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Article

Highly Porous Cyanometallic Spin-Crossover Frameworks Employing Pyridazino[4,5-d]pyridazine Bridge

by
Volodymyr M. Hiiuk
1,
Sergiu Shova
2,3,
Kostiantyn V. Domasevitch
1 and
Il’ya A. Gural’skiy
1,*
1
Department of Chemistry, Taras Shevchenko National University of Kyiv, 64 Volodymyrska St., 01601 Kyiv, Ukraine
2
CEEC Institute, Ningbo University of Technology, No. 201, Fenghua Road, Ningbo 315211, China
3
“Petru Poni” Institute of Macromolecular Chemistry, 41A Aleea Gr. Ghica Voda, 700487 Iasi, Romania
*
Author to whom correspondence should be addressed.
Inorganics 2022, 10(11), 195; https://doi.org/10.3390/inorganics10110195
Submission received: 13 October 2022 / Revised: 28 October 2022 / Accepted: 29 October 2022 / Published: 2 November 2022
(This article belongs to the Special Issue Inorganics: 10th Anniversary)
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Abstract

:
Single crystals of two spin-crossover (SCO) cyanometallic coordination polymers based on the pyridazino[4,5-d]pyridazine ligand (pp) of the composition [Fe(pp)M(CN)4]∙G (where M = Pd, Pt; G = guest molecules) were obtained by a slow diffusion technique. A single-crystal X-ray analysis showed that both compounds adopted the structure of porous 3D frameworks, consisting of heterometallic cyano-bridged layers and interlayer pillar pp ligands, with a total solvent accessible volume of ca. 160 Å3 per iron(II) ion (about 37% of the unit cell volume). These frameworks displayed hysteretic SCO behaviour with T1/2 of 150/190 K (heating/cooling) for Pd complex and 135/170 K (heating/cooling) for Pt complex, which was confirmed by variable-temperature SCXRD experiments. This research shows the perspective of using pp ligand for building porous MOFs with spin transitions.

1. Introduction

Iron(II) spin-crossover (SCO) porous coordination polymers (PCPs) occupy a special place among the various types of metal-organic frameworks (MOFs). Iron(II) ions in such types of polymers are able to undergo a reversible switch between two different electronic states (high-spin (HS) and low-spin (LS) states) under external stimuli. This causes significant changes in various physical properties of the compound including magnetic, electrical, and mechanical properties [1,2,3,4]. SCO behaviour of PCPs is often highly sensitive to the presence of guest molecules in the framework cavities. There are already many examples of how the inclusion of both small molecules and large aromatic systems in 3D Hofmann-type PCPs shows an exceptional effect on the main SCO parameters (temperature, sharpness, completeness, hysteresis) [5,6]. Moreover, the strategy of controlled incorporation and exchange of guest molecules is effective to produce multi-step SCO materials [7,8,9]. Thus, the combination of SCO properties, high porosity, and structural diversity make SCO-PCPs attractive components for the design of new switchable materials. The distinct influence of guest molecules on SCO properties of PCPs may be of interest for potential chemical sensing applications [10,11].
Among the first reported SCO-PCPs, there are 2D frameworks with general formula [Fe(L)2(NCS)2]·Guest, where L = some bis-monodentate pyridine-like ligand such as trans-1,2-di(4-pyridyl)ethylene (dpe) [12,13,14,15], trans-4,4′-azopyridine (azpy) [16,17], 2,3-bis(4′-pyridyl)-2,3-butanediol (bpbd) [18,19], or 1,2-bis(4′-pyridyl)-1,2-ethanediol (bped) [20]. Complexes of this type usually exhibit guest-dependent gradual SCO behaviour with low transition temperatures (below 200 K). The adsorption of guest molecules leads to significant changes in the coordination geometry around iron(II) centres, while the desorption causes stabilization of the HS state of the framework [13,17,20].
The most known and well-studied members of SCO-PCPs that exhibit chemo-responsive behaviour are Hofmann-type iron(II) complexes of the composition [Fe(pz)M(CN)4] (where M = Ni, Pt, Pd; pz = pyrazine) [21,22,23,24,25,26,27,28,29,30]. These PCPs are 3D porous frameworks, consisting of cyano-bridged layers and interlayer pillar pz ligands, with hysteretic SCO around room temperature. Having high porosity, pz complexes are able to adsorb various guest molecules including gases [22,27,30], different organic molecules [28,29], and even chemically reactive dihalogen molecules [23,25]. Such adsorption results in different SCO behaviour depending on the guest molecules and different types of host-guest interactions. A remarkable example is the CS2 molecule that stabilizes the LS state of the iron(II) sites in [Fe(pz)Pt(CN)4], whereas the benzene molecule stabilizes the HS state. The adsorption of small molecules such as CO2 and N2 has practically no effect on SCO [24]. Thus, guest-induced reversible modifications can be used as an intrinsic stimulus for the fine-tuning SCO properties of a material. Other examples of bridging ligands used to design 3D Hofmann-type clathrates with [M(CN)4]2− units are 1,4-bis(4-pyridylbutadiyne) (bpb) [31,32,33], (1H-1,2,4-triazole-3,5-diyl)dipyridine (Hbpt) [34], 4,4′-di(pyridylthio)methane (dpsme) [35], 1,4-bis(4-pyridylethynyl)benzene (bpeben) [36], bis(4-pyridyl)acetylene (bpac) [37,38,39], azpy [40], and dpe [41].
SCO-PCPs based on them also demonstrate guest-dependent SCO properties and this makes them perspective for further practical applications. For example, the [Fe(bpb)Pt(CN)4] framework is capable hosting up to two guest aromatic molecules (such as naphthalene or nitrobenzene) per iron(II) centre [31]. The use of the [Fe(bpac)Pt(CN)4] complex makes it possible to detect volatile organic compounds (such as mono- and polyhalogen-substituted benzenes) via changes in the spin state [39].
The use of linear [M(CN)2]− (where M = Ag, Au) linkers with various pillar azine ligands is also a well-working synthetic strategy for the design of SCO-PCPs [42,43,44,45,46,47,48,49,50,51]. In contrast to complexes with square-planar [M(CN)4]2− (where M = Ni, Pt, Pd) linkers, a 2D [Fe{M(CN)2}2]∞ net with larger meshes is generated here, which assumes the presence of larger solvent-accessible voids. Moreover, the use of bent pillar azine ligands, as well as the introduction of different guest molecules, tends to cause distortions in the Hofmann layer leading to symmetry breaking. This is also one of the factors of stimulating multi-step SCO in complexes [8,52,53,54,55,56,57,58,59].
Thus, π-deficient heterocyclic N-donor ligands are mainly used to design SCO coordination polymers. Therefore, our interest was attracted by a structurally simple, geometrically regular condensed pyridazine ligand: pyridazino[4,5-d]pyridazine (pp; Scheme 1), which is one of the most electron deficient systems (and can even undergo inverse electron-demand [4 + 2]-cycloadditions as a bis-azadiene) [60].
Herein, we present the results in the area of SCO-PCPs. Single crystals of SCO iron(II) complexes with pillar bicyclic pyridazino[4,5-d]pyridazine ligand of the composition [Fe(pp)M(CN)4]∙G (where M = Pd (1), Pt (2); G = guest molecules) have been obtained. Both compounds adopt the structure of 3D frameworks containing guest available pores and exhibiting hysteretic SCO behaviour. Since the pp ligand is characterized by large distances between donor centres compared to its structural analogue, pyrazine, one could expect the formation of larger framework cavities and, consequently, an increased porosity of the obtained SCO-PCPs compared to pz complexes.

2. Results and Discussion

An analysis of the correlations between the SCO properties of a complex and its structure is essential for more advanced design of switchable materials; therefore, we carried out a single crystal X-ray diffraction analysis of 1 and 2 in both the LS and HS states. The corresponding crystallographic data are summarized in Table 1. The selected structural parameters are given in Table 2.
It was found that both complexes crystallize in the monoclinic P2/m space group, which is maintained after the spin transition. There is only one crystallographically independent iron(II) site in both HS and LS structures. It should be noted that analogous SCO compounds belonging to the same space group have also already been reported. For example, Hofmann-type clathrates with the composition [Fe(bpb)M(CN)4]∙xGuest (where M = Ni, Pt; Guest = (trifluoromethyl)benzene) display complete one-step SCO [33]. Another example is the HS form of [Fe(pz)Pt(CN)4]·pz stabilized by the inclusion of a pyrazine molecule in the framework as a guest molecule [24,29]. However, most similar frameworks with pillar ligands such as pz, bpeben, dpe, azpy, and bpac crystallize in the tetragonal P4/mmm space group [23,24,26,27,28,36,37,38,40,41].
In the title complexes, iron(II) has a coordination environment of an elongated FeN6 pseudo-octahedron (Figure 1a). The equatorial positions of the octahedron are occupied by four N atoms of four crystallographically equivalent square-planar [M(CN)4]2− (M = Pt, Pd) linkers generating corrugated 2D {FeM(CN)4}∞ layers with (4,4)-net topology which lay in the ab plane. Cyanometallic layers lay one on top of each other and are supported by bridging pp ligands, which occupy the axial positions of iron(II). Thus, a porous 3D Hofmann-type framework (Figure 1b–d) is formed by analogy with complexes based on pyrazine [21].
Structural changes in the coordination environment of the metal are observed during a thermally induced spin transition. Changes in the unit cell parameters for both complexes upon LS to HS transition are Δa = +1.8%, Δb = +3.9%, Δc = −3.0% for 1 and Δa = +1.2%, Δb = +3.3%, Δc = −3.7% for 2. As a result, expansion along the a and b axes and contraction along the c axis are observed. The Fe−N≡C angles deviate from 180° by 20.7° (293 K) and 12.7° (125 K) for 1 and 22.9° (293 K) and 13.0° (123 K) for 2. Such large values of Fe−N≡C angles clearly confirm the significant corrugation of the cyanometallic layers for both complexes. The M−C≡N angles deviate from linearity by 4.1° (293 K) and 6.5° (125 K) for [Pd(CN)4]2− and 2.1° (293 K) and 5.4° (123 K) for [Pt(CN)4]2−. The C−M−C angles of both complexes do not change with temperature and are equal to 180°.
At 293 K, the average <Fe−N> bond lengths are 2.168(2) Å for 1 and 2.163(5) Å for 2, which correspond to the HS state of iron(II) ions. A decrease in temperature to 123 K leads to the shortening of the average <Fe−N> bond lengths by about 0.2 Å to 1.953(3) Å for 1 and 1.961(5) Å for 2, which is consistent with complete HS to LS transitions. Comparing the equatorial and axial Fe−N bond lengths, we notice that the former is always slightly shorter than the latter in both HS and LS states. The total change of the volume of the unit cell is 6.1% and 4.2% for 1 and 2, respectively. As expected, the volume of the FeN6 octahedron drops from 13.536 to 9.916 Å3 for 1 and from 13.454 to 10.028 Å3 for 2 upon HS to LS transitions.
The geometry around the iron(II) centres is sensitive to temperature change, and more precisely to the spin state of the iron(II) ions. At 293 K, the iron(II) octahedral distortion parameters (the sum of deviations from 90˚ for 12 “cis” N−Fe−N angles of FeN6 octahedron) are ΣHS = 32.0° for 1 and ΣHS = 27.3° for 2. At 123 K, the ΣLS is reduced to 21.2° and 24.0° for 1 and 2, respectively. Thus, LS iron(II) is characterized by a more regular FeN6 octahedron with more linear coordination of cyanide ligands due to stronger Fe–N bonds.
The gate size of the pores in these SCO-PCPs is defined by the Fe···Fe distances through the pillar pp ligand and the [M(CN)4]2− linkers (Figure S1). For 1 it is 9.34 × 7.19−7.46 Å in the HS state and 8.87 × 7.06–7.18 Å in the LS state. For 2 it is 9.33 × 7.18–7.46 Å in the HS state and 8.91 × 7.10–7.22 Å in the LS state. As expected, guest solvent molecules used for crystallization (H2O and CH3OH) are located inside the available pores of both complexes. However, we are unable to propose any reasonable structural model for them in the pores since they are highly disordered, even at 124 K. Therefore, electron density of guest solvent molecules was removed by the solvent mask routine. Although the removal of guest solvents with this procedure excludes the visualization of possible host-guest interactions and reduces some quality of the structural model, we note that this did not affect the general conclusions made regarding the topology of the frameworks, as well as the correct interpretation of the SCO behaviour of these PCPs.
The total number of electrons corresponding to solvent molecules per unit cell is 35.2 at 293 K and 33.6 at 125 K for 1 and 35.2 at 293 K and 13.4 at 123 K for 2. The total solvent accessible volume per unit cell without considering the disordered solvent molecules for 1 was calculated as 159.1 Å3 at 293 K and 146.5 Å3 at 125 K, which corresponds to 36.8% and 36.0% of the unit-cell volume, respectively. For 2, it was calculated as 160.0 Å3 (37.1%) at 293 K and 149.3 Å3 (36.0%) at 123 K (Table 2). As a result, an almost twofold increase in porosity is observed compared to the [Fe(pz)Pt(CN)4] framework, for which the solvent-accessible voids in the HS and LS states are 90.4 Å3 (22.4%) and 63.4 Å3 (18.1%), respectively [24]. However, it should be noted that to date, Hofmann-type SCO-PCPs of the general formula [Fe(L)Pt(CN)4] have already been obtained based on ligands of various sizes and chemical nature with larger values of the solvent-accessible voids: 849.6 Å3 (53.8%) for bpb [31,33], 707.1 Å3 (47.1%) for dpsme [35], 511 Å3 (48.9%) for bpeben [36], 293.6 Å3 (41.7%) for bpac [37,38], 286 Å3 (43%) azpy [40], 272.7 Å3 (39.8%) for dpe [41] (all these values are given for the LS state of the complexes since, unlike pp derivatives, most crystals of these compounds deteriorate rapidly during X-ray diffraction experiments at RT).
The preparation of bulk samples with described phases appeared to be a problematic task, which is why the SCO behaviour of both complexes was confirmed by variable-temperature single-crystal X-ray diffraction (SCXRD) experiments. This approach was used due to the difficulty of collecting enough crystals for magnetic measurement, which is the most convenient method for monitoring SCO. The temperature dependences of the crystal lattice parameters of 1 and 2 are shown in Figure 2 and Figure S2.
As expected, the crystallographic parameters change from LS to HS. There is a positive thermal expansion along a and b axes, while a negative thermal expansion takes place along c axis. From 120 to 200 K, the a and b parameters expand by ∼2% and ∼4%, respectively, while the c axis shrinks by ∼4% for both complexes. This indicates the strong coupling of the spin transition and lattice expansion/contraction. The total change of the volume of the unit cell is ∼5% for both complexes. Thus, the microscopic structural changes of the single crystal provoke its significant macroscopic changes, which is an important feature of the obtained compounds since it can be used for the development of molecular machines [61]. While most magnetic measurements are usually done in a sweep mode, the current diffraction measurements were performed in a settle regime. Thus, one should consider the small fluctuation upon thermalization at each temperature that can cause the width of obtained hysteresis loops to be slightly underestimated.
We attempted to explain the possible reason of these lattice deformations for both complexes by overlaying their crystal structures in the LS and HS states (Figure 3). If the expansion along the a and b axes can be explained by the increases in the molecular volume and Fe−N bond lengths upon LS to HS transitions (Figure 3a,b), then the contraction of the lattice along the c axis has some specific reason. There is a slightly different crystal packing of pp ligands along the c axis. Consequently, this SCO-driven packing of pp ligands leads to anisotropic expansion along the b axis and contraction along the c axis, as shown in Figure 3c,d.
The average value of transition temperatures for all crystal lattice parameters in the cooling/heating regimes are ca. 150/190 K and 135/170 K for 1 and 2, respectively. The width of the thermal hysteresis loop is ca. 40 K for 1 and 35 K for 2. The observed hysteresis loop is almost twice as wide as the desolvated [Fe(pz)Pt(CN)4] framework, which is characterized by a 24 K hysteresis centred at 295 K (T1/2↓ = 285 K and T1/2↑ = 309 K) [24]. The presence of a wide thermal hysteresis loop clearly demonstrates the existence of a significant level of cooperativity for the single crystals of both pp complexes.

3. Materials and Methods

Single crystals of 1 and 2 were formed by a slow diffusion method within three layers in a 5 mL tube. K2[M(CN)4] (where M = Pd, Pt) (0.010 mmol) and pp (0.025 mmol) in water (1 mL) from one side and Fe(OTs)2∙6H2O (0.010 mmol) in methanol (1 mL) from another side were left to diffuse through a layer of water–methanol (1:1, 2 mL) for 3 weeks.
The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction using an Oxford-Diffraction XCALIBUR E CCD diffractometer (Oxford Diffraction Ltd., Abingdon, Oxfordshire, UK) with graphite-monochromated Mo-Kα radiation at 293/125 K for 1 and 293/123 K for 2. SCXRD experiments in the form of pre-experiments were carried out in cooling and heating regimes on a selected single crystal at various temperatures (Tables S1 and S2). Data collection at low temperatures was performed using an Oxford Instruments open-flow N2 Cryostream (Oxford Cryosystems Ltd., Long Hanborough, Oxford, UK) for cooling. The unit cell determination and data integration were carried out using the CrysAlisPro package from Oxford Diffraction (Yarnton, Oxfordshire, UK). Absorption correction using spherical harmonics was applied. The structures were solved by intrinsic phasing methods with SHELXT and refined by full-matrix least-squares on F2 with SHELXL using the graphical interface of Olex2 (SHELX program from Institute of Inorganic Chemistry, Göttingen, Germany and Olex2 software from Durham University/EPSRC, Durham, UK) [62,63,64]. A solvent mask procedure integrated in Olex2 was used to remove the electron density from MeOH and H2O guest molecules. All non-hydrogen atoms were refined anisotropically. Aromatic hydrogen atoms were geometrically fixed and refined using a riding model. Crystallographic data for 1 and 2 are listed in Tables S3–S32. Specific details of each refinement are given in the crystallographic information files (CIF-files). Crystallographic data for the structures have been deposited with the Cambridge Crystallographic Data Centre, CCDC: 2212767 (1—293 K), 2212768 (1—125 K), 2212765 (2—293 K), and 2212766 (2—123 K). Graphical representations of the structures were produced using Diamond 3.1 software (Crystal Impact GbR, Bonn, Germany). The distortion parameters (Σ) were calculated using the OctaDist tool (OctaDist development team: the Computational Chemistry Research Unit at Thammasat University (Pathum Thani, Thailand), the Functional Materials and Nanotechnology Center of Excellence at Walailak University (Thasala, Nakhon Si Thammarat, Thailand) and the Switchable Molecules and Materials group at University of Bordeaux (Nouvelle-Aquitaine, Bordeaux, France)) [65].

4. Conclusions

In this work, we have reported the synthesis and structural studies of two SCO-PCPs based on the pp ligand. Complexes 1 and 2 are isostructural to each other and display strong cooperative SCO behaviour with a wide thermal hysteresis loop at low temperatures. Due to the use of a more extended ligand (pp), obtained complexes show a twofold increase in porosity compared to the well-studied PCP [Fe(pz)Pt(CN)4]. The total solvent accessible volume of 1 and 2 are about 160 Å3 per iron(II) ion, which corresponds to 37% of the unit cell volume.
This research shows how the combination of SCO properties and high porosity makes pp complexes attractive multifunctional elements for various applications and implies their use as objects of further study on the influence of the guest effect on SCO behaviour including guest detection and separation studies.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics10110195/s1, Figure S1: View of the 1D channel of 1 (a) and 2 (b) along the a-axis direction. The gate sizes of the pores of 1 and 2 in the LS (blue) and HS (red) states; Figure S2: Temperature dependences of β angles of 1 (a) and 2 (b); Table S1: Selected crystallographic data for 1 extracted from SCXRD pre-experiments at various temperatures; Table S2: Selected crystallographic data for 2 extracted from SCXRD pre-experiments at various temperatures.; Crystallographic data for 1 and 2 are listed in Tables S3–S32.

Author Contributions

V.M.H.: Conceptualization, Methodology, Formal analysis, Investigation, Visualization. S.S.: Methodology, Formal analysis, Investigation. K.V.D.: Formal analysis, Investigation. I.A.G.: Conceptualization, Methodology, Formal analysis, Investigation, Supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This work has been supported by Ministry of Education and Science of Ukraine (projects 22BF037-03 and 22BF037-09). Access to the research infrastructure developed through the European Social Fund for Regional Development, Competitiveness Operational Programme Axis 1, Action: 1.1.3, Project “Infra SupraChem Lab—Center for Advanced Research in Supramolecular Chemistry” (Contract 339/390015/25.02.2021, cod MySMIS: 108983) is gratefully acknowledged.

Data Availability Statement

Crystallographic data are freely available at the Cambridge Crystallographic Data Centre under 2212765-2212768.

Acknowledgments

V.M.H. thanks the Krzysztof Skubiszewski Foundation for the financial support.

Conflicts of Interest

The authors declare no conflict of interest.

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Inorganics 10 00195 sch001 550
Scheme 1. Molecular structure of the pyridazino[4,5-d]pyridazine (pp) ligand.
Scheme 1. Molecular structure of the pyridazino[4,5-d]pyridazine (pp) ligand.
Inorganics 10 00195 sch001
Inorganics 10 00195 g001 550
Figure 1. Crystal structure of [Fe(pp)Pt(CN)4] (2) in the HS state: (a) Representation of a key fragment showing the coordination environment of iron(II); (b) The basic cavity of the structure; (c) View along b direction showing the corrugated cyanometallic layers and pillar coordination of these layers by pp ligands; (d) View in ab plane showing the 2D {FePt(CN)4}∞ layer with (4,4)-net topology. Colour code: Fe (olive green), Pt (brown), N (blue), C (gray). Hydrogen atoms in (b–d) are omitted for clarity. Guest solvent molecules were removed.
Figure 1. Crystal structure of [Fe(pp)Pt(CN)4] (2) in the HS state: (a) Representation of a key fragment showing the coordination environment of iron(II); (b) The basic cavity of the structure; (c) View along b direction showing the corrugated cyanometallic layers and pillar coordination of these layers by pp ligands; (d) View in ab plane showing the 2D {FePt(CN)4}∞ layer with (4,4)-net topology. Colour code: Fe (olive green), Pt (brown), N (blue), C (gray). Hydrogen atoms in (b–d) are omitted for clarity. Guest solvent molecules were removed.
Inorganics 10 00195 g001
Inorganics 10 00195 g002 550
Figure 2. Temperature dependences of the crystal lattice parameters (a axis, b axis, c axis, and unit cell volume) of 1 (a) and 2 (b) upon heating (●) and cooling (■).
Figure 2. Temperature dependences of the crystal lattice parameters (a axis, b axis, c axis, and unit cell volume) of 1 (a) and 2 (b) upon heating (●) and cooling (■).
Inorganics 10 00195 g002
Inorganics 10 00195 g003 550
Figure 3. Superimposition of the LS (blue) and HS (red) sub-lattices of 1 (a,c) and 2 (b,d) along the c-axis and b-axis directions. Hydrogen atoms and disordered solvent are omitted for clarity.
Figure 3. Superimposition of the LS (blue) and HS (red) sub-lattices of 1 (a,c) and 2 (b,d) along the c-axis and b-axis directions. Hydrogen atoms and disordered solvent are omitted for clarity.
Inorganics 10 00195 g003
Table
Table 1. Crystallographic data for 1 and 2 in the LS and HS states.
Table 1. Crystallographic data for 1 and 2 in the LS and HS states.
[Fe(pp)Pd(CN)4]∙G (1)[Fe(pp)Pt(CN)4]∙G (2)
Temperature (K)293125293123
Spin StateHSLSHSLS
Empirical Formula *C10H4FeN8PdC10H4FeN8PdC10H4FeN8PtC10H4FeN8Pt
Mr398.46398.46487.15487.15
Crystal Systemmonoclinicmonoclinicmonoclinicmonoclinic
Space GroupP2/mP2/mP2/mP2/m
a (Å)7.1903(3)7.0619(6)7.1806(5)7.0971(6)
b (Å)7.4599(2)7.1811(5)7.4575(5)7.2163(4)
c (Å)8.4271(4)8.6859(7)8.4389(8)8.7642(8)
β (°)107.071(5)112.392(10)107.185(9)112.610(10)
V (Å3)432.11(3)407.27(6)431.72(6)414.36(6)
Z1111
ρcalc (g cm−3)1.5311.6251.8741.952
μ (mm−1)1.8801.9958.9339.307
Total Solvent Accessible Volume/Cell (Å3)159.1146.5160.0149.3
Solvent Electrons/Cell35.233.635.213.4
Goodness-of-Fit on F21.0651.0590.8911.019
Final R Indexes [I >= 2σ(I)]R1 = 0.0251, wR2 = 0.0588R1 = 0.0425, wR2 = 0.0886R1 = 0.0373, wR2 = 0.0585R1 = 0.0359, wR2 = 0.0737
Final R Indexes **
[All Data]		R1 = 0.0309, wR2 = 0.0606R1 = 0.0469, wR2 = 0.0905R1 = 0.0383, wR2 = 0.0593R1 = 0.0367, wR2 = 0.0744
CCDC Number2212767221276822127652212766
* Disordered water and methanol guest molecules (G) were masked upon the refinement. ** R1 = Σ||Fo| − |Fc||/Σ|Fo| and wR2 = {Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]}1/2 for Fo2 > 2σ(Fo2).
Table
Table 2. Selected structural parameters of 1 and 2.
Table 2. Selected structural parameters of 1 and 2.
[Fe(pp)Pd(CN)4]∙G (1)[Fe(pp)Pt(CN)4]∙G (2)
Temperature (K)293125293123
Spin StateHSLSHSLS
˂Fe−N˃average (Å)2.168(2)1.953(3)2.163(5)1.961(5)
˂Fe−N˃pp (Å)2.204(2)1.976(3)2.199(5)1.980(5)
˂Fe−N˃CN (Å)2.150(2)1.942(3)2.145(4)1.951(4)
Fe···Fe between Adjacent Layers (Å)9.335(1)8.865(1)9.326(1)8.908(1)
Voct(FeN6) (Å3)13.5369.91613.45410.028
∑ (°)32.021.227.324.0
∠ M−C≡N (°)4.16.52.15.4
∠ Fe−N≡C (°)20.712.722.913.0
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Hiiuk, V.M.; Shova, S.; Domasevitch, K.V.; Gural’skiy, I.A. Highly Porous Cyanometallic Spin-Crossover Frameworks Employing Pyridazino[4,5-d]pyridazine Bridge. Inorganics 2022, 10, 195. https://doi.org/10.3390/inorganics10110195

AMA Style

Hiiuk VM, Shova S, Domasevitch KV, Gural’skiy IA. Highly Porous Cyanometallic Spin-Crossover Frameworks Employing Pyridazino[4,5-d]pyridazine Bridge. Inorganics. 2022; 10(11):195. https://doi.org/10.3390/inorganics10110195

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Hiiuk, Volodymyr M., Sergiu Shova, Kostiantyn V. Domasevitch, and Il’ya A. Gural’skiy. 2022. "Highly Porous Cyanometallic Spin-Crossover Frameworks Employing Pyridazino[4,5-d]pyridazine Bridge" Inorganics 10, no. 11: 195. https://doi.org/10.3390/inorganics10110195

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