In order to examine the competition between hydrogen bonds and halogen bonds when confronted with a probe molecule containing multiple potential acceptor sites and one hydrogen-bond donor, five heteroaryl-2-imidazoles were synthesized and subsequently co-crystallized with fifteen different halogen-bond donors. 30 of the 75 experiments resulted in the formation of co-crystals, and fifteen of these produced crystals were suitable for single-crystal X-ray diffraction analysis. A systematic analysis of the primary intermolecular interactions in these fifteen structures shows that the halogen bond is formed with the best acceptor site (as predicted by DFT molecular electrostatic potential surface calculations) demonstrating that a suitably activated iodine-based halogen-bond donor can compete with a strong hydrogen-bond donor in the directed assembly of molecular solid-state architectures.

The synthesis and characterization of two Pt(II) Complexes with the isomeric ligands 4,5-dihydro-5-oxo- [1,2,4]triazolo-[ 1,5-a]pyrimidine (5HtpO) and 4,7-dihydro-7-oxo-[ 1,2,4]-triazolo-[ 1,5-a]pyrimidine (7HtpO) are described, as well as a Ru(III) complex with 7HtpO. The crystal structure of cis-[PtCl2(7HtpO)2].2H2O has been solved by X-ray diffraction analysis. In vitro activity of the new isolated complexes against the epimastigote form of T. cruzi, procyclic form of T. b. brucei and promastigote form of L. donnovani and P. characias has also been studied. The three complexes markedly affect the growth of the parasites and none of them shows cytotoxicity against macrophage of the J774.2 line at the heaviest dosages used.

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Keywords: Copper / N,O ligands / Metal-metal interactions / Structure elucidationFour binuclear copper(II) compounds with the anionic form of the ligand 4,5-dihydro-5-oxo[1,2,4]triazolo[1,5-a]pyrimidine (5tpO − ) have been isolated, their formulae being(3), and [Cu 2 (CH 3 CO 2 ) 2 (5tpO) 2 (H 2 O) 2 ] (4) (phen = 1,10-phenanthroline, biim = bisimidazole). A related mononuclear complex, [Cu(phen) 2 (5HtpO) 2 ](NO 3 ) 2 (5), has also been prepared. The crystal structure of compounds 1−3 has been determined by X-ray diffraction, showing their binuclear nature with four (1) or two (2, 3) bridging 5tpO − moieties. The triazolopyrimidine ligand binds the copper atoms through N3 and N4 in compounds 1 and 3, whereas a novel binding mode through N3 and the exocyclic oxygen atom has been found

In the search for coordination compounds showing significant second harmonic generation (SHG) activity, reaction of Ag(I) ions with the 4-hydroxypyrimidine (4-Hpymo) and 5-nitro-2-hydroxypyrimidine (HNP) ligands generated four crystalline 1D polymers, Ag(4-pymo)‚nH 2 O (n ) 2.5, 0), Ag(NP)(NH 3 ), and Ag(NP), the latter two crystallizing in acentric space groups. Their synthesis, complete characterization, and structural determination, by conventional single-crystal and laboratory X-ray powder diffraction methods, are presented and discussed in the frame of diazaaromatic-ligand-and metal-containing species. XRPD has also allowed the detection of the polyhydrated, elusiVe Ag(4-pymo)‚nH 2 O (n ) 2, 3) species. Powders of Ag(NP) have shown an SHG activity close to that of standard urea. By applying the geometrical model proposed by Zyss, it is shown that the NP ligand is a highly promising chromophore, the oxo and nitro functionalities cooperatively promoting a high hyperpolarizability.