Mixed-halide systems

Centered Zirconium Clusters Mixed-halide Systems... 

In the present article, we will survey the known synthetic procedures to intrazeolite semiconductor QD s and quantum supralattices (QS s this name has been chosen to refer to these structures, since they do not alter the crystallographic unit cell of the host, as the more common name of superlattice would imply). This is followed by two examples from our recent work concerning the I-VII pure and mixed halide system Ag,X-SOD (3) and the VI-VI system n(WC>3)-M56Y (Ozkar, S. Ozin, G.A. /. Phys. Chem., in press.). Some key properties of these materials will be briefly described that relate to QSE s, LFE s, electronic and vibrational coupling between QD s. The paper concludes with a very brief survey of some of the pertinent physics behind these early observations and how they might relate to the NLO properties of these materials. 

Several mixed halide systems have been studied, including the Pb,Rb,Tl -Cl, K,Pb,Rb-Cl, " Na,Rb,Pb-Br, Li-PbClj-UCU, and BiCl3-SnCl2 systems. 

Early in their work on molten salt electrolytes for thermal batteries, the Air Force Academy researchers surveyed the aluminum electroplating literature for electrolyte baths that might be suitable for a battery with an aluminum metal anode and chlorine cathode. They found a 1948 patent describing ionicaUy conductive mixtures ofAlCh and 1-ethylpyridinium halides, mainly bromides [6]. Subsequently the salt 1-butylpyridinium chloride -AICI3 (another complicated pseudo-binary) was found to be better behaved than the earlier mixed halide system, so the chemical and physical properties were measured and published [7]. I would mark this as the start of the modern era for ionic liquids, because for the first time a wider audience of chemists started to take interest in these totally ionic, completely nonaqueous new solvents. 

In the mixed halide system AsQs.SbCls.AsClg the component species are ASCI4+, with As-Cl distances from 2.03 to 2.07 A and angles very close to 109° SbClg-, with Sb-Cl distances from 2.34 to 2.38 A and AsCls molecules with pyramidal geometry (angles 97—106°) and As-Cl distances of 2.07—2.08 A. All three species have mirror symmetry. 

Similar to the mixed-halide (Cl, I) 6-13 system, where more chlorine-rich reactions produced a new structure type, materials with an unprecedented zirconium cluster structure are obtained in the Na-Zr-(C1/I)-B system (also with. other cations, see below), when larger Cl/I ratios are used than above. Compounds characterized are Na[(Zr6B)(Cl,I)i4] and Ao.5[(Zr6B)(Cl,I)i4] (with A = Ca, Sr, Ba) [25, 26]. Single crystals of the cubic Na[(Zr6B)Clio.94(i)l3.o6] and... 

This structure type evidently requires the simultaneous existence of two differently sized halide types, and thus exists only in mixed hahde systems. Recent investigations revealed this cubic stracture also for cluster phases with other interstitial atoms, i.e., the cation-free Si-centered [(Zr6Si)Cli2-xl2+x] [28]. 

John D. Corbett once said There are many wonders still to be discovered [4]. This certainly holds generally for all the different areas and niches of early transition cluster chemistry and especially for the mixed-hahde systems. The results reported above so far cover a very Hmited selection of only chloride/iodide systems and basically boron as the interstitial. Because of the very sensitive dependence of the stable stracture built in the soHd-state reaction type on parameters like optimal bonding electron counts, number of cations present, size and type of cations (bonding requirements for the cations), metal/halide ratio, and type of halide, a much larger mixed-hahde cluster chemistry can be expected. Further developments, also in mixed-hahde systems, can be expected by using solution chemistry of molecular clusters, excised from solid-state precursors. 

This selectivity for preferred reaction displacing the halide is found withboth P(III) and P(V) mixed halide/ester systems (Equation4.15)38 and has been noted in several patents to be of value for phosphonite synthesis (Equation 4.16).39 40... 

As an alternative to the Grignard reagent system noted previously,38 aluminum acetylides react selectively with mixed halide/ester species to replace only the halide (Equation 4.18).49... 

There are several interesting families of inorganic mixed-valence compounds that we have not discussed here (see Yvon, 1979 McCarley, 1982). For example, there are metal-cluster compounds such as the Chevrel phases, M,jMo6X8(X = S or Se) and condensed metal-cluster chain compounds such as TlMojScj, TijTe, NaMo O and M PtjO. TTF halides and TTF-TCNQ complexes (Section 1.9) constitute molecular mixed-valent systems in which the mixed valency is associated with an entire molecule the charge on TTF in such compounds is nonintegral. The structure of TTF-Br(, 79 and... 

Halide ligands are found in homoleptic complexes as well as in mixed ligands systems. Halide complexes of Ir(IV) such as [IrCl6]2 [16918-91-5] are readily reduced to Ir(III) species, eg [IrCl6]2 [14648-50-1], in neutral or basic solution, or in the presence of reducing agents such as KI, oxalate, or... 

The dependence of the principal components of the nuclear magnetic resonance (NMR) chemical shift tensor of non-hydrogen nuclei in model dipeptides is investigated. It is observed that the principal axis system of the chemical shift tensors of the carbonyl carbon and the amide nitrogen are intimately linked to the amide plane. On the other hand, there is no clear relationship between the alpha carbon chemical shift tensor and the molecular framework. However, the projection of this tensor on the C-H vector reveals interesting trends that one may use in peptide secondary structure determination. Effects of hydrogen bonding on the chemical shift tensor will also be discussed. The dependence of the chemical shift on ionic distance has also been studied in Rb halides and mixed halides. Lastly, the presence of motion can have dramatic effects on the observed NMR chemical shift tensor as illustrated by a nitrosyl meso-tetraphenyl porphinato cobalt (III) complex. 

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