The construction of Cu(i)/Cu(ii) coordination polymers based on pyrazine–carboxylate: Structural diversity tuned by in situ hydrolysis reaction

Abstract

The reaction of a new ligand, N,N′-(5,7-dihydro-1,3,5,7-tetraoxobenzo[1,2-c:4,5-c′]dipyrrole-2,6(1H,3H)-diyl)bis-(9CI)-3-pyrazinecarboxamide (L), with CuCl₂·2H₂O, CuI, or Cu(ClO₄)·2H₂O yields five coordination polymers. Among these polymers are three new coordination polymers, [Cu^II₂(μ₃-pzc)₂(μ₁-Cl)₂]_n (1), [Cu^ICu^II(μ₂-pzc)₂(μ₂-Cl)(H₂O)]_n (2a), and {[Cu^I₂Cu^II(μ₂-pzc)₂(μ₃-I)₂(H₂O)]·H₂O}_n (3), as well as two previously reported coordination compounds, [Cu^ICu^II(μ₂-pzc)₂(μ₂-Cl)(H₂O)]_n (2b) and [Cu^II(pzc)₂] (4), in which 2-pyrazinecarboxylate (Hpzc) was obtained from in situ hydrolysis of the L ligand. Compound 1 is a two-dimensional (2D) double-layer structure, which can be viewed as a binodal (3,3)-connected network with the Schläfli symbol of (6²·10) (6·10²). Compounds 2a and 2b are two supramolecular isomers, both of them are (4,4) nets in topological view but showing different packing modes. Compound 3 has a 3D open framework constructed from the linkages of 1D sawtooth chains of iodide copper(I) clusters with [Cu^II(μ₂-pzc)] subunits. Compound 4 is a mononuclear complex. Interestingly, except for compounds 2b and 4, all the other compounds cannot be directly synthesized using Hpzc and the corresponding Cu ions as initial reactants under the same reaction conditions. This finding indicates that the structural diversity of this system is tuned by the in situ hydrolysis reactions.