Syntheses, crystal structures, magnetic properties, and EPR spectra of tetranuclear copper(II) complexes featuring pairs of "Roof-Shaped" Cu2X2 dimers with hydroxide, methoxide and azide bridges

Hydroxo- and methoxo-bridged tetranuclear copper(II) complexes of the tetramacrocyclic ligand 1,2,4,5-tetrakis (1,4,7-triazacyclonon-1-ylmethyl)benzene (L-dur): have been prepared from [Cu4Ldur(H2O)(8)](ClO4)(8). 9H(2)O (1) Addition of base to an aqueous solution of I gave [Cu4Ldur(mu (2)-OH)(4)](ClO4)(4) (2). Diffusion of MeOH into a DMF solution of 2 produces [Cu4Ldur(mu (2)-OMe)(4)](ClO4)(4). HClO4.2/3MeOH (3), a complex which hydrolyzes on exposure to moisture regenerating 2. The structurally related azido-bridged complex, [Cu4Ldur(mu (2)-N-3)(4)](PF6)(4). 5H(2)O . 6CH(3)CN (4), was produced by reaction of L-dur With 4 molar equiv of Cu(OAc)(2).H2O and NaN3 in the presence of excess KPF6. Compounds 2-4 crystallize in the triclinic space group P (1) over bar (No. 2) with a = 10.248(1) Angstrom, b = 12.130(2) Angstrom, c = 14.353(2) Angstrom, alpha = 82.23(1)degrees, beta = 60.79(1)degrees, gamma = 65.71(1)degrees, and Z = 1 for 2, a = 10.2985(3) Angstrom, b = 12.1182(4) X, c = 13.9705(3) Angstrom, alpha = 89.978(2)degrees, beta = 82.038(2)degrees, gamma = 65.095(2)degrees, and Z = 1 for 3, and a = 12.059(2) Angstrom, b = 12.554(2) Angstrom, c = 14.051(2) Angstrom, alpha = 91.85(1)degrees, beta = 98.22(1)degrees, gamma = 105.62(1)degrees, and Z = 1 for 4. The complexes feature pairs of isolated dibridged copper(II) dimers with "roof-shaped" Cu2(mu (2)-X)? cores (X = OH-. OMe-, N-3(-)), as indicated by the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 degrees for 3, and 153 degrees for 4). This leads to Cu Cu distances of 2.962(4) Angstrom for 3, 2.962(1) Angstrom for 3, and 3.006(5) Angstrom for 4. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic coupling (J = -27 cm(-1)) for the hydroxo-bridged copper(II) centers in 2 and very strong antiferromagnetic coupling (J = -269 cm cm(-1)) for the methoxo-bridged copper(II) centers in 3. Pairs of copper(II) centers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) reported thus far for bis(mu (2)-1,1-azido)-bridged dicopper units. Spectral measurements on a neat powdered sample of 4 at 33.9 GHz or 90 Ghz confirm the spin-triplet ground state for the azido-bridged copper(II) pairs.