Date of Award
Doctor of Philosophy
Polyatomic anions of the group IV and V post-transition elements can be isolated as stable salts by the reaction in ethylenediamine (en) of alkali metal alloys with crypt, a strong complexing agent for the alkali metal cations. The preparations and crystal structure solutions of five new phases are reported;The alloy compositions KSnBi or KPbSb react to form black pseudohexagonal plates of the isostructural monoclinic salts (2,2,2-crypt-K('+))(,2)Sn(,2)Bi(,2)('2-)(.)en or (2,2,2-crypt-K('+))(,2)Pb(,2)Sb(,2)('2-)(.)en, respectively. The Sn(,2)Bi(,2)('2-) and Pb(,2)Sb(,2)('2-) anions have essentially tetrahedral geometries, with the four metal atoms disordered over the four sites, equally for Sn(,2)Bi(,2)('2-) and ranging from 67% Pb to 27% Pb for Pb(,2)Sb(,2)('2-). Bond distances vary from 2.934 (ANGSTROM) to 2.971 (ANGSTROM) in Sn(,2)Bi(,2)('2-) and from 2.918 (ANGSTROM) to 3.006 (ANGSTROM) in Pb(,2)Sb(,2)('2-);The similar reaction of KGeSb, KPbSb or KAuSb produces bluish-black crystals of (2,2,2-crypt-K('+))(,2)Sb(,4)('2-), isostructural to the known triclinic Bi(,4)('2-) salt. The Sb(,4)('2-) anion is effectively square planar (D(,4h)) with an average bond length of 2.750 (ANGSTROM), appropriate for the expected 1.25 bond order. The KGeSb reaction also produces dark red rods of the triclinic salt (2,2,2-crypt-K('+))(,3)Sb(,7)('3-)(.)2en. The Sb(,7)('3-) anion, which is also known in the nonisostructural salt (2,2,2-crypt-Na('+))(,3)Sb(,7)('3-), has approximately C(,3v) symmetry with an average bond distance of 2.797 (ANGSTROM);The alloy composition KSn(,2) reacts to form reddish-black triclinic crystals of (2,2,2-crypt-K('+))(,3)Sn(,9)('3-)(.)1.5en. With 21 skeletal electrons, the new Sn(,9)('3-) anion is paramagnetic as ESR and magnetic susceptibility measurements confirm. The cluster configuration is tricapped trigonal prismatic (D(,3h)) with a height to edge ratio of 1.08, which is midway between that observed for 20-electron (0.99) and 22-electron (1.16) nine-atom D(,3h) species. This trend is consistent with extended Huckel MO calculations which indicate successive occupation of the LUMO a(,2)'' in the 20-electron species. These findings provide a direct explanation for the anomalous closo configuration of the (2n+4)-electron Bi(,9)('5+) ion;Partial crystal structure results for the disordered compounds (2,2,2-crypt-Na('+))(,2)Ge(,4)('2-) and (2,1,1-crypt-Li('+))(,4)Sn(,9)('4-) are also reported. The former apparently contains the tetrahedral Ge(,4)('2-) anion, and the latter contains the previously known Sn(,9)('4-) anion in;a configuration which may be interpreted as a disorder of C(,4v) and D(,3h) symmetries; ('1)DOE Report IS-T-1110. This work was performed under Contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Susan Carol Critchlow
Critchlow, Susan Carol, "Homo- and heteropolyatomic anions of the post-transition elements of group IV and V: Synthesis and crystal structure characterization " (1983). Retrospective Theses and Dissertations. 8464.