Coordinate Structures of PrIII, GdIII, TmIII, and YbIII Complexes with Nitrilotriacetic Acids

The crystal and molecular structures of the [Pr^III(nta)(H₂O)₂]·H₂O (nta = nitrilotriacetic acids), K₃[Gd^III(nta)₂(H₂O)]·6H₂O, and K₃[Yb^III(nta)₂]·5H₂O complexes have been determined by single-crystal X-ray structure analyses. In [Pr^III(nta)(H₂O)₂]·H₂O, the Pr^IIINO₈ part forms a nine-coordinate pseudo-monocapped square antiprismatic structure in which one N and three O atoms are from one nta ligand in the same molecule, three O atoms from another nta ligand in the neighboring molecule and two O atoms from two coordinate water molecules. In K₃[Gd^III(nta)₂(H₂O)]·6H₂O, the [Gd^III(nta)₂(H₂O)^3- complex anion has a nine-coordinate pseudo-monocapped square antiprismatic structure in which each nta acts as a tetradentate ligand with one N atom of the amino group and three O atoms of the carboxylic groups. In K₃[Yb^III(nta)₂]·5H₂O, each nta also acts as a tetradentate ligand with one N atom of amino group and three O atoms of the carboxylic groups, but the [Yb^III(nta)₂ ^3- complex anion has an eight-coordinate structure with a distorted square antiprismatic prism. All the results including those for [Tm^III(nta)(H₂O)₂]·2H₂O confirm the inferences on the coordinate structures and coordination numbers of rare earth metal complexes with the nta ligand.     

Inner-sphere oxidation of ternary nitrilotriacetatocobalt(II) complexes involving oxalate and phthalate by periodate

The oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ and [Co^II(nta)(ph)(H₂O)₂]³⁻ (nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ by periodate, obeys the following equation: d[Co^III]/dt = [Co^II(nta)(ox)(H₂O)₂³⁻][H₅IO₆] {k ₄ K ₅ + (k ₅ K ₆ K ₂/[H⁺]} while the reaction of [Co^II(nta)(ph)(H₂O)₂]³⁻ with periodate in aqueous acidic medium obeys the following rate law: d[Co^III]/dt = k ₆ K ₈[Co^II]_T [I^VII]_T/{1 + [H⁺]/K ₇ + K ₈[I^VII] _T }. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes by periodate is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions.     

Mechanism of electron transfer reaction of ternary nitrilotriacetatocobalt(II) complexes involving succinate and malonate as secondary ligands

The mechanism of oxidation of ternary complexes, [Co^II(nta)(S)(H₂O)₂]^3? and [Co^II(nta)(M)(H₂O)]^3? (nta = nitrilotriacetate acid, S = succinate dianion, and M = malonate dianion), by periodate in aqueous medium has been studied spectrophotometrically over the (20.0–40.0) ± 0.1°C range. The reaction is first order with respect to both [IO₄^?] and the complex, and the rate decreases over the [H⁺] range (2.69–56.20) × 10^?6 mol dm^?3 in both cases. The experimental rate law is consistent with a mechanism in which both the hydroxy complexes [Co^II(nta)(S)(H₂O)(OH)]^4? and [Co^II(nta)(M)(OH)]^4? are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant for the oxidation of the [Co^II(nta)(S)(H₂O)₂]^3?, k₁ (3.60 × 10^?3 s^?1), is greater than the value of k₆ (1.54 × 10^?3 s^?1) for the oxidation of [Co^II(nta)(M)(H₂O)]^3? at 30.0 ± 0.1°C and I = 0.20 mol dm^?3. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 103–113, 2008     

Investigation on sonocatalytic damage of BSA under ultrasonic irradiation by Fe<Superscript>III</Superscript> complexes with some aminocarboxylic acid

The interaction of BSA and Fe^III complexes ([Fe^III(gly)(H₂O)₄]²⁺, [Fe^III(ida)(H₂O)₃]⁺, and [Fe^III(nta)(H₂O)₂], gly—glyane, ida—iminodiacetic acid, nta—triglycolamic acid) as well as the sonocatalytic damage to BSA was studied by UV-vis and fluorescence spectra. In addition, the influences of ultrasonic irradiation time and Fe^III complex concentration were also examined on the sonocatalytic damage to BSA. The results showed that the fluorescence quenching of BSA solution caused by the Fe^III complexes belonged to the static quenching process. The BSA and Fe^III complexes interacted with each other mainly through weak interaction and coordinate actions. The binding association constants (K) and binding site numbers (n) were calculated. The results were as follows: K ₁ = 0.5353 × 10⁴ l mol⁻¹ and n ₁ = 0.9812 for [Fe^III(gly)(H₂O)₄]²⁺, K ₂ = 1.4285 × 10⁴ l mol⁻¹ and n ₂ = 1.0899 for [Fe^III(ida)(H₂O)₃, and K ₃ = 0.4411 × 10⁴ l mol⁻¹ and n ₃ = 0.9471 for [Fe^III(nta)(H₂O)₂]. Otherwise, under ultrasonic irradiation the BSA were obviously damaged by the Fe^III complexes. The damage degree rose up with the increase of ultrasonic irradiation time and Fe^III complex concentration. And that, [Fe^III(nta)(H₂O)₂] exhibited in a way higher sonocatalytic activity than [Fe^III(gly)(H₂O)₄]²⁺ and [Fe^III(ida)(H₂O)₃]⁺.     

Syntheses and crystal structures of butterfly M2Te2 complexes of molybdenum and tungsten with functionalized cyclopentadienyl ligands

Reactions of singly-bonded dinuclear complexes [(η⁵-CH₃O₂CC₅H₄)₂M₂(CO)₆] (I, M?=?Mo; II, M?=?W) with the diarenylditelluride [4-CH₃C₆H₄Te]₂ in refluxing toluene for 4–6?h afforded dinuclear complexes 1 and 2 trans/ae-[(η⁵-RC₅H₄)₂M₂(CO)₄(μ-ArTe)₂] (Ar?=?4-CH₃C₆H₄Te). Complexes 1 and 2 were also synthesized by reactions of triply-bonded dinuclear complexes [(η⁵-CH₃O₂CC₅H₄)₂M₂(CO)₄] (III, M?=?Mo; IV, M?=?W) with [4-CH₃C₆H₄Te]₂ in refluxing toluene for 1?h. Both complexes have been characterized by elemental analysis, ¹H NMR, ¹³C NMR and IR spectroscopy and X-ray diffraction. Preliminary low-temperature NMR experiments on complexes 1 and 2 have revealed that in solution each complex goes through a rapid inversion of the butterfly four-membered ring M₂Te₂.     

Fluorimetric Detection of Phosphates in Water Using a Disassembly Approach: A Comparison of FeIII-, ZnII-, MnII- and MnIII-salen Complexes

Details of the reaction sequence used for the fluorimetric detection of phosphates by disassembly of transition metal Schiff base complexes were investigated for [Fe^III(salen)(H₂O)]⁺, [Zn^II(salen)], [Mn^II(salen)(H₂O)₂], and [Mn^III(salen)(H₂O)]⁺. The reactivity of these compounds towards phosphorus oxoanions of differing charge, number of donor atoms and steric hindrance was detected by UV/Vis and fluorescence spectroscopy in both aprotic organic and aqueous media. Selectivity of [Fe^III(salen)(H₂O)]⁺ towards pyrophosphate over all other tested phosphorus-containing analytes was strongly supported. [Zn^II(salen)] showed a faster reactivity but was much less selective. In contrast, [Mn^III(salen)(H₂O)]⁺ proved to be more stable than the iron complex but generally showed little reactivity towards phosphorus oxoanions. The influence of the charge of the central atom was investigated using the Mn^II analogue [Mn^II(salen)(H₂O)₂]. As expected, the reduced charge resulted in a reactivity comparable to the Zn^II complex in organic solution but lead to hydrolysis of the complex in water. Finally, the reaction products of [Fe^III(salen)(H₂O)]⁺ with phosphates were characterized by IR spectroscopy and mass spectrometry, providing further insights into the reaction mechanism of the disassembly process.     

Syntheses and structural determinations of the nine-coordinate rare earth metal: Na4[DyIII(dtpa)(H2O)]2·16H2O,Na[DyIII(edta)(H2O)3]·3.25H2O and Na3[DyIII(nta)2(H2O)]·5.5H2O

Three complexes, Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and Na₃[Dy^III (nta)₂(H₂O)]?·?5.5H₂O, have been synthesized in aqueous solution and characterized by FT–IR, elemental analyses, TG–DTA and single-crystal X-ray diffraction. Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O crystallizes in the monoclinic system with P2₁/n space group, a?=?18.158(10)?Å, b?=?14.968(9)?Å, c?=?20.769(12)?Å, β?=?108.552(9)°, V?=?5351(5)?ų, Z?=?4, M?=?1517.87?g?mol^?1, D _c?=?1.879?g?cm^?3, μ?=?2.914?mm^?1, F(000)?=?3032, and its structure is refined to R ₁(F)?=?0.0500 for 9384 observed reflections [I?>?2σ(I)]. Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O crystallizes in the orthorhombic system with Fdd2 space group, a?=?19.338(7)?Å, b?=?35.378(13)?Å, c?=?12.137(5)?Å, β?=?90°, V?=?8303(5)?ų, Z?=?16, M?=?586.31?g?mol^?1, D _c?=?1.876?g?cm^?3, μ?=?3.690?mm^?1, F(000)?=?4632, and its structure is refined to R ₁(F)?=?0.0307 for 4027 observed reflections [I?>?2σ(I)]. Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O crystallizes in the orthorhombic system with Pccn space group, a?=?15.964(12)?Å, b?=?19.665(15)?Å, c?=?14.552(11)?Å, β?=?90°, V?=?4568(6)?ų, Z?=?8, M?=?724.81?g?mol^?1, D _c?=?2.102?g?cm^?3, μ?=?3.422?mm^?1, F(000)?=?2848, and its structure is refined to R ₁(F)?=?0.0449 for 4033 observed reflections [I?>?2?σ(I)]. The coordination polyhedra are tricapped trigonal prism for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O and Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O, but monocapped square antiprism for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O. The crystal structures of these three complexes are completely different from one another. The three-dimensional geometries of three polymers are 3-D layer-shaped structure for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, 1-D zigzag type structure for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and a 2-D parallelogram for Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O. According to thermal analyses, the collapsing temperatures are 356°C for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, 371°C for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and 387°C for Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O, which indicates that their crystal structures are very stable.     

Synthesis,characterization and magnetic properties of cyanide bridged 1-D metal-coordination polymers based on [FeIII(s-bqdi)2(CN)2]−

A new series of transition metal complexes K[M^II(s-bqdi)₂][Fe^III(s-bqdi)₂(CN)₂]?·?10H₂O (s-bqdi?=?semibenzoquinonediiminate, M^II?=?Co (2), Ni (3), and Cu (4)) have been synthesized. These complexes have been characterized by elemental analyses, FT IR, Far IR, FAB mass, UV-Vis, TGA, CV measurements, and powder XRD. The powder XRD patterns of 2, 3, and 4 show that they are isostructural with hexagonal primitive lattice structures. The coordination polymers display 1-D chain networks. Magnetic properties of the Co^IIFe^III complex studied by a SQUID magnetometer reveal low-temperature antiferromagnetic interaction.     

Synthesis,crystal structure,and luminescent properties of metal complexes bearing 2,6-pyridine-diacylhydrazide ligands: supramolecular assemblies via intermolecular interactions

Four metal complexes of N,N′-bis(salicyl)-2,6-pyridine-dicarbohydrazide ligand (H₆L), [Co^II(H₄L)(H₂O)₂]·2DMF (1), [Zn^II(H₄L)(H₂O)₂]·2DMF (2), [Cd^II(H₄L)(Py)₂]·DMF·Py (3), and [Co^IICo₂^III(H₄L)₄(H₂O)₄]·DMF·H₂O (4), were synthesized and characterized by elemental analysis, IR, and single-crystal X-ray diffraction analysis. Structural studies revealed that complexes 1–3 present discrete mononuclear structures and complex 4 displays a centrosymmetric mixed-valence trinuclear structure. All four complexes are further extended into interesting two- or three-dimensional supramolecular frameworks. The luminescent properties of 2 and 3 were studied, which show emissions with maxima at 485 nm upon excitation at 396 nm for 2 and 476 nm upon excitation at 397 nm for 3, respectively.     

Organic acid effect on the structures of Cd(II) metal-organic complexes based on 2-(3-pyridyl)imidazo[4,5-<Emphasis Type="Italic">f</Emphasis>]-1,10-phenanthroline

Three new Cd(II) complexes consisting of phenanthroline derivative and organic acid ligands, formulated as [Cd₃(3-PIP)₂(L¹)₆] (I), [Cd(3-PIP)(L²)] · H₂O (II), and [Cd(3-PIP)(L³)] (III) (3-PIP = 2-(3-pyridyl)imidazo[4,5-f]-1,10-phenanthroline, HL¹ = 3,5-dinitrobenzoic acid, H₂L² = oxalic acid, H₂L³ = benzene-1,3-dicarboxylic acid), have been synthesized via the hydrothermal reaction and characterized by single-crystal X-ray diffraction, elemental analyses and FT-IR spectra. Complex I is a trinuclear structure. Complex II features a 1D zigzag chain. Complex III shows a twisted double chain of binuclear units sustained by double carboxylate bridges. Three complexes are further extended into 3D supramolecular frameworks by hydrogen bonding and π-π-stacking interactions. The structural differences among I–III show that the organic carboxylates have important effects on the structures. Furthermore, the supramolecular interactions are the critical factors in determining the final structures of the complexes. In addition, the thermal stabilities and luminescent properties of complexes I and II are also investigated.     

Thermal and spectral properties of Cu(II)-5-halogenosalicylates with or without nicotinamide

Summary This paper deals with the preparation and investigation of thermal and spectral properties of the complexes Cu(5-ClSal)₂·2H₂O (I), Cu(5-BrSal)₂·2H₂O (II), Cu(5-ClSal)₂(nia)(H₂O) (III), Cu(5-BrSal)₂(nia)(H₂O) (IV), and Cu(5-ISal)₂(nia)(H₂O) (V) (where Sal=salicylate, and nia=nicotinamide). TG, DTG, DTA, EPR, IR and electronic spectra have been used to study thermal and spectral properties of the complexes. The chemical composition of the complexes, the solid intermediates and the resultant products of thermolysis have been identified by means of elemental analysis and complexometric titration. Schemes of the decomposition of the complexes are suggested. Heating of the compounds first resulted in the release of water molecules. The thermal stability of these complexes can be ordered in the sequence: I <II <IV=V< III. The final product of the thermal decomposition was CuO in all cases. IR data suggested a bidentate coordination of carboxylates to Cu(II) in complexes I-II and bridging ones for complexes III-V.     

Oligonuclear 3d–4f Complexes as Tectons in Designing Supramolecular Solid‐State Architectures: Impact of the Nature of Linkers on the Structural Diversity

Heteronuclear cationic complexes, [LCuLn]³⁺ and [(LCu)₂Ln]³⁺, were employed as nodes in designing high‐nuclearity complexes and coordination polymers with a rich variety of network topologies (L is the dianion of the Schiff base resulting from the 2:1 condensation of 3‐methoxysalycilaldehyde with 1,3‐propanediamine). Two families of linkers have been chosen: the first consists of exo‐dentate ligands bearing nitrogen‐donor atoms (bipyridine (bipy), dicyanamido (dca)), whereas the second consists of exo‐dentate ligands with oxygen‐donor atoms (anions derived from the acetylenedicarboxylic (H₂acdca), fumaric (H₂fum), trimesic (H₃trim), and oxalic (H₂ox) acids). The ligands belonging to the first family prefer copper(II ) ions, whereas the ligands from the second family interact preferentially with oxophilic rare‐earth cations. The following complexes have been obtained and crystallographically characterized: [LCu^II(OH₂)Gd^III(NO₃)₃] ( 1 ), [{LCu^IIGd^III(NO₃)₃}₂(μ‐4,4′‐bipy)] ( 2 ), [LCu^IIGd^III(acdca)_1.5(H₂O)₂] ? 13 H₂O ( 3 ), [LCu^IIGd^III(fum)_1.5(H₂O)₂] ? 4 H₂O ? C₂H₅OH ( 4 ), [LCu^IISm^III(H₂O)(Hfum)(fum)] ( 5 ), [LCu^IIEr^III(H₂O)₂(fum)]NO₃ ? 3 H₂O ( 6 ), [LCu^IISm^III(fum)_1.5(H₂O)₂] ? 4 H₂O ? C₂H₅OH ( 7 ), [{(LCu^II)₂Sm^III}₂fum₂](OH)₂ ( 8 ), [LCu^IIGd^III(trim)(H₂O)₂] ? H₂O ( 9 ), [{(LCu^II)₂Pr^III}(C₂O₄)_0.5(dca)]dca ? 2 H₂O ( 10 ), [LCu^IIGd^III(ox)(H₂O)₃][Cr^III(2,2′‐bipy)(ox)₂] ? 9 H₂O ( 11 ), and [LCuGd(H₂O)₄{Cr(CN)₆}] ? 3 H₂O ( 12 ). Compound 1 is representative of the whole family of binuclear Cu^II–Ln^III complexes which have been used as precursors in constructing heteropolymetallic complexes. The rich variety of the resulting structures is due to several factors: 1) the nature of the donor atoms of the linkers, 2) the preference of the copper(II ) ion for nitrogen atoms, 3) the oxophilicity of the lanthanides, 4) the degree of deprotonation of the polycarboxylic acids, 5) the various connectivity modes exhibited by the carboxylato groups, and 6) the stoichiometry of the final products, that is, the Cu^II/Ln^III/linker molar ratio. A unique cluster formed by 24 water molecules was found in crystal 11 . In compounds 2 , 3 , 4 , 9 , and 11 the Cu^II–Gd^III exchange interaction was found to be ferromagnetic, with J values in the range of 3.53–8.96 cm^?1. Compound 12 represents a new example of a polynuclear complex containing three different paramagnetic ions. The intranode Cu^II–Gd^III ferromagnetic interaction is overwhelmed by the antiferromagnetic interactions occurring between the cyanobridged Gd^III and Cr^III ions.     

Self-assembly of metal(II) tetraaza macrocyclic complexes with cyclobutane-1-carboxylic acid-1-carboxylate ligand linked by hydrogen bond

The reaction of [M(L)]Cl₂ · 2H₂O (M = Ni²⁺ and Cu²⁺, L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) with 1,1-cyclobutanedicarboxylic acid (H₂-cbdc) generates 1D and 2D hydrogen-bonded infinite chains [Ni(L)(H-cbdc⁻)₂] (1) and [Cu(L)(H-cbdc⁻)₂] (2). (H-cbdc⁻ = cyclobutane-1-carboxylic acid-1-carboxylate). These complexes have been characterized by X-ray crystallography, spectroscopy, and cyclic voltammetry. The crystal structure of 1 shows a distorted octahedral coordination geometry around the nickel(II) ion, with four secondary amines and two oxygen atoms of the H-cbdc⁻ ligand at the trans position. In 2, the coordination environment around the central copper(II) ion shows a Jahn–Teller distorted octahedron with four Cu–N bonds and two long Cu–O distances. The cyclic voltammogram of the complexes undergoes two one-electron waves corresponding to M^II/M^III and M^II/M^I processes. The electronic spectra and electrochemical behavior of the complexes are significantly affected by the nature of the axial H-cbdc⁻ ligand.     

Regulating Spin Dynamics of Nitronyl Nitroxide Biradical Lanthanide Complexes through Introducing Different Transition Metals

Four biradical-Ln complexes with different transition metal ions, namely [LnM(hfac)₅(NITPh-PyPzbis)] (M^II=Mn^II and Ln^III=Gd 1 , Dy 2 ; M^II=Ni^II and Ln^III=Tb 3 , Dy 4 ), were prepared by the reaction of Ln(hfac)₃ ⋅ 2H₂O, Mn(hfac)₂ ⋅ 2H₂O or Ni(hfac)₂ ⋅ 2H₂O with NITPh-PyPzbis biradical (hfac=hexafluoroacetylacetonate, NITPh-PyPzbis=5-(3-(2-pyridinyl)-1H-pyrazol-1-yl)-1,3-bis(1’-oxyl-3’-oxido- 4’,4’,5’,5’-tetramethyl-4,5-hydro-1H-imidazol-2-yl)benzene). In complexes 1 – 4 , the NITPh-PyPzbis biradical chelates one Ln^III ion by means of its aminoxyl moieties and the transition metal ion is introduced through the two N donors from the pyridyl pyrazolyl moiety. Magnetic investigations indicate that complex 4 displays visible maxima in frequency/temperature-dependent χ′′ signals with two-step relaxation processes, but complex 2 exhibits no slow magnetization relaxation. The comparison of structure parameters of both Dy complexes indicates that the symmetries of coordination spheres of two Dy ions are D_2d for 2 and C_2v for 4 , which thus probably results in different magnetic relaxation behaviors. This work provides new insight for improving properties of Ln-biradical based SMMs.     

Synthesis,spectral and thermal studies of monomeric,homobimetallic and polymeric complexes containing benzoyldithiocarbazate

New mixed ligand complexes of benzoyldithiocarbazate (H₂BDT) have been synthesized and characterized by elemental analyses, spectral studies (i.r., u.v.–vis., mass), thermal analysis and electrical conductivity measurements. The complexes have the general formulae: [M₂(BDT)(OX)₂] · xH₂O; [Co₂(BDT)(OX)₂(H₂O)₄]; [M(HBDT)(OX)-(H₂O)], [Ni(BDT)(py)₂] _n and [Ni(BDT)(L)] _n where M = Mn^II, Ni^II and Cu^II; BDT = dithiocarbazate dianion; OX = 8-hydroxyquinolinate; x = 1 or 2; M = Zn^II or Cd^II; HBDT = dithiocarbazate anion and L = 2,2-bipyridyl or 1,10-o-phenanthroline. For the [M₂(BDT)(OX)₂] · xH₂O, [Co₂(BDT)(OX)₂(H₂O)₄], [Ni(BDT)(py)₂] _n and [Ni(BDT)(L)] _n complexes, benzoyldithiocarbazate acts as a dibasic-tetradentate ligand in the enol form via the enolic oxygen, the hydrazide nitrogens and the thiolate sulphur, while it acts as a monobasic-tridentate ligand in the keto form in the [M(HBDT)(OX)(H₂O)] complexes. The thermal behaviour of the complexes has been studied by t.g.–d.t.g. techniques. Kinetic parameters of the thermal decomposition process have been computed by Coats–Redfern and Horowitz–Metzger methods. It is obvious that the thermal decomposition in the complexes occurs directly at the metal–ligand bonds except for the Zn^II and Cd^II complexes in which decomposition seems to be at a point in the benzoyldithiocarbazate moiety. From the calculated kinetic data it can be concluded that the dehydration processes in all complexes have been described as phase-boundary controlled reactions. The activation energy values reveal that the thermal stabilities of the homobimetallic complexes lie in the order: Mn^II < Ni^II < Co^II, while the monomeric Cd^II complex has more enhanced thermal stability than the Zn^II complex.     

Kinetics of the oxidation of diaqua(nitrilotriacetato)-chromium(III) by periodate in aqueous solutions

Summary The kinetics of oxidation of [Cr^III(nta)(H₂O)₂] (nta is nitrilotriacetate) by periodate obey the rate law d[Cr^VI]/dt=(k₂[IO ₄ ^– ]+k₃[IO ₄ ^– ]²)[Cr^III(nta)(H₂O)₂] under fixed conditions. The activation parameters are reported and we propose that electron-transfer proceeds via an inner-sphere mechanism.     

Heterotrimetallic Coordination Polymers: {CuIILnIIIFeIII} Chains and {NiIILnIIIFeIII} Layers: Synthesis,Crystal Structures,and Magnetic Properties

The use of the [Fe^III(AA)(CN)₄]^? complex anion as metalloligand towards the preformed [Cu^II(valpn)Ln^III]³⁺ or [Ni^II(valpn)Ln^III]³⁺ heterometallic complex cations (AA=2,2′‐bipyridine (bipy) and 1,10‐phenathroline (phen); H₂valpn=1,3‐propanediyl‐bis(2‐iminomethylene‐6‐methoxyphenol)) allowed the preparation of two families of heterotrimetallic complexes: three isostructural 1D coordination polymers of general formula {[Cu^II(valpn)Ln^III(H₂O)₃(μ‐NC)₂Fe^III(phen)(CN)₂ {(μ‐NC)Fe^III(phen)(CN)₃}]NO₃ ? 7 H₂O}_n (Ln=Gd ( 1 ), Tb ( 2 ), and Dy ( 3 )) and the trinuclear complex [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃] ? NO₃ ? H₂O ? CH₃CN ( 4 ) were obtained with the [Cu^II(valpn)Ln^III]³⁺ assembling unit, whereas three isostructural heterotrimetallic 2D networks, {[Ni^II(valpn)Ln^III(ONO₂)₂(H₂O)(μ‐NC)₃Fe^III(bipy)(CN)] ? 2 H₂O ? 2 CH₃CN}_n (Ln=Gd ( 5 ), Tb ( 6 ), and Dy ( 7 )) resulted with the related [Ni^II(valpn)Ln^III]³⁺ precursor. The crystal structure of compound 4 consists of discrete heterotrimetallic complex cations, [Cu^II(valpn)La^III(OH₂)₃(O₂NO)(μ‐NC)Fe^III(phen)(CN)₃]⁺, nitrate counterions, and non‐coordinate water and acetonitrile molecules. The heteroleptic {Fe^III(bipy)(CN)₄} moiety in 5 – 7 acts as a tris‐monodentate ligand towards three {Ni^II(valpn)Ln^III} binuclear nodes leading to heterotrimetallic 2D networks. The ferromagnetic interaction through the diphenoxo bridge in the Cu^II?Ln^III ( 1 – 3 ) and Ni^II?Ln^III ( 5 – 7 ) units, as well as through the single cyanide bridge between the Fe^III and either Ni^II ( 5 – 7 ) or Cu^II ( 4 ) account for the overall ferromagnetic behavior observed in 1 – 7 . DFT‐type calculations were performed to substantiate the magnetic interactions in 1 , 4 , and 5 . Interestingly, compound 6 exhibits slow relaxation of the magnetization with maxima of the out‐of‐phase ac signals below 4.0 K in the lack of a dc field, the values of the pre‐exponential factor (τ_o) and energy barrier (E_a) through the Arrhenius equation being 2.0×10^?12 s and 29.1 cm^?1, respectively. In the case of 7 , the ferromagnetic interactions through the double phenoxo (Ni^II–Dy^III) and single cyanide (Fe^III–Ni^II) pathways are masked by the depopulation of the Stark levels of the Dy^III ion, this feature most likely accounting for the continuous decrease of χ_M T upon cooling observed for this last compound.     

CoLn dinuclear complexes (Ln = Gd,Tb, Dy,Ho and Er) as platforms for 1,5-dicyanamide-bridged tetranuclear Co2Ln2 complexes: A magneto-structural and theoretical study

Five acetate-diphenoxo triply-bridged Co^II-Ln^III complexes (Ln^III = Gd, Tb, Dy, Ho, Er) of formula [Co(μ-L)(μ-Ac)Ln(NO₃)₂] and two diphenoxo doubly-bridged Co^II-Ln^III complexes (Ln^III = Gd, Tb) of formula [Co(H₂O)(μ-L)Ln(NO₃)₃]·S (S = H₂O or MeOH), were prepared in one pot reaction from the compartmental ligand N,N′,N′′-trimethyl-N,N′′-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylene triamine (H₂L). The diphenoxo doubly-bridged Co^II-Ln^III complexes were used as platforms to obtain 1,5-dicyanamide-bridged tetranuclear Co^II-Ln^III complexes (Ln^III = Gd, Tb, Dy, Ho, Er). All exhibit ferromagnetic interactions between the Co^II and Ln^III ions and in the case of the Gd^III complexes, the J_CoGd were estimated to be ∼+0.7 cm⁻¹. Compound 3 exhibits slow relaxation of the magnetization.     

Crystal structures of some lanthanide(III) complexes with acylhydrazone and their coordination chemistry

Three new lanthanide(III) complexes with N-(2-propionic acid)-salicyloylhydrazone (H₂L, C₁₀H₁₀N₂O₄) ligand [La(HL)₂(NO₃)(H₂O)₂]₃ ·4H₂O(I), [Gd(HL)₃] · 2(C₂H₅)₃ N(II) and [Er(L)(HL)(H₂O)₂] · 2H₂O(III) has been synthesized and characterized by elemental analyses, IR, UV, and molar conductivity. The crystal structures of three complexes have been determined by X-ray single-crystal diffractometer. In complex I, the La³⁺ ion is ten-coordinated by two tridentate ligands, one bidentate nitrate, and two water molecules. In complex II, the Gd³⁺ ion has a coordination number of nine by three tridentate ligands. In complex III, the Er³⁺ ion is eight-coordinated by two tridentate ligands and two water molecules. In all structures, tridentate ligands are coordinated by carboxyl O and acyl O atoms and azomethine N atom to form two stable five-membered rings sharing one side in the keto mode as indicated by the results of crystal structures and infrared spectral analysis.