• KISHALAY BHAR

Articles written in Journal of Chemical Sciences

• Syntheses, molecular and crystalline architectures, and luminescence behaviour of terephthalate bridged heptacoordinated dinuclear lead(II) complexes containing a pentadentate N-donor Schiff base

One-pot synthesis using a 2:2:1:2 molar ratio of Pb(OAc)2·3H2O, L, piperidinum terephthalate (ptp) and NaClO4/NH4PF6 at room temperature affords two dinuclear compounds of the type [Pb2(L)2(𝜇- tp)](ClO4/PF6)2 (1/2) [L=N,N'-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine and tp = terephthalate dianion]. The compounds are characterized by microanalytical, spectroscopic, thermal and other physicochemical results. X-ray structural analyses of 1 and 2 reveal that each heptacoordinated lead(II) centre with a PbN5O2 chromophore are bound by five N atoms of L and connected through O atoms of a bis(bidentate) tp bridge. The arrangements of L and tp suggest a gap around the metal centre due to occupation of a stereo-active lone pair of electrons reflecting a hemidirected coordination around the metal centre. The complexes exhibit reasonable thermal stabilities with the tolerate temperatures ca. 255°C for 1 and 263°C for 2. The complexes display intraligand ($\pi-\pi^\ast$) fluorescence in the solid state and in DMF solutions at room temperature.

• Synthesis, molecular and crystalline architectures, and properties of a mononuclear complex [CoII (benzidine)2(NCS)2(OH2)2]

One mononuclear cobalt(II) compound of the type [Co(bnzd)2(NCS)2(OH2)2] (1) (bnzd = benzidine) has been isolated through a single-pot reaction of the molecular building components in MeOH-H2O solvent mixture at room temperature and characterized by physico-chemical and spectroscopic methods. The crystal structure of complex 1 has an octahedral geometry with trans, trans, trans orientations in the order (N$^a$,N$^a$), (N$^t$,N$^t$), (O$^w$,O$^w$) [N$^a$ = N(amine), N$^t$ = N(thiocyanate) and O$^w$ = O(water)]. In crystalline state, individual units of 1 are associated by weak cooperative O-H…N, O-H…S and N-H…S hydrogen bonds resulting in a 3D network structure. The compound is redox active and shows luminescence in MeOH solution. Thermal decomposition pattern of 1 reveals the presence of two coordinated water molecules. Variabletemperature magnetic susceptibility measurement shows significant orbital contribution and numerical matrix diagonalization method gives the best fit parameters: 𝛼 = Ak = 1.43; 𝜆 = −130 cm-1; 𝛥 = −864 cm-1; TIP = 0.000975; R = $1.19 \times 10^{−4}$.

• Syntheses, structures and properties of two dinuclear mercury(II) iodide compounds containing tetradentate tripodal amine/pentadentate N-donor Schiff base: Control of molecular and crystalline architectures by varying ligand matrices

Two dinuclear mercury(II) iodide complexes of the types [(L1)Hg(𝜇-I)HgI3] (1) and [Hg2(L2) (I)4]·H2O (2) [L1 = tris(2-aminoethyl)amine and L2 = N,N'-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine] have been synthesized and characterized usingmicroanalytical, spectroscopic, thermal and other physicochemical results. Structures of both the compounds are solved by X-ray diffraction measurements. Structural analyses show that one mercury (II) centre in 1 adopts a distorted tetrahedral geometry with an HgI4 chromophore surrounded by four iodides, while the other has a distorted trigonal bipyramidal environment with an HgN4I chromophore bound by four N atoms of L1 and one bridging iodide. Pentadentate Schiff base (L2) in 2 shows unusual binucleating bis(bidentate) behaviour to bind two different mercury(II) centres—Hg1 with an HgN3I2 chromophore in a distorted square pyramidal geometry and Hg2 with an HgN2I2 chromophore in a tetrahedral environment. Weak intermolecularN-H…I hydrogen bonds in 1 and cooperative C-H$\ldots$𝜋 and $\pi\ldots \pi$ interactions in 2 promote dimensionalities. The Schiff base complex, 2, shows intraligand ($\pi-\pi^\ast$) fluorescence in DMF solution at room temperature, whereas compound 1 containing tripodal amine is fluorescent-inactive.

• An anti-ferromagnetic terephthalate-bridged trigonal prismatic dinuclear manganese(II) complex: Synthon of rare anion$^{\ldots} \pi$ interaction promoting dimensionality

A dinuclear compound [Mn2(L)2(𝜇-tp)](PF6)2·3.57H2O (1) [L = N,N′-(bis(pyridin-2-yl)benzylidene)-1,3-propanediamine and tp = terephthalate dianion] has been isolated and characterized on the basis of microanalytical, spectroscopic and other physicochemical properties. X-ray structural study showed interesting bis(bidentate) bridging motif of tp in the dicationic dinuclear unit [Mn2(𝜇-tp)]2+. Each manganese(II) centre adopts a rare distorted trigonal prismatic geometry with an MnN4O2 chromophore.Chelation of the tetradentate Schiff base (L) along with bis(bidentate) bridging of two O atoms of tp complete hexacoordination around each manganese(II) centre. The dinuclear units of 1 are associated through cooperative C-H$\cdots$F hydrogen bonds and $\pi^{\cdot} \pi$, C-H$^{\cdots} \pi$ and rare anion$^{\cdots} \pi$ interactions to promote the dimensionality in a graded manner. Variable temperature magnetic susceptibility measurement of 1 in the 2-300 K temperature range revealed weak antiferromagnetic interaction presumably due to long bridging arm of tp.

• Synthesis and characterization of phenoxo-bridged dinuclear zinc(II) halide complexes: Role of electron withdrawing group on phosphatase activity

Three phenoxo-bridged dinuclear zinc(II) halide complexes [Zn(L2)(X)]2 (X = Cl, Br, I) were isolated from a reduced Schiff base [HL2 = 2-(((2-(dimethylamino)ethyl)amino)methyl)-4-nitrophenol]. Ligand and complexes were characterized using different physico-chemical and spectroscopic methods. Structural study confirms that [Zn(L2)(Cl)] 2 contains a discrete dinuclear unit where two zinc(II) ions are bridged by the two phenoxo oxygen atoms of the deprotonated ligand (L2). The complex adopts a rare cis-orientation with respect to chloride ions. The rate of hydrolysis of 4-NPP ((4-nitrophenyl)phosphatehexahydrate) in the presence of zinc(II) complexes was measured by initial rate method giving kcat values in the order I > Cl > Br and mechanistic pathway was monitored using ESI-mass spectroscopy. It is worth mentioning that presence of an electron withdrawing − NO2 group in HL2 eventually increases the Lewis acidity of zinc(II) which in turn reduces the nucleophilic character of metal bound water molecule in the intermediate state causing an overall decrease in the rate of hydrolysis of 4-NPP as compared to our previous work with HL1 (2-((2-(dimethylamino)ethylamino)methyl)phenol).

• Synthesis, structure and solid-state electrical conductivity of bis(1,2-diphenylethylene-1,2-dithiolate)nickel(II)

One nickel(II)-dithiolene complex bis(1,2-diphenylethylene-1,2-dithiolate)nickel(II) has been synthesized and crystallographically characterized. The complex is square planar at its metal centre. The compound in its solid-state is found to conduct electricity at room temperature. Variation of conduction is also found on raising the temperature. Instead of a metal…metal orbital overlap, the electron density is expected here to pass through some other covalent and electrostatic bonds of the compound in solid-state resulting in electricity conduction.

• # Journal of Chemical Sciences

Volume 135, 2023
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Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019