Synthesis and variable coordination modes of a bis-thiophene-appended macrocycle in complex with cobalt(III)

The bis-thiophene appended cyclam derivative L³ (trans-6,13-dimethyl-6,13-bis(thiophene-3′-ylmethylamino)-1,4,8,11-tetraazacyclotetradecane) has been synthesised, characterised and complexed with Co^III. The crystal structure of the diprotonated ligand as its cyanoborohydride salt [H₂L³][NCBH₃]₂ is reported. Variable coordination modes to Co^III have been identified that find the ligand binding either as a tetradentate (cyclam-like) macrocycle in the structurally characterised complexes trans-[CoL³Cl₂]Cl and trans-[CoL³(NCBH₃)(OH)]Cl or as a hexadentate in [CoL³]Cl₃ where both functionalised exocyclic amines coordinate in trans coordination sites. In this case, we have found that the structure of the hexadentate coordinated complex [CoL³]³⁺ is significantly tetragonally elongated due to steric effects of the thiophene rings and this also leads to a very large 500 mV anodic shift in the Co^III/II redox potential relative to the unsubstituted hexaamine complex of Co^III.     

Crystal structure,thermal behavior,and microbiological activity of a thiosemicarbazide-type ligand and its cobalt complexes

The synthesis of a potentially bioactive mixed-valence Co^III/Co^II complex with 2-acetylpyridine S-methylisothiosemicarbazone (HL) ligand is described. The crystal and molecular structure of the formed [Co^IIIL₂][Co^IICl₃ py]·Me₂CO (I) compound (py stands for pyridine) is determined by single-crystal X-ray crystallography. It’s thermal decomposition along with the decomposition of the ligand and six structurally related complexes with formulas [CoL₂]NO₃·MeOH (1), [CoL₂]Br·MeOH (2), [CoL₂]HSO₄·MeOH (3), [CoL₂]₂[Co^II(NCS)₄] (4), [Co(HL)(L)]I₂·2MeOH (5), and [Co(HL)(L)][Co^IICl₄]·MeOH (6) was determined by simultaneous TG/DSC measurements. The decomposition pattern is evaluated using TG/DTA-MS data. The results were related to the solvent/moisture content and the decomposition mechanism of the compounds. The antimicrobial activity of the ligand and of all the complexes was tested in vitro for selected gram-negative and gram-positive bacteria and fungi. The activity of the ligand against all tested bacteria is comparable with those obtained for standard antibiotics, while it is less active against fungi. Surprisingly, the activity of the complexes is very low. The low antimicrobial activity of the complexes may be in connection with their high thermodynamic and kinetic inertness in solution. The results are also supported by the relatively high thermal stability of the complexes.     

Electrochemical polymerization of 3,4-ethylenedioxythiophene in aqueous solution containing N-dodecyl-β-d-maltoside

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were synthesized electrochemically by direct anodic oxidation of 3,4-ethylenedioxythiophene (EDOT) at relatively low monomer concentration (0.005-0.01 mol L⁻¹) in aqueous solution containing green nonionic sugar-based surfactant N-dodecyl-β-d-maltoside (DM), which has good biocompatibility and biodegradability. The moderate interaction between DM through the hydroxy groups and EDOT monomer led to the decrease of monomer oxidation onset. Different surfactants, such as anionic sodium dodecylbenzenesulfate (SDBS), nonionic triton X-100 (TX100), were also tested for comparison. As-formed PEDOT films were characterized electrochemically and spectroscopically using FTIR and UV-visible techniques. PEDOT nano-materials with good thermal stability and conductivity of 26.2 S cm⁻¹ can be synthesized in water-DM micellar solution, which can be proved by the results of scanning electron microscopy (SEM). PEDOT prepared from water-DM media with good biocompatibility can be a good candidate for application in biosensors.     

Acridine-based ligands from cobalt(II) mediated rearrangement of diphenylamine-based starting materials

The synthesis and characterisation of two cobalt(II) complexes, [Co^IIL^Br-acrCl₂] (1a) and [Co^IIL^H-acrCl₂] (1b), with acridine head-units resulting from an unexpected ligand rearrangement from a diphenylamine head-unit, and the intended cobalt(II) complex, Co^IIL^Br-dpa(Cl)(H₂O) (2), are reported. Single crystals of the two dark green acridine-based cobalt(II) complexes, 1a and 1b, form in a one-pot reaction of cobalt(II) chloride, the chosen diphenylamine-2,2′-dicarboxaldehyde (Ia 4,4-′dibromo- or Ib unsubstituted), triethylamine and two equivalents of 2,4-dimethylaniline in acetonitrile, in 23% yield. In contrast, the intended diphenylamine-based complex was isolated in two steps: first isolation of the Schiff base ligand, then complexation with cobalt(II) chloride and deprotonation with potassium tert-butoxide, in methanol/dichloromethane, giving 2 as a bright yellow solid in 67% yield. All three complexes feature cobalt(II) centres, with N₂Cl₂ approximately tetrahedral coordination for 1a and 1b confirmed by single crystal structure determinations. It is proposed that after one imine ‘arm’ forms, cobalt(II) coordination facilitates the other aldehyde undergoing an intramolecular cyclisation to form the new heterocyclic acridine head-unit. The structures of both of the resulting acridine-based complexes, 1a and 1b, and that of the originally intended Schiff base ligand, HL^Br-dpa, were confirmed by single-crystal X-ray diffraction. These are the first examples of complexes of an acridine ligand of this type.     

Synthesis and ROMP activity of aminophenol-substituted tungsten(VI) and molybdenum(VI) complexes

Tungsten(VI) and molybdenum(VI) complexes [MO(L¹)Cl₂] and [M(X)(L²)Cl₃] (X = O, NPh) with tridentate aminobis(phenolate) ligand L¹ = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) and bidentate aminophenolate ligand L² = 2,4-di-tert-butyl-6-((dimethylamino)methyl)phenolate) were prepared and characterised. These complexes are principally stable in open atmosphere under ambient conditions. When activated with Et₂AlCl, they exhibited high activity in ring-opening metathesis polymerisation (ROMP) of 2-norbornene (NBE) and its derivatives. Especially complexes [M(NPh)(L²)Cl₃], which are easily available from corresponding metal oxides MO₃ by a simple three-step synthesis, were found very efficient ROMP catalysts for NBE (M = Mo, W) and 2-norbornen-5-yl acetate (M = Mo).     

Complexes of Cu(I) and Pd(II) with (+)-camphor and (–)-cavrone thiosemicarbazones: Synthesis,structure, and cytotoxicity of the Pd(II) complex

CuLCl, CuL¹Cl, PdLCl₂, and PdL¹Cl₂ complexes [L and L¹ being (+)-camphor and (–)-carvone thiosemicarbazones, respectively] have been synthesized. The structure of binuclear [Pd₂L²²Cl₄] complex has been determined by means of X-ray diffraction. The L² ligand (dehydrogenated (–)-carvone thiosemicarbazone) is coordinated via the bridging S atom to two Pd atoms. The complexes of Cu(I) and Pd(II) presumably have polynuclear and binuclear structure, respectively. These facts are in good agreement with IR and NMR spectroscopy as well as mass spectrometry data which indicate the coordination of L and L¹ ligands via the S atom. The influence of L¹ and PdL¹Cl₂ on viability of the Hep2 cell line has been studied. The PdL¹Cl₂ complex is more cytotoxic than L¹ ligand.     

Synthesis and characterization of CuII and CoII complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPT) by chemical and tribochemical reactions

Four Cu^II and Co^II complexes–[Cu(L₁)Cl₂(H₂O)]3/2H₂O · 1/2EtOH, [Cu(L₁)₂Cl₂]6H₂O, [Co(L₁)Cl₂]3H₂O · EtOH, and [Co₂(L₁)(H₂O)Cl₄]1.5H₂O · EtOH (L₁ = 2,4,6-tri(2-pyridyl)-1,3,5-triazine; TPT)–were synthesized by conventional chemical method and used to synthesize another four metal complexes–[Cu(L₁)I₂(H₂O)]6H₂O, [Cu(L₁)₂I₂]6H₂O, [Co(L₁)I(H₂O)₂]I · 2H₂O, and [Co₂(L₁)I₄(H₂O)₃]–using tribochemical reaction, by grinding it with KI. Substitution of chloride by iodide occurred, but no reduction for Cu^II or oxidation of Co^II. Oxidation of Co^II to Co^III complexes was only observed on the dissolution of Co^II complexes in d₆-DMSO in air while warming. The isolated solid complexes (Cu^II and Co^II) have been characterized by elemental analyses, conductivities, spectral (IR, UV-Vis, ¹H-NMR), thermal measurements (TGA), and magnetic measurements. The values of molar conductivities suggest non-electrolytes in DMF. The metal complexes are paramagnetic. IR spectra indicate that TPT is tridentate coordinating via the two pyridyl nitrogens and one triazine nitrogen forming two five-membered rings around the metal in M : L complexes and bidentate via one triazine nitrogen and one pyridyl nitrogen in ML₂ complexes. In binuclear complexes, L is tridentate toward one Co^II and bidentate toward the second Co^II in [Co₂(L₁)Cl₄]2.5H₂O · EtOH and [Co₂(L₁)I₄(H₂O)₃]. Electronic spectra and magnetic measurements suggest a distorted-octahedral around Cu^II and high-spin octahedral and square-pyramidal geometry around Co^II.     

A miniaturized and integrated galvanic cell for the potentiometric measurement of ions in biological liquids

A procedure for an all-plastic electrochemical cell comprising miniaturized planar indicator and reference electrodes is described. All electrodes are based on conducting polymers, are fully integrated, and contain no internal electrolyte. The reference microsensors were deposited via electrochemical polymerization from a water solution containing the monomer 3,4-ethylenedioxythiophene (EDOT) or 1-methylpyrrole (MPy) and a biochemical buffer 3-(N-morpholino) propanesulfonic acid [MOPS], 2-(N-morpholino) ethanesulfonic acid [MES], or 2-hydroxy-5-sulfobenzoic acid [SSA]). Ion-sensitive microelectrodes were prepared by the deposition of the ion-sensitive membrane solution (Ca²⁺, K⁺, and Cl⁻) directly onto the mediating poly-EDOT (PEDOT), PEDOT–SSA, PEDOT–MES, PEDOT–MOPS, or poly-MPy–MOPS layers.     

Synthesis and characterisation of new pyrazole-phosphinite ligands and their ruthenium(II) arene complexes

The new potentially bidentate pyrazole-phosphinite ligands [(3,5-dimethyl-1H-pyrazol-1-yl)methyl diphenylphosphinite] (L¹) and [2-(3,5-dimethyl-1H-pyrazol-1-yl)ethyl diphenylphosphinite] (L²) were synthesised and characterised. The reaction of L¹ and L² with the dimeric complexes [Ru(η⁶-arene)Cl₂]₂ (arene = p-cymene, benzene) led to the formation of neutral complexes [Ru(η⁶-arene)Cl₂(L)] (L = L¹, L²) where the pyrazole-phosphinite ligand is κ¹-P coordinated to the metal. The subsequent reaction of these complexes with NaBPh₄ or NaBF₄ produced the [Ru(η⁶-p-cymene)Cl(L²)][BPh₄] and [Ru(η⁶-benzene)Cl(L²)][BF₄] compounds which contain the pyrazole-phosphinite ligand κ²-P,N bonded to ruthenium. All the complexes were fully characterised by analytical and spectroscopic methods. The structure of the complex [Ru(η⁶-p-cymene)Cl(L²)][BPh₄] was also determined by a X-ray single crystal diffraction study.     

Synthesis,spectroscopic, thermal,and antimicrobial studies of tetradentate 12 and 14 member Schiff bases and their complexes with Fe(III), Co(II), and Cu(II)

Two Schiff bases, L¹ (5,6;11,12-dibenzophenone-2,3,8,9-tetramethyl-1,4,7,10-tetraazacyclododeca-1,3,7,9-tetraene) and L² (6,7;13,14-dibenzophenone-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene), bearing functionalized pendant arms have been synthesized by cyclocondensation of 3,4-diaminobenzophenone with 2,3-butanedione and 2,4-pentanedione, respectively. Mononuclear macrocyclic complexes [FeL¹Cl₂]Cl, [FeL²Cl₂]Cl, [ML¹Cl₂], and [ML²Cl₂] (where M?=?Co(II) and Cu(II)) have been prepared by reacting iron(III), cobalt(II), and copper(II) with the preformed Schiff base. The ligands and their corresponding metal complexes were characterized by elemental analyses, ESI-mass spectra, conductivity, magnetic moments, UV-Vis, EPR, IR, ¹H-, and ¹³C-NMR spectral studies, and TGA-DTA/DSC data. The TGA profiles exhibit a two-step pyrolysis, although the iron complexes decompose in three steps, leaving behind metal oxides as the final product. The ligands and complexes were screened in vitro against Gram-positive bacteria, Gram-negative bacteria, and fungi.     

Synthesis, structural features and biological activities of three asymmetric pyridazine–triazole coordination polymers

The complexes [CuL₂Cl₂]_n (1), [CoL₂Cl₂(H₂O)₂]·L (2) and [MnL₂Cl₂(H₂O)₂]·L (3) (L = 3-chloro-6-(1H-1,2,4-triazol-1-yl) pyridazine) were synthesized and characterized by physicochemical and spectroscopic methods. X-ray crystallographic analysis reveals that the Cu(II) center of complex 1 is located in a slightly distorted tetragonal pyramidal environment and bridged by chlorine atoms to generate infinite 1D chains, which are further connected into 2D supramolecular structures by C–H…Cl hydrogen bonds. The Co(II) and Mn(II) atoms in complexes 2 and 3 both have a distorted octahedral coordination sphere, and the crystal lattices include hydrogen bonds and π–π stacking interactions to yield 3D supramolecular frameworks. The antioxidant activities (influence on O₂ ^?? and ^?OH) and antibacterial activities of the ligand L and its three complexes were also investigated.     

Spectral study of complexation ofcis,cis-1,3,5-tri[2-(diphenylphosphinyl)ethylamino]cyclohexane with copper(ii) and cobalt(ii) ions

The complexation ofcis,cis-1,3,5-tri[2-(diphenylphosphinyl)ethylamino]cyclohexane (L¹) with Cu²⁺ and Co²⁺ cations has been studied in different solvents by means of UV-Vis, ESR, and IR spectroscopy. It has been shown that in the CuL¹ complex the metal ion is pentacoordinated by three nitrogen atoms and two phosphinyl groups of the ligand and has a tetragonal-pyramidal environment. The conformation of the coordination polyhedron for the CuL¹ complex depends on the solvent. In the CoL¹ complex, as well as in the CoL² complex, where L² is 1,4,7-tris(2-diphenylphosphinylethyl)-1,4,7-triazacyclononane, the Co²⁺ ion has an octahedral environment and is bound to all donor atoms of the ligands.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1199–1202, July, 1993.The authors are grateful to A. G. Matveeva and Yu. M. Polikarpov for the fruitful discussions.     

Ruthenium(II) ligated to tetradentate diaminodithioethers: synthesis,characterisation and electrochemistry

Ruthenium(II) complexes containing two tetradentate ligands, 1,2-bis(o-aminophenylthio)ethane (L¹) and 1,2-(oaminophenylthio)xylene (L²), have been prepared. The complexes, which are of the type Ru(L)Cl₂ [L = L¹ (1);/L² (2)], [Ru(L)(PPh₃)Cl]Cl [L = L¹ (3); L² (4)] and [Ru(L)(bpy)](PF₆)₂ [L = L¹ (5);/L² (6)], were characterised by elemental analysis, i.r., u.v.-vis. and n.m.r. spectroscopy and their electrochemical behaviour has been examined by cyclic voltammetry using a glassy carbon working electrode and an Ag/AgCl electrode as the reference electrode. This revised version was published online in June 2006 with corrections to the Cover Date.     

Syntheses and structural transformations of oxorhenium(V) complexes with triazine and imidazole derivatives: mixed ligand complexes with thiocyanate, 8-hydroxyquinoline and 1,10-phenanthroline

Mononuclear oxorhenium(V) complexes [ReO(HL¹ or H₂L²)(PPh₃)(OH₂)Cl]Cl, {H₂L^{1 =} 1-(2-hydroxyphenyl)butane-1,3-dione-3-(5,6-diphenyl-1,2,4-triazine-3-ylhydrazone) and H₃L^{2 =} 1-(2-hydroxyphenyl)butane-1,3-dione-3-(1H-benzimidazol-2-ylhydrazone)}, have been synthesized by ligand exchange with trans-trichloromonooxo-bis(triphenylphosphine) rhenium(V). The reaction of a 1?:?1 mixture of either NH₄SCN, 1,10-phenanthroline (1,10-phen) or 8-hydroxyquinoline (8-OHquin) and H₂L¹ or H₃L², with trans-ReOCl₃(PPh₃)₂ yielded the mononuclear oxorhenium(V) complexes, [ReO(HL¹ or H₂L²)(PPh₃) (SCN)Cl], [ReO(HL¹)(1,10-phen)Cl]Cl, [ReO(H₂L²)(1,10-phen)(OH₂)]Cl₂·H₂O and [ReO(HL¹ or H₂L²) (8-Oquin)Cl]. Thermal studies on these complexes showed structural transformations from mononuclear into binuclear complexes. [Re₂O₃(HL¹ or H₂L²)₂(PPh₃)₂Cl₂], [Re₂O₂(μ-L¹ or L²)₂(SCN)₂] and [Re₂O₃ (H₂L²)₂(1,10-phen)₂]Cl₂, were synthesized pyrolytically in the solid state from the respective precursor rhenium complexes. The structures of all complexes and the corresponding thermal products were elucidated using elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments and ¹H NMR and TG-DSC measurements. The prepared complexes and their thermal products have octahedral configurations. The ligands H₂L¹ or H₃L² behave as monoanionic bidentate or monoanionic tetradentate ligands towards the oxorhenium ions. The antifungal activities of the metal complexes towards Alternaria alternata and Aspergillus niger were tested and showed comparable behavior with well known antibiotics.     

3,4-Ethylenedioxythiophene (EDOT)-based π-conjugated oligomers: Facile synthesis and excited-state properties

A facile synthetic method to produce soluble 3,4-ethylenedioxythiophene (EDOT) oligomers was developed by using iron (III) nitrate nonahydrate as the oxidizing reagent. Two EDOT oligomers, i.e. octomers and octodecamers were obtained as the major products. Their UV–vis absorption, fluorescence at room temperature and 77 K, and triplet transient difference absorption have been measured in CH₂Cl₂ solutions or glassy solutions. With increased conjugation length from EDOT octomers (A) to EDOT octodecamers (B), the UV–vis absorption, fluorescence and the triplet transient difference absorption band shift to longer wavelength. Both the oligomers also exhibit reasonably high efficiency to generate singlet oxygen.     

Nickel(II) and copper(II) complexes with chiral bis-α-thiooxime,the derivative of natural terpenoid (+)-3-carene: Synthesis and structures

Chiral bis-α-thiooxime (H₂L¹), the derivative of the natural monoterpenoid (+)-3-carene, was synthesized and used to prepare paramagnetic complexes of the composition M(H₂L¹)Cl₂ (M=Ni, Cu). The crystal structures of [Ni(H₂L¹)Cl₂] (I) and [Cu(H₂L¹)Cl₂] (II) were determined by X-ray diffraction analysis. Crystals I and II consist of mononuclear acentric molecules. The Ni²⁺ ion in a molecule of complex I coordinates two N atoms and two S atoms of a tetradentate chelating ligand (the H₂L¹ molecule) and two Cl atoms. The NiCl₂N₂S₂ coordination core forms octahedron compressed along the apical N atoms. In a molecule of complex II, the Cu²⁺ ion coordinates two S atoms and the N atom of a tridentate chelating H₂L¹ ligand and two Cl atoms. The CuCl₂NS₂ coordination core forms a trigonal bipyramid.     

Synthesis, Spectral and Thermal Analyses of Novel Bi- and Polyhomonuclear Complexes of Pyrimidine Bisazo-dianil Derivatives

Seven new bi‐ and polyhomonuclear transition metal complexes with three polyhydroxlated bisazodianil ligands were synthesized and characterized. The ligands were derived from condensation of 6‐(5‐formyl‐2‐hydroxyphenylazo)‐2,4‐dihydroxypyrimidine with aliphatic diamines (H₈L¹, H₈L² and H₆L³). The data of elemental and thermal analyses, molar conductance measurement, IR, electronic and ESR spectra as well as magnetic moment measurements support the formation of [L¹Co₇Cl₆(H₂O)₁₀]·22H₂O ( 1 ), [H₂L²Mn₆Cl₆(H₂O)₈]·3H₂O·2EtOH ( 3 ), [L²Co₈Cl₈(H₂O)₁₂]·24H₂O ( 4 ), [H₄L³Co₂Cl₂(H₂O)₂]·8H₂O·2EtOH ( 6 ) with a tetrahedral geometry and [H₂L¹Ni₅Cl₄(H₂O)₁₆]·19H₂O·EtOH ( 2 ), [L²Ni₈Cl₈(H₂O)₂₈]·8H₂O·EtOH ( 5 ) with an octahedral geometry while [H₆L³Cu₃(H₂O)₇]Cl₃·10H₂O ( 7 ) has a distorted tetrahedral arrangement. The mode of bonding between the metal ions and the ligand molecules is determined and the metal‐metal interaction was studied. The activation thermo‐kinetic parameters for the thermal decomposition steps of the complexes E*, ΔH*, ΔS*, and ΔG* were calculated.     

A chiral cobaltous complex with acetone <Emphasis Type="Italic">S</Emphasis>-1,1′-binaphtyl-2,2′-diimine

Crystallization of cobalt(II) chloride and S-(?)-1,1′-binaphtyl-2,2′-diamine (L) from an acetone solution has afforded a chiral complex [CoL^*Cl₂]·Me₂CO (L^* = the acetone diimine derivative of binaphtyldiamine). The compound has been structurally characterized.     

Liquid secondary ion mass spectrometry of several β-diketonates of cobalt(III) and chromium(III)

The positive, liquid secondary ion (LSI) mass spectra of six cobalt(III) and three chromium(III) (β-diketonates ligand = L^?) were examined in a 3-nitrobenzyl alcohol matrix. The complexes of both metals yield clean, matrix-free mass spectra, but there are important differences between them. The cobalt compounds show prominent peaks assignable to the molecular ion, CoL ₃ ⁺ , of the monomeric chelates, together with abundant dimeric ions, such as Co₂L ₄ ⁺ and Co₂L ₃ ⁺ ; in contrast, chromium complexes show protonated monomers, CrL₃H⁺, in addition to ionized monomers, CrL ₃ ⁺ , and only minor formation of dimeric ions. The collisionally-activated dissociation (CAD) mass spectrum of Co₂L ₄ ⁺ shows fragmentation to CoL ₂ ⁺ and Co₂L ₃ ⁺ . That of Co₂L ₃ ⁺ shows fragmentation only to dimeric ions, including Co₂L ₂ ⁺ and, for thienyl or phenyl substituted ligands, to Co₂L₂Ar⁺ or Co₂LAr⁺ (Ar = thienyl or phenyl). Neither Co₂L ₄ ⁺ nor Co₂L ₃ ⁺ dissociates to the CoL ₃ ⁺ ion. The LSI mass spectrum of a mixture of two different cobalt chelates shows dimeric ions containing both types of ligand, which can be explained by ion-molecule reactions in the selvedge region. The differing behaviors of the cobalt and chromium complexes is attributed to the relatively greater stability of the +2 oxidation state for cobalt than for chromium.     

The coordination chemistry ofN,N′-ethylenebis(2-acetylpyridine imine) andN,N′-ethylenebis(2-benzoylpyridine imine); two potentially tetradentate ligands containing four nitrogen atoms

Summary New complexes of the general formulae [ML_A(H₂O)₂]-Cl₂ (M=Ni or Cu), [ML_AX₂] (M=Co or Cu; X=Cl or Br), [NiL_ABr₂]·H₂O, [ML_A] [MCl₄] (M=Pd or Pt), [NiL_B(H₂O)₂]Cl₂·2H₂O, [ML_BCl₂] (M=Co, Ni, Cu, Pd or Pt; X=Cl or Br) and [ML_B] [MCl₄] (M=Pd or Pt), where L_A=N,N-ethylenebis(2-acetylpyridine imine) and L_B=N, N-ethylenebis(2-benzoylpyridine imine), have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, t.g./d.t.g. methods, magnetic susceptibilities and spectroscopic (i.r., far-i.r., ligand field,¹Hn.m.r.) studies. Monomeric pseudo-octahedral stereochemistries for the Co^II, Ni^II and Cu^II complexes andcis square planar structures for the compounds [ML_BX₂] (M=Pd or Pt; X=Cl or Br) are assigned in the solid state. The molecules L_A and L_B behave as tetradentate chelate ligands in the Co^II, Ni^II, Cu^II and Magnus-type Pd^II and Pt^II complexes, bonding through both the pyridine and methine nitrogen atoms. A bidentateN-methine coordination of the Schiff base L_B is assigned in the [ML_BX₂] complexes (M=Pd or Pt; X=Cl or Br). The anomalous magnetic moment values of the Co^II complexes are discussed.