The ternary metal nucleotide complexes [Ni(en)_1.3(H₂O)_1.4(H₂O)₂][Ni(5′-dGMP)₂(en)_0.7-(H₂O)_0.6(H₂O)₂]·7H₂O (1) and [Ni(en)₂(H₂O)₂][Ni(5′-GMP)₂(H₂O)₄]·6H₂O (2)(en = ethylenediamine, 5′-dGMP = 2′-deoxyguanosine 5′-monophosphate, 5′-GMP = guanosine 5′-monophosphate) have been prepared and their structures analyzed by X-ray diffraction methods. Both compounds crystallise in the space group C222₁ with a= 8.810(1), b= 25.090(4), c= 21.084(1)Å, and Z= 4 for (1) and a= 8.730(1), b= 25.691(4), c= 21.313(5)Å, and Z= 4 for (2). The structures were deduced from the analogous Co^III complexes and refined by full-matrix least-squares methods to final R values of 0.087 and 0.131 for 1 211 and 954 reflections for (1) and (2) respectively. An interesting feature of the deoxyribonucleotide complex (1) is that en is not totally labilized from the metal centre on nucleotide co-ordination, as observed in corresponding ribonucleotide complexes. Apart from extensive intra- and inter-molecular hydrogen bonding, the structures are stabilized by significant intracomplex base–base and base–sugar interactions. The nucleotides in both complexes have an anti base, C(2′)-endo sugar pucker, and gauche–gauche conformation about the C(4′)–C(5′) bond.