RuII state, two unpaired electrons exist within the Ru2 core, making the dinuclear complex paramagnetic with a large zero-field splitting parameter, while three unpaired electrons are generated in the accidentally degenerate Ru-Ru bond orbitals in the case of the mixed-valent RuII-RuIII state, resulting as more paramagnetic with a comparatively small D value [1,2,3,4]. In the former case, the magnetic moments at room temperature were observed in the range of 2.6–3.2 µB per RuII-RuII unit [2], on the other hand, the observed magnetic moments at room temperature are in the range of 3.6 to 4.4 µB per RuII-RuIII unit in the latter case, which is a little higher than that of the spin-only value for the S = 3/2 spins [2]. The axial sites of dinuclear cores are available for many kinds of donor ligands, and coordination polymer formation can be achieved by the introduction of bidentate or multidentate linkers such as N,N′-bidentate ligands [3,4]. Among many kinds of donor groups, metal cyanides can be used as unique linkers, having a CN group of a triple bond, which may be expected to have an advantage in communicating electrons between the bridged metal atoms. To date, dicyanidometalate, Ag(CN)2 [5] and Au(CN)2 [6,7], tricyanidometalate, Cp*Ir(CN)3 [8], tetracyanidometalate, MII(CN)42− (MII = NiII, PdII, PtII) [9], and hexacyanidometalate MIII(CN)63− (M = FeIII [10], CoIII [11]) ions have been used for assemblies of rhodium(II) carboxylates. For ruthenium carboxylates, heterometallic assemblies of RuIIRuIII carboxylates with dicyanidoargentate(I) [12], dicyanidoaurate(I) [13], tetracyanidonickelate(II) [14,15], tetracyanidopalladate(II) [16,17], tetracynidoplatinate(II) [18], hexacyanidochromate(III) [19,20,21,22,23], hexacyanidoferrate(III) [19,20,21,24,25], hexacyanidocobaltate(III) [19,20,21,24,25] and octacyanidotungstate(V) [26,27,28] have been reported. In these complexes, the observed magnetic interactions via the cyanidometalate are mostly antiferromagnetic between the 3/2 spins of RuII-RuIII units. In this study, we examined tetracyanidoaurate(III) for the metal assembly of tetrakis(µ-carboxylate)diruthenium(II,III), aiming to develop new molecular magnetic compounds. Tetracyanidometalate has another interesting point of view from coordination chemistry, trans and cis-orientation of this linker to connect two Ru2 units. In the case of tetracyanidonickelate(II), it was difficult to grow single-crystals for these systems [14,15], although we barely obtained small crystals of the heterometallic compound of Ru2(CH3COO)4+ with Pt(CN)42− and X-ray crystallography, using SPring 8 radiation revealed a µ4-bridging of tetracyanidoplatinate(II) to form a layer sheet [18]. In this study, we synthesized and characterized new heterometallic complexes of RuII-RuIII carboxylates Ru2(RCOO)4+ (R = CH3, C2H5, i-C3H7, t-C4H9) with tetracyanidoaurate(III) (Scheme 1). We successfully isolated single crystals of these complexes, and the molecular structures were disclosed by single-crystal X-ray diffraction to reveal the orientation of the linking ligands. Magnetic interactions between the RuII-RuIII units via the linking ligands as well as the adsorption properties for N2 gas were investigated.

2. Results and Discussion

2.1. Synthesis of Heterometallic Compounds of Ruthenium(II,III) Carboxylates with Tetracyanidoaurate(III)

The present complexes were prepared by the reactions of [Ru2(RCOO)4(H2O)2]BF4 and K[Au(CN)4] in a 1:1 molar ratio in aqueous solutions as reddish orange precipitate or crystals. The elemental analytical data of the present complexes are in agreement with the 1:1 adduct formulation of [Ru2(RCOO)4Au(CN)4]n.

2.2. Infrared Spectra of the Heterometallic Compounds [Ru2(RCOO)4Au(CN)4]n

The IR spectra of the complexes show antisymmetric stretching νas(COO) and symmetric stretching νs(COO) bands at 1437–1487 and 1400–1433 cm−1, respectively, with a Δ value of 32–64 cm−1 (Figures S1–S4), which are comparable to those of the starting material [Ru2(t-C4H9COO)4(H2O)2]BF4 (νas(COO) 1486 cm−1 and νs(COO) 1425 cm−1) with the syn-syn mode of µ-carboxylato bridges [29] and in accordance with the structures of tetrakis(µ-carboxylate)diruthenium(II,III) units, as described in Section 2.4. The crystal structure analysis revealed that the Au(CN)4 moieties take the trans-bridging mode concerning the coordination to the Ru2(RCOO)4+ moieties for the acetate complex [Ru2(CH3COO)4Au(CN)4]n (1) and the pivalate complex [Ru2(t-C4H9COO)4Au(CN)4]n (4), while the cis-bridging mode was observed for the propionate complex [Ru2(C2H5COO)4Au(CN)4]n (2) and the isobutyrate complex [Ru2(i-C3H7COO)4Au(CN)4]n (3). It is recognized that the higher-frequency shift of ν(CN) of metal cyanides is suggestive of bridging CN groups [29]. The CN ion is known to act as a strong σ-donor with a poor π-acceptor. Thus, the σ-donation tends to raise the ν(CN), although the π-backbonding is expected to decrease the ν(CN) [29]. As shown in Figure 1, the CN stretching-vibration bands of the present complexes appeared at 2182—2225 cm−1, while the ν(CN) band of K[Au(CN)4] was observed at 2190 cm−1, confirming the bridging of the Au(CN)4 moieties to the Ru2(RCOO)4+ moieties. The higher-energy ν(CN) (2204 cm−1 in 1, 2225 cm−1 in 2, 2220 cm−1 in 3, 2211 cm−1 in 4) may be ascribed to the bridged CN groups and the lower-energy ν(CN) (2182 cm−1 in 1, 2186 cm−1 in 2, 2186 cm−1 in 3, 2182 cm−1 in 4) may be ascribed to the uncoordinated CN groups. It is notable that the energy difference between the higher- and lower-energy CN-stretching bands of the complexes 2 and 3 with the cis-bridging mode are considerably larger than those of the complexes 1 and 4 with the trans-bridging mode.

2.3. Electronic Spectra of the Heterometallic Compounds [Ru2(RCOO)4Au(CN)4]n

The solid-state diffuse reflectance spectra resemble each other as depicted in Figure 2. The present complexes display a broad band at approximately 220–290 nm with a shoulder at 300–310 nm in the UV region, which may be assigned to charge transfer and d-d bands of the Au(CN)4 moieties [30] and LMCT transition of σ(axial ligand)→σ*(Ru2), respectively [31,32,33]. In the visible region, a broad absorption appears at 436–452 nm, which may be ascribed to π(Ru-O, Ru2)→σ*(Ru-O) and π(Ru-O, Ru2)→π*(Ru2) transitions [31,32,33]. A broad absorption at approximately 1000 nm, which can be ascribed to δ(Ru2)→δ*(Ru2) transition, and a weak absorption at 1500 nm assignable to π*(Ru2)→δ*(Ru2) transition were observed in the NIR region [31,32,33]. The diffuse reflectance spectra are in accordance with the formation of the heterometallic compounds [Ru2(RCOO)4Au(CN)4]n.

2.4. Crystal Structures of the Heterometallic Compounds [Ru2(RCOO)4Au(CN)4]n

Single crystals of complexes 14 suitable for X-ray crystal structure analysis were grown by the slow evaporation of the aqueous solutions of the reaction materials. Crystallographic data are collected in Table 1. Selected bond distances and angles are given in Table S1. The acetate complex [Ru2(CH3COO)4Au(CN)4]n (1) crystallized in the hexagonal lattice. A perspective drawing of the structure of 1 is shown in Figure 3a. The structure consists of a 1-D chain molecule with an alternating arrangement of Ru2(CH3COO)4+ and Au(CN)4 moieties, where two cyanido groups of each Au(CN)4 moiety are coordinated to the axial sites of two Ru2(CH3COO)4+ moieties in a trans-bridging mode. The crystallographic C2 axis contains the N2, C8, Au1, C9, and N3 atoms, forming a square planar Au(CN)4 unit with C2 symmetry-related N1 and C7 and C7i and N1i atoms, where the superscript i denotes the equivalent position (2−x, 1−x+y, 5/3−z). The Au-C distances are 1.991(4)–2.008(4) Å. Another crystallographic C2 axis contains C6, C5, C1, and C2 atoms, and thus the paddlewheel-type Ru2 core with four syn-syn acetato-bridges has the crystallographic C2 axis through the midpoints of Ru1 and Ru1ii, O1 and O1ii, and O4 and O4ii, where the superscript ii denotes the equivalent position (x, xy, 7/6−z). The Ru1-Ru1ii, Ru1-O(equatorial), and Ru1-N1(axial) distances are 2.2695(7) Å, 2.010(3)—2.023(3) Å and 2.286(3) Å, respectively, which are in the usual range as observed in tetrakis(µ-carboxylato)diruthenium(II,III) clusters [1,2,3,4]. The Ru1ii-Ru1-N1 angle is 172.34(9)°, deviating from the linear arrangement and causing a wave-like chain structure. This structure is similar to those found in (PPh4)n[Rh2(RCOO)4Ag(CN)2]n (R = CH3, C6H5, and C2H5OCH2) [5] and (PPh4)n[Rh2(RCOO)4Au(CN)2]n (R = CH3, CH3OCH2, and C2H5OCH2) [6]. The crystal structure of 1 is shown in Figure 4a. There are no voids in the crystal structure. The pivalate complex [Ru2(t-C4H9COO)4Au(CN)4]n (4) crystallized in the triclinic lattice. The molecular structure of 4 is similar to that of 1, taking a trans-bridging mode of the tetracyanidoaurate(III) moiety for linking the two tetrakis(µ–pivalato)diruthenium(II,III) moieties, as shown in Figure 3d. The crystallographic inversion centers are located at the midpoints of the Ru1-Ru1i and Ru2-Ru2ii bonds, where the superscripts i and ii denote the equivalent positions (1−x, −y, 1−z) and (2−x, 2−y, −z), respectively. The Au-C, Ru-Ru, Ru-Oeq, and Ru-Nax distances are 1.992(3)–2.005(3) Å, 2.2673(4)–2.2689(5) Å, 2.0132(10)–2.0261(19) Å, and 2.278(2)–2.283(3) Å, respectively, which are similar to those of 1. The Ru-Ru-Nax angles are 172.75(7) and 173.71(6)°, which are also similar to that of 1, in accordance with the wave-like chain structure. There are very small voids in the crystal (Figure 4d). The propionate complex [Ru2(C2H5COO)4Au(CN)4]n (2) and the isobutyrate complex [Ru2(i-C3H7COO)4Au(CN)4]n (3) crystallized in the monoclinic lattice. The ORTEP views of the molecular structures of 2 and 3 are depicted in Figure 3b,c, respectively. The 1-D chain molecule consisting of alternating Ru2(C2H5COO)4+ or Ru2(i-C3H7COO)4+ and Au(CN)4 moieties form in the crystal structures. However, each Au(CN)4 moiety takes a cis-bridging mode to connect the dinuclear ruthenium moieties, in contrast to the cases for the acetate complex 1 and the pivalate complex 4, resulting in a zig-zag chain molecule in the propionate complex 2 and the isobutyrate complex 3. The Au-C, Ru-Ru, Ru-Oeq, and Ru-Nax distances are 1.995(3)–2.005(3) Å, 2.2665(3) Å, 2.009(2)–2.033(2) Å, and 2.263(2)–2.264(2) Å for 2, and 1.998(2)–2.000(2) Å, 2.2734(3) Å, 2.0219(15)–2.0270(15) Å, and 2.2728(18) Å for 3, respectively, which are similar to those of 1 and 4. The Ru-Ru-Nax angles are 174.96(7)—175.67(6)° for 2 and 175.35(5)° for 3, which are a little larger than those of 1 and 4. In these complexes, there are almost no voids in the crystal structures (Figure 4b,c). In these zig-zag chain molecules, two cis-cyanido groups of tetracyanidoaurate ion are free from coordination, and were found for the first time in heterometallic compounds of dinuclear metal carboxylates with tetracyanidometalate ions. In [{Ru2(CH3COO)4}2Ni(CN)4]n [14], [{Ru2(C2H5COO)4}2Pd(CN)4]n [16], and [{Ru2(CH3COO)4}2Pt(CN)4]n [18], four cyanido groups of tetracyanidometalate ion are coordinated to ruthenium atoms to form a 2D sheet in the crystals [16]. 5COO0. In the present complexes, each ruthenium atom takes an equivalent oxidation state of 2.5 between the II and III oxidation states as found in the RuII-RuIII carboxylates reported thus far [1,2,3,4].

2.5. Magnetic Properties of the Heterometallic Compounds [Ru2(RCOO)4Au(CN)4]n

Figure 5 shows the variable-temperature magnetic moment in the measured 4.5–300 K temperature range for [Ru2(CH3COO)4Au(CN)4]n (1) as a representative example. The magnetic properties of the present complexes are similar to each other (Figures S5–S7 for 2, 3, and 4, respectively). The magnetic moments (per RuII-RuIII unit) at 300 K of 1, 2, 3, and 4 are 4.24, 4.26, 4.37, and 4.29 μB, respectively, which are close to each other, suggesting the presence of three unpaired electrons per RuII-RuIII unit with an S = 3/2 state, although the moment values are a little higher the spin-only value, as in most cases for the reported mixed-valent RuII-RuIII carboxylates, where the magnetic moments were observed in the range of 3.6–4.4 µB at room temperature [1,2,3,4]. A decrease in the magnetic moments was observed with decreasing temperature, followed by a further steep decrease close to 5 K, which can be ascribed to the zero-field splitting parameter (D) within the Ru2(RCOO)4+ unit and the antiferromagnetic interaction between the Ru2(RCOO)4+ units through the axial Au(CN)4 linker. The magnetic data were simulated using Equations (1)–(4) described below for the S = 3/2 system with the zero-field splitting parameter D and the magnetic interaction between the Ru2(RCOO)4+ units being taken into account by the mean-field approximation [4,34,35,36]:
χ′ = χ/{1 − (2zJ/Ng2μB2)χ}
where z is the number of interacting neighbors, J is the magnitude of the intermolecular interactions, and χ is the magnetic susceptibility.
χ = (χ// + 2χ)/3
where χ// and χ are magnetic susceptibility terms defined as follows:
χ// = (Ng2μB2/kT){1 + 9exp(−2D/kT)}/4{1 + exp(−2D/kT)}
χ = (Ng2μB2/kT)[4 + (3kT/D){1 − exp(−2D/kT)}]/4{1 + exp(−2D/kT)}
The simulation gave the following parameter values: g = 2.21, D = 75 cm−1, zJ = −0.10 cm−1 for 1, g = 2.21, D = 75 cm−1, zJ = −0.10 cm−1 for 2, g = 2.23, D = 75 cm−1, zJ = −0.10 cm−1 for 3, g = 2.24, D = 75 cm−1, zJ = −0.15 cm−1 for 4. The obtained D values are normal for mixed-valent RuII-RuIII carboxylates and their derivatives [4]. The small zJ values mean that the magnetic interaction through the tetracyanidoaurate(III) linker is very weak and it was difficult to differentiate the magnetic interaction through the cis- and trans-linkers. Similar weak antiferromagnetic interactions were observed in the related heterometallic complexes of ruthenium(II,III) carboxylate with dicyanidoargentate(I) (zJ = −0.10, −0.50 cm−1) [12], tetracyanidonickelate(II) (zJ = −0.20 cm−1) [15], tetracynidopalladate(II) (zJ = −0.10 cm−1) [17], and tetracyanidoplatinate(II) (zJ = −0.10 cm−1) [18].

2.6. N2-Adsorption Properties of the Heterometallic Compounds [Ru2(RCOO)4Au(CN)4]n

The adsorption properties of the present complexes were measured for N2 at 77 K and the isotherms are given in Figure 6 for 1 and Figures S8–S10 for 2, 3, and 4, respectively. The adsorption isotherms of the present complexes are similar to each other and considered to be of Type II behavior (IUPAC classification) with SBET of 0.728 m2 g−1 for 1, 1.75 m2 g−1 for 2, 2.91 m2 g−1 for 3, and 1.49 m2 g−1 for 4. The nonporous properties are in accordance with the crystal structures of the present complexes.

3. Materials and Methods

All of the reagents and solvents were purchased from commercial sources and used without further purification.
The precursor complexes [Ru2(CH3COO)4(H2O)2]BF4 [12], [Ru2(C2H5COO)4(H2O)2]BF4, [Ru2(i-C3H7COO)4(H2O)2]BF4, and [Ru2(t-C4H9COO)4(H2O)2]BF4 [28] were prepared by the methods described in the literature.
Synthesis of [Ru2(CH3COO)4Au(CN)4]n (1): To an aqueous solution (5 cm3) of [Ru2(CH3COO)4(H2O)2]BF4 (50.0 mg, 0.0891 mmol), an aqueous solution (5 cm3) of K[Au(CN)4] (30.5 mg, 0.0897 mmol) was added. The solution was stirred overnight. The resulting reddish-brown precipitate was collected, washed with water, and desiccated in vacuo. Yield: 48.7 mg, 72.2%. Found C 19.21, H 1.81, N 7.21%. Calcd for C12H14AuN4O9Ru2 ([Ru2(CH3COO)4Au(CN)4]·H2O): C 19.03, H 1.86, N 7.40%. IR (KBr, cm−1): ν(CN) 2204, 2182; νas(COO) 1437, νs(COO) 1400. Diffuse reflectance spectra: λmax 266, 304 sh, 450 br (π(Ru-O, Ru2)→σ*(Ru-O); π(Ru-O, Ru2)→π*(Ru2)), 1026 (δ(Ru2)→δ*(Ru2)), 1502 (π*(Ru2)→δ*(Ru2)) nm.
Synthesis of [Ru2(C2H5COO)4Au(CN)4]n (2): This compound was prepared by the reaction of [Ru2(C2H5COO)4(H2O)2]BF4 (10.1 mg, 0.0164 mmol) and K[Au(CN)4] (5.5 mg, 0.016 mmol) in a similar manner to that of 1. Yield: 4.6 mg, 35%. Found C 24.20, H 2.46, N 7.01%. Calcd for C16H20AuN4O8Ru2: C 24.16, H 2.53, N 7.04%. IR (KBr, cm−1): ν(CN) 2225, 2186; νas(COO) 1465, νs(COO) 1433. Diffuse reflectance spectra: λmax 270, 306 sh, 436 (π(Ru-O, Ru2)→σ*(Ru-O))), 468 (π(Ru-O, Ru2)→π*(Ru2)), 1018 (δ(Ru2)→δ*(Ru2)), 1500 (π*(Ru2)→δ*(Ru2)) nm.
Synthesis of [Ru2(i-C3H7COO)4Au(CN)4]n (3): This compound was prepared by the reaction of [Ru2(i-C3H7COO)4(H2O)2]BF4 (10.1 mg, 0.0150 mmol) and K[Au(CN)4] (5.2 mg, 0.015 mmol) in a similar manner to that of 1. Yield: 6.1 mg, 47%. Found C 28.39, H 3.02, N 6.51%. Calcd for C20H28AuN4O8Ru2: C 28.21, H 3.31, N 6.58%. IR (KBr, cm−1): ν(CN) 2220, 2186; νas(COO) 1471, νs(COO) 1421. Diffuse reflectance spectra: λmax 282 br, 452 br (π(Ru-O, Ru2)→σ*(Ru-O); (π(Ru-O, Ru2)→π*(Ru2)), 1016 (δ(Ru2)→δ*(Ru2)), 1498 (π*(Ru2)→δ*(Ru2)) nm.
Synthesis of [Ru2(t-C4H9COO)4Au(CN)4]n (4): This compound was prepared by the reaction of [Ru2(t-C4H9COO)4(H2O)2]BF4 (10.0 mg, 0.0138 mmol) and K[Au(CN)4] (4.6 mg, 0.014 mmol) in a similar manner to that of 1. Yield: 7.4 mg, 59%. Found C 31.45, H 3.82, N 5.98%. Calcd for C24H36AuN4O8Ru2: C 31.76, H 4.00, N 6.17%. IR (KBr, cm−1): ν(CN) 2211, 2182; νas(COO) 1487, νs(COO) 1423. Diffuse reflectance spectra: λmax 278, 310 sh, 448 br (π(Ru-O, Ru2)→σ*(Ru-O); π(Ru-O, Ru2)→π*(Ru2)), 1016 (δ(Ru2)→δ*(Ru2)), 1498 (π*(Ru2)→δ*(Ru2)) nm.
Elemental analyses of C, H, and N were conducted with a Thermo-Finnigan FLASH EA1112 series CHNO-S analyzer (Thermo-Finnigan, Milan, Italy). IR spectra were recorded as KBr discs with a JASCO MFT-2000 FT-IR spectrometer (JASCO, Tokyo, Japan). Powder reflectance spectra were recorded with a Shimadzu Model UV-3100 UV-vis-NIR spectrophotometer (Shimadzu, Kyoto, Japan). Magnetic susceptibility measurements were conducted using a Quantum Design SQUID susceptometer (MPMS-XL7, Quantum Design North America, San Diego, CA, USA) with a magnetic field of 0.5 T over a temperature range of 4.5–300 K. The magnetic susceptibility χM is the molar magnetic susceptibility per mole of [Ru2(RCOO)4Au(CN)4] unit and was corrected for the diamagnetic contribution calculated from Pascal’s constants [37]. N2-adsorption measurements were conducted by a MicrotracBEL BELSORP-mini II (MicrotracBEL, Osaka, Japan). The samples were evacuated at 298 K for 2 h prior to the measurements.
All measurements for single-crystal X-ray diffraction were made using a Bruker Smart APEX CCD diffractometer (Bruker, Billerica, MA, USA) with graphite monochromated Mo Kα radiation (λ = 0.71073 Å). The structures were solved using intrinsic phasing methods and refined by full-matrix least-squares methods. The hydrogen atoms were included at their positions calculated geometrically. All of the calculations were carried out using the SHELXTL software package [38]. Crystallographic data have been deposited with Cambridge Crystallographic Data Centre: Deposit numbers CCDC-2157503, 2157501, 2157498, and 2157500 for 1, 2, 3, and 4, respectively. Copies of the data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (accessed on 10 March 2022) (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ, UK; Fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).

4. Conclusions

In this study, four new heterometallic Ru2Au complexes were synthesized by the reaction of tetrakis(µ-carboxylato)diruthenium(II,III) with tetracyanidoaurate(III). We have found that the acetate Ru2Au complex and the pivalate Ru2Au complex are wave-like chain molecules with the trans-bridging mode of the teracyanidoaurate(III) linkers, while the propionate Ru2Au complex and the isobutyrate Ru2Au complex are zig-zag chain molecules with the cis-bridging mode of the Au(CN)4 linkers. The different bridging modes of the Au(CN)4 linkers may come from the symmetrical difference in the substituent R groups of the carboxylato-bridges of the Ru2(RCOO)4+ core. It may be considered that more symmetrical CH3- and t-C4H9- groups cannot allow the steric hindrance between these alkyl groups for the cis-bridging mode, while the C2H5- and i-C3H7- groups can accommodate the cis-bridging mode because of the lower symmetry of the alkyl groups. The temperature dependence of the magnetic susceptibilities suggested that the magnetic interaction of the Ru2(RCOO)4+ spins through the Au(CN)4 moieties is very weak, based on the 3/2 spin state of the RuII-RuIII unit of the present complexes, which should be confirmed by the magnetization measurements at very low temperatures in further studies.

Supplementary Materials

The following are available online at https://www.mdpi.com/article/10.3390/magnetochemistry8050048/s1, Figure S1: Infrared spectra of [Ru2(CH3COO)4Au(CN)4]n (1); Figure S2: Infrared spectra of [Ru2(C2H5COO)4Au(CN)4]n (2); Figure S3: Infrared spectra of [Ru2(i-C3H7COO)4Au(CN)4]n (3); Figure S4: Infrared spectra of [Ru2(t-C4H9COO)4Au(CN)4]n (4); Figure S5: Variable temperature of magnetic moment μeff for [Ru2(C2H5COO)4Au(CN)4]n (2). The solid black line was calculated and drawn with the parameter values described in the text; Figure S6: Variable temperature of magnetic moment μεff for [Ru2(i-C3H7COO)4Au(CN)4]n (3). The solid black line was calculated and drawn with the parameter values described in the text; Figure S7: Variable temperature of magnetic moment μeff for [Ru2(t-C4H9COO)4Au(CN)4]n (4). The solid black line was calculated and drawn with the parameter values described in the text; Figure S8: Nitrogen adsorption isotherm of [Ru2(C2H5COO)4Au(CN)4]n (2). Solid line is guide for the eye; Figure S9: Nitrogen adsorption isotherm of [Ru2(i-C3H7COO)4Au(CN)4]n (3). Solid line is guide for the eye; Figure S10: Nitrogen adsorption isotherm of [Ru2(t-C4H9COO)4Au(CN)4]n (4). Solid line is guide for the eye; Table S1: Some selected structural parameters of the present complexes 14.

Author Contributions

Conceptualization, M.M.; methodology, M.M. and M.H.; in-vestigation, Y.T., D.Y. and H.T.; data curation, M.M.; writing—original draft preparation, M.M.; writing—review and editing, M.M., M.T. and M.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Scheme 1. Chemical structures of tetrakis(µ-carboxylato)diruthenium(II,III) cations (R = CH3, C2H5, i-C3H7, t-C4H9) and tetracyanidoaurate(III) anion.
Scheme 1. Chemical structures of tetrakis(µ-carboxylato)diruthenium(II,III) cations (R = CH3, C2H5, i-C3H7, t-C4H9) and tetracyanidoaurate(III) anion.
Magnetochemistry 08 00048 sch001
Figure 1. Infrared spectra of [Ru2(CH3COO)4Au(CN)4]n (1), [Ru2(C2H5COO)4Au(CN)4]n (2), [Ru2(i-C3H7COO)4Au(CN)4]n (3), and [Ru2(t-C4H9COO)4Au(CN)4]n (4) in the 2300–2000 cm−1 region.
Figure 1. Infrared spectra of [Ru2(CH3COO)4Au(CN)4]n (1), [Ru2(C2H5COO)4Au(CN)4]n (2), [Ru2(i-C3H7COO)4Au(CN)4]n (3), and [Ru2(t-C4H9COO)4Au(CN)4]n (4) in the 2300–2000 cm−1 region.
Magnetochemistry 08 00048 g001
Figure 2. Diffused reflectance spectra of [Ru2(CH3COO)4Au(CN)4]n (1) (dark-blue line), [Ru2(C2H5COO)4Au(CN)4]n (2) (pink line), [Ru2(i-C3H7COO)4Au(CN)4]n (3) (orange line), and [Ru2(t-C4H9COO)4Au(CN)4]n (4) (right-blue line).
Figure 2. Diffused reflectance spectra of [Ru2(CH3COO)4Au(CN)4]n (1) (dark-blue line), [Ru2(C2H5COO)4Au(CN)4]n (2) (pink line), [Ru2(i-C3H7COO)4Au(CN)4]n (3) (orange line), and [Ru2(t-C4H9COO)4Au(CN)4]n (4) (right-blue line).
Magnetochemistry 08 00048 g002
Figure 3. The ORTEP view of molecular structures of (a) [Ru2(CH3COO)4Au(CN)4]n (1), (b) [Ru2(C2H5COO)4Au(CN)4]n (2), (c) [Ru2(i-C3H7COO)4Au(CN)4]n (3), and (d) [Ru2(t-C4H9COO)4Au(CN)4]n (4), with thermal ellipsoids (50% probability level). The hydrogen atoms have been omitted for clarity.
Figure 3. The ORTEP view of molecular structures of (a) [Ru2(CH3COO)4Au(CN)4]n (1), (b) [Ru2(C2H5COO)4Au(CN)4]n (2), (c) [Ru2(i-C3H7COO)4Au(CN)4]n (3), and (d) [Ru2(t-C4H9COO)4Au(CN)4]n (4), with thermal ellipsoids (50% probability level). The hydrogen atoms have been omitted for clarity.
Magnetochemistry 08 00048 g003aMagnetochemistry 08 00048 g003b
Figure 4. Packing diagrams of (a) [Ru2(CH3COO)4Au(CN)4]n (1), (b) [Ru2(C2H5COO)4Au(CN)4]n (2), (c) [Ru2(i-C3H7COO)4Au(CN)4]n (3), and (d) [Ru2(t-C4H9COO)4Au(CN)4]n (4). The hydrogen atoms have been omitted for clarity.
Figure 4. Packing diagrams of (a) [Ru2(CH3COO)4Au(CN)4]n (1), (b) [Ru2(C2H5COO)4Au(CN)4]n (2), (c) [Ru2(i-C3H7COO)4Au(CN)4]n (3), and (d) [Ru2(t-C4H9COO)4Au(CN)4]n (4). The hydrogen atoms have been omitted for clarity.
Magnetochemistry 08 00048 g004aMagnetochemistry 08 00048 g004b
Figure 5. Variable temperature of magnetic moment μeff for [Ru2(CH3COO)4Au(CN)4]n (1). The solid black line was calculated and drawn with the parameter values described in the text.
Figure 5. Variable temperature of magnetic moment μeff for [Ru2(CH3COO)4Au(CN)4]n (1). The solid black line was calculated and drawn with the parameter values described in the text.
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Figure 6. Nitrogen adsorption isotherm of [Ru2(CH3COO)4Au(CN)4]n (1). The solid line is a guide for the eye.
Figure 6. Nitrogen adsorption isotherm of [Ru2(CH3COO)4Au(CN)4]n (1). The solid line is a guide for the eye.
Magnetochemistry 08 00048 g006
Table 1. Crystallographic data and structure refinement of 14.
Table 1. Crystallographic data and structure refinement of 14.
Complexes1234
Chemical formulaC12H12AuN4O8Ru2C16H20AuN6O8Ru2C20H28AuN4O8Ru2C24H36AuN4O8Ru2
FW739.36795.47851.57907.67
Temperature, T (K)90909090
Crystal systemhexagonalmonoclinicmonoclinictriclinic
Space groupP6122P21/nC2/cP1
a (Å)11.8315 (10)9.1142 (7)16.6865 (16)9.1719 (8)
b (Å) 16.7312 (14)17.9811 (18)9.8063 (9)
c (Å)23.2375 (19)15.8456 (13)9.2176 (9)19.6140 (17)
α (°) 77.3160 (10)
β (°) 104.6400 (10)104.7720 (10)80.9730 (10)
γ (°) 88.4590 (10)
V3)2817.1 (5)2337.9 (3)2674.3 (5)1699.7 (3)
Z6442
Dcalcd (g cm−3)2.6152.2602.1151.774
Crystal size (mm)0.72 × 0.23 × 0.150.45 × 0.13 × 0.110.55 × 0.15 × 0.140.37 × 0.23 × 0.13
μ (mm−1)9.4287.5826.6365.226
θ range for data collection (°)1.988–28.8041.802–28.7801.696–28.7591.077–28.845
Reflections collected/unique17,112/230114,237/55888386/319010,479/7764
[R1(I > 2σ(I)); wR2 (all data)] (a)R1 = 0.0153R1 = 0.0207 R1 = 0.0156 R1 = 0.0230
ωR2 = 0.0380ωR2 = 0.0512ωR2 = 0.0383ωR2 = 0.0584
GOF1.1361.1001.1181.042
(a) R1 = ∑||Fo| − |Fc||/∑|Fo|; ωR2 = [∑ω(Fo2Fc2)2/∑(Fo2)2]1/2.
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Mikuriya, M.; Tanaka, Y.; Yoshioka, D.; Tsuboi, M.; Tanaka, H.; Handa, M. Heterometallic Chain Compounds of Tetrakis(µ-carboxylato)diruthenium and Tetracyanidoaurate. Magnetochemistry 2022, 8, 48. https://doi.org/10.3390/magnetochemistry8050048

AMA Style

Mikuriya M, Tanaka Y, Yoshioka D, Tsuboi M, Tanaka H, Handa M. Heterometallic Chain Compounds of Tetrakis(µ-carboxylato)diruthenium and Tetracyanidoaurate. Magnetochemistry. 2022; 8(5):48. https://doi.org/10.3390/magnetochemistry8050048

Chicago/Turabian Style

Mikuriya, Masahiro, Yusuke Tanaka, Daisuke Yoshioka, Motohiro Tsuboi, Hidekazu Tanaka, and Makoto Handa. 2022. "Heterometallic Chain Compounds of Tetrakis(µ-carboxylato)diruthenium and Tetracyanidoaurate" Magnetochemistry 8, no. 5: 48. https://doi.org/10.3390/magnetochemistry8050048

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