A mixed-valence copper coordination polymer generated by a hydrothermal metal/ligand redox reaction process

The title coordination polymer, poly[(mu(4)-2-oxidoisophthalato-kappa(6)O(1),O(2):O(2),O(3):O(3'):O(3'))(mu(2)-quinoxaline-kappa(2)N:N')copper(I)copper(II)], [Cu(2)(C(8)H(3)O(5))(C(8)H(6)N(2))](n), contains two crystallographically distinct Cu ions, one quinoxaline (QA) unit and one 2-oxidoisophthalate trianion (L) derived from 2-hydroxyisophthalic acid (H(3)L). The Cu(II) ion is strongly coordinated by four O atoms in a distorted square geometry, of which two belong to two phenoxide groups and the other two to carboxylate groups of two L ligands. In addition, the Cu(II) cation interacts weakly with a symmetry-related carboxylate O atom which belongs to the L ligand in an adjacent layer, giving a square-pyramidal coordination geometry. The Cu(I) ion is trigonally coordinated by two N atoms from two QA molecules and one O atom from an L carboxylate group. The Cu(I) centres are bridged by QA ligands to give a chain along the c axis. Two Cu(II) ions and two L ligands form a [Cu(2)L(2)](2-) ;metallo-ligand', which coordinates two Cu(I) ions. Thus, the chains of Cu(I) and QA are linked by the [Cu(2)L(2)](2-) metallo-ligand to yield a two-dimensional (6,3) sheet. These sheets are further linked by symmetry-related carboxylate O atoms of neighbouring layers into a three-dimensional framework. The in situ reaction from benzene-1,2,3-tricarboxylic acid (H(3)L1) to L in the present system has rarely been observed before, although a few novel in situ reactions, such as ligand oxidative coupling, hydrolysis and substitution, have been observed during the hydrothermal process.