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 igands in aqueous media, affording isolable materials with distinct solid-state lattice properties. D-(-)-quinic acid is a cellular a-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)center dot nH(2)O (1) and [Zn-3(C7H11O6)(6)](n)center dot nH(2)O (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.