{[Hg(SCN)3]2(n-L)}2-: An Efficient Secondary Building Unit for the Synthesis of 2D Iron(II) Spin-Crossover Coordination Polymers

Abstract

[EN] We report an unprecedented series of two-dimensional (2D) spin-crossover (SCO) heterobimetallic coordination polymers generically formulated as {Fe-II[(He(SCN)(3))(2)](L)(x))}center dot Solv, where x = 2 for L = tvp (trans-(4,4'-vinylenedipyridine)) (1tvp), bpmh ((1E,2E)-1,2-bis(pyridin-4-ylmethylene)hydrazine) (1bpmh center dot nCH(3)OH; n = 0, 1), by eh ( (1E,2E)-1,2-bis (1-(pyridin-4-yl) ethyliden e) hydrazine) (Ibpeh center dot nH(2)O; n = 0, 1) and x = 2.33 for L = 0 0 bpbz (1,4-bis(pyridin-4-yl)benzene) (1bpbz center dot nH(2)O; n = 0, 2/ 3). The results confirm that self-assembly of Fell, [Hg-II(SCN)(4)](2-), and ditopic rodlike bridging ligands L containing 4-pyridyl moieties favors the formation of linear [Fe(mu-L)](n)(2n+) chains and in situ generated binuclear units {[Hg-II(SCN)(3)](2)(mu-L)}(2)-. The latter act as bridges between adjacent chains generating robust 2D layers. The [(FeN6)-N-II] centers are equatorially surrounded by four NCS- groups and two axial N atoms of the organic ligand L. The compound 1tvp and the unsolvated form of 1bpmh undergo complete SCO centered at T-1/2 = 177 and 226 K, characterized by the enthalpy and entropy variations Delta H = 12.3 and 10.5 kJ mol(-1) and Delta S = 69.4 and 48 J KT-1 mol(-1), respectively. The almost complete SCO of the unsolvated form of 1bpeh occurs at ca. T-1/2 = 119 K and exhibits a complete LIESST effect. Regardless of the degree of solvation, a half-spin conversion at T-1/2 < 100 K occurs for 1bpbz center dot nH(2)O, which becomes almost complete at p = 0.65 GPa. The labile solvent molecules present in 1bpmh center dot CH3OH and 1bpely center dot H2O have a dramatic influence on the corresponding SCO behavior.