Pro-ligand 5-[(E)-2-(3-pyridyl)-1-diazenyl]-2hydroxybenzoic acid, H′HL meta , was employed for the synthesis of four organotin(IV) complexes, using suitable tri-and diorganotin (IV) precursors, [nBu 3 Sn(HL meta )] n (1), [Bz 3 Sn(HL meta )] n •C 6 H 5 CH 3 (2), [Ph 3 Sn(HL meta )] 4 •C 6 H 5 CH 3 (3), and {[nBu 2 Sn(L meta )] 2 } n •2nDMSO (4). The coordination behavior of compounds 1−3 in solution was judged from the results of the 119 Sn NMR spectroscopic characterization, while the 119 Sn MAS NMR technique was utilized to probe 4, owing to its low-solubility issue. The solid-state structures of 1−4 were determined from single-crystal X-ray diffraction data. The structural analysis revealed that by changing the Sn-R substituents, the molecular coordination geometries and supramolecular structural motifs in the resulting compounds are widely affected. However, one common feature in the crystal structures of these compounds is a strong tendency for the terminal pyridyl nitrogen to bind with the tin atom of an adjacent complex molecule, which influences the ligand bonding interactions and leads to either macrocycle or polymer formation. In compounds 1−3, the triorganotin moieties are embedded in trigonal− bipyramidal coordination polyhedra arising from the ligand in the monodeprotonated salicylate form, [HL meta ] − , by complexation through the carboxylate group, resulting in 1D coordination polymers with a zigzag-type topology for compounds 1 and 2, and a tetranuclear 44-membered macrocyclic ring structure in the case of 3. The different outcome is a result of the all anti-conformation of the [HL meta ] − ligands in compounds 1 and 2, compared with alternating syn-and anti-conformation of the four ligands in 3, and is without doubt related to the variation of the triorganotin functionality. In compound 4, the tin atoms coordinate to the salicylate group of dianionic [L meta ] 2− by chelate ring formation with both the carboxylate and phenolate groups. The combination of syn-conformation of the ligand and secondary building block formation through 4-membered Sn 2 O 2 rings gives rise to 1D tapes containing 22-membered tetranuclear macrocycles. The case study reported herein showed that heteroditopic pyridyl-carboxylate ligands derived from salicylic acid by diazonium coupling are providing an interesting ligand family for complexation and self-assembly studies with a large number of single main group and transition ions and preformed di-or oligonuclear tectons.

A cocrystal of the antihypertensive drug chlorthalidone (CTD) with caffeine (CAF) was obtained (CTD-CAF) by the slurry method, for which a 2:1 stoichiometric ratio was found by powder and single-crystal X-ray diffraction analysis. Cocrystal CTD-CAF showed a supramolecular organization in which CAF molecules are embedded in channels of a 3D network of CTD molecules. The advantage of the cocrystal in comparison to CTD is reflected in a threefold solubility increase and in the dose/solubility ratios, which diminished from near-unit values for D0D to 0.29 for D0CC. Furthermore, dissolution experiments under non-sink conditions showed improved performance of CTD-CAF compared with pure CTD. Subsequent studies showed that CTD-CAF cocrystals transform to CTD form I where CTD precipitation inhibition could be achieved in the presence of pre-dissolved polymer HPMC 80–120 cPs, maintaining supersaturation drug concentrations for at least 180 min. Finally, dissolution experiments under sink conditions unveiled that the CTD-CAF cocrystal induced, in pH-independent manner, faster and more complete CTD dissolution when compared to commercial tablets of CTD. Due to the stability and dissolution behavior of the novel CTD-CAF cocrystal, it could be used to develop solid dosage forms using a lower CTD dose to obtain the same therapeutic response and fewer adverse effects.

Ligands derived from 2,x- and 3,y-pyridinedicarboxylic acid (x = 3–6; y = 4–5) are widely used building blocks for the formation of metal-coordination polymers (MCPs), as they show a large variety of bridging modes and angles. Metal complexation occurs either only with the carboxylate groups or through N,O-chelate ring formation. In this contribution, the supramolecular chemistry and solvatomorphism of diorganotin complexes with 2,5-pyridinedicarboxylate (25pdc) formed in the presence of a series of coordinating and noncoordinating solvents were explored in detail. Five novel diorganotin 25pdc’s of composition [Me2Sn­(25pdc)­(py)]3­·3.04C5H5N­·1.86H2O (1), {[Me2Sn­(25pdc)]­·[Me2Sn­(25pdc)­(H2O)]} n ­2nC7H8O (2), {[nBu2Sn­(25pdc)]4} n ­·4nC6H5NO2 (3), [nBu2Sn­(25pdc)­(gly)] n (4), and {[nBu2Sn­·(25pdc)]3} n ­·nCHCl3 (5) were achieved and analyzed in the context of previously reported tri- and diorganotin complexes with the same ligand. The comparative study revealed that upon coordination to diorganotin species the ligand exhibits N,O-chelate ring formation with the carboxylate group in the 2-position and bridging to other tin atoms primarily by the 5-carboxylate group, giving macrocyclic, one-, two-, or three-dimensional MCPs. On the contrary, triorganotin moieties are mostly bound only by the ligand carboxylate groups without N→Sn binding. The assemblies of diorganotin 25pdc’s mostly contain trinuclear or tetranuclear macrocycles with a large predominance of the generally uncommon [3 + 3] metal–organic aggregates. For the trinuclear macrocycles, different configurations having 12-, 18-, 21-, or 27-membered rings were encountered. The metal atoms in diorganotin 25pdc’s prefer pentagonal-bipyramidal environments, which are achieved through coordination by solvent molecules (H2O, DMSO, py) or intermolecular O→Sn bond formation. In solution, di-n-butyltin 25pdc exhibits supramolecular isomerism, giving a tetrameric aggregate in the noncoordinating solvent chloroform and a trimeric species in the presence of coordinating solvents, such as DMSO, pyridine, or methanol, due to solvent→Sn bond formation.

Refractory aromatic sulfur compounds present in gasoline, diesel, and jet fuels cause serious environmental problems and must be removed to minimize the emissions of SO x , according to environmental regulations worldwide. Herein, we present a novel approach for the removal of organosulfur compounds from model liquid fuel solutions employing a nonporous host crystalline material (A1) that undergoes transformation into cocrystals with aromatic sulfur compounds like benzothiophene (BT) and dibenzothiophene (DBT) (i.e., A1⊃BT and A1⊃DBT). In experiments using a single component in cyclohexane solutions, crystalline A1 reached a quantitative uptake of DBT after 12 h at 25 °C with equimolar or slightly increased molar ratios of DBT over A1 (e.g., 1.45 ± 0.05 mmol of S/g of A1, which is equivalent to 267.3 ± 9.3 mg of DBT/g of A1 at C 0 = 3000 ppmwS). The crystalline material A1 can be recycled from cocrystal A1⊃DBT by a two-step process: (i) the generation of the solid A1⊃toluene upon extraction of DBT in toluene and (ii) the subsequent thermal treatment at 150 °C for desolvation to recover microcrystalline A1; after four recycling processes, the uptake capacity of A1 is maintained at 97.5%. In competitive experiments using a five-component equimolar cyclohexane solution containing BT, DBT, 4,6-dimethyldibenzothiophene (DMDBT), fluorene (FLUO), and naphthalene (NAPH), the uptake efficiency of A1 after 12 h at 25 °C followed the trend: DBT > FLUO > NAPH > BT > DMDBT. The selective uptake of DBT in these model fuel solutions is explained by matching of the π-electron rich guest with π-electron deficient diamine linkers and concomitant CH−π interactions within the enclosed cavities of the double-tweezer B←N host A1, as exhibited in the X-ray crystal structure. Size fitting is important for guest selectivity because attempts to isolate cocrystals with DMDBT were unsuccessful. Crystal-to-cocrystal is a solution mediated phase transformation that competes favorably in the removal of DBT with several examples of high-surface nano/microporous materials and composites used in batch adsorption experiments, and A1 can be recycled without compromising efficiency. Thus, crystal-to-cocrystal transformation emerges as a remarkable methodology for the quantitative removal of aromatic organosulfur compounds from liquid fuels because it can be extended to many other aromatic fuel contaminants by using the appropriate host molecule to cocrystallize with it.

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