Characterisation of a Binary Transition Metal Complex of a 3',5'-Cyclic Nucleotide [1], Preparation and Structure of a Nickel(II) Complex of Guanosine 3',5'-Cyclic Monophosphate

[Ni(3',5'-cGMP)(H20)5][3',5'-cGMP] • 5 H 2 0 (1) was isolated from an aqueous solution of Ni(N03)2 and guanosine 3'.5'-cvclic monophosphate at a pH of 0.5. 1 is orthorhombic P2i2i2i with a = 19.020(4), 6 = 7.718(1), c = 12.316(2) A, Z = 2, Dc = 1.70 g-cm-». The structure was refined to R = 0.085 and Rw = 0.077 for 1364 independent reflections. The structure of 1 is disordered. The nickel atom has a site occupation factor of 0.5 with the 3',5'-cGMP moieties of both cation and anion disordered over the same fourfold general positions. Direct metal binding of the purine N(7) is observed with the octahedral coordination of the nickel atom being completed by 5 water oxygens, one of which forms an intramolecular 0 H 0 hydrogen bond to the guanine 0(6)' The purine base adopts the syn conformation relative to the ribose ring with £CN = —93.3(8)°. The nucleotide bases are stacked in columns along the b screw dyad axes. Parallel to these columns are cavities which are filled by the water molecules and the complexed nickel cations.