Polymorphism and spin crossover in mononuclear Fe ~(II) species containing new dipyridylamino-substituted s-triazine ligands

摘要

Four new dipyridylamino-substituted s-triazine ligands DBB (N ~2,N ~2,N ~4,N ~4-tetrabenzyl-N ~6,N ~6-di(pyridin-2-yl)-1,3,5-triazine-2,4,6-triamine), DDB (N ~2,N ~2,N ~4,N ~4-tetrabutyl-N ~6,N ~6-di(pyridin-2-yl)-1,3,5-triazine-2,4,6-triamine), DCCl (6-chloro-N ~2,N ~2-dicyclohexyl-N ~4,N ~4-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine) and DDT (N ~2,N ~2,N ~4,N ~4-tetraphenyl-N ~6,N ~6-di(pyridin-2-yl)-1,3,5-triazine-2,4,6-triamine), have been incorporated into eight new, 0D Fe ~(II) compounds of type [Fe ~(II)(NCX) _2(L) _2]·Solvent (where NCX = NCS ~-, NCSe ~- or N(CN) _2 ~-). The polymorphic compounds α-trans-[Fe ~(II)(NCS) _2(DBB) _2] (1) and β-trans-[Fe ~(II)(NCS) _2(DBB) _2] (2) display, respectively, a relatively abrupt, complete, one-step spin transition with T ～ 170 K, and a more gradual, complete, one-step spin transition with T ～ 300 K. Gradual, one-step spin transitions are observed for trans-[Fe ~(II)(N(CN) _2) _2(DBB) _2]·2CH _3CH _2OH (3) and trans-[Fe ~(II)(NCSe) _2(DCCl) _2]·2CH _3OH (6) with T ～ 280 K for both, while the one-step spin transition observed for a desolvated sample of trans-[Fe ~(II)(NCSe) _2(DDB) _2]·2CH _3OH (4) is relatively abrupt, showing hysteresis with T ↑ = 285 K and T ↓ = 275 K. The compounds cis-[Fe ~(II)(NCS) _2(DDB) _2] (5) and trans-[Fe ~(II)(NCS) _2(DDT) _2]·4CH _2Cl _2 (7) remain high spin, while structural data on trans-[Fe ~(II)(NCSe) _2(DDT) _2]·4CH _2Cl _2 (8) suggests a spin transition at low temperatures. It is likely that distortion of the Fe ~(II)N _6 octahedron, intermolecular interactions and molecular conformation are crucial in deciding both the T and abruptness of the spin transition for these species, although the nature of their influence varies. Variable temperature powder X-ray diffraction measurements on the polymorphs 1 and 2 reveal anisotropy in the unit cell parameters as the spin transition occurs.