Dicopper(II) Complexes Bridged by Single N−N Bonds. Magnetic Exchange Dependence on the Rotation Angle between the Magnetic Planes

Abstract

A series of dicopper(II) complexes with two tetradentate (N4) diazine ligands (PAHAP (1), PMHAP (2)) is reported, in which the two dx2-z2 type copper centers are bridged by a single N−N bond. Varying the coligands leads to a situation where the angle between the copper planes can be varied. For small angles (<80°) ferromagnetic coupling prevails, whereas at larger angles antiferromagnetic exchange is observed between the copper(II) centers. This is associated with the degree of alignment of the nitrogen p orbitals in the diazine bridge, and is supported by molecular orbital calculations on the complexes and appropriate models. Structures are reported for PAHAP (1) (picolinamide azine), [Cu2(PAHAP)Cl4]·H2O (3), [Cu2(PAHAP)Br4]·H2O (5), [Cu2(PAHAP)(H2O)6](NO3)4 (6), and [Cu2(PMHAP-H)(NO3)3] (8). 1 crystallized in the orthorhombic system, space group Pbca (No. 61), with a = 19.845(4) Å, b = 13.178(5) Å, c = 9.383(8) Å, and Z = 8. 3 crystallized in the monoclinic system, space group C2/c (No. 15), with a = 26.732(6) Å, b = 8.670(9) Å, c = 16.436(4) Å, β = 100.88(2)°, and Z = 8. 5 crystallized in the monoclinic system, space group C2/c (No. 15), with a = 27.336(2) Å, b = 8.859(4) Å, c = 16.795(3) Å, β = 100.78(1)°, and Z = 8. 6 crystallized in the monoclinic system, space group C2/c (No. 15), with a = 20.983(4) Å, b = 7.505(4) Å, c = 17.219(3) Å, β = 104.22(1)°, and Z = 4. 8 crystallized in the triclinic system, space group P1̄ (No. 2), with a = 7.8380(14) Å, b = 8.015(3) Å, c = 15.655(4) Å, α = 99.81(3)°, β = 101.74(2)°, γ = 94.524(17)°, and Z = 2. The antiferromagnetically coupled complexes [Cu2(PAHAP)Cl4] (4) and [Cu2(PAHAP-H)(N3)2(NO3)] (7) are also reported.