Stepwise single-crystal-to-single-crystal phase transition in copper-based coordination polymers triggered by solvent release

Abstract

A new copper-based coordination polymer, [Cu(bib)₃(MeOH)₂](BF₄)₂ (bib = 1,4-bis(imidazol-1-yl)benzene), was isolated and structurally characterized by single-crystal X-ray diffraction. This novel phase, herein denoted as UdP-7·2MeOHα, undergoes a series of single-crystal-to-single-crystal (SC–SC) transformations upon thermal treatment, yielding three new crystalline phases: UdP-7·2MeOHβ, UdP-7·MeOH, and UdP-7. Each transition is associated with discrete structural rearrangements driven by the progressive loss of coordinated methanol and supramolecular reorganization, leading from a 1D coordination polymer to an extended 2D layered architecture. While the α-to-β transition is fully reversible and maintains most of the structural features, the subsequent transformations involve significant shifts in Cu–N interactions and chain proximity, culminating in the formation of a new layered framework in UdP-7 [Cu(bib)₃](BF₄)₂. This study highlights the rich structural adaptability of bib-based copper polymers and provides a detailed crystallographic insight into their temperature-induced evolution.