Inter- and intra-molecular condensation patterns of (en)PdII with trans-[a2PtL2]2+ (a = am(m)ine, L = 2-aminopyridine): PtPd3 and Pt2Pd4 species with multiple amide bridges. Unexpected trapping of a pair of nitrate ions by a Pt2Pd4 double cone

Abstract

Reaction of trans-[a₂Pt(Hampy)₂]X₂ (a = NH₃, 2; a = MeNH₂, 3; Hampy = 2-aminopyridine; X = NO₃ or ClO₄) with an excess of [(en)Pd(H₂O)₂]²⁺ in aqueous solution leads to two types of condensation products: (i) tetranuclear PtPd₃ species, in which the deprotonated “a” ligands (μ-NH₂, μ-MeNH) and the deprotonated amino group of the 2-aminopyridine (ampy) ligands are chelated by two (en)Pd^II entities and in addition a single Pd^II ion (without en) cross-links the amido functions of ampy in a nearly linear fashion. The four metal ions thus form a diamond arrangement with a short (<2.5 Å) Pt→Pd dative bond. (ii) Hexanuclear Pt₂Pd₄ species, in which (en)Pd^II moieties bridge exclusively amido groups of four ampy ligands in such a way that an open rectangular box (or double cone) is formed. This allows two nitrate counter ions to become inserted in the cavity of the +8 charged cation. Thus in both cases the ampy ligand acts as a μ₃-ligand, either in an intramolecular or an intermolecular fashion.