EPR and UV–vis study on solutions of Cu(II) dmit complexes and the complexes entrapped in zeolite A and ZIF-Cu(IM)2 (original) (raw)
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Geometry and Framework Interactions of Zeolite-Encapsulated Copper(II)−Histidine Complexes
Journal of the American Chemical Society, 2000
The coordination geometry of zeolite-encapsulated copper(II)-histidine (CuHis) complexes, prepared by ion exchange of the complexes from aqueous solutions into zeolite NaY, was determined by a combination of UV-vis-NIR diffuse reflectance spectroscopy (DRS), X-band EPR, electron-spin-echo envelope modulation (ESEEM), and high field (W-band) pulsed ENDOR techniques. X-band EPR spectroscopy detected two distinct complexes, A and B, which are different from the prevailing Cu(II) bis-His complex in the exchange solution (pH 7.3 with a His:Cu(II) ratio of 5:1). Moreover, the relative amount of complex B was found to increase with increasing Cu(II) concentration. The EPR parameters of complex A are g ⊥ ) 2.054, g | ) 2.31, and A | ) 15.8 mT, whereas those of complex B are g ⊥ ) 2.068, g | ) 2.25, A | ) 18.3 mT, and A ⊥ ( 14 Ν) ∼ 1.3 mT. The presence of the 14 N superhyperfine splitting shows that in complex B three nitrogens are coordinated to the Cu(II). Furthermore, DRS exhibits a shift of the d-d absorption band of Cu(II) from 15 200 cm -1 in complex A to 15 900 cm -1 in complex B, indicating an increasing ligand field strength in the latter. The coordination of the imino nitrogen of the imidazole group was detected in the two complexes via the ESEEM frequencies of the remote nitrogen. In contrast, only complex A exhibited 27 Al modulation, which indicates that the Cu(II) binds to zeolite framework oxygens. 2 H and 1 H W-band ENDOR measurements on samples where the exchangeable protons were replaced with 2 H, and using specifically labeled histidine (His-R-d--d 2 ), lead to the unambiguous determination of the coordination configuration of the two complexes. Complex A is a mono-His complex where both the amino and imino nitrogens are coordinated and the other equatorial ligands are provided by a zeolite oxygen and a water molecule. Complex B is a bis-His complex, which is situated in the center of the supercage, and all equatorial coordination sites are provided by the His molecules. These are amino and imino nitrogens of one His molecule and the imino nitrogen and carboxylate oxygen of the second His molecule. Complex A can be converted into complex B by stirring the zeolite in a high pH solution, whereas complex B is converted into complex A by using a low pH solution, thus indicating that complex A is stabilized by the presence of intrazeolitic protons. On the basis of the structure of the complexes, the dependence of their relative amounts on the pH and Cu(II) concentration in the exchange solution, the His: Cu(II) ratio in the zeolite, the amount of exchanged Na(I) ions, and the steric constraints imposed by the zeolite framework, a model for the ion exchange processes and the intrazeolite reactions leading to the formation of the two complexes is presented.
Inorganic Chemistry, 1988
The synthesis and spectroscopic properties of copper complexes with the ligands 1,6-bi~(5-methyl-4~imidazolyl)-2,5-dithiahexane (abbreviated bidhx) and 1,6-bis(4-imidazolyl)-2,5-dithiahexane (abbreviated bhdhx) are described. The compound [Cu-(bhdhx)CI]BF, (A) crystallizes in the triclinic space group Pi with a = 10.066 (3) A, b = 8.253 (2) A, c = 11.864 (3) A, a = 104.85 (2)O, , 9 = 100.46 (3)O, y = 114.72 (2)O, V = 817.16 A), and Dx = 1.79 g/cm3 for Z = 2. The compound [Cu(bidhx)-Cl(BF,)] (B) crystallizes in the monoclinic space group P2Jn with a = 13.975 (5) A, b = 8.347 (3) A, c = 17.156 (6) A, ( 3 = 116.34 (2)O, V = 1793.42 A', and Dx = 1.73 g/cm' for Z = 4. The compound [Cu(bidhx)(NCS)(N03)] (C) crystallizes in the monoclidic space group PZl/n with u = 9.641 (2) A, b = 8.040 (3) A, c = 25.480 (6) A, j 3 = 92.56 (2)O, V = 1973.1 A3, and Dx = 1.569 g/cm3 for Z = 4. The structures were solved by heavy-atom techniques and refined by least-squares methods to rqidual R, values of 0.039 (A), 0.033 (B), and 0.053 (C). The coordination geometry of the copper ion in compound A is compressed trigonal bipyramidal, with the two imidazole nitrogens along the main axis at 1.94 and 1.96 A and the chloride anion and the two thioether sulfur atoms at longer distances in the equatorial plane (CuC1 = 2.27, Cu-S = 2.53 and 2.49 A). The cop r ion chloride anion (at 2.30 A), and one thioether sulfur (at 2.44 A) in the pquatorial plane and one thioether sulfur and a fluorine of the tetrafluoroborate anion in the axial positions at 2.75 and 2.59 A, respectively. The only difference in composition between compounds A and B is the presence of a methyl group at position 4 of the imidazole moieties of the bidhx ligand. This small difference apparently causes the drastic change in coordination geometry for A and B. The copper ion in compound C is also in an elongated octahedral environment, with the two trans imidazole nitrogens (at 1.97 A), one thioether sulfur (at 2.37 A), and one thiocyanate nitrogen (at 1.97 A) coordinating in the equatorial plane; one thioether sulfur and the nitrate ion are at long semicoordinating distances on the axial positions (Cu-S = 2.75, Cu-0 = 2.70 A). Introducing a stronger coordinating anion, like NCS (compound C), causes only a small change in coordination geometry. The different structures can be understood on the basis of the coordination plasticity of the Cu(I1) ion.
Characterization of Two New Copper(II) Complexes with Saccharinate and Benzimidazole as Ligands
Zeitschrift Fur Anorganische Und Allgemeine Chemie, 2000
The crystal structure of the complexes [Cu(sac) 2 -(bzim) 2 (H 2 O)] (1) and [Cu(sac) 2 (bzim)(H 2 O)(EtOH)]2 EtOH (2) (sac = saccharinate anion; bzim = benzimidazole; EtOH = ethanol) was determined by single crystal X-ray diffractometry. Complex 1 crystallizes in the monoclinic C2/c space group with Z = 8 whereas complex 2 belongs to the triclinic P1 space group with Z = 2. Room temperature mag-netic susceptibilities as well as electronic and IR spectra of both complexes were discussed. Their thermal behaviour was investigated by means of TG and DTA methods.
ESR study of some Cu(II)-4-substituted-2-Thiazolylhydrazone complexes
Applied Magnetic Resonance, 1997
The Cu(II) complexes with 2-N-acetyl-salicylidene-hydrazino-4-chlor-methyl thiazole (LI) and 2-N-acetyl salicylidene-hydrazino-4-thiazolyl acetic ester (Ln) were prepared and investigated by ESR measurements. The powder ESR spectnma at room temperature of CuLnC1 is quasi-isotropic (g = = 2.113), while for CuL~C1 is characteristic of monomeric species with axial symmetry (g~~ = 2.234, g~ = 2.073). The isotropic ESR spectra of the CuLC1 compounds in DMSO solution suggest the presence of pseudo-tetrahedral monomeric species. The anisotropic spectra were obtained for adsorbed CuLCI DMSO solutions on NaY zeolite. The parallel hyperfine structure shows the coexistente of two magnetic nonequivalent monomeric species. The estimation of some LCAO-MO coefficients using Kivelson and Neiman's approximation reveals a dominant ionic character for copper-ligand bonds.
Polyhedron, 2012
Two new mixed ligand complexes, [Cu(en) 2 ](4-hpythol) 2 Á2H 2 O (4-hpythol = 5-(4-hydroxy-phenyl)-1,3,4thiadiazole-2-thiol) (2) and [Cu(en) 2 (5-thot) 2 ] (5-thot = 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione (3), have been prepared, containing en as the co-ligand. The starting ligands, potassium salts of thiohydrazide carbodithioate (RCSNHNHCSSK)/hydrazine carbodithioate (RCONHNHCSSK), underwent cyclization during the crystallization or complexation in the presence of ethylenediamine (en) and converted to 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol and 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione, respectively. The metal complexes have been characterized with the aid of elemental analyses, IR, magnetic susceptibility and single crystal X-ray studies. The ligand 4-hpythol and complexes 2 and 3 crystallize in the triclinic and monoclinic systems, space group P 21/n, P 1 and P 21/c, respectively. The ligand is present in the deprotonated thiol form in [Cu(en) 2 ](4-hpythol) 2 Á2H 2 O (2), where it is ionically bonded through the thiol sulfur atom, while potassium N 0-(thiophene-2-carbonyl) hydrazinecarbodithioate after cyclization is present as the thione form in [Cu(en) 2 (5-thot) 2 ] (3) and is covalently bonded through the N atom of the resulting oxadiazole-2-thione. The most noteworthy feature of 4-hpythol (1) is its existence in the thiol form in the solid state. Complex 3 show irreversible redox behavior, assignable to a M 2+ /M 3+ one electron transfer. ESR signals were registered for complexes 2 and 3. Both complexes contain extended hydrogen bonding, providing supramolecular frameworks.
2002
Stable CUI and Cu" complexes with the novel ligand 1,6-bis(2-benzimidazolyl)-2,5-dithiahexane [BBDH, (C7H5N2-CH2-S-CH2-),] have been prepared. The bulky nature of the ligand prevents planar four-coordination of Cu". The X-ray structure of [Cu(BBDH)CI]C1.2C2H50H shows that CUI' is in a distorted trigonal-bipyramidal coordination geometry consisting of two axial benzimidazole N atoms and two thioether S atoms and a C1-ion as equatorial ligands. The compound crystallizes in the monoclinic space group P21/c with a = 14.930 (3) A, b = 17.109 (4) A, c = 10.774 (2) A, 0 = 97.23 (2) O , V = 2730 A3, dmd = 1.43 (1) g ~m-~, and dd = 1.414 g cm-3 for Z = 4. The structure was solved by direct methods and refined with use of full-matrix least-squares techniques. The residual R value was 0.07 1 for 3023 independent reflections (I > 1,96[u(I)]] whose intensities were measured on an automatic diffractometer. The ESR and ligand field spectra of solid Cu" BBDH compounds are consistent with a trigonal-bipyramidal coordination geometry. The spectroscopic data of solutions indicate a change in coordination geometry compared to that in the solid state. The NMR spectra of CUI BBDH compounds suggest binding of benzimidazole N atoms to the metal.
Four copper(II) and three zinc(II) coordination compounds with bis(1-methylimidazol-2-yl)ketone (BIK) of general formula X(BIK) 2 Y 2 (X = Cu(II), Zn(II), while Y = Cl, Br, NO 3 or ClO 4 ) were synthesized and characterized by elemental analysis and FTIR spectroscopies to be compared with the literature data. As a follow-up of our previous thermoanalytical studies on imidazole-substituted coordination compounds, the thermal behaviour of the synthesized Cu(II) and Zn(II) BIK complexes was investigated using thermogravimetry, where three consecutive releasing steps were ascribed to a complex decomposition process. All the complexes investigated showed the same reaction mechanisms, identified on the basis of the percentages of mass loss calculated from the TG curves. The decomposition mechanisms were confirmed by EGA analysis, performed by coupling the TG analyzer to a MS spectrometer. In particular, the first step is ascribed to the release of two anions, followed by the loss of four methyl groups (side chains) and two bridge-carbonyl groups. The residual tetra-imidazole copper(II) or zinc(II) compound decomposes in a final step to give the metal(II) oxide as the final residue. Both the initial decomposition temperatures and the kinetic rate constants associated to the first decomposition step indicated a higher stability of the Cu(BIK) 2 Y 2 complexes with respect to the corresponding Zn ones. As far as the effect of the presence of the anion on the thermal stability is concerned, it can be demonstrated that both the perchlorate Cu(II) and Zn(II) complexes have the lower thermal stability (lower E values), while the thermal stabilities of the bromide, chloride and nitrate Cu(II) and Zn(II) complexes are substantially comparable. Finally, the model mechanism that shows the best fit between theoretical and reconstructed g(˛) vs. ˛ dependencies for the first decomposition step is, as showed in a previous paper for the analogues Mn(II) complexes, the three-dimensional diffusion model (D3). Selection of the best kinetic triplet associated to the first decomposition step was successfully validated by comparing the experimental and reconstructed portion of the TG curves of Cu(BIK) 2 (NO 3 ) 2 within the corresponding temperature interval.