In Situ Construction of Three Anion-Dependent Cu(I) Coordination Networks as Promising Heterogeneous Catalysts for Azide–Alkyne “Click” Reactions

Three Cu­(I) coordination networks, namely, {[Cu₂(bpz)₂­(CN)­X]·CH₃CN}_<i>n</i>, (X = Cl, <b>1</b>; I, <b>3</b>), {[Cu₆(bpz)₆­(CH₃CN)₃­(CN)₃Br]·2OH·14CH₃CN}_<i>n</i>, (<b>2</b>, bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole), were prepared by using solvothermal method. The cyanide ligands in these networks were generated in situ by cleavage of C–C bond of MeCN under solvothermal condition. The structures of these networks are dependent on halogen anions. Complex <b>1</b> is a ladderlike structure with μ₂-CN^– as rung and μ₂-bpz as armrest. The Cl^– in <b>1</b> is at terminal position but does not extend the one-dimensional (1D) ladder to higher dimensionalities. Complex <b>2</b> is a three-dimensional (3D) framework comprised of novel planar [Cu₃Br] triangle and single Cu nodes, which are extended by μ₂-bpz and μ₂-CN^– to form a novel (3,9)-connected <b>gfy</b> network. Density functional theory calculations showed that single-electron delocalization of Br atom induces the plane structure of [Cu₃Br]. Complex <b>3</b> also possesses a similar ladderlike subunit as in <b>1</b>, but the I^– acts as bidentate bridge to extend the ladder to 3D framework with a four-connected <b>sra</b> topology. The three networks show notable catalytic activity on the click reaction. The compared catalytic results demonstrate that complex <b>2</b> possesses the best catalysis performance among three complexes, which is ascribed to the largest solvent-accessible void (porosity: <b>2</b> (29.4%) > <b>1</b> (25.7%) > <b>3</b> (17.6%)) and the more Cu­(I) active sites in <b>2</b>. The present combined structure–property studies provide not only a new synthetic route to obtain a new kind of catalyst for click reaction but also the new insights on catalyst structure–function relationships