title: Positional and compositional disorder in a ruthenium(II) piano-stool complex.
abstract: In (η⁶-p-cymene)(difluorophosphinato-κO){2-[(1H-pyrazol-1-yl)methyl-κN²]pyridine-κN}ruthenium(II) 0.85-hexafluorophosphate 0.15-tetrafluoroborate, [Ru(PO₂F₂)(C₁₀H₁₄)(C₉H₉N₃)](PF₆)0.85(BF₄)0.15, (I), the [PO₂F₂]⁻ ligand exhibits positional disorder due to one F atom and one O atom sharing the same two positions related by a mirror reflection across the O-P-F plane. The correct composition of this coordinated anion was successfully determined to be [PO₂F₂]⁻ by refining the complex with various tetrahedral anions in which terminal atoms have similar atomic form factors. The noncoordinated counter-ion is compositionally disordered between [PF₆]⁻ and [BF₄]⁻. The difficulty in determining the correct composition of this anion illustrates the importance of a crystallographer remaining impartial and open to encountering unexpected moieties in the process of elucidating a structure.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA. iguzei@chem.wisc.edu
authors.forename: Ilia A
authors.initials: IA
authors.lastname: Guzei
authors.forename: Brian S
authors.initials: BS
authors.lastname: Dolinar
authors.forename: Nozipho
authors.initials: N
authors.lastname: Khumalo
authors.forename: James
authors.initials: J
authors.lastname: Darkwa
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
chemical_list: D056831:Coordination Complexes; D011725:Pyridines; D012428:Ruthenium
keywords: compositional disorder; crystal structure; idealized geometry