[en] Hydrothermal treatment of CuCl₂.2H₂O, MoO₃, and 3,4'-dipyridylketone (3,4'-dpk) in 1:1:2 mole ratio afforded the new mixed metal oxide phases [Cu₂(MoO₄)₂(3,4'-dpk)(H₂O)] (1) or [Cu₄(3,4'-dpk)₄(Mo₈O₂₆)] (2), depending on the pH of the initial reaction mixture. Compound 1 possesses unique one-dimensional (1-D) [Cu₂(MoO₄)₂(H₂O)]_n ribbons constructed from the linkage of {Cu^II₄O₆} tetrameric units through isolated [MoO₄]^2- tetrahedra. These ribbons in turn are connected into a two-dimensional (2-D) coordination polymer structure by tethering 3,4'-dpk ligands. Compound 2, containing monovalent copper ions, manifests an unprecedented 'X-rail' 1-D extended structure with (6²8)₄(6⁶) topology formed from the bracketing of discrete [β-Mo₈O₂₆]^4- anions by four [Cu^I(3,4^'-dpk)]_nⁿ⁺ chains. The variable temperature magnetic susceptibility behavior of 1 was fit to a linear tetramer model, with g=2.03(3), J₁=25.8(7) cm^-1 and J₂=-46(1) cm^-1. Antiferromagnetic inter-tetramer interactions (zJ'=-0.21(3) cm^-1) were also evident. Crystallographic data: 1 monoclinic, P2₁/c, a=10.3911(11) A, b=6.9502(6) A, c=22.958(2) A, β=100.658(7)^o, V=1629.5(3) A³, R₁=0.1256, and wR₂=0.2038; 2 triclinic, P1-bar,a=10.9000(3) A, b=11.7912(4) A, c=13.5584(4) A, α=102.482(2)^o, β=102.482(2)^o, γ=117.481(2)^o, V=1450.98(8) A³, R₁=0.0428, and wR₂=0.0630. - Graphical abstract: [Cu₂(MoO₄)₂(3,4'-dpk)(H₂O)] (1, 3,4'-dpk=3,4'-dipyridylketone) and [Cu₄(3,4'-dpk)₄(Mo₈O₂₆)] (2) have been prepared by hydrothermal methods. 1 possesses 1-D [Cu₂(MoO₄)₂(H₂O)]_n ribbons containing magnetically interacting {Cu₄O₆} tetramers. The ribbons are connected into 2-D by 3,4'-dpk ligands. The reduced phase 2 manifests an unprecedented 1-D 'X-rail' chain motif