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    Electrical conductivity and DFT investigations of a 2D CuI-TCNQII− framework
    Sutton, AL ; Abrahams, BF ; Commons, CJ ; Dharma, AD ; Goerigk, L ; Hardin, SG ; Hudson, TA ; Robson, R (Royal Society of Chemistry, 2023-11-21)
    A stacked 2D Cu(i) coordination polymer displays electrical conductivity with DFT calculations revealing a band structure comprised of donor TCNQII− and acceptor 2,5-dimethylpyrazine p-orbitals.
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    Multifunctional Coordination Polymer Exhibiting Reversible Mechanical Motion Allowing Selective Uptake of Guests and Leading to Enhanced Electrical Conductivity
    Elliott, RW ; Sutton, AL ; Abrahams, BF ; D'Alessandro, DM ; Goerigk, L ; Hua, C ; Hudson, TA ; Robson, R ; White, KF (AMER CHEMICAL SOC, 2021-09-06)
    A remarkably flexible, multifunctional, 2D coordination polymer exhibiting an unprecedented mode of reversible mechanical motion, enabling pores to open and close, is reported. Such multifunctional materials are highly sought after, owing to the potential to exploit coexisting electronic and mechanical functionalities that underpin useful technological applications such as actuators and ultrasensitive detectors. The coordination polymer, of composition Mn(F4TCNQ)(py)2 (F4TCNQ = 2,3,5,6-tetrafluoro-7,7,8,8-tetracycanoquinodimethane; py = pyridine), consists of Mn(II) centers bridged by F4TCNQ dianions and coordinated by py molecules that extend above and below the 2D network. Exposure of Mn(F4TCNQ)(py)2, in its collapsed state, to carbon dioxide results in a pore-opening process at a threshold pressure for a given temperature. In addition to carbon dioxide, a variety of volatile guests may be incorporated into the pores, which are lined with electron-rich F4TCNQ dianions. The inclusion of electron-deficient guests such as 1,4-benzoquinone, nitrobenzene, maleic anhydride, and iodine into the pores is accompanied by a striking color change associated with a new host-guest charge-transfer interaction and an improvement in the semiconductor behavior, with the iodine adduct showing an increase in conductivity of almost 5 orders of magnitude. Experimental and density functional theory calculations on this remarkable multifunctional material demonstrate a reduction in the optical band gap with increasing electron affinity of the guest.
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    Semi-conducting mixed-valent X(4)TCNQ(I-/II-)(X = H, F) charge-transfer complexes with C6H2(NH2)(4)
    Sutton, AL ; Abrahams, BF ; D'Alessandro, DM ; Goerigk, L ; Hudson, TA ; Robson, R ; Usov, PM (Royal Society of Chemistry, 2020-07-21)
    We report further characterisation on the previously described [C6H2(NH2)4][TCNQ] charge-transfer (CT) complex. An in-depth analysis of the crystallographic data aided by spectroscopic methods indicates the compound is mixed-valent with TCNQI−/II− species. The analogous F4TCNQ CT complex has been synthesised and spectroscopic methods suggest that [C6H2(NH2)4][F4TCNQ] is also mixed-valent. Electrical conductivity measurements on both complexes indicate semi-conductor behaviour, with [C6H2(NH2)4][TCNQ] exhibiting a σ300K = 9.8 × 10−4 S cm−1 and an Ea = 0.10(1) eV. Density functional theory studies on both CT complexes reveal band structures suggestive of ambipolar transport, with a super-exchange mechanism.
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    Clam-like Cyclotricatechylene-based Capsules: Identifying the Roles of Protonation State and Guests as well as the Drivers for Stability and (Anti-)Cooperativity
    Mehta, N ; Abrahams, BF ; Goerigk, L (WILEY-V C H VERLAG GMBH, 2020-04-17)
    Cyclotricatechylene (ctcH6 ) is a bowl-shaped macrocyclic compound that can be used as a building block for self-assembled capsules. ctcH6 and its derivatives in various protonation states - here collectively labeled as CTC - form dimers that resemble the shape of a clam. These clam-shaped entities have been studied experimentally by Abrahams, Robson, and co-workers [B. F. Abrahams, N. J. FitzGerald, T. A. Hudson, R. Robson and T. Waters, Angew. Chem. Int. Ed. 2009, 48, 3129-3132] where the capsules acted as an excellent host for large alkali-metal cations. In this study, we present a detailed analysis based on accurate dispersion-corrected Density Functional Theory approaches that reveals the factors that stabilise such CTC-based capsules at different protonation states and their interaction with various encapsulated guests. Our results show that the capsules' overall stability results as an interplay of hydrogen bonding, London dispersion, and electrostatic effects. The most stable capsules with group-1 and group-2 cations as guests contain only six phenolic hydrogens, as opposed to the maximum possible number of twelve. Inclusion of larger alkali-metal cations is favoured due to larger London-dispersion contributions. Cations are favoured as guests over isoelectronic neutral species, as the resulting host-guest complexes experience additional stability due to cooperative effects. In fact, using the latter to drive the formation of specific capsules could be used in future strategies aimed at synthesising similar aggregates; our results provide an insightful understanding and useful guidance for such future endeavours.
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    A Semiconducting Cationic Square-Grid Network with FeIII Centers Displaying Unusual Dynamic Behavior
    Hudson, TA ; Sutton, AL ; Abrahams, BF ; D'Alessandro, DM ; Davies, CG ; Goerigk, L ; Jameson, GNL ; Moubaraki, B ; Murray, KS ; Robson, R ; Usov, PM ; Yang, G (WILEY-V C H VERLAG GMBH, 2020-04-16)
    The synthesis, structure and properties of a 2D FeIII network material of composition [Fe(O‐bipy)2Cl](TCNQ)2 (O‐bipy = 4,4'‐bipyridyl N,N'‐dioxide; TCNQ = 7,7,8,8‐tetracyanoquinodimethane) are presented. The structure consists of a square grid in which square pyramidal FeIII centers are linked to four equivalent centers through O‐bipy ligands. Pairs of TCNQ radical anions are located within rectangular cavities of the 2D network. The apical position on each Fe center is occupied by a chloride ion. Magnetic studies are indicative of weak antiferromagnetic coupling. Electrical conductivity measurements reveal that the compound is a semiconductor and on the basis of DFT calculations it is proposed that electrical conduction occurs via charge hopping between interlayer TCNQ anions. Mössbauer spectra indicate a rare example of the Goldanskii–Karyagin effect and are suggestive of unusual dynamic processes.