A novel and highly regioselective synthesis of new carbamoylcarboxylic acids from dianhydrides.

A regioselective synthesis has been developed for the preparation of a series of N,N'-disubstituted 4,4'-carbonylbis(carbamoylbenzoic) acids and N,N'-disubstituted bis(carbamoyl) terephthalic acids by treatment of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (1) and 1,2,4,5-benzenetetracarboxylic dianhydride (2) with arylalkyl primary amines (A-N). The carbamoylcarboxylic acid derivatives were synthesized with good yield and high purity. The specific reaction conditions were established to obtain carbamoyl and carboxylic acid functionalities over the thermodynamically most favored imide group. Products derived from both anhydrides 1 and 2 were isolated as pure regioisomeric compounds under innovative experimental conditions. The chemo- and regioselectivity of products derived from dianhydrides were determined by NMR spectroscopy and confirmed by density functional theory (DFT). All products were characterized by NMR, FTIR, and MS.

Photophysics of a cis axially disubstituted macrocycle: rapid intersystem crossing in a tin(IV) phthalocyanine with a half-domed geometry.

We have studied the photophysical properties of a tin(IV) phthalocyanine which coordinates two myristate groups through their carboxylate functionalities in a cis disposition at the tin center. Such a coordination mode, anisobidentate through the same side of the macrocycle, makes this phthalocyanine acquire a capped or half-domed shape. This bis myristate tin(IV) molecule shows an intersystem crossing channel which populates the triplet manifold with high efficiency and with a time constant of 300 ps, about an order of magnitude faster than planar phthalocyanines, including some previously reported tin(IV) phthalocyanines. For comparison purposes, we also include the description of a planar silicon(IV) phthalocyanine that keeps the more common stereochemistry, of trans type, with the same axial myristate groups. The characterization of these systems included steady state and time-resolved spectroscopy through femtosecond fluorescence up-conversion and transient absorption. We also studied the initial S(n) → S(1) internal conversion dynamics when these compounds are excited to upper states with 387.5 nm light. In addition, we include measurements of the rate for singlet oxygen production through the formation of an ESR-active adduct in aerated solutions. Such measurements indicate that, associated to its photophysics, the tin(IV) phthalocyanine produces (1)O(2) with an efficiency significantly larger than the silicon(IV) counterpart, making it an interesting option for sensitization applications. Finally, we performed excited state calculations at the TD-DFT level which describe the effects of the reduced symmetry together with the state ordering and indicate the presence of near dark intermediate states between the Q and B transitions for both of these macrocycles.

The role of conformational changes in the signal enhancement of a selective chemosensor of Pb2+.

In this work, the complexes formed by a fluoroionophore with three dications (M(2+) = Ca(2+), Hg(2+) and Pb(2+)) were studied theoretically, by applying both Density Functional Theory and its Time Dependent version (TDDFT). The experimental information concerning this fluoroionophore-Pb(2+) complex indicates a large increment in the absorption and emission signals. From a theoretical point of view, by using the structure with minimum energy of the fluoroionophore free as reference; distortions in the structure are observed when the complexes are formed and consequently important changes in terms of certain properties occur. Although there are increments in signal intensity in the case of the three ions considered here, TDDFT predicts that the Pb(2+) complex will manifest the most pronounced response and this conforms to experimental observations. Thus, we can associate the experimentally observed behavior with conformational changes. In order to corroborate this hypothesis we have analyzed the fluoroionophore-M(2+) structure complexes, both with ions, without ions and without the ionophore (which binds the ions); it is evident that if the ligand manifests geometric distortions, then the absorption signal will increase. The inert pair effect induces the particular conformation of the complex, when the Pb(2+) is present, acting as a lone pair, which is revealed when the electron localization function is analyzed. If structural distortions are present then the charge distribution and consequently the dipolar moment also present significant changes.

Simple charge-transfer model for metallic complexes.

In the chemistry of metallic complexes, two important concepts have been used to rationalize the recognition and selectivity of a host by a guest: preorganization and complementarity. Both of these concepts stem from geometrical features. Less explored in the literature has been the interactional complementarity, where mainly the electronic factors in the intermolecular forces are involved. Because the charge transfer between a species rich in electrons (ligand) and another deficient in them (cation) is one of the main intermolecular factors that control the binding energies in metallic complexes, for such systems, we propose a simple model based on density functional theory. We define an interactional energy in which the geometrical energy changes are subtracted from the binding energies and just the electronic factors are taken into account. The model is tested for the complexation between bidentate and cyclic ligands and Ca, Pb, and Hg metal dications. The charge-transfer energy described by our model fits nicely with the interactional energy. Thus, when the geometrical changes do not contribute in a significant way to the complexation energy, the interactional energy is dominated by charge-transfer effects.

Performance of the Effective Core Potentials of Ca, Hg, and Pb in Complexes with Ligands Containing N and O Donor Atoms.

This paper presents a systematic study of the performance of the relativistic effective core potentials (RECPs) proposed by Dolg-Stoll-Preuss, Christiansen-Ermler, and Hay-Wadt for Ca(2+), Hg(2+), and Pb(2+). The RECPs performance is studied when these cations are combined with ethyleneglycol, 2-aminoethanol, and ethylenediamine to form bidentate complexes. First, the description of the bidentate ligands is analyzed with the Kohn-Sham method by using SVWN, BLYP, and B3LYP exchange-correlation functionals, and they are compared with the Møller-Plesset perturbation theory (MP2); for all these methods the TZVP basis set was used. We found that the BLYP exchange-correlation functional gives similar results like those obtained by the B3LYP and MP2 methods. Thus, the bidentate metal complexes were studied with the BLYP method combined with the RECPs. To compare RECPs performance, all the systems considered in this work were studied with the relativistic all-electron Douglas-Kroll (DK3) method. We observed that the Christiansen-Ermler and Dolg-Stoll-Preuss RECPs give the best energetic and geometrical description for Ca and Hg complexes when compared with the all-electron method. For Pb complexes the spin-orbit effect and the basis set superposition error must be taken into account in the RECP calculations. In general, the trend showed in the complexation energies with the all-electron method is followed by the complexation energies computed with all the pseudopotentials tested in this work.

Role of Hartree-Fock and Kohn-Sham orbitals in the basis set superposition error for systems linked by hydrogen bonds.

In this work the effect of the basis set superposition error (BSSE) is explored with the counterpoise method on the occupied and unoccupied Hartree-Fock (HF) and Kohn-Sham (KS) orbitals. Three different systems linked by hydrogen bonds, H(2)O...FH, H(2)O...H(2)O, and H(2)O...CFH(3), were studied by using the basis set families cc-pVXZ and aug-cc-pVXZ (X = D, T, Q). The basis sets were tested with the HF method and two approximations for the exchange-correlation functional of KS: a generalized gradient approximation and a hybrid approach. In addition to these methods, the second-order Møller-Plesset perturbation theory, MP2, was considered. It was found that the presence of the "ghost" basis set affects the orbitals in two ways: (1) The occupied KS orbitals are more sensitive to the presence of this "ghost" basis set than the occupied HF orbitals. For this reason the BSSE observed in HF is less than that obtained with KS. (2) The unoccupied HF orbitals are more sensitive to the presence of the "ghost" basis set than their corresponding occupied orbitals. Because the MP2 method uses both, occupied and unoccupied HF orbitals, to compute the total energy, the contribution of the BSSE is bigger than that obtained with HF or KS methodologies.