Silver(I) complexes of N-4-halophenyl-N′-4-pyridyl ureas. Isostructurality, urea⋯nitrate hydrogen bonding, and Ag⋯halogen interaction

Abstract

Silver-pyridyl complexes of N-4-X-phenyl-N′-4-pyridyl urea (X = Cl, Br, I, F, H; L1-L5) are crystalline solids of the formula [Ag(L) 2](S)(NO3) (S = MeCN) for chloro, bromo and iodo ligands (1-3). Solid solution crystals 7-9 of bromo and iodo derivatives were prepared with L2:L3:mixed ligands ratio of 46:37:17, 65:19:16 and 94:0:6 (mixed = bromo-Ag-iodo) in the product. The significance of Ag⋯halogen interaction decreases in the expected order I > Br > Cl in isostructural crystal structures. Interestingly, the polar δ+ region of the C-X bond interacts with nitrate O- in a near-linear approach and the equatorial δ- region approaches Ag+ metal atom at a bent angle, consistent with charge polarization at the heavy halogens. The fluoro and protio ligand silver complexes 4-6 are quite different from structures 1-3. Urea-nitrate N-H⋯O hydrogen bonds have R22(8), R21(6), R43(14) and R44(16) cyclic motifs. © 2008 The Royal Society of Chemistry.