Magneto-Structural Relationships in a Series of Dinuclear Oxalato-Bridged (Diphenyldipyrazolylmethane)copper(II) Complexes

A series of oxalato-bridged dinuclear copper(II) complexes of the general formula [Cu2(Pz2CPh2)2(X)2((mu)-C2O4)] (X = Cl- (1), NO3- (2), ClO4- (3); Pz2CPh2 = diphenyldipyrazolylmethane) or [Cu2(Pz3m2CPh2)2(H2O)2((mu)-C2O4)](NO3)2·H2O (4) (Pz3m2CPh2 = diphenylbis(3-methylpyrazolyl)methane) was synthesized where the axial ligand was systematically varied to study its effect on structure and magnetic coupling. The structures of compounds 1, 2, and 4 have been elucidated by single-crystal X-ray diffraction. [Cu2(Pz2CPh2)2(Cl)2((mu)-C2O4)] and [Cu2(Pz2CPh2)2(NO3)2((mu)-C2O4)] are isostructural and crystallize in the triclinic system, space group P1, Z = 2, with a = 8.6155(8) (angstrom), b = 10.1435(9) (angstrom), c = 11.3612(11) (angstrom), (alpha) = 95.535(2)°, (beta)= 110.303(2)°, and (gamma)= 106.111(2)° for 1 and with a = 8.863(7) (angstrom), b = 10.241(9) (angstrom), c = 11.425(10) (angstrom), (alpha)= 98.985(14)°, (beta)= 110.449(13)°, and (gamma)= 103.664(14)° for 2. [Cu2(Pz3m2CPh2)2(H2O)2((mu)-C2O4)]·NO3·H2O crystallizes in the monoclinic system, space group C2/c, Z = 4, with a = 23.4588(14) (angstrom), b = 8.8568(5) (angstrom), c = 21.7818(13) (angstrom), (alpha)=(gamma)= 90°, and (beta)= 100.8890(10)°. Variable-temperature magnetic susceptibility studies indicate that all four compounds are strongly antiferromagnetically coupled (2J/k = -364, -344 cm^-1 (2), -424 cm^-1 (3), and -378 cm^-1 (4)). Magnetic and EPR results are discussed with respect to structural parameters to explore possible magneto-structural correlations.