Coordination Of Cd Research Articles

Novel concentration-driven structural interconversion in shape-specific solids supported by the octahedral [Re(6)(mu3-Se)8]2+ cluster core.

A complex containing the face-capped octahedral [Re(6)(mu(3)-Se)(8)](2+) cluster core, cis-[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](SbF(6))(2) (1), is used as a ditopic ligand with an enforced right angle between the two 4,4'-dipyridyl moieties for the coordination of Cd(2+) ion. Two coordination polymers, [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)](2)[Cd(NO(3))(2)]](SbF(6))(4).21C(4)H(10)O.21CH(2)Cl(2) (2) and [[Re(6)(mu(3)-Se)(8)(PPh(3))(4)(4,4'-dipyridyl)(2)][Cd(NO(3))(3)]](NO(3)).2C(4)H(10)O.CH(2)Cl(2) (3), are obtained. The relative concentration of Cd(2+) determines which species is isolated, and the conversion of the first structure into the second is demonstrated experimentally.

Coordination properties of a new hexaazamacrocycle containing thiophene units as pendant arms

The synthesis of the macrocyclic ligand 1,4,7,13-tetramethyl-10,16-bis(o-thiophenylmethyl)-1,4,7,10,13,16-hexaazacyclooctadecane (L2) is reported. This compound presents a hexaaza macrocyclic backbone bearing two thiophenylmethyl side arms. Ligand protonation and Cu(II), Zn(II), Cd(II) and Pb(II) coordination were studied by means of potentiometric measurements. In the metal complexes all nitrogens seem to be involved in metal coordination, while the sulfur atoms of the heteroaromatic subunits do not participate in metal binding, as confirmed by the crystal structure of [PbL2Cl]·BPh4. In the [PbL2Cl]+ cation the metal is enveloped by the macrocyclic ligand, coordinated by the six nitrogens and a chloride anion with a distorted monocapped trigonal prismatic geometry. Although L2 forms complexes of lower stability with respect to other N-functionalized hexaazamacrocycles, this ligand displays selective coordination of the larger Cd(II) and Pb(II) over Zn(II). All the metal complexes under investigation are readily extractable from aqueous solutions to organic solvents. Therefore, L2 is a promising selective extracting agent for metal cations.

Complexation Properties of the Metallothionein Fragment Lys-Cys-Thr-Cys-Cys-Ala [56-61] MT I with Zinc and Cadmium Using Square Wave Voltammetry

An electrochemical study using square wave voltammetry of the complexing properties of the peptide Lys-Cys-Thr-Cys-Cys-Ala [56–61] MT 1 (FT), a part of the metallothionein structure, with cadmium and zinc was performed. The applied technique allows one to obtain well-defined peaks corresponding to the free metal ions as well as providing evidence that different forms of coordination of Cd(II) and Zn(II) with the peptide exist. FT is capable of complexing Cd2+and Zn2+ separately in a concentration equal to FT, obtaining complexes with a ratio of 1:1. However, the total metal ion concentration bound to the FT is higher when both cations are simultaneously present. The maximum total concentration that can be complexed with FT is a ratio of [Zn]:[Cd]:[FT] like 0.6:1.0:1.0 which leads to the ratio of Zn4Cd7S21, comparable to that of the metallothionein structure. The coordination of Cd(II) with FT not only depends on the Cd:FT ratio, but also on the proportion in which Zn(II) is added. However, the Zn(II) complexes are not affected by the presence of Cd-FT complexes in solution. The complexation equilibrium was investigated going from acid to basic solutions and viceversa. From the slopes of the variation Ep=f (pH), the number of thiol groups at which the cations are bound were evaluated. This study allows us to enable comparisons between the behavior of [Zn]:[Cd]:[FT] with that of Cd,Zn metallothioneins.

Kinetics and mechanism of ester hydrolysis by metal complexes of 2,6-diacetylpyridine dioxime

The rate constants of the cleavage of 4-nitrophenyl acetate by the 2,6-diacetylpyridine dioxime (H 2dapd) in pH interval 6-8 increase 10 3–10 4 times in the presence of Pb(II), Mn(II) and Cd(II), and 2–100 times in the presence of Ni(II), Hg(II), Pr(III) and Zn(II). Complexation of the oxime ligand with Co(II) and Cu(II) does not affect the reaction rate. The complex with Cd(II) operates in a catalytic regime with respect of the oxime ligand. Spectrophotometric study of the coordination of Cd(II) and Zn(II) with H 2dapd reveals formation of M(H 2dapd) 2+, M(Hdapd) + and M 2(Hdapd) 2 2+ complexes. Formation constants of these complexes as well as acid dissociation constants of free and complexed H 2dapd were calculated from spectrophotometric titration results. The reactive species are monomeric complexes of the type M(Hdapd) + whereas the dimers are unreactive. The reactivity of M(Hdapd) + complexes correlates with basicity of the coordinated oximate anion. The complexes of Cd(II), Mn(II) and Pb(II) unexpectedly possess higher reactivity than much more basic free oximate anion probably because of stabilisation of carbonyl oxygen by chelation with metal cation in the transition state.

Coordination of Cd(II) by N-alkylamino sugars in aqueous solution as studied by potentiometry and NMR spectroscopy

The Cd(II) coordination of 1-(2-aminoethylamino)-1-deoxy- d-alditols (1a–b) and of 1-(2-aminopropylamino)-1-deoxy- d-alditols (2a–b) was investigated by means of 113Cd NMR spectroscopy and potentiometry. The influence of the sugar chains on the basicity of the amino groups was determined with 13C chemical shift pH titration curves. It appears that the inductive effects of the sugar moieties give rise to a decrease in p K a of the secondary amino function. The Cd(II) stability constants for ligands 1a–b and 2a–b and the Ni(II) stability constants for 1a were determined by potentiometry. 113Cd NMR spectroscopy was employed to study the structures of the Cd(II) complexes of 1a–b and 2a–b. From the 113Cd chemical shifts for CdL and CdL 2, it could be concluded that at neutral pH both primary and secondary nitrogen atoms are involved in coordination. 13C NMR shows that additional coordination of a hydroxyl group of the carbohydrate chain occurs at high pH (pH 12).

On the polarizabilities of the doubly charged ions of group IIB

New values are derived for the polarizabilities of the group IIB cations Zn++, Cd++ and Hg++. Ab initio electronic structure computations show the polarizabilities of isolated Zn++ and Cd++ ions to be enhanced considerably by electron correlation, the best current polarizabilities being 2·83 au and 5·42 au. Analysis of experimental refractive index data for both aqueous solutions at infinite dilution and solid crystalline difluorides yields in-solution Zn++, Cd++ and Hg++ polarizabilities of 4·02 au, 7·50 au and 15·40 au compared with values 4·72 au and 6·42 au for Zn++ and Cd++ in solid ZnF2 and CdF2. Ab initio computations also show the increases in the Zn++ and Cd++ polarizabilities in the condensed phase to originate from the mechanisms enhancing the polarizability of Ag+ in solid AgF. The increases predicted when Zn++ and Cd++ enter a point charge lattice originate from the component of the lattice potential which lifts the degeneracy of the free ion d orbitals. Location of these cations at the centre of an octahedron or cube of helium atoms modelling overlap with neighbouring anions also increases these cation polarizabilities. These enhancements are greater in octahedral than in cubic coordination because the environments of the eg and t2g d orbitals differ more in the former. The approximately octahedral coordination of Cd++ in solution compared with its cubic coordination in solid CdF2 explains why this cation polarizability is greater in solution than in the solid difluoride. The Zn++ ion is octahedrally coordinated in both these environments, having a larger polarizability in the latter where it interacts more strongly with its surroundings. The total molar polarizability of solid CdO cannot be explained as a sum of contributions from individual ions having reasonable values for their polarizabilities.

Catena-[Cd{μ-S(CH2)3NHMe2}Br2

The title complex, catena-poly[dibromocadmium-μ-3-dimethylamino-1-propanethiolato], contains polymeric chains of alternating Cd and S atoms with Cd-S bond lenght of 2.515(3) and 2.520(3) A. Distorted tetrahedral coordination of Cd [with a wide S-Cd-S angle of 126.95(5) o ] is completed by two Br ligands [Cd-Br 2.5834(15) and 2.6400(14) A]. The longer Cd-Br bond is to a Br atom involved in inter-chain hydrogen bonding with the ammonium group of a mercaptoamine ligand of an adjacent chain, to give two-dimensional sheets

Defect structures in cadmium-nickel ferrites

The cation-deficient solid solutions of cadmium ferrite (CdFe 2O 4) and nickel ferrite (NiFe 2O 4) obtained by prolonged thermal treatment from stoichiometric samples have been investigated by X-ray powder diffraction, magnetic measurements and chemical analysis. The stoichiometric Cd xNi 1−xFe 2O 4 samples were prepared from coprecipitated xCd(OH) 2·(1− x)Ni(OH) 2·2Fe(OH) 3-hydroxides, sintered at 1000°C during one hour. It has been found that because of the CdO volatility, stoichiometric preparations with x = 0.9 and x = 1.0 should be synthesized with the excess of 8% and 10% Cd(OH) 2 respectively. The linear increase of spinel lattice constant with increasing Cd-content and the observed X-ray reflection intensities confirm the stoichiometry and the tetrahedral coordination of Cd 2+-ions. Thermal treatment above 1000°C leads to the defect spinel structures with the Cd 2+-deficiency, composed from solid solutions with the general formula Cd 2+ x−αFe 3+ 1−x+α[Ni 2+ 1−xFe 3+ 1+x−α/3□ α/3]O 4, corresponding to a solid solution of stoichiometric (Cd, Ni)-ferrite with the maghemite, γFe 2O 3.

Zur Polymorphie des Cadmiumsulfits, Kristallstrukturen von CdSO3-I, CdSO3-II und CdSO3-III / Polymorphic Cadmium Sulfites, Crystal Structures of CdSO3-I, CdSO3 -II, and CdSO3-III

The crystal structures of the anhydrous cadmium sulfites CdSO3-I (P21/c, Z=4), CdSO3-II (P21/c, Z=8), and CdSO3-III (R3̄̄, Z=18 for the hexagonal cell) have been determined by means of single crystal X-ray diffraction data. The final R for the 1475, 2349, and 2138 observed reflections are 0.040, 0.034, and 0.073. Coordination of Cd is trigonal-prismatic, a hitherto unknown coordination of Cd in salts of oxoacids, in CdSO3-I and CdSO3-II, and octahedral in CdSO3-III. The CdO6-polyhedra are arranged in two-dimensional (CdSO3-I) and three-dimensional (CdSO3-II and CdSO3-III) networks. SO3 2- groups act as monodentate and in CdSO3-I and CdSO3-II also as bidentate ligands. Cd−O distances range from 224.5(3) to 244.6(3) pm, with an average of 231.5 pm for the trigonal-prismatic and of 231.0 pm for the octahedral coordination. S−O dis-tances range from 152.3(3) to 155.3(3) pm with an average of 153.7 pm, the O−S−O angles from 99.2(2) to 106.7(3)° with an average of 103.2°.

NMR studies of the Zn(II) and Cd(II) interaction with leucylglycine peptide in aqueous solutions

The coordination of Zn(II) and Cd(II) ions with leucylglycine in the whole pD range in water solutions was examined by the PMR and 13C NMR methods. At pD below 5 only the glycyl terminal was found to coordinate the metal ion. The amine and carbonyl groups of the leucyl part interact at higher pDs. The structures of the free and of the complexed peptide were discussed.