Gallium isopropoxide: Synthesis, properties, “coordination polymerism”. New pentanuclear gallium oxoisopropoxochloride

Abstract

Conditions for the synthesis of gallium isopropoxide (I) by anodic dissolution of the metal in i-PrOH (in the presence of Bu₄NBr supporting electrolyte) and by exchange reaction of GaCl₃ with i-PrONa were studied. In the latter case, the crude product was a waxy substance (II) infinitely soluble in the alcohol and hydrocarbons and containing 12–30% Cl, which cannot be removed by adding an excess of i-PrONa due to the formation of insoluble NaGa(OPr-i)₄. During 1.5–2 months, II is solidified to give non-melting nonvolatile amorphous product (III) poorly soluble in the alcohol. Upon heat treatment of II in vacuum, compound I is distilled off as an oily liquid consisting, according to mass spectrometry, of [Ga(OPr-i)₃]₂ dimer molecules. It can be retained for a long period of time in the presence of the [Ga(OPr-i)₃]₄ tetramer crystals. The existence of oligomeric molecules of different size up to polymers (“coordination polymerism”) in the materials is related to the possibility of tetrahedral or octahedral coordination of the metal atom. From concentrated solutions of components, the oxoalkoxochloride [Ga₅(µ₅-O)(µ-OPr-i)₈Cl₅] (IV) is crystallized. Its molecule is a flattened tetragonal pyramid. The equatorial plane formed by four gallium atoms has the µ₅-O group at the center. The axial Ga atom has an octahedral coordination. All eight sides of the pyramid are drawn together by the µ-OPr-i groups, and the chlorine atoms occupy the terminal positions. (CIF file CCDC no. 693282.)