Characterisation of a Binary Transition Metal Complex of a Purine 3 -Nucleotide, {[Cua(3 -GMP)2(3 -GMPH)2(H20)5] 7 H20}„. [1] Phosphate-only Binding of Copper(II)

{[Cu3(3'-GMP)2(3'-GMPH)2(H20)5] • 7 H 2 0 } „ (1) was isolated from an aqueous solution of Cu(N03)2 and guanosine 3'-monophosphate at a pH of 4.4. 1 is monoclinic space group C 2 with a = 29.140(7), b = 6.865(5), c = 16.980(7)Ä, ß = 90.31(3)°, Z = 2, D c = 1.81 g cm-". The structure was refined to R — 0.065 with i?w = 0.060 for 2642 independent reflections. It is disordered about a crystallographic diad axis with one of the copper atoms Cu(2) sited on this axis. This and the other independent copper atom Cu(l) both display square pyramidal geometries. Cu(l) binds N(7) of a guanine base, two phosphate O atoms of nucleotide molecules not symmetry-related to one another and two water oxygens. The guanine base involved in this coordination adopts a syn-conformation relative to the ribose ring with = —118.5°. Cu(2) is coordinated by four phosphate O atoms of different nucleotide molecules and one water oxygen. The second guanine base, which is not involved in metal binding, displays the anZi-conformation relative to the ribose ring.