Spin Crossover in Six-Coordinate [Fe(L)2(NCX)2] Compounds with L=DPQ=2,3-bis-(2'-pyridil)-quinoxaline, ABPT=4-amino-3,5-bis(pyridin-2-yl)-1,2,4-trazole and X=S, Se: synthesis, magnetic properties and single crystal studies

Abstract

[EN] The iron(II) compounds of formulae [Fe(DPQ)2(NCS)2]·CO(CH)3)2(DPQ = 2,3-bis-(2¿-pyridyl)-quinoxaline) (1) and [Fe(ABPT)2-(NCX)2] (ABPT = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) X = S (2) and Se (3) were synthesized and the crystal structure of 1 determined by X-ray diffraction methods. It crystallizes in the monoclinic system . The structure is made up of discrete [Fe(DPQ)2(NCS)2] units. Each metal atom is in a distorted FeN6 octahedral environment, the Fe¿N bonds ranging from 2.013(8) Å to 2.425(8) Å. Variable-temperature magnetic susceptibility data in the temperature range 290¿4.2 K revealed that 1 is high spin, in contrast to 2 and 3 which show a moderately cooperative high spin ¿ low spin (HS ¿ LS) transition, centred at and 224 K for 2 and 3 respectively. The thermodynamic model of Slichter and Drickamer was applied to account for the magnetic data. The intermolecular interaction parameter, the enthalpy and entropy changes associated with the spin transition of 2 were estimated as ¿ = 2.3 kJ mol¿1, ¿H = 10.7 kJ mol¿1 and ¿S = 58 J mol¿1K¿1 respectively.