Complex ions in crystals

M Simulation of symmetry by molecules or complex ions in crystals has been discussed by Linus Pauling, Phys. Rev., 36, 430 (1930). 

Distances in Molecules and Complex Ions in Crystals Resonating between Two or More Electronic Structures. 

Hornig, D. F. The vibrational spectra of molecules and complex ions in crystals. I. General theory. J. chem. Phys. 16, 1036—1076 (1948). 

Reding, F. P., and D. F. Horning Vibrational Spectra of Molecules and Complex Ions in Crystals (V). Ammonia and Deutero-Ammonia. J. chem. Physics 19, 594, 601 (1951). 

Since the coordination number of tantalum or niobium in fluoride and oxyfluoride compounds cannot be lower than 6 due to steric limitations, further decrease of the X Me ratio (lower than 6) leads to linkage between complex ions in order to achieve coordination saturation by sharing of ligands between different central atoms of the complexes. The resulting compounds have X Me ratios between 6 and 4, and form crystals with a chain-type structure. 

This monograph compiles the latest research on the chemistry of complex fluorides and oxyfluorides of tantalum and niobium, and covers synthesis and fluorination processes, crystal structure peculiarities and crystal chemical classification, as well as the behavior of complex ions in fluorine solutions and melts. 

Evaporation of solutions of alumina in sulfuric acid yields crystals of A12(S04)3T6H20. If a group I sulfate is also present, the products are alums MA1(S04)2T2H20, in which aluminum exists as [Al(OH2)fi]3+. Analogous selenates but not tellurates have been prepared. Basic salts, e.g. Al2(OH)2(SO4)210H2O, and solids obtained from aluminum sulfate solutions above 100 °C also contain complex ions in which the coordination sphere of Al3+ is occupied by OH groups and/or water molecules rather than sulfate ions. Thermal decomposition of the hydrate A12(S04)3-16H20 yields practically anhydrous A12(S04)3 at 450 °C further decomposition to... 

Cobalt has an electronic configuration I j 2.v 2/Z 3.v 3pl 3i/74j-. The two 4, electrons arc readily removed producing the ordinary Cu ion. In principle, if the odd 3complex ions or crystal lattices in which cases additional electron orhitals are tilled. 

Sedimentary geochemistry. The aqueous phase dominates weathering, leaching, transportation, and precipitation processes in the sedimentary cycle. The behaviour of transition metal ions to chemical attack depends on the relative stabilities of hydrated and complex ions in solution and bonded cations in crystal structures. The break-down of minerals and leaching of ions takes place through substitution reactions, which depend on kinetic and mechanistic fac-... 

Many lanthanides in the form of complexes emit fluorescence when excited with light absorbed by ligands. Lanthanide ions in crystals or in solution also exhibit fluorescence. The fluorescence observed due to energy transfer from the triplet state of the ligand to excited state of Ln3+ is known as enhanced fluorescence. The fluorescence emission spectra of Tb3+ aquo ion in the absence and presence of porcine trypsin at pH 6.3 is shown in Fig. 11.3. 

In order to test such an application we have calculated the spin and charge structure factors from a theoretical wave function of the iron(III)hexaaquo ion by Newton and coworkers ( ). This wave function is of double zeta quality and assumes a frozen core. Since the distribution of the a and the B electrons over the components of the split basis set is different, the calculation goes beyond the RHF approximation. A crystal was simulated by placing the complex ion in a lOxIOxlOA cubic unit cell. Atomic scattering factors appropriate for the radial dependence of the Gaussian basis set were calculated and used in the analysis. 

With regard to the formation of ionic compounds, it is not too relevant whether the 8p or 7d shell is occupied in the neutral atom, as studied in extenso by Mann and Wdber (50). Instead, the significant question for more ionic compounds is whether in the ions, after all outer s, p and d electrons are removed, some g or f electrons will be in frontier orbitals or whether they might be easily excited to an outer electron shell so that they can be removed as well. Prince and Waber (103) showed that even in the divalent state of element 126 one g electron has changed to an / electronic state. However, the 8s electrons are not the first to be removed. Thus, the divalent ions will be expected to act as soft Lewis acids and possibly form covalent complex ions readily. Crystal or ligand fields influence the nature of the hybridization. Details such as directionality of bonds... 

However, it should be noted that, for U02 S04 1, the most eharacteristie eoordination of sulfate ions relative to the uranyl ions is not bidentate bridging (B, Fig. 10) but tridentate bridging (T, Fig. 10). Due to the inelusion of third O atom into the coordination, electron-donor ability of sulfate ions increases significantly they have El= 3Ei = 6.3e. For this reason, the most stable electroneutral complexes have the composition [U02(S04)(H20)2], since for them Ne = 7.8 + 6.3 + 2-1.9 = 17.9 e and ANe = 0.1 e i.e. less than for the complexes XIX. This explains why the [U02(S04)(H20)2] complexes occur in crystal structures more frequently than the [U02(S04)(H20)3] complexes. 

One of the motivations for studying ammonia complexes is that (before deuterium and oxygen isotopes were available) they offered one of the rare opportunities to get an idea about the constitution of aqua ions in solution. However, this does not always proceed as smoothly as in the case of nickel(II). Bjerrum found that Zn(NH3)/2 does not react further with aqueous ammonia, as confirmed by crystal structures containing this tetrahedral complex. However, the zinc(II) aqua ions in crystals are octahedral with N = 6 like magnesium(II) and nearly all 3d group aqua ions. 

In general the optical activity exhibited by a crystal will persist in other states of aggregation only if it is due to the asymmetry of the finite molecule or complex ion. In this case it is also necessary that the energy of activation for racemization (change d 1) must exceed a certain value ( 80 klmol" at room temperature). The optical activity cannot, of course, be demonstrated unless there is a means of resolution (separation of d and / forms) or at least of altering the relative amounts of the two isomers. The optical activity of many crystals (e.g. quartz, cinnabar, NaC103) arises from the way in which the atoms are linked in the crystal it is then a property of the crystalline material only. 

The nearest neighbours of an atom in a molecule, complex ion, or crystal, define a polyhedral coordination group, the number of vertices of which is the coordination number (c.n.) of the atom. It is convenient to describe the structures of many essentially ionic crystals in terms of the coordination groups around the cations. It is to be expected that coordination polyhedra with triangular faces will be prominent because these are the most compact arrangements of atoms in a 60... 

For many (but not all) first row metal ions, A is very small and the spin and orbital angular momenta of the electrons operate independently. For this case, the van Vleck formula (equation 20.16) has been derived strictly, equation 20.16 applies to free ions but, in a complex ion, the crystal field partly or fully quenches the orbital angular momentum. Data in Tables 20.7 and 20.8 reveal a poor fit between observed values of p.eff and those calculated from equation 20.16. 

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