Layered and caged solid state materials : structure and physical properties
The first chapter of this thesis describes the synthesis and structural study of a new layered ternary chromium sulfide, BaCrS[sub 2]. This solid state compound crystallizes in the orthorhombic, central symmetric space group Pmmn (no. 59) with a = 4.2606(6) Å, b = 4.7944(7) Å, c = 9.443(1) Å, V = 192.89(5) Å ^3, and Z = 2. The refinement data are Rl= 0.0335 and wR2 = 0.0808 for I>2?(I). The solid is similar to a previously known structure BaNiS[sub 2] in which the Ni atom is coordinated to five sulfur atoms in a square pyramidal fashion. In the title compound, the square pyramid distorts such that the two S(basal)-Cr-S(basal) angles are no longer equal. Thus, the BaCrS[sub 2] solid is orthorhombic whereas BaNiS[sub 2] is tetragonal. The distortion from the square pyramidal coordination in the title compound is traced to the broken degeneracy of the d[sub xy] and d[sub xz] set by a computational analysis. The second chapter details the synthesis, single crystal study, solid state Raman spectroscopic measurements and computational analysis of layered solids BaZn[sub 2]Si[sub 2] and BaZn[sub 2]Sn[sub 2]. BaZn[sub 2]Si[sub 2] crystallizes in the ThCr[sub 2]Si[sub 2]-type lattice of space group I4/mmm (No. 139) with lattice constants a = 4.4918(3) Å, c = 10.2673(9) Å, V = 207.16(3) Å ^3, and Z = 2. BaZn[sub 2]Sn[sub 2] crystallizes in the related CaBe[sub 2]Ge[sub 2]-type lattice of space group P4/nmm (No. 129) with a = 4.7418(3) Å, c = 11.346(1) Å, V = 255.11(3) Å ^3, and Z = 2. The refinement data are R1 = 0.0295, 0.0586 and wR2 = 0.0791, 0.1393 with I>2?(I) for BaZn[sub 2]Si[sub 2] and BaZn[sub 2]Sn[sub 2], respectively. Raman spectra of these two solids are remarkably similar despite the fact they crystallize in two distinct lattices. The third chapter examines a class of metallomulticage compounds. One area of current interest in solid state chemistry is in the study of transition metal multicage compounds. This is because of their structural and physical properties. The electron count of these types of compounds is intriguing due to possible charge disproportion in these cage-like compound. An example is Ba[sub 4]Cu[sub 3]Ge[sub 20]. In this compound the charge on the Ge can be represented as: 2 [Ge[sub 20]]^-11 => [Ge[sub 20]]^-10 + [Ge[sub 20]]^-12 which is similar to what has been proposed for the high T[sub c] cuprate superconductors. This compound has already been synthesized previous in other research groups; however, the physical properties are still unknown. An analysis of the electronic structure of a new solid material can be performed using computational techniques and predictions can then be made as to how the material can be modified. The theoretical analysis can then be used to determine what should occur in the synthesis of a series of compounds, Ba[sub 4]Cu[sub 3]Ge[sub 20-x]Si[sub x], where silicon has been used to replace germanium. The theoretical calculations and the resulting arc melting synthesis of this series will be discussed.