Molecules 2014, 19, 1956-1975; doi:10.3390/molecules19021956 molecules ISSN 1420-3049 www.mdpi.com/journal/molecules Article A Variable Temperature X-ray Diffraction Investigation of [PPN + ][S 4 N 5 − ]: Supramolecular Interactions Governing an Order/Disorder Transformation and the First High Resolution X-ray Structure of the Anion René T. Boeré 1,2, *, Tracey L. Roemmele 1,2 and Maria K. Krall 1 1 Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada; E-Mails: roemtl@uleth.ca (T.L.R.); maria.ksiazek2@uleth.ca (M.K.K.) 2 The Canadian Centre for Advanced Fluorine Technologies, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada * Author to whom correspondence should be addressed; E-Mail: boere@uleth.ca; Tel.: +1-403-329-2045; Fax: +1-403-329-2057. Received: 14 January 2014; in revised form: 29 January 2014 / Accepted: 30 January 2014 / Published: 12 February 2014 Abstract: The title salt, triphenyl(P,P,P-triphenylphosphineimidato-N)-phosphorus(1+) 1,3,5,7-tetrathia(1,5-S IV )-2,4,6,8,9-pentaazabicyclo[3.3.1]nona-1,4,6,7-tetraene(1−), CAS [48236-06-2], prepared by the literature method, is found by crystallography to be a 1:1 CH 3 CN solvate. Disorder exists for the N atoms of the anion. A VT crystal structure study was conducted at 100 K, 120 K, 140 K, 172 K, 200 K, 240 K and 280 K. The 100 K structure is superior, with only 10% of a second anion position oppositely-oriented w.r.t the diad axis of point group 2mm. At 120 K, an adjacent two-site disorder is encountered, but at higher temperatures three-site disorder with both opposite and adjacent placements of S 4 N 5 − ions is required w.r.t. the primary component. At 240 and especially 280 K, the anion nitrogen atoms appear fully scrambled amongst the six possible sites on the edges of an S 4 tetrahedron with 83.3% occupancy for each. The PPN + geometry does not show strong cation-cation interactions. However, there are numerous supramolecular contacts corresponding mostly to non-classical H-bonds between PPN + ions and S 4 N 5 − as well as CH 3 CN. The geometry of the anion is corroborated from B3LYP/6-311++G(3df) DFT calculations, and the infra-red spectrum was assigned with excellent agreement between experimental and calculated frequencies. OPEN ACCESS