Metal ion influences distortion of the ligand in the structure of [M{2-MeO(O)CC6H4NHC(S)NP(S)(OiPr)2}2] (M = Zn(II), Cd(II)) complexes: a driving force for intermolecular aggregation.

Reaction of the in situ deprotonated N-thiophosphorylated thiourea 2-MeO(O)CC6H4NHC(S)NHP(S)(OiPr)2 () with MCl2 (M = Zn(II), Cd(II)) in aqueous ethanol leads to complexes of the formula . Both compounds crystallise in the triclinic space group P1[combining macron] with Z = 2 and the metal cations are found in a tetrahedral S2S coordination environment formed by the C-S and P-S sulfur atoms. The crystal structures reveal intramolecular N-HO[double bond, length as m-dash]C hydrogen bonds formed within the 2-MeO(O)CC6H4NH fragments. Both structures are further stabilised by intermolecular ππ stacking interactions, which are more efficient in . Here, a pronounced dimeric intermolecular aggregate is observed which goes along with a pronounced distortion of the chelate [(S)CNP(S)](-) backbone of the ligand upon coordination to Cd(II) as well as a significantly distorted coordination tetrahedron CdS2S. The aggregation is also reflected in the positive electrospray ionisation (ESI) mass spectrum of the Cd(II) complex, which exhibits peaks for the dimeric cations [Cd2L3](+), [Cd2L4 + H](+) and [Cd2L4 + Na](+), while for the Zn(II) analogue only monomeric species were observed. Quantum chemical ETS-NOCV (ADF) calculations confirm the higher stability of dimers in compared with . The ππ stacking interactions are prodominantly due to dispersion contributions, though the electrostatic and orbital interaction components are also important. QTAIM (ADF) type calculations additionally quantify the covalent and non-covalent interactions in the momomers.