title: One-dimensional zigzag chains of Cs-: the structures and properties of Li+ (cryptand[2.1.1])Cs- and Cs+ (cryptand[2.2.2])Cs-.
abstract: The crystal structure and properties of lithium (cryptand[2.1.1]) ceside, Li+ (C211)Cs-, are reported. Li+ (C211)Cs- is the second ceside and third alkalide with a one-dimensional (1D) zigzag chain of alkali metal anions. The distance between adjacent Cs- anions, 6 A, is shorter than the sum of the van der Waals radii, 7 A. Optical, magic angle spinning NMR, two-probe alternating and direct current conductivity, and electron paramagnetic resonance measurements reveal unique physical properties that result from the overlap of adjacent Cs- wave functions in the chain structure. The properties of cesium (cryptand[2.2.2]) ceside, Cs+ (C222)Cs-, were also studied to compare the effects of the subtle geometric changes between the two 1D zigzag chain structures. Li+ (C211)Cs- and Cs+ (C222)Cs- are both low-band-gap semiconductors with anisotropic reflectivities and large paramagnetic 133Cs NMR chemical shifts relative to Cs- (g). An electronic structure model consistent with the experimental data has sp2-hybridized Cs- within the chain and sp-hybridized chain ends. Ab initio multiconfiguration self-consistent field calculations on the ceside trimer, Cs3(3-), support this model and indicate a net bonding interaction between nearest neighbors. The buildup of electron density between adjacent Cs- anions is visualized through an electron density difference map constructed by subtracting the density of three cesium atoms from the short Cs3(3-) fragment.
authors.affiliation: Department of Chemistry and Biochemistry, San Francisco State University, 1600 Holloway Avenue, San Francisco, California 94132, USA. ichimura@sfsu.edu
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Ichimura
authors.forename: Rui H
authors.initials: RH
authors.lastname: Huang
authors.forename: Qingshan
authors.initials: Q
authors.lastname: Xie
authors.forename: Philip
authors.initials: P
authors.lastname: Morganelli
authors.forename: Amy
authors.initials: A
authors.lastname: Burns
authors.forename: James L
authors.initials: JL
authors.lastname: Dye