title: Anisotropic thermal expansion in a metal-organic framework.
abstract: Ionothermal reaction between Mn(II)(acetate)2·4H2O and 1,3,5-benzenetricarboxylic acid (H3BTC) in either of the two ionic liquids 1-ethyl-3-methylimidazolium bromide (EMIMBr) and 1-ethyl-3-methylimidazolium tosylate (EMIMOTs) resulted in the formation of the new metal-organic framework (MOF) EMIM[Mn(II)BTC] (BTC = 1,3,5-benzenetricarboxylate). The compound crystallizes in the orthorhombic space group Pbca with unit-cell parameters of a = 14.66658 (12), b = 12.39497 (9), c = 16.63509 (14) Å at 100 K. Multi-temperature single-crystal (15-340 K) and powder X-ray diffraction studies (100-400 K) reveal strongly anisotropic thermal expansion properties. The linear thermal expansion coefficients, αL(l), attain maximum values at 400 K along the a- and b-axis, with αL(a) = 115 × 10(-6) K(-1) and αL(b) = 75 × 10(-6) K(-1). At 400 K a negative thermal expansion coefficient of -40 × 10(-6) K(-1) is observed along the c-axis. The thermal expansion is coupled to a continuous deformation of the framework, which causes the structure to expand in two directions. Due to the rigidity of the linker, the expansion in the ab plane causes the network to contract along the c-axis. Hirshfeld surface analysis has been used to describe the interaction between the framework structure and the EMIM cation that resides within the channel. This reveals a number of rather weak interactions and one governing hydrogen-bonding interactions.
authors.affiliation: Department of Chemistry and Center for Materials Crystallography, Aarhus University, Langelandsgade 140, Aarhus C, 8000, Denmark.
authors.forename: Solveig Røgild
authors.initials: SR
authors.lastname: Madsen
authors.affiliation: Inorganic Chemistry, Georg-August Universität, Tammanstrasse 4, Göttingen, Denmark.
authors.forename: Nina
authors.initials: N
authors.lastname: Lock
authors.affiliation: Department of Chemistry and Center for Materials Crystallography, Aarhus University, Langelandsgade 140, Aarhus C, 8000, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Overgaard
authors.affiliation: Department of Chemistry and Center for Materials Crystallography, Aarhus University, Langelandsgade 140, Aarhus C, 8000, Denmark.
authors.forename: Bo Brummerstedt
authors.initials: BB
authors.lastname: Iversen
keywords: metal–organic framework; multi-temperature X-ray diffraction; thermal expansion