Spectroscopic and theoretical studies on cobalt(II) complex of maleonitriledithiolate and 5-nitro-1,10-phenanthroline

The molecular structure, electronic and infrared spectroscopic properties for the title complex Co(mnt)(5-NO2-phen) (mnt2-=maleonitriledithiolate, 5-NO2-phen=5-nitro-1,10-phenanthroline) were studied in this paper. With semi-empirical PM3 and non-empirical density functional theory (DFT) methods, the gaseous molecular geometry of the complex was optimized and corresponding vibrational spectra was obtained. The calculated results of structure and frequency from DFT were more reasonable than those from PM3, and the two methods were both agreed with the experimental values. A complete assignment to the IR spectra of such a complicated molecule has been exhibited. An electronic spectra was calculated by ZINDOS/S method. The results showed that the calculated values agreed with the observed ones.     

Spectroscopic and theoretical studies on cobalt (II) complex of maleonitriledithiolate and 5-nitro-1,10-phenanthroline

The molecular structure, electronic and infrared spectroscopic properties of the title complex Co(mnt)(5-NO(2)-phen) (mnt(2-) = maleonitriledithiolate, 5-NO(2)-phen = 5-nitro-1,10-phenanthroline) were studied in this paper. With non-empirical density functional theory (DFT) methods, the gaseous molecular geometry of the complex was optimized and corresponding vibrational spectra was obtained. A complete assignment to the IR spectra of such a complicated molecule has been exhibited. And the established scientific method could give a complete and accurate analysis about the vibrational spectra of this complex. An electronic spectra was calculated by ZINDOS/S method. The results showed that the calculated values agreed with the observed ones.     

Infrared and electronic spectra of copper (II) complex of maleonitriledithiolate and 4,4'-dimethyl-2, 2'-bipyridine and their theoretical studies

The molecular structure and binding, as well as infrared and electronic spectroscopic properties for the title complex Cu(mnt)(dmbpy)(mnt(2-)=maleonitriledithiolate, dmbpy=4,4'-dimethyl-2,2'-bipyridine) were studied in this paper. With semi-empirical PM3 and non-empirical DFT (B3LYP/6-311G*) methods, the molecular geometry of the complex was optimized and corresponding vibrational spectra in the gaseous state were obtained. The calculated results derived from DFT were more reasonable than those from PM3. The point group of Cu(mnt)(dmbpy) in isolated gaseous state was C(2), in which Cu(II) adopted a distorted tetrahedral geometry and the dihedral angle between the N(2)Cu and S(2)Cu planes was about 29.814 degrees. And a complete assignment to the IR spectra of such a complicated molecule was exhibited. With ZINDO/S method an electronic spectrum was calculated. The results showed that the calculated values generally agreed with the observed ones. And a detailed explain was made on its electronic spectra.     

Spectroscopic and thermodynamic studies on solvatochromic nickel(II) complexes

Summary The solvatochromic and thermochromic behaviour of a series of mixed Ni(II) complexes with unsubstituted and substituted -diketones and diamines in the solvents 1,2-dichloroethane (DCE), acetonitrile (An), acetone (AC),n-butanol (n-BuOH), formamide (FA), N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and pyridine (PY) has been studied and characterized on the basis of electronic spectra. Spectrophotometric methods have been used to evaluate equilibrium constants and their enthalpic and entropic terms for the formation of Ni(-dik)(diam)L ⁺ and Ni(-dik)(diam)L ₂ ⁺ . Increasing donor strength of the donor-solvents (L) and (or) increasing electronwithdrawing parameters of the substituents at the -diketone and the diamine ligands lead to increasing formation constants, paralleled by relative increase in the stability of the five-coordinated species Ni(-dik)(diam)L ⁺. The results are discussed in terms of the extended donor-acceptor concept.On leave of absence from the Faculty of Education, Ain Schams University, Roxy, Cairo, Egypt     

Spectroscopic studies on some complexes of nickel(II) and palladium(II) with thiosemicarbazides

Summary The electronic absorption spectra of the complexes M(L)Cl₂ and M(L)₂Cl₂ [M=Ni^II or Pd^II; L=thiosemicarbazide (tsc), 1-phenylthiosemicarbazide (1-phtsc), or 4-phenylthiosemicarbazide (4-phtsc)] were investigated in a number of solvents. The complexes Ni(tsc)Cl₂, Ni(tsc)₂Cl₂, Ni(4-phtsc)Cl₂ and Ni(4-phtsc)₂Cl₂ exist in a distorted O_h geometry when dissolved in any of the solvents used. On the other hand, the complex Ni(1-phtsc)₂Cl₂, although weakly paramagnetic, proved to be planar. Theoretical and experimental results proved that the complex has neither O_h nor T_d geometry. Molecular orbital calculations were performed on some selected complex ions assuming a local point group symmetry of D_2h.     

Acid-Base Properties of the Ground and Excited States of Ruthenium(II) Bis(2,2'-bipyridine) 3-Carboxyl-2,2'-bipyridine

Acid-base properties for ruthenium(II) bis(2,2'-bipyridine) 3-carboxyl-2,2'-bipyridine reveal a ground state pK(a) of 0.82 +/- 0.07 and an excited state pK(a) of 2.31 +/- 0.05, a 1.5 pH unit increase from the ground state. The excited state pK(a) is temperature independent while the ground state pK(a)(0) increases with temperature and has DeltaH(0) and DeltaS(0) values of -990 +/- 149 cm(-)(1) and -4.57 +/- 0.48 cm(-)(1) K(-)(1), respectively. The acidic form of the complex emits at lower energy than the basic form at both 296 and 77 K. The emission energy maxima are solvent dependent and decrease in energy when the solvent changes from 4:1 (v/v) 2-MeTHF-CH(2)Cl(2) to water and when the pH decreases. Changes in excited state lifetimes with emission energy follow the energy gap law with an intercept of 49 +/- 1 and a slope of (2.11 +/- 0.09) x 10(-)(3). Emission quantum yields for protonated and deprotonated species in 4:1 (v/v) 2-MeTHF-CH(2)Cl(2) are 0.023 +/- 0.001 and 0.110 +/- 0.002, respectively. The temperature dependence of the emission lifetimes gives energy barriers of 270 cm(-)(1) for the complex in aqueous solution at pH -0.5, and 990 cm(-)(1) in aqueous solution at pH 4.5, and 1920 cm(-)(1) in 4:1 (v/v) 2-MeTHF-CH(2)Cl(2.)     

Synthesis and spectroscopic studies on chromium(III) complex containing mixed-valence chrysenesemiquinone-chrysenecatecholate ligands and 2,2'-bipyridine coligand

The synthesis and spectroscopic properties of Cr(bpy)(chrySQ)(chryCat), a complex containing chromium(III) metal ion and chrysenequinone ligand in its partially reduced (chrySQ) and fully reduced (chryCat) forms, are described. The complex has been prepared by two different routes from Cr(CO)6 and Cr(chrySQ)3. Variable temperature magnetic susceptibility measurements indicated a strong antiferromagnetic coupling between Cr(III) (S=3/2) and chrysenesemiquinone radical (S=1/2), giving a magnetic coupling constant J=-342 cm(-1). Ligand-based redox couples were observed in the electrochemical studies that consist of quasi-reversible chrySQ/chryCat and bpy/bpy*- reductions and chryCat/chrySQ oxidation at negative potentials and irreversible chrySQ/chryBQ oxidation at positive potential. However, the metal was inert in the studied potential range. The electronic spectra of the complex revealed interesting properties. In addition to interaligand pi-pi* and n-pi* transitions, other bands corresponding to Cr(t(2g))-->chrySQ(pi*) and Cr(t(2g))-->bpy(pi*) metal-to-ligand charge-transfer MLCT transitions were observed. The infrared spectral analysis was informative in assigning the vibrations due to SQ and Cat ligands. Also, it was a useful tool in confirming the coordination of bpy ligand to chromium metal ion.     

A fluorescent chemosensor for copper(II) based on a carboxylic acid-functionalized tris(2,2'-bipyridine)-ruthenium(II) complex.

In this research, bis(2,2'-bipyridine)(4-methyl-2,2'-bipyridine-4'-carboxylic acid)ruthenium(II).2PF(6)- complex (1), was first used as a fluorescent chemosensor to recognize Cu(II) in EtOH/H(2)O (1:1, v/v) solution. The response of the sensor is based on the fluorescence quenching of complex 1 by binding with Cu(II). The analytical performance characteristics of the proposed Cu(II)-sensitive chemosensor were investigated. The sensor can be applied to the quantification of Cu(II) with a linear range covering from 5.0 x 10(-8) to 1.0 x 10(-4) M and a detection limit of 4.2 x 10(-8) M. The experiment results show that the response behavior of 1 to Cu(II) is pH independent in medium condition (pH 4.0 - 8.0), and show excellent selectivity for Cu(II) over other transition metal cations.     

Spectroscopic, thermal and electrochemical studies on some nickel(II) thiosemicarbazone complexes

Several complexes of thiosemicarbazone derivatives with Ni(II) have been prepared. Structural investigation of the ligands and their complexes has been made based on elemental analysis, magnetic moment, spectral (UV-Vis, i.r., (1)H NMR, ms), and thermal studies. The i.r. spectra suggest the bidentate mononegative and tridentate (neutral, mono-, and binegative) behavior of the ligands. Different stereochemistries were suggested for the isolated complexes. The thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used to study the thermal decomposition and kinetic parameters of some ligands and complexes using the Coats-Redfern and Horowitz-Metzger equations. The redox properties and stability of the complexes toward oxidation waves explored by cyclic voltammetry are related to the electron withdrawing or releasing ability of the substituent of thiosemicarbazone moiety. The samples displayed Ni(II)/Ni(I) couples irreversible waves associated with Ni(III)/Ni(II) process.     

Spectroscopic and biological studies on newly synthesized nickel(II) complexes of semicarbazones and thiosemicarbazones

Nickel(II) complexes, having the general composition Ni(L)2X2, have been synthesized [where L: isopropyl methyl ketone semicarbazone (LLA), isopropyl methyl ketone thiosemicarbazone (LLB), 4-aminoacetophenone semicarbazone (LLC) and 4-aminoacetophenone thiosemicarbazone (LLD) and X=Cl-, 1/2SO(4)2-]. All the Ni(II) complexes reported here have been characterized by elemental analyses, magnetic moments, IR, electronic and mass spectral studies. All the complexes were found to have magnetic moments corresponding to two unpaired electrons. The possible geometries of the complexes were assigned on the basis of electronic and infrared spectral studies. Newly synthesized ligand and its nickel(II) complexes have been screened against different bacterial and fungal growth.     

Spectroscopic studies on polymeric cobalt(II) and nickel(II) complexes with bridging succinonitrile and succinonitrile isotopomer ligands

A series of cobalt(II) and nickel(II) complexes were synthesized using succinonitrile and its [1,4-13C2], [15N2]-, [2,2,3,3-2H4]- and [1,4-13C,-2,2,3,3-2H4]- isotopomers as bridging ligands. Spectroscopic studies, as well as X-ray powder diffraction profiles, were used to identify the nature of the octahedral coordination sphere of the central metal ions and to assign the vibrational spectra in full detail. The succinonitrile ligands were found to be in trans configuration in all the complexes studied and to be coordinated via the lone pairs of their nitrile nitrogens. The rule of mutual exclusion was found to be fulfilled for the succinonitrile ligands under the Ci symmetry of the complexes and the vibrations of the succinonitrile ligands were found to appear in either the infrared or the Raman spectra. All succinonitrile isotopomers exhibited blue-shifts of 43-71 cm(-1) upon coordination, while most of the other vibrations remained unchanged or underwent small shifts of only a few wavenumbers. The mass differences of the succinonitrile isotopomers were found to shift mainly the vibrations of the respective affected part of the molecules in comparison with the normal succinonitrile. The exchange of the halides, which are coordinated to the central metal ion, was also found to influence the vibrations of the associated water molecules and we could identify vibrational bands arising due to the H-bond interaction between the halides and the water molecules. Finally, we showed that all complexes under consideration have, spectroscopically, the same symmetry.