Spin crossover in hexakis(1-(2-chloroethyl)-tetrazole)iron(II) complexes; synthesis and magnetic properties

The spin-crossover complexes [Fe(teec)(6)](X)(2) (with teec = 1-(2-chloroethyl)-tetrazole and X = BF4, ClO4, PF6) possess two iron(II) sites each having a different spin-crossover behaviour. The magnetic behaviour of the complexes obtained by slow crystallisation differs strongly from those obtained by precipitation. This difference results in either a spin crossover of 50% (X = C104, crystalline), two gradual steps (X = BF4, PF6), or two steps, of which one is gradual and the other having a thermal hysteresis (X = ClO4 precipitated). Both 57 Fe Mossbauer spectroscopy and magnetic susceptibility measurements have been recorded as a function of T. The crystal structure of [Fe(teec)6](BF4)2 has been determined using X-ray synchrotron powder diffraction. of [Fe(teec)(6)](ClO4)(2) only the cell parameters could be determined. The ligand field spectra of the low-spin and high-spin states clearly indicate a (1)A-->T-5(2) spin transition with 10 Dq(LS)/10 Dq(HS) = 1.72. (C) 2002 Elsevier Science B.V. All rights reserved.