Chemically modified silica gel with p-dimethylaminobenzaldehyde for selective solid-phase extraction and preconcentration of Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) by ICP-OES

Silica gel-bound amines phase modified with p-dimethylaminobenzaldehyde (p-DMABD) was prepared based on chemical immobilization technique. The product (SG-p-DMABD) was used as an adsorbent for the solid-phase extraction (SPE) Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) prior to their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The uptake behaviors of SG-p-DMABD for extracting these metal ions were studied using batch and column procedures. For the batch method, the optimum pH range for Cr(III) and Ni(II) extraction was ≥ 3, for Cu(II), Pb(II) and Zn(II) extraction it was ≥ 4. For simultaneous enrichment and determination of all the metals on the newly designed adsorbent, the pH value if 4.0 was selected. All the metal ions can be desorbed with 2.0 mL of 0.5 mol L^− 1 of HCl. The results indicate that SG-p-DMABD has rapid adsorption kinetics using the batch method. The adsorption capacity for these metal ions is in the range of 0.40-1.15 mmol g^− 1, with a high enrichment factor of 125. The presence of commonly coexisting ions does not affect the sorption capacities. The detection limits of the method were found to be 1.10, 0.69, 0.99, 1.10 and 6.50 μg L^− 1 for Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was 5.0% (n = 8) for all metal ions. The method was applied to the preconcentration of Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) from the certified reference material (GBW 08301, river sediment) and water samples with satisfactory results.     

Magnetic properties and DMRG modeling of the 1D bimetallic thiocyanate bridged compound {(CuL1)[Co(NCS)4]} (L1 = N-rac-5,12-Me2-[14]-4,11-dieneN4)

The magnetic properties of the bimetallic compound {(CuL₁)[Co(NCS)₄]}, where L₁ = N-rac-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene have been numerically analysed on the basis of the anisotropic Heisenberg spin-chain model. In the model the single-ion anisotropy of the Co(II) ions is taken into account and the interchain interactions are neglected. The thermodynamic properties are calculated using the DMRG technique adapted to the molecular-based chains for the first time which is reliable in the entire temperature region. The high accuracy results of our simulations have been successfully fitted to the corresponding experimental susceptibility and magnetization data measured for the powder sample and the model parameters (the exchange coupling J, the absolute value of the anisotropy constant D, the anisotropic g factors) have been estimated. The quantum model parameters are consistent with the previous findings, although the ferromagnetic interactions between Cu(II) and Co(II) ions through the thiocyanate bridge are somewhat weaker (J/k_B = 1.0 ± 0.1) than found before.     

Selective solid phase extraction of trace cadmium(II) and lead(II) from biological and natural water samples by ofloxacin-modified-silica gel

Ofloxacin was successfully used as a chemical modifier to improve the reactivity of silica gel in terms of selective binding and extraction of heavy metal ions. This new functionalised silica gel (SG-ofloxacin) was as an effective sorbent for the solid-phase extraction (SPE) of Cd(II) and Pb(II) in biological and natural water samples and their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective adsorption of trace levels of Cd(II) and Pb(II) were optimised with respect to different experimental parameters using the batch and column procedures. The time for 70% sorption for Cd(II) and Pb(II) was less than 2 min. Complete elution of the adsorbed metal ions from the SG-ofloxacin was carried out using 2.0 mL of 0.5 mol L^?1 of HCl. Common coexisting ions did not interfere with the separation and determination at pH 4.0. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.17 and 48.69 mg g^?1 for Cd(II) and Pb(II), respectively. The detection limits of the method were found to be 0.29 and 0.13 ng mL^?1 for Cd(II) and Pb(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was lower than 3.0% (n = 5). The method was applied to the recovery of Cd(II) and Pb(II) from the certified reference material (GBW 08301, river sediment) and to the simultaneous determination of these cations in different water and biological samples with satisfactory results and yielding 100-folds enrichment factor.     

Magnetism of metal-nitroxide compounds involving bis-chelating imidazole and benzimidazole substituted nitronyl nitroxide free radicals

Coordination compounds based on imidazole and benzimidazole substituted nitronyl nitroxide radicals with transition metal ions and trivalent lanthanide ions are described from the perspective of their magnetic properties.For the transition metal compounds the crystal structures show various metal-nitroxide dimensionalities including mononuclear (0D), one-dimensional (1D) and two-dimensional (2D) complexes. The mononuclear complexes were isolated with most metal ions of the first transition series. One copper(II) complex shows a copper(II)-radical ferromagnetic coupling (J = +75 cm⁻¹) while for the other mononuclear compounds, mainly with manganese(II), the metal-radical interactions are antiferromagnetic. The one-dimensional and two-dimensional complexes are manganese(II) compounds which show canting effects leading to weak ferromagnetism.For the trivalent lanthanide ions [La(III), Gd(III) and Eu(III)], three series of mononuclear complexes were obtained in which the metal center is bound to four, two or one nitroxide radicals depending on the counter ions and ancillary ligands. Unexpectedly, in most gadolinium(III) complexes, the Gd(III)-radical interactions were found to be antiferromagnetic in contradiction with other foundings and previous theoretical models. In support to the magnetic studies, the optical properties of the lantanide complexes have also been investigated and are briefly described.     

The enthalpimetric determination of some common metals using hydrogen sulphide as the titrant

Summary The heat of precipitation of some metal sulphides has been used to assay some metal salt solutions. The hydrogen sulphide has been used as the precipitant and in a enthalpimetric system as the titrant. The method has been used for the determination of Cu(II), Cd(II), Hg(II), Bi(III), Fe(III) in single salt solutions and in admixture with some other ions. All the metals gave sharp end points in the enthalpograms and extrapolation was not required.

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Enthalpimetrische Bestimmung einiger üblicher Metalle mit Hilfe von Schwefelwasserstoff als Titrationsmittel

Zusammenfassung Die Fällungswärme einiger Metallsulfide wurde zur Analyse von Metallsalzlösungen benutzt. Schwefelwasserstoff diente als Fällungsmittel und im enthalpimetrischen System als Titrationsmittel. Kupfer(II), Cadmium(II), Quecksilber(II), Wismut(III) und Eisen(III) wurden allein und in Mischungen bestimmt. Alle Metalle ergaben im Enthalpigramm scharfe Endpunkte, so daß keine Extrapolierung notwendig war.

On leave from the University of Chiengmai, Thailand.     

Polarized spectroscopy and hybrid materials of chiral Schiff base Ni(II), Cu(II), Zn(II) complexes with included or separated azo-groups

Chiral Schiff base complexes containing azo-groups, bis(N-R-1-naphtylethyl-4-phenyldiazenylsalicydenaminato) nickel(II), copper(II), and zinc(II) complexes affording a distorted square planar trans-[MN₂O₂] coordination geometry were prepared newly. Organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) cast films of them (a containing type) or the analogous chiral Schiff base complexes, bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato) nickel(II), copper(II), and zinc(II), and azobenzene (AZ) (a separated type) were assembled for comparison of polarized UV light induced molecular arrangement caused by Weigert effect. Investigation of parameters for optical anisotropy of metal complexes as well as AZ suggested that the degree of increasing optical anisotropy of the containing type is higher than that of the separated type based on π-π^∗ (of which characteristic band appeared around 380 nm), n-π^∗, and d-d bands of polarized absorption electronic spectra. Rigid nickel(II) or zinc(II) complexes are easy to increase optical anisotropy than flexible copper(II) complexes for both types.     

Silica gel surface modified with sulfanilamide for selective solid-phase extraction of Cu(II), Zn(II) and Ni(II)

A new chelating matrix has been prepared by immobilising sulfanilamide (SA) on silica gel (SG) surface modified with 3-chloropropyltrimethoxysilane as a sorbent for the solid-phase extraction (SPE) Cu(II), Zn(II) and Ni(II). The determination of metal ions in aqueous solutions was carried out by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective sorption of trace levels of Cu(II), Zn(II) and Ni(II) were optimised with respect to different experimental parameters using the batch and column procedures. The presence of common coexisting ions does not affect the sorption capacities. The maximum sorption capacity of the sorbent at optimum conditions was found to be 34.91, 19.07 and 23.62 mg g^?1 for Cu(II), Zn(II) and Ni(II), respectively. The detection limit of the method defined by IUPAC was found to be 1.60, 0.50 and 0.61 µg L^?1 for Cu(II), Zn(II) and Ni(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was 4.0% (n = 8). The method was applied to the recovery of Cu(II), Zn(II) and Ni(II) from the certified reference material (GBW 08301, river sediment) and to the simultaneous determination of these cations in different water samples with satisfactory results.     

Conformational study of Co(II), Ni(II), and Cr(III) complexes of the edta-type: Crystal structure of 1D polymeric trans(O)-Ba[Co(1,3-pddadp)] · 8H2O complex stabilized by infinite water tapes

The trans(O⁶) isomer of the Ba[Co(1,3-pddadp)] · 8H₂O complex (where 1,3-pddadp represents hexadentate 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate ion) has been prepared and characterized by X-ray crystallography. In the crystal structure the complex cations and anions are bridged by carboxylate oxygen atoms from the in-plane coordinated glycinate rings (G-rings) of [Co(1,3-pddadp)]²⁻ and by the barium-coordinated water molecules, thus forming 1D polymeric chains, separated by infinite water tapes hydrogen bonded to the [Co(1,3-pddadp)]²⁻ carboxylate oxygens from the out-of-plane β-alaninate rings (R-rings). Conformational analysis of the three possible geometrical isomers: trans(O⁵), trans(O⁵O⁶), and trans(O⁶) of the [Co(1,3-pddadp)]²⁻ complex, with ligand acting as hexadentate, as well as of the corresponding complexes of Ni(II) and Cr(III) has been performed using the consistent force field (CFF) method, with the parameters developed previously for edta-type complexes of chromium(III) and supplemented with new parameters for cobalt(II) and nickel(II). The energy-minimized structure of the trans(O⁵O⁶) isomer represents the global minimum for the [M(1,3-pddadp)]ⁿ⁻ (M = Co(II), Ni(II), and Cr(III)) species. The occurrence of the least energetically favored trans(O⁶) isomer in a crystal and the exceptional conformation of the axially oriented β-alaninate rings can be accounted for by the stabilizing role of the infinite tapes of planar cyclic water pentamers and hexamers which act as a “glue” to reinforce the coordination polymeric chains.     

Green synthesis and characterization of Tb-Fe-O-Cu ceramic nanocomposite and its application in simultaneous electrochemical sensing of zinc,cadmium and lead

In this work, a green technique for preparing TbFeO₃/CuO was reported by employing Crataegus and Lantana Camara leaves as fuel and alkalizing agents, respectively. The new sensor based on the perovskite-type nanocomposite was employed as a sensitive and selective platform to detect Pb(II), Zn(II) and Cd(II) simultaneously. TbFeO₃/CuO/Carbon paste electrode (CPE) exhibited a large specific surface area and great electrical conductivity, which enhanced electron transport in the electrochemical process considerably. Moreover, square wave anodic stripping voltammetry (SWASV) was used for the investigation of some factors influencing the sensor sensitivity like pH, modifier concentration, as well as accumulation time and potential. Therefore, the low detection limit (LOD) and a wide linear range were obtained at optimum conditions. In this study, a linear range between 0.9 and 110 µg/L for three ions and LOD of 0.48, 0.29 and 0.12 for zinc, cadmium and lead were achieved, respectively. Moreover, TbFeO₃/CuO/CPE was employed to detect zinc, cadmium and lead ions simultaneously in the real samples so that the results have shown consistency with a standard inductively coupled plasma (ICP).     

Synthesis and characterization of Cu,Ni and Zn binding capability of some amino- and imidazole hydroxamic acids: Effects of substitution of side chain amino-N for imidazole-N or hydroxamic-N-H for -N-CH3 on metal complexation

Solution equilibrium studies on Cu(II)-, Ni(II)- and Zn(II)-N-Me-β-Alaninehydroxamic acid (N-Me-β-Alaha), -N-Me-α-alaninehydroxamic acid (N-Me-α-Alaha), -Imidazole-4-carbohydroxamic acid (Im-4-Cha), -N-Me-imidazole-4-carbohydroxamic acid (N-Me-Im-4-Cha) and -Imidazole-4-acetohydroxamic acid (Im-4-Aha) systems have been performed by pH-potentiometry, UV–Vis spectrophotometry, EPR, CD, ESI-MS and ¹H NMR methods. According to the results: (i) the amino-N atoms are more basic in N-Me-α-Alaha and N-Me-β-Alaha than the hydroxamate function, but the trend is just the opposite between the imidazole-N(3) and hydroxamate. (ii) The metal ion anchor is always the hydroxamate part in the amino acid derivatives, while it is always the imidazole-N(3) in the studied imidazolehydroxamic acids. (iii) The three studied N-Me derivatives do not form metallacrowns. Only hydroxamate type chelate is formed with N-Me-β-Alaha, but with N-Me-α-Alaha a new type of coordination mode (via amino-N and hydroxamate-O) also exists. N-Me-Im-4-Cha also forms a dinuclear complex, [M₂L₃], with Cu(II) and Ni(II) (but not with Zn(II)). In this complex, one of the three ligands might bridge the two metal ions (five-membered hydroxamate-(O,O) plus five-membered (N_im, O_carb) bridging bis-chelating mode), while each of the additional two ligands binds to one metal. (iv) The two studied N–H derivatives, having dissociable proton on the hydroxamic-N, are able to form metallacrown species. A pentanuclear complex, [M₅L₄H₋₄], is exclusively formed above pH 4 between Cu(II) and Im-4-Aha. Interestingly, this 12-metallacrown-4 type complex, although together with various mononuclear binding isomers, appears also with Ni(II) and Zn(II). Unfortunately, the complexes of Im-4-Cha are not soluble in water at physiological pH at all.     

Synthesis,characterization, and polychelatogenic properties of poly(acrylic acid-co-acrylamide)

The radical copolymerization of acrylic acid with acrylamide was carried out at different monomer ratios in solution (DMF) at 60°C. The corresponding homopolymers were also synthesized to compare their metal ion binding abilities. All the copolymers were characterized by elemental analysis. The metal ion binding properties of these water-soluble polymers with Cu(II), Co(II), Ni(II), Cd(II), Zn(II), Pb(II), Hg(II), Fe(III), and Cr(III) ions were investigated in aqueous solution using the Liquid-Phase Polymer-Based Retention (LPR) technique. Poly(acrylic acid-co-acrylamide) showed a higher retention compared to the homopolymers for all the metal ions except of Hg(II), which was not retained. Besides, the retention of Cd(II) is higher than that an addition of the retention of both homopolymers. It may be attributed to a synergic effect. Maximum capacity for Cu(II) at pH 5.0 was determined to be 1 mmol g⁻¹ (63.5 mg g⁻¹). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2461–2467, 1997     

Modified cyclodextrin polymers as selective ion carriers for Pb(II) separation across plasticized membranes

In the present work the hydrophobic β-cyclodextrin (β-CD) polymers have been used as macrocyclic ion carriers for separation of Pb(II), Zn(II), and Cu(II) ions from dilute aqueous solutions by transport across polymer inclusion membranes. The β-CD polymers were prepared by cross-linking of β-CD with 2-(1-docosenyl)-succinic anhydride derivatives in anhydrous N,N-dimethylformamide in the presence of NaH. The metal ions were transported from aqueous solutions containing heavy metal ions through plasticizer triacetate membranes with dimer and polymer β-CD derivatives into distilled water. The selectivity of lead(II) over other metal ions in the transport through polymer inclusion membrane was very high, especially for dimer cyclodextrin carrier. In the case of competitive transport of Pb(II), Cu(II), and Zn(II) ions through plasticized immobilized membranes the selectivity of process is controlled via formation of ion pairs of β-CD hydroxyl groups with metal cations. The polymer and dimer of β-CD linked by 2-(1-docosenyl)-derivative used as ionic carriers for competitive transport of metal ions show preferential selectivity order: Pb(II)  Cu(II) > Zn(II). Application of ion carriers mixtures (β-CD polymers and palmitic acid) causes the increase of Pb(II) maximal removal from dilute aqueous solution. The weight-average molecular weight (M_W) and the chemical structure of the β-CD polymers were determined using high-performance size exclusion chromatography with refractive index detector, and ¹H NMR spectroscopy.     

The role of chiral dopants in organic/inorganic hybrid materials containing chiral Schiff base Ni(II), Cu(II) and Zn(II) complexes

Chiral Schiff base complexes containing azo-groups, bis(N-R-1-cyclohexylethyl-4-phenyldiazenylsalicydenaminato) nickel(II), copper(II) and zinc(II) complexes, and without azo-groups, bis(N-R-1-cyclohexylethyl-3,5-dichlorosalicydenaminato) nickel(II), copper(II) and zinc(II) complexes, affording a distorted square planar trans-[MN₂O₂] coordination geometry were prepared. Organic/inorganic hybrid materials in polymethylmethacrylate (PMMA) spincoat films of the complexes (both the azobenzene (AZ) containing type and the latter complexes of the AZ separated type) were assembled for a comparison of polarized UV light induced molecular arrangement caused by the Weigert effect. Investigation of the parameters for the optical anisotropy of the metal complexes as well as AZ suggested that the degree of increasing optical anisotropy of the containing type was higher than that of the separated type based on π-π^∗ (of which a characteristic band appeared around 380 nm) and n-π^∗ bands of polarized absorption electronic spectra. In the AZ containing type, the rigid nickel(II) or zinc(II) complexes easily increase the optical anisotropy compared to the flexible copper(II) complexes. In the AZ separated type, interestingly, enhancement of some CD bands suggests the role of chiral dopants of some complexes without azo-groups for AZ.     

Application of Multivariate Calibration Methods for the Simultaneous Multiwavelength Spectrophotometric Determination of Fe(II), Cu(II), Zn(II), and Mn(II) in Mixtures

Abstract

A sensitive method for the simultaneous spectrophotometric determination of Fe(II), Cu(II), Zn(II), and Mn(II) in mixtures has been developed with the aid of multivariate calibration methods, such as classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS). The method is based on the spectral differences of the analytes in their complexation reaction with 4‐(2‐pyridylazo)‐resorcinol (PAR) and the use of full spectra with wavelengths in the range of 300–600 nm. It was found that both the spectral positive and negative bands obtained against the PAR blank, are proportional to the concentration for each metal complex. The obtained linear calibration concentration ranges are 0.025–0.6, 0.05–0.8, 0.025–0.8, and 0.05–0.8 µg ml^?1 for Fe(II), Cu(II), Zn(II), and Mn(II), respectively, and the LODs for the four metal ions were found to be approximately 1–3×10^?2 µg ml^?1. The proposed method was applied to a verification set of synthetic mixtures of these four metal ions, with models built in three different wavelength ranges, i.e., 300–450, 450–600, and 300–600 nm, corresponding to the positive, negative bands and their combinations, respectively. It was shown that the PLS model for the 300–600 nm range gave the best results (RPE_T=6.9% and average recovery ～100%; cf. PCR: RPE_T=9.5% and average Recovery ～110%). This method was also successfully applied for the determination of the four metal ions in pharmaceutical preparations, chicken feedstuff, and water samples.     

SEVERAL COORDINATION MODES OF 5-AMINO-1,3,4-THIADIAZOLE-2-SULFONAMIDE (HATS) WITH Cu(II), Ni(II) AND Zn(II): MIMETIC TERNARY COMPLEXES OF CARBONIC ANHYDRASE-INHIBITOR

Abstract

The coordination properties of 5-amino-1,3,4-thiadiazole-2-sulfonamide (Hats) with Cu(II), Ni(II) and Zn(II) ions, are analyzed. Although the ligand presents several donor atoms, we have only observed three coordination behaviors: (i) as a monodentate ligand through the N_sulfonamido atom, (ii) as a bridging ligand linking the metal ions through the N_sulfonamido and N_thiadizole atoms and (iii) as a bridging ligand linking metal ions through the N and O atoms of the sulfonamidate group. It is noteworthy that coordination mode (iii) is observed for the first time in heterocyclic sulfonamides complexes. In addition, the conformation of the Hats as counter-ion is analyzed and compared with the conformations that the ligand adopts in metal complexes.     

S = 1/2 Heisenberg antiferromagnetic spin chain [Cu(dmbpy)(H2O)2SO4] (dmbpy = 4,4′-dimethyl-2,2′-bipyridine): Synthesis,crystal structure and enhanced magnetocaloric effect

[Cu(dmbpy)(H₂O)₂SO₄] in the form of small blue crystals was prepared from the aqueous-ethanolic reaction mixture formed of CuSO₄ and dmbpy (dmbpy = 4,4′-dimethyl-2,2′-bipyridine). Its crystal structure consists of chains in which hexacoordinated Cu(II) atoms are linked by (μ₂-SO₄)²⁻ anions. The Cu(II) atom exhibits elongated tetragonal bipyramidal coordination with one chelate bonded dmbpy and two aqua ligands placed in the equatorial plane while the axial positions are occupied by bridging sulfato ligands. The study of electron spin resonance and specific heat enabled to identify the studied material as an S = 1/2 Heisenberg antiferromagnetic chain with weak intrachain exchange interaction, 2J/k_B = −1.12 K and a small anisotropy of g – factor, Δg/g ≈ 0.1. The analysis of the magnetic entropy revealed pronounced release of the entropy at the saturation magnetic field, which for spin chains induces quantum phase transition, namely B_sat = 1.56 T. The maximum isothermal change of the entropy ΔS_M = 2.86 J/Kmol is comparable to that released in a critical region for materials with magnetic phase transitions. The obtained results suggest that the existence of a quantum critical point significantly influences finite-temperature properties.     

Synthesis,structure and properties of three one-dimensional coordination polymers {[M(II)L(NCS)2](DMF)2} n (M(II)=cadmium(II), zinc(II), manganese(II); L=1,4-bis[2-(2-pyridyl)benzimidazolato]butane)

A tetradentate N-donor ligand 1,4-bis[2-(2-pyridyl)benzimidazolato]butane (L) was prepared for construction of a coordination framework. Three one-dimensional coordination polymers {[M(II)L(NCS)₂](DMF)₂} _n (M(II) = cadmium(II), 1, zinc(II), 2, manganese(II), 3) were obtained by reaction of metal ions and L in the presence of KSCN in DMF/water. The complexes are isostructural and consist of 1D zigzag [M(II)L(NCS)₂] _n chains and DMF molecules. Within the chains, the metal atoms are each octahedrally coordinated by four N atoms of L and two N atoms of the SCN^? anions. Complexes 1 and 2 in the solid state at room temperature exhibit intense photoluminescence at 453 and 433 nm, respectively.     

Syntheses,crystal structures and magnetic properties of heteronuclear bimetallic compounds of [Cu(pdc)2][M(H2O)5]·2H2O [M=Ni(II), Co(II), Mn(II); pdc=2,6-pyridinedicarboxylato]

The complexes [M(H₂O)₅][Cu(pdc)₂]·2H₂O [M=Ni(II) 1, Co(II) 2, Mn(II) 3; pcd=2,6-pyridinedicarboxylato] are prepared and their crystal structures, magnetic susceptibilities and UV-Visible properties reported. In all cases, the Cu(II) ion occupies the chelating site in the pdc ligand, while the M(II) occurs as a pentaaqua ion bridged to the [Cu(pdc)₂] moiety through a carboxylate as demonstrated by both UV-Visible spectroscopy and X-ray diffraction. Single crystal X-ray diffraction shows the three complexes to be isostructural. Weak antiferromagnetic interactions between the metal ions are observed in 1 and 3, while the magnetic behavior of 2 is dominated by single ion anisotropy.     

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.     

High frequency electron paramagnetic resonance (HFEPR) study of a high spin Co(II) complex

Variable high-frequency electron paramagnetic resonance data were collected for a single crystal of [Zn(hmp)(dmb)Cl]₄ (1) doped with a small quantity of high spin Co(II), where dmb is 3,3-dimethyl-1-butanol and hmp- is the monoanion of 2-hydroxy-methylpyridine. The lack of solvent in the lattice of complex 1 results in very little disorder. Consequently, the EPR spectra are extremely sharp, enabling precise comparisons with theoretical simulations. We find the ground state of the Co(II) ions to be an effective spin S′ = 1/2 Kramers’ doublet with a highly anisotropic g-tensor. The anisotropy is found to be of the easy-axis type, with the single-ion easy axis directions tilted away from the crystallographic c direction by 58°.