And coordination complex ions

Gas-Phase Thermochemistry of Organometallic and Coordination Complex Ions... 

Linkage isomerism This is a special type of structural isomerism in which the differences arise from a particular ligand which may coordinate to a metal ion in more than one way. In Table 1-3 we indicated that a ligand such as thiocyanate could bond to a metal through either the nitrogen or the sulfur atom, and the complex ions [Co(NH3)5(ACS)]2+ and [Co(NH3)5(5CN)]2+ are related as linkage isomers. 

The latter two are mutually compatible and consistent with a highly ordered and compact six-coordinate complex ion. It has been proposed that a major part of the volume decrease arises from the intramolecular electron-transfer process accompanied by a shortening of the Co— C02 bond (as supported by XANES and EXAFS studies) and an increase in electrostriction. Only a relatively minor contribution to the large negative reaction volume is suggested to result from the intrinsic effect of CH3CN addition (123). 

The compound Gd(H20)6 Cl3 is eight coordinate with six water molecules and two chloride ions coordinating to the metal ion 331). The third chloride remains ionic. The complex units are held together by hydrogen bonds through both the ionic and coordinated chloride ions. Each noncoordinated Cl" ion forms six Cl... H-0 bonds and each coordinated Cl- ion forms three Cl... H-0 bonds in addition to the Cl—Gd bond. The coordination geometry around Gd(III) has been described as distorted dodecahedron. In [Eu(H20)6 C12]C1, the coordination geometry has been described as distorted square antiprism 332). Similar compounds of Nd(III), Sm(III), Dy(III), Ho(III), and Er(III) are isostructural. 

Geometry of molecules and ions, structural isomerism of simple organic molecules and coordination complexes, dipole moments of molecules, relation of properties to structure... 

Not all coordination compounds are neutral molecules like Pt(NH3)2Cl2. Many are salts, such as [Ni(NH3)6]Cl2 and K3[Fe(CN)6], which contain a complex cation or anion along with enough ions of opposite charge to give a compound that is electrically neutral overall. To emphasize that the complex ion is a discrete structural unit, it is always enclosed in brackets in the formula of the salt. Thus, [Ni(NH3)6]Cl2 contains [Ni(NH3)6]2+ cations and Cl- anions. The term metal complex (or simply complex) refers both to neutral molecules, such as Pt(NH3)2Cl2, and to complex ions, such as [Ni(NH3)6]2+ and [Fe(CN)6]3-. 

The synthesis of lanthanide complexes [244] with multidentate diethylenetriamine (dien) gave rise to two types of complexes, Ln(dien)3(N03>3 for Ln = La-Gd, and Ln(dien)2(N03)3 for Ln = La-Yb. The tris complexes contain ionic nitrate while the bis complexes contain both ionic and coordinated nitrate ions. The coordination number is nine in the tris complexes while it is not known with certainty in the bis complexes. With triethylene triamine (tren) two types of complexes [Ln(tren)(N03)3] and Ln(tren)2(N03)3 have been isolated. In the bis complexes both ionic and coordinated nitrate groups are present for larger lanthanides (La-Nd) but only ionic nitrate for smaller lanthanides (Sm-Yb). When perchlorate is the anion [245] Ln(tren)(C104)3 (Ln = Pr, Gd, Er) and Ln(tren)2(C104)3 for Ln = La, Pr, Nd, Gd, Er complexes were obtained. The monocomplexes contain coordinated perchlorate ions while the bis complexes contain ionic perchlorate ions. 

Rigorous chemical correlation of optical configuration of octahedral complexes must therefore rest at present on reactions where no bond to the metal is broken. Unlike organic chemistry few such cases have been reported. Fortunately even rather trivial cases are of value for example, coordinated water and coordinated hydroxide ion have different ligand field strengths, and thus the changes of O. R. D. and C. D. in reactions such as... 

CNO The isomeric fulminate ion, CNO (Figure 3-5), can be drawn with three similar structures, but the resulting formal charges are unlikely. Because the order of electronegativities is C < N < O, none of these are plausible structures and the ion is predicted to be unstable. The only common fulminate salts are of mercury and silver both are explosive. Fulminic acid is linear HCNO in the vapor phase, consistent with structure C, and coordination complexes of CNO with many transition metal ions are known with MCNO structures. ... 

Further hydrolysis leads to binuclear and oligonuclear complex ions. The situation is similar with [Fe(H20) ] ". Only [Cr(H20)5] is kinetically stable at neutral pH. In the so-called basic aluminum chloride solutions at pH 4—8, the cation [Alj304(0H)24(H20),2] is formed [81]. It has a spherical Keggin-hke structure with a central tetrahedrally coordinated Al " " ion, analogous to the structure of the phosphomolybdate anion [PMoj204q] . 

By the photoimmobilization of Cu, V, Mo, W, Ti and Ag complex ions on silica gel the systems including the metal ions in a low oxidation degree were synthesized. Their coordination sphere was consisted of hydroxy ions, water and isopropanol molecules. 

The kinetic and activation parameters have been determined for water exchange on several poly(aminocarboxylate) ligands coordinated to Gd together with either one or two coordinated water molecules. In these systems the metal ion is nine-coordinate and the exchange rate constant is reduced by two or three orders of magnitude. [88] Distinctly positive AV values were obtained (D-activation) these could be explained by the steric crowding of the metal ion and the complex ion rigidity relative to the fully aquated ion. 

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