Tetranuclear zinc complexes of ligands containing the 2-pyridyl oxime chelating site

Modeling the Solvent Extraction of Cadmium(II) from Aqueous Chloride Solutions by 2-pyridyl Ketoximes: A Coordination Chemistry Approach

The goal of this work is to model the nature of the chemical species [CdCl₂(extractant)₂] that are formed during the solvent (or liquid-liquid) extraction of the toxic cadmium(II) from chloride-containing aqueous media using hydrophobic 2-pyridyl ketoximes as extractants. Our coordination chemistry approach involves the study of the reactions between cadmium(II) chloride dihydrate and phenyl 2-pyridyl ketoxime (phpaoH) in water-containing acetone. The reactions have provided access to complexes [CdCl₂(phpaoH)₂]∙H₂O (1∙H₂O) and {[CdCl₂(phpaoH)]}_n (2); the solid-state structures of which have been determined by single-crystal X-ray crystallography. In both complexes, phpaoH behaves as an N,N'-bidentate chelating ligand. The complexes have been characterized by solid-state IR and Raman spectra, and by solution ¹H NMR spectra. The preparation and characterization of 1∙H₂O provide strong evidence for the existence of the species [CdCl₂(extractant)₂] that have been proposed to be formed during the liquid-liquid extraction process of Cd(II), allowing the efficient transfer of the toxic metal ion from the aqueous phase into the organic phase.

Crowding out: ligand modifications and their structure directing effects on brucite-like {Mx(μ3-OH)y} (M = Co(ii), Ni(ii)) core growth within polymetallic cages

Previous employment of the ligands 2-methoxy-6-[(methylimino)methyl]phenol (L₁H) and 2-methoxy-6-[(phenylimino)methyl]phenol (L₂H) has resulted in the self-assembly of pseudo metallocalix[6]arene complexes of general formulae: [M₇(μ₃-OH)₆(L_x)₆](NO₃)_y (M = Ni(ii), x = 1, y = 2 (1) and Co(ii/iii), x = 2, y = 3 (2)). Extrapolating upon this work, we report the coordination chemistry of ligands 2-methoxy-6-{[(2-methoxyphenyl)imino]methyl}phenol (L₃H), 2-[(benzylimino)methyl]-6-methoxyphenol (L₄H), 2-[(benzylamino)methyl]-6-methoxyphenol (L₅H) and 2-[(benzylamino)methyl]-4-bromo-6-methoxyphenol (L₆H), whose structures are modifications of ligands L_1-2H. These ligands are employed in the synthesis and characterisation of the dimetallic complex [Ni(ii)₂(L₃)₃(H₂O)](NO₃)·2H₂O·3MeOH (3); the monometallic complexes [Ni(ii)(L₄)₂] (4) and [Co(iii)(L₄)₃]·H₂O·MeOH (5a); and the tetranuclear pseudo metallocalix[4]arene complexes: [(NO₃)⊂Co(ii)₄(μ₃-OH)₂(L₅)₄(H₂O)₂](NO₃)·H₂O (6), [(NO₃)⊂Ni(ii)₄(μ₃-OH)₂(L₅)₄(H₂O)₂](NO₃)·H₂O (7) and [Ni(ii)₄(μ₃-OH)₂(L₆)₄(NO₃)₂]·MeCN (8). The tetrametallic 'butterfly' core topologies in 6-8 are discussed with respect to their structural and topological relationship with their heptanuclear [M₇] (M = Co(ii), Ni(ii)) pseudo metallocalix[6]arene ancestors (1 and 2).

Crystal structure of bis(acetato-κ1 O)-bis(1-(pyridin-2-yl)ethan-1-one oxime-κ2 N,N′)zinc(II), C18H22N4O6Zn

C18H22N4O6Zn, monoclinic, P21/c (no. 14), a = 9.9422(18) Å, b = 16.904(3) Å, c = 15.5509(19) Å, β = 128.569(7)°, V = 2043.4(6) Å3, Z = 4, R gt(F) = 0.0347, wR ref(F 2) = 0.0663, T = 293(2) K.

Solution structural characterization of an array of nanoscale aqueous inorganic (0 ≤ x ≤ 6) clusters by 1H-NMR and QM computations

NMR spectroscopy is the go-to technique for determining the solution structures of organic, organometallic, and even macromolecular species. However, structure determination of nanoscale aqueous inorganic clusters by NMR spectroscopy remains an unexplored territory. The few hydroxo-bridged inorganic species well characterized by ¹H Nuclear Magnetic Resonance spectroscopy (¹H-NMR) do not provide enough information for signal assignment and prediction of new samples. ¹H-NMR and quantum mechanical (QM) computations were used to characterize the NMR spectra of the entire array of inorganic flat-Ga_13-x In _x (0 ≤ x ≤ 6) nanoscale clusters in solution. A brief review of the known signals for μ₂-OH and μ₃-OH bridges gives expected ranges for certain types of protons, but does not give enough information for exact peak assignment. Integration values and NOESY data were used to assign the peaks of several cluster species with simple ¹H-NMR spectra. Computations agree with these hydroxide signal assignments and allow for assignment of the complex spectra arising from the remaining cluster species. This work shows that ¹H-NMR spectroscopy provides a variety of information about the solution behavior of inorganic species previously thought to be inaccessible by NMR due to fast ligand and/or proton exchange in wet solvents.

Combining azide, carboxylate, and 2-pyridyloximate ligands in transition-metal chemistry: ferromagnetic Ni(II)5 clusters with a bowtie skeleton

The combined use of the anion of phenyl(2-pyridyl)ketone oxime (ppko(-)) and azides (N(3)(-)) in nickel(II) carboxylate chemistry has afforded two new Ni(II)(5) clusters, [Ni(5)(O(2)CR')(2)(N(3))(4)(ppko)(4)(MeOH)(4)] [R' = H (1), Me (2)]. The structurally unprecedented {Ni(5)(μ-N(3))(2)(μ(3)-N(3))(2)}(6+) cores of the two clusters are almost identical and contain the five Ni(II) atoms in a bowtie topology. Two N(3)(-) ions are end-on doubly bridging and the other two ions end-on triply bridging. The end-on μ(3)-N(3)(-) groups link the central Ni(II) atoms with the two peripheral metal ions on either side of the molecule, while the Ni···Ni bases of the triangles are each bridged by one end-on μ-N(3)(-) group. Variable-temperature, solid-state direct- (dc) and alternating-current (ac) magnetic susceptibility, and magnetization studies at 2.0 K were carried out on both complexes. The data indicate an overall ferromagnetic behavior and an S = 5 ground state for both compounds. The ac susceptibility studies on 1 reveal nonzero, frequency-dependent out-of-phase (χ(M)") signals at temperatures below ~3.5 K; complex 2 reveals no χ(M)" signals. However, single-crystal magnetization versus dc field scans at variable temperatures and variable sweep rates down to 0.04 K on 1 reveal no noticeable hysteresis loops, except very minor ones at 0.04 K assignable to weak intermolecular interactions propagated by nonclassical hydrogen bonds.