Thermal spin crossover and LIESST effect observed in complexes [Fe(L ~(Ch))_2(NCX)_2] [L~(Ch) = 2,5-Di(2-Pyridyl)-1,3,4-chalcadiazole; Ch = O, S, Se; X = S, Se, BH_3]

摘要

Two new complexes belonging to the family [Fe~(II)(L) _2(NCX)_2] have been synthesized and structurally characterized. Complexation of the ligand L~O = 2,5-di(2-pyridyl)-1,3, 4-oxadiazole results in the formation of two derivatives of [Fe ~(II)(L~O)_2(NCS)_2] (1) with the common s-trans and the rarely observed s-cis conformation. No thermal spin crossover (SCO) was observed for the amorphous bulk material of the mixture. Using the new ligand L~(Se) = 2,5-di(2-pyridyl)-1,3,4-selenadiazole, compound [Fe~(II)(L~(Se))_2(NCS)_2]·1. 4DCM·0.6MeOH (2·1.4DCM·0.6MeOH) was structurally characterized by single crystal X-ray diffraction. Bulk material of [Fe ~(II)(LSe)_2(NCS)_2]·MeOH (2·MeOH) exhibits a thermally induced SCO with small hysteresis [T _(1/2)(↓) = 91 K, T_(1/2)(↑) = 96 K]. LIESST and reflectivity studies have been performed on the SCO complexes [Fe ~(II)(LS)_2(NCS)_2], [Fe ~(II)(LS)_2(NCSe)_2], [Fe ~(II)(LS)_2(NCBH_3)_2] ·H_2O [L~S = 2,5-di(2-pyridyl)-1,3,4-thiadiazole], and 2·MeOH. All complexes belong to the T_0 = 90 K line [T(LIESST) = T_0-0.3T_(1/2)]. [Fe~(II)(L ~S)_2(NC_S)_2], that exhibits a two-stepped thermal SCO process, has been found to also exhibit two well-separated T(LIESST) temperatures [T(LIESST, 1) = 44 K; T(LIESST, 2) = 53 K].