Jayanta K. Nath

Water assisted anion chains and anion dependent fluorescence emission in salts of N,N′-bis(3-imidazol-1-ylpropyl)naphthalenediimide

In this article we demonstrate the role of anion–π interactions of different anions with protonated N,N′-bis(3-imidazol-1-ylpropyl)naphthalenediimide (L). The compound L shows fluorescence quenching with hydrochloric acid and hydrobromic acid, whereas it shows fluorescence enhancement with perchloric, sulphuric, phosphoric and nitric acid. A similar trend in fluorescence emission of the corresponding salt in the solid state is also observed. The fluorescence quenching is attributed to the anion–π interactions of the chloride and bromide with H2L, whereas the oxy-anion-containing acids cause fluorescence enhancement by protonation of L. The structures of the salts of N,N′-bis(3-imidazol-1-ylpropyl)naphthalenediimide (L), namely [H2LCl2]·2H2O (1), [H2LBr2]·2H2O (2), [H2L(ClO4)2] (3), [H2L(HSO4)2]·H2O (4), [H2L(MeSO4)2] (5), [H2L(HPO4)]·H2O (6) [H2L(NO3)2] (7), [H2L(SiF6)]·1.5H2O (8) are studied. Chloride and bromide ions form a hydrogen bonded halide–water chain; whereas the hydrogen phosphate salt forms a one dimensional water bridged polymeric chain. Planar nitrate anions appear as pairs and form planar assemblies with imidazolium ions and such assemblies are sandwiched between naphthalenediimide rings; whereas bisulphate and methylsulphate salts guide formation of helical supramolecular arrangements of H2L2+ ions. The perchlorate anions facilitate formation of a zigzag 2-D network structure and the SiF62− anions guide formation of a spiral chain-like structure to hold the SiF62− anions.

Solvatoemissive dual fluorescence of N-(pyridylmethyl)-3-nitro-1,8-naphthalimides

Solvatoemissive dual fluorescence emission observed in the three positional isomers of N-(n-pyridylmethyl)-3-nitro-1,8-naphthalimide [n = 2 (1), 3 (2), 4 (3)] are described. Dual fluorescence emission in this class of compounds occurs from the excited states with extended conjugation via π-stacking interactions. The crystal structure of the compound 1 and the chloride salt of 2 were determined. The compound 1 forms dimeric assemblies through π-stacking interactions. Whereas the structure of the chloride salt of 2 is composed of dimeric assemblies of the cationic part which hold cyclic hydrated anionic assemblies through weak C-H…Cl interactions. Anionic hydrated assemblies between water and chloride ions have cyclic tetrameric structure through O-H…Cl interactions.

Twisted conformations in complexes of N-(3-imidazol-1-yl-propyl)-1,8-naphthalimide and fluorescence properties

A series of complexes of N-(3-imidazol-1-yl-propyl)-1,8-naphthalimide (L) with divalent ions of manganese, cobalt, zinc, cadmium and mercury are structurally characterized. The metal complexes [ML2Cl2] {M = Zn (1), Cd (2), Hg (3)} are isomorphous and have a distorted tetrahedral geometry with a bend conformation of L. The thiocyanate complex [ZnL2(SCN)2] has a distorted tetrahedral geometry with L in bent conformation but with a different geometry from that in the structure of complex 1. The manganese and cobalt thiocyanate complexes [ML4(SCN)2]·2CH3CN (M = Mn, Co) are isomorphous and have a distorted octahedral geometry with the thiocyanate ligands occupying the axial positions. The cadmium complex [CdL3(SCN)2DMF]·DMF has a distorted octahedral geometry with thiocyanate ligands in the axial positions. The tetrahedral complexes [ML2Cl2] {M = Zn (1), Cd (2)} in the solid state show emission at shorter wavelengths than the single emission peak observed from the ligand, whereas the fluorescence emission of [ML2(SCN)2] {M = Zn (1), Cd (2)} occurred at longer wavelengths than L. On the other hand, [HgL2Cl2] (3) showed a single emission peak with higher intensity but at 31 nm shorter wavelength than the emission peak of the parent ligand. Two types of bend orientations of the ligand L, namely parallel arrangement of imidazole with the 1,8-naphthalimide ring and non-parallel arrangement in the tetrahedral complexes are observed. The former case favors intra-molecular charge transfer to show shorter wavelength emission, whereas the non-parallel arrangement facilitates exciplex leading to emission at longer wavelengths.

Cyclic aromatic imides as a potential class of molecules for supramolecular interactions

Cyclic aromatic imide based compounds can be a choice to meet the growing interests in soft materials as nano-dimensional materials. They serve as templates to build upon or act as host components to contribute to the knowledge of crystal engineering. Such compounds serve as the simplest building blocks of dipolar planar motifs and significantly contribute to the assemblies through the stacking effects of dipolar rings. The carbonyl groups of the imides provide extra stability to self-assemblies by participating in a weak interaction scheme. Interactions of the carbonyl groups also provide directional effects to the supramolecular assemblies. Due to the concern of imide based compounds in the biological, environmental, and non-conventional energy and material sectors, these units generate great impetus to use them as supramolecular systems and use of a crystal engineering approach provides the answers to many important issues at the molecular level. In this article, various aspects of aromatic imides focusing around their interactions with different substrates that could attract the interest of crystal engineering and supramolecular chemists are presented by taking representative examples.

Unusual solvent-mediated hydrolysis of dicarboxylate monoester ligands in copper(II) complexes toward simultaneous crystallization of new dicarboxylate derivatives

A series of copper(II) complexes, [Cu(cmb)2(im)2] (1), [Cu(cmn)2(im)4] (3) and [Cu(cmp)2(im)2] (5), bearing various dicarboxylate monoester derivatives, [cmb = 2-carbomethoxy-benzoate; cmn = 8-carbomethoxy-naphthalene-1-carboxylate; cmp = 2-carbomethoxy-phenyl-2-benzoate], were generated from copper(II) acetate, imidazole (im) and an aromatic anhydride [phthalic, 1,8-naphthalic or biphenic anhydride for 1, 3 or 5, respectively]. Unusual solvent-mediated transformations of the crystals of two copper dicarboxylate monoester complexes to new crystals of the corresponding dicarboxylate derivatives by the hydrolysis of ester groups were observed and investigated. Crystals of 1 underwent a transformation to crystals of copper(II) phthalate 2D coordination polymer {[Cu2(pht)2(im)4·H2O]·H2O}n (2) (pht = phthalate) upon moistening with aqueous methanol. Similarly, crystals of 3, after wetting with aqueous dimethylformamide (DMF), were transformed to crystals of a metallacycle [Cu(nap)(im)(DMF)(H2O)]2 (4) (nap = 1,8-naphthalenedicarboxylate). In contrast to 1 and 3, the crystals of 5 were found to be stable under ambient conditions. Compounds 1–5 were characterized by IR and UV-vis spectroscopy and single crystal and powder X-ray diffraction. Topological analysis showed that in the 1→2 transformation the overall 2D network topology was modified from the 4-connected H-bonded sql net [Shubnikov tetragonal plane net] to the 3-connected metal–organic hcb net [Shubnikov hexagonal plane net/(6, 3)], whereas no topology change was detected during an analogous 3→4 transformation, with both structures exhibiting topologically equal H-bonded sql nets.