title: Synthesis, structure and band gap energy of covalently linked cluster-assembled materials.
abstract: We have synthesized a series of cluster assembled materials in which the building blocks are As(7)(3-) clusters linked by group 12 metals, Zn, Cd and Hg, to investigate the effect of covalent linkers on the band gap energy. The synthesized assemblies include zero dimensional assemblies of [Zn(As(7))(2)](4-), [Cd(As(7))(2)](4-), [Hg(2)(As(7))(2)](4-), and [HgAsAs(14)](3-) in which the clusters are separated by cryptated counterions, and assemblies in which [Zn(As(7))(2)](4-), [Cd(As(7))(2)](4-) are linked by free alkali atoms into unusual three-dimensional structures. These covalently linked cluster-assembled materials have been characterized by elemental analysis, EDX and single-crystal X-ray diffraction. The crystal structure analysis revealed that in the case of Zn and Cd, the two As(7)(3-) units are linked by the metal ion, while in the case of Hg, two As(7)(3-) units are linked by either Hg-Hg or Hg-As dimers. Optical measurements indicate that the band gap energy ranges from 1.62 eV to 2.21 eV. A theoretical description based on cluster orbital theory is used to provide a microscopic understanding of the electronic character of the composite building blocks and the observed variations in the band gap energy.
authors.affiliation: Department of Chemistry, Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Sukhendu
authors.initials: S
authors.lastname: Mandal
authors.forename: Arthur C
authors.initials: AC
authors.lastname: Reber
authors.forename: Meichun
authors.initials: M
authors.lastname: Qian
authors.forename: Ran
authors.initials: R
authors.lastname: Liu
authors.forename: Hector M
authors.initials: HM
authors.lastname: Saavedra
authors.forename: Saikat
authors.initials: S
authors.lastname: Sen
authors.forename: Paul S
authors.initials: PS
authors.lastname: Weiss
authors.forename: Shiv N
authors.initials: SN
authors.lastname: Khanna
authors.forename: Ayusman
authors.initials: A
authors.lastname: Sen