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Coordination polymers (CPs) built by coordination bonds between metal ions/clusters and multidentate organic ligands exhibit fascinating structural topologies and potential applications as functional solid materials. The title coordination polymer, poly[diaquabis(μ4-biphenyl-3,4′,5-tricarboxylato-κ4O3:O3′:O4′:O5)tris[μ2-1,4-bis(1H-imidazol-1-yl)benzene-κ2N3:N3′]dicopper(II)dicopper(I)], [CuII2CuI2(C15H7O6)2(C12H10N4)3(H2O)2]n, was crystallized from a mixture of biphenyl-3,4′,5-tricarboxylic acid (H3bpt), 1,4-bis(1H-imidazol-1-yl)benzene (1,4-bib) and copper(II) chloride in a water–CH3CN mixture under solvothermal reaction conditions. The asymmetric unit consists of two crystallographically independent Cu atoms, one of which is CuII, while the other has been reduced to the CuI ion. The CuII centre is pentacoordinated by three O atoms from three bpt3− ligands, one N atom from a 1,4-bib ligand and one O atom from a coordinated water molecule, and the coordination geometry can be described as distorted trigonal bipyramidal. The CuI atom exhibits a T-shaped geometry (CuN2O) coordinated by one O atom from a bpt3− ligand and two N atoms from two 1,4-bib ligands. The CuII atoms are extended by bpt3− and 1,4-bib linkers to generate a two-dimensional network, while the CuI atoms are linked by 1,4-bib ligands, forming one-dimensional chains along the [20] direction. In addition, the completely deprotonated μ4-η1:η1:η1:η1 bpt3− ligands bridge one CuI and three CuII cations along the a (or [100]) direction to form a three-dimensional framework with a (103)2(10)2(42.6.102.12)2(42.6.82.10)2(8) topology via a 2,2,3,4,4-connected net. An investigation of the magnetic properties indicated a very weak ferromagnetic behaviour.