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

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 center dot center dot center dot halogen interaction decreases in the expected order I > Br > Cl in isostructural crystal structures. Interestingly, the polar delta(+) region of the C-X bond interacts with nitrate O- in a near-linear approach and the equatorial delta(-) 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 center dot center dot center dot O hydrogen bonds have R-2(2)(8), R-1(2)(6), R-3(4)(14) and R-4(4)(16) cyclic motifs.