Homo- and heterochiral coordination polymers of silver with diaminocyclohexane as bridging ligand: Trends in alkylbenzoates

Abstract

Reaction of Ag 2CO 3 with four methyl-substituted derivatives of benzoic acid afforded silver benzoates; no additional anions are involved in these solids. One of the silver carboxylates was studied by X-ray diffraction: in the crystal, silver 3,5-dimethylbenzoate monohydrate consists of carboxylato-bridged discrete dinuclear molecules with a short Ag⋯Ag separation of 2.7719(5) Å and one weakly bonded hydrate water molecule per cation. The binary silver carboxylates were combined with either racemic or enantiopure trans-1,2-diaminocyclohexane and resulted in four homochiral and four heterochiral crystalline solids. All eight structures feature cationic chain polymers, carboxylate anions and hydrate water. In three of the solids derived from the racemic ligand, the individual cationic chains are homochiral. In all structures, the primary coordination of the Ag(I) centers by nitrogen is essentially linear. Despite the chemical similarity in the anions, the backbone of the polymers proved to be conformationally soft with variable Ag–N–C–C torsion angles. In the resulting structures, the diamine ligand may bridge two cations in a wide distance range between ca. 3.0 and ca. 7.2 Å. Both the chirality of the trans-1,2-diaminocyclohexane ligand and the substitution pattern of the benzoate anion have strong impact on the nature of secondary interactions perpendicular to the polymer strands: either weak coordination by carboxylato or hydrate water oxygen atoms or argentophilic interactions are encountered. The Ag⋯Ag contacts increase the dimensionality of the solids from chain polymers to layer structures.