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Molecular and Electronic Structure of Six-Coordinate Low-Spin Oxo-Bridged Dimers Formed by the Interaction of (/x-Oxo)bis((phthalocyaninato) iron (III)) with Nitrogen Bases

The synthesis and characterization of a series of binuclear copper(II) complexes of binucleating ligands formed by the condensation of pyridine-2-carbaldehyde, salicylaldehyde, and acetylacetone with 1,3-diaminopropan-2-ol and 1,5-diaminopentan-3-ol are reported. All compounds have an endogenous bridging ligand alkoxide group and, in addition, have bridging exogenous ligands such as pyrazolate, 3,5-dimethylpyrazolate, and acetate ions that bridge through two atoms. The crystal and molecular structure of the µ-pyrazolate-bridged dicopper(II) complex of l,3-bis(salicylideneamino)propan-2-ol of formula C20H20CUN4O4 having space group Pbcn and cell dimensions a = 14.983 (2) A,b = 8.276 (5) A, and c = 31.163 (4) Á was solved for 1033 non-zero structure factors (/ > 2.5 (1)). The crystal system is orthorhombic with Z = 8. Full-matrix least-squares refinement gave a final R factor of 0.0762. The ligand is binucleating, and the two copper(II) ions are bridged by the secondary alkoxo group and the pyrazolate moiety. Both copper(II) centers have essentially planar coordination of N202 donor sets. The compound contains an uncoordinated molecule of water. There are no significant intermolecular interactions between neighboring binuclear entities. The intramolecular Cu---Cu distance is 3.359 (4) Á. Magnetic susceptibilities for all the compounds in the solid state are measured over the temperature range 4.2-300 K. The magnetic behavior may be satisfactorily treated by the Bleaney-Bowers equation for a spin-coupled 5=1/2 system in which the singlet-triplet separation is 2J. When the magnetic data for a series of previously reported analogues having single-atom bridges and the present two-atom-bridged species are compared, it is observed that -J decreases in the order OR" = pyrazolate > acetate ~OH" > Cl". Structural data indicate that distortions from trigonal-planar toward pyramidal geometry of the endogenous alkoxo bridging ligand lead to a less negative value for J. In several compounds, this effect leads to net ferromagnetism. the active center in the type 3 copper proteins5*"8 has encouraged(1) (a) La Trobe University, (b) Monash University, (c) The University of Adelaide, (d) Deceased, March 18, 1985.(2) (a) Barnes,

Structural characterization of an iron(iii) complex of a hexadentate tetrakis(picoly1)diamine ligand reveals a novel tetranuclear structure in which two p-0x0-bis(p-acetate)-bridged { Fe2(0)(MeC02)2L6}2+ cores are linked b y aliphatic chains; the electronic structures of this complex and related complexes are similar t o those of the m e t forms of hemeryt h ri n.