Cobalt(II) complexes with pentadentate Schiff bases 2,6-diacetylpyridine hydrazones: Syntheses and structures

Seven new cobalt(II) complexes based on the Schiff bases, 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H₂L¹) and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H₂L²), are synthesized and studied by X-ray diffraction analysis: [Co(H₂L¹)(NCS)₂] · 2.25H₂O (I), [Co(H₂L²)(NCS)₂] · CH₃OH (II), [Co(H₂L²)(NCS)(H₂O)]NCS (III), [Co(H₄L¹)(NCS)₂](NO₃)₂ · 2H₂O (IV), [Co(H₄L¹)(NCS)₂][Co(NCS)₄] · 0.75H₂O (V), [Co(H₄L²)(NCS)₂][Co(NCS)₄] · 1.75H₂O (VI), and [Co(H₂L²)(NCS)(CH₃OH)]₂[Co(NCS)₄] · 2CH₃OH (VII) (CIF files CCDC 941186 (I), 1457906 (Ia), 1457905 (II), 941187 (III), 1457907 (IV), 1457908 (V), 1457909 (VI), and 941188 (VII)). The organic ligands in the complexes act as pentadentate neutral H₂L or doubly protonated (H₄L)²⁺ coordinated through the same set of donor atoms N₃O₂. In all compounds I–VII, the coordination polyhedron of the Co²⁺ ion in a complex with the Schiff bases has a shape of a pentagonal bipyramid. The hydrazones are arranged in the equatorial plane of the bipyramid. Its axial vertices are occupied by the nitrogen atoms of the NCS￣ anions in compounds I, II, and IV–VI and by the nitrogen atoms of NCS￣ and oxygen of the water molecule in compound III or methanol in compound VII. The NO ₃ ^- anions or [Co(NCS)₄]^2￣ complex anions obtained by the reactions are involved along with the NCS￣ anions in the formation of compounds IV–VII.     

Ni(II) complexes of stereo-isomeric hexazamacrocyclic ligands derived from 2,6-diacetylpyridine

The nitrate and perchlorate Ni(II) complexes of the stereo-isomeric hexazamacrocyclic ligands L¹ (3,6,14,17,23,24-hexaazatricyclo[17.3.1.18,12]tetracosa-1(23),8,10,12(24),19,21-hexaene,2,7,13,18-tetramethyl) and L² (3,7,15,19,25,26-hexaazatricyclo[19.3.1.19,13]hexacosa-1(25),9,11,13(26),21,23-hexaene,2,8,14,20-tetramethyl) derived from 2,6-diacetylpyridine have been synthesized and characterized by microanalysis, LSI-MS, conductivity measurements, IR, UV–Vis spectroscopy and magnetic studies. Crystal structures of L¹·2H₂O as well as of the complexes [NiL¹](ClO₄₎₂$[{\text{NiL}}^1]({\text{ClO}}_4{)}_2$ and [NiL²](NO₃₎₂$[{\text{NiL}}^2]({\text{NO}}_3{)}_2$ have been determined. The X-ray studies show the presence of mononuclear endomacrocyclic complexes with the metal ion coordinated to all the nitrogen donor atoms from the macrocyclic framework in a N6 core. The geometry around the metal ions can be described as distorted octahedral. The nitrate and perchlorate anions do not coordinate to the metal ions, but they are involved in intermolecular interactions through hydrogen bonds to the amine groups of the macrocyclic ligands.     

Antitumor activity of manganese(II) and cobalt(III) complexes of 2-acetylpyridine schiff bases derived from S-methyldithiocarbazate: Synthesis,characterization, and crystal structure of the manganese(II) complex of 2-acetylpyridine S-methyldithiocarbazate

Transition metal complexes [Mn(L)₂] (I) and [Co(L)₂] · (ClO₄) · H₂O (II), where HL = 2-acetylpyridine S-methyldithiocarbazate, have been synthesized. Complex I was characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction studies. The manganese(II) atom in complex I adopts a distorted octahedral geometry with the Schiff base coordinated to it as a uninegatively charged tridentate chelating agent via the pyridine and azomethine nitrogen atoms and the thiolate sulfur atom. Biological studies carried out in vitro against K562 leukemia cancer cell line have shown that the free ligand and its metal complexes exhibited significant and different antitumor activity, since they exhibit IC₅₀ values in the μM range.     

Palladium(II) Schiff base complexes derived from sulfanilamides and aminobenzothiazoles

Schiff bases (HL) derived from sulfanilamides or aminobenzothiazoles add to Pd(OAc)₂ to give complexes of the type PdL₂ (1–7) in moderate to excellent yields. Reactions of Schiff bases containing pyrimidine groups, however, gave several products arising from competing coordination of the pyrimidine nitrogen. Palladium complexes and Schiff bases have been investigated as antifungal agents against Aspergillus niger and Aspergillus flavus.     

Synthesis,crystal structure and characterization of two new copper(II) complexes of Schiff bases derived from furfurylamine

Two new mononuclear complexes of copper(II), namely [CuL₂] (1) and [CuL′₂] (2) have been synthesized by reacting copper perchlorate with furfurylamine and salicylaldehyde or 2-hydroxyacetophenone, where L = (2-hydroxybenzyl-2-furylmethyl)imine and L′ = (2-hydroxymethylbenzyl-2-furylmethyl)imine, the respective asymmetric bidentate Schiff bases that are formed in situ to bind the Cu(II) ion. The complexes have been characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction studies. Structural studies reveal that the mononuclear units of both the complexes (1) and (2) adopt square planar geometry supported by weak intermolecular C–H···π interactions.     

Synthesis,characterization, and crystal structure of three cobalt(II) complexes with Schiff bases derived from rimantadine

By condensation of rimantadine and substituted salicylaldehyde, three new Schiff bases, HL¹, HL² and HL³, were synthesized. Then, a mixture of one of the new ligands and cobalt(II) chloride hexahydrate in ethanol led to 1, 2, and 3, respectively. These complexes were characterized by melting point, elemental analysis, infrared spectra, molar conductance, thermal analysis, and single-crystal X-ray diffraction analysis. X-ray diffraction analysis reveals that 1 crystallizes in the orthorhombic system, Pbcn space group; each asymmetric unit consists of one cobalt(II) ion, two deprotonated ligands, and one lattice water. The central cobalt is four coordinate via two nitrogens and two oxygens from the corresponding Schiff base ligand, forming a distorted tetrahedral geometry. Complexes 2 and 3 crystallize in the monoclinic system, P2₁/c space group; each asymmetric unit consists of one cobalt(II), two corresponding deprotonated ligands, one lattice water, and one methanol. The central cobalt is also four-coordinate via two nitrogens and two oxygens from the corresponding Schiff base ligand, forming a distorted tetrahedral geometry.     

Electrochemical studies of copper(II) complexes derived from bulky Schiff bases. The crystal structure of bis[N-(1- adamantyl)-salicylaldiminato]copper(II)

Three Schiff base ligands and their corresponding copper(II) complexes have been prepared and characterized. Elemental analyses, mass spectra, i.r., electronic spectra, eff and the X- ray crystal structure for one of the complexes, as well as elemental analyses, mass spectra, i.r., electronic and 1H n.m.r. spectra of the ligands, have been obtained. The X-ray study shows that the geometry around the metal atom is intermediate between square planar and tetrahedral. Electrochemical studies on the complexes reveal a dependence of the CuII/CuI potentials on the extent of distortion of the planar structure observed in solid state.     

Synthesis, structural characterization and antibacterial activity of 2,6-diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases and their copper(II) complexes

2,6-Diacetylpyridine bis(benzenesulfonohydrazide) Schiff bases (L¹, L² and L³) and their Cu(II) complexes of the general formula [CuL·H₂O] were synthesized and characterized by various spectroscopic techniques. The crystal structure of [CuL³·(py)]·py was investigated by single crystal X-ray structure analysis. The Cu(II) cation has near square pyramidal, penta-coordinate geometry. The binegatively charged tetradentate Schiff base is asymmetrically coordinated to the Cu(II) ion via the pyridine N atom, the azomethine N atom, the sulfonyl O atom and the deprotonated hydrazine N atom. There is a pyridine molecule apically coordinated to the Cu(II) ion. All the Schiff bases and their copper(II) complexes were screened by the disc diffusion method against multi-drug resistant (MDR) gram-negative and gram-positive bacteria. The minimum inhibitory concentration (MIC) values were also determined. These results show that the antibacterial activity of the Schiff bases against Methicillin-resistant Staphylococcus aureus (MRSA) is enhanced when they are chelated with the copper(II) ion.     

Syntheses and crystal structures of three copper(II) complexes with bulky Schiff bases derived from rimantadine

The reactions of copper(II) chloride dihydrate and three bulky Schiff base ligands derived from rimantadine and salicylaldehyde (or methoxy-substituted salicylaldehydes), generated C₃₈H₄₈CuN₂O₂ (1), C₄₀H₅₂CuN₂O₄ (2), and C₄₀H₅₂CuN₂O₄ (3), respectively. These complexes were characterized by infrared spectra, UV–vis, elemental analysis and molar conductance. X-ray single-crystal diffraction analysis reveals that 1 has two different spatial configurations, 1a and 1b. For 1a, each asymmetric unit consists of one mononuclear copper(II) molecule. For 1b, each asymmetric unit consists of two copper(II) mononuclear molecules. All the complexes crystallize in the monoclinic system, P2₁/c space group for 1a and 2; P2₁/n space group for 1b; C2/c space group for 3. Each complex for 1–3 consists of one copper(II) and two corresponding deprotonated ligands. The central copper(II) in all complexes is four-coordinate via two nitrogens and two oxygens from the corresponding Schiff base ligands. The geometry around copper in 1a, 1b, and 2 is distorted square planar, but square planar in 3.     

The preparation and characterization of mono- and bis-chelated cadmium(II) complexes of the di-2-pyridylketone Schiff base of S-methyldithiocarbazate (Hdpksme) and the X-ray crystal structure of the [Cd(dpksme)2] · 0.5 MeOH complex

New cadmium(II) complexes of empirical formulae, [Cd(dpksme)X] (dpksme = anionic form of the Schiff base; X = NCS^–, Cl^–, I^–) and [Cd(dpksme)₂] · 0.5MeOH, respectively have been prepared and characterized. The mono-ligated cadmium(II) complexes, [Cd(dpksme)X] are four-coordinate and tetrahedral but the bis-ligand complex, [Cd(dpksme)₂] · 0.5MeOH is six-coordinate and octahedral. The crystal and molecular structure of [Cd(dpksme)₂] · 0.5MeOH has been determined by X-ray diffraction. The complex has a distorted mer-octahedral structure in which the ligands are coordinated as uninegatively charged tridentate chelating agents via the pyridine nitrogen atoms, the azomethine nitrogen atoms and the thiolate sulfur atoms. The distortion from regular octahedral geometry is ascribed to the restricted bite angles of the ligands. The Schiff base and its cadmium(II) complexes exhibit mild antibacterial activities against Shigella dysenteriae, Bacillus cereus, Staphylococcus aureus and Escherichia coli. They are also mildly fungitoxic against the phytopathogenic fungi, Alternaria alternata and Macrophomina phaseolina.     

Preparation and x-ray crystal structure of a seven-coordinate cobalt(II) complex with 2,6-diacetylpyridine bis(2-picolinoylhydrazone)

Summary A new seven-coordinate cobalt(II) complex has been synthesized with 2,6-diacetylpyridine bis(2-picolinoylhydrazone) (H₂dappc) and its crystal and molecular structure has been determined by x-ray diffraction methods from counter data and refined toR 0.0449 for 2128 observed reflections. The complex crystallizes in a triclinic cell, space group P¯1, with dimensions:a=13.759(8),b=7.685(3),c=13.816(7) Å, =86.50(5), =66.48(5), =85.28(5)° andZ=2. The complete structure consists of [Co(H₂dappc)(OH₂)₂] cations, chloride anions and solvating H₂O molecules, interlinked by hydrogen bonds. The geometry around the cobalt is that of a distorted pentagonal bipyramid with the H₂dappc ligand forming the equatorial plane and two H₂O molecules occupying the axial positions.     

Synthesis and characterization of pentagonal bipyramidal organotin(IV) complexes of 2,6-diacetylpyridine Schiff bases of S-alkyl- and aryldithiocarbazates

New organotin(IV) complexes with empirical formula Sn(SNNNS)R₂, where SNNNS is the dianionic form of 2,6-diacetylpyridine Schiff bases of S-methyldithiocarbazate (H₂dapsme) or S-benzyldithiocarbazate (H₂dapsbz) and R = Ph or Me, have been prepared and characterized by IR, UV-Vis, NMR and Mössbauer spectroscopic techniques and conductance measurements. The molecular structures of the Sn(dapsme)R₂ (R = Ph and Me) have been determined by single crystal X-ray diffraction techniques. Both complexes have a distorted pentagonal-bipyramidal geometry in which the tin is coordinated by a dinegatively charged pentadentate chelating agent via pyridine nitrogen, two azomethine nitrogens, and two thiolate sulfurs. The five donors (N₃S₂) provided by the Schiff base occupy the equatorial plane close to a pentagonal planar array while the carbanion ligands occupy axial sites.     

Mononuclear and binuclear lanthanum(III) complexes of macrocyclic ligands derived from 2,6-diacetylpyridine

Two novel series of complexes of types [La(DAPCH)X₂]X and [La(DAPTC)X₂]X (DAPCH = a potentially pentadentate ligand derived from 2,6-diacetylpyridine and carbohydrazide; DAPTC = a potentially tridentate ligand derived from 2,6-diacetylpyridine and thiocarbohydrazide; X = Cl, Br or NO₃) have been synthesized and characterized by elemental analyses, conductance measurements and IR spectral data. All these complexes contain terminal hydrazinic nitrogen atoms with an unshared electron pair and may take part in nucleophilic condensations. Therefore, the reactions of these complexes with 2,6-diacetylpyridine have also been studied which cause ring closure and formation of macrocyclic ligand complexes. Two types of cyclic products, viz. mononuclear [La(mac)X₂]X, [La(mac′)X₂]X and binuclear [La₂(mac)X₄]X₂, [La₂(mac′)X₄]X₂ (mac- = macrocyclic ligand derived from DAPCH and 2,6-diacetylpyridine; mac′ = macrocyclic ligand derived from DAPTC and 2,6-diacetylpyridine; X = Cl, Br or NO₃) have been isolated by carrying out the reactions by different methods. The IR spectra of these cyclic products are reported.     

Spectroscopic and biological properties of platinum complexes derived from 2-pyridyl Schiff bases

The reactions of a range of aromatic primary amines with pyridine-2-carboxaldehyde were reported, highlighting the effect of the substituents of the amine on the outcomes of the Schiff base reactions. The variant products of the Schiff base reactions were reacted with cis-[PtCl₂(DMSO)₂], generating platinum(II) complexes with PtCl₂(N^N) general formula. The ligands and platinum(II) complexes were identified and characterized by IR and NMR spectroscopic methods. Single crystal XRD offered structural confirmation for three of the organic compounds and two platinum complexes. The spectral, antimicrobial, DNA-binding and molecular docking of the platinum complexes were studied, highlighting the effect of the different functional group in the Schiff base ligands on their properties. In general, introducing the electron-withdrawing group nitro or acetyl in the 2-pyridyl Schiff base ligands, results in a red-shift in the absorption maxima of the platinum complex. In addition, the enhancement in the antimicrobial activities and the increase in the ct-DNA-binding affinity were also observed when the nitro or acetyl functional group is introduced to the Schiff base ligand in the platinum(II) complex.     

Palladium(II) and platinum(II) halide complexes with 2,6-dimethyl-4H-pyran-4-thione

Summary 2,6-Dimethyl-4H-pyran-4-thione (DMTP) acts as a sulphur donor towards Pt^II and Pd^II halides yielding adducts of general formula [M(DMTP)₂X₂] (M=Pd or Pt; X=Cl, Br or I). When complex syntheses are performed in benzene, the solvated species [M(DMTP)₂X₂]·C₆H₆ (M=Pd or Pt; X=Cl or Br) are obtained. The compounds have been characterized by i.r. and n.m.r. (¹H and¹³C) spectroscopy and by thermogravimetric data. The adduct geometry and the influence of benzene are discussed.     

Synthesis, 119Sn Mössbauer spectroscopic studies and X-ray crystal structure determination of new seven-coordinate diorganotin(IV) complexes with S,N,N,N,S-pentadentate Schiff bases derived from 2,6-diacetylpyridine of S-methyl- and S-benzyldithiocarbazates

The reactions of the ligands 2,6-diacetylpyridine bis(S-methyldithiocarbazate)] (H₂dapmdtc) and 2,6-diacetylpyridine bis(S-benzyldithiocarbazate)] (H₂dapbdtc) with R_4-m SnCl _m (R = Me, ⁿ Bu, Ph; and m = 2) led to the formation of six seven-coordinate diorganotin(IV) complexes, which were studied by microanalysis, i.r., n.m.r (¹H, ¹¹⁹Sn) and Mössbauer spectroscopies. The X-ray structures determination of complexes [Me₂Sn(dapmdtc)], [Me₂Sn(dapbdtc)] and [Ph₂Sn(dapbdtc)] revealed the presence of neutral seven-coordinated complexes. The structures consist of monomeric units in which the Sn(IV) atom exhibits distorted pentagonal bipyramidal (PBP) geometry, with the S,N,N,N,S-donor systems of the ligands lying in the equatorial plane and organic groups in the apical positions. A correlation between Mössbauer and X-ray data based on the point-charge model is discussed.     

Transition metal complexes of the Schiff base derived from S-methyldithiocarbazate with 2-aminobenzaldehyde

Summary New complexes of general formula [M(NNS)X] (NNS⁻ = anion of the Schiff base of 2-aminobenzaldehyde with S-methyldithiocarbazate; M = Ni, Cu, Pd or Pt; X = Cl, Br, I, NCS, NO₃ or AcO), [Ni(NNS)(HNNS)]NO₃ and [Co(NNS)₂]Cl were prepared and characterised. The magnetic and spectral evidence suggests a square-planar structure for the mono-ligated complexes and an octahedral structure for the bis-chelated complexes. The copper(II) complexes have been shown to display high antifungal activities against the pathogenic fungi, Alternaria alternata and Curvularia geniculata.     

Synthesis and mesogenic properties of binuclear copper(II) complexes derived from salicylaldimine Schiff bases

The synthesis and mesomorphic (liquid crystal) properties of new binuclear dihalocopper(II) complexes derived from N- and ring-substituted salicylaldimine Schiff bases are reported, together with the mesomorphic properties of their monomeric precursor complexes. With just N-substituents both the dichlorodicopper(II) binuclear complexes and their mononuclear analogues are waxy solids with melting points that increase with their N-chain length. However, with both N- and ring-substituents in the 4-positions, the mononuclear and binuclear complexes are each liquid crystalline or mesogenic, except in case of the mononuclear complexes where the N-substituent is straight chain alkyl. The other mononuclear complexes exhibit a variety of liquid crystal phases: smectic A, C, and E (SA, SC, and SE, respectively). The liquid crystal phase SA is observed in the binuclears with shorter chain N-substituents p-R-O-C6H4- and shorter chain ring-substituents. The chain lengths were increased until the phase behavior expanded to a further form SC in the case of an N-substituent p-C14H29O-C6H4- and a -OC12H25 ring substituent. This points the way toward achieving multiphase behavior with these binuclear systems. The Cu-Br analogues of the binuclear complexes behave similarly but with significant qualitative differences, specifically lower mesophase stability and higher melting temperatures. The structures of the nonmesogenic binuclears ([Cu(N-dodecylSal)X]2, X=Cl, Br) were determined with the aid of X-ray crystallography. These are prototypes for the structures of the binuclear complexes and especially for the shape of the central Cu2O2 X2 core in the binuclears: distorted planar coordination about the copper with distortion toward tetrahedral measured by a characteristic twist angle tau (0 degrees planar; 90 degrees tetrahedral). The binuclear complexes also show magnetic coupling which can be used to estimate the geometry. For [Cu(N-dodecylSal)X]2 tau>36 degrees, which corresponds to weaker coupling than observed in the mesogenic binuclears where a stronger magnetic coupling indicates a geometry closer to planar (tau=25 degrees). The mesophases were characterized by differential scanning calorimetry (DSC) analysis and optical polarized microscopy.