Bonding properties of penta-coordinate CuII-N chromophores: structures and electronic spectra of copper(II) complexes of tris(2-aminoethyl)amine (tren). Molecular structures of [Cu(tren)(N-acetylhistamine)](ClO4)2 and [Cu(tren)(2-methylimidazole)](ClO4)2

“…In the case of NO 2 – anion, the spectral changes for the second step indicate the formation of a complex species with trigonal bipyramidal coordination around the Cu II ion. Indeed, trigonal bipyramidal Cu II complexes usually exhibit a broad band extending from 500 to 1000 nm with two components . Although the low energy band is often more intense than the high-energy counterpart, in the present case this situation appears to be reversed, with the band envelope showing a shoulder on the low energy side.…”

Section: Resultsmentioning

confidence: 52%

Cooperative Anion Recognition in Copper(II) and Zinc(II) Complexes with a Ditopic Tripodal Ligand Containing a Urea Group

et al. 2014

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The ability of Cu(II) and Zn(II) complexes of the ditopic receptor H2L [1-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenyl)-3-(3-nitrophenyl)urea] for anion recognition is reported. In the presence of weakly coordinating anions such as ClO4(-), the urea group binds to the metal ion (Cu(II) or Zn(II)) through one of its nitrogen atoms. The study of the interaction of the metal complexes with a variety of anions in DMSO shows that SO4(2-) and Cl(-) bind to the complexes through a cooperative binding involving simultaneous coordination to the metal ion and different hydrogen-bonding interactions with the urea moiety, depending on the shape and size of the anion. On the contrary, single crystal X-ray diffraction studies show that anions such as NO3(-) and PhCO2(-) form 1:2 complexes (metal/anion) where one of the anions coordinates to the metal center and the second one is involved in hydrogen-bonding interaction with the urea group, which is projected away from the metal ion. Spectrophotometric titrations performed for the Cu(II) complex indicate that this system is able to bind a wide range of anions with an affinity sequence: MeCO2(-) ∼ Cl(-) (log K11 > 7) > NO2(-) > H2PO4(-) ∼ Br(-) > HSO4(-) > NO3(-) (log K11 < 2). In contrast to this, the free ligand gives much weaker interactions with these anions. In the presence of basic anions such as MeCO2(-) or F(-), competitive processes associated with the deprotonation of the coordinated N-H group of the urea moiety take place. Thus, N-coordination of the urea unit to the metal ion increases the acidity of one of its N-H groups. DFT calculations performed in DMSO solution are in agreement with both an anion-hydrogen bonding interaction and an anion-metal ion coordination collaborating in the stabilization of the metal salt complexes with tetrahedral anions.

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“…9,14a,16a,20 However, there are many literature reports describing crystal structures of Cu 2+ complexes adopting one of these geometries and showing an intense absorption band at the expected wavelength accompanied by weaker bands or shoulders at the wavelength corresponding to the other geometric arrangement. [6][7][8]18 In most cases those spectra are interpreted by considering that the appearance of the weaker band is inherent to the species whose structure is revealed in the X-ray analysis, a proposal supported by the observation of twin peaks of comparable intensity in the solid-state electronic spectra of some complexes whose crystal structure reveals the existence of a single geometric environment of the metal ion. 21 However, the alternative possibility of two bands in the electronic spectra caused by the existence of a mixture of geometric isomers in solution cannot be ruled out.…”

Section: Introductionmentioning

confidence: 99%

“…Cu 2+ complexes with open-chain and macrocyclic polydentate amine ligands are frequently pentacoordinate, − although the complexes can adopt structures that can be described as either square pyramidal (sp) or trigonal bipyramidal (tbp) depending mainly on the actual nature of the ligand. The appearance of a coordination number of five is not limited to polyaza ligands, and there is even recent evidence that strongly suggests a pentacoordinate nature of the Cu 2+ aqua ion .…”

Section: Introductionmentioning

confidence: 99%

Geometric Isomerism in Pentacoordinate Cu²⁺ Complexes: Equilibrium, Kinetic, and Density Functional Theory Studies Reveal the Existence of Equilibrium between Square Pyramidal and Trigonal Bipyramidal Forms for a Tren-Derived Ligand

et al. 2008

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A ligand (L1) (bis(aminoethyl)[2-(4-quinolylmethyl)aminoethyl]amine) containing a 4-quinolylmethyl group attached to one of the terminal amino groups of tris(2-aminoethyl)amine (tren) has been prepared, and its protonation constants and stability constants for the formation of Cu(2+) complexes have been determined. Kinetic studies on the formation of Cu(2+) complexes in slightly acidic solutions and on the acid-promoted complex decomposition strongly suggest that the Cu(2+)-L1 complex exists in solution as a mixture of two species, one of them showing a trigonal bipyramidal (tbp) coordination environment with an absorption maximum at 890 nm in the electronic spectrum, and the other one being square pyramidal (sp) with a maximum at 660 nm. In acidic solution only a species with tbp geometry is formed, whereas in neutral and basic solutions a mixture of species with tbp and sp geometries is formed. The results of density functional theory (DFT) calculations indicate that these results can be rationalized by invoking the existence of an equilibrium of hydrolysis of the Cu-N bond with the amino group supporting the quinoline ring so that CuL1(2+) would be actually a mixture of tbp [CuL1(H(2)O)](2+) and sp [CuL1(H(2)O)(2)](2+). As there are many Cu(2+)-polyamine complexes with electronic spectra that show two overlapping bands at wavelengths close to those observed for the Cu(2+)-L1 complex, the existence of this kind of equilibrium between species with two different geometries can be quite common in the chemistry of these compounds. A correlation found between the position of the absorption maximum and the tau parameter measuring the distortion from the idealized tbp and sp geometries can be used to estimate the actual geometry in solution of this kind of complex.

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Bonding properties of penta-coordinate CuII-N chromophores: structures and electronic spectra of copper(II) complexes of tris(2-aminoethyl)amine (tren). Molecular structures of [Cu(tren)(N-acetylhistamine)](ClO4)2 and [Cu(tren)(2-methylimidazole)](ClO4)2

Cited by 23 publications

References 20 publications

Reversible Coordinative Bonds in Molecular Recognition

Reversible Coordinative Bonds in Molecular Recognition

Cooperative Anion Recognition in Copper(II) and Zinc(II) Complexes with a Ditopic Tripodal Ligand Containing a Urea Group

Geometric Isomerism in Pentacoordinate Cu²⁺ Complexes: Equilibrium, Kinetic, and Density Functional Theory Studies Reveal the Existence of Equilibrium between Square Pyramidal and Trigonal Bipyramidal Forms for a Tren-Derived Ligand

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Bonding properties of penta-coordinate CuII-N chromophores: structures and electronic spectra of copper(II) complexes of tris(2-aminoethyl)amine (tren). Molecular structures of [Cu(tren)(N-acetylhistamine)](ClO4)2 and [Cu(tren)(2-methylimidazole)](ClO4)2

Cited by 23 publications

References 20 publications

Reversible Coordinative Bonds in Molecular Recognition

Reversible Coordinative Bonds in Molecular Recognition

Cooperative Anion Recognition in Copper(II) and Zinc(II) Complexes with a Ditopic Tripodal Ligand Containing a Urea Group

Geometric Isomerism in Pentacoordinate Cu2+ Complexes: Equilibrium, Kinetic, and Density Functional Theory Studies Reveal the Existence of Equilibrium between Square Pyramidal and Trigonal Bipyramidal Forms for a Tren-Derived Ligand

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Geometric Isomerism in Pentacoordinate Cu²⁺ Complexes: Equilibrium, Kinetic, and Density Functional Theory Studies Reveal the Existence of Equilibrium between Square Pyramidal and Trigonal Bipyramidal Forms for a Tren-Derived Ligand