Sp3d2 hybrid orbital structure

A transargononic structure for sulfur, with six bonds formed by sp3d2 hybrid orbitals, was suggested for sulfur in the octahedral molecule SF6 long ago, and also for one of the sulfur atoms, with ligancy 6, in binnite (Pauling and Neuman, 1934). Some transargononic structures of metal sulfides have been proposed recently by Franzen (1966). 

The basic idea in this approach is that six atomic orbitals are used to form six hybrid orbitals that are directed toward the corners of an octahedron, the known structure of complexes containing Ti3+. Hybrid orbital types that meet these requirements are d2sp3 and sp3d2. In the case of the Ti3+ ion, two of the 3d orbitals are empty so the dx yi and dzi, the 4s orbital, and the three 4p orbitals can form a set of d2sp3 hybrids. Moreover, the orbitals will be empty as is required for the metal to accept the six pairs of electrons from the six ligands. The electrons in the complex ion [Ti(H20)6]3+ can now be represented as follows ... 

Aluminum has 3d orbitals relatively accessible, and not only may the valency of aluminum rise above four, but some d character may be present in the bonds of the tetravalent and also in the bonds of the trivalent aluminum compounds. At present only few organic aluminum compounds with five- and six-coordinated aluminum are known (sp3d and sp3d2 hybrids see Sections III,D and IV,C). The differences between the behavior of aluminum and boron compounds can partially be explained by the possibility of formation of these structures (trigonal bipyramid, octahedron). 

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