Chi-Keung Lam

Novel Anionic Host Lattices Built of Squarate and Thiourea Molecules

Abstract The new inclusion complexes [(C2H5)4N+]2C4O42−·4(NH2)2CS·2H2O (1), [(C2H5)4N+]2C4O42−·6(NH2)2CS (2) and [(C2H5)4N+]2C4O42−·2(NH2)2CS·2H2O (3) have been prepared and characterized by X-ray crystallography. In the crystal structure of (1), infinitely extended squarate–water chains inter-link adjacent puckered thiourea layers to generate a three dimensional host lattice with large uni-directional rectangular channels each containing a double column of well-ordered tetraethylammonium cations. In complex (2), well-ordered tetraethylammonium cations are stacked in single columns within the channel-type thiourea-squarate host lattice constructed by the cross-linkage of two types of layers. In complex (3), well-ordered teteraethylammonium cations are sandwiched between puckered layers generated by the cross-linkage between zigzag (C4O42−·2H2O)∞ chains and singly hydrogen-bonded dimeric thiourea ribbons.

Engineering the weak N–H⋯π hydrogen bond in 4-tritylbenzamide host and controlling the interaction through guest selection

The title amide host 1 crystallizes in the wheel-and-axle framework via amide N–H⋯O dimer and includes several aromatic and aliphatic guest molecules in cavities of 40 A2 size between supramolecular axles. Bulky triphenylmethyl groups make it impossible for the second NH donor to engage in strong hydrogen bonding and this promotes a weak intermolecular N–H⋯π interaction in inclusion adducts of aromatic and hydrophobic guests (structure type 1, guest = xylenes, chloro/bromo-toluene). On the other hand, the N–H⋯π interaction is absent for guests with CO groups because of stronger N–H⋯Oguest hydrogen bonding (type 2, guest = EtOAc, MeNO2). Crystal structures of both types are virtually identical except for the rotation of CONH2 group that transforms the N–H⋯π interaction to the N–H⋯O hydrogen bond. In addition to controlling the occurrence of the weak N–H⋯π hydrogen bond through host⋯guest recognition, a third structure type with N–H⋯Ohost and N–H⋯π hydrogen bonds is present in the anisole adduct. Amide group conformations, strong and weak hydrogen bonds, and close packing of aromatic residues determine the three structure types of composition 1·(guest)0.5 in space group P. The CH2Cl2 solvate, 1·(CH2Cl2)1.5, has a different crystal packing in space group C2/c with guest molecules included in channels between amide dimers and also between Ph3C groups. The design and control of the weak N–H⋯π hydrogen bond are shown for the first time in a family of isomorphous crystal structures. Infrared spectroscopy and variable temperature X-ray diffraction are consistent with the hydrogen bond nature of the N–H⋯π interaction. Differential scanning calorimetry and thermal gravimetric analysis confirm the functional behavior of inclusion host 1 and show differences in the release of CH2Cl2 molecules from the two types of channels. Crystal latttice energies follow the order structure type 3 < type 2 < type 1 in the range of −90 to −76 kcal mol−1 per host molecule.

Formation and crystal structure of an unexpected inclusion complex of a metal-free phthalocyanine and oxalic acidElectronic supplementary information (ESI) available: experimental procedure to prepare compound 3 and its characterising data. See http://www.rsc.org/suppdata/cc/b1/b111133g/

Treatment of 3-(2,4-dimethyl-3-pentyloxy)phthalonitrile (2) with CeCl3 in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in n-pentanol gives the corresponding metal-free phthalocyanine 3, which unexpectedly traps the oxalic acid in the crystal lattice forming a 1:1 inclusion complex.

Hexagonal Host Framework of sym-Aryloxytriazines Stabilised by Weak Intermolecular Interactions

ABSTRACT 2,4,6-Tris(4-halophenoxy)-1,3,5-triazine 1 is a convenient C3 starting material for the self-assembly of hexagonal open frameworks mediated via the halogen…halogen trimer synthon and the π-stacked Piedfort Unit (PU). We examine in this paper crystal structures of 2,4,6-tris(2-iodo-3-pyridyloxy)-1,3,5-triazine 2 , 2,4,6-tris(3-iodophenoxy)-1,3,5-triazine 3 , 2,4,6-tris(6-methyl-3-pyridyloxy)-1,3,5-triazine 4 , and 2,4,6-tris[4-(4′-bromophenyl) phenoxy)]-1,3,5-triazine 5 . Triazine 2 forms isostructural 2:1 host⋅guest adducts (guest = mesitylene, collidine) in the rhombohedral space group R3¯ such that the host architecture is stabilised by the C3i-PU and a helix of C─H…N interactions. The crystal structure of 3 is different from its chloro/bromo derivatives signifying the importance of the more polarisable I atom compared to Cl, Br. Pairs of C─H…O and C─H…N hydrogen bonds and C3i-PU sustain the columnar structure of 3 (space group R3¯). The PU has pseudo trigonal symmetry in picolinoxy triazine 4 (space group P21/n). In contrast to the phenyl derivatives, the extended aryl arms in biphenyl 5 do not adopt a trigonal conformation: two biphenyl groups are oriented parallel that participate in Br…Br and Br…π interactions. We note that 1 and 2 readily form hexagonal host lattices for guest inclusion, while 3 , 4 , and 5 crystallise in solvent-free form. Thermal measurements (TGA, DSC) indicate that guest release occurs at a higher temperature in the cage type host⋅guest clathrates compared to the channel inclusion compounds for the same solvent. Statistics from the Cambridge Structural Database using CSD Symmetry show that the phenoxytriazine scaffold is unique among the trigonal molecules for the carry-over of symmetry relation from molecule to crystal. The ease of predicting crystal packing and space group in this family of compounds ( 1 , 2 ) makes them good candidates for the crystal engineering of host frameworks.

Carbonate and oxalate dianions as prolific hydrogen-bond acceptors in supramolecular assemblyElectronic supplementary information (ESI) available: synthesis details for 1 and 2; Figs. 5 and 6. See http://www.rsc.org/suppdata/cc/b3/b306649e/Dedicated to Prof. James Trotter on the occasion of his 70th birthday.

In the new inclusion compound [(C2H5)4N+]2 x CO3(2-) x 7(NH2)2CS, the carbonate ion is surrounded by twelve convergent NH donor groups from six thiourea molecules to form a hydrogen-bonded aggregate shaped like two concave three-leaved propellers sharing a common core, whereas in [(n-C3H7)4N+]2 x C2O4(2-) x 4(NH2)2CS the oxalate ion serves as a hub for binding four thiourea molecules to generate a cross-shaped structural motif.

An engineered N–H⋯π interaction: crystal structure of 4-tritylbenzamide–p-xylene (2∶1)

The title host–guest crystal structure is designed to contain an N–H⋯π interaction. The crystal structure is stabilised by an N–H⋯O hydrogen-bonded amide dimer and weak N–H⋯π and C–H⋯O hydrogen bonds. The phenyl rings of triphenylmethyl groups interact via the edge-to-face herringbone T-motif.

Isostructurality in inclusion compounds based on interchangeability of equivalent synthons in a hydrogen-bonded host lattice

Abstract The new inclusion complex bis(tetra–n–propylammonium) squarate–urea–water (1/6/2), [(n–C3H7)4N+]2C4O42−·6(NH2)2CO·2H2O, has a three-dimensional anionic host framework containing large uni-directional channels that accommodate the hydrophobic cations. Replacement of its dumbbell-shaped hydrogen-bonded moiety (H2O–C4O42−–H2O) by the equivalent synthon (H2O–Br−)2 generates the known crystal structure of (n–C3H7)4N+Br−·(NH2)2CO·H2O, thereby providing an interesting example of isostructurality in the realm of inclusion compounds.

Novel layer- and channel-type anionic host lattices built of thiourea, 2-thiouracil anion and water

Abstract New inclusion complexes 3[(C2H5)4N+C4H3N2OS−]·(NH2)2CS·H2O (1) and (n-C3H7)4N+C4H3N2OS−·(NH2)2CS·2H2O (2) have been prepared and characterized by X-ray crystallography. In the crystal structure of 1, thiourea molecules, 2-thiouracil anions and water molecules generate a layer structure extending parallel to the (101) family of planes that involve typical O–H···O, N–H···O, O–H···S and N–H···S, N–H···N−hydrogen bonds, as well as weak C–H···O and C–H···S hydrogen bonds. The tetraethylammonium cations are arranged orderly between the stacked layers in a sandwich-like packing mode. Complex 2 features a three-dimensional host lattice containing intersecting open channels extending along the [001], [110] and [1 1 0] directions that are constructed through conventional hydrogen bonds. The tetra-n-propylammonium cations are accommodated in a zigzag fashion within each channel.

2,4,6-Tris(4-nitrophenoxy)-1,3,5-triazine: a hexagonal host framework stabilised by the NO2-trimer supramolecular synthon

The title molecule forms a honeycomb network of molecular and nitro-trimer synthons with guest species included in the hexagonal voids.

Rhodizonate and croconate dianions as divergent hydrogen-bond acceptors in the self-assembly of supramolecular structures

The C5O5(2-) and relatively unstable C6O6(2-) dianions, each serving as a hub for binding with a set of convergent NH donor groups of four phenylurea molecules, have been generated in situ and stabilized in nearly isostructural hydrogen-bonded host lattices.