Ruthenium(II) carbonyl complexes containing tridentate Schiff bases

New ruthenium(II) complexes, [Ru(CO)(B)(LL)(PPh₃)] (where, LL = tridentate Schiff bases; B = PPh₃, pyridine, piperidine or morpholine) have been prepared by reacting [RuHCl(CO)(PPh₃)₃] or [RuHCl(CO)(PPh₃)₂(B)] with Schiff bases containing donor groups (O, N, X) viz., salicylaldehyde thiosemicarbazone (X = S), salicylaldehyde semicarbazone (X = O), o-hydroxyacetophenone thiosemicarbazone (X = S) and o-hydroxyacetophenone semicarbazone (X = O). The new complexes were characterised by elemental analysis, spectral (i.r., ¹H- and ³¹P-n.m.r.), data.     

Spin Selectivity in Electron Transfer in Photosystem I

Photosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons’ spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high‐spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300 K and vanishes at temperatures below about 150 K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high‐spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology.     

Effect of terminal N-substitution in 2-oxo-1,2-dihydroquinoline-3-carbaldehyde thiosemicarbazones on the mode of coordination, structure, interaction with protein, radical scavenging and cytotoxic activity of copper(II) complexes

Four 2-oxo-1,2-dihydroquinoline-3-carbaldehyde N-substituted thiosemicarbazone ligands (H(2)-OQtsc-R, where R = H, Me, Et or Ph) and their corresponding new copper(II) complexes [CuCl(2)(H(2)-OQtsc-H)]·2H(2)O (1), [CuCl(2)(H(2)-OQtsc-Me)]·2H(2)O (2), [CuCl(2)(H(2)-OQtsc-Et)(CH(3)OH)]Cl (3) and [CuCl(H-OQtsc-Ph)]·CH(3)OH (4) have been synthesized in order to correlate the effect of terminal N-substitution on coordination behaviour, structure and biological activity. Single crystal X-ray diffraction studies revealed that the complexes 1, 2 and 3 have square pyramidal geometry around the central metal ion. In the complexes 1 and 2, the copper ion is coordinated by the ligand with ONS donor atoms, one chloride ion in apical position and the other chloride in the basal plane. Complex 3 consists of [CuCl(2)(H(2)-OQtsc-Et)(CH(3)OH)](+) cation and a chloride as counter ion. The copper ion is coordinated by the ligand with ONS donor atoms and by one chloride ion in the basal plane. One methanol molecule is bonded through its neutral oxygen in the apical position. Complex 4 is square planar with the ligand coordinating through uni-negative tridentate ONS(-) and by one chloride ion in the basal plane. The binding of complexes with lysozyme protein was carried out by fluorescence spectroscopy. Investigations of antioxidation properties showed that all the copper(II) complexes have strong radical scavenging properties. The cytotoxicity of the complexes 3 and 4 against NIH 3T3 and HeLa cell lines showed that synergy between the metal and ligands results in a significant enhancement in the cell death with IC(50) of ~10-40 μM. A size dependence of substitution at terminal N in the thiosemicarbazones on the biological activities of the complexes has been observed.     

Room temperature conductance switching in a molecular iron(iii) spin crossover junction

Herein, we report the first room temperature switchable Fe(iii) molecular spin crossover (SCO) tunnel junction. The junction is constructed from [Fe^III(qsal-I)₂]NTf₂ (qsal-I = 4-iodo-2-[(8-quinolylimino)methyl]phenolate) molecules self-assembled on graphene surfaces with conductance switching of one order of magnitude associated with the high and low spin states of the SCO complex. Normalized conductance analysis of the current–voltage characteristics as a function of temperature reveals that charge transport across the SCO molecule is dominated by coherent tunnelling. Temperature-dependent X-ray absorption spectroscopy and density functional theory confirm the SCO complex retains its SCO functionality on the surface implying that van der Waals molecule—electrode interfaces provide a good trade-off between junction stability while retaining SCO switching capability. These results provide new insights and may aid in the design of other types of molecular devices based on SCO compounds.

Herein, we report the first room temperature switchable Fe(iii) molecular spin crossover (SCO) tunnel junction.     

Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity

The reactions of ruthenium(II) complexes, [RuHCl(CO)(PPh₃)₂(B)] [B = PPh₃, pyridine (py) or piperidine (pip)], with bidentate Schiff base ligands derived by condensing salicylaldehyde with aniline, o-, m- or p-toluidine have been carried out. The products were characterised by analytical, i.r., electronic, ¹H-n.m.r. and ³¹P-n.m.r. spectral studies and are formulated as [RuCl(CO)(L)(PPh₃)(B)] (L = Schiff base anion; B = PPh₃, py or pip). An octahedral structure has been tentatively proposed for the new complexes. The Schiff bases and the new complexes were tested in vitro to evaluate their activity against the fungus Aspergillus flavus.     

Anthrone-spirolactam and quinoline hybrid based sensor for selective fluorescent detection of Fe3+ ions

The synthesis of a novel, and highly selective Fe³⁺ ion sensor based on anthrone-spirolactam and its quinoline hybrid ligand is reported. The designed ligand displayed selective detection of Fe³⁺ ions with enhanced fluorescence emission. The complexation of Fe³⁺ ion led to a red shift of 32 nm from 420 nm to 452 nm, and a several fold increase in intensity with fluorescent green emission. The complexation (detection) of Fe³⁺ ions with ligand resulted in chelation enhanced fluorescence and intramolecular charge transfer through the inhibition of C=N isomerization. This hybrid sensor shows high sensitivity and selectivity, spontaneous response, and works on a wide pH range a minimum detection limit of 6.83 × 10⁻⁸ M. Importantly, the sensor works through the fluorescence turn-on mechanism that overcomes the paramagnetic effect of Fe³⁺ ions. The binding mechanism between the ligand and the Fe³⁺ ions was established from the Job's plot method, optical studies, Fourier transfor infrared spectroscopy, NMR titration, fluorescence life-time studies, and density functional theory optimization. The sensor displayed excellent results in the quantification of Fe³⁺ ions from real water samples. Furthermore, due to its biocompatibility nature, fluorescent spotting of Fe³⁺ ions in live cells revealed its bioimaging applications.     

Synthesis, characterization, and detailed electrochemistry of binuclear ruthenium(III) complexes bridged by bisacetylacetonate. Crystal and molecular structures of [[Ru(acac)2]2(tae)] (acac = 2,4-pentanedionate ion, tae = 1,1,2,2-tetraacetylethanate dianion)

Binuclear beta-diketonatoruthenium(III) complexes [[Ru(acac)(2)](2)(tae)], [[Ru(phpa)(2)](2)(tae)], and [(acac)(2)Ru(tae)Ru(phpa)(2)] and binuclear and mononuclear bipyridine complexes [[Ru(bpy)(2)](2)(tae)](PF(6))(2) and [Ru(bpy)(2)(Htae)]PF(6) (acac = 2,4-pentanedionate ion, phpa = 2,2,6,6-tetramethyl-3,5-heptanedionate ion, tae = 1,1,2,2-tetraacetylethanate dianion, and bpy = 2,2'-bipyridine) were synthesized. The new complexes have been characterized by (1)H NMR, MS, and electronic spectral data. Crystal and molecular structures of [[Ru(acac)(2)](2)(tae)] have been solved by single-crystal X-ray diffraction studies. Crystal data for the meso isomer of [[Ru(acac)(2)](2)(tae)] have been confirmed by the dihedral angle result that two acetylacetone units of the bridging tae ligand are almost perpendicular to one another. A detailed investigation on the electrochemistry of the binuclear complexes has been carried out. The electrochemical behavior details of the binuclear complexes have been compared with those of the mononuclear complexes obtained from the half-structures of the corresponding binuclear complexes. Studies on the effects of solvents on the mixed-valence states of Ru(II)-Ru(III) and Ru(III)-Ru(IV) complexes have been carried out by various voltammetric and electrospectroscopic techniques. A correlation between the comproportionation constant (K(c)) and the donor number of the solvent has been obtained. The K(c) values for the binuclear complexes have been found to be low because of the fact that two acetylacetone units of the bridging tae ligand are not in the same plane, as revealed by the crystal structure of [[Ru(acac)(2)](2)(tae)].     

Bithiophene triarylborane dyad: An efficient material for the selective detection of CN− and F− ions

A new fluorescent chemosensor based on bithiophene coupled dimesitylborane (BMB-1) was synthesized and characterized. BMB-1 was used for colorimetric and turn-on fluorescent sensing of cyanide (CN⁻) and fluoride (F⁻) ions, in the presence of other competitive anions in an aqueous (CH₃CN–H₂O) medium. BMB-1 showed a hypsochromic shift (blue shift) with addition of CN⁻ and F⁻ ions in absorption studies. The lower detection level of CN⁻ and F⁻ ions is 1.37 × 10⁻⁹ and 1.75 × 10⁻⁹ M, respectively. The BMB-1 binding mechanism is based on the nucleophilic addition of CN⁻ and F⁻ ions in the internal charge transfer transition of bithio moiety to the boranylmesitylene unit, and the color changes were observed under UV light. This result is further confirmed by Fourier transform infrared spectroscopy, mass spectrometry and density functional theory calculations. Also, the BMB-1 probe is found to be a good adsorbent for the removal of F⁻ ions in real water samples using the adsorption technique.     

New Ru(II)–dmso complexes with heterocyclic hydrazone ligands towards cancer chemotherapy

The synthesis and characterization of ruthenium(II) complexes, [RuCl₂(dmso)₂(bfmh)] (1; dmso = dimethyl sulfoxide, bfmh = benzoic acid furan-2-ylmethylene-hydrazide), [RuCl₂(dmso)₂(btmh)](2; btmh = benzoic acid thiophen-2-ylmethylene-hydrazide), [RuCl₂(dmso)₂(bfeh)](3; bfeh = benzoic acid (1-furan-2-yl-ethylidene)-hydrazide) and [RuCl₂(dmso)₂(bpeh)](4; bpeh = benzoic acid (1-pyridin-2-yl-ethylidene)-hydrazide) are described. The ligands, when treated with either cis-[RuCl₂(dmso)₄] or trans(Cl)–[RuCl₂(dmso)₂(bpy)], resulted in the same products. This has been confirmed by IR spectra and single crystal X-ray diffraction studies. The redox behaviors of the complexes have been found to be strongly dependent on the electronic nature of the moieties present in the hydrazone ligands. The binding of the complexes to Herring sperm DNA has been studied by absorption titration and cyclic voltammetry. But, due to the random change in the absorption on the addition of DNA, only a qualitative result rather than a quantitative result has been obtained. All the complexes have been found to bind DNA through different modes to different extents. The antibacterial properties of the ligands and the complexes have been studied against five pathogenic bacteria and also the minimum inhibitory concentrations (MIC) of all the ligands and complexes 2 and 4 have been evaluated.     

Hydrolytic cleavage of Schiff bases by [RuCl2(DMSO)4]

New hexa-coordinated Ru(II) complexes of the type [RuCl₂(DMSO)₂(diamine)] (diamine = o-phenylenediamine and ethylenediamine) have been prepared by reacting cis-[RuCl₂(DMSO)₄] with Schiff bases (H₂sal-en, 1; H₂nap-en, 2; H₂sal-o-pdn, 3; H₂nap-o-pdn, 4) in a 1:1 ratio. The ligands, which were expected to act as tetradentate (N₂O₂) chelates under the normal reaction conditions, were found to undergo hydrolytic cleavage to form the diamine and the corresponding aldehyde. All the complexes have been characterized by analytical and spectroscopic (IR, electronic and¹H NMR) data. Single-crystal X-ray analysis of the complex [RuCl₂(DMSO)₂(o-pndn)] revealed that the coordination environment around the ruthenium metal consists of a N₂S₂Cl₂ octahedron.