Preparation and physico-chemical properties of the ternary complexes formed between adenosine 5′-triphosphoric acid, bis(2-pyridyl)amine, and divalent metal ions. Crystal and molecular structures of the compounds containing MgII and CaII

Abstract

Ternary compounds formed between M (Mg^II, Ca^II, Sr^II, Mn^II, Co^II, Cu^II, or Zn^II), adenosine 5′-triphosphate [adenosine 5′-triphosphate(4–)= atp], and bis(2-pyridyl)amine(bipyam) have been prepared. The solid compounds are crystalline and have a stoicheiometry described by the formula M(Hatp)(Hbipyam)·nH₂O (n= 2–9). X-Ray powder diffraction patterns are similar. Potentiometric titrations in aqueous solution show the presence of two ionizable protons. Visible spectra suggest an octahedral co-ordination geometry. I.r. spectra indicated essentially the same type of metal–ligand interactions in all the complexes and show that Hatp^3– co-ordinates to the metal through the oxygen atoms of the α, β, and γ phosphate groups. The ternary compounds where M = Mg^II(1) or Ca^II(2) have been studied by single-crystal X-ray diffraction techniques and their molecular structures determined. The two species are isostructural and can be formulated as [Mg(H₂O)₆][Hbipyam]₂[Mg(Hatp)₂]·12H₂O (1) and [Ca(H₂O)₆][Hbipyam]₂[Ca(Hatp)₂]·9H₂O (2). Both (1) and (2) crystallise in space group C222₁(Z= 4), with a= 22.734(3), b= 10.233(3), c= 30.997(4)Å for (1) and a= 22.965(3), b= 10.154(3), c= 32.390(4)Å for (2). X-Ray diffraction data were collected on a Philips automatic diffractometer and the structures solved by direct methods using the SIR (Semi-invariant Representation) package and refined by full-matrix least squares to final R values of 0.111 and 0.124 (1 088 and 1 008 independent observed reflections) for (1) and (2) respectively. In the [M(Hatp)₂]^4– units the metal ions lie on a two-fold axis with an octahedral co-ordination geometry completed by the oxygen atoms of the α, β, and γ phosphate groups of two symmetry-related Hatp^3– molecules. The co-ordination polyhedron of (1) is nearly regular but in (2) it is significantly distorted. The phosphate chains have a folded configuration in both (1) and (2). In both complexes there are no bonding interactions between the metal ions and the adenine base. The metal atoms of the [M(H₂O)₆]²⁺ cations are also located on two-fold axes while the six co-ordinated water molecules form hydrogen bonds with the phosphate chains. The Hbipyam⁺ molecules do not co-ordinate to the metal ions and are disordered around two-fold axes. Strong stacking interactions exist between Hbipyam⁺ and purine rings.