Structural investigations of copper(II) complexes containing unsymmetrical β-diketonate and monothio-β-diketonate ligands

Abstract

The crystal structures of the complexes Cu(txhd)2 and Cu(S-tmhd)2 (where txhd is the anion of 2,2,6-trimethylheptane-3,5-dione and S-tmhd is the anion of 5-mercapto-2,2,6,6-tetramethyl-4-hepten-3-one) were determined. In the solid state, both complexes are square planar. In each case, only one geometrical isomer (trans or cis) was observed in the crystals; arguments are presented that both isomers are present in bulk samples of Cu(txhd)2, while from electronic considerations, the monothio-β-diketonate ligands probably have cis geometry in Cu(S-tmhd)2. Calculations of molecular volumes for structurally similar Cu[t-BuC(O)CHC(O)R]2 complexes showed that there is a slight decrease in packing efficiency as the steric bulk of R increases. More importantly, strong ring-stacking interactions, such as those found for Cu(acac)2 are not observed, or are greatly attenuated, in complexes with bulkier peripheral substituents. [Cu(txhd)(μ3-OEt)]4, an impurity that co-sublimed with Cu(txhd)2, was isolated in low yield. The tetrameric structure, which is isomorphous with known [Cu(tmhd)(μ3-OEt)]4 (where tmhd is the anion of 2,2,6,6-tetramethylheptane-3,5-dione), has a cubane-like core.