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

• Published in: Inorganic chemistry 2018-02, Vol.57 (3), p.1562-1571
• Main Authors: Zhang, Daopeng, Valverde-Muñoz, Francisco Javier, Bartual-Murgui, Carlos, Piñeiro-López, Lucía, Muñoz, M. Carmen, Real, José Antonio
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b02906

We report an unprecedented series of two-dimensional (2D) spin-crossover (SCO) heterobimetallic coordination polymers generically formulated as {FeII[(HgII(SCN)3)2]­(L) x }·Solv, where x = 2 for L = tvp (trans-(4,4′-vinylenedipyridine)) (1tvp), bpmh ((1E,2E)-1,2-bis­(pyridin-4-ylmethylene)­hydrazine) (1bpmh·nCH 3 OH; n = 0, 1), bpeh ((1E,2E)-1,2-bis­(1-(pyridin-4-yl)­ethylidene)­hydrazine) (1bpeh·nH 2 O; n = 0, 1) and x = 2.33 for L = bpbz (1,4-bis­(pyridin-4-yl)­benzene) (1bpbz·nH 2 O; n = 0, 2/3). The results confirm that self-assembly of FeII, [HgII(SCN)4]2–, and ditopic rodlike bridging ligands L containing 4-pyridyl moieties favors the formation of linear [Fe­(μ-L)] n 2n+ chains and in situ generated binuclear units {[HgII(SCN)3]2(μ-L)}2–. The latter act as bridges between adjacent chains generating robust 2D layers. The [FeIIN6] 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 ΔH = 12.3 and 10.5 kJ mol–1 and ΔS = 69.4 and 48 J K–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·nH 2 O, which becomes almost complete at p = 0.65 GPa. The labile solvent molecules present in 1bpmh·CH 3 OH and 1bpeh·H 2 O have a dramatic influence on the corresponding SCO behavior.