Reactions of trichlorogermane HGeCl₃ and dichlorogallane HGaCl₂ with pyridine donors

The weak base pyridine has been found to deprotonate trichlorogermane HGeCl₃ with quantitative formation of pyridinium trichlorogermanate(II), Py-H⁺GeCl₃^-, the pyramidal structure of the anion resembling that of the isoelectronic AsCl₃ molecule. This course of the reaction supports the assignment of an inverse polarization (-)Ge-H(+) of the bond in HGeCl₃ as compared to the (+)Si-H(-) bond in trichlorosilane HSiCl₃, which is known to form a 1:2 adduct with pyridine instead. Germanium tetrachloride also undergoes simple addition reactions with pyridine leading ultimately e.g. to GeCl₄L₂ with L = 4-ethyl-pyridine. Dichlorogallane gives 1:1 addition compounds (HGaCl₂L) with L = pyridine, 4-dimethylamino-pyridine, 4-cyano-pyridine, and 3,5-dimethyl-pyridine, the molecular structures of which have been determined by single crystal X-ray diffraction. Simple tetrahedral arrays of substituents around the gallium center with only minor distortions, and characteristic Ga-H stretching vibrations in the IR spectra, show that the Ga-H bond is untouched in the addition reactions. The addition of two equivalents of 3,5-dimethyl-pyridine to HGaCl₂ affords the 1:2 complex which was shown to have a trigonal-bipyramidal geometry with the hydride ligand in an equatorial position. In order to provide benchmark data, the 1:1 adducts GaCl₃(L) and GaH₃(L) with L = 3,5-dimethyl-pyridine were also prepared and structurally characterized. Pyridinium tetrachlorogallate(III) takes up pyridine, but the extra ligand is attached to the cation via hydrogen bonding leaving the anion unchanged: [Py-H ⋯ Py]⁺[GaCl₄]^-.