The new three-dimensional cobalt(II) complex of formula [Co-2(bpm)(H2O)(2)(CO3)(OH)]NO3. 4H(2)O (1) is obtained from aqueous solutions containing cobalt(II) nitrate hexahydrate, 2,2'-bipyrimidine (bpm), and potassium bicarbonate. The cobalt atoms are bridged by bischelating bpm, single mu(2)-hydroxide, and mu(4)-carbonate groups. Uncoordinated nitrate anions and crystallization water molecules occupy the prismatic holes of the three-dimensional cationic skeleton, and they are held by hydrogen bonds with the hydroxo groups and coordinated water molecules. Variable-temperature magnetic susceptibility measurements reveal the occurrence of an overall antiferromagnetic behavior with a maximum of the susceptibility at 11.5 K.