Covalent organic frameworks (COFs) have emerged as highly crystalline porous organic materials. Their potential has been demonstrated for use in various applications, particularly sensing with the nitrogen-rich analogs.

A crosslinked hydrogel was synthesized using a hybrid backbone of karaya gum starch and grafted with polyacrylic acid. It showed a maximum swelling ratio of 30.5 g/g at pH 10 and was explored as an oral drug delivery carrier using paracetamol and aspirin as model drugs. In vitro release experiments revealed that maximum drug release at pH 7.4 in comparison to pH 1.2 (simulated intestinal vs gastric fluid) and neutral medium. The release profiles of these drugs showed no initial burst. It also showed good hemocompatibilty and non-cytotoxicity for its employment as a site specific drug delivery agent.

A new mixed pyridyl–carboxylate ligand with two picolinate chromophores and a flexible linear spacer, potassium 2,2′-(butane-1,4-diylbis((pyridin-2-ylmethyl)azanediyl))diacetate (K₂bpbd), which is obtained in high yield and spectroscopically characterized, has been utilized to make new lanthanide complexes, namely, [Ln(bpbd) (H₂O)₂(NO₃)]·xH₂O, where Ln = Tb (1) and x = 6, Ln = Sm (2) and x = 7, and Ln = Dy (3) and x = 7. These complexes have been extensively characterized by various spectroscopic techniques (UV–vis and Fourier transform infrared spectroscopy), elemental analyses, thermogravimetric analysis, field emission scanning electron microscopy, and powder X-ray diffraction. These show very intense characteristic luminescence features that confirm the antenna effect of the ligand on the metal center. These complexes have been utilized for the detection of various nitroaromatic compounds. Among these three complexes, 1 is found to be the best for the selective sensing of 2,4,6-trinitrophenol in water with a detection limit of (0.35 ± 0.05) ppm. Its Stern–Volmer constant, K_SV [(5.48 ± 0.1) × 10⁴ M^–1], is one of the highest among similar sensors reported so far.

In a one-pot self-assembly reaction of Co(OAc)₂·4H₂O, thiophene-2,5-dicarboxylic acid (H₂tdc) and four different bis(tridentate) polypyridyl spanning ligands under ambient conditions, a series of structurally diverse metal–organic frameworks has been synthesised and characterized by single crystal X-ray diffraction: {[Co₂(tdc)₂(tpbn)(H₂O)₂]·solvent}_n (solvent = 2H₂O, 1; solvent = 2CH₃OH, 2H₂O, 1a), {[Co₂(tdc)₂(tphn)]·solvent}_n (solvent = H₂O, 2; solvent = CH₃OH, 2.5H₂O, 2a), {[Co₂(tdc)₂(tpchn)(H₂O)₂]·solvent}_n (solvent = 5H₂O, 3; solvent = C₂H₅OH, 2H₂O, 3a), and {[Co₂(tdc)₂(tpxn)]·solvent}_n (solvent = 6H₂O, 4; when no solvent, 4a), where tpbn (N,N′,N′′,N′′′-tetrakis(2-pyridylmethyl)-1,4-diaminobutane), tphn = N,N′,N′′,N′′′-tetrakis(2-pyridylmethyl)-1,6-diaminohexane, tpchn = N,N′-(cyclohexane-1,4-diylbis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine) and tpxn = N,N′-(1,4-phenylenebis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine). There is a profound effect of the nature of spacer between the alkyl nitrogens in the spanning ligands (flexible vs. semiflexible) on the molecular structures of 1a–4a. The notable differences are (a) the binding mode of the tridentate part of polypyridyl ligands to the Co(II) center is facial in 1a, 3a and 4a but meridional in 2a, (b) the Co(II) centers in 1a–3a are hexacoordinated (with a coordinated water in 1a and 3a) but are pentacoordinated in 4a, and (c) the binding mode of tdc linker is bis(monodentate) in 1a, 3a and 4a but chelated in one end and monodentate in the other end in 2a. Thus, the overall framework structure of 1a, 2a, 3a and 4a is cis-decalin type 2D polymer, ladder-shaped 1D polymer, hexagonal 2D net and cis-decalin type 2D polymer, respectively. Their thermal stabilities have been established by thermogravimetric analysis (TGA). The presence of an unsaturated metal center in 4 has provided us an opportunity for its use as an efficient Lewis acid catalyst for the Knoevenagel condensation reaction of malononitrile with various aldehydes (100% conversion in 60 minutes with 2 mol% catalyst in methanol).