The Nature of Bond Orbitals in Quadricovalent Complexes of Transition Elements

Abstract

In quadricovalent complexes of transition elements (Ni^(II), Pd^(II), Pt^(II), Au^(III), Ag^(II), Cu^(II)) the central atom uses four s or d orbitals of its outer shell for unshared electron pairs and two s or d and two p orbitals for bond formation. The problem here is to find the strongest possible four hybrid bond orbitals obtained by combining the two s—d and the two p orbitals available for bond formation. The strongest bond orbitals thus obtained are directed from the middle towards the four corners of a square, as it is expected from experimental evidence; they are composed of 4/9 s, 14/9 d, and two p orbitals, the strength being 2.943. These strongest possible orbitals are presumably used in complex of Ni^(II), Pt^(II), Au^(III), and Cu^(II), but probably not in complexes of Pd^(II) and Ag^(II); in the latter two cases there must be assumed square bond orbitals of composition s^nd^(2−n)p^2 with n somewhere between 1 and 4/9, i.e., orbitals of character between that of the strongest square bond orbitals of composition s^(4/9)d^(14/9)p^2 mentioned above and that of sdp^2 square orbitals discovered by Pauling.