A series of zinc dipicolinate (2,6-pyridinedicarboxylate; pdc) complexes [H2tmbpy][Zn(pdc)2]·5H2O () {H2tmbpy = 1,3-bis(4-pyridinium)propane(2+)}, [H2bpy][Zn(pdc)2]·6H2O () {H2bpy = 4,4'-bipyridinium(2+)}, [H2bpy][Zn(pdc)2]·3.5(4np)·2H2O () {4np = 4-nitrophenol}, [H2tmbpy][Zn(pdc)2]·4(2,7dhn)·3H2O () {2,7dhn = 2,7-dihydroxynaphthalene}, [H2bpy][Zn(pdc)2]·2(2,7dhn)·5H2O (), [H2bpy][Zn(pdc)2]·2(pyrogl)·6H2O () {pyrogl = pyrogallol}, and [H2tmbpy][Zn(pdc)2]·2(2,6dhn)·8H2O () {2,6dhn = 2,6-dihydroxynaphthalene} were synthesized and characterised. Different packing patterns in these complexes arise from differences in the abilities of cations to π-stack with zinc dipicolinate units. In , the planar [H2bpy](2+) moieties are π-stacked with adjacent 4,4'-bipyridinium cations and [Zn(pdc)2](2-) anions, whereas in , π-stacks are formed exclusively between [Zn(pdc)2](2-) moieties. 4-Nitrophenol can selectively replace the [H2bpy](2+) cations to form adduct , thus representing a novel host-guest system for molecular recognition of 4-nitrophenol. This recognition does not occur upon treatment of 4-nitrophenol with which bears a nonplanar [H2tmbpy](2+) cation. Host-guest interactions of pyrogallol, 2,6-dihydroxynaphthalene, and 2,7-dihydroxynaphthalene with the parent complexes and were studied, resulting in the crystallization of . The crystal structures of show that guest organic molecules are accommodated in the layers of zinc dipicolinate anions. The formation of different water clusters is also discussed. In addition, topological analysis and classification of the H-bonded patterns driven by strong hydrogen bonds between the [H2bpy](2+) or [H2tmbpy](2+) cations and the [Zn(pdc)2](2-) anions, and organic guest molecules were carried out. This analysis revealed: (i) discrete 0D dimeric (in and ) or tetrameric (in ) motifs with 1M2-1 or 1,3M4-1 topology, respectively, (ii) infinite 1D zigzag chains with 2C1 topology in , and (iii) infinite 2D layers with the hcb [Shubnikov hexagonal plane net/(6,3)] topology in .

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Htea = dianion of triethanolamine, bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline) having tetranuclear cations with end to end distance~1.69 nm and~1.62 nm respectively were characterized. These complexes are weakly fluorescent in sol-ution and fluorescence of respective complexes decreases upon interactions with nitrophenols. Complexes from reactions of 1 and 2 with nitrophenols were isolated and structurally characterized. They also show lower fluorescence in solid state than respective parent complex due to oxygen-p interactions. Complex 2 underwent cation exchange to form new tetranuclear oxido cobalt complexes possessing [MCl 4 ] 2À ( M= Zn or Cd) anion.

A visible light-promoted, efficient, green, and sustainable strategy has been adopted to unlatch a new pathway toward the synthesis of a library of medicinally important 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) moieties using substituted aromatic aldehydes and sterically hindered 3-methyl-1-phenyl-2-pyrazoline-5-one in excellent yield. This reaction shows high functional group tolerance and provides a cost-effective and catalyst-free protocol for the quick synthesis of biologically active compounds from readily available substrates. Synthesized compounds were characterized by spectroscopic techniques such as IR, 1 HNMR, 13 CNMR, and single-crystal XRD analysis. All the synthesized compounds were evaluated for their antiproliferative activities against a panel of five different human cancer cell lines and compared with Tamoxifen using MTT assay. Compound 3m exhibited maximum antiproliferative activity and was found to be more active as compared to Tamoxifen against both the MCF-7 and MDA-MB-231 cell lines with an IC 50 of 5.45 and 9.47 μM, respectively. A molecular docking study with respect to COVID-19 main protease (M pro ) (PDB ID: 6LU7 ) has also been carried out which shows comparatively high binding affinity of compounds 3f and 3g (−8.3 and −8.8 Kcal/mole, respectively) than few reported drugs such as ritonavir, remdesivir, ribacvirin, favipiravir, hydroxychloroquine, chloroquine, and olsaltamivir. Hence, it reveals the possibility of these compounds to be used as effective COVID-19 inhibitors.

Interplay of weak interactions of di‐aqua‐bis‐ethylenediammine copper(II) 2,2′‐biquinoline‐4,4′‐dicarboxylate hydrate (1) were used to modulate solid state fluorescence emissions. Complex 1 forms porous self‐assembly in solid state by hydrogen bonds between cations, anions and lattice water molecules. Fluorescence spectroscopy, thermogravimetry, powder XRD, IR‐spectroscopy and surface analysis were used to establish the breakdown and regeneration of porous hydrogen bonded sub‐assemblies by dehydration and rehydration. Complex 1 is non‐fluorescent in solid state but anhydrous form of the complex 1 is highly fluorescent. In the solid state self‐assembly of the complex 1, π‐stacking among biquinoline rings contributes to quenching. Dehydration of solid sample of complex 1 generates a fluorescent state, and subsequent absorption of moisture by the anhydrous complex quenches fluorescence. In solution, competition between chelation by ethylenediamine and coordination by 2,2′‐biquinoline‐4,4′‐dicarboxylic acid with copper(II) ions is reflected in the ON and OFF states generated by judicious manipulation of chelation effects. Complex 1 is one among a series of bis‐chelated ethylendiamine copper(II) aromatic carboxylate complexes which have layered structures. It is also a precursor of nano‐dimensional copper oxide; 25–50 nm size copper oxide particles are formed by thermal decomposition of complex 1 at 500 °C.