Structural and Magnetic Properties of Dicopper(II) Complexes of Polydentate Diazine Ligands

Abstract

A series of dinuclear copper(II) complexes of three polydentate diazine ligands (PAHAP, PHMAP, and PAHOX) is reported. The PAHAP and PHMAP complexes involve tetradentate ligand coordination with an N−N bridge between the metal centers. For PAHOX, one case involves oxime (N−O) bridges, while, in another, μ2-SO4 bridges are present. Free rotation of the copper magnetic planes around the N−N bond occurs for the PAHAP complexes and is influenced by secondary ligand steric effects (cis), but, for PHMAP, additional coordination fixes the complex in a trans configuration. Preliminary structures are reported for [Cu2(PAHAP)(NCS)4(DMF)2]·2DMF (1) and [Cu2(PAHAP)(bipy)2(NO3)2](NO3)2·4H2O (2), and full structures are reported for [Cu2(PAHAP)(aln)2(H2O)2](NO3)2·3H2O (3), [Cu2(PAHAP)(gly)2(NO3)(H2O)](NO3)·3H2O (4), [Cu2(PHMAP-H)(NO3)3(H2O)(MeOH)] (6), [Cu2(PAHOX-H)2](ClO4)2 (7), and [Cu(PAHOX)(SO4)]2·2H2O (8). Complex 3 crystallized in the triclinic system, space group P1̄ (No. 2), with a = 17.503(4) Å, b = 18.378(4) Å, c = 10.742(4) Å, α = 93.44(3)°, β = 93.19(3)°, γ = 62.98(2)°, and Z = 4. Complex 4 crystallized in the triclinic system, space group P1̄, with a = 11.506(12) Å, b = 12.525(18) Å, c = 10.319(4) Å, α = 94.47(7)°, β = 106.58(5)°, γ = 114.55(9)°, and Z = 2. Complex 6 crystallized in the triclinic system, space group P1̄, with a = 7.4754(1) Å, b = 8.7430(1) Å, c = 17.9942(2) Å, α = 84.690(1)°, β = 83.190(1)°, γ = 66.885(1)°, and Z = 2. Complex 7 crystallized in the monoclinic system, space group C2/c, with a = 33.5849(6) Å, b = 7.6016(1) Å, c = 22.6654(3) Å, β = 106.949(1)°, and Z = 8. Complex 8 crystallized in the monoclinic system, space group P21/n, with a = 9.866(2) Å, b = 10.128(2) Å, c = 15.418(1) Å, β = 108.051(8)°, and Z = 4. Antiferromagnetic exchange for 1, 3, 4, and 6 (−2J = 51.1, 45.6, 1.5, and 208 cm-1, respectively) is consistent with the angle of rotation (α) of the copper magnetic planes about the N−N bond. A linear relationship is found between α and 2J for a combined series of nine related complexes over an angle range of 105°. An estimate of the inherent ferromagnetism in the system is obtained from magnetic measurements close to the calculated angle of accidental orthogonality (2J = 27 cm-1).

Synthesis, Structure, and Magnetism of a Series of Self-Assembled Polynuclear Mn(II), Co(II), and Cu(II) Cluster Complexes

“…The large negative J clearly de"nes the trans N}N linkage between Cu(2) and Cu(5) as a dominant intramolecular antiferromagnetic interaction, entirely consistent with previous results on dicopper(II) systems, where a linear correlation was observed between J and the rotational angle of the copper magnetic planes about the N}N bond. At large angles approaching 1803, 2J values around !200 cm\ were observed (32).…”

“…J is tentatively assigned to the Mn}O}Mn bridging interaction, in reasonable agreement with the properties of 1, which has a comparable Mn}O}Mn angle. The trans arrangement of Mn(II) centers about the N}N bridge would be expected to produce antiferromagnetic coupling (32).…”

“…A close examination of the structure reveals that within the pseudo-square Cu O core all bridging connections are strictly orthogonal, while the connection between Cu(2) and Cu (5) is nonorthogonal through the diazine N}N linkage (N (2)}N(3)). The almost trans disposition of Cu(2) and Cu(5) via this bridge would dictate that coupling between Cu(2) and Cu(5) should be antiferromagnetic, and moderately strong (32). Given the connections between Cu(2) and the surrounding copper centers Cu(1), Cu(3), and Cu(5), the Cu(2)}Cu(5) exchange route would be considered to dominate.…”

Dinuclear Copper(II) Complexes with Bis‐thiocarbohydrazone Ligands

“…Other azine-bridged dicopper systems with roughly parallel copper coordination planes also exhibit moderate to large antiferromagnetic coupling. [10][11]22,23] Indeed, Thompson et al [24] have elucidated the way in which the coupling crosses over (i.e., -2J = 0) at an interplane twist angle of about 85°. The coupling is antiferromagnetic at lower twist angles, -2J approaching 225 cm -1 when the coordination planes are parallel (interplane angle 0°).…”

Self‐Assembly of a Spin‐Coupled Octanuclear Copper(II) Circular Array from a Single‐Stranded Ligand

“…This ferromagnetic exchange interaction is in broad agreement with other structures that possess two and three Cu-N-N-Cu linkages with dihedral angles below approximately 808. [13][14][15][16] The formation of the circular array is quite remarkable as it requires four octadentate ligands and the inclusion of eight solvent molecules to satisfy the coordination algorithm of the eight five-coordinate copper(ii) centers. Compounds 1-3 also represent a rare example of a polynuclear copper(ii) circular array containing more than six copper(ii) centers.…”