On the interrelationship of µ-OH bridged dimers, trimers, and tetramers of (en)PtII and their Ag+ adducts

Abstract

[(en)Pt(-OH)2Pt(en)]2+, a dinuclear -hydroxo bridged complex (with en = ethylenediamine) crystallizes with excess AgNO3 in high yield as the trinuclear complex [{(en)Pt(-OH)2Pt(en)}Ag](NO3)3 (Pt2Ag, 1) from water. The two halves of the complex are significantly bent (dihedral angle 42.2°) and the three metals form a triangle with the following distances: Pt1Pt2, 2.9729(9) , Pt1Ag1, 2.818(1) and Pt2Ag1, 2.809(1) . The shortness of the PtAg distances and the dispositions of the three metal ions strongly suggest that dative bonds from Pt to Ag are responsible for the bending of the two halves of the edge-sharing dinuclear [(en)Pt(-OH)2Pt(en)]2+ complex. This scenario appears to be yet another cause of bending of edge-sharing dinuclear -OH bridged metal complexes of d8 metal ions, adding to those involving PtPt bonding, or anion binding, among others. Comparison with related -OH dimers of cis-(NH3)2PtII or (tmeda)PtII (tmeda = N,N,N,N-tetramethylethylenediamine), which do not display Ag+ binding, suggests that the feature of Ag+ binding is not common to all cis-bis(am(m)ine) complexes of PtII. Interestingly the complete removal of Ag+ from 1 does not lead to the -OH dimer but rather to the known -OH tetramer [{(en)Pt(-OH)}4]4+.