Homo- and heteropolynuclear platinum complexes stabilized by dimethylpyrazolato and alkynyl bridging ligands: Synthesis, structures, and luminescence

Abstract

This work describes the synthesis of cis-[Pt(CCPh)2(Hdmpz)2] (1) and its use as a precursor for the preparation of homo- and heteropolynuclear complexes. Double deprotonation of compound 1 with readily available MI (M = Cu, Ag, Au) or MII (M = Pd, Pt) species affords the discrete hexanuclear clusters [{PtM2(-CCPh)2(-dmpz)2}2] [M = Cu (2), Ag (3), Au (4)], in which both Pt(CCPh)2(dmpz)2 fragments are connected by four d10 metal centers, and are stabilized by alkynyl and dimethylpyrazolate bridging ligands, or the trinuclear complexes [Pt(-CCPh)2(-dmpz)2{M(CP)}2] (M = Pd (5), Pt (6); CP = CH2-C6H4-P(o-tolyl)2-C,P), respectively. The X-ray structures of complexes 1-4 and 6 are reported. The X-ray structure of the platinum-copper derivative 2 shows that all copper centers exhibit similar local geometry being linearly coordinated to a nitrogen atom and 2 to one alkynyl fragment. However in the related platinum-silver (3) and platinum-gold (4) derivatives the silver and gold atoms present three different coordination environments. The complexes have been studied by absorption and emission spectroscopy. The hexanuclear complexes exhibit bright luminescence in the solid state and in fluid solution (except 4 in the solid state at 298 K). Dual long-lived emission is observed, being clearly resolved in low-temperature rigid media. The low-energy emission is ascribed to MLMCT Pt(d)/(CCPh)Pt(pz)/M(sp)/*(CCPh) modified by metal-metal interactions whereas the high-energy emission is tentatively attributed to an emissive state derived from dimethylpyrazolate-to-metal (d10) LMCT transitions (dmpz)M(d10).