Lorena Machi

Structural and spectroscopic studies of binuclear Cu2+ and Co2+ complexes with an amide-based naphthalenophane

Abstract Binuclear Cu2+ and Co2+ complexes with a chelating naphthalenophane were characterized by single-crystal X-ray analyses, electronic absorption spectroscopy and luminescence spectroscopy: the naphthalenophane is 2,9,22,29-tetraoxo-4,7,24,27-tetrakis(carboxymethyl)-1,4,7,10,21,24,27,30-octaaza[10.10](1,5)naphthalenophane (abbreviated as LH4). The Cu2+ complex crystallized as [Cu2L]0 from acidic solution and [Cu2(LH−4)]4− from basic solution: the coordination geometry around each metal ion in [Cu2L]0 is a square pyramid with an amide oxygen atom, two amino nitrogen atoms and two carboxylate oxygen atoms; the amide nitrogen atoms in [Cu2(LH−4)]4− are deprotonated and construct a square planar coordination geometry together with amino nitrogen atoms around each metal ion. The formation of the two structures is due to a change in the coordination linkage of the amide groups. [Cu2(LH−4)]4− shows strong metal–ligand charge transfer bands caused by the coordination of the amide nitrogen atoms that are directly bonded to the naphthyl groups. In the Co2+ complex, [Co2L(H2O)2]0, each metal ion has a seven-coordination geometry; the emission and excitation bands in the luminescence spectra showed a red shift upon metal complexation. In all metal complexes studied, the naphthyl groups are distorted from the planar structure, as a result of metal complexation that causes contraction of the macrocyclic rings.

High steric constraints and molecular distortion in methyl-substituted amide-based paracyclophanes and the binuclear Cu2+ complexes: X-ray structures, NMR and absorption spectra

Abstract Chelating paracyclophanes that are sterically constrained to a great extent have been synthesized and characterized by X-ray crystallography and NMR spectroscopy: the macrocycles studied are 2,9,18,25-tetraoxo-4,7,20,23-tetrakis(carboxymethyl)-1,4,7,10,17,20,23,26-octaaza[10.10]paracyclophane, abbreviated as ( L pd)H 4 , and its 2,5-dimethyl- p -phenylene and tetramethyl- p -phenylene derivatives, abbreviated as ( L dmpd)H 4 and ( L tmpd)H 4 , respectively. Steric interaction between tetramethylphenylene and amide groups in the tetramethyl derivative defines the conformation of the macrocyclic cavity, and causes unusual spectroscopic and chemical properties including the extreme line-broadening of 1 H NMR signals and the low basicity of amino nitrogen; such properties are not observed for the other macrocycles, in which steric interaction between phenylene and amide groups is less effective. The complexation of the highly strained ligand ( L tmpd)H 4 with Cu 2+ ions has been studied by X-ray crystallography and solution electronic spectroscopy. The macrocycle forms a binuclear complex of [Cu 2 (LH −4 )] 4− type in which four amide nitrogen atoms are deprotonated and each metal ion is coordinated to two amide nitrogen atoms and two amino nitrogen atoms. In the binuclear chelate molecule, the severe contraction of the macrocyclic ring forces the phenylene groups distorted to a boat form, due to the steric effect of the tetramethyl substituents. As a result, the metal–ligand charge-transfer interaction in the binuclear complex differs from that in the mononuclear chelate of the same macrocycle.

Charge-transfer complexes of benzylviologen (1,1′-dibenzyl-4,4′-bipyridinium(2+) cation) with cyanocuprate(I) and the structure of (BzV)3Cu9(CN)15·H2O

Reactions between 1,1′-dibenzyl-4,4′-bipyridinium(2+) (benzylviologen, BzV) chloride and cyanocuprates(I) gave two charge-transfer complexes having different colors: dark brown (BzV)3Cu9(CN)15·H2O and light brown (BzV)Cu(CN)3·2H2O. An X-ray crystal analysis of the former compound showed that nine crystallographically nonequivalent Cu atoms form three kinds of triad Cu(CN)Cu screws, which are linked by CN groups resulting in a unique three-dimensional network structure. Three of the nine Cu atoms have distorted tetrahedral (td) coordination geometries while the others have triangular plane (tp) geometries. Each screw consists of a (-tp-td-tp-)n array. There are three crystallographically nonequivalent viologen molecules. Certain CuCN moieties are located above a viologen ring or by the side of a viologen ring, with close interatomic contacts. These close contacts are characteristic of the charge-transfer complex and are responsible for the deep color of the complex.

Metal–ligand interactions in benzodioxotetraaza-macrocyclic metal chelates

Abstract Reactions of ethylenediaminetetraacetic (edta) dianhydride with o-phenylenediamine (od) and 9,10-diaminophenanthrene (phn) gave (edtaod)H2 and (edtaphn)H2, respectively, in which a chelating edta unit and an aromatic diamine unit are linked by two amide bonds. The complexation of these new 12-membered macrocycles with transition metal ions was studied by X-ray crystallography, potentiometric titrations, UV–Vis absorption spectroscopy and fluorescence spectroscopy. The absorption spectra are sensitively changed by metal complexation. The spectral changes are the most significant for the Cu2+ complexes, and are well correlated with the species distribution diagram. The X-ray study of the Cu2+ complex, [Cu(edtaod)]0, has shown that a square plane is formed around the central metal ion by an amide oxygen atom, a carboxylate oxygen atom and an amino nitrogen atom from a ligand molecule and a carboxylate oxygen atom from the adjacent chelate molecule. The amide nitrogen atoms in [Cu(edtaod)]0 are readily deprotonated and result in the formation of [Cu(edtaodH−1)]− and [Cu(edtaodH−2)]2− in neutral and basic media. The coordination of deprotonated amide nitrogen atoms to a Cu2+ ion leads to a strong metal–ligand interaction, which causes an intense charge-transfer band in [Cu(edtaodH−1)]−, new UV absorption bands in [Cu(edtaodH−2)]2− and the effective quenching of emission in the Cu2+ complex of (edtaphn)H2.

PHOTOCHEMICAL SYNTHESES OF FULLERENE-AMINE ADDUCTS AND THEIR CHARACTERIZATION WITH 1H NMR SPECTROSCOPY

Abstract Photoreactions of C 60 with aromatic or aliphatic amines in contact with air gave a new type of amine adduct with a general compound formula of C 60 (amine) x (OH) y O z ; the amine was di-2-pyridylamine, morpholine or N , N -dimethylethylenediamine. The N , N -dimethylethylenediamine adduct was obtained as a hydrochloride. Its 1 H NMR spectrum showed that the adduct cation, obtained after functionalizing C 60 , formed an ion pair with a benzenesulfonate anion.

Pyrene bichromophores composed of polyaminopolycarboxylate interlink: pH response of excimer emission

Fluorescent response to pH has been studied on water-soluble pyrene-based bichromophores, (edtapy)H2 and (dtpapy)H3, in which two pyrenyl groups are linked by an ethylenediaminetetraacetate (EDTA) and a diethylenetriaminepentaacetate (DTPA) unit, respectively, through amide linkages. The excimer emission of the EDTA derivative is strengthened sharply with increasing pH at two steps; the first step is associated with the dissociation of acidic hydrogen from amino nitrogen in partially protonated species (edtapy)H− and the second step is attributable to the amide group. The excitation spectra have evidenced the formation of a static excimer in the ground state of completely deprotonated species (edtapy)2 − . The close contact between pyrenyl groups in (edtapy)2 − has been confirmed by density functional theory, which has also shown that the close contact is broken when amino nitrogen is protonated. The DTPA derivative exhibits a strong excimer emission, which shows an intensity–pH profile of an ‘off–on–off–on’ type. This rare pH response is ascribable to multiple protonation sites in the DTPA chain, as confirmed by 1H NMR. The novel pH-sensing capabilities in specific pH regions are due to the combination of the fluorescent group with the polyaminopolycarboxylate chains whose conformations are reversibly altered by protonation–deprotonation processes.

Coordination of histamine and imidazole with macrocyclic Zn2+, Cd2+ and Cu2+ chelates of dioxotetraazacycloalkanediacetates

Abstract Coordination of histamine and imidazole with macrocyclic Cu 2+ , Zn 2+ and Cd 2+ chelates has been studied by 1 H NMR and electronic spectroscopy: the macrocyclic ligands studied are 2,9-dioxo-1,4,7,10-tetraaza-4,7-cyclododecanediacetic acid, abbreviated as (12edtaen)H 2 , and 2,9-dioxo-1,4,7,10-tetraaza-4,7-cyclotridecanediacetic acid, (13edtapn)H 2 . A molecule of histamine or imidazole takes the place of a water molecule in [M(12edtaen)(H 2 O)] 0 and [M(13edtapn)(H 2 O)] 0 . The formation constants of [ZnL(hsH + )] + (hsH + : histaminium ion) are of the same order of magnitude as the corresponding [CdL(hsH + )] + , although the electron donation of hsH + in the Zn 2+ complexes is less significant than that in the Cd 2+ complexes. The Cu 2+ chelate with the 13-membered macrocycle forms [Cu(13edtapnH −2 )] 2− , in which deprotonated amide nitrogen atoms are coordinated. In a reaction between this metal chelate and hsH + , one of the vacant coordination sites of the Cu 2+ chelate is occupied by an hsH + molecule and [Cu(13edtapnH −2 )(hsH + )] − is formed. Such a complexation reaction does not occur with imidazole. The complexation of hsH + occurs with two binding sites of each component: the central metal ion towards the hsH + ring nitrogen, and a pendant carboxymethyl group in the macrocyclic ligand towards the pendant arm of hsH + .

Charge transfer in the viologen (1,1′-dialkyl-4,4′-bipyridinium ion) salts of cyanocuprate(I)

Abstract The viologen salts of cyanocuprate(I), HV2+[Cu(CN)3]2−·2H2O and MV2+[Cu3(CN)5]2− (HV2+=1,1′-diheptyl- 4,4t - bipyridinium ion; MV2+=1,1′-dimethyl-4,4′-bipyridinium ion), were obtained by mixing a solution of the appropriate alkylviologen halide with a solution containing CuCN and NaCN. The resulting red-brown materials exhibited charge-transfer bands with maxima at 370 and 500 nm in the solid state, and at 350 nm in aqueous solution. The presence of CuI ions and viologen dications was deduced from the X-ray photoelectron spectra of the solid compounds. An X-ray crystal analysis of HV[Cu(CN)3]·2H2O showed that a copper atom was located on a triangular plane formed by three CN carbon atoms. A [Cu(CN)3]2− ion and an HV2+ ion were stacked face-to-face to form an ion pair with a close CuC contact of 3.2 A. This CuC contact is responsible for the cation–anion charge transfer. The ion pairs are so stable that the charge-transfer bands are found even in solution.

Bichromophoric Naphthalene Derivatives of Ethylenediaminetetraacetate: Fluorescence from Intramolecular Excimer, Protonation and Complexation with Zn2+ and Cd2+

Chelating water-soluble bichromophoric compounds were designed by linking two naphthalene rings with an ethylenediaminetetraacetate (edta) chain through amide linkages, and characterized by fluorescence and NMR spectroscopies: the bichromophores studied were 1,4-bis(methylenecarboxy)-1,4-bis(N-1-naphthylacetamide)-1,4-diazabutane, abbreviated as (edta1nap)H2, and the corresponding 2-naphthylacetamide, abbreviated as (edta2nap)H2. Completely deprotonated species M2 − that formed in basic solution exhibited an intense emission from intramolecular excimer at 440 nm for (edta1nap)2 − and 404 nm for (edta2nap)2 − , while emission from monomeric naphthyl group was comparatively very weak. Geometry optimization based on Density Functional Theory showed that two naphthyl groups in an M2 − molecule faced each other in such a way that an intramolecular excimer was readily formed by light excitation. Protonation on amino nitrogen affected monomer–excimer interconversion in different modes for the two compounds: the excimer emission was strengthened in the resulting (edta1nap)H− , but was weakened in (edta2nap)H− . Upon coordination with Zn2+, the excimer band of (edta1nap)2 − as well as (edta2nap)2 − was strengthened in a linear manner with [Zn]/[L]; concurrently monomer emission was weakened. Coordination of (edta2nap)2 − with Cd2+ resulted in a large decrease in the excimer emission, while the emission of (edta1nap)2 − was almost unchanged. The formation of intramolecular excimer, which is highly sensitive to protonation and complexation, is due to the strictly defined molecular conformation.

Structural and spectroscopic studies of a metacyclophane and its binuclear Cu2+ complex

Abstract In a new chelating metacyclophane, 2,9,18,25-tetraoxo-4,7,20,23-tetrakis(carboxymethyl)-1,4,7,10,17,20,23,26-octaaza[10.10]metacyclophane, the amino nitrogen atoms have a higher basicity than that of the corresponding paracyclophane, although the local electron densities on the donor atoms are identical in the two isomers. The molecular structure of a binuclear Cu2+ complex with the metacyclophane has been studied by X-ray crystal analysis: the coordination geometry around each metal ion is described by a compressed trigonal bipyramid. The solution electronic spectra of the Cu2+ complex change with pH as a result of the conversion of the coordination sites of the amide groups.