Marzio Rancan

Double Level Selection in a Constitutional Dynamic Library of Coordination Driven Supramolecular Polygons

A constitutional dynamic library (CDL) of Cu(II) metallo-supramolecular polygons has been studied as a bench test to examine an interesting selection case based on molecular recognition. Sorting of the CDL polygons is achieved through a proper guest that is hosted into the triangular metallo-macrocycle constituent. Two selection mechanisms are observed, a guest induced path and a guest templated self-assembly (virtual library approach). Remarkably, the triangular host can accommodate several guests with a degree of selectivity ranging from ∼1 to ∼10(4) for all possible guest pairs. A double level selection operates: guests drive the CDL toward the triangular polygon, and, at the same time, this is able to pick a specific guest from a set of competitive molecules, according to a selectivity-affinity correlation. Association constants of the host-guest systems have been determined. Guest competition and exchange studies have been analyzed through variable temperature UV-Vis absorption spectroscopy and single crystal X-ray diffraction studies. Molecular structures and electronic properties of the triangular polygon and of the host-guest systems also have been studied by means of all electrons density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations including dispersive contributions. DFT outcomes ultimately indicate the dispersive nature of the host-guest interactions, while TDDFT results allow a thorough assignment of the host and host-guests spectral features.

A templating guest sorts out a molecular triangle from a dimer–trimer constitutional dynamic library

Cu(II) and a bis-β-diketone ligand generate a small constitutional dynamic library (CDL). The designed introduction of a well suited guest drives the self-sorting of the system toward a supramolecular triangle. Alternatively, the triangle self-assembly is templated by the same guest in a one-pot synthesis.

Studies of Finite Molecular Chains: Synthesis, Structural, Magnetic and Inelastic Neutron Scattering Studies of Hexa- and Heptanuclear Chromium Horseshoes

We report the synthesis and structural characterisation of a family of finite molecular chains, specifically [{[R(2)NH(2)](3)[Cr(6)F(11)(O(2)CCMe(3))(10)]}(2)] (in which R=nPr 1, Et 2, nBu 3), [{Et(2)NH}(2){[Et(2)NH(2)](3)[Cr(7)F(12)(O(2)CCMe(3))(12)][HO(2)CCMe(3)](2)}(2)] (4), [{[Me(2)NH(2)](3)[Cr(6)F(11)(O(2)CCMe(3))(10)]2.5 H(2)O}(4)] (5) and [{[iPr(2)NH(2)](3)[Cr(7)F(12)(O(2)CCMe(3))(12)]}(2)] (6). The structures all contain horseshoes of chromium centres, with each Cr...Cr contact within the horseshoe bridged by a fluoride and two pivalates. The horseshoes are linked through hydrogen bonds to the secondary ammonium cations in the structure, leading to di- and tetra-horseshoe structures. Through magnetic measurements and inelastic neutron scattering studies we have determined the exchange coupling constants in 1 and 6. In 1 it is possible to distinguish two exchange interactions, J(A)=-1.1 meV and J(B)=-1.4 meV; J(A) is the exchange interactions at the tips of the horseshoe and J(B) is the exchange within the body of the horseshoe (1 meV=8.066 cm(-1)). For 6 only one interaction was needed to model the data: J=-1.18 meV. The single-ion anisotropy parameters for Cr(III) were also derived for the two compounds as: for 1, D(Cr)=-0.028 meV and |E(Cr)|=0.005 meV; for 6, D(Cr)=-0.031 meV. Magnetic-field-dependent inelastic neutron scattering experiments on 1 allowed the Zeeman splitting of the first two excited states and level crossings to be observed. For the tetramer of horseshoes (5), quantum Monte Carlo calculations were used to fit the magnetic susceptibility behaviour, giving two exchange interactions within the horseshoe (-1.32 and -1.65 meV) and a weak inter-horseshoe coupling of +0.12 meV. Multi-frequency variable-temperature EPR studies on 1, 2 and 6 have also been performed, allowing further characterisation of the spin Hamiltonian parameters of these chains.

Chemistry and supramolecular chemistry of chromium horseshoes

Synthetic and structural studies of Cr horseshoes are reported which show that these compounds demonstrate a rich supramolecular chemistry through H-bonding interactions, and can act as ligands for metal clusters.

Nanostructured Copper Oxide on Silica–Zirconia Mixed Oxides by Chemical Implantation

N,N-Dialkylcarbamato complexes of copper(II), [Cu(O(2)CNR(2))(2)] (R = All = allyl, C(3)H(5); iPr, CH(CH(3))(2)) were prepared with the aim of functionalizing silica and nanostructured silica-zirconia matrices. The mixed matrices for the grafting reactions were prepared by copolymerizing MAPTMS (methacryloxypropyltrimethoxysilane), the precursor for the silica matrix, with the zirconium tetranuclear derivative [Zr(4)O(2)(OMc)(12)] (OMc = methacrylate), the precursor for the zirconia nanoparticles. Suspension of the silica and silica-zirconia matrices in a solution of the copper dialkylcarbamate led to the functionalization of the respective substrates. The composition, microstructure, morphology, and physicochemical nature of the copper species grafted on the matrices were investigated by FTIR, X-ray photoelectron spectroscopy (XPS), EPR, X-ray absorption spectroscopy (XAS), XRD, TEM, and dinitrogen adsorption. The effect of selected experimental parameters (the nature of the copper precursor and of the matrix, grafting time, thermal treatment) on the grafting reaction was investigated. The Cu/Si ratio is increased by increasing the grafting time and the ZrO(2)-SiO(2) matrix is more reactive to attack by the carbamato complexes than either prepared or commercial SiO(2). After functionalization of the matrix, thermal treatment yielded nanostructured copper(II) oxide clusters, average diameter 12-15 nm, uniformly supported on the silica and on the silica-zirconia matrices.

Varying spin state composition by the choice of capping ligand in a family of molecular chains: detailed analysis of magnetic properties of chromium(III) horseshoes

We report a detailed physical analysis on a family of isolated, antiferro-magnetically (AF) coupled, chromium(III) finite chains, of general formula (Cr(RCO(2))(2)F)(n) where the chain length n = 6 or 7. Additionally, the chains are capped with a selection of possible terminating ligands, including hfac (= l,l,l,5,5,5-hexafluoropentane-2,4-dionate(l-)), acac (= pentane-2,4-dionate(l-)) or (F)(3). Measurements by inelastic neutron scattering (INS), magnetometery and electron paramagnetic resonance (EPR) spectroscopy have been used to study how the electronic properties are affected by n and capping ligand type. These comparisons allowed the subtle electronic effects the choice of capping ligand makes for odd member spin 3/2 ground state and even membered spin 0 ground state chains to be investigated. For this investigation full characterisation of physical properties have been performed with spin Hamiltonian parameterisation, including the determination of Heisenberg exchange coupling constants and single ion axial and rhombic anisotropy. We reveal how the quantum spin energy levels of odd or even membered chains can be modified by the type of capping ligand terminating the chain. Choice of capping ligands enables Cr-Cr exchange coupling to be adjusted by 0, 4 or 24%, relative to Cr-Cr exchange coupling within the body of the chain, by the substitution of hfac, acac or (F)(3) capping ligands to the ends of the chain, respectively. The manipulation of quantum spin levels via ligands which play no role in super-exchange, is of general interest to the practise of spin Hamilton modelling, where such second order effects are generally not considered of relevance to magnetic properties.

Bi12O17Cl2/(BiO)2CO3 Nanocomposite Materials for Pollutant Adsorption and Degradation: Modulation of the Functional Properties by Composition Tailoring

Bi12O17Cl2/(BiO)2CO3 nanocomposite materials were studied as bifunctional systems for depuration of wastewater. They are able to efficiently adsorb and decompose rhodamine B (RhB) and methyl orange (MO), used as model pollutants. Bi12O17Cl2/(BiO)2CO3 nanocomposites were synthesized at room temperature and ambient pressure by means of controlled hydrolysis of BiCl3 in the presence of a surfactant (Brij 76). Cold treatments of the pristine samples with UV light or thermal annealing at different temperatures (370–500 °C) and atmospheres (air, Ar/30% O2) were adopted to modulate the relative amounts of Bi12O17Cl2/(BiO)2CO3 and hence the morphology, surface area, ζ-potential, optical absorption in the visible range, and the adsorption/degradation of pollutants. The best performance was achieved by (BiO)2CO3-rich samples, which adsorbed 80% of MO and decomposed the remaining 20% by visible light photocatalysis. Irrespective of the dye, all of the samples were able to almost complete the adsorption step within 10 min contact time. Bi12O17Cl2-rich composite materials displayed a lower adsorption ability, but thanks to the stronger absorption in the visible range they behaved as more effective photocatalysts. The obtained results evidenced the ability of the employed strategy to modulate sample properties in a wide range, thus pointing out the effectiveness of this approach for the synthesis of multifunctional inorganic materials for environmental remediation.

Hybrid Organic/Inorganic Perovskite–Polymer Nanocomposites: Toward the Enhancement of Structural and Electrical Properties

Hybrid organic/inorganic perovskite nanoparticles (NPs) have garnered remarkable research attention because of their promising photophysical properties. New and interesting properties emerge after combining perovskite NPs with semiconducting materials. Here, we report the synthesis and investigation of a composite material obtained by mixing CH3NH3PbBr3 nanocrystals with the semiconducting polymer poly(3-hexylthiophene) (P3HT). By the combination of structural techniques and optical and magnetic spectroscopies we observed multiple effects of the perovskite NPs on the P3HT: (i) an enlargement of P3HT crystalline domains, (ii) a strong p-doping of the P3HT, and (iii) an enhancement of interchain order typical of H-aggregates. These observations open a new avenue toward innovative perovskite NP-based applications.

Theoretical Investigation of the Electronic Properties of Three Vanadium Phthalocyaninato (Pc) Based Complexes: PcV, PcVO, and PcVI

The electronic properties of three vanadium phthalocyaninato (Pc) based complexes (PcV, PcVO, and PcVI; I-III, respectively) were theoretically investigated and corresponding VL2,3-edge XAS spectra modeled. Ground state (GS) DFT outcomes indicated that II is more stable than III by 141 kcal/mol; moreover, the Ziegler transition state method allowed us to estimate the PcV-X bond dissociation energy and to quantify σ/π contributions to the V-X interaction. As such, the Nalewajski-Mrozek V-X and V-N bond multiplicity indexes (V-O/V-I = 2.48/1.22; V-N = 0.64, 0.51, and 0.58 in I-III, respectively) state that the V-X bond strength and nature affect the V-N interaction. The coordination of X to V in the I → II/I → III reactions implies the transfer of two/one electrons from I to X. In both cases, the oxidation involves only the V ion; moreover, V 3d based orbitals from which electrons are transferred were identified. Literature I/IIL2,3-edge XAS data were modeled by exploiting the DFT/ROCIS method. The same protocol was adopted to predict IIIL2,3-edge XAS spectra. Theoretical results indicated that, along the whole series, spectral features lying at the lowest excitation energies (EEs) are mostly generated by states having the same GS spin multiplicity and involve 2pV → SOMO (single occupied molecular orbital) single electronic excitations. XAS features at higher EEs include only states with the same GS spin multiplicity in I, while states with both ΔS = 0 and ΔS = +1 (S = total spin quantum number) are present in II and III with significant, in some cases prevailing, contributions from metal to ligand charge transfer (MLCT) excitations. Beyond the role played by MLCT transitions in determining XAS patterns, it is noteworthy that they involve only Pc-based empty orbitals with no participation of the X-based virtual levels.