Lattices compounds

Structure of nickel arsenide showing (a) 3 unit cells, (b) a single unit cell NiaAsa and its relation to (c) the unit cell of the layer lattice compound Cdia (see text). 

Table 2. Structure Types, Boron Coordination and Representatives op Metal Borides with Isolated B Atoms (Filled Metal Host Lattice Compounds)...

The structure of coordination polymers formed with 3,6-bis(pyridin-3-yl)-l,2,4,5-tetrazine and zinc salts can be controlled by the choice of alcoholic solvents. Infinite lattice compounds of the form [Zn2L2(N03)4(Me0H)2(//-L)] and [Zn2(/U-L)3(N03)4](CH2C12)2) have been structurally characterized. The former structure shows an alternating single- and double-bridged species whereas the latter exists as a non-interpenetrated ladder complex.273... 

The complexes of alkali metal ions and of their salts described in paras. II—V may also be considered as lattice compounds because they do not necessarily persist in solution. Where the charge on the cation is neutralised by a small anion to give a salt, the solid may contain ion pairs coordinated by the additional ligand molecules, or the ions may be separated by the ligands, which usually form hydrogen bonds to the anion. When the cation is neutralised by a polydentate anion, the co-... 

The names described here can be used to develop further names with a little more manipulation. Addition compounds (a term that covers donor-acceptor complexes as well as a variety of lattice compounds) of uncertain structure can be named by citing the names of the constituent compounds and then indicating their proportions. Hydrates constitute a large class of compounds that can be represented by this means. 

An interstitial compound consists of a metal or metals and certain metalloid elements, in which the metalloid atoms occupy the interstices between the atoms of the metal lattice. Compounds of this type are, for example. TaC, TiC, ZrC. NbC, and similar compounds of carbon, nitrogen, boron, and hydrogen with metals. 

LATTICE COMPOUNDS. Chemical compounds formed between deh-nile sloichioinctric amounts of two molecular species that owe their stability to packing in the crystal lattice, and not to ordinary valence forces. 

Representative examples of rare earth complexes with halides and pseudohalides are given in Table 4.12. Some oxyanions such as nitrates are included in a separate listing. The formulas given for halide complexes as hexahalides are misleading since these compounds are extended lattice compounds and are not always octahedral. 

Many layer-lattice compounds can intercalate additional metal atoms of the same element as comprised in the original structure (e.g. niobium in niobium diselenide), but molybdenum disulphide will not do so. The behaviour may be determined by the availability of electrons suitably oriented to form bonds with the additional metal atoms, although it seems unlikely that this single factor applies to all intercalation effects. 

Haltner, A.J., Sliding Behaviour of Some Layer Lattice Compounds in Ultrahigh Vacuum, ASLE Trans., 9, 136, (1966). 

Potash alum, KAl(S04)2l2H20, contains K+, AF+ and tetrahedral 5042-ions. Six of the water molecules are octahedrally co-ordinated to the AF+ and six are used to hnk these [Al(H20)g +] ions to neighbouring sulphate ions. It is thus a lattice compound rather than a complex. Unipositive ions smaller than K+ do not form very stable alums. The radius must be small the large lanthanide M + ions do not form alums. 

The term addition compounds covers donor-acceptor complexes (adducts) and a variety of lattice compounds. The method described here, however, is relevant not just to such compounds, but also to multiple salts and to certain compounds of uncertain structure or compounds for which the full structure need not be communicated. 

Irradiation of imides (125)-(129) in solution gives oxetanes (130) in high yield. In the crystalline state the outcome is controlled by the conformations adopted about the imide unit in the crystal lattice. Compound (125) crystallises in a chiral space group and forms the oxetane in high enantiomeric excess. In addition to solid state oxetane formation, (126) and (127) also yield (131) and (132)... 

YbPdSb. Transport, bulk magnetic and caloric measurements (Le Bras et al. 1995, Suzuki et al. 1995, Bonville et al. 1997) clearly show that cubic YbPdSb is a Kondo-lattice compound. CEF interaction puts a Fg quartet lowest on which the Kondo coupling acts with a strength of T 7 K. 

Kitaoka et al. (1985a) showed with Si NMR (K(T), l/T ) that CeRu2Si2 is a non-magnetic Kondo-lattice compound below 7 = 12 K. They found that K depended on temperature, while did not. was about 30 at 4.2 K, and... 

Preliminary studies have also been made for the compound CeSuj that is a borderline case between a mixed-valent compound and a Kondo lattice compound (see sect. 4). MAQO have been observed for the c, C44 and (cn — Cyj) modes (Niksch et al. 1985, Suzuki et al. 1987a). Because the experiments were performed for r > 1 K only small Fermi surface pieces have been observed with normal electron masses. Heavy masses observed by conventional de Haas-van Alphen experiments (Johannsen et al 1984) have not be detected so far. As in the case of LaBg the — Cj2 mode also exhibits for CeSnj the rotational invariance phenomenon (Suzuki et al. 1987a). 

Recently MAQO experiments have also been performed for the Kondo lattice compound CePbj, see Niki et al. (1987). Figure 43 shows relative velocity changes for the c - Cj2 mode for B k in the temperature range between 0.38 K to 1.7 K. For magnetic fields from 18-23 T a clear MAQO with frequency F = 617 T is observed with an effective mass m lm = 43. More extensive experiments have to be performed in order to determine the Fermi surface geometry. The complicated B-T phase diagram will be discussed in sect. 4. 

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