Premium
Anisotropic thermal expansion in a metal–organic framework
Author(s) -
Madsen Solveig Røgild,
Lock Nina,
Overgaard Jacob,
Iversen Bo Brummerstedt
Publication year - 2014
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520614003497
Subject(s) - thermal expansion , anisotropy , materials science , metal , composite material , metallurgy , physics , optics
Ionothermal reaction between Mn II (acetate) 2 ·4H 2 O and 1,3,5‐benzenetricarboxylic acid (H 3 BTC) 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, α L ( l ), attain maximum values at 400 K along the a ‐ and b ‐axis, with α L ( a ) = 115 × 10 −6 K −1 and α L ( 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.