A Direct Carbon-13 and Nitrogen-15 NMR Study of Samarium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures

Multinuclear magnetic resonance studies of trivalent lanthanide inner-shell ion-pairing with nitrate and isothiocyanate are continuing. For NCS^– solutions in water–acetone–Freon mixtures at low temperature, generally –100 to –125°C, ligand exchange is slow enough to permit the observation of ¹³C and ¹⁵N NMR signals for coordinated and free anions. For samariuni(III) solutions, four coordinated NCS^–signals, displaced about +35 ppm and +250 ppm from free anion, are observed in the ¹³C and ¹⁵N NMR spectra, respectively. The ¹³C and ¹⁵N NMR data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Sm(NCS)²⁺ through Sm(NCS) ₄ ¹ . The coordination numbers reach a maximum of about three moles of NCS^– per mole of Sm(III) with both nuclides, a result confirmed by spectral appearance showing the dominance of Sm(NCS)₃ at the highest concentration studied. An analysis of the chemical shifts indicates that binding occurs at the nitrogen atom of NCS^–. In water–methanol, due to the higher dielectric constant of such mixtures, coordination was less extensive. A competitive binding study with Ci^– by ³⁵Ci NMR demonstrated conclusively the superior coordinating ability of NCS^–.     

A direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of lutetium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of lutetium(III)-isothiocyanate complex formation in aqueous solvent mixtures has been completed. At –100°C to –120°C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate¹H,¹³C, and¹⁵N NMR signals for coordinated and free water and isothiocyanate ions. In the¹³C and¹⁵N spectra of NCS^–, resonance signals for five complexes are observed over the range of concentrations studied. The¹³C chemical shifts of complexed NCS^– varied from –0.5 ppm to –3 ppm from that of free anion. For the same complexes, the¹⁵N chemical shifts from free anion were about –11 ppm to –15 ppm. The magnitude and sign of the¹⁵N chemical shifts identified the nitrogen atom as the binding site in NCS^–. The concentration dependence of the¹³C and¹⁵N signal areas, and estimates of the fraction of anion bound at each NCS^–:Lu³⁺ mole ratio, were consistent with the formation of [(H₂O)₅Lu(NCS)]²⁺ through [(H₂O)Lu(NCS)₅]^2–. Although proton and/or ligand exchange and the resulting bulk-coordinated signal overlap prevented accurate hydration number measurements, a good qualitative correlation of the water¹H NMR spectral results with those of¹³C and¹⁵N was possible.     

Direct 1H, 13C, and 15N NMR Study of Lanthanum(III), Thulium(III), and Ytterbium(III) Complex Formation with Nitrate and Isothiocyanate

An ¹H, ¹³C, and ¹⁵N NMR study has been completed for the complexes of La(III), Tm(III), and Yb(III) with nitrate and isothiocyanate in aqueous solvent mixtures. Signals for four complexes are observed for both the Tm³⁺–NO₃ ^– and Yb³⁺–NO₃ ^– solutions, with the species identified as the mono-, di-, tetra-, and either the penta - or hexanitrato. These results are consistent with those determined for the nitrate complexes of the Ce(III)–Eu(III) metal ions. The chemical shifts for the Tm(III) and Yb(III) nitrate complexes indicate a pseudocontact binding mechanism prevails. The complexes of diamagnetic La(III) with NO₃ ^– produce three signals in the ¹⁵NO₃ ^– spectra, with assignments paralleling those observed with the paramagnetic lanthanides. Three complexes are formed in the La³⁺–NCS^– solutions, with signals assigned to the mono-, di-, and triisothiocyanato species.     

A Direct Carbon-13 and Nitrogen-15 NMR Study of Cerium(III)–Isothiocyanate Complexation in Aqueous Solvent Mixtures

A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water–acetone–Freon mixtures at low temperature, –85––125°C, ligand exchange is slow enough to permit the observation of ¹³C and ¹⁵N NMR signals for coordinated and free anions. For the Ce³⁺–NCS^– system, four coordinated anion signals, displaced from the free anion signal by about +450 to +550 ppm for ¹⁵N and +50 to +80 ppm for ¹³C, are observed. The ¹³C and ¹⁵N spectral data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Ce(NCS)²⁺ through Ce(NCS)^1- ₄. In water–methanol, the extent of complexing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS^– and Cl^– ion binding, carried out using ³⁵Cl NMR, is presented.     

Multinuclear Magnetic Resonance Study of Zinc(II) and Cadmium(II) Complexing with Isothiocyanate

A study of zinc(II) and cadmium(II) complexes with isothiocyanate ion has been completed, using a low-temperature, multinuclear magnetic resonance technique that permits the observation of separate resonance signals for bound and free ligand, and Cd(II) metal ion. The Zn²⁺–NCS^– complexes were studied by ¹H, ¹³C, and ¹⁵N NMR spectroscopy. In the ¹H spectra, the intensity of the coordinated water signal, corresponding to a Zn(II) hydration number of six in the absence of NCS^–, decreases dramatically as this anion is added, indicating the complexing process involves more than a simple 1:1 ligand replacement. The ¹³C and ¹⁵N NMR spectra reveal signals for four species, most reasonably assigned to a series of tetrahedrally coordinated Zn²⁺–NCS^– complexes. In the Cd²⁺–NCS^– solution spectra, the ¹³C and ¹⁵N signals for four complexes also are observed and they are three line patterns, corresponding to a doublet from ¹¹³Cd J-coupling, and a dominant central peak, resulting from bonding to magnetically inactive Cd isotopes. The ¹¹³Cd spectra, showing signals for four complexes, correlate well in all respects with the ¹³C and ¹⁵N results, including coupling in specific cases. The spectral results for both metal ions reflect binding at the nitrogen atom of NCS^–, with the complexes changing from an octahedral to a tetrahedral configuration when doing so. Confirming evidence for these conclusions also was provided by several infrared measurements of these metal–ion systems.     

Direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexing

A hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexation in aqueous mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate¹H,¹³C, and¹⁵N NMR signals are observed for coordinated and bulk water molecules and anions. The¹H NMR spectra reveal signals for the hexahydrate and the mono-through triisothiocyanato complexes, as well as two small signals attributed to [Mg(H₂O)₅(OH)]¹⁺ and [Mg(H₂O)₄(OH)(NCS)]. Accurate hydration numbers were obtained from signal area integrations at each NCS^– concentration. In the¹⁵N NMR spectra, signals also were observed for the mono-through triisothiocyanato complexes, and a small signal believed to be due to [Mg(H₂O)₄(OH)(NCS)]. Coordination number contributions for NCS^– were measured from these spectra and when combined with the hydration numbers they totalled essentially six at each anion concentration. Signals for [Mg(H₂O)₅(NCS)]¹⁺ through [Mg(H₂O)₃(NCS)₃]^1– also were observed in the¹³C NMR spectra and the area evaluations were comparable to the¹⁵N NMR results. An analysis of the magnitude and sign of the coordinated NCS^– chemical shifts identified the nitrogen atom as the anion binding site. All spectra indicated [Mg(H₂O)₅(NCS)]¹⁺ and [Mg(H₂O)₄(NCS)₂] were the dominat isothiocyanato complexes over the entire range of anion concentrations. The inability to detect evidence for complexes higher than the triisothiocyanato reflects the competitive binding ability of water molecules and perhaps the decreased electrostatic interaction between NCS^– and negatively charged higher complexes.     

A direct carbon-13 and nitrogen-15 NMR study of europium(III) complexation-nitrate and europium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature nuclear magnetic resonance spectroscopic study of europium(III)-nitrate contact ion-pairing has been completed, and preliminary results for europium(III)-isothiocyanate have been obtained. In water-acetone-Freon mixtures, at –110°C to –120°C, four¹⁵N NMR signals are observed for coordinated nitrate ion. Area evaluations of the signals and their concentration dependence indicate the formation of Eu(NO₃)²⁺, Eu(NO₃) ₂ ¹⁺ , and two higher complexes, possibly the tetra-, with either the penta-or hexanitrato. This correlates well with similar¹⁵N NMR results obtained for Ce(III), Pr(III), Nd(III), and Sm(III). As a result of a higher dielectric constant, complex formation is significantly less in water-methanol mixtures, wheein only three complexes form with Eu(NO₃) ₂ ¹⁺ dominating at the highest anion concentrations. Competitive complexing experiments in water-methanol also were made by³⁵Cl NMR chemical shift and linewidth measurements, as well as¹⁵N NMR. Initial experiments with the Eu³⁺-NCS^– system show four coordinated anion signals, displaced from the bulk anion peak by about –250 ppm and –2,500 ppm in the¹³C and¹⁵N NMR spectra, respectively. Area evaluations are consistent with the presence of Eu(NCS)²⁺ through Eu(NCS) ₄ ^1- in these solutions. A consideration of the chemical shifts identified the nitrogen atom as the site of binding in the NCS^–. A discussion of these preliminary results, as well as those for several other metal-ions, will be presented.     

A direct carbon-13 and nitrogen-15 nmr study of europium(iii)-isothiocyanate complex formation in aqueous solvent mixtures

A continuation of the contact ion-pairing studies of the trivalent lanthanides by direct, low-temperature, multinuclear magnetic resonance techniques has been completed for the europium(III)-isothiocyanate system. In water-acetone-Freon-22 solvent mixtures, ligand exchange is sufficiently slow at — 100°C to - 125°C to permit the observation of¹³C and¹⁵N NMR signals for Eu³⁺-NCS^- contact ion-pair complexes. With each nuclide, signals for four complexes are observed, displaced approximately 250 ppm upfield from free anion in the^13C spectra, and 2,500 ppm upfield from bulk NCS^- in the¹⁵N spectra. The concentration dependence of the signal areas is consistent with the formation of Eu(NCS)²⁺ through Eu(NCS) ₄ ^1- , with water molecules completing the solvation shell. In the¹⁵N NMR spectra, the large chemical shifts identified the nitrogen atom as the NCS^- binding site. Also, the observation of two¹⁵N NMR signals for isomers of Eu(NCS) ₂ ¹⁺ was possible in several spectra. In methanol, a medium of higher dielectric constant, complex formation was diminished, with signal area integrations confirming the dominance of Eu(NCS) ₁ ²⁺ . A comparative binding study of Cl^- and NCS^- also was made by³⁵C1 NMR chemical shift and linewidth measurements in water-methanol mixtures. The much stronger coordinating ability of NCS^- was evident in these experiments, but there is a strong possibility of Eu³⁺-Cl^- ion-pairing in the absence of this anion.     

A direct carbon-13 and nitrogen-15 NMR study of samarium(III) complexation with nitrate and isothiocyanate in aqueous solvent mixtures

The extent of inner-shell, contact ion-pairing between samarium(III)-nitrate and in a preliminary manner, samarium(III)-isothiocyanate, has been determined by a direct, low-temperature, multinuclear magnetic resonance technique. In water-acetone mixtures containing Freon-12 or Freon-22, the slow exchange condition is achieved at –110 to –120°C, permitting the observation of¹⁵N NMR resonance signals for bulk and coordinated nitrate. In these mixtures, signals are observed for Sm(NO₃)²⁺, Sm(NO₃) ₂ ⁺ , and two higher complexes, possibly the tetranitrato with either the penta-or hexanitrato.¹H NMR signals for bound water molecules in these mixtures were observed, but accurate hydration numbers can not yed be determined. In anhydrous or aqueous methanol mixtures,¹⁵N NMR signals for only three complexes are observed, with the dinitrato clearly dominating. Using¹⁵N and³⁵Cl NMR chemical shift and linewidth measurements, the superior complexing ability of nitrate compared to perchlorate and chloride, was demonstrated. Successful preliminary¹³C and¹⁵N NMR measurements of Sm³⁺-NCS^– interactions in water-acetone-Freon-22 mixtures also have been made. The¹³C NMR spectra reveal signals for five complexes, presumably Sm(NCS)²⁺ through Sm(NCS) ₅ ^2– . In the¹⁵N NMR spectra, signals for only three complexes are observed (the result of insufficient spectral resolution.) displaced about +240 ppm from bulk anion.     

Crystal structures and spectroscopic properties of copper(II) pseudohalide complexes with two sparteine epimers, having a CuN4 chromophore

Tetrahedrally distorted copper(II) sparteine pseudohalide complexes having a CuN₄ chromophore were prepared and characterized by various spectroscopic techniques and X-ray crystallography. Among them, the crystal structures of copper(II) isothiocyanate complexes with two sparteine epimers, (−)-l-sparteine (Sp) and (−)-α-isosparteine (α-Sp), were determined. The N_Sp–Cu–N_Sp plane in copper(II) (−)-l-sparteine isothiocyanate [Cu(Sp)(NCS)₂] and copper(II) (−)-α-isosparteine isothiocyanate [Cu(α-Sp)(NCS)₂] is twisted by 58.2(6)° and 52.2(9)°, respectively, from the N_NCS–Cu–N_NCS plane. Based on the values of the dihedral angles and tilted distances of these two complexes, the geometry around Cu(II) in Cu(α-Sp)(NCS)₂ is more distorted from the perfect tetrahedron than that in Cu(Sp)(NCS)₂. For copper(II) sparteine pseudohalide (NCS⁻ and N₃⁻) complexes having a CuN₄ chromophore, the EPR and the optical spectral data were collected. The results of X-ray crystallography and ESR spectroscopy are in a good agreement with the assumption that the degree of distortion from planarity to tetrahedron will reduce the A_|| value of four-coordinate copper(II) sparteine pseudohalide complexes.     

A direct nitrogen-15 NMR study of neodymium(III)-nitrate complex formation in aqueous solvent mixtures

A study of contact ion-pair formation between the neodymium (III) and nitrate ions in aqueous solvent mixtures has been carried out by a direct, low temperature, nitrogen-15 (¹⁵N) nuclear magnetic resonance (NMR) technique. At low temperatures, –90 to –120°C ligand exchange is slow enough to permit the observation of¹⁵N NMR signals for uncomplexed nitrate ion, and this anion in the primary solvation shell of Nd(III). In aqueous mixtures with inert acetone and Freon-12, resonance signals for Nd(NO₃)²⁺, Nd(NO₃) ₂ ¹⁺ , and two higher complexes are observed. Signal areas indicate these additional species are possibly a combination of the tetra-, penta-, and hexanitrato complexes, but not the trinitrato. In water-methanol, a medium of higher dielectric constant, complexation is much less and signals only for the mono-and dinitrato complexes are observed. The effect of solvent on complexation is demonstrated more clearly by a series of measurements in water-methanol-acetone mixtures.     

Formation Thermodynamics of Binary and Ternary Lanthanide(III) Complexes with 1,10-Phenanthroline and Chloride in N,N-Dimethylformamide

Formation thermodynamics of binary and ternary lanthanide(III) (Ln = La, Ce, Nd, Eu, Gd, Dy, Tm, Lu) complexes with 1,10-phenanthroline (phen) and the chloride ion have been studied by titration calorimetry and spectrophotometry in N,N-dimethyl-formamide (DMF) containing 0.2 mol-dm^–3 (C₂H₅)₄NClO₄ as a constant ionic medium at 25°C. In the binary system with 1,10-phenanthroline, the Ln(phen)³⁺ complex is formed for all the lanthanide(III) ions examined. The reaction enthalpy and entropy values for the formation of Ln(phen)³⁺ decrease in the order La > Ce > Nd, then increase in the order Nd < Eu < Gd < Dy, and again decrease in the order Dy > Tm > Lu. The variation is explained in terms of the coordination structure of Ln(phen)³⁺ that changes from eight to seven coordination with decreasing ionic radius of the metal ion. In the ternary Ln³⁺-Cl^–-phen system, the formation of LnCl(phen)²⁺, LnCl₂(phen)⁺, and LnCl₃(phen) was established for cerium(III), neodymium(III), and thulium(III), and their formation constants, enthalpies, and entropies were obtained. The enthalpy and entropy values are also discussed from the structural point of view.     

Structural studies on 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazan chelates with cerium(III), thorium(IV) and uranium(VI)

Summary Solid complexes of 3-acetyl-1,5-diaryl and 3-cyano-1,5-diaryl formazans were prepared and characterized by elemental analysis, IR, NMR, TGA and DTA analyses. Based on these studies, the suggested general formula for the complexes is [M(HL) _m (OH^–) _n or (NO ₃ ^– or Cl^–) _x ·(H₂O) _y or (C₂H₅OH orDMSO) _z , where HL=formazanM=Ce³⁺, Th⁴⁺, and UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 andz=0–3. The metal ions are expected to have coordination numbers 6–8.

---

Strukturuntersuchungen an 3-Acetyl-1,5-diaryl- und 3-Cyan-1,5-diaryl-formazan-Chelaten mit Cer(III), Thorium(IV) und Uran(VI)

Zusammenfassung Die hergestellten Chelate wurden mittels Elementaranalyse, IR, NMR, TGA und DTA charakterisiert. Darauf basierend wird die generelle Formel [M(HL) _m (OH^–) _n bzw. (NO ₃ ^– oder Cl^–) _x ·(H₂O) _y oder (C₂H₅OH bzw.DMSO) _z ] vorgeschlagen, wobei HL=Formazan,M=Ce³⁺, Th⁴⁺ oder UO ₂ ²⁺ ,m=1–2,n=0–3,x=0–3,y=0–4 undz=0–3. Die Metallionen haben Koordinationszahlen von 6–8.

     

Synthesis,structural characterization and biological studies of neodymium(III) and samarium(III) complexes with mercaptotriazole Schiff bases

A series of neodymium(III) and samarium(III) complexes of type [Ln(L)Cl(H₂O)₃] have been synthesized with Schiff bases (LH₂) derived from 3‐(phenyl/substituted phenyl)‐4‐amino‐5‐mercapto‐1,2,4‐triazoles and isatin. The structures of the complexes were established using elemental analysis, molar conductivities, magnetic moments, infrared, NMR (¹H, ¹³C) and UV–visible spectra, X‐ray diffraction and mass spectrometry. The thermal behaviour of these compounds under non‐isothermal conditions was investigated using thermogravimetry and differential thermogravimetry. The intermediates obtained at the end of various thermal decomposition steps were identified from elemental analysis and infrared spectral studies. All the ligands and their complexes were also screened for their antibacterial activity against Staphylococcus aureus and Bacillus subtilis and antifungal activity against Aspergillus niger, Aspergillus flavus and Colletotrichum capsici. The screening results were correlated with the structural features of the compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

Kinetics of oxidation of thiocyanate ion by manganese(III) in pyrophosphate medium

Summary Mn^III is stabilized by pyrophosphate in weakly acidic solutions. The nature of the complex formed was elucidated spectrophotometrically. The kinetics of Mn^III oxidation of thiocyanate in pyrophosphate medium was investigated over the pH range 2–3. The oxidation followed first order kinetics with [Mn^III]. The effects of varying [Mn^III], [NCS^–], added Mn^II and metal ions, pH, total [P₂O _f7 ^p4– ] and added ClO _f4 ^p– , Cl^– and SO _f4 ^p2– were studied. The order in [NCS^–] was unity, and increasing [H⁺] increased the rate. Retardations with added P₂O _f7 ^p4– and Mn^II were observed. Complexation of NCS^– as K₂Zn(NCS)₄ decreased the reactivity without any change in overall mechanism. The dependence of the reaction rate on temperature was examined, and activation parameters were computed from Arrhenius and Eyring plots. A mechanism consistent with the results is proposed.     

Potentiometric and spectral studies of complex formation of La(III), Pr(III) and Lu(III) with aspartic acid and asparagine

The composition and stability of La³⁺, Pr³⁺ and Lu³⁺ complexes with aspartic acid and asparagine were analysed. The formation of complexes of the typeML andMHL was determined for La³⁺ and Pr³⁺ with aspartic acid, and of the typeMHL for Lu³⁺ with aspartic acid. For La³⁺, Pr³⁺ and Lu³⁺ with asparagine the formation ofML(OH) complexes was observed. By means of¹H NMR and¹³C NMR studies the participation in the coordination of both -COOH groups was determined for aspartic acid, whereas for asparagine the participation of the -COOH group was determined in complexes with La³⁺, Pr³⁺, and of the -COOH and the -NH₂ groups in the complex with Lu³⁺.

---

Potentiometrische und spektroskopische Untersuchungen an La(III), Pr(III) und Lu(III)-Komplexen von Asparaginsäure und Asparagin

Zusammenfassung Die Zusammensetzung und die Stabilität von La³⁺, Pr³⁺ und Lu³⁺-Komplexen mit Asparaginsäure und Asparagin wurden untersucht. Es wurde die Bildung von La³⁺ und Pr³⁺-Komplexen des TypsML undMHL, und ein Lu³⁺-Komplex des TypsMHL mit Asparaginsäure festgestellt. Für diese drei Lanthaniden wurde auch die Bildung von Komplexen des TypsML(OH) mit Asparagin beobachtet. Mit Hilfe von¹H-NMR und¹³C-NMR-Untersuchungen wurde für Asparaginsäure die Teilnahme der beiden -COOH-Gruppen, für Asparagin die Teilnahme der -COOH-Gruppe in den Komplexen mit La³⁺, Pr³⁺ und der-COOH und -NH₂-Gruppen in dem Komplex mit Lu³⁺ an der Koordinierung festgestellt.

     

Complexes of Bifunctional DO3A-N-(α-amino)propinate Ligands with Mg(II), Ca(II), Cu(II), Zn(II), and Lanthanide(III) Ions: Thermodynamic Stability,Formation and Dissociation Kinetics,and Solution Dynamic NMR Studies

The thermodynamic, kinetic, and structural properties of Ln³⁺ complexes with the bifunctional DO3A-ACE⁴⁻ ligand and its amide derivative DO3A-BACE⁴⁻ (modelling the case where DO3A-ACE⁴⁻ ligand binds to vector molecules) have been studied in order to confirm the usefulness of the corresponding Gd³⁺ complexes as relaxation labels of targeted MRI contrast agents. The stability constants of the Mg²⁺ and Ca²⁺ complexes of DO3A-ACE⁴⁻ and DO3A-BACE⁴⁻ complexes are lower than for DOTA⁴⁻ and DO3A³⁻, while the Zn²⁺ and Cu²⁺ complexes have similar and higher stability than for DOTA⁴⁻ and DO3A³⁻ complexes. The stability constants of the Ln(DO3A-BACE)⁻ complexes increase from Ce³⁺ to Gd³⁺ but remain practically constant for the late Ln³⁺ ions (represented by Yb³⁺). The stability constants of the Ln(DO3A-ACE)⁴⁻ and Ln(DO3A-BACE)⁴⁻ complexes are several orders of magnitude lower than those of the corresponding DOTA⁴⁻ and DO3A³⁻ complexes. The formation rate of Eu(DO3A-ACE)⁻ is one order of magnitude slower than for Eu(DOTA)⁻, due to the presence of the protonated amine group, which destabilizes the protonated intermediate complex. This protonated group causes the Ln(DO3A-ACE)⁻ complexes to dissociate several orders of magnitude faster than Ln(DOTA)⁻ and its absence in the Ln(DO3A-BACE)⁻ complexes results in inertness similar to Ln(DOTA)⁻ (as judged by the rate constants of acid assisted dissociation). The ¹H NMR spectra of the diamagnetic Y(DO3A-ACE)⁻ and Y(DO3A-BACE)⁻ reflect the slow dynamics at low temperatures of the intramolecular isomerization process between the SA pair of enantiomers, R-Λ(λλλλ) and S-Δ(δδδδ). The conformation of the C_α-substituted pendant arm is different in the two complexes, where the bulky substituent is further away from the macrocyclic ring in Y(DO3A-BACE)⁻ than the amino group in Y(DO3A-ACE)⁻ to minimize steric hindrance. The temperature dependence of the spectra reflects slower ring motions than pendant arms rearrangements in both complexes. Although losing some thermodynamic stability relative to Gd(DOTA)⁻, Gd(DO3A-BACE)⁻ is still quite inert, indicating the usefulness of the bifunctional DO3A-ACE⁴⁻ in the design of GBCAs and Ln³⁺-based tags for protein structural NMR analysis.     

Lanthanide(III) Nitrate Complexes of Two 17 Membered N3O2-Donor Macrocycles

The interaction of lanthanide(III) ions with two N₃O₃-macrocycles, L¹ and L², derived from 2,6-bis(2-formylphenoxymethyl)pyridine and 1,2-diaminoethane has been investigated. Schiff-base macrocyclic lanthanide(III) complexes LnL¹(NO₃)₃ · xH₂O (Ln = Nd, Sm, Eu or Lu) have been prepared by direct reaction of L¹ and the appropriate hydrated lanthanide nitrate. The direct reaction between the diamine macrocycle L² and the hydrated lanthanide(III) nitrates yields complexes LnL²(NO₃)₃· H₂O only for Ln = Dy or Lu. The reduction of the Schiff-base macrocycle decreases the complexation capacity of the ligand towards the Ln(III) ions. The complexes have been characterised by elemental analysis, molar conductivity data, FAB mass spectrometry, IR and, in the case of the lutetium complexes, ¹H NMR spectroscopy.     

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

Synthesis,crystal structure and antibacterial activity of manganese(III) and cobalt(III) complexes containing pentadentate Schiff bases of a common amine and thiocyanate

Abstract

Four new mononuclear Schiff base manganese(III) and cobalt(III) complexes viz. [Mn(L¹)(NCS)] (1), [Mn(L²)(NCS)] (2), [Co(L³)(NCS)] (3), and [Co(L⁴)(NCS)]·0.5CH₃OH·0.5H₂O (4), containing thiocyanate as a common pseudohalide ion are reported. The pentadentate Schiff base ligands H₂L¹, H₂L², H₂L³, and H₂L⁴ were obtained by the condensation of substituted salicylaldehydes with N-(3-aminopropyl)-N-methylpropane-1,3-diamine. The syntheses of the complexes have been achieved by the reaction of manganese(II) perchlorate or cobalt(II) perchlorate with the respective Schiff bases in the presence of thiocyanate in methanol medium. Complexes 1–4 have been characterized by microanalytical, spectroscopic, single-crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 adopt nearly similar structures containing the MN₄O₂ (M?=?Mn, Co) chromophore in which each central M(III) ion adopts a distorted octahedral geometry. Weak intermolecular H-bonding interactions are operative in these complexes to bind the molecular units. The antibacterial activity of 1–4 and their constituent Schiff bases has been tested against some common bacteria.