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

Coordination compounds of Cu(II) thenoyltrifluoroacetonate with stable 2-imidazoline nitroxides were synthesized; their structure and magnetic properties were investigated. The complex with a pyrazole nitroxide was isolated as two polymorphous modifications. For both polymorphs, the structure is comprised of Cu(tta)₂(NITPz^1.3Me) molecules shaped as nearly regular pyramids with four O atoms of the two tta ligands lying at the base. The solid polymorphs are constructed from formal binuclear fragments appearing when the pyramid bases of two neighboring molecules approach each other forming rather short contacts Cu - S (3.848 and 3.596 Å), due to which the polymorphs differ considerably in magnetic properties. In the modification with longer Cu - S distances, there are no exchange interactions between the paramagnetic centers of the neighboring Cu(tta)₂(NITPz^1.3Me) molecules whereas in the polymorph with shorter Cu - S distances the interactions are significant and analogous to those in real dimer molecules based on the Cu(AcO)₂ matrix with a nitroxide.