Stepwise ortho Chlorination of Carboxyl Groups for Promoting Structure Variance of Heterometallic Uranyl-Silver Coordination Polymers of Isonicotinate.

Abstract

We report the syntheses and characterization of four new heterometallic uranyl-silver compounds from isonicotinic acid derivatives with a stepwise ortho chlorination of carboxyl group, that is, isonicotinic acid (H-PCA), 3-chloroisonicotinic acid (H-3-MCPCA), and 3,5-dichloroisonicotinic acid (H-3,5-DCPCA). Compound 1, (UO2)Ag4(3,5-DCPCA)6(3,5-DCPy)2, from H-3,5-DCPCA displays a heterometallic three-dimensional (3D) framework through the connection of 3,5-DCPCA and in situ-formed 3,5-dichloropyridine (3,5-DCPy) with the aid of multiple argentophilic interactions. Compounds 2 ((UO2)Ag(3-MCPCA)3) and 3 ((UO2)Ag2(3-MCPCA)4), which differ from each other in coordination modes of uranyl center, are both heterometallic 3D reticular frameworks from 3-MCPCA based on highly coordinated silver nodes. All these heterometallic uranyl-silver compounds are different from the hydrothermal products from chlorine-free H-PCA ligand in the presence of uranyl and silver ions, U-Ag-PCA ((UO2Ag(OH)(PCA)2)) and 4 ((UO2)Ag2(OH)(H2O)2(PCA)4) due to highly coordinated silver ions found in 1-3, among which carboxyl groups of isonicotinate expected to coordinate with uranyl are the biggest contributors. Detailed structural analysis reveals that the inclination of the carboxyl group of isonicotinate driven by large steric hindrance from bulky ortho chlorine atoms at its ortho positions enables it to participate in the coordination sphere of silver ion and promote the formation and structure variance of 3D heterometallic uranyl-silver frameworks.