Synthesis, structure, EPR, and DFT calculation on dinuclear paddle wheel Cu(II) complexes with bis-chelate rings

Abstract

A series of diester-dicarboxylic acids, L¹H₂, L²H₂, L³H₂, L⁴H₂, and L⁵H₂ and their dinuclear Cu₂ complexes [Cu(L¹)CH₃CN]₂ (1), [Cu(L²)H₂O]₂ (2), [Cu(L³)CH₃CN]₂ (3), [Cu(L⁴)EtOH]₂ (4), and [Cu(L⁵)CH₃CN]₂ (5), were synthesized. The crystal structures obtained for 1, 2, and 4 and the density functional theory optimized structures for 2, 3, and 5 illustrated the formation of tetracarboxylate “paddle wheel” complexes. The phthalyl and diphenyl head groups and the spacer moieties were appropriately altered and the size of the chelate ring expanded from 15-membered in 1 to 21-membered in 5. The dinuclear units have strong Cu–Cu interaction with EPR spectra exploring spin coupled features.

Keywords:

• Carboxylates
• Dinuclear
• Paddle wheel complexes
• Copper(II)
• Bis-chelate

Acknowledgments

We are grateful to Dr D. Srinivas for recording the EPR spectra. This study is supported by Department of Science and Technology New Delhi (India) vide Project Number SR/S1/IC-19/2005. PMSK acknowledges Council for Scientific and Industrial Research (CSIR), India, for Senior Research Fellowship Award.