Irán F. Hernández-Ahuactzi

Macrocyclic Diorganotin Complexes of γ-Amino Acid Dithiocarbamates as Hosts for Ion-Pair Recognition

The dimethyl-, di-n-butyl-, and diphenyltin(IV) dithiocarbamate (dtc) complexes [{R2Sn(L-dtc)}x] 1-7 (1, L = L1, R = Me; 2, L = L1, R = n-Bu; 3, L = L2, R = Me, x = infinity; 4, L = L2, R = n-Bu; 5, L = L3, R = Me, x = 2; 6, L = L3, R = n-Bu, x = 2; 7, L = L3, R = Ph, x = 2) have been prepared from a series of secondary amino acid (AA) homologues as starting materials: N-benzylglycine (alpha-AA derivative = L1), N-benzyl-3-aminopropionic acid (beta-AA derivative = L2), and N-benzyl-4-aminobutyric acid (gamma-AA derivative = L3). The resulting compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR ((1)H, (13)C, and (119)Sn) spectroscopy, thermogravimetric analysis, and X-ray crystallography, showing that in all complexes both functional groups of the heteroleptic ligands are coordinated to the tin atoms. By X-ray diffraction analysis, it could be shown that [{Me2Sn(L2-dtc)}x] (3) is polymeric in the solid state, while the complexes derived from L3 (5-7) have dinuclear 18-membered macrocyclic structures of the composition [{R2Sn(L3-dtc)}2]. For the remaining compounds, it could not be established with certainty whether the structures are macrocyclic or polymeric. A theoretical investigation at the B3LYP/SBKJC(d,p) level of theory indicated that the alpha-AA-dtc complexes might have trinuclear macrocyclic structures. The macrocyclic complexes 5-7 have a double-calix-shaped conformation with two cavities large enough for the inclusion of aliphatic and aromatic guest molecules. They are self-complementary for the formation of supramolecuar synthons that give rise to 1D molecular arrangements in the solid state. Preliminary recognition experiments with tetrabutylammonium acetate have shown that the [{R2Sn(L3-dtc)}2] macrocycles 6 and 7 might interact simultaneously with anions (AcO(-)), which coordinate to the tin atoms, and organic cations (TBA(+)), which accommodate within the hydrophobic cavity (ion-pair recognition).

Supramolecular networks in molecular complexes of pyridine boronic acids and polycarboxylic acids: synthesis, structural characterization and fluorescence properties

3- and 4-pyridineboronic acids have been combined with trimesic and pyromellitic acids to give three molecular complexes of compositions [(3PBAH+)(H2TMA−)] (1), [(3PBAH+)2(H2PMA2−)] (2), and [(4PBAH+)2(H2PMA2−)]·2H2O (3) (3PBA = 3-pyridineboronic acid, 4PBA = 4-pyridineboronic acid, H3TMA = trimesic acid, H4PMA = pyromellitic acid). The products have been characterized by elemental analysis, infrared spectroscopy, single-crystal X-ray diffraction analysis and luminescence spectroscopy. The structural analysis revealed that the hydrogen bonding interactions of the resulting 2D and 3D assemblies involve at least one of the following charge-assisted synthons: –B(OH)2⋯−OOCR, RCOOH⋯−OOCR or PyN+–H⋯−OOCR. The dimensions are enhanced by additional hydrogen bonds as well as π–π stacking interactions, which include B⋯π interactions in two crystal structures. Intermolecular close contacts have also been examined by Hirshfeld surface analysis, which by means of the associated 2D fingerprint plots enabled similarities and differences in the crystal structures to be revealed. Solid-state photoluminescence spectroscopy of compounds 1–3 revealed that variations of the π–π stacking in the molecular aggregates induced changes in the emission behavior.

Structural and conformational changes in [M(1,10-diaza-18-crown-6)Cl2] (M = Pd, Pb) complexes: a crystallographic and theoretical study

The 1 : 1 adduct formation between crown ether (1,10-diaza-18-crown-6) and PdCl2 was observed as an inclusion compound and the molecular structure of complex PdLCl2 (L = 1,10-diaza-18-crown-6) was analyzed using a single crystal X-ray diffraction technique. Two different isomers were isolated upon changing the crystallization solvent system, i.e. CH2Cl2 afforded isomer PdLCl2(a) and a 1 : 1 CH2Cl2 : MeOH solvent system produced isomer PdLCl2(b); both structures were compared with a previously reported isomer PdLCl2(c) that exhibited a different structural arrangement. The three crystalline structures showed trans/syn, trans/anti and cis/syn relationships in relation to the Cl–Pd–Cl angle and the hydrogen atoms at the HN–Pd–NH moieties, respectively. In addition, DFT computational studies revealed the trans/syn isomer to be the most stable conformation by 5.8 kcal mol−1 and allowed the proposal of a potential mechanism for the conversion of this isomer into the trans/anti and cis/syn isomers. Along the same line, the related lead complex PbLCl2(d) was recrystallized from CH2Cl2 and analyzed using a single crystal X-ray diffraction technique, which showed to be structurally different to another previously reported structure of this complex PbLCl2(e), due to the inert pair effect. The analysis was expanded by comparing both series of structures with other relevant analogous complexes of different transition metals.

Molecular Tectonics with Di- and Trinuclear Organotin Compounds

Di- and trinuclear organotin(IV) complexes, in which the metal atoms are separated by large aromatic connectors, are useful building blocks for self-assembly. This is demonstrated by the preparation of [1+1], [2+2], and [2+3] macrocyclic and cage-type structures in combination with organic aromatic dicarboxylates. The linkage of the metal atoms by organic binders and the option of varying the number of reactive M-X sites generate versatile building blocks enabling molecular tectonics instead of the node-based strategy generally employed in metallo-supramolecular self-assembly.