Factors Influencing Tetranuclear [2 x 2] Grid vs Dinuclear Side-by-Side Structures for Silver(I) Complexes of Pyridazine-Based Bis-Bidentate Ligands

Silver(I) complexes of five bis-bidentate Schiff-base ligands, derived from 3,6-diformylpyridazine and substituted anilines (2,4-dimethylaniline L-o,L-p-Me; 3,5-dichloroaniline L-m,L-m-Cl; 2-aminobiphenyl Lo-Ph; p-toluidine Lp-Me; 4-aminophenol Lp-OH; p-anisidine Lp-OMe), have been prepared. The ligands have a wide range of steric and electronic properties due to variation in the extent and nature of the substitution of the aniline rings. Four of the resulting complexes were structurally characterized by X-ray crystallography: three of the four, [Ag-2(L-o,L-p-Me)(2)](BF4)(2), [Ag-2(L-m,L-m-Cl)(2)](BF4)(2) and [Ag-2(Lo-Ph)(2)](BF4)(2) formed dinuclear side-by-side complexes, while [Ag-4(Lp-Me)(4)](BF4)(4) gave a tetranuclear [2 x 2] grid. The previously reported tetranuclear [2 x 2] grid [Ag-4(Lp-OMe)(4)](BF4)(4) was recrystallized in the presence of benzene to see if this would alter the architecture of this complex. It did not: the [2 x 2] grid architecture was retained despite the benzene molecules of solvation. Given the flexibility of silver(l) with regard to coordination geometry, the molecular structure of these complexes is influenced mostly by the ligand rather than the metal ion. In each case, the factors which influence the molecular architecture are presented and discussed. Substituent effects on the electrostatics of the intramolecular ligand-ligand pi-pi interactions (XED2.8) account for some of the differences observed in the structures.