Synthesis, crystal structure, electrochemistry and thermal analysis of an oxalato bridged Cr(III)-Pb(II) heterometallic coordination compound

Oxalato bridged Cr(III)-Pb(II) compound of molecular formula [{Pb(phen)₂}₂Cr(ox)₂(phen)] [Cr(ox)₂(phen)](NO₃)₂ (1) [ox = oxalate anion, C₂O₄^2-, phen = 1,10-phenanthroline] has been synthesized and characterized by X-ray crystallography, FT-IR and fluorescence spectroscopy, electrochemical and thermal analysis. The single crystal diffraction analysis revealed that the asymmetric unit of complex 1comprises of a trinuclear cationic species [{Pb(phen)₂}₂Cr(ox)₂(phen)]³⁺(where metals are bridged by oxalate anions in η⁴μ mode) counterbalanced by an anionic complex [Cr(ox)₂(phen)]^- and two nitrate anions. Chromium atoms exhibit a distorted octahedral environment in both fragments, while the six-coordinated lead atoms show an hemidirected coordination geometry that allows the formation of weaker Pb…ONO₂ interactions (tetrel bonds). At room temperature complex 1 exhibits fluorescence at 365 and 383 nm in methanol (λ_ex= 268 nm, Φ = 0.38). In addition, the complex is redox active and the cyclic voltammograms recorded at different scan rate showed that the irreversible peak corresponds to the Cr⁺³/Cr²⁺ couple. Thermogravimetric analysis indicates that the compound starts to decompose at 33.7 °C and collapses at ∼ 277 °C.