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Structural stabilization among the three compounds namely K34In92.30Li2.70, K14Na20In91.82Li13.18 and K14Na20In96.30 reveals an intimate relationship between structure and valence electron requirements. The electronic tuning within the complicated network structure is realized by substitution of part of the iridium by electron-poorer lithium atoms.

The synthesis and characterization of the new BaTi3 compound is done by physical property measurements and electronic structure calculations. The unique geometric features of the anionic thallium layers gives rise to unusual competition between inter and intracluster bonds.

Open-shell Sr3In5 was synthesized and characterized and an unusual electron deficiency beyond the Zintl boundary was observed.

Sc(sub9)Te(sub2) structure was investigated, comprising distorted columns of scandium metal and a corrugated layer of tellurium atoms, separating rumpled metal layers.

Research was conducted to prepare a derivative of the unknown W5Si3-type Ca5Sn3. The structure has an inherent problem of short A-A separations along the tetrahedral chains that lie on the side faces of the tetragonal cell and partial substitution of a smaller cation like Mg2+ was more appropriate. The reaction yielded a second compound in the process, Ca6.2Mg3.8Sn7. Results indicate the effect that different cations have on phase stability. Findings also suggest the existence of a new type of infinite tin chain derived from square-planar tin units. Its synthesis and crystal structure are described.

A family of compounds has been found in which pairs of octahedral rare-earth-metal clusters, each centered by a late transition metal Z, share a common edge. These R10Z2 units, sheathed and interbridged by iodine atoms, occur in the quaternary phases Rb2La10I17Co2, Cs2La10I17Z (Z=Co,Ni,Ru,Os), Cs2Ce10I17Os2 and Cs2Pr10I17Z2 (Z=Co,Ru,Os) and in the ternary La10I15Os2. All are obtained as black, air-sensitive crystals from reactions of RI3, R, Z and RbI or CsI as appropriate in welded Nb containers at 800-850 degrees C.

A new Zintl phase NaGaSn2 was produced in pure form from stoichiometric reactions of the elements in sealed Ta at approximately 450 degrees C. Its orthorhombic framework structure has one-dimensional helical pores at about 6 angstroms in diameter that bind relatively well-ordered sodium countercations at 50% occupancy. Gallium is disordered over both tetrahedral framework sites with the site with more gallium and more negative having closer sodium neighbors.

The crystal X-ray structures of cubic Na4K6Tl13 and K9Tl13 are found to be similar and these structures contain isolated, centered icosahedra of Tl(sub 13)(super 10-) and Tl(sub 13)(super 11-) in bcc and ccp arrangements, respectively. The presence of alkali metal sodium stabilize these icosahedral clusters. Mixing of 6p1/2 and 6p3/2 levels in the clusters reduces relativistic separations relative to that in the thallium atom.

The fusion of certain elements in scaled Ta containers resulted in the synthesis of a novel thallium compound containing isolated Tl(sub 5)(super 7-) and Tl(sub 9)(super 9-) groups which were subjected to slow cooling and annealing at 250 degrees centigrade. This compound, which was paramagnetic and a poor conductor, exhibited geometric and electronic relations when the four adjoining vertices from a centered icosahedral Tl13 were removed.

The inconsistently melting line compound KTl contains the hypoelectronic cluster and novel naked cluster Tl (sub 6) (super 6-) in the form of tetragonally contracted octahedra. The C2h octahedron contains a thallium octahedron which is contracted tetraogonally to generate a bigger rectangular waist, a smaller axial-waist distance and a 1.0 angstrom difference in trans distances. The Tl (sub 6) (super 6-) is non-isostructural with a beta-brass or classic NaTl.

Investigations of K10In10Z (Z = Ni, Pd, or Pt) involved gradual cooling of the suitable fixed mixture in welded Ta to obtain an isostructural title compound in high yield. Single crystal methods revealed that the structure of the Ni phase formed close-packed layers of Ni-centered In10 clusters that are separated by potassium ions inside and between the cluster layers. An ideal tetracapped trigonal prism (C3v) of In centered by Z through axial compression along the 3-fold axis and opening of the capped triangular face, can be used to obtain the geometry of the clusters.

The isostructural compounds Y4Br4Os and Er4Br4Os were synthesized and characterized by single-crystal X-ray crystallography. The structures consisted of osmium-centered square antiprisms of the host metals with the bromine atoms capping the four adjoining metal triangles. Magnetic susceptibility data for Er4Br4Os followed the Curie-Weiss law while the yttrium analogue proposed a Pauli magnetism.

Synthetic explorations in the Ca[Au.sub.5]-Ca[Au.sub.4]Bi-Bi[Au.sub.2] system have shown five separate solid solution regions that show three distinct substitution patterns in the Ca[Au.sub.5] parent. The DTA analyses have shown that the phases resulting from spinodal decomposition have nearly the same melting point and they are interconvertible through peritectic reactions.

High yields of the novel Ba[Hg.sub.2][Tl.sub.2] are achieved from reactions of the appropriate cast alloys and the tetragonal barium structure is refined from both single-crystal X-ray and neutron powder diffraction data. The thallium characteristics are close to those in numerous alkali-metal-Tl cluster systems and other active metal-mercury phases are all distinctly electron-richer and more reduced and without appreciable net 5d, 6s contributions to Hg-Hg bonding.

The techniques of pseudogap electronic tuning and syntheses are employed for the development of the Ca-Au-In icosahedral quaicrystal (i-QC), as well as two other approximant crystals (ACs) under a rigid band assumption. The results show that both the ACs contain triacontahedral clusters as the basic building blocks at the body-centered and primitive cubic unit cell levels respectively.

A study reports the detailed structural analysis of [Sc.sub.3][Mg.sub.0.18(1)][Zn.sub.17.73(3)] and [Sc.sub.11.18(9)][Mg.sub.2.5(1)][Zn.sub.73.6(2)], for the respective 1/1 and 2/1 approximant crystals (ACs) of the Sc-Mg-Zn icosahedral quasicrystal (i-QC) system. Among the results found is that the fundamental building blocks for both ACs at the unit cell level are triacontahedral clusters centered by smaller multiply endohedral Tsai-type arrays.

The syntheses and characterizations of two metallic compounds A[Au.sub.4][ln.sub.2] (A = K, Rb) are reported in a structure in which infinite ID tunnels are present in the Au-In framework, analogous to those of some microporous zeolites. Both of the reported phases of A[Au.sub.4][ln.sub.2] are inert to air and water at room temperature, and the K compound exhibits well-ordered cations in the tunnel.

The electronic structure of zintl phases Ca5Ge3 is presented by means of semiempirical and first-principles density functional methods. The FP-APW calculations shows that alkaline-earth metal and germanium d and p pie orbitals of dimeric Ge2 (super-6) mix to form a conduction band.

The replacement of Mg in Mg2Cu6Ga5 with the electron-richer Sc gives strong p-d orbital mixing that enhances the depth of the pseudogap and results in the formation of the icosahedral quasicrystals. The achievements of electronic tuning to afford both approximants and quasicrystals phases via pseudogap and empty bonding state predictions represent a promising route to new quasicrystals.

A novel and quite different structure type that contains chains in which square anti-prismatic scandium alternate with scandium cubes, each cluster being centered by a ruthenium or osmium atom is discovered. These compounds were synthesized via typical high-temperature solid-state chemical reactions and characterized by single crystal X-ray diffraction methods in space group P4/nmc for the refined stoichiometries Sc(sub 13.21(2))Ru3Te8 and Sc(sub 13.82(2))Os3Te8.

New scandium and yttrium rich telluride compounds have been studied to determine metal framework constructions.

SrAu3Ge was synthesized by direct fusion of the mixed elements at high temperature followed by annealing treatments, and its structure was determined by single crystal X-ray diffraction means in space group (Pearson symbol: tP10) P4/nmm, a = 6.264(1) Å, c = 5.5082(9) Å, Z = 2 at room temperature. The structure of SrAu3Ge, a reapportioned ∞2 × ∞2 × 1 superstructure of CeMg2Si2 (P4/mmm), exhibits checkerboard nets of corner-shared bicapped Au squares (or corner-shared Au(Au4/2)Ge octahedra), in which the apical Au-Ge pairs in adjoining nets are strongly interbonded in the c direction. This motif contrasts with that of the common BaAl4 (I4/mmm) prototype in which Al squares in comparable layers are alternately monocapped by Al from the top or the bottom. Typical examples show valence electron counts (vec) between 12 and 16 for the BaAl4 type and that for CeMg2Si2 is similar, 15. The special stability of SrAu3Ge, with vec = 9, derives from significant relativistic contribution of the Au 5d10 states to the Au-Ge and Au-Au bonding. These factors are also recognized in the marked redistribution of Au and Ge site occupancies from those in CeMg2Si2. SrAu3Ge exhibits a pronounced uniaxial negative thermal expansion along c, with a coefficient of -1.57 versus 2.16 × 10-5 K-1 in a and b. The reticulated Au5Ge octahedral layers expand in the ab plane on heating, whereas the strong, interlayer Au-Ge bonds remain fixed. [ABSTRACT FROM AUTHOR]

Synthetic explorations in the CaAu5 – CaAu4Bi–BiAu2 system at 400 °C reveal five separate solid solution regions that show three distinct substitution patterns in the CaAu5 parent: (I) CaAu4(Au1 – mBim) with 0 ⩽ m ⩽ 0.15(1), (II) 0.33(1) ⩽ m ⩽ 0.64(1), (III) 0.85(4) ◀ m ◀ 0.90(2); (IV) (Ca1—r)Au4(Bi1—sAus) with 0 ⩽ r ⩽ 0.39(1) and 0 ⩽ s ⩽ 0.12(2); (V) (Ca1— – p – qAupBiq)Au4Bi with 0.09(2) ⩽ p ⩽ 0.13(1) and 0.31(2) ⩽ q ⩽ 0.72(4). Single crystal X–ray studies establish that all of these phase regions have common cubic symmetry F43m and that their structures (MgCu4Sn–type, an ordered derivative of MgCu2) all feature three– dimensional networks of Au4 tetrahedra, in which the truncated tetrahedra are centered and capped by Ca/Au, Au/Bi, or Ca/Au/Bi mixtures to give 16–atom Friauf polyhedra. TB–LMTO–ASA and –COHP calculations also reveal that direct interactions between Ca–Au and Ca–Bi pairs of atoms are relatively weak and that the Bi–Au interactions in the unstable ideal CaAu4Bi are antibonding in character at EF but that their bonding is optimized at ±1 e. Compositions between the five nonstoichiometric phases appear to undergo spinodal decompositions. The last phenomenon has been confirmed by HRTEM, STEM–HAADF, EPMA, and XRD studies of the nominal composition CaAu4.25Bi0.75. Its DTA analyses suggest that the phases resulting from spinodal decomposition have nearly the same melting point (˜ 807 °C), as expected, and that they are interconvertible through peritectic reactions at ˜ 717 °C. [ABSTRACT FROM AUTHOR]