Supramolecular architectures in metal(II) (Cd/Zn) halide/nitrate complexes of cytosine/5-fluorocytosine

Abstract

Three new metal(II)-cytosine (Cy)/5-fluorocytosine (5FC) complexes, namely bis(4-amino-1,2-dihydropyrimidin-2-one-κN)diiodidocadmium(II) or bis(cytosine)diiodidocadmium(II), [CdI(CHNO)], (I), bis(4-amino-1,2-dihydropyrimidin-2-one-κN)bis(nitrato-κO,O')cadmium(II) or bis(cytosine)bis(nitrato)cadmium(II), [Cd(NO)(CHNO)], (II), and (6-amino-5-fluoro-1,2-dihydropyrimidin-2-one-κN)aquadibromidozinc(II)-6-amino-5-fluoro-1,2-dihydropyrimidin-2-one (1/1) or (6-amino-5-fluorocytosine)aquadibromidozinc(II)-4-amino-5-fluorocytosine (1/1), [ZnBr(CHFNO)(HO)]·CHFNO, (III), have been synthesized and characterized by single-crystal X-ray diffraction. In complex (I), the Cd ion is coordinated to two iodide ions and the endocyclic N atoms of the two cytosine molecules, leading to a distorted tetrahedral geometry. The structure is isotypic with [CdBr(CHNO)] [Muthiah et al. (2001). Acta Cryst. E57, m558-m560]. In compound (II), each of the two cytosine molecules coordinates to the Cd ion in a bidentate chelating mode via the endocyclic N atom and the O atom. Each of the two nitrate ions also coordinates in a bidentate chelating mode, forming a bicapped distorted octahedral geometry around cadmium. The typical interligand N-H...O hydrogen bond involving two cytosine molecules is also present. In compound (III), one zinc-coordinated 5FC ligand is cocrystallized with another uncoordinated 5FC molecule. The Zn atom coordinates to the N(1) atom (systematic numbering) of 5FC, displacing the proton to the N(3) position. This N(3)-H tautomer of 5FC mimics N(3)-protonated cytosine in forming a base pair (via three hydrogen bonds) with 5FC in the lattice, generating two fused R(8) motifs. The distorted tetrahedral geometry around zinc is completed by two bromide ions and a water molecule. The coordinated and nonccordinated 5FCs are stacked over one another along the a-axis direction, forming the rungs of a ladder motif, whereas Zn-Br bonds and N-H...Br hydrogen bonds form the rails of the ladder. The coordinated water molecules bridge the two types of 5FC molecules via O-H...O hydrogen bonds. The cytosine molecules are coordinated directly to the metal ion in each of the complexes and are hydrogen bonded to the bromide, iodide or nitrate ions. In compound (III), the uncoordinated 5FC molecule pairs with the coordinated 5FC ligand through three hydrogen bonds. The crystal structures are further stabilized by N-H...O, N-H...N, O-H...O, N-H...I and N-H...Br hydrogen bonds, and stacking interactions.

Kinetic Resolution of dl-Hydrobenzoins Catalyzed by Copper(II) Complexes of C 2-Symmetric Thiophene-Derived Ligands

“…7 We have now demonstrated that the additional thiophene moiety present in ligand 1g has a beneficial effect on the outcome of the reaction, especially when sterically small and highly reactive acylation reagents, such as acetyl chloride or acetic anhydride, are used. Based on precedents in the literature, 26 27 28 29 30 the thiophene sulfur atom should coordinate only weakly to the copper ion, but we propose that this might further confine the asymmetric pocket in a manner that is decisive for discrimination between the two enantiomers in the kinetic resolution (see Supporting Information, Figure S57). Attempts to crystallize the complexes formed from Cu(II) and the thiophene ligands unfortunately failed; consequently, the exact structure of the Cu(II) complex is unknown.…”