Marcello Colapietro

Molecular structure of nitrobenzene in the planar and orthogonal conformations - A concerted study by electron diffraction, X-ray crystallography, and molecular orbital calculations

The molecular structure and ring distortions of nitrobenzene have been determined by gas-phase electron diffraction and ab initio molecular orbital (MO) calculations as well as from the structures of six derivatives studied by X-ray crystallography. The experimental value of the ring angle at the ipso position isα = 123.4 ± 0.3° in the free molecule; this is about 1.5° less than the hitherto reported values. Regression analysis of the ring angles in the six derivatives studied by X-ray crystallography yieldsα = 122.7(1)° for nitrobenzene in a crystalline environment. The small difference in the two values of a is interpreted as an effect of intermolecular interactions in the crystal. The value produced by the MO calculations,α = 122.3° at the 6–31G* (5D) level, is smaller than either of the experimental results. As regards the ring angles at the meta and para positions, the three techniques of structure determination consistently indicate that these are larger than 120° by a few tenths of a degree. Other important geometrical parameters from the electron diffraction study are 〈rg(C-C)〉 = 1.399 ± 0.003 Å,rg(C-N) = 1.486 ± 0.004 Å,rg(N-O) = 1.223 ± 0.003 Å, and A sO-N-O = 125.3 ± 0.2°. X-ray diffraction experiments on 3,5-dimethyl-4-nitrobenzoic acid and 3,5-dimethylbenzoic acid and ab initio MO calculations provide solid evidence that the geometry of nitrobenzene is little affected when the nitrogroup is twisted by 90° out of the planar equilibrium conformation. This indicates that the extent of π-electron transfer from the benzene ring to the nitro group is small. The barrier to rotation is estimated to be 17 ± 4 kJ mol−1 from the electron diffraction data.

Synthesis and spectroscopic investigations (IR, NMR and Mössbauer) of tin(IV) and organotin(IV) derivatives of bis(pyrazol-1-yl) alkanes: X-ray crystal structures of bis(4-methylpyrazol-1-yl) methane and its dimethyltin(IV) dichloride adduct

A series of 1:1 adducts of the type [(L)RnSnX4−n]·zH2O (L ≡ bis(4-methylpyraazol-1-yl)ethane (L4), bis(3,4,5-timethylpyrazol-1-yl)methane (LT), 1,2-bis(pyrazol-1-yl)ethane (LA) or 1,2-bis(3,5-dimethylpyrazol-1-yl)ethane (LB); R ≡ Me, Et, Bu or Ph; X ≡ I, Br or Cl; n = 0, 1 or 2; z = 1, 1.5 or 2), and the likely polynuclear [(LA)5(SnCl4)4]·(H2O)5 and [(LB)2(SnCl4)3]·12[Et2O] have been characterized in the solid state and in solution by analyses, spectral (IR, Mossbauer, and 1H, 13C and 119Sn NMR) data and conductivity measurements. When LT reacts with SnCl4, cleavage of a carbon (sp3)-nitrogen bond was observed and the adduct [(3,4,5-trimethyl-pyrazole)2SnCl4] was obtained. The diorganotin(IV) complexes generally dissociate in chloroform or in acetone solution, while the trichlorotin(IV) and tetrachlorotin(IV) adducts probably retain the hexacoordinate configuration. The crystal structures of L4 and of the adduct [(L4)(CH3)2SnCl2] have been determined by X-ray analysis. In the adduct the tin atom is coordinated to two halide atoms, two methyl groups and two N atoms, with trans-(CH3)2Sn in a slightly distorted octahedral configuration. The long SnN bond distance (2.436(6)A) indicated weak donor ability of the N2 donor L4. Comparison is made with the X-ray crystal structures of several R2SnX2N2-type compounds.

Synthesis, characterisation and optical properties of symmetrical and unsymmetrical Pt(II) and Pd(II) bis-acetylides. Crystal structure of trans-[Pt(PPh3)2(CC–C6H5)(CC–C6H4NO2)]

Abstract Symmetric trans-[Pt(PPh3)2(CCR)2] and unsymmetrical trans-[Pt(PPh3)2Cl(CCR)], (R=C6H4–pNO2, C6H4–pOCH3), Pt(II) acetylides were prepared and characterised, as well as unsymmetrical Pt(II) bis-acetylides, trans-[Pt(PPh3)2(CCR)(CCR′)], (R=C6H4–pNO2, R′=C6H5; R=C6H4–pOCH3, R′=C6H5; R=C6H4–pOCH3, R′=C6H4–pNO2; R=C6H4–pNO2, R′=[(η5-C5H4)Fe(η5-C5H5)]). Also symmetric Pd(II) bis-acetylides, trans-[Pd(PPh3)2(CCR)2] (R=C6H4–pNO2, C6H5) were synthesised and characterised by IR, NMR, and UV–vis spectroscopies. The optical properties of the new complexes were compared within a series of known Pt(II) complexes containing different phosphines and cis–trans configuration. The absorption and photoluminescence spectra indicate that the emission is found in the range 355–600 nm, depending on the nature of the acetylide ligand bound to Pt. Measurements of SHG for the unsymmetrical bis-acetylides dispersed in polymethylmethacrylate (PMMA) show that the second-order nonlinear optical (NLO) properties depend on the strength of the donor–acceptor substituent of the acetylide ligand. Third-order NLO properties (in particular the nonlinear absorption coefficient α2) were measured by the Z-scan technique; strong push–push and pull–pull substituents on the Pt(II) symmetric bis-acetylides induce electronic delocalisation and tuning of the NLO properties. The single crystal X-ray structure of trans-[Pt(PPh3)2(CC–C6H5)(CC–C6H4NO2)] shows that the unsymmetrical molecule crystallised in the Pbca centric space groups.

Coexistence of stripes and superconductivity: Tc amplification in a superlattice of superconducting stripes

Abstract Here we report direct evidence for charge ordering in the oxygen doped La 2 CuO 4.1 superconductor by x-ray diffraction using a third generation synchrotron source. We observe 1D charge ordering and oxygen ordering in an optimally doped superconductor (T c =40K) well beyond the phase separation regime. The order parameter of the anharmonic 1D CDW shows a critical behavior (T co -T) 0.5 T co =190K. The oxygen ordering and the polaron 1D CDW with its associated orbital wave, realize a superlattice of quantum stripes with a wavevector that at the density of charge carriers, r s ∼6, in the superconducting stripes satifies the shape resonance condition for T c amplification.

Synthesis and spectroscopic characterization of new Cu(I) complexes containing triaryl- tricycloalkylphosphines and heterocyclic anionic or neutral N-donor ligands. Crystal and molecular structure of [(Cy3P)2(pzH)Cu]ClO4.CH3OH (Cy = cyclohexyl, pzH = pyrazole).

The reaction of (PPh3)4CuClO4, (PPh3)2CuCl, (Cy3P)2CuNO3 and (Cy3P)2CuClO4 with an excess of monodentate heterocyclic N-donor ligand (QH in general, in detail: ImH=imidazole, 1-MeimH=1-methylimidazole, 2-MeimH=2-methylimidazole, 4-Phim=4-phenylimidazole, BimH=benzimidazole, 1-BzimH=1-benzylimidazole, pzH=pyrazole, pz′H=3,5-dimethylpyrazole) in diethyl ether or benzene resulted in the formation of new 2:2:1 [(PPh3)2(QH)2Cu]ClO4 (QH=ImH, 1-MeimH, 2-MeimH, 4-PhimH, BimH, pzH) and [(PCy3)2(QH)2Cu]NO3 (QH=4-PhimH, BimH), 1:3:1 [(PPh3)(1-BzimH)3Cu]ClO4, [(PCy3)(1-MeimH)3Cu]ClO4 and [(PCy3)(QH)3Cu]NO3 (QH=ImH, 1-MeimH, pzH), 2:1:1 [(PPh3)2O(QH)CuCl] (QH=ImH, 2-MelmH, 4-PhimH, BimH, 1-BzimH), [(PCy3)2 (QH)Cu]NO3 (QH=1-BzimH, pz′H) and [(PCy3)2 (QH)Cu]ClO4 (QH=2-MeimH, 4-PhimH, BimH, 1-BzimH, pzH, pz′H), 1:2:1 [(PCy3)(2-MeimH)2Cu]NO3and [(PCy3)(ImH)2Cu]ClO4 and 1:1:1 [(PPh3) (1-MeimH)CuCl] adducts. With the bidentate donors bis(pyrazol)-1-yl)methane (L1), bis(3,5-dimethylpyrazol-1-yl)methane (L2) and bis(4-methylpyrazol-1-yl)methane (L4), 2:1:1 [(PPh3)2(L)Cu]ClO4 and 1:1:1 [(PCy3)(L)Cu]ClO4 complexes were obtained, whereas the exopolydentate bis (1,2,4-triazol-l-yl) methane (L3) in similar conditions yielded 1:1:1 [(PPh3)(L3)Cu]ClO4 and [(PCy3)(L3)Cu]NO3, and 1:2:1 [(PCy3)(L3)2Cu]ClO4 derivatives. Breaking of the bridging C(sp3)-N bond in the bidentate bis (pyrazol-1-yl)methane occurred when the reaction between L1 and (PCy3)2CuNO3 was carried out in diethyl ether under aerobic conditions, the derivative [(PCy3)(pzH)3Cu]NO3 being formed. In methanol in the presence of base, ImH, 2-MeimH, 4-PhimH and BimH react with (PPh3)2CuCl giving the sparingly soluble complexes [(PPh3)2(Im)Cu]·1/2H2O, [(PPh3)2(2-Meim)Cu]·H2O, [(PPh3)(4-Phim)Cu] and [(PPh3)(Bim)Cu], respectively. Reaction of [(PPh3)2(ImH)2Cu]ClO4 with PCy3, PBz3 (Bz=benzyl), P(p-tolyl)3, and (Ph2PCH2)2 (abbreviated Diphos) resulted in the formation of compounds [(PPh3)(PCy)3(ImH)2Cu]ClO4, [(PPh3)(PBz3)(ImH)Cu]ClO4, [(PPh3)P(p-tolyl)3(ImH)2Cu]ClO6 and [(Diphos)2Cu]ClO4, respectively, whereas reaction with 1,10-phenanthroline (Phen) and 2,2′-bipyridyl (Bipy) produced [(PPh3)2(ImH)(Phen)Cu]ClO4 and [(PPh3)2(ImH)(Bipy)Cu]ClO4, respectively. While PCy3, PBz3 and P(p-tolyl)3 were not able to displace the triphenylphosphine from [(PPh3)2(L1)Cu]ClO4, Phen and Bipy in the same conditions formed the derivatives [(PPh3)2(Phen)Cu]ClO4 and [(PPh3)2(Bipy)Cu]ClO4. All of the complexes were characterized by IR and far-IR data, conductivity, 1H NMR and in some cases also with UV, 13C and 31P NMR and molecular weight measurements. The structure of [(Cy3P)2(pzH)Cu]ClO4·CH3OH was determined by single crystal X-ray diffraction: monoclinic, space group Pn,Z=2,a=9.949(7),b=13.128(4),c=16.588(8) A, β=91.15(7)°. The copper atom exhibited a distorted ideal trigonal planar geometry involving two phosphine groups (CuP:2.262(9) and 2.272(6) A; PCuP: 132.3(7)°) and one pyrazole ligand (CuN:2.047(18)A) coordinating through a pyridine-like nitrogen atom. The pyrazole donor of one molecule was hydrogen bonded to a molecule of methanol, which in turn was hydrogen bobded to the ionic perchlorato group.

Comparison of the structure and magnetic order in a series of layered Ni(II) organophosphonates, Ni[(RPO3)(H2O)] (R = C6H5, CH3, C18H37).

The reaction of nickel chloride with phenyl phosphonic acid under hydrothermal conditions resulted in the isolation of yellow-green single crystals of Ni[(C(6)H(5)PO(3))(H(2)O)]. The structure of the compound has been solved by X-ray single-crystal diffraction studies. Ni[(C(6)H(5)PO(3))(H(2)O)] crystallizes in the orthorhombic space group Pmn2(1) and is isostructural with the Mn(II), Fe(II), and Co(II) analogues. It presents the typical features of the hybrid 2D structures, consisting of alternating inorganic and organic layers. The former are formed by six-coordinated nickel(II) ions bridged by oxygen atoms into the layers. The inorganic layers are capped by the phenyl phosphonate groups, with phenyl groups of two adjacent ligands forming a hydrophobic bilayer region, and van der Waals contacts are established between them. The magnetic properties investigated by means of dc and ac susceptibility measurements point to an AF exchange coupling between nearest neighboring Ni(II) ions. Below 5 K, the compound orders magnetically showing the typical features of a canted antiferromagnet. The magnetic behavior and magnetic dimensionality of Ni[(C(6)H(5)PO(3))(H(2)O)] have been fully analyzed and compared to those of the Ni(II) parent compounds Ni[(RPO(3))(H(2)O)] (where R = CH(3), C(18)H(37)), which exhibit different symmetries of the inorganic layers and lengths of the R groups.

Synthesis and characterization of some Tin(II) and Tin(IV) derivatives of 4-acyl-5-pyrazolones. Crystal structure of bis(1-phenyl-3-methyl-4-acetyl-pyrazolon-5-ato)Tin(II)

Abstract Stable, four-coordinated (Q)2Sn compounds have been prepared, where QH is 1-phenyl-3-methyl-4-RC( O)-pyrazol-5-one (R = CH3, CF3, n-C6H13, C6H5,pF-C6H4,p-Cl-C6H4,p-Br-C6H4,p-I-C6H4,p-NO2-C6H4,p-CH3O-C6H4). They have been characterized through analytical data, IR and1H,13C and119Sn NMR spectroscopy. In the crystal structure of the title compound (8), the tin atom is found in a distorted ψ trigonal bipyramidal environment, with the tin lone pair occupying an equatorial site. The diaxial angle O Sn O is bent [149.8(2)°] and two sets of Sn O distances are found [Sn O(1) = 2.141 (5)A˚; Sn O(3) = 2.133 (5)A˚; Sn O(2) = 2.296 (6)A˚; Sn O(4) = 2.313 (6)A˚]. Oxidative addition of iodomethane or dihalogens (Br2 or I2) to (Q)2Sn provides a route to new (Q)2RnSnIVX2-n compounds (where X = Br or I;R = CH3 or X).

Synthesis and characterization of derivatives of copper(I) with n-donor ligands—I. Azole and bis(azolyl)alkane compounds. Crystal structure of nitrato bis(tri-p-tolylphosphine)copper(I)

Abstract Several new complexes of the type [Cu(NO 3 )(PPh 3 ) 2 (L) m ] (L = 3-methylpyrazole, 4-methylpyrazole, 3,5-dimethylpyrazole, 4-bromopyrazole or bis(4-methylpyrazol-1-yl)methane, m = 1; L = pyrazole, 1,2,4-triazole or 2-methylimidazole, m = 2), [Cu(NO 3 )(PPh 3 )] (L = 3,4,5-trimethylpyrazole or 4-phenylimidazole), [Cu(NO 3 ) (PAr 3 ) n (L) 3 ] (Ar = p - or m -tolyl, n = 0 or 1, L = pyrazole), [CuX(PPh 3 ) 2 (L)] (X = Cl, Br or I, L = pyrazole or 3,5-dimethylpyrazole) and [CuX(PPh 3 )(L)] (X = Cl or Br, L = bis (pyrazol-1-yl)methane, bis(3,5-dimethylpyrazol-1-yl)methane or bis(triazol-1-yl)methane) have been prepared and characterized by analytical and spectral data. The compounds [CuX(PPh 3 ) 2 (L)] (X = Cl, Br or I, L = pyrazole or 3,5-dimethylpyrazole) are fluxional at temperature above 240 K. The dinuclear compound [Cu 2 (PPh 3 ) 3 (pzH) 2 ] was obtained when the reaction between [CuI(PPh 3 ) 3 ] and pyrazole (pzH) was carried out in methanol containing alkali. In the crystal structure of the title compound, the copper atom is found in a strongly distorted tetrahedral coordination [PCuP: 128.0(1)°] with two long CuO distances [2.217(9) and 2.184(9) A].

High Tc superconductivity in a critical range of micro-strain and charge density in diborides

Expansion of the superlattice of boron layers, with AB2 structure, due to different intercalated A atoms has been studied to understand the emergence of high Tc superconductivity in the diborides. The structure of these metal heterostructures at the atomic limit (MEHALs) (with A = Al, Mg, Ti, Hf, Zr) has been measured by synchrotron x-ray diffraction. The increasing atomic radius of the intercalated A ions induces an increase of (1) the separation between the boron layers and (2) the tensile micro-strain e of the B–B distance within the boron layers. The results show that the superconductivity in these MEHALs appears in a critical region in a phase diagram controlled by two variables, the micro-strain and the charge density (e, ρ).

Organotin(IV) polypyrazolylborates VII. Hydridotris (3,4,5-trimethyl-1 H-pyrazol-1-yl) borates. X-ray crystal structures of K(HB(3,4,5-Me3Pz)3] and [HB(3,4,5-Me3Pz)3 SnMeCl2]

Abstract Tin(IV) and organotin(IV) compounds containing hydridotris(3,4,5-trimethyl-1 H-pyrazol-1-yl)borate (L3), [RnSnCl4-n-1L3] (R=Me, n = 0–2) have been synthesised and studied by NMR (1H, 13C, 119Sn) spectroscopic techniques. The compounds are not fluxional and contain six-coordinate tin(IV) with a tridentate ligand. X-ray crystal structure of [MeSnCl2L3] is reported together with that of the parent potassium hydridotris(3,4,5-trimethyl-1 H-pyrazol-1-yl)borate, K(C18H28N6B) and comparisons are made.