The structures of the complexes M(C₅H₅N)₃(NO₃)₂[M = Co^II(I), Cu^II(II), and Zn^II(III)] have been determined by three-dimensional X-ray analyses. The crystals in each case are monoclinic, space group C2/c, with Z= 4 in unit cells of dimensions : (I), a= 12·584, b= 9·435, c= 16·327 Å, β= 109·48°; (II)a= 12·783, b= 9·199, c= 16·055 Å, β= 108·35°; and (III)a= 12·60, b= 9·40, c= 16·27 Å, β= 108·9°. The structures were solved by the heavy-atom method and refined by least-squares, full-matrix calculations to final R values of (I) 0·07 (1104 data), (II) 0·08 (1138 data), and (III) 0·11 (1020 data). The overall molecular geometries of the complexes are similar with the three pyridine and two nitrate groups co-ordinated to the metal in monomeric structures. The crystal packings are almost identical but the degree of asymmetry of the nitrato-co-ordination increases as Co < Zn Cu. Consideration of the stereochemistries suggest that the large distortions present in the copper complex are a result of the static Jahn-Teller effect.