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Brammer, Lee
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Publications (5/5 displayed)
- 2022Metal–ligand Lability and Ligand Mobility Enables Framework Transformation via Ligand Release in a Family of Crystalline 2D Coordination Polymerscitations
- 2021Multi-stimulus linear negative expansion of a breathing M(O2CR)4-node MOFcitations
- 2015Coordination polymer flexibility leads to polymorphism and enables a crystalline solid-vapour reactioncitations
- 2015Coordination polymer flexibility leads to polymorphism and enables a crystalline solid-vapour reaction:A multi-technique mechanistic studycitations
- 2013Chemical transformations of a crystalline coordination polymercitations
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article
Multi-stimulus linear negative expansion of a breathing M(O2CR)4-node MOF
Abstract
The metal–organic framework (Me<sub>2</sub>NH<sub>2</sub>)<sub>2</sub>[Cd(NO<sub>2</sub>BDC)<sub>2</sub>] (SHF-81) comprises flattened tetrahedral Cd(O2CR)<sub>4</sub><sup>2-</sup> nodes, in which Cd(II) centres are linked via NO<sub>2</sub>BDC<sup>2-</sup> ligands (2-nitrobenzene-1,4-dicarboxylate) to give a doubly interpenetrated anionic network, with charge balanced by two Me<sub>2</sub>NH<sub>2</sub><sup>+</sup> cations per Cd centre resident in the pores. The study establishes that this is a twinned α-quartz-type structure (trigonal, space group P3<sub>x</sub>21, x = 1 or 2), although very close to the higher symmetry β-quartz arrangement (hexagonal, P6<sub>x</sub>22,<br/>x = 2 or 4) in its as-synthesised solvated form [Cd(NO<sub>2</sub>BDC)<sub>2</sub>]·2DMF·0.5H<sub>2</sub>O (SHF-81-DMF). The activated MOF exhibits very little N<sub>2</sub> uptake at 77 K, but shows significant CO<sub>2 </sub>uptake at 273–298 K with an isosteric enthalpy of adsorption (ΔH<sub>ads</sub>) at zero coverage of -27.4 kJ mol<sub>-1</sub> determined for the MOF directly activated from SHF-81-DMF. A series of in situ diffraction experiments, both single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD), reveal that the MOF is flexible and exhibits breathing behaviour with<br/>observed changes as large as 12% in the a- and b-axes (|Δa|, |Δb| < 1.8 °A) and 5.5% in the c-axis (|Δc| < 0.7 °A). Both the solvated SHF-81-DMF and activated/desolvated SHF-81forms of the MOF exhibit linear negative thermal expansion (NTE), in which pores that run parallel to the c-axis expand in diameter (a- and b-axis) while contracting in length (c-axis) upon increasing temperature. Adsorption of CO<sub>2</sub> gas at 298 K also results in linear negative<br/>expansion (Δa, Δb > 0; Δc < 0; ΔV > 0). The largest change in dimensions is observed during activation/desolvation from SHF-81-DMF to SHF-81 (Δa, Δb < 0; Δc > 0; ΔV < 0). Collectively the nine in situ diffraction experiments conducted suggest the breathing behaviour is continuous, although individual desolvation and adsorption experiments do not rule out the possibility of a gating or step at intermediate geometries that is coupled with continuous dynamic behaviour towards the extremities of the breathing amplitude.