Methyl 2-pyridyl Ketone Oxime Research Articles

New MnIIMnIII8 and MnII2MnIII10MnIV2 clusters from the reaction of methyl 2-pyridyl ketone oxime with [Mn12O12(O2CR)16(H2O)4

The syntheses, crystal structures and magnetic properties of two mixed-valence Mn clusters [MnIIMnIII8O6(mpko)3(O2CMe)11] (1) and [MnII2MnIII10MnIV2O12(mpko)6(O2CPh)12(H2O)2] (2) are reported. They were obtained from the corresponding reactions in MeCN of [Mn12O12(O2CR)16(H2O)4] (R = Me (3), Ph (4)) with eight equivalents of methyl(pyridine-2-yl)ketone oxime (mpkoH). The cores of 1 and 2 are structurally related: 1 possesses a [Mn9(µ3-O)6]14+ core with an unusual topology comprising a near-planar MnIII-centered MnIII6 hexagon with additional MnII and MnIII ions above and below the plane. Complex 2 possesses a [Mn14(µ4-O)2(µ3-O)10]18+ core that can be described as a dimer of two Mn7 incomplete-cores of 1. It is also a rare example of a Mn cluster containing three Mn oxidation states. Fits of variable-temperature, solid-state dc magnetic susceptibility data collected in a 0.1 T field in the 5.0–300 K range established that 1 and 2 possess ground state spins of S = 3/2 and S = 1, respectively, which were confirmed by ac in-phase susceptibility data.

Structural and magnetic properties of polynuclear oximate copper complexes with different topologies

Two new copper(II) complexes containing the methyl(2-pyridyl)ketone oxime ligand (mpkoH) [Cu3(OH)(ClO4)2(mpko)3]·CH3OH (1) and [Cu(ClO4)(mpko)(mpkoH)]n (2) have been prepared from Cu(ClO4)2 and mpkoH in different metal-to-ligand molar ratios. In addition, the compound [Cu{(mpko)2BF2}(H2O)](BF4) (3) [(mpko)2BF2 is the fluoroboration product of the oxime] has been obtained when replacing Cu(ClO4)2 by Cu(BF4)2. Compound 1 is an isolated triangle with a {Cu3(µ3-OH)}5+ core, whereas 2 is a chain of CuII ions linked by anionic mpko− bridges. 1 exhibits strong antiferromagnetic competing interactions, as well as antisymmetric exchange. On the other hand, very weak ferromagnetic interactions are found in 2. The magnetic properties of these compounds have been analyzed by magnetic measurements and EPR spectra.

MOF-like supramolecular network of Mn3 single-molecule magnets formed by extensive π–π stacking

[Mn3O(dhb)3(mpko)3](ClO4) (4) has been obtained from the carboxylate substitution reaction of triangular [Mn3O(O2CMe)3(mpko)3](ClO4) (mpkoH=methyl(2-pyridyl)ketone oxime) with 3,5-dihydroxybenzoic acid (dhbH). Complex 4 possesses an equilateral triangle [Mn3O]7+ core with the dhb− and mpko− ligands on opposite sides of the Mn3 plane. All dhb− and mpko− groups are involved in π–π stacking interactions with those on neighboring Mn3 molecules to give a 3-D supramolecular network resembling a metal–organic framework (MOF), with periodic voids resulting from a repeating unit comprising an [Mn3]8 rhombohedron. Variable-temperature, solid-state magnetic susceptibility studies in the 5.0–300K temperature range reveal the predominance of antiferromagnetic inter-Mn3 exchange couplings. Alternating current magnetic susceptibility studies on 4 show that the single-molecule magnet (SMM) behavior characteristic of [Mn3O(O2CR)3(mpko)3]+ complexes has been lost. This work demonstrates that constructing MOF-like networks from SMMs by weak interactions is feasible but that even these can introduce significant inter-SMM exchange interactions that weaken or destroy the SMM properties.

Doubly Thiocyanato(S,N)-Bridged Dinuclear Complexes of Mercury(II) from the Use of 2-pyridyl Oximes as Capping Ligands

The reactions between Hg(SCN)2 and the 2-pyridyl oximes, 2-pyridine aldoxime (paoH), methyl 2-pyridyl ketone oxime (mepaoH), pyridine-2-amidoxime (NH2paoH) and di-2-pyridyl ketone oxime (dpkoxH), have been investigated. The products in Me2CO or Me2CO/MeOH are the dinuclear complexes [Hg2(SCN)4(paoH)2] (1), [Hg2(SCN)4(mepaoH)2] (2), [Hg2(SCN)4(NH2paoH)2] (3) and [Hg2(SCN)4(dpkoxH)2] (4), whose structures have been determined by single-crystal X-ray crystallography. The molecular structures consist of centrosymmetric dinuclear molecules in which the two HgII ions are bridged by two bidentate bridging 1: 1: (1,3) SCN- groups forming a planar (1, 2) or non-planar (3, 4), 8-membered metallacyclic ring. The HgII centers are each chelated by a N(2-pyridyl), N(oxime)-bidentate ligand and are bound to one terminal S-bonded thiocyanato group. Due to the very long HgII-N (bridging SCN-) distances in 3, this complex can also be described as pseudodimer. The second 2-pyridyl ring of each dpkoxH ligand in 4 remains uncoordinated. The 2D lattice of 1 and 2 is built through H-bonding and - stacking interactions. Hydrogen bonds and S...S interactions generate 3D networks in 3 and 4. The IR spectra of the complexes are discussed in terms of the coordination modes of the ligands involved (SCN-, 2-pyridyl oximes). 1H NMR spectra in d6-DMSO indicate that the complexes decompose in solution. Keywords: Coordination chemistry, crystal structures, dinuclear mercury(II) complexes, 1H NMR spectra, infrared spectroscopy, oxime group, 2-pyridyl oxime ligands, thiocyanato ligands.

Nickel(II) complexes with methyl(2-pyridyl)ketone oxime: Synthesis, crystal structures and DFT calculations

The synthesis and structural characterization of the three novel nickel(II) complexes [Ni(OOCPh)2(mpkoH)2] (1), [Ni(NO3)2(mpkoH)2] (2) and [Ni(mpkoH)3](NO3)2⋅½H2O (3⋅½H2O), with mpkoH=methyl(2-pyridyl)ketone oxime is reported. Geometry optimization and population analyses were performed by means of DFT calculations for the previously mentioned compounds as well as for [NiCl2(mpkoH)2] (4). Electronic UV–vis spectra were also simulated in the TD-DFT framework to assign the origin of the absorption bands and in doing so, to have a clear picture of the absorptive features of the coordination compounds under investigation.

A new linear trinuclear cobalt complex bearing oximato and azido ligands: synthesis, structure, and magnetic characterization

The reaction of CoCl2 · 6H2O, mpkoH (methyl 2-pyridyl ketone oxime), NEt3, and NaN3 in a 1 : 1 : 2 : 1 molar ratio affords a linear trinuclear complex, [CoII(mpko)4(N3)4(H2O)2] (1). Complex 1 has been characterized by single-crystal X-ray diffraction, elemental analysis, and infrared spectrum. Three cobalt ions are in the center of distorted octahedra, which are connected by two μ-1,1 azides and two oxime oxygen atoms to form a linear trinuclear structure. Discrete units of 1 are connected to form a stable 3-D supramolecular network by C–H···O and C–H···N weak interactions. Variable temperature magnetic susceptibility measurements reveal that 1 exhibits antiferromagnetic behavior.

Employment of methyl 2-pyridyl ketone oxime in 3d/4f-metal chemistry: dinuclear nickel(ii)/lanthanide(iii) species and complexes containing the metals in separate ions

The use of methyl 2-pyridyl ketone oxime (mpkoH) for the synthesis of Ni(II)/Ln(III) (Ln = lanthanide) complexes, using "one-pot" reactions in the absence of an external base, is described. Depending on the reaction and crystallization conditions employed, two families of complexes have been obtained. The first family consists of true heterometallic species and involves complexes [NiLn(mpko)(3)(mpkoH)(3)](ClO(4))(2), where Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er. The second family contains the pseudo heterometallic complexes [Ni(mpkoH)(3)](2)[Ln(NO(3))(6)](ClO(4)), where Ln = La, Ce, Pr, Nd and Sm. The crystal structures of [NiCe(mpko)(3)(mpkoH)(3)](ClO(4))(2) (1), [NiDy(mpko)(3)(mpkoH)(3)](ClO(4))(2) (8) and [Ni(mpkoH)(3)](2)[La(NO(3))(6)](ClO(4)) (11) have been determined by single-crystal, X-ray crystallography. Complexes 1·1.2MeOH·0.6H(2)O and 8·1.2MeOH·0.6H(2)O crystallise in the monoclinic space group P2(1)/a and are isomorphous; there are two crystallographically independent cations in the unit cell, but their interatomic distances and angles differ little. The Ni(II) and Ln(III) ions are bridged by three oximate groups belonging to the η(1):η(1):η(1):μ mpko(-) ligands. The Ni(II) centre is octahedrally coordinated by the six nitrogen atoms of the mpko(-) ligands in a facial arrangement. The Ln(III) centre is bound to an (O(oximate))(3)N(6) set of donor atoms, the nitrogen atoms belonging to the three N,N'-bidentate chelating mpkoH ligands. The stereochemistry of the Ln(III) atoms has been evaluated by means of continuous shape measures (CShM). The two crystallographically independent Ce(III) atoms in 1 have tricapped trigonal prismatic and capped square antiprismatic coordination geometries, while the polyhedra of the Dy(III) atoms in 8 are both close to a tricapped trigonal prism. The octahedral Ni(II) atoms in 11 are both facially bound to a N(6) set of donor atoms from three N,N'-bidentate chelating mpkoH ligands, while the 12-coordinate La(III) centre in [La(NO(3))(6)](3-) is coordinated by six bidentate chelating nitrato groups. Variable-temperature, solid state dc magnetic susceptibility studies were carried out on complexes 2, 6, 7 and 8. The dc susceptibility data for 6 in the 2.0-300 K range have been fit to a model with one J value, revealing an antiferromagnetic Ni(II)···Gd(III) exchange interaction [J = -1.1 cm(-1) based on H = -J (Ŝ(Ni)·Ŝ(Gd))]. Antiferromagnetic Ni(II)···Pr(III), Ni(II)···Tb(III) and Ni(II)···Dy(III) exchange interactions have also been suggested for 2, 7 and 8, respectively. The combined work demonstrates the usefulness of mpko(-) in the preparation of interesting Ni(II)/Ln(III) compounds, without requiring the presence of external base and ancillary organic ligands.

Mononuclear and Dinuclear Manganese(II) Complexes from the Use of Methyl(2‐pyridyl)ketone Oxime

The reactions of methyl(2-pyridyl)ketone oxime, (py)C(Me)NOH, with manganese(II) sulfate monohydrate have been investigated. The reaction between equimolar quantities of MnSO4 · H2O and (py)C(Me)NOH in H2O lead to the dinuclear complex [Mn2(SO4)2{(py)C(Me)NOH}4] · (py)C(Me)NOH, 1 · (py)C(Me)NOH, while employment of NaOMe as base affords the compound [Mn(HCO2)2{(py)C(Me)NOH}2] (2). The structures of both compounds have been determined by single crystal X-ray diffraction. In both complexes, the organic ligand chelates through its nitrogen atoms. The IR data are discussed in terms of the nature of bonding and the structures of the two complexes.

Triangular Ni(II) complexes from the use of 2-pyridyl oximes

The reactions of representative 2-pyridyl oximes with Ni II salts in the presence of a base have been investigated. The synthetic study has led to the new triangular complexes [Νi 3(ppko) 6]·2H 2O·0.5EtOH·MeOH ( 1·2H 2O·0.5EtOH·MeOH), [Νi 3(mpko) 3(HCO 2) 2(mpkoH) 2](ClO 4) ( 2) and [Νi 3(ppko) 3(HCO 2) 2(ppkoH) 2](ClO 4) ( 3), where ppko − is the anion of phenyl(2-pyridyl)ketone oxime and mpko − is the anion of methyl(2-pyridyl)ketone oxime. The structures of compounds 1 and 2 have been determined by single crystal X-ray diffraction. The ppko − ligand in 1 adopts four different coordination modes including the unique N pyridylO oximate chelating one which gives rise to a 6-membered chelating ring, while the neutral and the deprotonated oxime ligands in 2 adopt three different coordination modes. The magnetic properties of 1 and 2 have been studied by variable-temperature dc magnetic susceptibility techniques which indicate antiferromagnetic interactions.

Selective Ethylene Oligomerization with Nickel Oxime Complexes

Two nickel-oxime complexes, Ni (2-pyridine aldoxime)2 dichloride (6) and Ni (methyl 2-pyridyl ketone oxime)2 dichloride (7), were prepared and characterized by X-ray crystallography. Both complexes are six-coordinate and have 2-pyridylimines as ligand backbones, where the two nitrogen atoms from each of the oxime ligands coordinate to the metal, but the oxygen atom remains protonated and does not participate in bonding to the metal center. The complexes were found to be selective ethylene dimerization catalysts in the presence of cocatalyst such as methylaluminoxane (MAO) or diethyl aluminum chloride (DEAC). With DEAC, the productivity is considerably higher than with MAO. Under optimum conditions the productivity values are as high as 200 kg/mol catalyst/h/bar (for 6) to 335 kg/mol catalyst/h/bar (for 7). The selectivities toward dimerization under these conditions are 84% and 77%, respectively, with the terminal isomer 1-butene being the only (≥99.5%) C4 product.

Employment of methyl 2-pyridyl ketone oxime in manganese non-carboxylate chemistry: MnII2MnIV and MnII2MnIII6 complexes

The employment of the anion of methyl 2-pyridyl ketone oxime (mpko(-)) as a tridentate chelating/bridging ligand in manganese chemistry is described. The inorganic anion (Br(-), ClO(4)(-)) used in the reaction affects the identity of the product. The reaction of MnBr(2) and one equivalent of mpkoH in the presence of a base affords [Mn(3)(OMe)(2)(mpko)(4)Br(2)] (3), which is mixed-valence (2Mn(II), Mn(IV)). The central Mn(IV) atom in each of the two, crystallographically independent, centrosymmetric molecules is coordinated by four oximate oxygen atoms belonging to the eta(1):eta(1):eta(1):mu mpko(-) ligands, and two eta(1):mu MeO(-) groups, while six coordination at each terminal Mn(II) atom is completed by four nitrogen atoms belonging to the 'chelating' part of two mpko(-) ligands, and one Br(-) ion. The Mn(II) atoms have trigonal prismatic coordination geometry. The reaction of Mn(ClO(4))(2).6H(2)O, mpkoH and OH(-) (1:2:1) in MeOH gives [Mn(8)O(4)(OMe)(mpko)(9)(mpkoH)](ClO(4))(4) (4), which is also mixed-valence (2Mn(II), 6Mn(III)) and possesses the novel [Mn(8)(mu(3)-O)(4)(mu-OMe)(mu-OR'')(2)](11+) core. The latter possesses a U-shaped sequence of four fused {Mn(II)Mn(III)(2)(mu(3)-O)}(6+) triangular units, with a Mn(III)-Mn(III) edge being shared between the central triangles. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on complexes 3 and 4 . The dc susceptibility data for 3 in the 5.0-300 K range have been fit to a model with two J values, revealing weak ferromagnetic Mn(II)Mn(IV) (J = +3.4 cm(-1)) and Mn(II)Mn(II) (J' = +0.3 cm(-1)) exchange interactions. Fitting of the magnetization vs. H/T data by matrix diagonalization and including only axial anisotropy (ZFS, D) gave ground state spin (S) and D values of S = 13/2, D = +0.17 cm(-1) for and S = 3, D = -0.09 cm(-1) for 4 . The combined work demonstrates the usefulness of mpko(-) in the preparation of interesting Mn clusters, without requiring the co-presence of carboxylate ligands.

A family of mononuclear Co III/2-pyridyloximate complexes and their conversion to trinuclear, mixed-valence linear [formula omitted] clusters

The use of the 2-pyridyl oxime ligands (LH) 2-pyridinealdoxime, methyl 2-pyridyl ketone oxime and phenyl 2-pyridyl ketone oxime in Co chemistry has been investigated and led to two families of compounds. The first family includes the mononuclear octahedral, low-spin complexes [Co III(L) 3], while the second family consists of the trinuclear, mixed-valent linear clusters [ Co III 2 Co II(L) 6]X 2 (X = ClO 4 - , PF 6 - ). The latter are prepared by the reactions of the former with an appropriate Co II source. The structural, physical and spectroscopic properties of the complexes are described.

Investigation of the MSO 4 · xH 2O (M = Zn, x = 7; M = Cd, x = 8/3)/methyl 2-pyridyl ketone oxime reaction system: A novel Cd(II) coordination polymer versus mononuclear and dinuclear Zn(II) complexes

The reactions of methyl 2-pyridyl ketone oxime, (py)C(Me)NOH, with MSO 4 · xH 2O (M = Zn, x = 7; M = Cd, x = 8/3), in the absence of an external base, have been investigated. The synthetic study has led to the two new complexes [Zn(SO 4){(py)C(Me)NOH}(H 2O) 3] · H 2O ( 1 · H 2O) and [Zn 2(SO 4) 2{(py)C(Me)NOH} 4] · (py)C(Me)NOH [ 2 · (py)C(Me)NOH], and the coordination polymer [Cd(SO 4){(py)C(Me)NOH}(H 2O)] n · [Cd(SO 4){(py)C(Me)NOH}(H 2O) 2] n ( 3). In the three complexes the organic ligand chelates through its nitrogen atoms. The sulfate anion in 1 · H 2O is monodentate; the complex molecule is the mer isomer considering the positions of the aqua ligands. The Zn II centers in 2 · (py)C(Me)NOH are bridged by two syn, anti η 1:η 1:μ 2 SO 4 2 - ligands; each metal ion has the cis– cis– trans disposition of the coordinated sulfate oxygen, pyridyl nitrogen and oxime nitrogens, respectively. The molecular structure of 3 is unique consisting of two different linear and ladder – type chains. π–π stacking interactions and/or hydrogen bonds lead to the formation of interesting supramolecular architectures in the three complexes. The thermal decomposition of complex 3 has been studied. Characteristic vibrational (IR, Raman) bands are discussed in terms of the nature of bonding and the structures of the three complexes.

A new Mn II4Mn III4 cluster from the use of methyl 2-pyridyl ketone oxime in manganese carboxylate chemistry: Synthetic, structural and magnetic studies

The use of methyl 2-pyridyl ketone oxime (mpkoH) in manganese benzoate chemistry is reported. The reaction of Mn(O 2CPh) 2 · 2H 2O with two equivalents of mpkoH in CH 2Cl 2 affords the mononuclear complex [Mn II(O 2CPh) 2(mpkoH) 2] ( 2) in high yield. The Mn II atom is coordinated by two monodentate PhCO 2 - groups and two N, N′-bidentate mpkoH chelates in a cis– cis– trans fashion. Reaction mixtures comprising (NBu n 4)[Mn III 4O 2(O 2CPh) 9(H 2O)] and mpkoH in CH 2Cl 2, [Mn IIMn III 2O(O 2CPh) 6(py) 2(H 2O)] and mpkoH in CH 2Cl 2, or Mn(O 2CPh) 2 · 2H 2O, NBu n 4 MnO 4 and mpkoH in MeOH/MeCN/CH 2Cl 2 all lead to the mixed-valent cluster [Mn II 4Mn III 4O 2(OH) 2(O 2CPh) 10(mpko) 4] ( 3) in moderate yields. The cluster molecule has the [Mn 8(μ 4-O) 2(μ 3-OH) 2] 14+ core (another description of the core is [Mn 8(μ 4-O) 2(μ 3-OH) 2(μ-OR′′) 4(μ-ONR‴) 4] 6+). Peripheral ligation is provided by two η 1, four η 1:η 1:μ and four η 1:η 2:μ 3 PhCO 2 - groups, as well as four η 1:η 1:η 1:μ mpko − ligands. Variable-temperature, solid-state dc and ac magnetic studies were carried out on complex 3 in the 5.0–300 K (dc) and 1.8–10 K (ac) ranges. The data reveal dominant antiferromagnetic interactions and a resulting S = 0 ground state, which is rationalized in terms of the strong antiferromagnetic coupling within the central { Mn 2 III O 2 } 2 + subunit.

Potentiometric study of binary complexes of methyl 2-pyridyl ketone oxime, phenyl 2-pyridyl ketone oxime and diacetyl monooxime with some transition and heavy metal ions in aqueous solution

The complexation reaction between some oximes including methyl-2-pyridylketone oxime (MPKO), phenyl-2-pyridylketone oxime (PPKO) and diacetyl monooxime (DMO) with some transition and heavy metal ions Co 2+, Ni 2+, Zn 2+, Pb 2+, Fe 2+, Fe 3+, Cr 3+ and La 3+ has been studied potentiometrically in aqueous solution at 25 ± 0.1 °C and ionic strength ( μ) of 0.1 M supported by KCl. The overall stability constants log β's of respective species were obtained by computer refinement of pH–volume data using BEST program. The best model among the several proposed models was selected according to the lowest σ fit value. The main species in binary systems are ML, ML 2, MLH, MLH 2, ML 2H, ML 2H 2, MOHL, M(OH) 2L, M(OH)L 2 and M(OH) 2L 2 (L = MPKO or PPKO or DMO).

Reactions of Nickel (II) Sulfate Hexahydrate with Methyl(2-pyridyl)ketone Oxime: Two Mononuclear Sulfato Complexes Containing the Neutral Ligand

The reactions of methyl(2-pyridyl)ketone oxime, (py)C(Me)NOH, with nickel(II) sulfate hexahydrate, in the absence of an external base, have been investigated. The reaction between equimolar quantities of NiSO4 ·6 H2O and (py)C(Me)NOH in H2O leads to the mononuclear complex [Ni(SO4){(py)C(Me)NOH}(H2O)3] ·H2O (1 ·H2O), while an excess of the organic ligand affords the 1 : 2 compound [Ni(SO4){(py)C(Me)NOH}2(H2O)] ·H2O (2 ·H2O). The structures of both compounds have been determined by single crystal X-ray diffraction. In both complexes the organic ligand chelates through its nitrogen atoms and the sulfate anion acts as a monodentate ligand. The thermal decomposition of complexes 1 ·H2O and 2 ·H2O has been studied. The IR data are discussed in terms of the nature of bonding and the structures of the two complexes.

Potentiometric and Spectrophotometric Studies of Copper(II) Complexes of Some Ligands in Aqueous and Nonaqueous Solution

AbstractStoichiometry and equilibrium study of copper‐ligands including mercaptobenzoxazole (MBO), 4‐propyl 2‐thiouracyl (PTU), methyl‐2‐pyridylketone oxime (MPKO), phenyl‐2‐pyridylketone oxime (PPKO), 4,6‐dihydroxy‐2‐mercaptopyrimidine (DHMP), N,N′‐phenylene bis(salicylaldimine) (PBS) and 1,2‐bis(2‐hydroxyphenyl)naphtaldiimine (BHNPDI) were conducted in aqueous and nonaqueous solution by potentiometry and spectrophotometry. Stability constants of the complexes are determined at 25 ± 1 °C and 0.1 or 0.05 M ionic strength in water or acetonitrile solvents. Oximes ligand protonation constants and copper‐ligands complexes' stability and hydrolysis constants were calculated using the BEST program in aqueous solution. The stability constants of copper‐ligands complexes were calculated using the KINFIT program in acetonitrile solution. The results of these two methods are made self‐consistent, then rationalized assuming an equilibrium model including the species, ML, MLH, MLOH and ML2 (where the charges of the species have been ignored for the sake of simplicity) (L = MBO, PTU, MPKO, PPKO, DHMP, BHNPDI and PBS).

“Switching On” the Properties of Single-Molecule Magnetism in Triangular Manganese(III) Complexes

The reaction between oxide-centered, triangular [MnIII3O(O2CR)6(py)3](ClO4) (R = Me (1), Et (2), Ph (3)) compounds and methyl 2-pyridyl ketone oxime (mpkoH) affords a new family of Mn/carboxylato/oximato complexes, [MnIII3O(O2CR)3(mpko)3](ClO4) [R = Me (4), Et (5), and Ph (6)]. As in 1-3, the cations of 4-6 contain an [MnIII3(mu3-O)]7+ triangular core, but with each Mn2 edge now bridged by an eta1:eta1:mu-RCO2- and an eta1:eta1:eta1:mu-mpko- group. The tridentate binding mode of the latter causes a buckling of the formerly planar [MnIII3(mu3-O)]7+ core, resulting in a relative twisting of the three MnIII octahedra and the central O2- ion now lying approximately 0.3 A above the Mn3 plane. This structural distortion leads to ferromagnetic exchange interactions within the molecule and a resulting S = 6 ground state. Fits of dc magnetization data for 4-6 collected in the 1.8-10.0 K and 10-70 kG ranges confirmed S = 6 ground states, and gave the following D and g values: -0.34 cm(-1) and 1.92 for 4, -0.34 cm(-1) and 1.93 for 5, and -0.35 cm(-1) and 1.99 for 6, where D is the axial zero-field splitting (anisotropy) parameter. Complexes 4-6 all exhibit frequency-dependent out-of-phase (chi" M) ac susceptibility signals suggesting them possibly to be single-molecule magnets (SMMs). Relaxation rate vs T data for complex 4 down to 1.8 K obtained from the chi" M vs T studies were supplemented with rate vs T data measured to 0.04 K via magnetization vs time decay studies, and these were used to construct Arrhenius plots from which was obtained the effective barrier to relaxation (Ueff) of 10.9 K. Magnetization vs dc field sweeps on single-crystals of 4.3CH2Cl2 displayed hysteresis loops exhibiting steps due to quantum tunneling of magnetization (QTM). The loops were essentially temperature-independent below approximately 0.3 K, indicating only ground-state QTM between the lowest-lying Ms = +/-6 levels. Complexes 4-6 are thus confirmed as the first triangular SMMs. High-frequency EPR spectra of single crystals of 4.3CH2Cl2 have provided precise spin Hamiltonian parameters, giving D = -0.3 cm(-1), B40 = -3 x 10(-5) cm(-1), and g = 2.00. The spectra also suggest a significant transverse anisotropy of E > or = 0.015 cm(-1). The combined work demonstrates the feasibility that structural distortions of a magnetic core imposed by peripheral ligands can "switch on" the properties of an SMM.

Cloud point extraction for the determination of copper, nickel and cobalt ions in environmental samples by flame atomic absorption spectrometry

A cloud point extraction procedure was presented for the preconcentration of copper, nickel and cobalt ions in various samples. After complexation with methyl-2-pyridylketone oxime (MPKO) in basic medium, analyte ions are quantitatively extracted to the phase rich in Triton X-114 following centrifugation. 1.0 mol L −1 HNO 3 nitric acid in methanol was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry (FAAS). The adopted concentrations for MPKO, Triton X-114 and HNO 3, bath temperature, centrifuge rate and time were optimized. Detection limits (3 SDb/m) of 1.6, 2.1 and 1.9 ng mL −1 for Cu 2+, Co 2+ and Ni 2+ along with preconcentration factors of 30 and for these ions and enrichment factor of 65, 58 and 67 for Cu 2+, Ni 2+ and Co 2+, respectively. The high efficiency of cloud point extraction to carry out the determination of analytes in complex matrices was demonstrated. The proposed procedure was applied to the analysis of biological, natural and wastewater, soil and blood samples.

Investigation of the Zinc Chloride / Methyl(2-pyridyl)ketone Oxime Reaction System: A Mononuclear Complex and an Inverse 12-Metallacrown-4 Cluster

The reactions of methyl(2-pyridyl)ketone oxime, (py)C(Me)NOH, with zinc chloride have been investigated. An excess of the ligand in EtOH/MeCN affords the mononuclear complex [ZnCl2{(py)C(Me)NOH}2] (1) in moderate yield. The metal ion is coordinated by two chloro ligands and two N,N′- chelating (py)C(Me)NOH molecules. The six-coordinate molecule is the ciscis- trans isomer considering the positions of the coordinated chlorine, pyridyl and oxime nitrogen atoms, respectively. The reaction between equimolar quantities of ZnCl2, (py)C(Me)NOH and LiOH·H2O in EtOH/MeCN leads to the tetranuclear cluster [Zn4(OH)2Cl2{(py)C(Me)NO}4] (2) in high yield. The molecule lies on a crystallographic inversion center and has an inverse 12-metallacrown- 4 topology. Two triply bridging hydroxides are accommodated within the metallacrown ring. Each (py)C(Me)NO− ligand adopts the 2.111 coordination mode (Harris notation), chelating one ZnII ion and bridging a ZnII 2 pair. Two metal ions are in a distorted O2N4 octahedral environment, whereas the other two are in a severely distorted tetrahedral O3Cl environment. Complex 2 joins a small family of structurally characterized zinc(II) metallacrown complexes. The IR data are discussed in terms of the nature of bonding and the structures of the two complexes.