Synthesis, characterization, X-ray crystal structure, luminescence, electrochemical and solvatochromism studies of new dimer of nickel and palladium complexes containing ferrocenyl imine ligand

A novel type of organometallic 2-R-2,4-dihydro-1H-3,1-benzoxazine with R = [M(η5-C5H4)(CO)3] (M = Re or Mn) units. Experimental and computational studies of the effect of substituent R on ring-chain tautomerism

Novel 2-cyrhetrenyl and cymantrenyl-2,4-dihydro-1H-3,1-benzoxazines.

Structural and spectroscopic characterization of a new luminescent NiII complex: bis{2,4-dichloro-6-[(2-hydroxypropyl)iminomethyl]phenolato-κ3O,N,O'}nickel(II)

The design and preparation of transition-metal complexes with Schiff base ligands are of interest due to their potential applications in the fields of molecular magnetism, nonlinear optics, dye-sensitized solar cells (DSSCs), sensing and photoluminescence. Luminescent metal complexes have been suggested as potential phosphors in electroluminescent devices. A new luminescent nickel(II) complex, [Ni(C₁₀H₁₀Cl₂NO₂)₂], has been synthesized and characterized by single-crystal X-ray diffraction and elemental analysis, UV-Vis, FT-IR, ¹H NMR, ¹³C NMR and photoluminescence spectroscopies, and LC-MS/MS. Molecules of the complex in the crystals lie on special positions, on crystallographic binary rotation axes. The Ni^II atoms are six-coordinated by two phenolate O, two imine N and two hydroxy O atoms from two tridentate Schiff base 2,4-dichloro-6-[(2-hydroxypropyl)iminomethyl]phenolate ligands, forming an elongated octahedral geometry. Furthermore, the complex exhibits a strong green luminescence emission in the solid state at room temperature, as can be seen from the (CIE) chromaticity diagram, and hence the complex may be a promising green OLED (organic light-emitting diode) in the development of electroluminescent materials for flat-panel-display applications.

Steric Enforcement about One Thiolate Donor Leads to New Oxidation Chemistry in a NiSOD Model Complex

Ni-containing superoxide dismutase (NiSOD) represents an unusual member of the SOD family due to the presence of oxygen-sensitive Ni-SCys bonds at its active site. Reported in this account is the synthesis and properties of the Ni^II complex of the N₃S₂ ligand [N₃S₂^Me2]^3- ([N₃S₂^Me2]^3- = deprotonated form of 2-((2-mercapto-2-methylpropyl)(pyridin-2-ylmethyl)amino)-N-(2-mercaptoethyl)acetamide), namely Na[Ni(N₃S₂^Me2)] (2), as a NiSOD model that features sterically robust gem-(CH₃)₂ groups on the thiolate α-C positioned trans to the carboxamide. The crystal structure of 2, coupled with spectroscopic measurements from ¹H NMR, X-ray absorption, IR, UV-vis, and mass spectrometry (MS), reveal a planar Ni^II (S = 0) ion coordinated by only the N₂S₂ basal donors of the N₃S₂ ligand. While the structure and spectroscopic properties of 2 resemble those of NiSOD_red and other models, the asymmetric S ligands open up new reaction paths upon chemical oxidation. One unusual oxidation product is the planar Ni^II-N₃S complex [Ni(L^ox)] (5; L^ox = 2-(5,5-dimethyl-2-(pyridin-2-yl)thiazolidin-3-yl)-N-(2-mercaptoethyl)acetamide), where two-electron oxidation takes place at the substituted thiolate and py-CH₂ carbon to generate a thiazolidine heterocycle. Electrochemical measurements of 2 reveal irreversible events wholly consistent with thiolate redox, which were identified by comparison to the Zn^II complex Na[Zn(N₃S₂^Me2)] (3). Although no reaction is observed between 2 and azide, reaction of 2 with superoxide produces multiple products on the basis of UV-vis and MS data, one of which is 5. Density functional theory (DFT) computations suggest that the HOMO in 2 is π* with primary contributions from Ni-dπ/S-pπ orbitals. These contributions can be modulated and biased toward Ni when electron-withdrawing groups are placed on the thiolate α-C. Analysis of the oxidized five-coordinate species 2^ox* by DFT reveal a singly occupied spin-up (α) MO that is largely thiolate based, which supports the proposed Ni^III-thiolate/Ni^II-thiyl radical intermediates that ultimately yield 5 and other products.

Comparative study of an osazone based ligand and its palladium(II) complex with human serum albumin: A spectroscopic, thermodynamic and molecular docking approach

An osazone based ligand, hexane-3,4-dione-bis(2'-phenylhydrazone) (LH₂), was synthesized by 1:2M Schiff base condensation of 3,4-hexanedione and phenylhydrazine in dehydrated methanol. Its palladium(II) complex (1) has also been synthesized. LH₂ and 1 have thoroughly been characterized by several spectroscopic and analytical means. DFT optimized structure of 1 shows that it is a monomeric Pd(II) complex having 'N₂Cl₂' coordination chromophore. Our BVS analysis also satisfactorily reproduces the oxidation number of the palladium center. 1 shows irreversible Pd(II)/Pd(I) reduction in its CV in methanol. 1 is three-fold more emissive than LH₂. This enhanced emission has also been supported by time correlated single photon counting (TCSPC) measurements at room temperature. Human serum albumin (HSA) binding aspects of both LH₂ and 1 have been investigated through various biophysical techniques. The binding constants as determined from Benesi-Hilderbrand plot using the absorbance spectral analyses were found respectively to be 1.18×10⁵ and 4.38×10⁴M^-1 for LH₂ and 1. The experimental findings confirm that both are good HSA binders. The thermodynamic parameters (∆G°, ∆H° and ∆S°) have also been evaluated by isothermal titration calorimetric (ITC) experiments. These parameters indicate that the binding processes are spontaneous both for LH₂ and 1. Molecular docking analyses reveal that both LH₂ and 1 reside in domain-I of HSA.