title: Anisotropic compressibility of the coordination polymer emim[Mn(btc)].
abstract: The effect of pressure on the crystal structure of a coordination polymer, emim[Mn(II)(btc)] (emim = 1-ethyl,3-methyl imidazolium cation, btc = 1,3,5-benzene-tricarboxylate), was investigated with single-crystal X-ray diffraction. At 4.3 GPa the unit-cell volume had decreased by 14% compared with ambient conditions. The unit-cell contraction is highly anisotropic, with the a- and b-axes decreasing by 5.5 and 9.5%, respectively, and the c-axis compressing a mere 0.25% up to 1.7 GPa followed by a 0.2% expansion between 1.7 and 4.3 GPa. The 0.2% increase in length of the c-axis in this interval happens above the quasi-hydrostatic limit of the pressure-transmitting medium and therefore it might be a consequence of strain gradients. Under ambient conditions, two MnO6 units are connected by two carboxylate ligands to form dimeric units. On increasing pressure, a non-bonded O atom from a bridging carboxylate group approaches the Mn atom, with the Mn-O distance decreasing from 2.866 (1) Å at 0.3 GPa to 2.482 (6) Å at 4.3 GPa, increasing the coordination environment of the Mn ion from six- to seven-coordinated.
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, DK-8000 Aarhus C, Denmark.
authors.forename: Solveig R
authors.initials: SR
authors.lastname: Madsen
authors.affiliation: School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, Scotland.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Moggach
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, DK-8000 Aarhus C, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Overgaard
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, DK-8000 Aarhus C, Denmark.
authors.forename: Bo
authors.initials: B
authors.lastname: Brummerstedt Iversen
keywords: anisotropic expansion; coordination polymer; diamond anvil cell; high pressure