EPR Evidence For Magnetic Exchange Through a Four-Carbon Aliphatic Bridge in a Binuclear Copper(II) Complex. Single Crystal X-Ray Structure of 7, 7′-(1, 4-Butanediyl)-Bis{2,12-Dimethyl-3,7,11,17-Tetraazabicyclo[11.3.1]Heptadeca-1(17),2,11,13,15-Pentaene)Nickel(II)} Perchlorate Monohydrate

The single crystal x-ray structure of the title, binuclear nickel(II) complex has been determined and the compound used as a host for EPR investigations of the analogous copper(II) complex. The impetus for this work was an earlier suggestion that magnetic exchange interactions detected by EPR spectroscopy on frozen solutions of the biscopper(II) complex were a result of a direct copper-copper interaction in a "closed" conformation of the binuclear species. Results reported here suggest that the complex exists in the open conformation where the distance between metal centres is maximized and that the magnetic exchange occurs by a super-exchange mechanism through the aliphatic chain. The │J│ value for the exchange interaction is greater than 0.018 cm -1 . Crystal data for [Ni 2 (C 34 H 50 N 8 ](CIO 4 ) 4 -H 2 O(298 K): monoclinic, space group P2 1 /n, a = 13.560(3), b = 11.678(2), c = 15.377(3) Å, β = 108.48(2)°, ρ caled = 1.588 g cm -3 for Z = 2 and M r = 1104.1, R = 0.068, R w = 0.076. The intramolecular Ni-Ni distance is 9.13 Å. The analogous copper complex is isomorphorus with the nickel complex.