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Coligand and solvent effects on the architectures and spin-crossover properties of (4,4)-connected Iron(II)
Xue-Ru Wu1, Hai-Yan Shi1, Rong-Jia Wei1
1†State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering and ‡Collaborative Innovation Center of Chemistry for Energy Materials, Xiamen University, Xiamen 361005, People's Republic of China.
Abstract:
The self-assemblies of 1,4-bis(pyrid-4-yl)benzene (bpb) and Fe(NCX)2 (X = S, Se, BH3) afforded six coordination polymers with the general formula of [Fe(bpb)2(NCX)2]·Y (X = S and Y = 3C2H5OH·2.5H2O for complex 4, X = S and Y = 2C2H5OH for 5, X = Se and Y = 2C2H5OH·H2O for 6, X = Se and Y = 0.67CH2Cl2·1.33C2H5OH·0.67H2O for 7, X = BH3 and Y = 3C2H5OH·2H2O for 8, X = BH3 and Y = 2CH2Cl2·2C2H5OH for 9). The frameworks of complexes 4 and 5 with the NCS(-) anion as coligand are supramolecular isomers, of which complex 4 features a threefold self-interpenetrated three-dimensional (3D) CdSO4-type topological structure with a Schläfli symbol of 6(5)·8, and complex 5 is a two-dimensional (2D) 4(4) rhombic grid network. These two complexes are purely high-spin systems. Complexes 6 and 7 with the NCSe(-) anion as coligand, both having the 3D 6(5)·8 CdSO4-type framework, show gradual and incomplete spin-crossover behaviors with transition temperature T1/2 being equal to 86 and 96 K, respectively. The usage of NCBH3(-) anion as coligand leads to the formation of 2D 4(4) rhombic grid networks for both complexes 8 and 9, which undergo relatively abrupt, complete spin crossover with T1/2 being equal to 247 and 189 K, respectively. The structural divergences are attributed to the coligands NCX(-) (X = S, Se, BH3) and solvent molecules. Meanwhile, a significant coligand effect is observed on the spin-crossover behaviors of these complexes, and the completeness and transition temperature of spin-state conversion depends on the nature of the coligand, that is, T1/2(NCS(-)) < T1/2(NCSe(-)) < T1/2(NCBH3(-)). These results further facilitate the design and synthesis of spin-crossover complexes with spin-state conversion.
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