How to force a classical chelating ligand to a metal non-chelating bridge: the observation of a rare coordination mode of diethanolamine in the 1D complex {[Cu2(Piv)4(H3tBuDea)](Piv)}n

Abstract

The novel chain coordination polymer {[Cu₂(Piv)₄(H₃tBuDea)](Piv)}_n (1) has been prepared through the self-assembly reaction of copper(II) nitrate with pivalic acid (HPiv) and N-tert-butyldiethanolamine (H₂tBuDea) in acetonitrile solution. Crystallographic analysis revealed the extremely rare non-chelating bridging coordination mode of diethanolamine ligand in 1, observed for the first time in transition metal complexes, as well as in complexes of diethanolamine having a non-coordinating aliphatic group at the N atom. Possible reasons for such a coordination and analysis of the main coordination modes of diethanolamine-based ligands are discussed. Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed that 1 represents a rare example of dicopper(II) tetracarboxylate that is a diamagnetic solid at room temperature. This behaviour is compared with literature examples and discussed on the basis of DFT calculations. Furthermore, 1 acts as an efficient catalyst for the mild hydrocarboxylation of linear and cyclic C₅–C₈ alkanes into the corresponding carboxylic acids.