Bond Valence Sums in Coordination Chemistry. The Calculation of the Oxidation State of Samarium in Complexes Containing Samarium Bonded Only to Oxygen

A simple method is presented for calculating the oxidation state of Sm in complexes where Sm is bonded only to 0 ligands. A total of 88 SmOn fragments with n = 4-12 were retrieved from the Cambridge Structural Database and were analyzed using the bond valence sum (BVS) method. New R0 values for Sm(ll)-0 of 2.116(21) A and for Sm(lll)-0 of 2.055(13) A were derived. The average Ro value of 2.086 A gives a good approximation of the oxidation state of the Sm ion, either +2 or +3, from the observed distances without any assumptions. The Sm-O distances for +2 and +3 complexes with coordination numbers of 4-11 are tabulated and reflect the requirement that the BVS must equal the oxidation state. The distances for CN = 12 were not included because of problems with the reported crystal structures. Several X-ray structure determinations where the BVS and the oxidation state did not agree are discussed.