Polynuclear copper(II) complexes with mu(2)-1,1-azide bridges. Structural and magnetic properties

Two novel, weakly antiferromagnetically coupled, tetranuclear copper(II) complexes [Cu-4(PAP)(2)(mu(2)-1,1-N-3)(2)(mu(2)-1,3-N-3)(2)(mu(2)-CH3OH)(2)(N-3)(4)] (1) (PAP=1,4-bis-(2'-pyridylamino)phthalazin and [Cu-4(PAP3Me),(2)(mu(2)-1,1-N-3)(2)(mu(2)1,3-N-3)(2)(H2O)(2)(NO3)(2)]-(NO3)(2) (2) (PAP3Me=1,4-bis-(3'-methyl-2'-pyridyl) aminophthalazine) contain a unique structural arrangement with two mu(2)1,1-azide intramolecular bridges, and two mu(2)-1,3-azide intermolecular bridges linking pairs of copper(II) centers. Four terminal azide groups complete the five-coordinate structures in 1, while two terminal waters and two nitrates complete the coordination spheres in 2. The dinuclear complexes [Cu-2(PPD)(mu(2)-1,1-N-3)(N-3)(2)(CF3SO3)]CH3OH) (3) and [Cu-2(PPD)(mu(2)-1,1-N-3)(N-3)(2)(H2O)(ClO4)] (4) (PPD=3,6-bis-(1'-pyrazlyl) pyridazine) contain pairs of copper centers with intramolecular mu(2)-1,1-azide and pyridazine bridges, and exhibit strong antiferromagnetic coupling. A one-dimensional chain structure in 3 occurs through intermolecular mu(2)-1,1-azide bridging interactions. Intramolecular Cu-N-3-Cu bridge angles in 1 and 2 are small (107.9 and 109.4 degrees, respectively), but very large in 3 and 4 (122.5 and 123.2 degrees, respectively),in keeping with the magnetic properties. 2 crystallizes in the monoclinic system, space group C2/c with a=26.71(1), b=13.51(3), c=16.84(1) Angstrom, beta=117.35(3)degrees and R=0.070, R(w)=0.050. 3 crystallizes in the monoclinic system, space group P2(1)/c with a=8.42(1), b=20.808(9), c=12.615(4) Angstrom, beta=102.95(5)degrees and R=0.045, R(w)=0.039. 4 crystallizes in the triclinic system, space group <P(1)over bar>, with a=10.253(3), b=12.338(5), c=8.072(4) Angstrom, alpha=100.65(4), beta=101.93(3), gamma=87.82(3)degrees and R=0.038, R(w)=0.036. The magnetic properties of 1 and 2 indicate the presence of weak net antiferromagnetic exchange, as indicated by the presence of a low temperature maximum in chi(m) (80 K (1), 65 K (2)),but the data do not fit the Bleaney-Bowers equation unless the exchange integral is treated as a temperature dependent term. A similar situation has been observed for other related compounds, and various approaches to the problem will be discussed. Magnetically 3 and 4 are welt described by the Bleaney-Bowers equation, exhibiting very strong antiferromagnetic exchange (-2J=768(24) cm(-1) (3); -2J=829(11) cm(-1) (4)).