The 4-aminopyridinium bis(dipicolinato)chromate(III) trihydrate salt: synthesis, crystal structure, EPR spectroscopy and antimicrobial activity

Abstract

A new hybrid salt [4-apyH][Cr(dipic) ₂ ]·3H ₂ O ( 1 ) ([4-apyH] ⁺ = [C ₅ H ₇ N ₂ ] ⁺ = 4-aminopyridinium cation, dipic ²⁻ = dipicolinato(2−) ligand) has been synthesized and characterized by elemental and thermal analyses, FT-IR and UV/Vis spectroscopies, EPR, single-crystal and powder X-ray diffraction. Salt 1 consists of one [Cr(dipic) ₂ ] ⁻ complex anion, one 4-aminopyridinium [4-apyH] ⁺ counter ion, and three water molecules of crystallization. Each Cr(III) center in the anionic complex exhibits a distorted octahedral coordination. The crystal structure of 1 features alternating layers of organic cations and complex anions. The packing within the structure is stabilized by hydrogen bonds, including O–H⋯O and N–H⋯O interactions, which connect water molecules, anionic complexes, and cationic entities. The thermogravimetric diagram shows two main weight losses, corresponding to the removal of water molecules and the decomposition of the framework, respectively. The molar conductivity Ʌ _m  = 129 S cm ²  mol ⁻¹ confirms the 1:1 electrolyte nature of salt 1 in water. The EPR spectrum is consistent with Cr ³⁺ ions in an octahedral environment. The antimicrobial activity of salt 1 has been evaluated in vitro against four pathogenic microorganisms, including three bacteria and one yeast. The results showed significant antibacterial activity against Helicobacter pylori PMSS and antifungal activity against Candida albicans N50 .