Charge, metal coordination number

Whereas the metal coordination number would appear to be largely determined by cation size, distribution of positive charge is undoubtedly determinative for the detailed structure of the anion. This has been further demonstrated by Hartl and co-workers in studies involving pairs of isomeric cations, e.g., [N(CH3)4]+ and [CH3)3CNH3]+ and[(CH3)3NH]+ and[(CH3)2CNH3]+ (102). All four cations crystallize with iodocuprate(I) anions of stoichiometry [Cu2I3] composed of cop-... 

In addition to the cation used to prepare the polymer, other cations with differing charges, sizes, coordination numbers and/or coordination geometries are used in these selectivity quotient measurements to verify specificity. Measurements are also made using polymers prepared with no metal cation (H or NH4 ) as experimental controls. The measurements required for these studies are made using a pH meter for [H ] and elemental analysis (inductively coupled plasma atomic emission spectrometry (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS))for [M"-"]. 

The ionic radius varies with the charge and coordination number of the ion a coordination number of 6 refers to octahedral coordination, and of 4 refers to tetrahedral unless otherwise specified. Data for the heavier d-block metals and the lanthanoids and actinoids are listed in Tables 22.1 and 24.1. 

What are the charge and coordination number of the central metal ion(s) in each compound of Problem 22.24 ... 

SECTION 12.5 Ionic solids consist of cations and anions held together by electrostatic attractions. Because these interactions are quite strong, ionic compounds tend to have high melting points. The attractions become stronger as the charges of the ions increase and/or the sizes of the ions decrease. The presence of both attractive (cation nion) and repulsive (cation-cation and anion anion) interactions helps to explain why ionic compounds are brittle. Like metals the structures of ionic compounds tend to be symmetric, but to avoid direct contact between ions of like charge the coordination numbers (typically 4 to 8) are necessarily smaller than those seen in close-packed metals. The exact structure depends on the relative sizes of the ions and the cation-to-anion ratio in the empirical formula. 

Extractive separation of metals is usually based on complex formation with inorganic and organic ligands. Therefore the use of the ideas, approaches, and methods of coordination chemistry has always been a most fruitful approach to the extraction of the elements. History shows that many problems of selectivity of separation or enhanced isolation have been successively solved by the rational application of coordination chemistry, e.g., the concept of hard and soft acids and bases. The efficiency of extraction depends on, inter alia, the ratio of charge and coordination number of metal ion. Study of this effect permitted the development of ways to improve separation due to changes in hydration of the species to be extracted. 

The precise nature of the complex depends on the charge, z, coordination number, N, and electronegativity, Xm> of the metal and the pH of the aqueous solution [8]. It is also necessary to consider the possible effects of ligand field stabilization which are most important for d and t/ ions [10]. The typical effects of charge and pH are shown schematically in Fig. I, where three domains corresponding to aquo, hydroxo, and oxo ions are defined [11,12]. This diagram explains in a qualitative manner why the hydrolysis of low-valent cations (z < 4) yields aquo, hydroxo, or aquo-hydroxo complexes... 

The Cu(NH3)42+ ion is commonly referred to as a complex ion, a charged species in which a central metal cation is bonded to molecules and/or anions referred to collectively as ligands. The number of atoms bonded to the central metal cation is referred to as its coordination number. In the Cu(NH3)42+ complex ion—... 

Relate the composition of a complex ion to its charge, coordination number, and the oxidation number of the central metal... 

The complexes can be considered to be Lewis acids, the acidity of which increases with the reduction in the metal s coordination number or when moving along the complex sequence from TaF72 or NbOFs2 to TaF6" or NbFs. The reduction in coordination number also leads to a reduction in the charge on the complex. 

Here the ligand (L) can be either a neutral molecule or a charged ion, and successive replacement of water molecules by other ligand groups can occur until the complex ML, is formed n is the coordination number of the metal ion and represents the maximum number of monodentate ligands that can be bound to it. 

However, EDTA has the widest general application in analysis because of its powerful complexing action and commercial availability. The spatial structure of its anion, which has six donor atoms, enables it to satisfy the coordination number of six frequently encountered among the metal ions and to form strainless five-membered rings on chelation. The resulting complexes have similar structures but differ from one another in the charge they carry. 

C18-0085. Write the chemical formulas, including charge, of the complexes that form between the following metal cations and ligands (a) Fe " and CN", coordination number = 6 (b) and NH3, coordination number = 4 and (c) and ethylenediamine (en), coordination number = 6. 

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