The reversible thermochromic behaviour of homoleptic [{V(OR)(4)}(n)] complexes in solution [R = Pr(i) (product I), Bu(s) (B(s)), Nep (N) and Cy (C)] is accounted for the existence of an aggregation equilibrium involving dimeric and monomeric species in which vanadium(iv) is respectively five- and four-coordinate. Bulky R groups such as Bu(t) and Pe(t) (tert-pentoxide) prevent aggregation and therefore give rise to exclusively mononuclear compounds (B(t) and P(t), respectively) that are not thermochromic. The complexes and their temperature-dependent interconversion were characterised by single crystal X-ray diffractometry, magnetic susceptibility measurements and electronic, FTIR and EPR spectroscopies in a wide temperature range. Equilibrium constants and enthalpy and entropy changes for the dimerization reactions have been determined and compared with literature data.

Two discrete mononuclear complexes, [Tb(bbpen)(NO 3 )] (I) and [Tb(bbppn)(NO 3 )] (II), for which H 2 bbpen = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine and H 2 bbppn = N,N′-bis(2-hydroxylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates II from I and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of H 2 bbppn is described here for the first time, while that of complex II has been redetermined in the monoclinic C2 space group in light of new diffraction data. In II, selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (ϕ) and luminescence excited-state lifetimes (at room temperature and 11 K) were measured for both complexes. Despite their similar molecular structures, I and II exhibit remarkably different ϕ values of 21 ± 2% and 67 ± 7%, respectively, under UV excitation at room temperature. Results of quantum-mechanical (DFT and TD-DFT) calculations and experimental PL measurements also performed for H 2 bbpen and H 2 bbppn confirmed that both ligands are suitable to work as "antennas" for Tb III . Considering the 5 D 4 lifetime profiles and the significantly higher absolute quantum yield of II, it appears that thermally active nonradiative pathways present in I are minimized in II due to differences in the conformation of the ethylenediamine bridge.

Atomic multipoles from the Quantum Theory of Atoms in Molecules(QTAIM), up to quadrupoles, and CHELPG charges are employed in the description of electrostatic properties of some small linear molecules: H 2 , HF, HCl, HBr, HCN, HNC, and CO. A proton is placed on the molecular axis in distances within the range 3-8 Å from the terminal atoms. The polarization of molecular electronic densities induced by the proton is readily included by the calculation of atomic multipoles in each proton-molecule arrangement. Electrostatic potentials at the proton position as given by QTAIM multipoles are always in better agreement with the reference results, calculated directly at the B3LYP/6-311G(3d,3p) level, than those predicted with CHELPG charges, particularly for cases in which QTAIM multipoles showed that the contribution of atomic charges to these potentials is not clearly predominant over other contributions as in H 2 , HCl, HBr, HNC, and CO. The lone pair at the carbon atoms in CO and HNC, as described by QTAIM atomic dipoles, is indispensable in studies of electrostatic properties of these molecules. Moreover, QTAIM multipoles are also able to describe properly the large polarizations induced by the proton along the proton-molecule distances studied.

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1 unity and proceeds through the coordinationinsertion mechanism. Molecular weights ranging from 6,379 to 13,950 g mol 21 and PDI values varying from 1.22 to 1.52 were obtained. Results of ROP kinetic studies for both E-CL and rac-LA confirm that the reaction rates are first-order with respect to monomers. The production of poly(E-caprolactone) shows a higher sensitivity of the reaction rate to temperature, while the polymerization of rac-LA is slower and more dependent on the thermal stability of the active species during the propagation step.

The distorted tetrahedral [V(OAd)] alkoxide (OAd = 1-adamantoxide, complex 1) is the first homoleptic, mononuclear vanadium(IV) alkoxide to be characterized in the solid state by X-ray diffraction analysis. The compound crystallizes in the cubic P4̅3 n space group with two highly disordered, crystallographically independent molecules in the asymmetric unit. Spin Hamiltonian parameters extracted from low temperature X- and Q-band electron paramagnetic resonance (EPR) experiments performed for polycrystalline samples of 1, both in the concentrated (bulk) form and diluted in the diamagnetic [Ti(OAd)] analogue, reveal a fully axial system with g < g , g and A ≫ A, A . Complex 1 has also been characterized by alternate current susceptometry with varying temperature (3-30 K) and static magnetic field (up to 8.5 T), showing field-induced slow relaxation of the magnetization with relaxation times ranging from ca. 3 ms at 3 K to 0.02-0.03 ms at 30 K, in line with relevant results described recently for other potential molecular quantum bits. Pulsed EPR measurements, in turn, disclosed long coherence times of ca. 4 μs at temperatures lower than 40 K, despite the presence of the H-rich ligands. The slow spin relaxation in 1 is the first observed for a tetracoordinate nonoxido vanadium(IV) complex, and results are compared here to those generated by square-pyramidal V(O) and trigonal prismatic V with oxygen donor atom sets. Considering that the number of promising d complexes investigated in detail for slow magnetization dynamics is still small, the present work contributes to the establishment of possible structural/electronic correlations of interest to the field of quantum information processing.