Copper(II) thenoyltrifluoroacetonate as acceptor matrix in design of heterospin complexes

Coordination compounds of Cu(II) thenoyltrifluoroacetonate with stable 2-im idazoline nitroxides were synthesized; their structure and magnetic propert ies were investigated. The complex with a pyrazole nitroxide was isolated a s two polymorphous modifications. For both polymorphs, the structure is com prised of Cu(tta)(2)(NITPz1,3Me) molecules shaped as nearly regular pyramid s with four O atoms of the two Ita ligands lying at the base. The solid pol ymorphs are constructed from formal binuclear fragments appearing when the pyramid bases of two neighboring molecules approach each other forming rath er short contacts Cu-S (3.848 and 3.596 Angstrom), due to which the polymor phs differ considerably in magnetic properties. In the modification with lo nger Cu-S distances, there are no exchange interactions between the paramag netic centers of the neighboring Cu(tta)(2)(NITPz(1,3Mc)) molecules whereas in the polymorph with shorter Cu-S distances the interactions are signific ant and analogous to those in real dimer molecules based on the Cu(AcO)(2) matrix with a nitroxide. (C) 2001 Elsevier Science Ltd. All rights reserved .