A new class of M(II)-Hg(II) (M=Cu(II), Co(II), Ni(II)) mixed-metal coordination polymers, Cu(2-pyrazinecarboxylate) 2 HgCl 2 (4), [Co(2-pyrazinecarboxylate) 2 (HgCl 2 ) 2 ] . 0.61H 2 O (5) and [Ni(2-pyrazinecarboxylate) 2 (HgCl 2 ) 2 ] . 0.77H 2 O (6), have been prepared by self assembly of metal-containing building blocks, M(2-pyrazinecarboxylate) 2 . (H 2 O) 2 (M=Cu(II), Co(II), Ni(II)), with HgCl 2 . Compounds 4-6 were characterized fully by IR, elemental analysis and single crystal X-ray diffraction. Compound 4 crystallized in the monoclinic space group C2/c, with a=17.916(5) 9, b=7.223(2) 9, c=13.335(4) 9, β=128.726(3) o , V=1346.2(6) 9 3 , Z=4. It contains alternating Hg(II) and Cu(II) metal centers that are cross-linked by 2-pyrazinecarboxylate spacers and chlorine co-ligands to generate a unique three-dimensional Hg(II)-Cu(II) mixed metal framework. Compound 5 crystallized in the triclinic space group P1, with a=6.3879(7) 9, b=6.6626(8) 9, c=13.2286(15) 9, α=96.339(2) o , β=91.590(2) o , γ=113.462(2) o , V=511.71(10) 9 3 , Z=1. Compound 6 also crystallized in the triclinic space group P1, with a=6.3543(8) 9, b=6.6194(8) 9, c=13.2801(16) 9, α=96.449(2) o , β=92.263(2) o , γ=113.541(2) o , V=506.67(11) 9 3 , Z=1. Compounds 5 and 6 are isostructural and in the solid state the Hg(II)...M(II)...Hg(II) units are connected by Hg 2 Cl 2 linkages to produce a novel M(II)-Hg(II) (M Co(II), Ni(II)) zigzag mixed-metal chain, in which a new type of M-M'-M'-M array was observed. The metal containing building blocks, M(2-pyrazinecarboxylate) 2 . (H 2 O) 2 (M Cu(II), Co(II), Ni(II)), exhibit different connectivities to HgCl 2 depending on the metal cation contained within them.