The first example of a Cu(II) Ag(I) mixed-metal coordination polymer, Ag[Cu(2-pyrazinecarboxylate) 2 ](H 2 O)(NO 3 ) (3), has been prepared via hydrothermal reaction of Cu(II)(2-pyrazinecarboxylate) 2 (1) or Cu(II)(2-pyrazinecarboxylate) 2 (H 2 O) 2 (2) with AgNO 3 in water (130 o C, 24 h). Compound 3 features linear Cu(1) (2-pyrazinecarboxylate) Ag (2-pyrazinecarboxylate) Cu(2) (2-pyr azinecarboxylate) Ag strands cross-linked by water molecules to form a two-dimensional cationic sheet network. These cationic sheets are further joined by inter-layer Ag...NO 3 - ...Cu linkages to give a novel cavity-containing three-dimensional network. Compound 3 was characterized by single-crystal X-ray diffraction (triclinic, P1; a=6.1672(12), b=8.3595(17), c=14.223(3) 9, α=77.35(3), β=86.80(3), γ=87.70(3) o , V=714.1(2) 9 3 , Z=2, T=296 K, D c a l c . =2.314 g cm - 3 , R 1 =0.048, wR 2 =0.121), thermogravimetry (DTA-TGA), IR and elemental analysis. In addition, the magnetic behavior of 3 was investigated and found to follow the Curie law (μ e f f =1.81 μ B ).