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Iron(II)-Schiff base complexes are a well-studied class of spin-crossover (SCO) active species due to their ability to interconvert between a paramagnetic high spin-state (HS, S = 2, 5T2) and a diamagnetic low spin-state (LS, S = 0, 1A1) by external stimuli under an appropriate ligand field. We have synthesized two mononuclear FeII complexes, viz., [Fe(L1)2](ClO4)2.CH3OH (1) and [Fe(L2)2](ClO4)2.2CH3CN (2), from two N6–coordinating tridentate Schiff bases derived from 2,6-bis[(benzylimino)methyl]pyridine. The complexes have been characterized by elemental analysis, electrospray ionization–mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR), solution state nuclear magnetic resonance spectroscopy, 1H and 13C NMR (both theoretically and experimentally), single-crystal diffraction and magnetic susceptibility studies. The structural, spectroscopic and magnetic investigations revealed that 1 and 2 are with Fe–N6 distorted octahedral coordination geometry and remain locked in LS state throughout the measured temperature range from 5–350 K. [ABSTRACT FROM AUTHOR]

Two new Co(II) complexes, [CoL2]X2∙2H2O, with N,N,N-tridentate triazine type ligand (L) and X = Cl− (1) or NO3− (2) are synthesized and characterized using elemental analysis, FTIR spectra, and single-crystal X-ray diffraction. Complexes 1 and 2 are crystallized in the centrosymmetric space groups P-1 and C2/c, respectively. The Co atoms are surrounded by two neutral tridentate ligands coordinated via nitrogen atoms, thus forming a distorted octahedral coordination sphere. Hirshfeld topology analyses of the molecular packing revealed that the polar Cl⋯H, O⋯H and N⋯H contacts are the most important intermolecular interactions while the nonpolar C⋯H and C⋯C (π–π stacking) contacts are weak and insignificant, respectively. DFT calculations indicated that the high-spin state is energetically more favored than the low-spin case. The Co(II) center transfers its spin density to the ligand donor atoms via the spin delocalization mechanism. Based on the atoms in molecules (AIM) results, all Co–N interactions have a predominant covalent character. The strength of the Co–N interactions decreases in the order Co–N(hydrazone) > Co–N(triazine) > Co–N(amine). The metal anti-bonding natural orbitals involved in the Co–N interactions have high and s-orbital characters. Both complexes showed good thermal stability up to 276°C and 250°C for complexes 1 and 2, respectively. [ABSTRACT FROM AUTHOR]

Schiff bases and their metal complexes have a number of biological activities such as antidepressant, analgesic, antimicrobial, antiviral, and antitumor. In the present studies, the 1-(( E)-(pentylimino)methyl)naphthalen-2-ol ligand is prepared by the reaction of 2-hydroxynaphthaldehyde with n-amyl amine. The ligand results in CoL, NiL and CuL complexes when reacted with the cobalt acetate, nickel acetate, and copper acetate salts respectively. The complexes along with their ligand are fully characterized by X-ray diffraction studies and biologically screened. The ligand structure reveals that it is a zwitterion species where the iminic nitrogen atom is protonated and the C-O bond shows a high double bond character. The cobalt complex has an octahedral geometry around the metal center and each nitrogen atom is in the trans position to the oxygen donor site. On the other hand, the copper complex shows a centrosymmetric square planar coordination, and in this case, the nitrogen sites are trans to each other. The complexes and the ligand are found to be more potent than the standard drugs used against some microbes in their preliminary biological studies. [ABSTRACT FROM AUTHOR]

μ 2 -Oxido bridged dinuclear vanadium(V) Schiff base complex with the general formula [VO 2 (L)] 2 ·2CH 3 OH was synthesized and characterized. The X-ray results show the complex is dinuclear with two μ-O bridging ions, and the vanadium centers have an octahedral N 2 O 4 coordination sphere. The tridentate Schiff base ligand L coordinated to vanadium(V) center as a monoanion in the basal plane. The basal plane is completed by one of the μ-O bridges. The other μ-O bridge coordinated to vanadium(V) center as apical direction. The two oxido bridged connected the two V v centers together with the V v - O -V v angle of 101.21(6)°, the V O distances of 1.70(6) and 2.31(7) Å and the V⋯V separation of 3.113(5) Å. Finally, the complex was calcinated at 600 °C for 3 h. The FT-IR spectrum of the product shows the formation of the V 2 O 5 particles. [ABSTRACT FROM AUTHOR]

Transition metal complexes, Na2[M(L1L2)].H2O, where M = Cu(II), Co(II) and Ni(II) ions ; L1 and L2 are the anions of phenylalanine (Phe-) and nitrilotriacetic acid (NTA3-)respectively have been synthesized and characterized by elemental analysis, spectral (IR,UV in solidstate), magnetic susceptibility and thermogravimetric analysis (TGA). All the complexes have been suggested to show six fold octahedral geometry around the metal ion. Phenylalanine and nitrilotriacetic acid demonstrate bidentate and tetradentate behavior respectively, coordinating through their respective nitrogen atom and the oxygen atom (s) of the carboxylate group. Thermal behavior of Ni(II) complex is quite different from those of Cu(II) and Co(II) complexes which show similar type of thermal behavior. Based on their decomposition temperature, the thermal stability of the three complexes can be rated as Cu > Ni > Co. [ABSTRACT FROM AUTHOR]

We have designed and prepared a novel N 3 -donor Schiff base ligand and synthesized the corresponding two mononuclear Fe(II) complexes and compared with their Zn(II) congener. Spectroscopic, Single-crystal XRD, magnetic and DFT calculations investigations reveal that both complexes have Fe__N 6 distorted octahedral geometry and their spin states locked in the low spin state throughout the measured temperature range. [Display omitted] Investigations on the spin states of octahedral Fe(II) complexes have received special attention due to their clear discrimination in the spin states of the d-orbitals. As a means to further understand the factors that influence the spin-crossover (SCO) phenomenon in Fe(II) systems, we herein report two mononuclear Fe(II) complexes, [Fe L 2 ](ClO 4) 2 ·2CH 3 OH (1) and [Fe L 2 ](BF 4) 2 ·CH 3 CN·CH 3 OH (2), derived from a novel N 3 -donor Schiff base ligand, 2,6-bis[(3- methylbenzylimino) methyl ]pyridine (L) with varying counteranion and the diamagnetic [Zn L 2 ](BF 4) 2 congener for a comparative investigation. The complexes have been synthesized and characterized by electrospray-ionization mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) spectroscopy, single-crystal X-ray diffraction (XRD) and magnetic susceptibility studies. Structural and magnetic investigations reveal that both 1 and 2 show Fe__N 6 distorted octahedral geometry and are locked in the diamagnetic LS state throughout the entire explored temperature range from 1.8 to 400 K. The LS state of [Fe L 2 ]2+ is also confirmed by comparing the experimentally found structural parameters, NMR chemical shifts and excitation energies in the visible region with density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Complexes of nickel(II), and copper(II) were synthesized with pantadentate ligand i.e. 3,3′-thiodipropionicacid-bis(5-amino-1,3,4-thiadiazole-2-thiol) (L). The ligand was synthesized by the condensation of thiodipropionic acid and 5-amino-1,3,4-thiadiazole-2-thiol in 1:2 ratio, respectively. Synthesized ligand was characterized by elemental analysis, mass, 1 H NMR, IR, and molecular modeling. All the complexes were characterized by elemental analysis, molar conductance, magnetic moment, IR, electronic spectra, ESR, and molecular modeling. The newly synthesized complexes possessed general composition [M(L)X 2 ] where M = Ni(II), Cu(II), L = pantadentate ligand and X = Cl − , CH 3 COO − . The IR spectral data indicated that the ligand behaved as a pantadentate ligand and coordinated to the metal ion through N 2 S 3 donor atoms. The molar conductance value of Ni(II), and Cu(II) complexes in DMSO corresponded to their electrolytic behavior. On the basis of spectral study, octahedral and tetragonal geometry was assigned for Ni(II) and Cu(II) complexes, respectively. In vitro fungicidal study of ligand and its complexes was investigated against fungi Candida albicans , Candida parapsilosis , Candidia krusei , and Candida tropicalis by means of well diffusion method. [ABSTRACT FROM AUTHOR]

Four new di- and triorganonitrato stannate complexes and related derivatives have been synthesized and characterized by infrared and Mössbauer spectroscopy. The structure of Et4N[NO3(SnClPh3)2(SnPh3NO3)] ( 1) has been determined by single-crystal X-ray diffraction analysis. In the trinuclear organostannate complex, each SnIV atom is five-coordinated and adopts a trigonal-bipyramidal trans-OXSnC3 (X=O or Cl) geometry. The overall coordination environment of the SnIV atoms is trans-octahedral for 2 and 3 or cis-trigonal-bipyramidal for 4. In the related derivatives, the NO3- anions behave as monodentate ligands. [ABSTRACT FROM AUTHOR]

New hydrazinium copper(II) hydrogen ethylenediaminetetraacetate monohydrate, [N 2H 5Cu(HEDTA)]H 2O has been prepared and characterized by analytical, spectral and thermal techniques. The conductivity value indicates the non-electrolyte nature of the complex. Analytical and bond length measurements indicate the distorted octahedral geometry around the copper ion with EDTA acting as pentadentate ligand. The crystal structure of the complex has been determined from single crystal X-ray analysis. The complex crystallizes in orthorhombic system; space group Pccn. The unit cell parameters are a = 25.1858(14) Å, B = 7.3305(4) Å, C = 15.8291(9) Å, α = 90°, β = 90°, γ = 90°, V = 2,922.4(3) Å 3 and Z = 8. The copper ion is six coordinated, three carboxylate oxygen atoms and two nitrogen atoms from EDTA occupy five coordination sites, while the sixth site is occupied by hydrazinium cation and a water molecule present outside coordination sphere as lattice water. The complex undergo multi-step degradation to give copper oxide as the final residue. Graphical Abstract: New hydrazinium copper(II) hydrogen ethylenediaminetetraacetate monohydrate, [N 2H 5Cu(HEDTA)]H 2O has been prepared and characterized by analytical, spectral, thermal and X-ray single crystal structure techniques.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

New cobalt(II) and nickel(II) complexes of 12-membered macrocyclic Schiff - base ligand containing thiosemicarbazone moiety as a part of ring have been prepared having general composition [MLX2] where M = Co(II) or Ni(II), L=3,4,9,10-tetra-2-furanyl-1,2,5,6,8,11- hexaazacyclododeca-7,12- dithione - 2,4,8,10 - tetraene, X = Cl-, NO3 -, NCS- . The complexes have been characterized by elemental analysis, molar conductance, magnetic susceptibility measurements, spectral (IR, electronic, EPR) techniques and thermal analysis. Spectroscopic studies suggested a six coordinated octahedral geometry for all the complexes. The IR spectra of complexes suggest that ligand is coordinated to the metal ion through its four imines nitrogen. Conductivity measurements supported the non electrolytic nature of the complexes. The antifungal activities of complexes have been studied against a number of pathogenic fungi under laboratory conditions. The complexes showed good antifungal results. Thermal analysis of reported complexes suggests the absence of water molecule either in or outside the coordination sphere. [ABSTRACT FROM AUTHOR]

A kinetic study of the substitution behavior of octahedral [Ru(terpy)(bipy)(OH2)]2+ and [Ru(terpy)(tmen)(OH2)]2+ {terpy = 2,2:6',2''-terpyridine, bipy = 2,2'-bipyridine and tmen = N,N,N',N'-tetramethylethylenediamine} with thiourea, 1,3'-dimethyl-2-thiourea, and acetonitrile nucleophiles (Nu) as a function of concentration in pH of 4.0 aqueous media using UV-Vis spectroscopy has been made. The reactions are first order in both the concentration of the Nu and the ruthenium complex in accordance to the two-term rate law kobs = k2[Nu] + k-2. The ligand effect of the cis-coordinated bidentates (NN) on the substitutional lability of the aqua leaving group in the [Ru(terpy)(NN)(OH2)]2+ complexes increases in the order: NN = dppro < dopro < phen ≈ bipy < tmen < diox < Me2phen. This order reflects the steric as well as the electronic properties of the bidentate ligand where the meridionally coordinated terpy enacts stereoelectronic rigidity on the bidentate ligand in addition to providing an efficient drainage of electron density at the metal centers. In the tmen complex, the retardation of the incoming groups caused by a dominant cis σ-effect from the tmen toward the metal center controls the rate of the reaction, as a result of the induced weakening of the scorpionatic effect of the steric tmen ligand due to the strong π-repulsive backbone of the meridionally coordinated terpy. [ABSTRACT FROM AUTHOR]

Condensation of 1H-pyrazole-3,5-dicarboxylic hydrazide with 1H-indole-2,3-dione (isatin) yield the compartmental ligand, which is capable of encapsulating two transition metal ions namely CoII, NiII, CuII, and ZnII. The ligand is a binuclear hexadentate chelate with N4O2 donating sites. The pyrazole core provides the diazine fragment, which serves as an endogenous bridge between the two metal centers. In CoII and NiII complexes, the ligand is in the imidol form and the subsequent coordination through the imidol oxygen. In other complexes, the lactonic oxygen takes part in ligation. All the complexes are non-electrolytes and soluble in DMSO, DMF, and acetonitrile. Spectral and magnetic studies along with analytical data suggest octahedral geometry for the CoII and NiII complexes, whereas the CuII and ZnII complexes are assigned square pyramidal geometry. The CuII and NiII complexes show one electron redox behavior and the rest are electrochemically inactive. [ABSTRACT FROM AUTHOR]

Abstract: By changing metal ions in the presence of N2O2-chelating Schiff-base ligand sal2hn [sal2hn= N,N′-bis(salicylidene)-1,2-diaminocyclohexane] and a large excess of NaN3 (reagent ratios (metal:L:)=2:1:8), tetranuclear copper(II) complex [Cu4(μ-sal2hn)2(μ 1,1-N3)2(N3)2] (1) and 1D chain coordination polymer of cobalt(III) complex {Na[Co(μ-sal2hn)(μ 1,1-N3)(N3)(H2O)(μ-O)} n (2) have been successfully obtained. Single-crystal X-ray analyses revealed that in complex 1 the copper(II) ions are bridged alternately by end-on (EO) azido and phenoxo-sal2hn ligands, while in complex 2 the cobalt(III) and sodium ions are bridged alternately by end-on (EO) azido and phenoxo-sal2hn ligands. Complex 1 crystallizes in the monoclinic system, space group P21/n, with a =11.6283(5)Å, b =19.5997(8)Å, c =9.1531(4)Å, β =90.540(6)°, V =2086.00(15)Å3, and Z =2, while complex 2 crystallizes in the monoclinic system, space group C21/c, with a =21.1473(5)Å, b =14.0604(3)Å, c =15.0452(6)Å, β =106.064(3)°, V =4298.9(2)Å3, and Z =8. [Copyright &y& Elsevier]

Abstract: Two different sets of Schiff base ligands, set-1 (HL1 , HL2 ) and set-2 (H2L3 , H2L4 ) which have been prepared by mixing 1,3-diaminopropane and aldehydes (3-methoxy-2-hydroxybenzaldehyde or 3-ethoxy-2-hydroxybenzaldehyde) in 1:1 and 1:2 ratios, respectively, are employed for the synthesis of complexes with cobalt perchlorate. The octahedral cobalt(III) complexes of general formula [Co(L)2]ClO4 (L= L1 for complex 1, L2 for complex 1a) are obtained from the mono-condensed ligands, whereas the di-condensed ligand H2L4 results in the formation of a unique type of mixed-ligand complex [Co(L2)(L4)]ClO4 (2) where the respective di- and mono-condensed Schiff bases simultaneously coordinate to the metal center. The complexes are completely characterized by elemental analyses, IR, UV–vis spectroscopy and cyclic voltammetric studies. The structures of 1 and 2 are unequivocally established by single crystal X-ray diffraction analysis. The behavior of the Schiff base ligands during the reactions is directed by the template effect of CoIII ion modulated by the perchlorate anion present in the medium. [Copyright &y& Elsevier]

Abstract: Complexes of Co(II), Ni(II), Cu(II) and Zn(II) containing macrocyclic tetradentate nitrogen donor (N4) ligand have been synthesized from the template condensation reaction between o-phthalaldehyde and o-phenylenediamine. The newly synthesized ligand and its complexes have been characterized on the basis of results of elemental analysis, molar conductance, magnetic susceptibility measurements, FT-IR, electronic, 1H FT NMR spectral data and Job''s method. Their thermal behaviour has been studied by the thermogravimetric analysis. An octahedral geometry has been proposed for all of these complexes except the copper complexes, which show distorted octahedral geometry. The low conductivity data suggest their non-ionic nature. The biological activities of the metal complexes have also been studied against different bacteria. [Copyright &y& Elsevier]

Abstract: The syntheses of two new cyclometalated ligands [2-(2′,4′-difluorophenyl)-4-tert-butylpyridine (F2 t Buppy) and 2-(2′,4′-difluorophenyl)-4-oxyhexylpyridine (F2HexOppy)] were carried out. Blue-light emitting iridium(III) complex dopants [Ir(F2 t Buppy)2(acac/pic)] (acac=acetylacetone; pic=picolinic acid) and [Ir(F2HexOppy)2(acac/pic)] were prepared using these cyclometalated ligands with acetylacetone and picolinic acid as their ancillary ligands. The structure of the complexes, [Ir(F2 t Buppy)2(acac)] and [Ir(F2 t Buppy)2(pic)] were authenticated by X-ray single-crystal structure analysis and showed an octahedral geometry. Comparative absorption and emission spectra of thin-films as well as their solution samples were studied. The variation of the lowest emitting states to their corresponding unsubstituted complexes, [Ir(F2ppy)2(acac/pic)] was also discussed. The electroluminescent (EL) device was fabricated using [Ir(F2 t Buppy)2(pic)] as the dopant (D-I) into the emitting layer and compared with two other EL devices where [Ir(F2MeOppy)2(acac)] (D-II) and FIrpic (D-III) dopants were used in the same device structure. The lower driving voltages obtained for D-I with respect to D-II and D-III devices were rationalized. The exceptional lowering of the luminance yield of the substituted dopants containing devices, D-I and D-II, to that of D-III which contains the unsubstituted dopant was also investigated. [Copyright &y& Elsevier]

Mono- and binuclear Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of Schiff-base ligands derived from 7-formyl-8-hydroxyquinoline with diaminonaphthalenes were prepared and characterized by elemental and thermal analysis, conductance measurements and IR spectroscopy. The structures of the solid complexes under study are established by using electronic and ESR spectroscopy and magnetic susceptibility measurements. The results show that Co(II), Zn(II) and Cd(II) complexes are tetrahedral, Ni(II) complexes are octahedral and Cu(II) complexes are either tetragonally distorted octahedral or square planar. All complexes and ligands were found to be highly active against fungi. [ABSTRACT FROM AUTHOR]

• An anionic complex of Cu(II) with N-acetylanthranilic ligand was prepared and analyzed by single crystal X-ray diffraction. • The complex is dimeric containing a Cu-Cu bond. • The complex exerted significant cytotoxic effect on MDA-MB-231 breast cancer cells and moderate anti-proliferative activity against PC-3 prostatic and T-24 bladder cancer cells. This paper presents the isolation of single crystals of an anionic Cu(II) complex (NH 4)(NHEt 3)[Cu 2 (L) 4 Cl 2 ]{HL = N -acetylanthranilic acid and NEt 3 = triethylamine}. The analyses revealed the complex packing in the triclinic "P-1" space group in addition to its dimeric structure and the octahedral geometry around the Cu(II)ions. In the complex, all the four carboxylate ligands are bridging the two Cu(II) centers and the charge on the anionic complex is compensated by an ammonium and protonated triethylamine ions. This Cu(II) complex is interestingly exerting highly significant cytotoxic effect on MDA-MB-231 breast cancer cells with IC 50 of 131.2 µg/ml and moderate anti-proliferative activity against both PC-3 prostatic cancer and T-24 transitional cell carcinoma cells with IC 50 of 200.7 and 300.3 µg/ml, respectively. [ABSTRACT FROM AUTHOR]