[Cu(pyrimidine)(NO3)2]n:: a coordination polymer with quasi-one-dimensional antiferromagnetic interactions

The new coordination compound [Cu(pyrimidine)-(NO3)(2)](n) (1) was synthesized by dehydration of [Cu(pyrimidine)(NO3)(2)(H2O)(2)](n) (2). The crystal structure of (1) was solved from neutron diffraction data. It crystallizes in a monoclinic structure, space group C2/c with four formula units per unit cell. The general structural motif of (2), namely the formation of infinite Cu-pyrimidine chains, is retained. In contrast to (2), where the Cu ions are six-coordinate, dehydration leads to four-coordinate copper in (1). The temperature dependence of the magnetic susceptibility of (1) is similar to that of (2) showing the characteristic features of a uniform one-dimensional S =1/2 Heisenberg chain with staggered g-tensors of neighbouring Cu ions. A broad maximum around 30 K is the signature of significant antiferromagnetic interactions (J/k = 46 K) along the Cu-pyrimidine chains which are significantly enhanced with respect to (2). A Curie tail below 5 K is attributed to the staggered susceptibility arising from the relative canting of the g-tensor principal axes of neighbouring Cu ions. (C) 2002 Elsevier Science B.V. All rights reserved.