Magnetic behavior and crystal structure of [Fe(cyclam)(NCS)2](TCNQ)2:: An unusual one-dimensional (TCNQ)2- radical-ion system

The compound [Fe(cyclam)(NCS)(2)](TCNQ)(2), where cyclam is 1,4,8,11 -tetraazacyclotetradecane and TCNQ is a partially reduced 7,7,8,8-tetracyanoquinodimethane fragment, has been obtained from the corresponding thiocyanate by metathesis reaction. The compound crystallizes in the triclinic system, space group P (1) over bar, a = 7.832(3) Angstrom, b = 8.008(2) Angstrom, c = 15.501(3) Angstrom, alpha = 79.85(2)degrees, beta = 85.11(2)degrees, gamma = 74.18(3)degrees, Z = 1. The crystalline lattice consists of one-dimensional TCNQ units, stacked along the a direction, and it is stabilized by interactions with the Fe(III) hexacoordinated complex cations. All of the TCNQ's are crystallographically equivalent, with bond parameters typical of partially reduced accepters with a formal charge of 0.5 electron. Two different distances between adjacent TCNQ units are observed, i.e., 3.29 and 3.42 Angstrom, indicating the presence of dimeric (TCNQ)(2)(-) in the chains. The temperature dependence of the magnetic susceptibility was described as due to two contributions: the first one comes from the Curie contribution of the Fe(III) complex while the second arises from the magnetic exchange interactions between the nearest neighbor TCNQ anions. The latter is typical of one-dimensional antiferromagnetic chains of S = 1/2 spins, localized on (TCNQ)(2)(-) units, and it could be fitted according to a one-dimensional Heisenberg antiferromagnet model.