Chira R. Bhattacharjee

Reactivity of tris(acetylacetonato) iron(III) with tridentate [ONO] donor Schiff base as an access to newer mixed-ligand iron(III) complexes.

Two new mixed-ligand iron(III) complexes, [Fe(L(n))(acac)(C(2)H(5)OH)] incorporating coordinated ethanol from the reaction solvent were accessed from the reaction of [Fe(acac)(3)] with [ONO] donor dibasic tridentate unsymmetrical Schiff base ligands derived from condensation of 2-hydroxy-1-napthaldehyde with 2-aminophenol (H(2)L(1)) or 2-aminobenzoic acid (H(2)L(2)). The thermal study (TGA-DTA) provided evidence for weakly bound ethanol which is readily substituted by neutral N-donor molecule imidazole, benzimidazole or pyridine to produce an array of newer complexes, [Fe(L(n))(acac)X] (n=1, 2; X=Im, Bim, Py). The compounds were characterized by elemental analyses, FT-IR, UV-vis, solution electrical conductivity, FAB mass, (1)H and (13)C NMR spectroscopy. Room temperature magnetic susceptibility measurements (μ(eff)∼5.8 B.M.) are consistent with spin-free octahedral iron(III) complexes. Cyclic voltammetry of ethanol complexes revealed a quasi-reversible one electron redox response (ΔE(p)>100 mV) for the Fe(III)/Fe(II) couple. Low half wave redox potential (E(1/2)) values suggested easy redox susceptibility. The ground state geometries of the ethanol and imidazole complexes have been ascertained to be distorted octahedral by density functional theory using DMol3 program at BLYP/DNP level.

Synthesis, structural characterization, and DFT studies of new mixed-ligand iron(III) Schiff-base complexes

Cationic iron(III) Schiff-base aquo complex of the type [FeL(H2O)2]NO3 (L = C12H18N2O2) was accessed from the interaction of Fe(NO3)3 ⋅ 9H2O with the [N2O2] donor Schiff base. Reaction of the aquated complex with bifluoride , thiocyanate (SCN−), or azide in 1 : 2 molar ratio in methanolic medium led to the synthesis of anionic mixed-ligand complexes, [FeLX2] n − (L = C12H18N2O2, X = F, NCS, N3). The tetradentate Schiff-base ligand was prepared from the condensation of acetylacetone and ethylenediamine following literature method and characterized by spectroscopic and single crystal X-ray diffraction technique. The complexes were characterized using elemental analysis, FT-IR, UV-Vis, mass spectroscopy, and solution electrical conductivity studies. The magnetic susceptibility measurements suggested high-spin Fe(III). The electronic structures of the compounds were analyzed by DFT method using B3LYP/6-31G(d,p) functional and overall, very good agreement between theoretical expectations and experimental data was achieved. The electrochemical behavior of the complexes was examined by cyclic voltammetric method.

Plastic columnar mesomorphism in half-disc-shaped oxovanadium(IV) Schiff base complexes

A new series of non-disc-like oxovanadium(iv) Schiff base complexes of the type [VO((4-C n H2n+1O)2salcn)], where n = 14, 16 or 18 and salcn is N,N ′-bis-salicylidene-1,2-cyclohexadiamine, containing 4-substituted alkoxy tails in the side aromatic rings, have been synthesised and their mesogenic properties investigated. The compounds were characterised by FT–IR, 1H NMR, 13C NMR, UV–Vis and FAB mass spectrometry. The mesomorphic behaviour of the compounds was studied using polarised optical microscopy and differential scanning calorimetry. The molecular organisation in the mesophase was determined by X-ray diffraction. It was found that the ligands did not show mesogenic behaviour, but their complexes exhibited a thermally stable enantiotropic highly ordered three-dimensional plastic mesophase with a columnar structure in the extended temperature range 155–166°C. The clearing temperature of the complexes was found to be lower than in the structurally analogous copper complexes. A density functional theory study was carried out using DMol3 at BLYP/DNP level to obtain a stable optimised structure. A square pyramidal geometry for the vanadyl complexes has been proposed.

Novel non-discoid chiral copper(II)-salen type [N2O2] donor Schiff base complexes with a cyclohexane diamine spacer: synthesis, electrochemistry, columnar mesomorphism and DFT study

A series of new non-discoid chiral copper(ii)-salen type complexes, [Cu((4-C n H2n+1O)2salen)], n = 14, 16, 18 and salen = N,N′-cyclohexane bis (salicylideneiminato), containing 4-substituted alkoxy tails in the side aromatic rings and a cyclohexane spacer, have been prepared and their mesogenic properties investigated. The compounds were characterised by Fourier transform infra-red spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, UV-vis spectroscopy and fast atom bombardment mass spectrometry. Mesomorphic properties of these compounds were studied by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction (XRD). The ligands are non-mesogenic but the complexes exhibited enantiotropic rectangular columnar mesophases (Colr) with extended temperature range (111–220°C). Molecular models for the organisation in the mesophases are proposed on the basis of the small-angle XRD diffraction patterns. Molecules with their planes tilted are stacked in columns which self-organise in a 2D-rectangular lattice with C2mm symmetry. Cyclic voltammetry carried out in CH2Cl2 solution revealed a single electron quasireversible response for the Cu(i)/Cu(ii) redox couple (E 1/2 = –0.226V, ΔE p = 453 mV). The more negative redox potentials indicated a planar coordination environment. Density functional theory calculations performed using the DMol3 program at the BLYP/DNP level revealed a near-square-planar arrangement around the metal centre with the cyclohexane ring tilted relative to the plane of the [N2O2] core of the Schiff base ligand.

Synthesis, characterisation and mesomorphic properties of a homologous series of oxovanadium(iv) complexes containing a bidentate [N,O] donor Schiff base mesogen

A series of oxovanadium(iv) complexes of the type [VO(L)2], [L = N-(4-n-alkoxysalicylaldimine)-4-hexadecyloxyaniline, n = 8, 10, 12, 14, 16 or 18] have been synthesised and characterised by FT–IR, 1H NMR, 13CNMR, UV–Vis, and FAB mass and magnetic susceptibility measurements. The ligands are coordinated to the vanadyl ion in a bidentate fashion. The mesomorphic behaviour of the ligands and their vanadyl complexes was investigated by polarising optical microscopy and differential scanning calorimetry. The compounds were all highly thermally stable, and their mesomorphic properties were found to depend on the length of the carbon chain. Both the ligands and their higher homologue complexes exhibited a SmC mesophase. In the case of the lower homologues the ligands exhibited the SmC phase but their complexes a SmA mesophase. The mesophase–isotropic transition temperatures for the complexes were significantly higher than those of the ligands. Variable temperature magnetic susceptibility measurements on the vanadyl complexes clearly suggested absence of any exchange interactions among the vanadyl spin centres. Cyclic voltammetry showed a quasi-reversible one-electron response at 0.51 V for the VO(iv)–VO(v) redox couple. Density functional theory studies carried out using DMol3 at the BLYP/DNP level to determine the energy-optimised structure revealed a distorted square pyramidal geometry for the vanadyl complexes, with the alkoxy tails projecting away from one another.

Synthesis, electrochemical and antimicrobial studies of mono and binuclear iron(III) and oxovanadium(IV) complexes of [ONO] donor tridentate Schiff-base ligands

Tridentate Schiff bases (H2L1 or H2L2) were derived from condensation of acetylacetone and 2-aminophenol or 2-aminobenzoic acid. Binuclear square pyramidal complexes of the type [M2(L1)2] · nH2O (M = Fe–Cl, n = 0; M = VO, n = 1) were accessed from interaction of H2L1 with anhydrous FeCl3 and VOSO4 · 5H2O, respectively. A similar reaction with H2L2, however, produced mononuclear complexes [ML2(H2O) x ] · nH2O (M=Fe–Cl, x = 0, n = 0; M=VO, x = 1, n = 1). The compounds were characterized using elemental analysis, FT-IR, UV-Vis, and NMR (for ligand only), and mass spectroscopies and solution electrical conductivity studies. Magnetic susceptibility measurements suggest antiferromagnetic exchange in binuclear Fe(III) and VO(IV) complexes. Thermo gravimetric analysis (TGA) provided unambiguous evidence for the presence of coordinated as well as lattice water in [VOL2(H2O)] · H2O. Cyclic voltammetric studies showed well-defined redox processes corresponding to Fe(III)/Fe(II) and VO(V)/VO(IV). In vitro antimicrobial activities of the compounds were investigated against Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeroginosa, Escherichia coli, Bacillus subtilis, and Proteus vulgaris. H2L1 and its binuclear complexes exhibited pronounced activity against all the microorganisms tested.

Influence of spacer group substituent on mesomorphism in copper complexes of ‘salen’ type Schiff bases bearing long alkoxy arm

Novel four-coordinate copper(II) complexes of the type [CuL], L = N, N′-di-(4-hexadecyloxysalicylidene)-4-substituted(X)l,2-diamino-benzene (X = H, CH3, NO2) were synthesised. The compounds were characterised by elemental analyses, Fourier transform infrared spectroscopy, 1H, 13C nuclear magnetic resonance, ultraviolet–visible spectroscopy and fast atom bombardment mass spectrometry. The liquid crystalline properties were ascertained using polarised optical microscopy, differential scanning calorimetry and powder X-ray diffraction technique. The ligands are non-mesomorphic, but the complexes with methyl (CH3) or no substituent on the aromatic spacer showed rectangular columnar (Colr) mesophase and rectangular plastic columnar (Colrp) phase, respectively. An antiparallel dimeric association of half-disc shaped molecule forming a disc-like arrangement in the mesophase is proposed on the basis of X-ray diffraction study. The complex with nitro (NO2) substituent in the spacer linkage decomposes before melting precluding any mesomorphic study. The density functional theory calculations carried out using Gaussian 09 program at B3LYP level revealed distorted square planar geometry around the metal centre. The natural charges and electronic configuration of the atoms of the complexes and free ligand were evaluated by natural bond orbital analysis.

Tunable Emissive Lanthanidomesogen Derived from a Room-Temperature Liquid-Crystalline Schiff-Base Ligand

A novel photoluminescent room-temperature liquid-crystalline salicylaldimine Schiff base with a short alkoxy substituent and a series of lanthanide(III) complexes of the type [Ln(LH)3(NO3)3] (Ln = La, Pr, Sm, Gd, Tb, Dy; LH = (E)-5-(hexyloxy)-2-[{2-(2-hydroxyethylamino)ethylimino]methyl}phenol) have been synthesized and characterized by FTIR, (1)H and (13)C NMR, UV/Vis, and FAB-MS analyses. The ligand coordinates to the metal ions in its zwitterionic form. The thermal behavior of the compounds was investigated by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The ligand exhibits an enantiotropic hexagonal columnar (Col(h)) mesophase at room temperature and the complexes show an enantiotropic lamellar columnar (Col(L)) phase at around 120 °C with high thermal stability. Based on XRD results, different space-filling models have been proposed for the ligand and complexes to account for the columnar mesomorphism. The ligand exhibits intense blue emission both in solution and in the condensed state. The most intense emissions were observed for the samarium and terbium complexes, with the samarium complex glowing with a bright-orange light (ca. 560-644 nm) and the terbium complex emitting green light (ca. 490-622 nm) upon UV irradiation. DFT calculations performed by using the DMol3 program at the BLYP/DNP level of theory revealed a nine-coordinate structure for the lanthanide complexes.

Liquid crystalline dinuclear copper(II) complexes accessed from photoluminescent tridentate [ONO]-donor Schiff base ligands

Two new liquid crystalline dinuclear copper(II) complexes of the type [Cu2L2 n], H2Ln = (E)-5-(hexadecyloxy)-2-((2-hydroxyethylimino) methyl) phenol(L) and (E)-5-(hexadecyloxy)-2-((2-hydroxypropylimino) methyl) phenol (L′), have been synthesised. The compounds were characterised by Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance, ultraviolet-visible spectroscopy, elemental analyses, solution electrical conductivity measurements and fast atom bombardment mass spectrometry. The phase behaviours of the compounds were examined by differential scanning calorimetry and polarised optical microscopy. Interestingly the ligand L showed a monotropic smectic A (SmA) mesophase at ∼75°C while the ligand L′ incorporating a methyl group in the spacer lacks any mesomorphism. The complexes were all found to exhibit a thermally stable enantiotropic SmA phase in the range ∼114–118°C. The ligands are blue light emitters with broad emission maxima at ∼469 nm. The density functional theory calculations revealed a distorted square planar structure around each copper(II) centre in the dinuclear framework.

Emissive ‘zinc(II)-salphen’ core: building block for columnar liquid crystals

A series of half-discoid [N2O2]-donor tetradentate alkoxy substituted salicylaldimine ligands, [N,N′-di- (4-n-alkoxysalicylidene)-4-Cl-l,2-diamino-benzene] (L; n = 12, 14, 16 and 18) have been prepared. The reaction of the ‘salphen’-type Schiff base ligand with Zn(OAc)2.4H2O afforded a series of mononuclear zinc(II) complexes. The ligands and the corresponding zinc(II) complexes were characterised by elemental analysis, Fourier transform infrared, proton nuclear magnetic resonance and ultraviolet-visible spectroscopy. Although the ligands are non-mesogenic, columnar mesomorphism is induced upon complexation with the metal. The p2gg symmetry of the rectangular columnar phase is confirmed by variable temperature powder X-ray diffraction study. Two ‘half-disc’-shaped molecules with four alkoxy legs are presumed to self-assemble via a dimeric interaction filling the space. In contrast to the ligands, the zinc(II) complexes all exhibited moderately intense green emission at room temperature both in solution and in the solid state. Density functional theory calculation, carried out using a DMol3 program, revealed a distorted square planar geometry for the complexes. The mesomorphic and photoluminescence property of the zinc complexes are collated as a function of spacer substituent, as well as alkoxy carbon chain length.