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The syntheses, crystal structures, and magnetic properties of 2-D Hofmann-like motif {FeII(alkyl-pyridine)2[AuI(CN)2]2} (alkyl = 3,4-dimethyl (1), 4-ethyl (2), 4-isopropyl (3)), {FeII(alkyl-pyridine)2[AuI(CN)2]2}∙1/2(alkyl-pyridine) (alkyl = 3,5-dimethyl (4)), and {FeII(X-Isonicotinate)2[AuI(CN)2]2} (X = allyl (5), phenyl (6)) have been investigated. In spite of a wide range of substituent sizes, the structures of 1-3, 5, and 6 are almost crystallographically identical. The 2-D layer consists of an octahedral FeII ion coordinated with the nitrogen atoms in [AuI(CN)2] linear units at equatorial positions and monodentate py derivatives at axial positions. The adjacent two layers interact via intermetallic Au–Au interactions, forming a bilayer structure. The distance between stacking bilayers is associated with bulky substituent ligands. With increasing bulkiness, the interlayer distance expands without any transformation in the crystal structure. Compound 4 possesses guest space where uncoordinated 3,5-dimethyl-pyridine is present. Compounds 1-4 and 6 undergo spin transitions. Only 5 retains the high-spin state characteristic. These constant structures are similar to formerly reported Ag derivatives {FeII(alkyl-pyridine)2[AgI(CN)2]2}. The related Ag and Au families are compared and discussed. [ABSTRACT FROM AUTHOR]

Instead of the conventionally utilized pyridine derivatives ligands for the Hofmann-like spin crossover (SCO) structure, here we used five-membered-aromatic-ring ligands to afford a new series of Hofmann-like compounds Fe(L)2[Ni(CN)4] (L = imidazole (1), 1-methylimidazole (2)). The synthesis, crystal structures, magnetic properties and thermal variation of the lattice constants for 1 and 2 were studied. The structures of the currently synthesized compounds were, as expected, found to be similar to that of traditional Hofmann-like 2D layer structure. Compound 1 showed a high spin state at all temperatures, while compound 2 displayed strong cooperative SCO centered at 144 K accompanied by a 35.2 K-wide hysteresis loop. Interestingly, compound 2 clearly showed anisotropic thermal expansion behaviour. [ABSTRACT FROM AUTHOR]

New Fe II guest-dependent spin crossover (SCO) coordination polymers, {Fe II 4-(3-pentyl)pyridine 2 [Au I (CN) 2 ] 2 ·(guest)} n (guest = 4-(3-pentyl)pyridine ( 1a ), non-guest ( 1b )) has been prepared and investigated by magnetic measurement and X-ray structure analysis. The adsorbed state has a two-step transition with a broad temperature-range intermediate state, whereas the desorbed state has a one-step transition. 1b is maintained HS state down to around 200 K. Below this temperature, 1b displays nearly 50% one-step transition. The first transition of 1a starts below ca. 280 K and almost completes at ca. 210 K. Below around 120 K, second transition starts and completes around 65 K, which 50% of high-spin is remaining. Interlayer spaces between two dimensional sheets are greater than other similar 2D Hoffman-like clathrates. [ABSTRACT FROM AUTHOR]

Abstract: A novel two-dimensional network bimetallic Fe Au spin crossover coordination polymer based on 3-phenylpyridine-coordinated iron centers and linear gold cyanide bridges {Fe(3-phenylpyridine)2[Au(CN)2]2} n (1), has been synthesized. The compound is characterized by elemental analysis, IR, single-crystal X-ray analysis at 300 and 90K and magnetic measurements. The FeII ions in 1 have octahedral FeIIN6 coordination geometries, which are linked by [Au(CN)2]− units at the equatorial plane to form a polymeric 2D sheet architecture. The two pyridine rings coordinate in axial position. Variable-temperature (2–300K) magnetic susceptibility measurements of 1 were performed to determine the spin transition behavior. SQUID data show that high and low spin states exist in a 1:1 ratio at 90K. However, only one kind of FeII atom is apparent crystallographically at 90K, indicating that the high and low spin sites are disordered in the polymeric 2D framework. [Copyright &y& Elsevier]

Abstract: A new novel 2D network bimetallic FeIIAuI spin crossover coordination compound based on 3-bromo-4-picoline and bridged cyano ligands, {FeII(3-bromo-4-picoline)2[AuI(CN)2]2} n (1), has been synthesized and characterized by elemental analyses and IR, using single-crystal X-ray analysis at 293K and at 90K and magnetic measurements. The FeII ions in 1 have octahedral FeN6 coordination geometries, which are linked by a [AuI(CN)2]− unit at the equatorial plane to form a polymeric 2D sheet architecture. The two pyridine rings coordinate at the axial positions. The structure of 1 comprises parallel 2D arrays and the layers interact by pairs, defining bilayers with strong binuclear aurophilic Au⋯Au interactions. Furthermore, intermolecular Au⋯Br and Br⋯Br distances in 1 are significantly smaller than the sums of the van der Waals radii. Variable-temperature (2–300K) magnetic susceptibility measurements of 1 have been performed to determine behaviors of spin transition. The susceptibility data of 1 indicates that about 50% of the HS states are changed to LS states at 75K. The Fe–N bond distances at 90K show that ratio of high spin states agree with the SQUID data. [Copyright &y& Elsevier]

Abstract: New interesting two-dimensional (2D) bi-metallic coordination polymers {FeII(3-fluoropyridine)2[AuI(CN)2]2} n (1), {MnII(3-fluoropyridine)2[AuI(CN)2]2} n (2) were synthesized and characterized by using single-crystal X-ray analysis and IR and elemental analyses. Both complexes are isostructural to each other and construct 2D {MII[AuI(CN)2]2} (M=Fe, Mn) sheet network structures, including the rhombus {}, which are called Hofmann-like structure. Both structures exhibit bilayer connections via Au–Au interactions. Complex 1 which shows two-step spin transition has been already found. However, only the structure of 1 in high-spin state (293K) was completely solved. Therefore, in this report, the high quality of crystal data of 1 in 100% low-spin state (80K) and 50% low-spin state (123K) are completely solved. Also magnetic property of 2 and structure of 2 at 293K have been studied. Furthermore, we have found that both compounds show strong fluorescent emissions in the solid state at room temperature. [Copyright &y& Elsevier]

The synthesis, crystal structures, and magnetic properties of a new two-dimensional (2D) Hofmann-like series, FeII(L)2[AgI(CN)2]2 (L = 3-cyano-4-methylpyridine (1), allyl isonicotinate (2), phenyl-isonicotinate (3), and benzyl nicotinate (4)) were studied. These compounds have a 2D sheet structure because of their strongly determinate self-assembly process. An octahedral FeII ion is coordinated with the nitrogen atoms of[AgI(CN)2 linear units at equatorial positions and monodentate pyridine derivatives at the axial position. The layers construct a parallel stacking array. Compounds 1–3 show pairs of layers constructed by intermetallic Ag···Ag interactions. Compound 4 shows a mono-layer structure. The substituent bulk of the ligands affects the interlayer space. Compounds 1–4 undergo a 100% spin transition. However, compound 1, incorporating a smaller group, has a relatively lower critical temperature (Tc = 182 K (1), Tc = 221 K (2), Tc = 227 (3) and Tc1 = 236 K, Tc2 = 215 K (4)). We investigated the correlations between our systematic crystal design, substituent size, and the spin crossover profiles. [ABSTRACT FROM AUTHOR]

Two spin crossover (SCO) coordination polymers assembled by combining FeII octahedral ion, 4-cyanopyridine (4-CNpy) and [Au(CN)2]− liner unit are described. These compounds, Fe(4-CNpy)2[Au(CN)2]2·1/2(4-CNpy) (1a) and {Fe(4-CNpy)2[Au(CN)2]2}-{Fe(H2O)2[Au(CN)2]2} (1b), present quite different supramolecular networks that show different magnetic behaviors. Compound 1a crystallizes in the centrosymmetric space group Pbcn. The asymmetric unit contains two 4-CNpy, one type of Fe2+, and two types of crystallographically distinct [Au(CN)2]− units which form Hofmann-like two dimensional layer structures with guest spaces. The layers are combined with another layer by strong gold-gold intermetalic interactions. Compound 1b crystallizes in the centrosymmetric space group Pnma. The bent bismonodentate [AuI(CN)2] units and FeII ions form a complicated interpenetrated three dimensional structure. In addition, 1b exhibits ferromagnetic interaction. [ABSTRACT FROM AUTHOR]