New insight into the three-coordinate divalent germanium compounds L2Ge∑ (L2 = PhNC(Me)CHC(Me)Nph, ∑ = Cl, I, Me, OMe). Structural, photoelectron spectroscopic, and theoretical analysis
Résumé
An experimental and theoretical study of the heteroleptic divalent germanium compounds containing the bidentate coordinating monoanionic β-diketiminate ligand L2Ge∑ (L2 = PhNC-(Me)CHC(Me)NPh; ∑ = Cl (1), I (2), Me (3), OMe (4)) has been performed in this contribution. The new stable germanium(II) compounds 3 and 4 have been synthesized by reaction of 1 with RLi (R = Me, OMe) and fully characterized. The crystal structures of 1-3 and their electronic structures have been determined by X-ray diffraction and UV-photoelectron spectroscopy (UPS), respectively. DFT calculations on 1 and 3 were carried out at the B3LYP level of theory. Natural bond orbital analysis for the model molecules 1′ and 3′ (without phenyl) gives information on the Ge-∑ bonding. It turns out from the NMR, mass spectroscopy, and X-ray molecular geometry properties together with the ab initio calculations that the three-coordinated germanium(II) compound L2GeX is best described by a model structure corresponding to a divalent germanium species weakly coordinated with the halide group, L2Ge+⋯X-. This view is confirmed by the particularly low energetic values of the X atom lone-pair ionizations.