Mercury coordination chemistry of a nitrogen/thioether sulfur ligand having an internal hydrogen bond donor: Generation of a thioether-coordinated dimercurous complex

Admixture of the chelate ligand bmnpa (N,N-bis(2-methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine) with an equimolar amount of Hg(ClO₄)₂·3H₂O in CH₃OH/CH₂Cl₂, followed by recrystallization from CH₃CN/Et₂O, yielded the Hg(II) perchlorate complex [(bmnpa)Hg(ClO₄)₂] (1). Addition of an equimolar amount of Me₄NOH·5H₂O to a CH₃CN solution of 1, followed by recrystallization from CH₃OH/Et₂O, yielded the dinuclear Hg₂²⁺ complex [(bmnpaHg)₂](ClO₄)₂ (4). X-ray crystallographic characterization of 1·0.5CH₃CN revealed a mononuclear structure having a primary coordination number of two with a distorted linear geometry, and four secondary bonds for an effective coordination number of six. The ¹H NMR spectrum of 1 in CD₃CN shows distinctive ³J_199Hg-1H coupling in the benzylic -CH₂- and thioether -SCH₃ resonances. Complex 4·CH₃OH exhibits a structure in the solid state wherein each mercury center of the Hg₂²⁺ ion displays thioether coordination and a distorted tetrahedral geometry. Complex 4 is the first dimercurous complex for which J_199Hg-1H coupling involving a -SCH₃ appendage is reported.