Hydrothermal Synthesis and Characterization of 2D M(II)-Quinate (M = Co,Zn) Metal−Organic Lattice Assemblies: Solid-State Solution Structure Correlation in M(II)-Hydroxycarboxylate Systems

Co(II) and Zn(II) ions exhibit variable reactivity toward O-containing ligands in aqueous media, affording isolable materials with distinct solid-state lattice properties. d-(−)-quinic acid is a cellular α-hydroxycarboxylate metal ion binder, which reacts with Co(II) and Zn(II) under pH-specific hydrothermal conditions, leading to the isolation of two new species [Co2(C7H11O6)4]n·nH2O (1) and [Zn3(C7H11O6)6]n·nH2O (2). Compound 1 was characterized by elemental analysis, spectroscopic techniques (FT-IR, UV−visible, EPR), magnetic studies, and X-ray crystallography. Compound 2 was characterized by elemental analysis, spectroscopic techniques (FT-IR, ESI-MS), and X-ray crystallography. The 2D molecular lattices in 1 and 2 reveal the presence of octahedral M(II) units bound exclusively to quinate in a distinct fashion, thereby projecting a unique chemical reactivity in each investigated system. The magnetic susceptibility and solid-state/frozen solution EPR data on 1 support the presence of a high-spin octahedral Co(II) in an oxygen environment, having a ground state with an effective spin of S = 1/2. Concurrent aqueous speciation studies on the binary Zn(II)−quinate system unravel the nature and properties of species arising from Zn(II)−quinate interactions as a function of pH and molar ratio. The physicochemical profiles of 1 and 2, in the solid state and in solution, earmark the importance of (a) select synthetic hydrothermal reactivity conditions, affording new well-defined lattice dimensionality and nuclearity M(II)−quinate materials, (b) structural speciation approaches delineating solid state−aqueous solution correlations in the binary M(II)−quinate systems, and (c) pH-specific chemical reactivity in binary M(II)−quinate systems reflecting structurally unique associations of simple aqueous complexes into distinctly assembled 2D crystalline lattices.