Structural Insights into the Coordination and Extraction Mechanism of Nickel(II) with Dinonylnaphthalene Sulfonic Acid and n‐Hexyl 3‐Pyridinecarboxylate Ester as Extractants

In this work, a nickel(II) synergist complex with methyl isonicotinate (B^I, a short chain analog of n‐hexyl 3‐pyridinecarboxylate ester) and naphthalene‐2‐sulfonic acid (HNS, a short chain analog of dinonylnaphthalene sulfonic acid) was synthesized and studied by single‐crystal X‐ray diffraction. The nickel(II) complex crystallizes in the monoclinic P 2₁/n space group with the composition [Ni(H₂O)₄(B^I)₂](NS)₂·2H₂O. The Ni(II) ions of these crystallographically independent molecules lie on an inversion center, forming a trans‐form distorted octahedral coordination structure. The nickel(II) ions can coordinate with four water molecules and two B^I ligands, resulting in a mono‐metallic structure [Ni(H₂O)₄(B^I)₂]²⁺. There is no direct interaction between nickel(II) and sulfonic oxygen atoms of the sulfonate anions, but hydrogen bonds form between sulfonic oxygen atoms and water molecules in the synergist complex. In order to further elucidate the solution structure of the nickel(II) complexes with the actual synergistic mixture containing n‐hexyl 3‐pyridinecarboxylate ester and dinonylnaphthalene sulfonic acid in the nonpolar organic phase, the nickel(II) complexes were studied by electrospray ionization mass spectrometry. The results indicated that the extracted nickel(II) complexes in the nonpolar solvent have a similar coordination structure as that of the crystalline nickel(II) synergist complex.     

Synthesis and spectroscopic characterization of bis(N-alkyldithiocarbamato)nickel(II) complexes: crystal structures of [Ni(S2CNH(n-Pr))2] and [Ni(S2CNH(i-Pr))2]

Bis(N-alkyldithiocarbamato)nickel(II) complexes (1–5) [Ni(S₂CNHR)₂] (where R?=?Me, Et, n-Pr, i-Pr, n-Bu) were synthesized by the reaction of NiCl₂?·?6H₂O and the corresponding sodium salt of N-alkyldithiocarbamate in 1?:?2 molar ratio in aqueous medium. These bis(N-alkyldithiocarbamato)nickel(II) complexes (1–5) were characterized by elemental analysis, UV-Visible, IR, and ¹H/¹³C-NMR spectroscopy. The crystallographic investigation of [Ni(S₂CNH(n-Pr))₂] (3) and [Ni(S₂CNH(i-Pr))₂] (4) revealed distorted square-planar geometry around nickel(II). The dithiocarbamates have anisobidentate coordination with nickel and the dithiocarbamates are trans.     

COORDINATION COMPOUNDS OF NICKEL WITH TRITHIOCYANURIC ACID

Abstract

Nickel(II) complexes with a combination of trithiocyanuric acid and diamines or triamines of composition [Ni(aepa)(ttcH)(H₂O)], [Ni(dien)(ttcH)(H₂O)], [Ni(dpta)(ttcH)(H₂O)] H₂O, [Ni(phen)₂(ttcH)]H₂O, [Ni(phen)₃](ttcH)-5H₂O and [Ni(1,2-pn)₃](ttcH)-H₂O (aepa = N-(2-aminoethyl)-1,3-propanediamine,dien = diethylenetriamine,dpta = dipropylenetnamine, phen = 1,10-phenanthroline, 1,2-pn = 1,2-diaminopropane. ttcH₃ = trithiocyanuric acid) have been prepared. The compounds have been characterized by means of elemental analysis, IR and electronic spectroscopies and magnetochemical measurements. Selected complexes were studied by thermal analysis. The compounds can be characterized as distorted octahedral Ni(II) complexes. It was found that the trithiocyanuric dianion can act either as a bidentate ligand or be situated out of the coordination sphere of nickel. The crystal and molecular structure of [Ni(dpta)(ttcH)(H₂O)] H₂O was determined. Crystals are monoclinic, space group P2₁/n, with a = 20.316(4), b = 7.967(2), c = 21.401(4) Å, β = 99.23(3)°, K=3419.1(13)ų, Z = 4, T = 293 K. The nickel(II) atom is six-coordinated by three nitrogen atoms from dipropylene-triamine, nitrogen and sulphur from trithiocyanuric acid, and an oxygen atom from a water molecule in a distorted octahedral geometry.     

Synthesis,Structure and Magnetic Properties of a Cyclic Heterotetranuclear Co3Fe Complex of 2-Mercaptophenol (H2mp) with tri-n-Butylphosphine Participation

Neutral heterotetranuclear complex Co₃Fe(mp)₄(Hmp)(PBuⁿ₃)₃ 2 (PBuⁿ₃ = tri-n-butylphosphine) of 2-mercaptophenol (H₂mp) was synthesized in a molar ratio of CoCl₂:FeCl₃:H₂mp:NaOMe:PBuⁿ₃ = 0.75:0.25:1:2:1 under anaerobic conditions. It represents partially Fe^III-substituted form of the asymmetric mixed-valence tetracobalt complex Co₄(mp)₄(Hmp)(PBuⁿ₃)₃ (1). 2 crystallizes in the triclinic space group Pl?, with a = 12.373(2) Å, b = 15.677(3) Å, c = 20.571(4) Å, α = 93.59(3)° β = 93.45(3)° γ = 112.30(3)°, V = 3669 ų, and Z = 2. The molecule exhibits a cyclic skeleton of Co₃FeS₄O₃ with two doubly μ₂-S bridges, one doubly μ₂-O bridge, and one singly μ₂-O bridge. The four mp^2? ligands display two different modes, O_bS_b-T and O_tS_b, while the monoanion Hmp^? is only terminally chelated to Fe³⁺ ion in HO_tS_t fashion (b stands for bridge, t for terminal, and T for trinuclear). The three Co centers are located in approximately square-based pyramidal environments, and the Fe atom in distorted trigonal bipyramidal geometry. Three types of main fragment ions were observed in the FAB mass spectrum of 2. The dissociation of the fragments follows the order: PBuⁿ₃ first, then Hmp and mp ligands. Moreover, the dissociation of Fe(Hmp) is first, followed by Co(mp) and Co(mp)₂, according with the fact that Fe(Hmp) is only loosely bonded. Variable-temperature magnetic susceptibility measurements showed that 2 exhibits weak magnetic exchange interactions.     

Synthesis and Characterization of Homoleptic and Heteroleptic Complexes Involving Dithiocarbamates,Triphenylphosphine, and Nickel(II)

Abstract

Six new nickel complexes of two dithiocarbamate ligands (cyfdtc = N-cyclohexyl-N- furfuryldithiocarbamate and bztpedtc = N-benzyl-N-[2-thiophenylethyl]dithiocarbamate) namely, (Ni[cyfdtc]₂) (1), (Ni[bztpedtc]₂) (2), (Ni[cyfdtc][NCS][PPh₃]) (3), (Ni[bztpedtc] [NCS][PPh₃]) (4), (Ni[cyfdtc][PPh₃]₂)ClO₄ (5), and (Ni[bztpedtc][PPh₃]₂)ClO₄ (6) have been prepared and characterized using IR, electronic, and NMR (¹H and ¹³C) spectra. A single crystal X-ray structural analysis was carried out for complex 3 and showed that nickel is in a distorted square planar arrangement with the NiS₂PN chromophore. The shift in ν_C?N of the heteroleptic complexes to higher frequencies compared with the parent complex is assigned to mesomeric delocalization of electron density from the

dithiocarbamate ligand toward the metal atom, which increases the contribution of polar thioureide form in mixed ligand complexes. Electronic spectral studies suggest square planar geometry for the complexes. In the ¹³C NMR spectra, the upfield shift of NCS₂ carbon signal for 3 and 4 from the chemical shift value of 1 and 2 is due to effect of PPh₃ on the mesomeric drift of electron density toward nickel throughout thioureide C?N bond.     

Speciation of the nickel(II) complexes with oxalic and malonic acids studied in 1.0 mol dm−3 NaCl at 25°C

In this article, we present the results of the speciation of the binary nickel(II)-oxalic acid (H₂L) and nickel(II)-malonic acid (H₂L) systems studied by electromotive forces measurements emf (H) using 1.0?mol?dm^?3 NaCl as the ionic medium at 25°C. The experimental data were analyzed by a computational least-squares program LETAGROP/FONDO, a version of the LETAGROP program, written to analyze regular formation function and reduced formation functions, taking into account the hydrolysis of the nickel(II) cation and the acid base reactions of the ligands which were kept fixed during the analysis. In the nickel(II)-oxalic acid system the complexes [NiHL]⁺, [NiL], [Ni(OH)L]^?, and [NiL₂]^2? were observed and for the nickel(II)-malonic acid system the complexes [NiHL]⁺, [NiL], [Ni(OH)L]^?, and [Ni(OH)₂L]^2? were detected. The stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.     

Synthesis and spectral studies on Ni(II) complexes involving N-furfuryl-N-substituted benzyldithiocarbamates and PPh3: Anagostic and C–H…π(chelate) interactions in (N-furfuryl-N-(4-fluorobenzyl)dithiocarbamato-S,S′)(thiocyanato-N)(triphenylphosphine)nickel(II)

Twelve new nickel(II) complexes of functionalized dithiocarabamates [Ni(S₂CNRR')₂](1-6) and [Ni(S₂CNRR')(NCS)(PPh₃)](7-12) [where R=furfuryl; R'=2-hydroxy benzyl (1,7), 3-hydroxy benzyl (2,8), 4-hydroxy benzyl (3,9), 4-methoxy benzyl (4,10), 4-fluoro benzyl (5,11), 4-chloro benzyl (6,12)] have been prepared and characterized by elemental analysis, IR, UV-Vis and NMR (¹H and ¹³C) spectroscopy. IR spectra of the complexes support the bidentate coordination of dithiocarbamate ligands. Electronic spectral studies on complexes 1-12 indicate square planar geometry around the nickel(II) central atom. In the ¹³C NMR spectra, the upfield shift of NCS₂ carbon signal for heteroleptic complex (7-12) compared to homoleptic complexes (1-6) is due to the effect of PPh₃ on the mesomeric drift of electron density toward nickel through thioureide C-N bond. Single crystal X-ray structural analysis of complex 11 confirms that the coordination geometry about the Ni(II) is distorted square planar. A rare intramolecular anagostic interaction C–H^…Ni [Ni???H=2.804 Å] is observed. The packing of complex 11 is stabilized by non-conventional C–H^…S, C–H?F and C–H?π(chelate, NiS₂C) bonding interactions.     

Synthesis,characterization, molecular and supramolecular structures of nickel(II) complexes derived from α-diketone and α-ketoaldehyde bisaroylhydrazones

A new series of nickel(II) complexes derived from symmetrical diacetyl bisaroylhydrazones [Ni(L¹-R)] and unsymmetric phenylglyoxal bisaroylhydrazones [Ni(L²-R)] have been prepared and characterized. X-ray crystal and molecular structures of [Ni(L¹-H)], [Ni(L¹-pCH₃O)] and [Ni(L¹-pNO₂)] have been determined. In these complexes, the Ni(II) is in a distorted square planar environment and the aroylhydrazone acts as dinegative tetradentate ligand forming a 5,5,5-tricyclic chelate ring. Reaction of [Ni(L¹-R)] with aqueous ammonia afforded the paramagnetic five coordinate [Ni(L¹-R)(NH₃)] while [Ni(L²-R)] gave the diamagnetic square planar [Ni(L²-R)(NH₃)] complexes. Reaction of [Ni(L¹-R)] complexes with imidazole gave the corresponding paramagnetic octahedral bis(imidazole) adducts. X-ray structures of both [Ni(L¹-H)(HIm)₂] and [Ni(L¹-pNO₂)(HIm)₂] suggest a distorted octahedral structure where the bisaroylhydrazone occupies the basal plane while the two imidazoles occupy the axial sites. The molecular units are associated together forming triple stranded helical chains. With imidazole the [Ni(L²-R)] series gave the corresponding diamagnetic mono(imidazole) [Ni(L²-R)(HIm)] complexes, The X-ray structure of {Ni(L²-pCH₃)(HIm)] suggest square planar arrangement around the Ni(II) where the bisaroylhydrazone acts as dinegative NNO tridentate ligand forming with the Ni(II) a 5,6-bicyclic chelate ring the fourth coordination site is occupied by imidazole nitrogen.     

Thermal, spectral and magnetic behaviour of 2,3,4-trimethoxybenzoates of Mn(II), Co(II), Ni(II) AND Cu(II)

Four new complexes of 2,3,4-trimethoxybenzoic acid anion with manganese(II), cobalt(II), nickel(II) and copper(II) cations were synthesized, analysed and characterized by standard chemical and physical methods. 2,3,4-Trimethoxybenzoates of Mn(II), Co(II), Ni(II) and Cu(II) are polycrystalline compounds with colours typical for M(II) ions. The carboxylate group in the anhydrous complexes of Mn(II), Co(II) and Ni(II) is monodentate and in that of Cu(II) monohydrate is bidentate bridging one. The anhydrous complexes of Mn(II), Co(II) and Ni(II) heated in air to 1273 K are stable up to 505–517 K. Next in the range of 505–1205 K they decompose to the following oxides: Mn₃O₄, CoO, NiO. The complex of Cu(II) is stable up to 390 K, and next in the range of 390–443 K it loses one molecule of water. The final product of its decomposition is CuO. The solubility in water at 293 K is of the order of 10^–3 mol dm^–3 for the Mn(II) complex and 10^–4 mol dm^–3 for Co(II), Ni(II) and Cu(II) complexes. The magnetic moment values of Mn²⁺, Co²⁺, Ni²⁺ and Cu²⁺ ions in 2,3,4-trimethoxybenzoates experimentally determined in the range of 77–300 K change from 5.64–6.57 μB (for Mn²⁺), 4.73–5.17 μB (for Co²⁺), 3.26–3.35 μB (for Ni²⁺) and 0.27–1.42 μB (for Cu²⁺). 2,3,4-Trimethoxybenzoates of Mn(II), Co(II) and Ni(II) follow the Curie–Weiss law, whereas that of Cu(II) forms a dimer.     

Synthesis and spectral studies on NiS<Subscript>4</Subscript>, NiS<Subscript>2</Subscript>PN,NiS<Subscript>2</Subscript>P<Subscript>2</Subscript> chromophores: Single-crystal X-ray structure of [Ni(dbpdtc)<Subscript>2</Subscript>] (dbpdtc = benzyl(4-(benzylamino)phenyl)dithiocarbamate)

Three complexes of a dithiocarbamate ligand (dbpdtc = benzyl(4-(benzylamino)phenyl)dithiocarbamate), namely [Ni(dbpdtc)₂] (1), [Ni(dbpdtc)(NCS)(PPh₃)] (2) and [Ni(dbpdtc)(PPh₃)₂]ClO₄ (3) have been prepared. The complexes were characterized by IR, electronic spectroscopy and cyclic voltammetry. A single-crystal X-ray structural analysis was carried out for complex 1 and showed that the nickel is in a distorted square planar environment with a NiS₄ chromophore. For the two mixed ligand complexes, the thioureide ν _C–N values were shifted to higher wavenumbers compared to [Ni(dbpdtc)₂], suggesting increased strength of the thioureide bond due to the presence of the π-accepting phosphine. Electronic spectral studies suggest square planar geometries for the complexes. Cyclic voltammetry showed easier reduction of nickel(II) to nickel(I) in the mixed ligand complexes compared to [Ni(dbpdtc)₂].     

Thermal decomposition of nickel(II), palladium(II), and platinum(II) complexes of <Emphasis Type="Italic">N</Emphasis>-allyl-<Emphasis Type="Italic">N</Emphasis>′-pyrimidin-2ylthiourea

Thermal decomposition of Ni(II), Pd(II), and Pt(II) complexes of N-pyrimidin-2ylthiourea (AllPmTu) have been studied by TG, DTG, and DTA and by electron impact (EI) mass spectra. The complexes have the molecular formulae as [Ni(AllPmTu)Cl₂(H₂O)], [Ni(AllPmTu)₂Cl₂(H₂O)₂], and [M(AllPmTu)Cl₂], where M = Pd^II or Pt^II, and [Pt(AllPmTu)₂]. The TG curves show that Ni(II) complexes decompose in three stages to yield NiO as a residue, while Pd(II) and Pt(II) decompose in two stages to yield MS residues. The initial mass losses correspond to elimination of allylamine for Pd(II) and Pt(II) complexes but, allyisothiocyanate for both Ni(II) complexes revealing that sulfur atom of thiourea part is involved in coordination to Pd(II) and Pt(II) but does not to Ni(II). Kinetic parameters (E ^#, n, ΔH ^#, ΔS ^#, ΔG ^#) of the decomposition stages are determined and correlated with bonding and structural properties of the complexes. The EI mass spectra of the complexes show fragments corresponding to the evolved and intermediate species.     

Die elektronenstruktur der ethen-nickel π-komplexe the electronic structure of ethylene nickel π-complexes

Nickel(0)-olefine π-complexes such as Ni(C₂H₄)₃ and Ni(C₂H₄)(PR₃)₂ [6] prepared by conventional ligand replacement reaction are diamagnetic and stable up to room temperature. Similar π-complexes e.g. Ni(C₂H₄) _n (withn = 1, 2 or 3) generated by cryo-condensation technique [3] may exist in a paramagnetic state which derives from the triplet ground state of the atomic nickel. The stability of (η²-ethylene) nickel has been explained byab initio-MO calculations relating the energies of the complexes to different terms (¹ S and³ F) of the nickel atom.

     

New homoleptic metal complexes of Schiff bases derived from 2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-one

New bidentate Schiff-base ligands 2-(2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazinecarbothioamide HL¹ and 2-(2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-ylidene)hydrazinecarboxamide HL² were synthesized from the condensation of 2,4-di-p-tolyl-3-azabicyclo[3.3.1]nonan-9-one with thiosemicarbazide and semicarbazide, respectively. Homoleptic complexes of these ligands, of general formula K[Cr(L ⁿ )₂Cl₂], K₂[Mn(L ⁿ )₂Cl₂], K₂[Fe(L¹)₂Cl₂] and [M(L ⁿ )₂] (where M = Co(II), Ni(II) Cu(II), Zn(II), Cd(II), and Hg(II) ions; n = 1 or 2) are reported. The mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometry for Cr(III), Mn(II), and Fe(II) complexes, square planar for Cu(II), Co(II), and Ni(II) complexes and tetrahedral for Zn(II), Cd(II), and Hg(II) complexes.     

Coenzyme M studies with nickel(II) compounds: Synthesis,structure, spectra and redox behaviors

Nickel(II) complexes of 1,6-bis(pyridyl)-2,5-dithiahexane (L¹), 1,7-bis(2′-pyridyl)-2,6-dithiaheptane (L²) and 1,9-bis(2′-pyridyl)-2,5,8-trithianonane (L³) have been prepared and their spectroscopic and redox behaviors were studied. [Ni(II)L¹(H₂O)₂](ClO₄)₂, and [Ni(II)L³(H₂O)](ClO₄)₂ were crystallized in single crystal form; their structures were solved by X-ray crystallography. The structures of the complexes are of distorted octahedral geometry. A red shift in the electronic spectra and a positive potential shift in electrochemical studies were detected during the addition of the sodium salt of 2-mercaptoethanesulfonic acid (CoM) to Ni(II) complexes containing L¹ and L². The high redox potential shifting difference (PSD) was observed with the addition of CoM to [NiL¹]²⁺, which accounts for the axial coordination of CoM with the nickel ion. However, [Ni(II)L³]²⁺ does not respond well with CoM addition due to the structural limitation around the Ni(II) ion. A destabilization of [Ni(II)L¹]²⁺ and [Ni(II)L²]²⁺ complexes and stabilization for [Ni(II)L³]²⁺ were noticed in their redox studies and these trends were inversely changed during anaerobic CoM addition to Ni(II) complexes. A nephelauxetic effect (β values) has been shown to establish a good relation with PSD.     

Ni(II) and Cu(II) complexes of new unsymmetrical N2O2 Schiff bases derived from 3-(2-aminobenzylimino)-1-phenylbutan-1-ol: synthesis,structure, antibacterial properties,and electrochemistry

Two new N₂O₂ unsymmetrical Schiff bases, H₂L¹ = 3-[({o-[(E)-(o-hydroxyphenyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol and H₂L² = 3-[({o-[(E)-(2-hydroxy-1-naphthyl)methylideneamino]phenyl}methyl)imino]-1-phenyl-1-buten-1-ol, and their copper(II) and nickel(II) complexes, [CuL¹] (1), [CuL²] (2), [NiL¹] (3), and [NiL²] (4), have been synthesized and characterized by elemental analyses and spectroscopic methods. The crystal structures of these complexes have been determined by X-ray diffraction. The coordination geometry around Cu(II) and Ni(II) centers is described as distorted square planar in all complexes with the CuN₂O₂ coordination more distorted than the Ni ones. The electrochemical studies of these complexes indicate a good correlation between the structural distortion and the redox potentials of the metal centers. The ligand and metal complexes were also screened for their in vitro antibacterial activity.     

Synthesis and characterization of TCNQ derivatives of Ni(II) and Cu(II) with pyrazole-based ligands

Reactions between nickel(II) and copper(II) salts [M(L) _n ](ClO₄)₂ [L: 2-(pyrazole-1-ylmethyl)pyridine; n = 3 for Ni(II) and n = 2 for Ni(II) and Cu(II)] and LiTCNQ or mixture of LiTCNQ/TCNQ and Et₃NH(TCNQ)₂ yielded [Ni(L)₃](TCNQ)₂ · H₂O, [Ni(L)₂(TCNQ)₂], [Ni(L)₃](TCNQ)₃, [Ni(L)₂(TCNQ)₃], and [Cu(L)₂(TCNQ)₃] · 3H₂O. These complexes were characterized by infrared, electronic absorption, variable temperature magnetic moments and electron paramagnetic studies. Magnetic moments increase with increase in temperature attributed to contribution from TCNQ, which has also been examined by electron paramagnetic resonance.     

Synthesis,characterization, fluorescence and redox features of new <Emphasis Type="Italic">vic</Emphasis>-dioxime ligand bearing pyrene and its metal complexes

A new vic-dioxime ligand, N,N′-bis(aminopyreneglyoxime) (LH₂), and its copper(II), nickel(II) and cobalt(II) metal complexes were synthesized and characterized by elemental analyses, IR, UVVIS and ¹H and ¹³C NMR spectra (for the ligand). Mononuclear complexes were synthesized by a reaction of ligand (LH₂) and salts of Co(II), Ni(II), and Cu(II) in ethanol. The complexes have the metal-ligand ratio of 1: 2 and metals are coordinated by N,N′ atoms of vicinal dioximes. The ligand acts in a polydentate fashion bending through nitrogen atoms in the presence of a base, as do most vic-dioximes. Detection of a H-bonding in the Co(II), Ni(II), and Cu(II) complexes by IR revealed the square-planar MN₄ coordination of mononuclear complexes. Fluorescent properties of the ligand and its complexes arise from pyrene units conjugated with a vic-dioxime moiety. Fluorescence emission spectra of the ligand showed a drastic decrease in its fluorescence intensity upon metal binding. The electrochemical properties of the complexes were studied by the cyclic voltammetry technique. The nickel complex displayed an irreversible oxidation process while the copper complex exhibited a quasi-reversible oxidation and reduction processes based on the copper Cu(II)/Cu(III) and Cu(II)/Cu(I) couples, respectively.     

Nickel(II) complexes of tetradentate NSNO pyridylthioazophenol ligands: Synthesis,characterization and crystal structure

Two sets of nickel(II) complexes of a series of tetradentate NSNO ligands were synthesized and isolated in their pure form. All these complexes, formulated as [Ni(L)Cl]₂ and [Ni(L)(N₃)]₂ [HL = pyridylthioazophenols], were characterized using physicochemical and spectroscopic tools. The solid-state structures of two complexes (1a and 2a) were established by X-ray crystallography. The geometry about the nickel ion of the complexes is octahedral and the complexes are dimeric in nature. In 1, two Ni(II) ions are bridged by two Cl⁻ anions while in 2 they are bridged by two azide ions in a μ-1,1-bridging fashion.     

Synthesis and spectral characterization of Schiff-base complexes derived from alanine and 2-acetylpyridine with some divalent metal acetates

Schiff-base complexes [ML(H₂O)₂(Ac)]nH₂O (M?=?Co(II), Ni(II) and Zn(II); L?=?Schiff-base ligand derived from 2-acetylpyridine and alanine and n?=?1–3/2) were synthesized and characterized by elemental analysis, spectral (FTIR, UV/Vis, MS, ¹H-NMR), thermal (TGA), conductance and magnetic moment measurements. The results suggest octahedral geometry for all the isolated complexes. IR spectra show that the ligand coordinates to the metal ions as mononegative tridentate through pyridyl nitrogen, azomethine nitrogen and carboxylate oxygen after deprotonation of the hydroxyl group. Semi-empirical calculations PM3 and AM1 have been used to study the molecular geometry and the harmonic vibrational spectra to assist the experimental assignments of the complexes.     

Synthesis and characterization of heterobimetallic Ni(II)–Zn(II) complexes from bis(2-hydroxy-1 -naphthaldehyde)succinoyldihydrazone

Monometallic zinc(II) and nickel(II) complexes, [Zn(H₂nsh)(H₂O)] (1) and [Ni(H₂nsh)(H₂O)₂] (2), have been synthesized in methanol by template method from bis(2-hydroxy-1-naphthaldehyde)succinoyldihydrazone (H₄nsh). Reaction of monometallic complexes with alternate metal(II) acetates as a transmetallator in 1 : 3 molar ratio resulted in the formation of heterobimetallic complexes [NiZn(nsh)(A)₃] and [ZnNi(nsh)(A′)₂] (A = H₂O (3), py (4), 2-pic (5), 3-pic (6), 4-pic (7)), (A′ = H₂O (8), py (9), 2-pic (10), 3-pic (11), and 4-pic (12)). The complexes have been characterized by elemental analyzes, mass spectra, molar conductance, magnetic moments, electronic, EPR, and IR spectroscopies. All of the complexes are non-electrolytes. Monometallic zinc(II) is diamagnetic while monometallic nickel(II) complex and all heterobimetallic complexes are paramagnetic. The metal centers in heterobimetallic complexes are tethered by dihydrazone and naphthoxo bridging. Zinc(II) is square pyramidal; nickel(II) is six-coordinate distorted octahedral except [ZnNi(nsh)(A)₂], in which nickel(II) has square-pyramidal geometry. The displacement of metal center in monometallic complexes by metal ion has been observed in the resulting heterobimetallic complexes.