Benny C. Chan

Rethinking Sensitized Luminescence in Lanthanide Coordination Polymers and MOFs: Band Sensitization and Water Enhanced Eu Luminescence in [Ln(C15H9O5)3(H2O)3]n (Ln = Eu, Tb)

A coordination polymer [Ln(C15H9O9)3(H2O)3]n (1-Ln = Eu(III), Tb(III)) assembled from benzophenonedicarboxylate was synthesized and characterized. The organic component is shown to sensitize lanthanide-based emission in both compounds, with quantum yields of 36% (Eu) and 6% (Tb). Luminescence of lanthanide coordination polymers is currently described from a molecular approach. This methodology fails to explain the luminescence of this system. It was found that the band structure of the organic component rather than the molecular triplet state was able to explain the observed luminescence. Deuterated (Ln(C15H9O9)3(D2O)3) and dehydrated (Ln(C15H9O9)3) analogues were also studied. When bound H2O was replaced by D2O, lifetime and emission increased as expected. Upon dehydration, lifetimes increased again, but emission of 1-Eu unexpectedly decreased. This reduction is reasoned through an unprecedented enhancement effect of the compounds luminescence by the OH/OD oscillators in the organic-to-Eu(III) energy transfer process.

Examining the robustness of a theophylline cocrystal during grinding with additives

The robustness of theophylline-p-hydroxybenzoic acid cocrystal (TP·pHBA) while grinding with additives in the solid state was evaluated through a series of solvent-drop grinding experiments with coformers containing various functional groups. Powder X-ray diffraction was used to qualitatively analyse the powders after grinding and identify the species present. The TP·pHBA cocrystal was found to be robust in the presence of benzoic acid (BA), p-nitrobenzoic acid (pNBA), p-(N,N-dimethylamino)benzoic acid (dMABA), m-hydroxybenzoic acid (mHBA), p-nitrophenol (pNP), hydroquinone (HDQ) and benzamide (BZA), but it disintegrates in the presence of salicylic acid (SA), 3,5-dinitrobenzoic acid (dNBA), acetamide (ACA) and melamine (MLM).

N-[2-(Pyridin-2-yl)ethyl]-derivatives of methane-, benzene- and toluenesulfonamide: prospective ligands for metal coordination

The molecular and supramolecular structures are reported of N-[2-(pyridin-2-yl)ethyl]methanesulfonamide, C8H12N2O2S, (I), N-[2-(pyridin-2-yl)ethyl]benzenesulfonamide, C13H14N2O2S, (II), and N-[2-(pyridin-2-yl)ethyl]toluenesulfonamide, C14H16N2O2S, (III). Although (II) and (III) are almost structurally identical, the N(amide)-C(ethyl)-C(ethyl)-C(pyridinyl) torsion angles for (I) and (II) are more closely comparable, with magnitudes of 175.37 (15)° for (I) and 169.04 (19)° for (II). This angle decreases dramatically with an additional methyl group in the para position of the sulfonamide substituent, resulting in a value of 62.9 (2)° for (III). In each of the three compounds there is an N-H...N hydrogen bond between the sulfonamide of one molecule and the pyridine N atom of a neighbor. Compound (I) forms hydrogen-bonded dimers, (II) uses its hydrogen bonding to connect supramolecular layers, and the hydrogen bonding of (III) connects linear chains to form layers. For arene-substituted (II) and (III), the different conformations afforded by the variable dihedral angles promote intermolecular π-π stacking in the benzene-substituted structure (II), but distorted intramolecular T-shaped π-stacking in the toluene-substituted structure (III), with a centroid-to-centroid distance of 4.9296 (10) Å.

1,3-Bis(chloro-meth-yl)benzene.

The title compound, C8H8Cl2, used in the synthesis of many pharmaceutical intermediates, forms a three-dimensional network through chlorine–chlorine interactions in the solid-state that measure 3.513 (1) and 3.768 (3) Å.

(1H-Imidazol-4-yl)methanol

The title compound, C4H6N2O, displays two predominant hydrogen-bonding interactions in the crystal structure. The first is between the unprotonated imidazole N atom of one molecule and the hydroxy H atom of an adjacent molecule. The second is between the hydroxy O atom of one molecule and the imidazole N—H group of a corresponding molecule. These interactions lead to the formation of a two-dimnensional network parallel to (10-1). C—H⋯O interactions also occur.

Benzo[1,2-b:4,5-b′]dithio­phene-4,8-dione

The title molecule, C10H4O2S2, is situated on a crystallographic center of inversion. In the crystal, weak hydrogen bonding contributes to the packing of the molecules.

N-Methyl-N-nitroso-p-toluene­sulfon­amide

The crystal structure of the title compound, C8H10N2O3S, displays predominant C—H⋯O hydrogen-bonding and π–π stacking interactions. The hydrogen bonds are between the O atoms of the sulfonyl group and H atoms on methyl groups. The π–π stacking interactions occur between adjacent aromatic rings, with a centroid–centroid distance of 3.868 (11) Å. These interactions lead to the formation of chains parallel to (101).

1,6-Di-bromo-naphthalen-2-ol methanol monosolvate.

The naphthol-containing molecule of the title compound, C10H6Br2O·CH3OH, crystallized as a methanol monosolvate and is planar to within 0.069 (1) Å for all non-H atoms. In the crystal, molecules are linked by two pairs of O—H⋯O hydrogen bonds, involving the methanol molecule, forming dimer-like arrangements. The crystal structure is further stabilized by π–π stacking [centroid–centroid distance = 3.676 (2) Å] and Br⋯Br interactions [3.480 (4) and 3.786 (1) Å], forming a three-dimensional structure.

1-Methyl-4H-3,1-benzoxazine-2,4(1H)dione

In its crystal structure, the title compound, C9H7NO3, forms π-stacked dimers, with a centroid–centroid distance of 3.475 (5) Å between the benzenoid and the 2,4 dicarbonyl oxazine rings. These dimers then form staircase-like linear chains through further π-stacking between the benzenoid rings [centroid–centroid distance of 3.761 (2) Å]. The methyl-H atoms are disordered due to rotation about the C—N bond and were modeled with equal occupancy.

Cs6Nb4Se22 and K12Nb6Se35.3: two new compounds containing the M4Q22 building block.

The title compounds, namely hexacaesium tetraniobium docosaselenide and dodecapotassium hexaniobium pentatriacontaselenide, were formed from their respective alkali chalcogenide reactive flux and niobium metal. Both compounds fall into the larger family of solid-state compounds that contain the M(2)Q(11) building block (M = Nb, Ta; Q = Se, S), where the metal chalcogenide forms dimers of face-shared pentagonal bipyramids. Cs(6)Nb(4)Se(22) contains two Nb(2)Se(11) building blocks linked by an Se-Se bond to form isolated Nb(4)Se(22) tetrameric building blocks surrounded by caesium ions. K(12)Nb(6)Se(35.3) contains similar Nb(4)Se(22) tetramers that are linked by an Se-Se-Se unit to an Nb(2)Se(11) dimer to form one-dimensional anionic chains surrounded by potassium ions. Further crystallographic studies of K(12)Nb(6)Se(35.3) demonstrate a new M(2)Se(12) building block because of disorder between an Se(2-) site (85%) and an (Se-Se)(2-) unit (15%). The subtle differences between the structures are discussed.