Enantiomorphic single component conducting nickel(ii) and platinum(ii) bis(diethyl-dddt) crystalline complexes

Abstract

Monoanionic and neutral nickel(II) and platinum(II) bis(dithiolene) complexes based on the 5,6-diethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (de-dddt) chiral ligand have been prepared in racemic and enantiopure forms. Neutral closed-shell species have been generated from monoanionic precursors upon electrocrystallization. The racemic anionic (TBA)[Ni(S,S-de-dddt)(R,R-de-dddt)] complex crystallized in the centrosymmetric space group P2₁/c, while the neutral complexes crystallized in the enantiomorphic tetragonal space group P4₁2₁2 or P4₃2₁2. Very subtle conformational differences concerning the orientation of the ethyl substituents are observed between the racemic and the enantiopure compounds, thus impacting the intermolecular interactions at the nanoscale level. Indeed, in the former, the ethyl substituents are all-axial in both independent complexes, while in the latter, one of the independent complexes shows a mixed (eq, eq, ax, ax) conformation and the other independent complex of the asymmetric unit shows the all-axial conformation. Such a tenuous difference at the molecular/nanoscale level strongly impacts the conductivity of the materials. Temperature dependent high pressure single crystal conductivity measurements show activated conductivity for all the materials, with room temperature conductivity values of up to 1.3 × 10⁻³ S cm⁻¹ for [Ni(S,S-de-dddt)₂] at 12.3 GPa and 3.0 × 10⁻⁴ S cm⁻¹ for [Pt(R,R-de-dddt)₂] at 12.9 GPa. Nevertheless, the racemic compounds are more conductive, i.e. 3.8 × 10⁻² S cm⁻¹ for [Ni(rac-de-dddt)₂] at 10.0 GPa and 1.5 × 10⁻³ S cm⁻¹ for [Pt(rac-de-dddt)₂] at 10.5 GPa, in agreement with the shorter and more numerous S⋯S intermolecular contacts observed in the crystal structures of the racemic complexes. Moreover, a detailed analysis of DFT calculations suggests that smaller band gaps and higher conductivities should occur for the racemic solids and for the Pt versus Ni complexes.