Structure of 2,4-dithiohydantoin complexes with copper and nickel: Solid-state NMR as verification method

Abstract

13C CPMAS NMR spectra were recorded for solid copper and nickel complexes of cycloalkanespiro-5-(2,4-dithiohydantoins), followed by calculation of shielding constants (DFT–GIAO). Reduction of Cu(II) to Cu(I) in the course of complexation with the studied dithiohydantoin ligands was proved. Dimeric structures for all studied complexes were suggested, with monoanions of ligand molecules coordinated in bridging way. The only exception is the Cu(I) complex of cyclooctanespiro-5-(2,4-dithiohydantoin), which is a mononuclear one. Intermolecular interactions, e.g. formation of infinite polymeric chains, are presumed for Cu–L1 complex. The applied combined (spectroscopic and theoretical) approach for structural determination is based on direct comparison between experimental and calculated changes in the NMR shifts due to complexation (Δ′ exp and Δ′ calc, defined as Δ exp ′ = δ compl exp - δ freeL exp and Δ calc ′ = δ compl calc - δ freeL calc , respectively). The presented results demonstrate that solid-state NMR spectroscopy can be applied as a verification method for structural studies of metal complexes with non-trivial polydentate ligands.