title: Large negative linear compressibility of Ag3[Co(CN)6].
abstract: Silver(I) hexacyanocobaltate(III), Ag(3)[Co(CN)(6)], shows a large negative linear compressibility (NLC, linear expansion under hydrostatic pressure) at ambient temperature at all pressures up to our experimental limit of 7.65(2) GPa. This behavior is qualitatively unaffected by a transition at 0.19 GPa to a new phase Ag(3)[Co(CN)(6)]-II, whose structure is reported here. The high-pressure phase also shows anisotropic thermal expansion with large uniaxial negative thermal expansion (NTE, expansion on cooling). In both phases, the NLC/NTE effect arises as the rapid compression/contraction of layers of silver atoms--weakly bound via argentophilic interactions--is translated via flexing of the covalent network lattice into an expansion along a perpendicular direction. It is proposed that framework materials that contract along a specific direction on heating while expanding macroscopically will, in general, also expand along the same direction under hydrostatic pressure while contracting macroscopically.
authors.affiliation: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, United Kingdom.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Goodwin
authors.forename: David A
authors.initials: DA
authors.lastname: Keen
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Tucker
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D019245:Compressive Strength; D003486:Cyanides / Q000737:chemistry*; D015394:Molecular Structure; D011312:Pressure; D018030:Silver Compounds / Q000737:chemistry*; D013696:Temperature
chemical_list: D003486:Cyanides; D018030:Silver Compounds; D003035:Cobalt