Intramolecular interactions in a heterometallic copper(ii)–lead(ii) tetranuclear β-diketonate complex: insights from thermodynamics, molecular spectroscopy and quantum chemical calculations

Abstract

Heterometallic complexes are key precursors for advanced materials, yet a comprehensive understanding of their formation, stability, and intramolecular interactions remains a challenge. This work presents a combined experimental and computational study of the volatile tetranuclear heterometallic complex [Cu(tmhd)₂Pb(hfac)₂]₂ (tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato; hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionato). Its formation from its monometallic precursors was found to be thermodynamically favourable, driven by negative changes in enthalpy and Gibbs free energy. Vaporisation studies, supported by mass spectrometry, revealed that the complex sublimes intact as a binuclear species, explaining its enhanced volatility. Density Functional Theory (DFT) calculations identified a paramagnetic triplet ground state and provided excellent agreement with the experimental molecular structure and literature experimental EPR spectra. A multi-method computational analysis (AIM, NCI, and NBO) unveiled a complex stabilising network of intramolecular interactions that extend beyond the expected bridging metal–oxygen bonds to include significant donor–acceptor Cu–Pb interactions and weak Cu–F contacts. The experimental IR and UV-Vis spectra were successfully assigned based on calculated data. Time-dependent DFT analysis confirmed the charge-transfer character of the complex, identifying bands corresponding to intra-ligand, d–d, and inter-metallic charge transfer transitions. This study also establishes a robust protocol for linking the thermodynamic, spectroscopic, and vaporization properties of a heterometallic complex directly to its electronic structure and specific non-covalent interactions.