Thermal and spectroscopic studies of terbium(III) and dysprosium(III) complexes with piperidin-4-ones

Terbium(III) and dysprosium(III) nitrate complexes with variously substituted 2,6-diphenylpiperidin-4-ones (L¹)-(L¹⁰) of general formula [Ln(L)(NO₃)₂(H₂O)₂]NO₃ have been synthesized. These complexes have been characterized by analytical, spectral and thermal studies. Molar conductance data show that these complexes are 1:1 electrolytes. The presence of two coordinated water molecules is confirmed by thermal and infrared spectral studies. IR spectral data indicate that piperidin-4-ones, in spite of having two coordinating sites, are monodentate, coordinating only through ring nitrogen. The IR and conductance data reveal the presence of two bidentate and one ionic nitrate groups. The nephelauxetic ratio (β), covalency factor (b^1/2) and Sinha’s parameter (δ) evaluated from electronic spectral data of dysprosium(III) complexes indicate a little covalency in metal-ligand bonding.     

Cobalt(II) complexes with hydantoin

Complexes of Co(II) with hydantoin (L, C₃H₄N₂O₂) have been synthesized. The complexes had the following compositions: [CoL₂(OH₂)₂](NO₃)₂ · 2H₂O, [CoL₂(OH₂)₂]Cl₂ · 3H₂O, and [CoL₂(OH₂)₂]SO₄ · 2H₂O. The individual character of the synthesized compounds are proved by the study of the IR absorption spectra (400–4000 cm^?1) of all the compounds and the initial ligand, as well as the X-ray diffraction patterns, thermograms, and thermogravigrams of the synthesized compounds. The coordination modes of the ligand and acido groups are revealed. The properties of the synthesized compounds are characterized.     

Cobalt(II) complexes with 2-aminoacetophenone N(4)-substituted thiosemicarbazones

Cobalt(II) complexes with 2-aminoacetophenone thiosemicarbazone and three N(4)-substituted thiosemicarbazones have been prepared in EtOH solution and characterized by physical and spectral methods. I.r. and electronic spectra of the thiosemicarbazones and their complexes, along with physical properties of the complexes, have been obtained. The 2-aminoacetophenone thiosemicarbazones coordinate both as neutral and anionic ligands via the thiosemicarbazone moiety's imine nitrogen and thione/thiolato sulfur [on loss of the N(2) hydrogen].     

Cobalt(II) halide complexes with ethyleneselenourea

The complexes obtained from ethyleneselenourea and cobalt(II) halides have been prepared and characterized. They have formula CoL₂X₂ (X = Cl, Br, I), tetrahedral stereochemistry and they are Se-bonded to the cobalt(II). They are comparatively studied with the previously reported complexes of cobalt(II) with ethylenethiourea, by IR and visible spectroscopy and magnetic susceptibilities. Using the average linand field approximation, the ethyleneselenourea is located at the very low end of the nephelauxetic series.     

Cobalt(II) complexes of 4-acetamidobenzaldehyde N(4)-substituted thiosemicarbazones

Cobalt(II) complexes of five 4-acetamidobenzaldehyde N(4)-substituted thiosemicarbazones have been prepared in EtOH solution and characterized by i.r., electronic and n.m.r. spectra, and by magnetic susceptibilities and molar conductivity measurements. The thiosemicarbazones coordinate as monoanionic or neutral ligands via the thiosemicarbazone azomethine nitrogen and thione/thiolato sulfur, the latter by loss of the thioamide hydrogen, N(2)H. The resulting cobalt(II) complexes exhibit a varied stereochemistry.     

Cobalt(II) complexes of creatinine

Summary Cobalt(II) complexes of creatinine [Co(creat)₂X₂] (X = Cl, Br, I or NCS) and [Co(creat)₂X₂(H₂O)₂] (X = HCO₂, HOCH₂CO₂ or CNCH₂CO₂) have been prepared. Their i.r. spectra show an increase in (NH) of the cyclic secondary amine group, compared to free ligand (3300 cm^–1), indicating that cyclic nitrogen is involved in coordination. The thiocyanate group coordinates through nitrogen and carboxylates coordinate as univalent unidentate ligands. The electronic spectra and magnetic moments suggest a d⁷ configuration for cobalt: a tetrahedral geometry (4.4 B.M.) for halide and thiocyanate complexes, and an octahedral geometry (5.0 B.M.) for the carboxylate complexes. On heating, the ligand moiety is lost and the respective cobalt halide or cobalt carboxylate is formed, which is converted finally into Co₃O₄. There is a correlation between the high intensity electronic transitions and the polarographic half-wave potentials.     

Ruthenium(II) complexes with 2-methyl-3-substituted (3H)-quinazolin-4-ones

A number of ruthenium(II) complexes of some polydentate ON, OO and ONO donors in the form of 2-methyl-3-substituted (3H)-quinazolin-4-ones have been synthesized and studied. The reaction between RuCl₂(DMSO)₄ and the uninegative bidentate ligands yielded complexes of the type Ru(DMSO)₂(OO)₂ (OO = MHQ, PHQ, MHEQ, MHPQ or MCMQ), displacing only two DMSO groups along with chlorides, whereas the neutral bidentate ligands gave RuCl₂(ON)₂ (ON = MAQ, PAQ, MANQ, PANQ, MAAQ, MAPQ, MPQ or PPQ), displacing all the DMSO groups. A uninegative terdentate ligand (MHAQ) with ONO donors, however, yielded a bis chelate of ruthenium(II).     

Cobalt(II), nickel(II) and copper(II) complexes of 4-(sulfonylazido)phenylazopyrazolones

Transition metal complexes of Co^II, Ni^II and Cu^II with 4-(4-azidosulfophenylazo)-5-phenyl-3,4-dihydro-2H-pyrazol-3-oneHL¹, 4-(4-azidosulfophenylazo)-5-methyl-2-phenyl-3,4-dihydro-2H-pyrazol-3-one HL² and 4-(3-azidosulfo-6-methoxyphenylazo)-5-methyl-2-phenyl-3,4-dihydro-2H-pyrazol-3-one HL³ were prepared and characterized by elemental analyses, molar conductances and magnetic susceptibilities and by i.r., electronic and e.s.r. spectral measurements as well as thermal (d.t.a and t.g.a.) analysis. The i.r. spectra indicate that HL acts as a bidentate ligand coordinating via the azo and enolic-oxygen linkages. The electronic spectral data and magnetic moments suggest a tetragonally distorted octahedral geometry for the complexes having the formula ML₂·2H₂O, (M = Co^II, Ni^II and Cu^II), square pyramidal geometry for CuL ₂ ³ H₂O and tetrahedral geometry for CoL ₂ ³ . The X-band e.s.r. spectra of the copper(II) complexes reveal anaxial symmetry for both CuL ₂ ² 2H₂O and CuL ₂ ³ H₂O while CuL ₂ ¹ O is isotropic in the solid state at room temperature. The d.t.a. curves show two exothermic peaks for all three complexes CoL ₂ ³ ,NiL ₂ ³ 2H₂O and CuL ₂ ³ H₂O and one endothermic peak for the latter two aqua complexes.     

Cobalt(II) perchlorate,tetrafluoroborate, nitrate and sulphate complexes with 4,6-dimethylpyrimidine-2(1H)-thione

Contrary to earlier reports in which no adducts of Co(II) metal ion with 4,6-dimethylpyrimidine-2(1H)-thione(HL) could be isolated starting from Co(ClO₄)₂ · 6H₂O, we now report bis- and tris-ligand Co(II) complexes of the type [Co(HL)₂(H₂O)₂]X₂ · H₂O (X = ClO₄, BF₄), [Co(HL)₂NO₃]NO₃, [Co(HL)₂SO₄] · 0.5H₂O and [Co(HL)₃]X₂ · 0.5H₂O (X = ClO₄, BF₄). They have been synthesized by refluxing 2:1 and 3:1 mixtures of HL and CoX₂ · nH₂O in ethanol-triethyl orthoformate. We also describe new Co(HL)₂X₂ · nH₂O complexes in which for X₂ = ClBr, ClI and BrI, n = 2; for X₂ = I₂, n = 1 and for X₂ = (SCN)₂, n = 0. Structural characterization of the complex species is made from electronic and vibrational spectra, magnetic susceptibility measurements in the solid state and conductivity measurements in DMF solution. The magnetic and electronic spectral data together with ligand-field parameters suggest a pseudo-octahedral environment for all the Co(II) complexes, with the exception of Co(HL)₂SO₄ · 0.5H₂O in which the Co(II) ion appears to be pentacoordinated. The IR spectra are consistent with a coordination involving N,S-chelation of the ligand through the non-protonated ring nitrogen atom and the exocyclic sulphur atom.     

Cobalt(II), nickel(II) and copper(II) with 2-substituted benzimidazole complexes

Summary Complexes of stoichiometries M(Acbim)₂X₂·nH₂O and M(Bzbim)₂X₂·nH₂O (M = Co, Ni or Cu; Acbim = 2-acetylbenzimidazole, Bzbim = 2-benzoylbenzimidazole; X = Cl, Br, NO₃ or ClO₄; n = 0, 1 or 2) have been prepared and characterised by spectroscopic and physicochemical methods. The ligands coordinate through carbonyl oxygen and tertiary nitrogen.     

Cobalt(II) halide complexes with imidazolidine-2-selone derivatives

Summary CoL₂X₂ (X = Cl, Br or I) complexes were obtained by reacting cobalt(II) halides withN-methyl-,N-ethyl-,N,N-dimethyl- andN,N-diethyl-imidazolidine-2-selone. The same ligands with cobalt(II) tetrafluoroborate gave CoL₄(BF₄)₂ complexes only with the disubstituted ligands. On the basis of i.r. and electronic spectra all the complexes are considered to be Se-bonded to the metal with a tetrahedral stereochemistry, as supported by magnetic measurements and colours. The ligand field parameters (Dq, B and ) for the [CoL₄]²⁺ ion are evaluated by using the averaged ligand field approximation. The influence of the substituents on these parameters are discussed and compared with those obtained for the analogous complexes with the sulphur parent ligands.This work was partially supported by C.N.R. of Rome, Italy.     

Cobalt(II) and nickel(II) complexes with 4-amino-6-methyl-5-oxo-3-phenylamino-1,2,4-triazine

Summary Cobalt(II) and nickel(II) complexes of 4-amino-6-methyl-5-oxo-3-phenylamino-1,2,4-triazine (ATAZ), MX₂(ATAZ)₂ · 2 H₂O (M = Co or Ni; X = Cl, Br, I or NCS), have been isolated. The electronic spectra, magnetic moments and i.r. spectra of the compounds have been studied.Pseudo-octahedral environments are proposed for the complexes: [MX₂(ATAZ)₂]. 2 H₂O (M = Ni or Co; X = Cl or Br) and [CoI₂(ATAZ)₂(H₂O)₂], and apseudo-tetrahedral structure for [NiX₂(ATAZ)₂] · 2 H₂O (X = I or NCS) and [Co(NCS)₂-(ATAZ)₂] · 2 H,O. However, [CoX₂(ATAZ)₂]. 2 H₂O (X = Cl or Br) give acetone solutions containing tetrahedral cobalt(II).     

Cobalt(II) chloride complexes in molten acetamide

The absorption spectra of Co(II) chloride species were studied in molten acetamide containing variable concentration of chloride ligand, in the wavelength range 400–800 nm, at 90°C. The stepwise formation of CoCl_j^(2-j) complexes (J = 1–4) was observed. Addition of chloride ligand (up to 4 molar) dramatically changed Co(II) absorption spectra due to change in co-ordination from octahedral through a severely distorted octahedral to tetrahedral co-ordination. Overall equilibrium constants β_j and consecutive stability constants K_j(j = 1–4) were calculated using SPELMA program for simultaneous computation of equilibrium constants and molar absorption coefficients for each complex species. Distribution of the Co(II) species was also calculated in the studied ligand concentration range.     

QTAIM study of transition metal complexes with cyclophosphazene-based multisite ligands II. Cobalt(II) complexes

[(CoLCl)CoCl₃], [(CoMeLCl)CoCl₃], [(CoLBr)CoBr₃], [CoLBr]⁺ and [CoMeLBr₂] complexes, L = hexakis(2-pyridyloxy)cyclotriphosphazene, MeL = hexakis(4-methyl-2-pyridyloxy)cyclotriphosphazene, in the most stable high spin states are investigated at DFT level of theory using hybrid B3LYP functional. The exchange coupling parameter evaluated using a broken symmetry treatment increases with the ligands mass. Electron density is evaluated in terms of QTAIM (Quantum Theory of Atoms-in-Molecule) topological analysis of electron density. The bonds of central Co atoms with phosphazene nitrogens are shorter, stronger and more polar than with the aromatic pyridine nitrogens and their higher ellipticities may be explained by the π contribution from the phosphazene ring. The atomic charges of phosphazene nitrogens are ca. twice more negative than at the pyridine ones.     

Cobalt(II), nickel(II) and copper(II) complexes of 1-hydroxy-2-naphthyl(4-X-styryl)ketones

Summary Metal(II) bis-chelates of the type ML₂nB [M=Co^II, Ni^II, and Cu^II, L=1-hydroxy-2-naphthyl(4-X-styryl)ketone, (X=H, Me, Cl, MeO), B=H₂O, Py; n=0, 2] have been prepared and characterised by element analyses, i.r., ligand field spectra, magnetic moments and thermal studies. The copper(II) chelates are anhydrous monomers oftrans-square-planar configuration. The cobalt(II) and nickel(II) chelates, obtained as dihydrates, possess a high-spintrans-octahedral structure. Their anhydrides are polymeric. All the pyridine adducts have high-spintrans-octahedral geometry. The (M–O), order, namely Cu >Ni>Co, parallels the Irving-Williams order. The weak ligand field strength of 1-hydroxy-2-naphthyl(4-X-styryl)ketones is ascribed to inhibition of extensive conjugation arising from deviation of the naphthoyl group from planarity.     

Dialkyl sulfoxides complexes with nickel(II) nitrate and perchlorate

Nickel(II) perchlorate and nitrate complexes containing dimethyl, di-n-propyl, di-n-butyl, di-i-butyl and di-t-butyl sulfoxides have been synthesized and characterized by IR and electronic spectroscopies, magnetic-susceptibility and electrolytic-conductance measurements. In the complexes containing perchlorate, the metal: sulfoxide molar ratio is 1:6 and the perchlorate groups are ionic. In the nitrate compounds, the molar ratio decreases from 1:6 to 1:2 according to the increase in the steric bulk of the alkyl group from methyl to t-butyl. The nitrate group may either be non-coordinating or behave as a monodentate or bidentate ligand. All the complexes contain O-bonded sulfoxide molecules and are characterized as high-spin, with an octahedral or distorted octahedral geometry. The dialkyl sulfoxides studied in this work fall in the same position as dimethyl sulfoxide in the spectrochemical and nephelauxetic series. Electrolytic conductivities suggest that the compounds containing ionic nitrate exhibit sulfoxide—nitrate exchange in nitromethane solutions.     

Cobalt(II), nickel(II) AND zinc(II) dicarboxylate complexes with hydrazine as bridged ligand

The complexes of chromium and molybdenum with salicylidene-2-aminophenol (shaH₂), salicylidene-2-aminoanisole (salanH₂), salicylidene-2-aminoaniline (salphenH₂) and biquinoline (biq) were studied using the thermogravimetric techniques. The thermal decomposition of all complexes was found to be first order reaction and the thermodynamic parameters corresponding to the different decomposition steps were reported. Molybdenum complexes were found to be more thermally stable and the order of stability was [Mo(CO)₄(biq)]>[MoO(salphen)]>[MoO₂(salphenH)₂]>[MoO₄(salan)₂]>[MoO(sha)]. Similar trend was found for chromium complexes where [Cr(CO)₄(biq)]>[Cr(CO)₂(salphen)] >[CrO₂(CO)₂(shaH₂)]>[CrO₂(CO)₂(salan)₂].     

Synthesis and spectral studies on Co (II) and Ni (II) complexes with polyfunctional quinazoline-(3H)-4-ones

A series of complexes of Co(II) and Ni(II) with 2-(R)-3-(X)-substituted quinazoline-(3H)-4-ones, where R = methyl/phenyl and X = furalamino, uramino and thiouramino have been synthesised and characterised by analytical, conductivity, thermal and magnetic, infrared and electronic spectral data. Based on analytical and conductivity studies the stoichiometries of the complexes have been established. Conductivity data also show that all these complexes are non-electrolytes. Infrared spectral data indicate that all the ligands manifest neutral bidentate with both the metal ions. Geometries for the complexes have been proposed based on electronic spectral data. Various electronic spectral parameters have been calculated for all the complexes and relevant conclusions have been drawn with respect to the nature of bonds present in them.     

Cobalt(II), nickel(II) and copper(II) complexes of bidentate bibenzimidazoles

Summary Complexes of cobalt(II), nickel(II) and copper(II) with novel bidentate bibenzimidazoles, [M(L-L)Cl₂], where L-L are methylenebis(1, 1-benzimidazole), methylenebis(2, 2-benzimidazole) and dimethylenebis(2, 2-benzimidazole) are described and characterized by different physical measurements. The four coordinate complexes have distorted tetrahedral or square coplanar structures. The bridging entity between the two donor groups apparently influences the ligand field strength and the ligands occupy a higher position than that of benzimidazole in the spectrochemical series.