Magnetic properties of donor-acceptor compounds of tetrathiofulvalene with bis-Dithiolene metal complexes

Abstract

Donor‐acceptor compounds of tetrathiofulvalene (TTF) with bis‐dithiolene (BDT) metal complexes are studied as flexible analogues to (TTF) ‐tetracyano‐quinodimethane. For BDT complexes, MS4C4X4, the X=CF3 derivatives with M=Ni and Pt, and the X=H derivative with M=Ni, have been examined magnetically for susceptibility and magnetization behavior. The 1:1 (TTF) (BDT) PtCF3 compound follows a Curie‐Weiss law with Θ=16K for dominant ferromagnetic interactions, but the susceptibility peaks near 12K indicating antiferromagnetic coupling. Its ferromagnetic subsystems are probably chain‐or layer‐like. The μeff value of (2.24μ B ) is inconsistent with two S=1/2 spins per formula. The 1:1 NiCF3 compound has a similar μeff (2.27 μ B ), but exhitibs dominant antiferromagnetic interactions with ϑ=−18K down to 40K. At lower temperature its Curie constant is reduced to that of a single spin with an indicated ferromagnetic intercept ϑ?+5K. Below 10K the magnetization‐field behavior tends toward saturation and a Curie point near 2.18K is suggested. A model of two nearly independent magnetic systems, analogous to CuSO4⋅5H2O is offered. The 2:1 X=H derivative (TTF)2(NiS4C4H4) is essentially paramagnetic (‖ϑ‖<2K) with one unpaired S=1/2 spin per formula.