Solvatomorphic diversity dictates the stability and solubility of metal–organic polyhedra

Abstract

The reaction between molybdenum(II) acetate and 5-aminoisophthalic acid (H₂Iso-NH₂) afforded [Mo₁₂O₁₂(μ₂-O)₁₂(Iso-NH₂)₁₂]¹²⁻, a novel molybdenum(V) metal–organic polyhedron (MOP) with a triangular antiprismatic shape stabilized by intramolecular N–H⋯O hydrogen bonds. The synthesis conditions, particularly the choice of solvent and reaction time, led to the precipitation of the Mo(V)-MOP in five distinct crystalline forms. These forms vary in their packing arrangements, co-crystallized solvent molecules, and counter-cations, with three phases containing dimethylammonium (dma⁺) and the other two containing diethylammonium (dea⁺). Each solvatomorph exhibits unique physical properties, including differences in porosity, and stability. These properties were discerned through empirical observations and supported by density functional theory calculations. Remarkably, the solubility of these MOP solvatomorphs in water was determined for the first time, with values of 4.30(2) g L⁻¹ for a (dma)₁₂[Mo(V)-MOP] phase, and 10.25(7) g L⁻¹ and 14.41(10) g L⁻¹ for two (dea)₁₂[Mo(V)-MOP] phases. Additionally, aqueous solutions of the Mo(V)-MOP were found to conduct electricity as weak electrolytes, showcasing their potential for applications in fields requiring partially ionized species.