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.