Orbital Complementary and Countercomplementary Effects in Superexchange Interaction Through Heterobridges in Binuclear Copper(ii) Complexes

Abstract

Low antiferromagnetism of μ-alkoxo-μ-carboxylatodicopper(II) complexes were reasonably explained in terms of the orbital countercomplementary effect based on Hoffmann’s theory for superexchange interaction.

Crystal Structure of a Binuclear Copper(II) Complex with μ-Alkoxo and μ-Pyridonato Bridges. Effect of the Dihedral Angle on the Superexchange Interaction

“…The 27-value based on the Bleaney-Bowers equation is +62.8 cm-1, indicating that weak ferro magnetic interaction is operating in this complex. This behaviour is quite different from that of the analogous derivatives, such as [Cu2(L)(CH3COO)] and [Cu2(L)(C6H5COO)], where weak antiferro magnetic interaction is operating [6].…”

“…Therefore, when the copper(II) ions are linked by alkoxide and benzoate ions and the angle C u -O -C u (O: alkoxo oxygen) is larger than 90°, the energies of cp% and cpa orbitals are lifted by the benzoate and alkoxide bridges, respectively, resulting in a diminished energy separation of <ps and cpa orbitals as compared with that of a single-alkoxide bridged complex. Thus, the reduced -27 value (+190 cm-1) is reasonably explained [6], Since the orbital phase of the highest a-donor orbital of 2 -py ridonate is the same as that benzoate, we can antici pate weak antiferromagnetism for [Cu2(L)(2-pyrido- Table IV According to Kahn et al [16], 7Af is als° depend ent on the dihedral angle between the two planes containing the copper(II) ion, and reaches nearly zero when the dihedral angle decreases from 180 to 130°. In the present complex [Cu2(L)(2-pyridonate)], the dihedral angle is 121°, which is near 130°.…”

“…After this, de Loth et al [5] reported an ab initio calculation on J of copper(II) acetate and pointed out that the superexchange mechanism considered by Hoffmann et al is only a part of the many contributions. In 1985, Nishida et al [6] have observed the appearance of the "orbi tal countercomplementary effect" in some binuclear copper(II) complexes and confirmed that Hoff m ann's treatment based on the simple "extended Hückel MO" is more appropriate to visualize the superexchange interaction.…”

“…The Schiff base ligand H3(L), derived from 1,3-diaminopropane-2-ol and acetylacetone, was prepared according to the published method [6],…”

Azide, water and adipate as bridging ligands for Cu(II): Synthesis, structure and magnetism of (μ4-adipato-κ-O)(μ-aqua)(μ-azido-κN1,N1)copper(II) monohydrate

“…Therefore, the ferromagnetic intra-chain Cu-Cu coupling found in compound 1 has to be explained with the counter-complementarity effect of the two antiferromagnetic couplings [29,30].…”