Spin crossover studies in tris(N,N?-dialkyldithiocarbamato)iron(III) complexes

Abstract

A series of fifteen complexes of the type [Fe(R′R′′NCS2)3] with symmetric (R′=R′′=n- C6H13, n-C8H17, CH2–CH=;CH2, C6H5, C6H11 and C6H5CH2), unsymmetric (R′ = CH3; R′′ = n-C4H9, C6H11, C6H5 and R′ = C2H5; R′′ = n-C4H9, C6H11, C6H5 and i-C3H7) and ring substituents (R′NR′′=pyrrolidyl and piperidyl) have been synthesized and their magnetic moments and Mossbauer spectra recorded from room temperature (RT) to liquid nitrogen temperature (LNT). Room temperature Mossbauer spectra of all the complexes exhibit an asymmetric doublet, which could be resolved into two doublets, each corresponding to low and high spin states in equilibrium. The crystal structure of tris(N, N′-diallyldithiocarbamato)iron(III) shows it to be monoclinic with trigonally distorted octahedral geometry and space group C2/c. Fe–S stretching vibrations in the far i.r. region also show equilibria, HS ↔ LS. Depending on the nature of the alkyl group substituent, variable temperature magnetic moment and Mossbauer spectral studies, all the complexes may be divided into three groups; high spin complexes exhibiting spin-crossover (6A1g→ 2T2g), high spin complexes exhibiting spin transition (6A1g → 4T1g) and intermediate spin complexes showing spin transition (4A1g→ 2T2g). On the basis of areas of the two doublets corresponding to high and low spin states, their percent contributions were calculated. Furthermore, magnetic moments of the equilibrium mixture calculated on the basis of respective areas compare well with the experimentally determined μeff values. ΔEQ values for both high and low spin states show linear decrease with increasing temperature.