Sanjay K. Verma

[M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n] {Co(III), Ni(II), Cu(II) or Zn(II)} complexes bearing pendant Schiff base moieties: spectral characterization, fluorescence, cyclic voltammetric and TGA/DTA study

A series of neutral mononuclear complexes [M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n] {R = Ph; M = Co(III) 1, Ni(II) 2, Cu(II) 3, Zn(II) 4; R = Naph; M = Co(III) 5, Ni(II) 6, Cu(II) 7, Zn(II) 8; n = 2 for 2–4, 6–8 and n = 3 for 1, 5} bearing pendant Schiff base moieties were synthesized through self-assembly involving N-[phenylmethylidene]-2-piperazin-1-ylethanamine (L1) or N-[naphthylmethylidene]-2-piperazin-1-ylethanamine (L2) with two equivalents each of CS2 and corresponding metal acetates. The complexes 1–8 were characterized by microanalysis, ESI-MS, IR, 1H, 13C NMR, DEPT 135, UV–visible absorption, and emission spectroscopy. Complexes 1, 3, and 8 exhibit fluorescence emissions at 342, 344, and 348 nm upon excitation at 273 (for 1 and 3) and 263 (for 8) with concomitant Stokes shifts of 69, 71, and 85 nm. The spectral and magnetic moment data support octahedral geometry around Co(III) and square planar/tetrahedral geometry around other metal centers. Thermal stabilities of 1–8 have been investigated by thermogravimteric analysis. The cyclic voltammograms clearly suggest that the complexes exhibit electroreduction principally associated with pendant imine moieties except Cu(II) complex 7 which displays quasi-reversible reduction corresponds to the Cu(II)/Cu(I) redox couples, in addition to reversible electroreduction of pendant imine groups associated with the coordinated ligands.

Synthesis, electrochemical, fluorescence and antimicrobial studies of 2-chloro-3-amino-1,4-naphthoquinone bearing mononuclear transition metal dithiocarbamate complexes [M{κ2S,S-S2C–piperazine–C2H4N(H)ClNQ}n]

A novel multifunctional ligand precursor 2-chloro-3-{2-(piperazinyl)ethyl}-amino-1,4-naphthoquinone (L) was synthesized by chemo-selective reaction of 2,3-dichloro-1,4-naphthoquinone and 2-(piperazin-1-yl)ethanamine and characterized, prior to use. A series of mononuclear transition metal dithiocarbamate complexes [M{κ2S,S-S2C–piperazine–C2H4N(H)ClNQ}n] {M = Mn(III) 1, Co(III) 2, Ni(II) 3, Cu(II) 4, Zn(II) 5; ClNQ = 2-chloro-1,4-naphthoquinone; n = 3 for 1–2 and n = 2 for 3–5} bearing pendant 2-chloro-3-amino-1,4-naphthoquinone groups were efficiently synthesized through a self-assembly process involving L, CS2 and corresponding metal acetates. 1–5 were characterized by microanalysis and standard spectroscopic methods such as ESI-MS, IR, 1H and 13C NMR and UV-visible absorption spectroscopy. Significantly, all compounds exhibit medium to very strong fluorescence emission bands in the visible region with concomitant Stokes shifts of ≈280 nm upon excitation at their respective λmax values. Thermal stability of complexes 1–5 has been investigated by thermogravimetric analysis. Cyclic voltammetric study clearly reveals that L and 1–5 are electro active with respect to the dominant redox-active naphthoquinone moiety. Further, L and 1–5 were tested against six important pathogen microorganisms viz. S. aureus, B. subtilis, E. coli, P. aeruginosa, C. albicans and A. niger by using the Broth dilution method. A broad spectrum of the strongest antimicrobial activity was determined for the copper(II) complex 4 and L. The enhanced antibacterial activity of L and copper(II) complex 4 against S. aureus apparently reveals them to be a superior antibacterial agent than the reference drug ciprofloxacin.

A Facile Synthesis, Crystallographic, Spectral, Thermal, and Electrochemical Investigations of Neutral [Cu2(Et2dtc)4] Dimer

A neutral dimeric complex [Cu2(Et2dtc)4] (dtc = dithiocarbamate) (1) was synthesized in single step under mild conditions. Structure of 1 has been studied using single-crystal XRD to gauge the influence of CH3 and CH2 groups of coordinated dithiocarbamate ligands on the association of the molecules in solid state. Evidently 1 features the ability of these groups to form intermolecular (sp3)C‒HΠ(chelate ring) and (sp3)C‒HS stacking interactions leading to fascinating 3D infinite network. Complex has been completely characterized by spectrophotometric methods, optical behavior, and thermal and cyclic voltammetry studies. Cyclic voltammetric study confirmed the binding affinity of 1 toward H2PO– 4. Supplemental materials are available for this article. Go to the publishers online edition of Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry to view the supplemental file.

Identification of unusual C–Cl⋯π contacts in 2-(alkylamino)-3-chloro-1,4-naphthoquinones: effect of N-substituents on crystal packing, fluorescence, redox and anti-microbial properties

The chemo-selective reaction of 2,3-dichloro-1,4-naphthoquinone with different primary amines affords access to a series of derivatives, such as 2-(alkylamino)-3-chloro-1,4-naphthoquinone (1–6) and 2-(benzylamino)-1,4-naphthoquinone (7), in good yields. All the compounds 1–7 were characterized thoroughly by microanalysis, standard spectroscopy and thermogravimetric methods. The supramolecular structures of 1–4 and 7 were studied by means of single-crystal X-ray diffraction to gauge the influence of substituents that are present on the amine functionality on the association of molecules in the solid state. The study showed that the introduction of various amine N-substituents induces conformational changes that apparently modify the nature and number of donor–acceptor sites for noncovalent interactions, leading to diverse crystal packing patterns. Interestingly, the introduction of 2-(benzylamino)- and 2-(2-pyridylmethylamino)- substituents in 2 and 4 successfully switched on the C–Cl⋯π synthon, which is scarcely seen in the crystal packing of organic molecules. Compounds 1, 2, 4 and 5 fluoresced in the range of 350–620 nm with concomitant Stokes shifts of 81, 131, 141 and 131 nm, respectively, and their cyclic voltammograms evidenced two quasi-reversible single-electron waves. All the compounds (except 5) exhibited their first endothermic peak on the DTA curves without any mass loss due to the phase change, attributable to the melting points of the respective compounds. Remarkably, compound 5 exhibited an enhanced antibacterial activity against S. aureus and proved to be a more potent antibacterial agent than the well-known drug “ciprofloxacin”.

Vacuum-Mediated Single-Crystal-to-Single-Crystal (SCSC) Transformation in Na-MOFs: Rare to Novel Topology and Activation of Nitrogen in Triazole Moieties

We report a rare example of facile in situ synthesis of Na-MOF1 that undergoes vacuum-mediated single-crystal-to-single-crystal (SCSC) transformations from rare parallel polycatenated kgd nets to new and novel 3-periodic 3,3,12-c net topology (named smm1). Further, SCSC transformation of Na-MOF1 to Na-MOF2 reveals activation of N–N atoms in 1,2,3-triazole unit. Na-MOF1 and Na-MOF2 were authenticated by single-crystal X-ray studies, and the bulk was confirmed by powder X-ray diffraction studies.