Spin crossover behavior in two-dimensional bimetallic coordination polymer FeII(3-bromo-4-picoline)2[AuI(CN)2]2: Synthesis, crystal structures, and magnetic properties

A New Systematic Construction of Novel Three-Dimensional Spin Crossover Coordination Polymers Based on the [AgI 2(CN)3] Building Unit

New three-dimensional spin crossover (SCO) coordination polymers systematically constructed by the novel building unit [AgI 2(CN)3], FeII(3-Br-5-CH3pyridine)2[AgI 2(CN)3][AgI(CN)2] (1), FeII(3-Br-5-Clpyridine)2[AgI 2(CN)3][AgI(CN)2] (2), and FeII(3,5-Brpyridine)2[AgI 2(CN)3][AgI(CN)2] (3), have been synthesized and characterized. The bismonodentate binuclear [Ag2(CN)3]- and mononuclear [AgI(CN)2]- units and FeII atoms assemble to form a 3D network structure. The structures of 1-3 are crystallographically identical, which made up the triply interpenetration combined with complicated intermolecular interactions including Ag···Ag, Ag···X (pyridine substituents) and π-stacking interactions. Magnetic and differential scanning calorimetry studies were performed for 1-3. These compounds display a similar SCO behavior, while the critical temperatures (T c) are shifted by the substituent effect. Due to the identical structures of 1-3, the order of T c clearly corresponds with the Hammett constant.

Systematic Design of Crystal Structure for Hofmann-Like Spin Crossover Fe(L)2[Ag(CN)2]2 Complexes

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.

New Iron(II) Spin Crossover Complexes with Unique Supramolecular Networks Assembled by Hydrogen Bonding and Intermetallic Bonding

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.

Crystal structure of poly[tetra-μ-cyanido-ethanol-bis(2-iodo-pyrazine)-digold(I)iron(II)]

In the title polymeric complex, [Au2Fe(CN)4(C4H3IN2)2(C2H6O)] n , the FeII cation is coordinated by two iodo-pyrazine mol-ecules, one ethanol mol-ecule and three di-cyano-aurate anions in a distorted N5O octa-hedral geometry. In the crystal, the di-cyano-aurate anions bridge the FeII cations to form polymeric chains propagating along the b-axis direction. Stabilization of the crystal structure is provided by O-H⋯N hydrogen bonds and π-π stacking between parallel iodo-pyrazine rings of neighbouring chains, the centroid-centroid distances being 3.654 (10) and 3.658 (9) Å.

Spin-crossover behavior in two new supramolecular isomers

Two spin-crossover (SCO) supramolecular isomers formulated as [Fe(Mebpt){Au(CN)2}]n·xH2O (1, x = 0, and 2·H2O, x = n, MebptH = 3-(5-methyl-2-pyridyl)-5-(2-pyridyl)-1,2,4-triazole) have been successfully isolated and characterized by single-crystal X-ray crystallography, thermogravimetric analysis, differential scanning calorimetry, variable-temperature powder X-ray diffraction, and magnetic measurements. Structural analysis reveals that 1 is a two-dimensional coordination layer and 2·H2O is a one-dimensional coordination ladder structure, in which the Mebpt(-) ligands are coordinated in trans and cis bridging mode in 1 and 2·H2O, respectively. Dramatically, their SCO properties are further influenced by the octahedral coordination configuration of Fe(II). In 1, only the Fe(II) centers in trans configuration exhibit spin transition (Tc = 303 K), while in 2·H2O and the dehydrated 2, gradual two-step SCO (Tc1 = 235 K, Tc2 = 313 K) and one-step SCO behaviors (Tc = 315 K) occur, respectively.

Crystal structure and magnetic properties of the spin crossover complex FeII(ethyl nicotinate)2[AuI(CN)2]2

A new Fe^II two-step spin crossover (SCO) coordination polymer, Fe^II(ethyl nicotinate)₂[Au^I(CN)₂]₂1, with four-inflection associated with phase transitions, has been synthesized.

Spin crossover iron(II) coordination polymer chains: syntheses, structures, and magnetic characterizations of [Fe(aqin)2(μ2-M(CN)4)] (M = Ni(II), Pt(II), aqin = quinolin-8-amine)

New Fe(II) coordination polymeric neutral chains of formula [Fe(aqin)2(μ2-M(CN)4)] (M = Ni(II) (1) and Pt(II) (2)) (aqin = Quinolin-8-amine) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction, and magnetic measurements. The crystal structure determinations of 1-2 reveal in both cases a one-dimensional structure in which the planar [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion acts as a μ2-bridging ligand, and the two aqin molecules as chelating coligands. Examination of the intermolecular contacts in the two compounds reveals that the main contacts are ascribed to hydrogen bonding interactions involving the amine groups of the aqin chelating ligands and the nitrogen atoms of the two non bridging CN groups of the [M(CN)4](2-) (M = Ni(II) (1) and Pt(II) (2)) anion. The average values of the six Fe-N distances observed respectively at room temperature (293 K) and low temperature (120 K), that is, 2.142(3) and 2.035(2) Å for 1, and 2.178(3) and 1.990(2) Å for 2, and the thermal variation of the cell parameters (performed on 2) are indicative of the presence of an abrupt HS-LS spin crossover (SCO) transition in both compounds. The thermal dependence of the product of the molar magnetic susceptibility times the temperature (χmT), in cooling and warming modes, confirms the SCO behavior at about 145 and 133 K in 1 and 2, respectively, and reveals the presence of a small thermal hysteresis of about 2 K for each compound.