A new synthetic approach for substitutional solid solutions in a 3D coordination polymer: Cation vacancy, and tunable photoluminescence

Solid solution featuring mixed valence in metal-organic coordination polymer (MOCP) is rare. Inspired by the flexibility of Pb²⁺ to undergo cation exchange, and its ability to adopt a variety of coordination numbers (CN) and chemical environments (CE), herein we report the first, to our knowledge, hetero-valent, single and multiple substituted MOCP with cation vacancy featuring tunable photoluminescence, which may pave a way towards a tunable, functional MOCP. The 3D Pb MOCP features 1D moiety which contains three unique Pb²⁺ sites, each with a different CN and CE, that can undergo cationic substitutions with exogenous divalent as well as aliovalent, e.g. mono- or trivalent cations under appropriate conditions. The formation of solid solution is confirmed by Single Crystal and Powder X-ray Diffractions, SEM-EDS, ICP-OES, as well as XPS. A tunable photoluminescent (PL) color exhibiting good antennae effect and retention of original 3D Pb host color is observed using as little as 6 wt% of Eu³⁺ dopant. More importantly, the PL intensity of Eu³⁺ substituted Pb MOCP increases as dopant amount increases even up to 80 wt% doping, a rather rare case and the first, to our knowledge, in MOCP solid solution.