Crystal structure of a new form of copper(II)—inosine 5′-monophosphate—2,2′-dipyridylamine ternary complex

Abstract

Two crystalline forms of the [Cu(II) (IMP) (DPA) (H 2O)] 2· nH 2O (IMP=inosine 5′-monophosphate, DPA=2,2′-dipyridylamine) complex were obtained from aqueous solution at pH=6.2. The crystals of the two forms belong to the monoclinic system, space group P2 1. The cell parameters are: a=9.445(2), b=33.902(4), c=7.802(2) Å, β=90.48(2)°, Z= 2, D c=1.69g cm −3 and μ(Mo Kα) = 10.49cm −1 (form α, n=4), and a=7.828(2), b=18.552(3), c=17.378(3) Å, β=91.16(2)°, Z=2, D c=1.66 g cm −3, μ(Mo Kα) = 10.40 cm −1 (form β, n=3.62). Bau and coworkers reported the preparation of form α by vapor diffusion of CH 3CN into aqueous solution containing Cu(NO 3) 2, Na 2IMP and DPA in a 1:1:1 molar ratio and the analysis of the compound by single crystal X-ray diffraction [1]. Intensities for 3412 reflections were collected from a crystal of form β in the present work. Graphite-monochromatized Mo Kα radiation was employed. The structure was refined to final R and R w values of 0.1000 and 0.1115 respectively. The dimeric units contain two copper ions in square-pyramidal coordination polyhedra. Each polyhedron consists of two nitrogen atoms of DPA, two oxygen atoms from two phosphate groups and a water molecule in the axial position. A statistical disorder was found in a nucleotide moiety of the dimer. Two sets of atomic positions corresponding to the purine system were refined with site occupation factors of 0.62(1) and 0.38(1) respectively. Also the ribose ring shows a disorder with two possible conformations. The puckering mode of the prevailing conformation is C(3′)-endo. In the other nucleotide molecule of the dimer the furanose puckering mode is C(3′)-endo. The rotation around the glycosyl linkages can be described as ‘anti’ in the structure of form β. The C(4)N(9)C(1′)O(4′) torsion angle values are −97(2) and −94(3)° for the disordered nucleotide molecule and +91(2) o for the other nucleotide moiety. Strong intermolecular DPADPA and purine-purine stacking interactions stabilize the crystal lattice. The differences on the nucleotide conformation between the structure of form α and form β can probably be ascribed to differences in the hydrogen bonds and stacking interactions.