Corrado Di Nicola

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).

Mechanochemical synthesis in copper(II) halide/pyridine systems: single crystal X-ray diffraction and IR spectroscopic studies

Whereas complexes of divalent metal halides (X = Cl, Br, I) with/from pyridine commonly crystallise as trans-[M(py)(4)X(2)]·2py, M on a site of 222 symmetry in space group Ccca, true for CuCl(2) and CuBr(2) in particular, the copper(II) iodide adduct is of the form [Cu(py)(4)I]I·2py, Cu on a site of mm2 symmetry in space group Cmcm, and five-coordinate (square-pyramidal), the same cationic species also being found in 2[Cu(py)(4)I](I(3))·[(py)(2)Cu(μ-I)(2)Cu(py)(2)] (structurally defined). Bromide or N-thiocyanate may be substituted for the unbound iodide ion in the solvated salt, resulting in complexes which crystallize in space group Ccca, but with both anions and the metal atom disordered. In [Cu(py)(4)(I(3))(2)], a pair of long Cu···I contacts approach a square-planar Cu(py)(4) array. Assignments of the ν(CuN) and ν(CuX) (X = Br, I, SCN) bands in the far-IR spectra are made, the latter with the aid of analogous assignments for [Cu(py)(2)X(2)] (X = Cl, Br), which show a dependence of ν(CuX) on the Cu-X bond length that is very similar to that determined previously for copper(i) halide complexes. The structure of the adventitious complex [(trans-)(H(2)O)(py)(4)CuClCu(py)(4)](I(3))(3)·H(2)O is also recorded, with six- and five-coordinate copper atoms; rational synthesis provides [{Cu(py)(4)}(2)(μ-Cl)](I(3))(3)·H(2)O with one water molecule less. In [{Cu(py)(4)Cl}((∞|∞))](I(3))·3py, square pyramidal [Cu(py)(4)Cl](+) cations, assisted by Cl···Cu interactions, stack to give rise to infinite polymeric strings. Several of these compounds were prepared mechanochemically, illustrating the applicability of this method to syntheses involving redox reactions as well as to complex syntheses involving up to five components. The totality of results demonstrates that the [Cu(II)(py)(4)] entity can be stabilized in an unexpectedly diverse range of mononuclear and multinuclear complexes through the presence of lattice pyridine molecules, the bulky triiodide ion, or a combination of both.

Structural and thermodiffractometric analysis of coordination polymers. Part I: tin derivatives of the Bim ligand [Bim = Bis(1-imidazolyl)methane]).

New polynuclear coordination species containing the ditopic bis(1-imidazolyl)methane (Bim) ligand have been prepared as microcrystalline powders and structurally characterized by ab initio X-ray powder diffraction methods. [Bim(Me2SnCl2)]n (1), [Bim(nBu2SnCl2)]n (3), [Bim(Ph2SnCl2)]n (4), [Bim(MeSnCl3)]n (5), and [Bim(PhSnCl3)]n (6) all contain 1D chains with octahedral tin atoms with trans N-Sn-N linkages (but 4, which displays a cis N-Sn-N linkage). Their thermodiffractometric analysis allowed the estimation of the linear thermal expansion coefficients and strain tensors derived there from. The potential-energy surface of the free Bim ligand (as defined by two torsional degrees of freedom about the two N-CH2 bonds), eventually controlling the length of the repeating unit (polymer elongation), has been estimated using molecular mechanics and correlated with experimental observations.

Structures from Powders: Polynuclear Hg(II) Complexes Containing the Flexible Bisimidazolylmethane Ligand

Several polynuclear Hg(II) complexes containing the flexible ditopic bisimidazolylmethane ligand (C(7)H(8)N(4), bim) have been prepared by reaction of equimolar quantities of mercury salts (acetate, cyanide, thiocyanate, chloride, and iodide) in EtOH or acetonitrile solution. Their crystal and molecular structures were retrieved from laboratory powder diffraction data, and their thermal properties were fully characterized, including the determination of the thermal expansion coefficients and the related strain tensor using thermodiffractometric methods. [Hg(bim)(CH(3)COO)(2)](2) consists of cyclic dimers with chelating acetates, while the [Hg(bim)X(2)](n) species (X = Cl, CN, SCN, and I) are one-dimensional polymers, with dangling X groups. A further complex of nominal Hg(2)(bim)Cl(2) formulation was also prepared, but the complexity and nonideality of its powder diffraction traces prevented the determination of its main structural features.

Selective catalytic oxidation of olefins by novel oxovanadium(IV) complexes having different donor ligands covalently anchored on SBA-15: a comparative study

Using a post-synthetic grafting method, mesoporous SBA-15 was functionalized first with aminopropyl silane reagents such as (3-aminopropyl)trimethoxysilane (APTMS) or bis[3-(trimethoxysilyl)propyl]amine (BTMSPA) and then with chlorinated ligands such as 4-(2-chloroacetyl)-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (H-AP) or 5-chloromethyl-8-quinolinol hydrochloride (H-HQ). Vanadyl cations [(VO)2+] were then immobilized over functionalized silica samples in order to prepare new oxovanadium(IV) based “quasi-homogeneous” catalysts, namely Ia (Ia′), Ib (Ib′), and IIa. Alternatively, a preformed oxovanadium(IV) complex such as [VO(AP)2(H2O)] has been immobilized over a previously functionalized SBA-15-NH2 silica support, affording catalyst Ic. Elemental analysis (C, H, N), N2 adsorption–desorption isotherms, FT-IR, 29Si and 13C CP-MAS NMR, XPS, ICP-AES, SEM-EDX and TG-DTG techniques have been used for the full characterization of these materials. Their catalytic properties in the H2O2 promoted oxidation of conjugated olefins like styrene, α-methyl and β-methylstyrene were investigated, in terms of activity, selectivity and recyclability, and compared with that shown by more simple systems prepared by the direct grafting of the vanadyl cation onto SBA-15 (catalyst A) or SBA-15-NH2 (catalyst B). Generally, high activity, selectivity and recyclability (over the first three runs) were shown by all anchored catalysts, with the only exception of A and B systems. A full account of the obtained results, along with insights into the effects due to the different strategies employed for the functionalization of SBA-15 on the properties of final anchored catalysts, are reported.

Effects of methyl groups in a pyrimidine-based flexible ligand on the formation of silver(I) coordination networks

A novel flexible ligand with methyl substituted pyrimidine rings and thioether spacers has been synthesised and the corresponding 1 : 1 silver(I) adducts have been obtained by interaction with different silver(I) salts AgX (where X = NO3−, BF4−, ClO4−, CH3SO3−, CF3CO2−, and CF3CF2CF2CO2−). The X-ray single crystal structure determination of two of the new silver(I) adducts (X = NO3− and CF3CO2−) has proved the formation of coordination polymers with Ag(I) ions almost linearly coordinated to two nitrogen atoms of the pyrimidine rings of the multitopic ligand used. The linear coordination mode shown by the new flexible ligand is induced by the presence of the substituents on the pyrimidine rings, regardless of the type of the AgX salt used in the formation of the respective silver(I) derivatives. This observation represents a neat change in comparison to the already reported series of complexes with unsubstituted (and otherwise identical) ligands, in which dinuclear coordination units have been invariably obtained. Computational investigations have been performed with the aim of explaining such an observed change. A computational comparison of a known dinuclear complex and its related polymeric one has been detailed here and has allowed us to highlight the importance of the introduced substituents in changing the ligand interactions internally to their coordination units and among adjacent units in the solid phases.