Reaction of bis(2-pyrrolidonato)mercury(II) ( 1) with zinc nitrate, cadmium nitrate, or mercury(II) chloride in methanol, yields the compounds [Hg 3Zn 2(C 4H 6NO) 6(NO 3) 3.33(CH 3O) 0.67] n ( 2), [Hg 3Cd(C 4H 6NO) 6(NO 3) 2] n ( 3), and [Hg 2(C 4H 6NO) 2Cl 2] n ( 4), respectively. Compound 2 is cubic P4 132 with a = 16.370(5) Å, Z = 4. The structure was refined on 565 reflections to R = 0.060. The compound forms a three-dimensional polymer made up of interleaving macrobicyclic units, each macrocycle being 80-membered and containing 10 mercury, 10 zinc, 20 carbon, 20 nitrogen and 20 oxygen atoms. One-third of the zinc atoms are tetrahedrally coordinated by three pyrrolidone oxygen atoms and a methoxide ion; the methoxide groups are replaced by bidentate nitrates on the other zinc atoms. A further nitrate ion symmetrically links a triad of mercury atoms lying within each macrobicycle. Compound 4 is monoclinic P2 1/ c with a = 8.563(2), b = 15.887(2), c = 10.533(2) Å, β = 113.55(1)°, Z = 4. The structure was refined on 1513 reflections to R = 0.051. The compound forms a loosely linked chain polymer in which units of 1 chelate via the oxygen atoms to the mercury atoms of HgCl 2 molecules, with a resultant bending ( ca 167°) of the ClHgCl angle. X-ray powder diffraction photographs show that compound 3 is isostructural with its previously reported cobalt(II) analogue and further information about the cadmium site in 3 was obtained from the EPR spectra of manganese(II)-doped samples.