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

Abstract

A series of fifteen complexes of the type [Fe(R 0 R 00 NCS 2 ) 3 ] with symmetric (R 0 =R 00 =n-C 6 H 13 , n-C 8 H 17 , CH 2 ACH@CH 2 , C 6 H 5 , C 6 H 11 and C 6 H 5 CH 2 ), unsymmetric (R 0 = CH 3 ; R 00 = n-C 4 H 9 , C 6 H 11 , C 6 H 5 and R 0 = C 2 H 5 ; R 00 = n-C 4 H 9 , C 6 H 11 , C 6 H 5 and i-C 3 H 7 ) and ring substituents (R 0 NR 00 ¼ pyrrolidyl and piperidyl) have been synthesized and their magnetic moments and Mo¨ssbauer spectra recorded from room temperature (RT) to liquid nitrogen temperature (LNT). Room temperature Mo¨ssbauer 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 0 -diallyldithiocarbamato)iron(III) shows it to be monoclinic with trigonally distorted octahedral geometry and space group C2/c. FeAS stretching vibrations in the far i.r. region also show equilibria, HSÐLS. Depending on the nature of the alkyl group substituent, variable temperature magnetic moment and Mo¨ssbauer spectral studies, all the complexes may be divided into three groups; high spin complexes exhibiting spin-crossover ( 6 A 1g fi 2 T 2g ), high spin complexes exhibiting spin transition ( 6 A 1g fi 4 T 1g ) and intermediate spin complexes showing spin transition ( 4 A 1g fi 2 T 2g ). 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 l eff values. DE Q values for both high and low spin states show linear decrease with increasing temperature.

Stabilization of High‐Valent FeIVS6‐Cores by Dithiocarbamate(1−) and 1,2‐Dithiolate(2−) Ligands in Octahedral [FeIV(Et2dtc)3−n(mnt)n](n−1)− Complexes (n=0, 1, 2, 3): A Spectroscopic and Density Functional Theory Computational Study

“…This phenomenon has first been observed for tris(dithiocarbamates) like 4 by Cambi and Cagnasso, [27] and was intensively studied by a wide range of physical methods. [10,12,13,28,29] It can be unambiguously attributed to a thermal spin crossover from low-spin Fe III (S = 1 / 2 ) to highspin Fe III (S = 5 / 2 ) in the solid state. This spin crossover is observed at temperatures above 150 K for 4.…”

Spin crossover studies in mixed ligand complexes of tris(N-ethyl, N′-n-butyldithiocarbamato)iron(III) with NN, NO and OO containing bidentate ligands and their thermal decomposition

“…Variable temperature Mössbauer spectral studies of [Fe(ebtc) 3 ] show spin crossover behaviour [23]. Typical Mössbauer spectra of 'phen' substituted complexes are shown in Fig.…”

Mössbauer spectroscopic studies of spin crossover in tris(N, N′-dialkyldithiocarbamato) iron (III) complexes: effect of alkyl substituents

“…Appropriate amount of ferric nitrate in ethanol was mixed with calculated amount of ligand salt in 1:3 mole ratio whence black coloured complexes were obtained as already described [4,5].…”