Anorganic-inorganic hybrid mixed-valence Cu I /Cu II tetranuclear polymer [Cu 4 (obpy) 4 (Mo 2 O 7 )] 1 (Hobpy ¼ 6-hydroxy-2,2 0 -bipyridine) has been prepared and structurally determined. [Cu 4 (obpy) 4 (Mo 2 O 7 )] 1 crystallizes in the triclinic space group P-1, with a ¼ 9.995(5), b ¼ 10.678(6), c ¼ 10.838(6) Å , a ¼ 90.698(6), ¼ 113.891(6), ¼ 106.018(6) , Z ¼ 1. Two [Cu 2 (obpy) 2 ] þ building units linked with one 2 -bridging molybdate dimer Mo 2 O 2À 7 result in a dumbbell-like tetranuclear complex, which extends to a one-dimensional chain by -stacking interaction between adjacent 2,2 0 -bipy ligands.