STRUCTURE AND MAGNETIC-PROPERTIES OF A LINEAR OXIMATO-BRIDGED TETRANUCLEAR COPPER(II) COMPLEX

The tetranuclear copper(II) complex of formula [Cu-2(dmg)(Hdmg)(terpy) ](2)(ClO4)(2) (1) (H(2)dmg=dimethylglyoxime and terpy=2,2':6',2 ''-ter pyridine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the triclinic system, s pace group P(-1), with a=14.382(3), b=13.728(3), c=8.979(2) Angstrom, alpha=96.99(2), beta=111.85(2), gamma=11122(3)degrees, V=1465.0(9) Ang strom(3), Z=1, D-c=1.607 g cm(-3), M-r=1418.0, F(000)=719, lambda(Mo K alpha)=0.71073 Angstrom, mu(Mo K alpha)=16.61 cm(-1) and T=298 K. A t otal of 4891 reflections were measured over the range 2 less than or e qual to theta less than or equal to 25 degrees and 4393 of them were u nique (l>2.5 sigma(l)) and used in the structural analysis. The struct ure of 1 may be described as two dimeric [Cu-2(dmg)(Hdmg)(terpy)](+) u nits linked by relatively long out-of-plane oxime bonds building a cat ionic centrosymmetric tetrameric entity with a linear Cu-4(NO)(8) core , and uncoordinated perchlorate anions. Within each dinuclear unit, th e partially deprotonated [Cu(dmg)(Hdmg)](-) complex unit coordinates t o the [Cu(terpy)](2+) fragment through in-plane oxime bonds in an asym metric fashion. The coordination geometry around both copper atoms is square pyramidal. The intra-and interdimer copper separations within t he tetranuclear complex are 3.674(5) and 3.994(6) Angstrom, respective ly. Variable-temperature magnetic susceptibility measurements (4.2-300 K) have been interpreted on the basis of the tetranuclear nature of t he compound. The nature and magnitude of the magnetic couplings are di scussed on the basis of the structural features and compared with that of related oximato-bridged copper(II) dinuclear complexes. (C) 1998 E lsevier Science S.A.