title: Pressure tuning between NH...N hydrogen-bonded ice analogue and NH...Br polar dabcoHBr complexes.
abstract: At normal conditions 1,4-diazabicyclo[2.2.2]octane hydrobromide [C(6)H(13)N(2)](+.)Br(-) forms centrosymmetric crystals, space group Pm2, NH(+)...N hydrogen-bonded linear polycationic chains with disordered protons in the structure. As in H(2)O ice Ih, the protons in [C(6)H(13)N(2)](+.)Br(-) crystals remain disordered at low temperatures. Above 0.4 GPa the [C(6)H(13)N(2)](+.)Br(-) crystals transform into a new polar NH(+)...Br(-) hydrogen bonded complex, space group Cmc2. It has been crystallized in-situ in a diamond anvil cell and its structure determined by X-rays. The low-pressure triggering of this transformation indicates that it is a possible source of defects in the real structure at normal conditions, where, along with disproportionation defects, they can be responsible for anomalous dielectric properties, including relaxor-like behavior of NH...N hydrogen-bonded compounds.
authors.affiliation: Faculty of Chemistry, Adam Mickiewicz University, Poznań, Poland.
authors.forename: Armand
authors.initials: A
authors.lastname: Budzianowski
authors.forename: Andrzej
authors.initials: A
authors.lastname: Katrusiak
mesh_terms: D000465:Algorithms; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011312:Pressure
chemical_list: C521552:1,4-diazabicyclo(2.2.2)octane hydrobromide; D019086:Bridged Bicyclo Compounds, Heterocyclic