Ge–Cu-Complexes Ph(pyO)Ge(μ2-pyO)2CuCl and PhGe(μ2-pyO)4CuCl—Representatives of Cu(I)→Ge(IV) and Cu(II)→Ge(IV) Dative Bond Systems

Phenylgermaniumpyridine-2-olate PhGe(pyO)3 (compound 1Ge) and CuCl react with the formation of the heteronuclear complex Ph(pyO)Ge(μ2-pyO)2CuCl (2Ge’) rather than forming the expected compound PhGe(μ2-pyO)3CuCl (2Ge). Single-point calculations (at the B2T-PLYP level) of the optimized molecular structures confirmed the relative stability of isomer 2Ge’ over 2Ge and, for the related silicon congeners, the relative stability of 2Si over 2Si’. Decomposition of a solution of 2Ge’ upon access to air provided access to some crystals of the copper(II) compound PhGe(μ2-pyO)4CuCl (3Ge). Compounds 2Ge’ and 3Ge were characterized by single-crystal X-ray diffraction analyses, and the Ge–Cu bonds in these compounds were analyzed with the aid of quantum chemical calculations, e.g., Natural Bond Orbital analyses (NBO), Non-Covalent Interactions descriptor (NCI), and topology of the electron density at bond critical point using Quantum Theory of Atoms-In-Molecules (QTAIM) in conjunction with the related silicon compounds PhSi(μ2-pyO)3CuCl (2Si), PhSi(μ2-pyO)4CuCl (3Si), as well as the potential isomers Ph(pyO)Si(μ2-pyO)2CuCl (2Si’) and PhGe(μ2-pyO)3CuCl (2Ge). Pronounced Cu→Ge (over Cu→Si) lone pair donation was found for the Cu(I) compounds, whereas in Cu(II) compounds 3Si and 3Ge, this σ-donation is less pronounced and only marginally enhanced in 3Ge over 3Si.