Resonance between dithiocarbamates and thioureide mesomeres coupled to metal−hydrogen anagostic bond transforming under pressure

The pressure-induced transformation of plane-square complex nickel(II) bis(N,N-diethyldithiocarbamate) between its soft dithiocarbamate (form I) and thioureide (form II) mesomeres is coupled to the interchange of anagostic Ni‧‧‧H−C interactions from methylene to the methyl group, respectively. At 1.23 GPa, the clearly visible giant anomalous compressibility of the crystal reveals a potential-energy difference of 5.4 kJmol-1 between the two complex forms. The structural and spectroscopic results, which are supported by quantum-mechanical calculations, connect this solid-state phase transition with the mesomeric transition, and this is accompanied by the conformational transformation of anagostic Ni‧‧‧H−C rearrangement and formation of the charge–assisted S-‧‧‧H−C bond under pressure.