Structural insights into the polymorphism of bismuth(III) di-𝑛-butyldithiocarbamate by X-ray diffraction, solid-state (¹³C/¹⁵N) CP-MAS NMR and DFT calculations

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>Two crystalline polymorphs of a binuclear tris(di-&#119899;-butyldithiocarbamato)bismuth(III) complex, I and II, with an empirical formula of [Bi{S₂CN(&#119899;-C₄H₉)₂}₃] were synthesised and characterised by X-ray diffraction (XRD), solid-state NMR and density functional theory (DFT) calculations. At the supramolecular level, these mononuclear molecular units interact in pairs via secondary Bi⋯S bonds, yielding binuclear formations of [Bi₂{S₂CN(&#119899;-C₄H₉)₂}₆]. The polymorph I (&#119875;1̅) contains two isomeric non-centrosymmetric binuclear molecules of [Bi₂{S₂CN(&#119899;-C₄H₉)₂}₆], which are related to each other as conformers, therefore having four structurally inequivalent bismuth atoms and twelve inequivalent dithiocarbamate ligands. In contrast, the structurally simpler polymorph II (&#119875;2₁/&#119899;) exists as a single molecular form of the corresponding centrosymmetric binuclear formation, comprising two structurally equivalent bismuth atoms and three structurally different dithiocarbamate groups. The polymorphs I and II were found to be interconvertible by altering the solvent system during the recrystallisation process. Sun <em>et al.</em> (2012) has reported a crystalline form of the title compound which resembles, but is not identical with, polymorph II. Experimental solid-state ¹³C and ¹⁵N cross-polarisation (CP) magic-angle-spinning (MAS) NMR spectra of both polymorphs I and II were in accord with the direct structural data on these complexes. Assignments of the resonance lines in the solid-state ¹³C and ¹⁵N NMR spectra were assisted by chemical shift calculations of the crystals using periodic DFT.</p></div>