A critical evaluation of homo- and hetero-leptic cadmium complexes using bond valence sums

Abstract

The effect of the donor atoms in Cd complexes on the determination of R0 values for the bond valence sum (BVS) is reported. A total of 1321 CdXmYn fragments with X and Y = O, N, S, Cl, Br, and I were used to calculate the R0 values for Cd—X bonds from both homoleptic and heteroleptic fragments. The R0 values determined from mixed CdXmYn fragments agree with those determined from the homoleptic species, with no significant differences in the values as a function of either electronegativity or hard–soft character of the atoms. The new R0 values derived from the homoleptic series recommended for use in calculating the BVS are as follows: Cd(II)—O of 1.875(13) Å, Cd(II)—N of 1.951(15) Å, Cd(II)—S of 2.279(7) Å, Cd(II)—Cl of 2.216(17) Å, Cd(II)—Br of 2.334(7) Å, and Cd(II)—I of 2.525(7) Å. These R0 values can be used to calculate the oxidation state of Cd in complexes where Cd is bonded to any combination of O, N, S, Cl, Br, and I donor atoms. Cases where the BVS does not agree with the expected oxidation state are discussed. In particular, the planarity of Cd porphyrins is discussed in terms of the BVS.Key words: bond valence sums, cadmium complexes, cadmium porphyrins, cadmium distances.