Federica Garau

New coordination polymers based on the triangular [Cu3(μ3-OH)(μ-pz)3]2+ unit and unsaturated carboxylates

By reacting copper(II) acrylate with pyrazole (Hpz), two trinuclear copper derivatives [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(H2O)2(Hpz)], 1, and [Cu3(mu3-OH)(mu-pz)3(CH2CHCOO)2(CH3OH)], 2, are obtained, in water and methanol respectively, while copper(II) methacrylate affords [Cu3(mu3-OH)(mu-pz)3(CH2C(CH3)COO)2], 3, independently from the solvent used. In 1 and 2 two triangular trinuclear units are connected through acrylate bridges forming hexanuclear clusters that, in the case of 2 are further connected through double syn-syn carboxylate bridges, generating a 1-D coordination polymer. In the case of 3 a different 1-D coordination polymer is obtained by alternating syn-syn and syn-anti double carboxylate bridges connecting the trinuclear clusters. In all cases H-bonds contribute both to the stabilization of these arrangements and to the formation of more extended supramolecular networks. Compounds 1-3 are valuable catalysts in the peroxidative oxidation with aqueous H2O2, in MeCN at 25 degrees C, of cycloalkanes (i.e. cyclohexane and cyclopentane) to the corresponding ketones and alcohols (overall yield up to 36%, TON = 36), following a radical mechanism as shown by radical trap experiments, and the effects of various factors are studied. Electrochemical experiments show that the copper(II) centres are reduced to copper(I) and copper(0).

Magnetic Properties and Vapochromic Reversible Guest-Induced Transformation in a Bispyrazolato Copper(II) Polymer: an Experimental and Dispersion-Corrected Density Functional Theory Study

Dispersion-corrected density functional theory (DFT-D) calculations, Electron Spin Resonance spectroscopy (EPR), and variable temperature magnetic moment measurements were used to investigate the structure and the electronic/magnetic properties of bispyrazolato-copper(II) coordination polymer and of its hydration product. The Cu(II) ions are antiferromagnetically coupled through the sigma system of the pyrazolate rings in both compounds. Theoretical electron density maps reveal that water molecules interact simultaneously and to a comparable extent with two Cu(II) centers (through the electronegative O end) and two pyrazolate rings (through the partly positively charged H atoms), which is compatible with the observed internuclear distances. DFT-D calculations indicate that low kinetic barriers are involved in the rearrangement of the host structure.

Density functional theory study of the binding capability of tris(pyrazol-1-yl)methane toward Cu(I) and Ag(I) cations.

Density functional theory (DFT) has been used to look into the electronic structure of [M(tpm)]+ molecular ion conformers (M = Cu, Ag; tpm = tris(pyrazol-1-yl)methane) and to study the energetics of their interconversion. Theoretical data pertaining to the free tpm state the intrinsic instability of its kappa3-like conformation, thus indicating that, even though frequently observed, the kappa3-tripodal coordinative mode is unlikely to be directly achieved through the interaction of M(I) with the kappa3-like tpm conformer. It is also found that the energy barrier for the kappa2-[M(tpm)]+ --> kappa3-[M(tpm)]+ conversion is negligible. As far as the bonding scheme is concerned, the tpm --> M(I) donation, both sigma and pi in character, is the main source of the M(I)-tpm bonding, whereas back-donation from completely occupied M(I) d orbitals into tpm-based pi* levels plays a negligible role.

Crystal structure, supramolecular assembly and preliminary reactivity behaviour of new heteropolytopic ligands based on oxalate/malonate skeleton and azolate moieties

Heteropolytopic oxalyl and malonyl diamide ligands, derived from 1H-pyrazole, 3,5-dimethyl-1H-pyrazole, 1H-indazole and 1H-1,2,3-benzotriazole, have been synthesised by reaction of the corresponding azole with oxalyldichloride and carbon suboxide respectively and fully characterized by elemental analyses, IR and NMR (1H, 13C). In the examined cases single crystal X-ray diffraction studies revealed important supramolecular assemblies based on H-bonds and/or π–π interactions. The reactivity behaviour toward metal salts is also described.

An experimental and theoretical investigation of the molecular and electronic structure of 2-amino-4-chloro-6-pyrazolyl-[1,3,5]triazine, forming supramolecular linear tapes in the solid state

The new derivative 2-amino-4-chloro-6-pyrazolyl-[1,3,5]triazine, 1, prepared by reaction of 2-amino-4,6-dichloro-[1,3,5]triazine with an excess of pyrazole, has been characterized by 1H, 13C and 15N NMR measurements and single crystal XRD structural determination. The non-equivalence of the NH2 hydrogens evidences the iminium character of this moiety. Compound 1, exploiting strong H-bonds, self-assembles generating supramolecular linear tapes. Theoretical calculations are in good agreement with experimental solid state and solution data. Electronic properties of 1 (lowest lying excitation energies and corresponding oscillator strength) have also been determined by time dependent DFT at the PBE level.