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 tetra macrocyclic ligand 1,2,4,5-tetrakis (1,4,7-triazacyclonon-1-ylmethyl)benzen e (L-dur): have been prepared from [Cu4Ldur(H2O)(8)](ClO4)(8). 9H(2)O (1) A ddition of base to an aqueous solution of I gave [Cu4Ldur(mu (2)-OH)(4)](Cl O4)(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 ex posure to moisture regenerating 2. The structurally related azido-bridged c omplex, [Cu4Ldur(mu (2)-N-3)(4)](PF6)(4). 5H(2)O . 6CH(3)CN (4), was produc ed by reaction of L-dur With 4 molar equiv of Cu(OAc)(2).H2O and NaN3 in th e 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) An gstrom, c = 14.353(2) Angstrom, alpha = 82.23(1)degrees, beta = 60.79(1)deg rees, 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 = 8 2.038(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 b y the dihedral angle between the two CuX2 planes (159 degrees for 2, 161 de grees 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. V ariable-temperature magnetic susceptibility measurements indicate weak anti ferromagnetic 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) cent ers in 4 display the strongest ferromagnetic interaction (J = 94 cm(-1)) re ported 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 t he spin-triplet ground state for the azido-bridged copper(II) pairs.