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Manganese is a metal with diverse (bio)chemical reactivity in aqueous media in the presence of biologically relevant ligands. Key to that reactivity is the existence of soluble and bioavailable forms of MnII across the physiological range of pH. To probe the interactions arising between MnII and the low-molecular-mass ligand D-(–)-quinic acid, research efforts were targeted at the synthetic aqueous chemistry in the requisite binary system. The pH-specific synthetic reaction of MnII with D-(–)-quinic acid led to the isolation of the new species [Mn2(C7H11O6)4]n·nH2O (1). Complex 1 was characterized by elemental analysis, spectroscopic techniques (EPR, FTIR), thermal and magnetic studies, and X-ray crystallography. The molecular lattice of 1 reveals the presence of dimeric units of MnII centers, with the quinate ligands coordinated to the metal ions through variable binding modes, indicating the diversity of chemical reactivity in the system. The octahedral MnII centers in the molecular assembly of 1 serve as chemical prototypes of the forms of interactions that most likely develop in biologically relevant fluids, similar to those encountered in plant exudates and plant cellular structures. Concurrently, the physicochemical features of 1 (from the 3D hydrogen-bonding network to the magnetic susceptibility properties and EPR spectral results) exemplify the key features that constitute the rudiments of MnII-organic hybrid lattices of specific functions and (bio)chemical reactivity patterns. The collective properties of 1 are discussed in the context of their occurrence in natural binary MnII-influenced systems and advanced metal-hybrid materials of potential applications. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The majority of reported nickel tetranuclear clusters have a dicubane-like structural core. The compound presented here is the second example possessing an Ni4O2 core based on a chair or butterfly “out-of-face” topology. This compound also belongs to the family of compounds characterized as metallacrowns with an [Ni−N−O−]n linkage and is the only example with three Ni−O−N−Ni strands bridging the nickel atoms. The values obtained from the fitting procedure are J1 = 55.8 cm−1, J2 = −67.2 cm−1, g = 2.2, ρ = 1.1%. These values suggest the presence of both ferromagnetic and antiferromagnetic interactions, while a small paramagnetic impurity is also present. This magnetic behaviour with antiferromagnetic internal coupling and ferromagnetic spin-alignment is the second example in the literature and the first in the metallacrown family. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)