Halogen-induced core structural evolution of four dinuclear copper(i) luminescent coordination compounds

Abstract

The reactions of [Cu(CH₃CN)₄]ClO₄ and 2-(diphenylphosphino)pyridine (dppy) with different halogen reagents NH₄X (X = Cl⁻, Br⁻ and I⁻) and four luminescent di-copper(I) coordination compounds, namely [Cu₂(μ-dppy)₃Cl]ClO₄·H₂O (1a), [Cu₂(μ-dppy)₃Br]ClO₄ (2a), Cu₂(μ-Br)₂(μ-dppy)(η-dppy)₂ (2b) and [Cu₂(μ-I)₂(μ-dppy)(η-dppy)₂] (3b), were isolated. Intriguingly, X-ray crystallographic studies reveal that there were two kinds of Cu₂-core structural configuration induced by the differently sized halogen anions. With Cl⁻ acting as a co-ligand, 1a featured a trefoil-like Cu₂-core with three μ₂-dppy in a head-to-head orientation bridging two Cu(I) and one terminal Cl⁻ occupying one axial position. On replacing Cl⁻ with I⁻, 3b comprised a butterfly-like Cu₂-core, being bridged by two I⁻ anions and one μ₂-dppy along with two terminal dppy. When Br⁻ was employed, both the above types of Cu₂-cores were obtained in 2a and 2b, respectively. All these four di-copper(I) compounds exhibit intense green photoluminescence with microsecond lifetimes.