Polynuclear copper(II) complexes with μ2-1,1-azide bridges. Structural and magnetic properties

Abstract

Two novel, weakly antiferromagnetically coupled, tetranuclear copper(II) complexes [Cu 4(PAP) 2( μ 2-1,1-N 3) 2( μ 2-1,3-N 3) 2( μ 2-CH 3OH) 2(N 3) 4 ( 1) (PAP = 1,4-bis-(2′-pyridylamino)phthalazine) and [Cu 4(PAP3Me) 2 ( μ 2-1,1-N 3) 2( μ 2-1,3-N 3) 2(H 2O) 2(NO 2) 2]- (NO 3) 2 ( 2) (PAP3Me = 1,4-bis-(3′-methyl-2′-pyridyl)aminophthalazine) contain a unique structural with two μ 2-1,1-azide intramolecular bridges, and two μ 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)( μ 2-1,1-N 3)(N 3) 2(CF 3SO 3)]CH 3OH) ( 3) and [Cu 2(PPD)( μ 2-1,1-N 3)(N 3) 2(H 2O)(ClO 4)] ( 4) (PPD = 3,6-bis-(1′-pyrazolyl)pyridazine) contain pairs of copper centers with intramolecular μ 2-1,1-azid and pyridazine bridges, and exhibit strong antiferromagnetic coupling. A one-dimensional chain structure in 3 occurs through intermolecular μ 2-1,1-azide bridging interactions. Intramolecular Cu-N 3-Cu bridge angles in 1 and 2 are small (107.9 and 109.4°, respectively), but very large in 3 and 4 (122.5 and 123.2°, 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) A ̊ , β = 117.35(3)° 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) A ̊ , β = 102.95(5)° and R = 0.045, R w = 0.039. 4 crystallizes in the triclinic system, space group P1, with a = 10.253(3), b = 12.338(5), c = 8.072(4) A ̊ , α = 100.65(4), β = 101.93(3), γ = 87.82(3)° 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 χ 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 well described by the Bleaney-Bowers equation, exhibiting very strong antiferromagnetic exchange (− 2 J = 768(24) cm −1 ( 3); − 2 J = 829(11) cm −1 ( 4)).