Copper(II) Complexes of a Series of Alkoxy Diazine Ligands: Mononuclear, Dinuclear, and Tetranuclear Examples with Structural, Magnetic, and DFT Studies

Picolyl hydrazide ligands have two potentially bridging functional groups (μ-O, μ-N−N) and consequently can
exist in different coordination conformers, both of which form spin-coupled polynuclear coordination complexes,
with quite different magnetic properties. The complex [Cu2(POAP-H)Br3(H2O)] (1) involves a μ-N−N bridge
(Cu−N−N−Cu 150.6°) and exhibits quite strong antiferromagnetic coupling (−2J = 246(1) cm-1). [Cu2(PZOAPZ-H)Br3(H2O)2] (2) has two Cu(II) centers bridged by an alkoxide group with a very large Cu−O−Cu angle of 141.7° but
unexpectedly exhibits quite weak antiferromagnetic exchange (−2J = 91.5 cm-1). This is much weaker than
anticipated, despite direct overlap of the copper magnetic orbitals. Density functional calculations have been carried out on compound 2, yielding a similar singlet−triplet splitting energy. Structural details are reported for
[Cu2(POAP-H)Br3(H2O)] (1), [Cu2(PZOAPZ-H)Br3(H2O)2] (2), [Cu2(PAOPF-2H)Br2(DMSO)(H2O)]·H2O (3),
[Cu4(POMP-H))4](NO3)4·2H2O (4), and PPOCCO (5) (a picolyl hydrazide ligand with a terminal oxime group) and
its mononuclear complexes [Cu(PPOCCO-H)(NO3)] (6) and [Cu(PPOCCO-H)Cl] (7). Compound 1 (C12H13Br3Cu2N5O4)
crystallizes in the monoclinic system, space group P21/c, with a = 15.1465(3) Å, b = 18.1848(12) Å, c = 6.8557(5) Å, β = 92.751(4)°, and Z = 4. Compound 2 (C10H13Br3Cu2N7O4) crystallizes in the triclinic system, space
group P1̄, with a = 9.14130(1) Å, b = 10.4723(1) Å, c = 10.9411(1) Å, α = 100.769(1), β = 106.271(1)°, γ =
103.447(1)°, and Z = 2. Compound 3 (C23H22Br2Cu2N7O5.5S) crystallizes in the monoclinic system, space group
P21/c, with a = 12.406(2) Å, b = 22.157(3) Å, c = 10.704(2) Å, β = 106.21(1)°, and Z = 4. Compound 4
(C52H48Cu4N20O18) crystallizes in the monoclinic system, space group P21/n, with a = 14.4439(6) Å, b = 12.8079(5) Å, c = 16.4240(7) Å, β = 105.199(1)°, and Z = 4. Compound 5 (C15H14N4O2) crystallizes in the orthorhombic
system, space group Pna21, with a = 7.834(3) Å, b = 11.797(4) Å, c = 15.281(3) Å, and Z = 4. Compound 6
(C15H13CuN5O5) crystallizes in the monoclinic system, space group P21/c, with a = 8.2818(9) Å, b = 17.886(2) Å,
c = 10.828(1) Å, β = 92.734(2)°, and Z = 4. Compound 7 (C15H13CuClN4O2) crystallizes in the orthorhombic
system, space group Pna21, with a = 7.9487(6) Å, b = 14.3336(10) Å, c = 13.0014(9) Å, and Z = 4. Density
functional calculations on PPOCCO are examined in relation to the anti-eclipsed conformational change that occurs
on coordination to copper(II).