Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. Although some of the descriptors that appear in our QSPRs were designed to describe chemical reactions, we infer that they serve in this study to quantify interactions between the cation and anion. Melting-point QSPRs were then derived from molecular orbital, thermodynamic, and electrostatic descriptors. Good correlations with the experimental data were found. The correlation coefficients for three-parameter melting-point QSPRs and for one-parameter density QSPRs exceed 0.9. Although some of the descriptors that appear in our QSPRs were designed to describe chemical reactions, we infer that they serve in this study to quantify interactions between the cation and anion.3

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The novel seven-coordinated BiF7 2- and SbF7 2- dianions have been prepared and characterized. The Cs2BiF7, Rb2BiF7, K2BiF7, and Na2BiF7 salts were obtained in high yield by heating BiF5 with an excess of the corresponding alkali metal fluorides to about 250 °C. Attempts failed to prepare the corresponding BiF8 3- salts or Li2BiF7 under similar conditions. The [N(CH3)4]2BiF7 salt was obtained by the combination of excess N(CH3)4F with BiF5 in CH3CN solution at −31 °C. The (NO2)2BiF7 salt was prepared from BiF5 and a large excess of liquid FNO at −78 °C and decomposes at room temperature to NOBiF6 and FNO. The corresponding Cs2SbF7, K2SbF7, and [N(CH3)4]2SbF7 salts were also synthesized in a similar fashion, but Na2SbF7 was not formed. The pronounced fluoride ion affinity of SbF6 - was further demonstrated by the formation of some Cs2SbF7 when dry CsF and CsSbF6 were ball-milled at room temperature. The BiF7 2- and SbF7 2- anions, which are the first examples of binary pnicogen compounds with coordination numbers in excess of six, were characterized by vibrational spectroscopy and ab initio electronic structure calculations. They possess pentagonal bipyramidal, highly fluxional structures of D 5 h symmetry, similar to those of IF7 and TeF7 -, which are isoelectronic with SbF7 2-. Although our theoretical calculations indicate that AsF7 2- is also vibrationally stable, experiments to prepare this dianion were unsuccessful.

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S NUMBER(S)AFRL-PR-ED-TP-1998-026 DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution unlimited. SUPPLEMENTARY NOTES