Copper(II) complexes of 1,4,5,8,9,12-hexaazatriphenylene with oxalate, squarate, perchlorate as auxiliary ligands or counter ion

The crystal structures of [Cu(hat)(H2O)(ox)].H2O (I), [Cu(hat)(H2O)(3)(sq)].3H(2)O (II) and [Cu(hat)(H2O)(2)](ClO4)(2).4H(2)O (III) have been determined from X-ray single crystal diffraction data (hat = 1, 4, 5, 8, 9, 12-hexaazatriphenylene, ox = oxalate, sq = squarate = dianion of 3,4-dihydroxy-cyclobut-3-ene-1,2-dione). Compound I crystallises in the triclinic system, space group ;P (1) over bar with a = 6.6626(10), b = 9.2001(14), c = 12.9954(19) Angstrom, alpha = 103.301(15), beta = 91.414(21), gamma = 105.523(13)degrees, Z = 2, compound H in the orthorhombic system, space group P2(1)2(1)2(1) with a = 6.9274(2), b = 8.4327(3), c = 34.0577(14) Angstrom, Z = 4; and compound III in the monoclinic system, space group C2/c with a = 22.6652(10), b = 9.2220(10), c = 16.1400(10) Angstrom, beta = 106.783(10)degrees, Z = 8. In I chelating hat and oxalate ligands and a coordinated water molecule make up a square pyramidal coordination sphere. The mono-nuclear units so described are, however. connected into dinuclear entities through a weak axial interaction between copper and an oxalate oxygen of a neighbouring molecule. In H copper has a distorted, elongated octahedral coordination geometry, being surrounded by a chelating hat, a mono-dentate squarate and three water molecules. The copper atom in III is bound to two mono-chelating hat units and two water molecules, it is situated on a two-fold axis and features an inverted Jahn-Teller geometry with two short and four intermediate distances at room temperature. X-band ESR spectra of I and H at room temperature exhibit the pattern gparallel to > g(perpendicular to) > 2.0 corresponding to the d(x2-y2) orbital ground state of copper(II) ion in elongated octahedral geometry in these complexes. In the case of complex III the room temperature spectrum exhibits the reverse pattern (g(perpendicular to) > g(parallel to) > 2.0); variable temperature X- and Q-band measurements reveal that the inverted spectrum is gradually converted to a normal axial spectrum as the temperature is lowered, signalling that the apparent compressed geometry at room temperature is caused by a 2D dynamic Jahn-Teller effect. Variable-temperature magnetic susceptibility measurements of I reveal the occurrence of a weak antiferromagnetic coupling (J = -1.0(1) cm(-1) with the Hamiltonian defined as (H) over cap = -J (S) over cap (A).(S) over cap (B)) between the copper ions. (C) 2002 Elsevier Science B.V. All rights reserved.