Recent Research Updates

Unique responsive and selective behaviour of homothiacalix[4]arene crystals is reported. A benzene disolvate adopting the 1,3-alternate conformation (HTCA-s1,3) can be converted to a guest-free non-porous phase (HTCA-a1,3) upon heating, with the host molecules retaining the same 1,3-alternate conformation. The process is reversible, with non-porous apohost crystals ‘opening up’ upon exposure to benzene vapour to reaccommodate the solvent molecules, as confirmed by SCXRD and sorption studies monitored in situ via PXRD analysis. The gate opening mechanism is selective, preventing cyclohexane molecules from passing through, which creates the opportunity to apply this system, for example, in benzene capture/separation. Furthermore, with a higher energy boost, the crystal of the HTCA-a1,3 apohost undergoes a significant conformational change, resulting in HTCA-a1,2, an apohost in which the host molecules adopt the 1,2-alternate conformation.

https://doi.org/10.1039/D5CC05862G

Structural diversity of anthraquinone substituted p-tert-butylthiacalix [4] arene in the partial cone conformation upon external stimuli

Crystallisation of anthraquinone substituted p-tert-butylthiacalix[4]arene in the partial cone conformation from a range of solvents led to the isolation of two solvates, containing a mixture of chloroform and acetonitrile (PC1a) or toluene (PC1d) molecules, the structures of which were uncovered by SCXRD studies. Upon heating, the former solvate undergoes a single-crystal-to-single-crystal transformation, leading to removal of the acetonitrile molecules from the host and repositioning of the chloroform molecules (PC1b). This is connected with rearrangements of the non-covalent interactions, nicely reflected by a change in the hydrogen bond acceptor of the weak C–H⋯O hydrogen bonds. The transformation process is reversible, as confirmed by exposure of the crystal to acetonitrile vapour. Furthermore, the guest free phase of PC1 was obtained by melt crystallisation (PC1c).

DOI: https://doi.org/10.1039/D4CE00387J

A series of new Ag(I) complexes with 2,6-bis[(imidazol-2-yl)thiomethyl]naphthalene (L) and a range of counterions (X−) such as PF6− (1, 2), SbF6− (3), and CF3SO3− (4) was prepared. As shown by SCXRD studies, all of these are 1D coordination polymers with a waved chain motive and general formula {[AgL]X}n. Two methanol solvates containing PF6− (1) and SbF6− (3) counterions are isostructural. The triflate counterion leads to the formation of a topologically equivalent structural motive, with a different conformation of the ligand in the 1D chain and a different crystal packing as a result of the presence of another set of intermolecular interactions. The presence of water in 2 leads to a significant change in the conformation of the ligand. The naphthalene rings show a different orientation towards the imidazole rings, which is energetically less favorable but is stabilized by an extended net of intermolecular interactions with the counterion, which leads to an efficient crystal packing.

A series of CuII complexes obtained under the same reaction conditions has been analyzed to gain insight into the effect of the ligand composition on the final reaction product. Dipodal ligands containing N-donor imidazole rings and a benzene ring as a spacer with different numbers of methyl substituents on the aromatic rings were selected for the study such as 1,3-bis(imidazol-1-yl­methyl)benzene (L1), 1,3-bis(imidazol-1-ylmethyl)-5-methylbenzene (L2), 1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (L3), 1,3-bis(2-methylimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (L4). L4 has not been reported previously and was synthesized for this study. The formed metal complexes show the presence of polymeric (ligand with no or one methyl substituent; 1–4), or discrete motifs (3- or 5-methyl substituents; 5–7). The new metal complexes 3, 5 and 6 were analyzed using single-crystal X-ray diffraction and powder diffraction. In addition, the structural analyses were supported by computational methods.

Solvent-induced polymorphism in dipodal N-donor ligands containing a biphenyl core

Structural diversity of Ag (I) complexes with the flexible ligand 1, 3-bis [(imidazol-2-yl) thiomethyl] benzene