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Metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlorates. They have the general stoichiometry ()z+. Their behavior underpins many aspects of environmental, biological, and industrial chemistry. This article focuses on complexes where water is the only ligand ("homoleptic aquo complexes"), but of course many complexes are known to consist of a mix of aquo and other ligands.〔Mark I. Ogden and Paul D. Beer "Water & O-Donor Ligands" in Encyclopedia of Inorganic Chemistry, Wiley-VCH, 2006, Weinheim. 〕 ==Stoichiometry and structure== Most common are the octahedral complexes with the formula ()2+ and ()3+. Some members of this series are listed in the table below. A few aquo complexes exist with coordination numbers lower than six. Palladium(II) and platinum(II), for example, form square planar aquo complexes with the stoichiometry ()2+. Aquo complexes of the lanthanide trications are eight- and nine-coordinate, reflecting the large size of the metal centres. Aquo complexes of about one third of the transition metals (Zr, Hf, Nb, Ta, Mo, W, Tc, Re, Os and Au) are either unknown or rarely described. Aquo complexes of M4+ centres would be extraordinarily acidic. For example, ()4+ is unknown, but ()3+ is well characterized. This acidification is related to the stoichiometry of the Zr(IV) aquo complex ()8+ (see zirconyl chloride. Similarly, ()5+ is unknown, but its conjugate base, ()2+ is highly stable. Univalent metal centres such as Cu(I) and Rh(I) rarely form isolable complexes with water. Ag(I) form tetrahedral ()+, a rare example of a tetrahedral aquo complex.〔 Some aquo complexes also contain metal-metal bonds. Two examples are ()4+ and ()4+.〔 :{| class=wikitable style=text-align:center !Complex!!colour!!electron config.!!M-O distance (Å)〔For Mn(II), Fe(II), Fe(III): T. K. Sham, J. B. Hastings, M. L. Perlman "Structure and dynamic behavior of transition-metal ions in aqueous solution: an EXAFS study of electron-exchange reactions" J. Am. Chem. Soc., 1980, 102 (18), pp 5904–5906. . For Ti(III), V(III), Cr(III): B. Kallies, R. Meier "Electronic Structure of 3d ()3+ Ions from ScIII to FeIII: A Quantum Mechanical Study Based on DFT Computations and Natural Bond Orbital Analyses" Inorg. Chem., 2001, 40 (13), pp 3101–3112. 〕||water exchange rate (s−1, 25 °C)〔!!M2+/3+ self-exchange rate (M−1s−1, 25 °C) |- | ()3+ | violet | (t2g)1 |2.025 |1.8 x 105 |n.a. |- | ()2+ | violet | (t2g)3 |2.12 |8.7 x 101| |fast |- | ()3+ | green | (t2g)2 |1.991 |5.0 x 102| |fast |- | ()2+ | blue | (t2g)3(eg)1 |2.06, 2.33 |1.2 x 108 |slow |- | ()3+ | violet | (t2g)3 |1.961 |2.4 x 10−6 |slow |- | ()2+ | pale pink | (t2g)3(eg)2 |2.177 |2.1 x 107 |n.a. |- | ()2+ | blue-green | (t2g)4(eg)2 |2.095 |4.4 x 106 |fast |- | ()3+ | pale yellow | (t2g)3(eg)2 |1.990 |1.6 x 102 |fast |- | ()2+ | pink | (t2g)5(eg)2 |2.08 |3.2 x 106 |n.a. |- | ()2+ | green | (t2g)6(eg)2 |2.05 |3.2 x 104 |n.a. |- | ()2+ | blue | (t2g)6(eg)3 |1.97, 2.30 |5.7 x 109 |n.a. |- |} 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Metal aquo complex」の詳細全文を読む スポンサード リンク
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