DICOPPER(II) COMPLEXES BRIDGED BY SINGLE N-N BONDS - MAGNETIC EXCHANGE DEPENDENCE ON THE ROTATION ANGLE BETWEEN THE MAGNETIC PLANES

A series of dicopper(II) complexes with two tetradentate (N-4) diazine ligands (PAHAP (1), PMHAP (2)) is reported, in which the two d(x)2(-z )2 type copper centers are bridged by a single N-N bond. Varying the c oligands leads to a situation where the angle between the copper plane s can be varied. For small angles (<80 degrees) ferromagnetic coupling prevails, whereas at larger angles antiferromagnetic exchange is obse rved between the copper(II) centers. This is associated with the degre e of alignment of the nitrogen p orbitals in the diazine bridge, and i s supported by molecular orbital calculations on the complexes and app ropriate models. Structures are reported for PAHAP (1) (picolinamide a zine), [Cu-2(PAHAP)Cl-4]. H2O (3), [Cu-2(PAHAP)Br-4]. H2O (5), [Cu-2(P AHAP)(H2O)(6)](NO3)(4) (6), and [Cu-2(PMHAP-H)(NO3)(3)] (8). 1 crystal lized in the orthorhombic system, space group Pbca (No. 61), with a = 19.845(4) Angstrom, b = 13.178(5) Angstrom, c = 9.383(8) Angstrom, and Z = 8. 3 crystallized in the monoclinic system, space group C2/c (No. 15), with a = 26.732(6) Angstrom, b = 8.670(9) Angstrom, c 16.436(4) Angstrom, beta = 100.88(2)degrees, and Z = 8. 5 crystallized in the mo noclinic system, space group C2/c (No. 15), with a = 27.336(2) Angstro m, b = 8.859(4) Angstrom, c = 16.795(3) Angstrom, beta = 100.78(1)degr ees, and Z = 8. 6 crystallized in the monoclinic system, space group C 2/c (No. 15), with a = 20.983(4) Angstrom, b = 7.505(5) Angstrom, c = 17.219(3) Angstrom, beta = 104.22(1)degrees, and Z = 4. 8 crystallized in the triclinic system, space group P (1) over bar (No. 2), with a = 7.8380(14) Angstrom, b = 8.015(3) Angstrom, c = 15.655(4) Angstrom, a lpha = 99.81(3)degrees, beta = 101.74(2)degrees, gamma = 94.524(17)deg rees, and Z = 2. The antifenromagnetically coupled complexes [Cu-2(PAH AP)Cl-4](4) and [Cu-2(PAHAP-H)(N-3)(2)(NO3)] (7) are also reported.