Long-Li Lai

Dihydrobenzoic acid modified nanoparticle as a MALDI-TOF MS matrix for soft ionization and structure determination of small molecules with diverse structures

Efficient structural characterization is important for quality control when developing novel materials. In this study, we demonstrated the soft ionization capability of the hybrid of immobilized silica and 2,5-dihydrobenzoic acid (DHB) on iron oxide magnetic nanoparticles in MALDI-TOF MS with a clean background. The ratio between SiO2 and DHB was examined and was found to affect the surface immobilization of DHB on the nanoparticle, critically controlling the ionization efficiency and interference background. Compared with commercial DHB, the functionalized nanoparticle-assisted MALDI-TOF MS provided superior soft ionization with production of strong molecular ions within 5 ppm mass accuracy on a variety of new types of synthetic materials used for solar cells, light emitting devices, dendrimers, and glycolipids, including analytes with either thermally labile structures or poor protonation tendencies. In addition, the enhancements of the molecular ion signal also provided high-quality product-ion spectra allowing structural characterization and unambiguous small molecule identification. Using this technique, the structural differences among the isomers were distinguished through their characteristic fragment ions and comprehensive fragmentation patterns. With the advantages of long-term stability and simple sample preparation by deposition on a regular sample plate, the use of DHB-functionalized nanoparticles combined with high-resolution MALDI-TOF MS provides a generic platform for rapid and unambiguous structure determination of small molecules.

Chair-Boat Form Transformation of Piperazine-Containing Ligand toward the Preparation of Dirhenium Metallacycles

A new generation of a flexible bipyridine-based ligand, 1,4-bis(4-pyridyl)-piperazine, with two main stable states (chair and twist-boat forms) was employed in the construction of unusual dirhenium metallacycles.

Formation of columnar liquid crystals on the basis of unconventional triazine-based dendrimers by the C3-symmetric approach.

Two series of unconventional triazine-based dendrimers with C(2) symmetry and C(3) symmetry were prepared. The newly prepared C(3)-symmetrical dendrimers were characterized by (1)H and (13)C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD showed that the C(3)-symmetrical dendrimers display columnar liquid-crystalline phases during thermal treatment, but the C(2)-symmetrical dendrimers were not observed to behave correspondingly. The molecular conformations of C(3)- and C(2)-symmetrical dendrimers were obtained by computer simulation with the MM2 model of the CaChe program in the gas phase. The simulation results reasonably explain the different mesogenicities of C(3)- and C(2)-symmetric dendrimers. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks for displaying columnar liquid-crystalline behavior.

Polypseudorotaxane architecture of poly-bis[4-(N-benzyl- pyridinium)]piperazine-hexa-thiocyanato-di-cadmium(II) with 2-D honeycomb-like [Cd(SCN)3]nn− anionic polymeric framework

An unusual, honeycomb-like cadmium-tri-thiocyanate polymeric framework was found in the studied hybrid material of general formula (L2+)n[Cd(SCN)3]2n2n− (3), where L2+ is bis[4-(N-benzylpyridinium)]piperazine dication. The perforated coordination net forms due to a template effect of the organic dications which reside in the holes penetrating the net in a polyrotaxane-like manner. The salt (L2+)(SCN)2·2H2O (4) was studied for comparison.

Host–guest key–lock hydrogen-bonding interactions: a rare case in the design of a V-shaped polycarboxylate Ni(II)-based chiral coordination polymer

A rare case in the design of a V-shaped polycarboxylate Ni(II)-based chiral coordination polymer from achiral ligands is described. Four metal–organic coordination networks, namely [Ni2(hfdpa)(bpypip)2(H2O)2](bpypip)·2.5H2O (1), [Ni3(Hodpa)2(bpypip)3(H2O)9] (2), [Ni2(odpa)(bpypip)2(H2O)2] (3), and [Cd2(bptc)(bpypip)2(H2O)2]·H2O (4), where H4hfdpa = 4,4′-(hexafluoroisopropylidene)diphthalic acid, H4odpa = 4,4′-oxydiphthalic acid, H4bptc = benzophenone-3,3′,4,4′-tetracarboxylic acid, and bpypip = N,N′-bis(pyrid-4-yl)piperazine, were prepared via a hydrothermal process. The structure of 1 exhibits a chiral three-dimensional porous framework, featuring left-handed Ni–O2C 21-screw helical chains along the crystallographic b axis and rectangular-shaped tubular open channels occupied by the uncoordinated bpypip and water molecules. Compound 2 possesses a 2-fold 2D + 2D → 2D interwoven sheet structure that is arranged interdigitally along the crystallographic a axis, forming an extensive three-dimensional supramolecular network through hydrogen-bonding. The structure of 3 shows a complicated 1D + 1D → 3D polyrotaxane coordination polymer entanglement, which suits a four-connected {6482}-net resembling the topology of a cds-net. Compound 4 has a complicated 2D + 2D → 3D coordination framework, which is simplified into a six-connected {496482}-net. In comparison with the crystal structures of the products, the uncoordinated bpypip ligands in 1, along with the guest water molecules, acts as a key for interacting with the coordinated V-shaped polycarboxylate hfdpa and coordinated bpypip ligands through simultaneous C–H⋯F, C–H⋯O, and C–H⋯N hydrogen-bonding, thereby assisting the generation of the chiral NiII coordination polymer. This type of host–guest key–lock interaction is unique and is observed for the first time by controlling the formation of a chiral coordination polymer.

Preparation of Unconventional Dendrimers that Contain Rigid NHTriazine Linkages and Peripheral tert-Butyl Moieties for CO2-Selective Adsorption

Three unconventional dendrimers that contained rigid NH-triazine linkages and peripheral tert-butyl moieties were prepared by using a convergent approach and characterized by (1)H and (13)C NMR spectroscopy, mass spectrometry, and elemental analysis. Based on a thermogravimetric analysis study, these dendrimers were observed to display thermal stability at about 300 °C. The NH-triazine moiety, which possessed protonated and proton-free nitrogen sites (like the imidazole unit), displayed the capture of polarizable CO2 molecules through hydrogen-bond and/or dipole-quadrupole interactions. In addition, the adsorption of various amounts of CO2 and N2 at different pressures suggests that the dendritic pores, which arise from the stacking of the middle co-planar and rim protuberant dendrimers, Gn -N∼N-Gn (n=1-3), either swell or shrink at high pressure, thus indicating that these dendrimers may have a breathing ability.

Variation in molecular stacking resulting from the different polarity of liquid crystalline molecules: synthesis and study of azo dye compounds

To investigate the effect of molecular polarity on the packing of liquid crystalline molecules, two liquid crystals, N,N-disubstituted aminophenylazo-4-alkylbenzenes, were synthesized and studied by single crystal structure determination. A comparison of the resulting molecular stacking with that of N,N -disubstituted aminophenylazo-4-butylbenzoate was made.

N,N-Disubstituted aminophenylazo-4-benzoates: preparation, mesogenic study, structure determination and molecular modelling

A series of alkyl N,N-disubstituted aminophenylazo-4-benzoates were prepared from the reactions of an acyl phenylpiperazine with a series of the diazonium salts. The mesogenic behaviours of the resulting dyes were studied by polarizing optical microscopy and differential scanning calorimetry. Single crystal structure determination, powder XRD, and molecular modelling of a representative compound were also undertaken to understand the relative structural conformation.

Anion-Directed Copper(II) Metallocages, Coordination Chain, and Complex Double Salt: Structures, Magnetic Properties, EPR Spectra, and Density Functional Study

A series of Cu(II) metallo-assemblies showing anion-directed structural variations, including five metallocages [(G(n-) )⊂{Cu2 (Hdpma)4 }]((8-n)+) (A(-) )8-n (G(n-) =NO3 (-) , ClO4 (-) , SiF6 (2-) , BF4 (-) , SO4 (2-) ; A(-) =NO3 (-) , ClO4 (-) , BF4 (-) , CH3 SO4 (-) ; Hdpma=bis(3-pyridylmethyl)ammonium cation), a complex double salt, namely, (H3 dpma)4 (CuCl4 )5 Cl2 , and a coordination chain, namely, [Cu2 (dpma)(OAc)4 ], are reported. The influence of the anion can be explained by its coordinating ability, the affinity of which for the Cu(II) center interferes significantly with metallocage formation, and its shape, which offers host-guest recognition ability to engage in weak metal-anion coordination and hydrogen bonding to the organic ligand, which are responsible for metallocage templation. EPR studies of these metallocages in the powder phase at room temperature and 77 K showed a trend of the g values (g|| >2.10>g⊥ >2.00) indicating a dx2-y2 -based ground state with square-pyramidal geometry for the Cu(II) centers. The magnetism of these metallocages can be interpreted as the result of a combination of relatively small magnetic coupling integrals and a substantial contribution of temperature-independent paramagnetism (TIP). The weak magnetic interaction is corroborated by the results of DFT calculations and the EPR spectra. Availability of the low-lying state for spin population was confirmed by a magnetization study, which revealed a magnetic moment approaching 2Nβ, which would explain the presence of the larger TIP term.

Infinite Copper(II) Coordination Architectures from a Resonative Aminotriazine-Derived Tripodal Ligand: Synthesis, Structures, and Magnetic Properties

The ligand 2,4,6-tris(2-picolylamino)-1,3,5-triazine (o-H3tpat) with essentially resonative structure and two copper(II)-based one-dimensional coordination chain structures, [Cu3Cl5(o-H2tpat)(H2O)]·MeOH·CH2Cl2 (1) and [Cu2(o-H2tpat)(H2O)(MeOH)(NO3)2](NO3)·3MeOH (2), with different structural patterns have been synthesized and characterized using single crystal X-ray diffraction analysis. For o-H3tpat, two crystalline forms showing different solid-state structural features are obtained from MeOH/Et2O (form I) and CH2Cl2/Et2O (form II), respectively. The o-H3tpat form I adopts an asymmetric-configured all-amino resonative tautomer with three cis-trans-trans-arranged pyridyl groups, whereas the o-H3tpat form II adopts also an identical resonative structure but where two of the three pyridyl groups are in a cis-manner and the third one is nearly coplanar with the central aminotriazine core. On the other hand, the designed tripodal ligand in both Cu(II)-complexes serves as a monoanion, o-H2tpat(-), which suits a propeller-configured all-imino resonative structure in 1 and a syn-anti-configured amino-imino-imino resonative structure in 2. These observations significantly indicate that the o-H3tpat ligand can self-adjust and interconvert its conformation via a possible structure transformation associated with proton-shift to adapt a change in the crystallization and self-assembly reaction systems. In the magnetic point of view, 1 is treated as repeated chains composed of infinite {Cu6Cl10} units wherein the hexanuclear unit is further decomposed to one {Cu(II)4Cl6} and two magnetically isolated {Cu(II)Cl2} subunits. Antiferromagnetic interactions are found for the Cu4 subunits (g = 2.33, 2J1 = -5.6 cm(-1), 2J2 = -8.6 cm(-1), 2J3 = -4.1 cm(-1), and J4 held to zero). For 2, it is considered as an infinite chain that composes of Cu2 units antiferromagnetically coupled (g = 2.03, 2J1 = -0.2 cm(-1)). The small antiferromagnetic exchange constants in both 1 and 2 suggest that the unpaired spins do not effectively interact through the tripodal o-H2tpat(-) ligands.