Sb- and Bi-based coordination polymers with N-donor ligands with and without lone-pair effects and their photoluminescence properties

Abstract

Fifteen new sublimable Sb- and Bi-based chlorido, bromido and iodido coordination polymers (CPs) with linear bispyridyl ligands are presented in this work and compared in terms of their crystal structures and photoluminescence properties. The Sb-CPs occur in two structural motifs: ¹_∞[Sb₂X₆(L)₂] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (1), 1,2-bis(4-pyridyl)ethane (bpa) (2), 4,4′-bipyridine (bipy) (X: Br, I; 3)) with two polymorphs showing negligible stereochemical demand of the lone-pair and ¹_∞[SbCl₃(bipy)] (3a) featuring a stereochemically active lone pair with significant 5p-contribution at Sb^III. This is accompanied by differences in the coordination polyhedra being octahedral for high s-character, whereas a high p-character of the lone pair results in a square pyramid as the coordination sphere. The Bi-CPs are represented by the general formula ¹_∞[Bi₂X₆(L)₂] (X: Cl (a), Br (b), I (c); L: 1,2-bis(4-pyridyl)ethylene (bpe) (4), 1,2-bis(4-pyridyl)ethane (bpa) (5)) and thus show no significant 6p-character of the lone pairs. For examining the parallels and differences between the Sb^III- and Bi^III-CPs, both are compared in terms of structures and luminescence properties, as well as with related literature known CPs. Altogether, this comparison of structures and properties allows for gaining new insights into the photoluminescence mechanisms of the Sb and Bi-containing CPs. For the first time, distinct hints on the participation of inter-valence charge transfer transitions in E³⁺-pairs (E: Sb, Bi) were observed for the Sb- and Bi-containing coordination polymers constructed from N-donor ligands.