Marvadeen A. Singh-Wilmot

Synthesis and characterization of a cadmium-dichloro compound of N , N , O -di-2-pyridyl ketone thiophene-2-carboxylic acid hydrazone (η 3-dpktch). The structure of [CdCl2(η 3-dpktch)]

The reaction between dpktch and CdCl2 in refluxing acetonitrile gave [CdCl2(η3-dpktch)] in good yield. Spectroscopic measurements divulge the coordination of dpktch and the elemental analysis confirmed its formulation. Optical measurements in N,N-dimethylformamide (dmf) and dimethylsulfoxide (DMSO) in the absence and presence of a proton donor/acceptor disclosed two highly sensitivity interlocked intra-ligand-charge-transfer transitions (ILCT) that are sensitive to their surroundings. Under basic conditions, a low-energy electronic transition with an extinction coefficient of 17,400 ± 2000 M−1cm−1 appeared at ∼403 nm and a peak minimum appeared at 326 nm. Under acidic conditions, a high energy electronic transition with extinction coefficient of 13,500 ± 2000 M−1cm−1 appeared at ∼330 nm and a shoulder appeared at ∼400 nm. The addition of an acid to a dmf solution of [CdCl2(η3-dpktch)] caused the disappearance of the low energy absorption band at 403 nm and a peak maximum appeared at 330 nm. The reverse was observed when a base was added to a DMSO solution of [CdCl2(η3-dpktch)]. Electrochemical measurements reveal reduction of coordinated CdCl2 and oxidation of electrodeposited cadmium metal along with ligand-based redox processes. X-ray crystallographic analysis on a monoclinic, P21/n single crystal of [CdCl2(η3-dpktch)], confirmed the N,N,O-coordination of dpktch and revealed digitated units of [CdCl2(η3-dpktch)] interlocked via a web of hydrogen bonds.

Eight rare earth metal organic frameworks and coordination polymers from 2-nitroterephthlate: syntheses, structures, solid-state luminescence and an unprecedented topology

Eight novel lanthanide metal organic frameworks (MOFs) and coordination polymers (CPs), La2(NTA)3(OH2)6 (1), [Nd(NTA)(HNTA)(OH2)2]·3H2O (2), [Nd2(NTA)3(OH2)2](H2O)3·2H2O (3), and [Ln2(NTA)3(OH2)2](H2O)2 (Ln = Sm (4), Eu (5), Gd (6), Tb (7), Er (8)), (H2NTA = 2-nitroterephthalic acid), have been synthesized under hydrothermal and slow evaporation conditions. The compounds are characterized by X-ray crystallography, elemental analyses, infrared spectroscopy and thermogravimetric analyses (TGA). Compounds 1–8 feature varying coordination modes of the NTA ligand, including two modes that are being reported for the first time. Compound 2 was crystallized by slow evaporation and features a supramolecular 3-D framework involving H-bonds and π–π stacking interactions. In compounds 1 and 3–8, which were made under hydrothermal conditions, non-covalent interactions are secondary and the 3-D network is built from strong covalent bonds. Compounds 1, 3, and 4–8 form a 3,4,5-c network having point symbol {4∧2.6}2{4∧2.8∧4}{4∧3.6.8∧6}2, a 4,4,6-c net with point symbol {4∧2.8∧4}{4∧4.6∧2}2{4∧8.6∧7}2 and an unprecedented 4,4,6-c net with point symbol {4∧2.6∧4}{4∧3.6∧3}2{4∧8.6∧6.8}2 respectively. The topologies are further simplified as parallel packing of rod-like SBUs; 1 and 2 form a distorted pcu network, 3 forms the nbo topology and 4–8 form the hex type topological network. From the crystal structure, solvent accessible voids for 2 and 3 are 138 A3 [13%] and 864 A3 [25%] of unit cell volume respectively. TGA data suggest that the framework in compounds 1, 2, 3, 5 and 7 are thermally stable up to 300 °C. Photoluminescence studies on compounds 5 and 7 indicate that NTA does not efficiently sensitize Eu3+ and Tb3+ emission due to alternate deactivation pathways available to the ligand. However, direct excitation in the visible region at 466 nm leads to red emission at room temperature in compound 5, the spectral profile of which suggests a lowering of the crystal field symmetry around Eu3+ and a quadrupolar contribution to the 5D0 → 7F2 peak. Emission from direct excitation of Tb3+ however is still quenched possibly due to back energy transfer to the ligand. This study is the second and most extensive report of lanthanide-based coordination networks involving nitroterephthalic acid and demonstrates its versatility as a building block for Ln-CPs and Ln-MOFs whose structures can be simplified as linked rod-shaped SBUs.

Stemodin-derived analogues with lipid peroxidation, cyclooxygenase enzymes and human tumour cell proliferation inhibitory activities.

A series of analogues, derived from the antiviral and cytotoxic diterpene stemodin, were prepared and evaluated for their lipid peroxidation (LPO), cyclooxygenase enzyme-1 (COX-1) and -2 (COX-2), and tumour cell proliferation inhibitory activities. Oxidation of stemodin produced stemodinone, which was then converted to stemod-12-en-2-one. Reaction of the latter under Petrow conditions (bromine; silver acetate/pyridine) yielded mainly dibrominated abeo-stachanes. Solvolysis of the dibromo compounds gave products of hydrolysis, some with rearranged skeleta. In the lipid peroxidation inhibitory assay three of the compounds exhibited prominent activity. Interestingly, all the analogues showed higher COX-1 enzyme inhibition than COX-2. Although a few of the diterpenes limited the growth of some human tumour cell lines, most compounds induced proliferation of such cells.