Vapour-adsorption and chromic behaviours of luminescent coordination polymers composed of a Pt(ii)-diimine metalloligand and alkaline-earth metal ions

Abstract

Four new bimetallic coordination polymers (CPs), {M[Pt(CN)₂(5,5′-dcbpy)]·4H₂O}_n (M = Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺; 5,5′-H₂dcbpy = 5,5′-dicarboxy-2,2′-bipyridine) were synthesized using four alkaline-earth metal ions and a Pt(II)-diimine metalloligand [Pt(CN)₂(5,5′-H₂dcbpy)]. All four CPs are isomorphous with the Zn complex, {Zn[Pt(CN)₂(5,5′-dcbpy)]·4H₂O}_n, which exhibits effective metallophilic interactions between Pt(II) ions. These CPs exhibited colourful thermochromic behaviour and solid-state solvatochromic-like behaviours when suspended in various solvents. Thermogravimetric analysis and vapour-adsorption measurements revealed that the CPs can reversibly adsorb water and MeOH vapours. The emission energy of the triplet metal-metal-to-ligand charge-transfer (³MMLCT) state varied markedly upon guest adsorption/desorption. The chromic and vapour-adsorption properties of these CPs depend strongly on the cross-linking M²⁺ ions.