Divalent structures mononuclear complexes

There are also carboxylates15 (Section 17-E-10), phosphates, catecholates, and oxalates. Most of the divalent iron oxalato compounds have a chain structure but the product of photoreduction of mononuclear [bipyH] [Feni(ojc)2(H20)2] gives a three-dimensional anionic polymeric network of [Fe2I(ox)3]2 1 and [Fen(bipy)3]2+ ions.16 Magnetic exchange typically occurs through the oxalate bridges.17 Six-coordinate iron(II) a-amino acid complexes are readily obtained from the reaction of the 4-coordinate Fe(mes)2(phen) and the protic amino add, AH, in THF 18... 

The contemporary interest in metal organophosphonate coordination chemistry has received considerable impetus from the applications of such materials as sorbents, catalysts and catalyst supports. The structural chemistry of the metal organophosphonate system is extremely rich " and is represented by mononuclear coordination complexes, molecular clusters, " one-dimensional materials, and layered phases. Extensive investigations have been reported on layered phosphonates of divalent, " trivalent, tetravalent, " and recently hexavalent elements. Several examples of three dimensional metal organophosphonate frameworks have also been described since the first report by Bujoli. " ... 

Metal-mediated reactions involving water are essential to life and catalytic industrial processes [1-3]. In biological systems, metalloenzymes containing various divalent metal ions catalyze the hydrolysis of amide, carboxylic ester and phosphate ester bonds using both mono- and multinuclear active-site structural motifs [4—6], Mononuclear metal centers are also found within the active sites of enzymes that catalyze the hydration, or the addition of water, to CO2 [Zn(II)] and nitriles [Co(III)/Fe(III)j [7-10]. In many of these processes, formation of a metal hydroxide moiety via deprotonation of a metal-coordinated water molecule is a key proposed step in the reaction pathway. Thus, a substantial amount of research over the past several years has been directed at dehneating how the structural and electronic environments of biological metal ions influence the pKa of a metal-bound water molecule. In this regard, studies directed at the preparation, characterization and elucidation of the reactivity of discrete metal aqua and hydroxo complexes have been paramoimt [11-13]. 

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