Heterobinuclear Adducts of Copper Tetradentate Schiff Bases with Metal Hexafluoroacetylacetonates

A series of heterobinuclear complexes was prepared by the reaction of copper tetradentate Schiff base complexes, Cu(TSB), with metal hexafluoroacetylacetonates, M(hfa)2 (M = Ni(II), Co(II), Fe(II), Mn(II)). The Schiff base ligands, H2((prp)2en) and H2((prp)2pr), were prepared from the condensation of o-hydroxypropiophenone, Hprp, with ethylenediamine, en, or 1,3-propylenediamine, pr, respectively. The crystal structures of three of the complexes, Cu((prp)2en)Fe(hfa)2, Cu((prp)2pr)Fe(hfa)2, and Cu((prp)2pr)Co(hfa)2, were determined and refined to R values of 6.1, 8.3, and 6.3% for 1107, 2258, and 1411 reflections, respectively. Cu((prp)2en)Fe(hfa)2 crystallizes in P21/c, Z = 4, with a = 13.576 (7) Å, b = 20.365 (5) Å, c = 12.606 (7) Å, and β = 97.70 (5)°. Cu((prp)2pr)Fe(hfa)2 and Cu((prp)2pr)Co(hfa)2 crystallize in P1, Z = 2, with a = 11.630 (4) Å, b = 12.443 (6) Å, c = 13.897 (4) Å, α = 90.83 (5)°, β= 95.26 (4)°, and γ = 116.19 (4)° and a = 11.821 (3) Å, b = 12.402 (5) Å, c = 13.885 (6) Å, α = 91.64 (3)°, β = 95.64 (3)°, and γ = 116.75 (3)°, respectively. The magnetic susceptibilities of all complexes were measured between 4 and 110 K. The strength of antiferromagnetic coupling, J, is shown to depend on the angle, Φ, between the O(1)-Cu-O(2) and O(1)-M-O(2) planes and on the Cu-O-M angle. Thus, a 5° increase in Φ in the pr series of Cu-Fe compounds over the value in the en series is accompanied by an increase in the quartet-sextet separation, -5J, from 30 to 115 cm-1. This series better models some of the electronic properties of cytochrome oxidase than a wide variety of literature binuclear complexes, and it lends support to a CuOFe center in the enzyme with a metal-metal separation of a little over 3 Å. © 1987 American Chemical Society