Carboxylic Building Blocks Research Articles

Aliphatic-Bridged Early Lanthanide Metal–Organic Frameworks: Topological Polymorphism and Excitation-Dependent Luminescence

Six new three-dimensional metal–organic frameworks based on early lanthanide(III) cations and trans-1,4-cyclohexanedicarboxylic acid (H2chdc) were obtained. Their crystal structures were determined by single-crystal X-ray diffraction analysis. The structure of [La2(H2O)4(chdc)3]·2DMF·H2O (1; DMF = N,N-dimethylformamide) contains one-dimensional infinite La(III)-carboxylate chains interconnected by cyclohexane moieties to form a highly porous polymeric lattice with 30% solvent accessible volume. Compounds [Ln2(phen)2(chdc)3]·0.75DMF (2Ln; Ln3+ = Ce3+, Pr3+, Nd3+ and Sm3+; phen = 1,10-phenanthroline) are based on binuclear carboxylate building blocks, which are decorated by chelate phenanthroline ligands and interconnected by cyclohexane moieties to form more dense isostructural coordination frameworks with primitive cubic pcu topology. Compound [Nd2(phen)2(chdc)3]·2DMF·0.67H2O (3) is based on secondary building units similar to 2Ln and contains a coordination lattice isomeric to 2Ln with a rare hexagonal helical snz topology. Thermal stability and luminescent properties were investigated. For 2Sm, a strong and nonmonotonous dependence of the luminescence color on the variation of excitation wavelength was revealed, changing its emission from pinkish red at λex = 340 nm to white at λex = 400 nm, and then to yellow at lower excitation energies. Such nonlinear behavior was rationalized in terms of the contribution of several different luminescence mechanisms. Thus, 2Sm is a rather rare example of a highly tunable monometallic lanthanide-based luminophore with possible applications in light-emitting devices and optical data processing.

Vibrational mode analysis of hydrogen-bonded organic frameworks (HOFs): synchrotron infrared studies.

Hydrogen-bonded organic frameworks (HOFs) are a promising class of porous crystalline materials for gas sorption and gas separation technologies that can be constructed under mild synthetic conditions. In forming three-dimensional networks of flexible hydrogen bonds between donor/acceptor subunits, these materials have displayed high stability at elevated temperature and under vacuum. Although the structural properties of HOFs are commonly characterized by diffraction techniques, new complimentary methods to elucidate phase behaviour and host-guest interactions at the molecular level are sought, particularly those that can be applied under changing physical conditions or solvent environment. To this end, this study has applied synchrotron far-IR and mid-IR spectroscopy to probe the properties of two known and one new HOF system assembled from tetrahedral amidinium and carboxylate building blocks. All three frameworks produce feature-rich and resolved infrared profiles from 30 to 4000 cm-1 that provide information on hydrogen-bonded water solvent networks and the HOF channel topography via lattice and torsional bands. Comparison of experimental peaks to frequencies and atomic displacements (eigenvectors) predicted by high-level periodic DFT calculations have allowed for the assignment of vibrational modes associated with the aforementioned physicochemical properties. Now compiled, the specific vibrational modes identified as common to charge-assisted hydrogen-bonding motifs, as well as low frequency lattice and torsional bands attributed to HOF pore morphology and water-of-hydration networks, can act as diagnostic features in future spectroscopic investigations of HOF properties, such as those toward the design and tuning of host-guest properties for targeted applications.

Caerulomycin and collismycin antibiotics share a trans-acting flavoprotein-dependent assembly line for 2,2\u2019-bipyridine formation

Linear nonribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) template the modular biosynthesis of numerous nonribosomal peptides, polyketides and their hybrids through assembly line chemistry. This chemistry can be complex and highly varied, and thus challenges our understanding in NRPS and PKS-programmed, diverse biosynthetic processes using amino acid and carboxylate building blocks. Here, we report that caerulomycin and collismycin peptide-polyketide hybrid antibiotics share an assembly line that involves unusual NRPS activity to engage a trans-acting flavoprotein in C-C bond formation and heterocyclization during 2,2’-bipyridine formation. Simultaneously, this assembly line provides dethiolated and thiolated 2,2’-bipyridine intermediates through differential treatment of the sulfhydryl group arising from l-cysteine incorporation. Subsequent l-leucine extension, which does not contribute any atoms to either caerulomycins or collismycins, plays a key role in sulfur fate determination by selectively advancing one of the two 2,2’-bipyridine intermediates down a path to the final products with or without sulfur decoration. These findings further the appreciation of assembly line chemistry and will facilitate the development of related molecules using synthetic biology approaches.

Designed Conformation and Fluorescence Properties of Self-Assembled Phenazine-Cored Platinum(II) Metallacycles.

A series of platinum(II) metallacycles were prepared via the coordination-driven self-assembly of a phenazine-cored dipyridyl donor with a 90° Pt(II) acceptor and various dicarboxylate donors in a 1:1:2 ratio. While the metallacycles display similar absorption profiles, they exhibit a trend of blue-shifted fluorescence emission with the decrease in the bite angles between the carboxylate building blocks. Comprehensive spectroscopic and dynamic studies as well as a computational approach were conducted, revealing that the difference in the degree of constraint imposed on the excited-state planarization of the phenazine core within these metallacycles results in their distinct photophysical behaviors. As such, a small initial difference in the dicarboxylate building blocks is amplified into distinct photophysical properties of the metallacycles, which is reminiscent of the efficient functional tuning observed in natural systems. In addition to the pre-assembly approach, the photophysical properties of a metallacycle can also be modulated using a post-assembly modification to the dicarboxylate building block, suggesting another strategy for functional tuning. This research illustrated the potential of coordination-driven self-assembly for the preparation of materials with precisely tailored functionalities at the molecular level.

Targeted Construction of Light-Harvesting Metal-Organic Frameworks Featuring Efficient Host-Guest Energy Transfer.

Metal-organic frameworks (MOFs) have emerged as promising light-harvesting platforms for energy-transfer materials. However, the targeted construction of MOFs with desirable photophysical properties and pore structures is still a challenge. Herein, 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene (tppe) is selected as the ligand for the construction of light-harvesting MOFs due to its highly emissive and rigid backbone, which could benefit the light-harvesting performance of the MOFs. Three MOFs (MOFs 1-3) were obtained on the basis of different metal centers (Zn2+ and Cd2+) and carboxylate building blocks. The complete structure characterization of the MOFs helps the illustration of the principles for structure tuning of this system. All three MOFs exhibit strong tppe-originated photoluminescence emission, with quantum yields as high as 47.6%. The fluorescence quantum yield and time-resolved fluorescence studies reveal that a remarkable energy-transfer efficiency (up to 96%) was achieved in this system. These results clearly indicate tppe-MOFs could be promising light-harvesting materials.

Syntheses, Structures and Properties of Co(II) and Co(II)/Zn(II) Coordination Polymers Based on Flexible Tris(imidazole) and Multicarboxylate Ligands

Two coordination polymers, namely, Co(BPDA)(titmb)·3H2O (1) and CoZn(BTC)(titmb)Br (2) (titmb = 1,3,5-tris(1-imidazol-1-ylmethyl)-2,4,6-trimethylbenzene, H2BPDA = 4,4′-carbonyldibenzoic acid and H3BTC = 1,3,5-benzenetricarboxylic acid), have been synthesized and characterized by elemental analyses, infrared spectra (IR), thermogravimetric analyses (TGA) and single-crystal X-ray diffraction. Single crystal structure analysis shows that complex 1 exhibits a three-dimensional (3D) twofold interpenetrating architecture with a very rare (3,5)-connected fsc-3,5-Cmce-2 topology, while complex 2 features an interesting three-dimensional (3D) (3,6)-connected framework by self-penetration of two sets of (10,3)-a nets with an unprecedented (63)2(612 ·83) topology. The results reveal that the carboxylic building blocks play a significant role in promoting the diversity of the observed structural motifs. Two complexes indicate high thermal stabilities. The emission in the blue region indicates that complexes 1 and 2 appear to be good candidate for a promising blue-light-emitting materials. Moreover, complex 1 has also modest power SHG activity. The two complexes with unique topology have been constructed by two different multicarboxylates and metal salts with the flexible titmb ligand. The results reveal that the carboxylic building blocks play a significant role in promoting the diversity of the observed structural motifs.

Syntheses and Crystal Structures of Three Cu(II) Coordination Polymers Based on 1,3,5-Tris(imidazol-1-yl)benzene and Benzene Carboxylate Ligands

Three coordination polymers, namely, Cu(HL1)(timb) (1), Cu3(L2)3(timb)2(H2O)2 ·2H2O·4CH3CN (2) and Cu(L3)0.5(timb)·H2O (3) (timb = 1,3,5-tris(imidazol-1-yl)benzene, H3L1 = 1,2,4-benzenetricarboxylic acid, H3L2 = 1,3,5-benzenetricarboxylic acid and H4L3 = 1,2,4,5-benzenetetracarboxylic acid), have been synthesized and characterized by elemental analyses, infrared spectra (IR), thermogravimetric analysis (TGA) and single-crystal X-ray diffraction. Single crystal structure analysis shows that complex 1 possesses a three-dimensional (3D) twofold interpenetrating architecture with a very rare (3,5)-connected (3·72)(32·75·83) topology. Complex 2 features an interesting 3D (3,4)-connected framework with an unprecedented (4·82)4(42·82·102)2(84·122) topology, whereas complex 3 exhibits a novel 3D (3,4,5)-connected framework with an unusual (4·63·86)2(42·84)(63)2 topology. The results reveal that the carboxylic building blocks play a significant role in promoting the diversity of the observed structural motifs. In addition, their thermal stabilities have also been investigated. Three Cu(II) complexes with unique topology have been constructed by three different benzene carboxylates and the timb ligand. The results reveal that the carboxylic building blocks play a significant role in promoting the diversity of the observed structural motifs.

Construction of lanthanide metal–organic frameworks with highly-connected topology based on a tetrapodal linker

By using a rigid tetrapodal linker 4,4′,4′′,4′′′-silanetetrayltetrabenzoic acid (H4L) and lanthanide metal ions, three new coordination polymers, namely, [NdL(H2O)][NH2(CH3)2]·(DMF)x·(H2O)y (x ≈ 2, y ≈ 4) (1), [Eu4L3(H2O)6]·(DMF)y·(H2O)x (x ≈ 2, y ≈ 4) (2) and [Er4L3(H2O)6]·(DMF)x·(H2O)z (x ≈ 2, z ≈ 5) (3), were solvothermally synthesized and structurally characterized. Compound 1 is a 3D framework with a (4,8)-connected flu structure, built from distorted cuboid dinuclear neodymium–carboxylate building block and a 4-connected tetrahedral L ligand. Compounds 2 and 3 are isostructural, possessing a non-interpenetrated three-dimensional network with rare (4,4,12) highly-connected topology. In compounds 2 and 3, the fully deprotonated L4− ligands act as pseudotetrahedral 4-connecting nodes and S-shaped tetranuclear lanthanide metal–carboxylate building blocks act as 12-connecting nodes. Compound 1 possesses permanent porosity as confirmed by N2, H2, O2, CO2 and CH4 gas adsorption measurements.

A three-dimensional cobalt(II)-coordination polymer based on 3,5-pyridinedicarboxylate

Hydrothermal reaction between cobalt(II) nitrate and 3,5-pyridinedicarboxylic acid in the presence of NaOAc and NaCl gave a 3-D cobalt(II)-coordination polymer, Co(3,5-pyridinedicarboxylato)(H 2O) ( 1). X-ray structure determination showed that compound 1 has a 3-D infinite network based on cobalt–carboxylate building blocks.

Pillared, 3D metal-organic frameworks with rectangular channels. Synthesis and characterization of coordination polymers based on tricadmium carboxylates.

Hydro(solvo)thermal reactions between cadmium(II) perchlorate and 4-pyridinecarboxaldehyde in the presence of various guest molecules have resulted in a series of 3-D coordination polymers based on tricadmium carboxylates [Cd6(isonicotinate)10(H2O)2](ClO4)2(EtOH)4(H2O)4, 1, [Cd3(isonicotinate)5 (EtOH)](ClO4)(EtOH)(4-nitroaniline)0.5, 2, and [Cd6(isonicotinate)11](ClO4)(EtOH)2(H2O)2(4-cyanopyridine)0.5, 3. X-ray single crystal structure determinations show that they exhibit similar pillared, 3D framework structures based on tricadmium carboxylate building blocks. Rectangular channels are clearly present in these polymeric networks and are occupied by perchlorate anions and disordered guest molecules. Quantitative NMR and X-ray powder diffraction studies and thermogravimetric analyses (TGA) reveal that these coordination networks are capable of accommodating different guest molecules. More significantly, the guest molecules can be readily removed via evacuation to result in nanoporous polymeric coordination networks retaining the framework structures of the pristine solids. Crystal data for 1: monoclinic space group P2(1)/n, a = 19.041(1) A, b = 23.654(1) A, c = 21.568(1) A, beta = 95.440(1) degrees, and Z = 4. Crystal data for 2: triclinic space group P1, a = 12.050(1) A, b = 12.277(1) A, c = 19.103(1) A, alpha = 91.669(1) degrees, beta = 96.850(1) degrees, gamma = 117.945(1) degrees, and Z = 2. Crystal data for 3: monoclinic space group P2(1)/n, a = 19.038(1) A, b = 23.834(1) A, c = 21.756(1) A, beta = 97.580(1) degrees, and Z = 4.

ChemInform Abstract: Synthesis of Phosphino Oxazoline Ligand Libraries from Amino Acid and Phosphino Carboxylate Building Blocks.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of Phosphino Oxazoline Ligand Libraries from Amino Acid and Phosphino Carboxylate Building Blocks

A modular route to new phosphine−oxazoline ligands is reported. The ability of these ligands to asymmetrically catalyze the addition of dimethyl malonate to 1,3-diphenylprop-2-enyl acetate was inve...