Synthesis and structural characteristics of metal–acyclovir (ACV) complexes: [Ni(or Co)(ACV)2(H2O)4]Cl2·2ACV, [Zn(ACV)Cl2(H2O)], [Cd(ACV)Cl2]·H2O and [{Hg(ACV)Cl2}x]. Recognition of acyclovir by Ni–ACV

Abstract

The monomeric [M(ACV)₂(H₂O)₄]Cl₂·2ACV (M = Ni^II 1 or Co^II 2), [Zn(ACV)Cl₂(H₂O)] 3 and the polymeric [Cd(ACV)Cl₂]·H₂O 4 [ACV = acyclovir = 9-(2-hydroxymethoxymethyl)guanine] complex have been prepared and characterised by X-ray diffraction and IR data; ¹H and ¹³C NMR have been used to interpret the structural characteristics of the complexes in solution. Compounds 1 and 2 exist as octahedral complexes with four H₂O ligands in the basal plane [Ni–OW 2.053(2) and 2.057(7) Å] and two axial ACV molecules linked to Ni through N(7) [Ni–N(7) 2.160(2) Å]. Two additional ACV molecules are included in the outer sphere of the complex, interacting by means of hydrogen bonds with the co-ordinated ACVs. This reveals the unprecedented recognition of free acyclovir molecules by Ni(or Co)-ACV (1 and 2). The monomeric zinc(II) complex 3 exhibits a distorted-tetrahedral geometry, involving two chlorides, the N(7) of the ACV ligand [Zn–N(7) 2.009(2) Å] and a water molecule. The hydrogen bonding of two guanine bases via NH₂ and N(3) (unit 1) with N(3) and NH₂ (unit 2) represents a novel type of interaction between nucleobases. In the case of the cadmium(II) complex 4 the structure is built by polymeric (CdCl₂)_n chains which are held together by ACV ligands. The cadmium cation is octahedrically coordinated by four chlorides, the N(7) from an ACV molecule and the hydroxylic oxygen from another ACV molecule, the latter two atoms being placed in cis disposition. On the other hand, the complex [{Hg(ACV)Cl₂}_x] 5 can be tentatively assigned as a polymer by comparison with analogous guanosine systems and spectroscopic and conductometric data.