Giorgio Nardin

Structure determination of the 2:1 derivatives of copper(I) bromide and iodide with bis(diphenylphosphino)methane. A simple structural scheme for the formation of (CuX)nLm species

Abstract The structures of the complexes (CuX)2DPM (X = Br, I; DMP = bis(diphenylphosphino)methane) were determined from three dimensional X-ray data collected by counter methods. The iodine derivative crystallizes in the space group Pbca with eight units in a cell defined by a = 17.128(9), b = 18.306(9) c, = 16.508 (8) A. The structure was refined by the least-squares method to a final R factor of 0.054 for 1336 non-zero independent reflections. The bromine derivative crystallizes in the space group P21/c with eight units in a cell defined by a = 23.707(1), b = 17.805(9), c = 16.991(1) A, β = 136.10(5)°. The final least-squares refinement, based on 2489 non-zero independent reflections, gave an R factor of 0.074. Both the compounds have similar structures with a centrosymmetric (CuX)4 core, in which two copper atoms have a tetrahedral geometry, while the other two are trigonal. The above structures are compared with those already reported for other compounds (CuX)nLm and a single scheme is proposed to rationalize the different geometries of the (CuX)n core on the basis of steric and electronic effects.

Cation‐site location in a natural chabazite

(Ca,Sr) chabazite, Cal.aSro.3A13.sSis.3024.13H20 from electron microprobe analysis, rhombohedral, R3m, a = 9.421(4)A, a = 94.20(1) °, U = 829 A 3, Z = 1, g(Mo Ka) = 0.82 mm-~; final R = 0.071 for 578 independent reflections. The location of three cation sites along the [ 1111 direction and of water molecules in the zeolitic cage is discussed and compared with that previously attributed on the basis of a two-dimensional analysis. Introduction. Chabazite is a natural zeolite of group 4, its framework being built up by double six-membered rings (D6R), linked by tilted four-membered rings (Fig. 1). The framework contains large ellipsoidal cavities of 6.7 x 10 A, entered by eight-membered rings (Breck, 1974). The ion-exchange properties and the role played by exchangeable cations in molecule-sieving properties justify the interest for a structural study of chabazites (Mortier, Pluth & Smith, 1977a,b; Pluth, Smith & Mortier, 1977; Barrer, 1978). On the other hand only two-dimensional X-ray diffraction analyses have been reported for hydrated natural chabazites (Smith, Rinaldi & Dent Glasser, 1963; Smith, Knowles & Rinaldi, 1964). From these results it was suggested that cations occupy but one site at x = 0.357, y = 0.494, z = 0.577, so that the crystal should contain two calcium ions and 13 water molecules per unit cell. To verify such an arrangement of cations and water molecules, we have undertaken the three-dimensional 0567-7408/82/020602-04501.00 X-ray analysis of a natural chabazite as the first step of a structural study of chabazites exchanged with transition-metal ions. The natural sample was from north-east Azerbaijan, Iran (Comin-Chiaramonti, Pongiluppi & Vezzalini, 1979). Wavelength dispersive microprobe analysis was carried out on eight single crystals of chabazite, using a fully automated ARLSEMQ instrument. The mean chemical analysis and the atomic ratios evaluated for 24 O atoms are given in Table 1. The chemical analysis indicates that the chabazite is particularly rich in strontium.

Synthesis, molecular structure, and characterization in solution of a new series of inorganic and organometallic Co(III) Schiff base complexes

Abstract A new series of inorganic and organometallic cobalt Schiff base complexes containing the tetradentate ligand tmsalen (4,4′,7,7′, tetramethylsalen) have been synthesized. They have been characterized by 1H NMR and UV–Vis spectroscopy and by ESI MS spectrometry, both in coordinating and non-coordinating solvents. Two inorganic complexes [Co(tmsalen)(L)2]ClO4, where L=py (2) and N-MeIm (3), two dimeric organometallic derivatives [RCo(tmsalen)]2 (R=CH3 (4) and CH2CF3 (7)) and one organometallic penta-coordinated species (R=i-Pr (6)) have been structurally characterized. It is noteworthy that the formation of organometallic dimeric and penta-coordinated species occurs even if the synthesis is carried out in presence of py. Solution data confirm the strong tendency to the penta-coordination of the complexes containing the most electron-donating alkyl groups, which maintain penta-coordination even in methanol.

Synthesis and characterization of palladium(II)-η3-allyl–ylide complexes. X-Ray crystal structure of [PdCl(η3-2-MeC3H4){Ph3PC(H)COMe}]

The complexes [PdCl(η3-2-XC3H4){Ph3PC(H)COR}][R = Me, X = H (1) or Me(2); R = Ph, X = H (3) or Me (4)] have been obtained in high yields by treatment of the dimers [{PdCl(η3-2-XC3H4)}2] with the keto-stabilized ylides Ph3PC(H)COMe [ampp, (acetylmethylene)triphenylphosphorane] and Ph3PC(H)COPh [bmpp, (benzoylmethylene)triphenylphosphorane] in CH2Cl2 solution. They have been characterized by analytical data, i.r., low-temperature 1H and 31P-{1H} n.m.r., and for complex (2) also by 13C n.m.r. spectroscopy. Spectroscopic evidence indicates that complexes (1)–(4) in solution at low temperature are present as two diastereoisomeric forms arising from co-ordination on the metal centre of the asymmetric ylidic carbon atom and of the η3-allyl ligand. In CH2Cl2 solution at room temperature the complexes are in equilibrium with their reagents. Reaction with PPh3 and [AsPh4]Cl gives [ PdCl(η3-2-XC3H4)(PPh3)] and [AsPh4][PdCl2-(η3-2-XC3H4)], respectively, and the free ylide. The X-ray crystal structure of complex (2) was determined showing that, in the solid state, only one diastereoisomer is present. The crystals are monoclinic, space group P21/n with a= 9.668(3), b= 14.879(4), c= 16.226(3)A, β= 99.85(2)°, and Z= 4. Final full-matrix least-squares refinement, based on 3 063 reflections, converged to R= 0.031. The keto-stabilized ylide ligand is C bonded to the metal with a Pd–C distance of 2.193(3)A.

Structural effects of the co-ordination of quadridentate Schiff bases to transition-metal atoms. Structure of NN′-(o-phenylene)bis(salicylideneamine) and of its cobalt(II) complex

Geometrical variations which occur when a quadridentate Schiff-base co-ordinates to a cobalt(II) atom are compared on the basis of the crystal structure analysis of the ligand NN′-(o-phenylene) bis(salicylideneamine)(I) and its CoII derivative in its orthorhombic (II) and monoclinic (III) modifications. Crystals of (I) are monoclinic, space group P21/c, with cell parameters: a= 6.064(3), b= 16.541(7), c= 13.306(7)A, β= 91.5(1)°. Crystals of (II) are orthorhombic, space group P212121, with a= 16.755(7), b= 17.532(8), c= 5.362(3)A, and of (III) are monoclinic, space group P21/nwith a= 10.681(5), b= 8.354(4), c= 18.185(8)A, β= 105.3(1)°. A total of 1 277 (I). 1 113 (II), and 2 558 (III) independent reflexions were used : the structures were solved from diffractometer data by the heavy-atom method and refined to final R factors of 0.056 (I), 0.046 (II), and 0.041 (III). The enolimine form is established for (I) in the solid state. Upon co-ordination, with formation of (II) and (III), the geometrical data suggest that the contribution to the resonance of a ketamine form becomes as important as that of the enolimine. This is in agreementwith a π-orbital delocalization of the electronic charge over the planar complex molecule.

Binding of nitrite and its reductive activation to nitric oxide at biomimetic copper centers

Abstract The reactivity of nitrite towards the copper(II) and copper(I) centers of a series of complexes with tridentate nitrogen donor ligands has been investigated. The ligands are bis[(1-methylbenzimidazol-2-yl)methyl]amine (1-bb), bis[2-(1-methylbenzimidazol-2-yl)ethyl]amine (2-bb), and bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]amine (ddah) and carry two terminal benzimidazole (1-bb, 2-bb) or pyrazole (ddah) rings and a central amine donor residue. While 2-bb and ddah form two adjacent six-membered chelate rings on metal coordination, 1-bb forms two smaller rings of five members. The binding affinity of nitrite and azide to the Cu(II) complexes (ClO4− as counterion) has been determined in solution. The association constants for the two ligands are similar, but nitrite is a slightly stronger ligand than azide when it binds as a bidentate donor. The X-ray crystal structure of the nitrite complex [Cu(ddah)(NO2)]ClO4 (final R=0.056) has been determined: triclinic P1¯space group, a=8.200(2) Å, b=9.582(3) Å, c=15.541(4) Å. It may be described as a perchlorate salt of a “supramolecular” species resulting from the assembly of two complex cations and one sodium perchlorate unit. The copper stereochemistry in the complex is intermediate between SPY and TBP, and nitrite binds to Cu(II) asymmetrically, with Cu-O distances of 2.037(2) and 2.390(3) Å and a nearly planar CuO2N cycle. On standing, solutions of [Cu(ddah)(NO2)]ClO4 in methanol produce the dinuclear complex [Cu(ddah)(OMe)]2(ClO4)2, containing dibridging methoxy groups. In fact the crystal structure analysis (final R=0.083) showed that the crystals are built up by dinuclear cations, arranged on a crystallographic symmetry center, and perchlorate anions. Electrochemical analysis shows that binding of nitrite to the Cu(II) complexes of 2-bb and ddah shifts the reduction potential of the Cu(II)/Cu(I) couple towards negative values by about 0.3 V. The thermodynamic parameters of the Cu(II)/Cu(I) electron transfer have also been analyzed. The mechanism of reductive activation of nitrite to nitric oxide by the Cu(I) complexes of 1-bb, 2-bb, and ddah has been studied. The reaction requires two protons per molecule of nitrite and Cu(I). Kinetic experiments show that the reaction is first order in [Cu(I)] and [H+] and exhibits saturation behavior with respect to nitrite concentration. The kinetic data show that [Cu(2-bb)]+ is more efficient than [Cu(1-bb)]+ and [Cu(ddah)]+ in reducing nitrite.

The crystal and molecular structure of N,N′-ethylene- bis-(acetylacetoneiminato)methylcobalt(III)

Abstract The crystal structure of N,N′ethylene-bis-(acetylacetoneiminato)methyl-cobalt(III), CoO2N2C13H23 has been determined by the heavy atom method and refined to a conventional R-value of 0.090 by the least-squares method using three-dimensional data. The crystals are orthorhombic, space group P212121, with four molecules in the unit cell of dimensions a=5.99±0.01 A, b=13.02±0.02 A, c=17.69±0.03 A. The measured and calculated densities were 1.44 and 1.43 g. cm−3, respectively. The crystal consist of monomeric molecules with a five-coordinate stereochemistry. The nearly planar tetradentate ligand occupies the four basal positions of a distorted rectangular-based pyramid, whose axial position is occupied by the methyl group. The bond lengths are 1.87±0.01 A (mean) for CoO, 1.87±0.01 A (mean) for CoN, 1.95±0.02 A for CoCH3.

Synthetic models for biological trinuclear copper clusters. Trinuclear and binuclear complexes derived from an octadentate tetraamine-tetrabenzimidazole ligand

The new tetraamino-tetrabenzimidazole ligand N,N ′{bis[3-(1-methyl-2-benzimidazolyl]amino}piperazine (L) has been synthesised together with a series of trinuclear and binuclear complexes. Two terminal binding sites with tridentate linkages (A sites) and one central binding site with the bidentate piperazine residue (B site) are used by the ligand to bind divalent metal centres in the trinuclear complexes [Cu H 3 L] 6+ , [Cu H 2 Zn H L] 6+ , and [Cu H 2 Co H L] 6+ . In the binuclear complex [Cu H 2 L] 4+ each nitrogen donor of the piperazine rine acts as an axial ligand for the two coppers bound to A sites, but these piperazine donors can be easily displaced by protonation to form the [Cu H 2 LH 2 )] 6+ species. The structure of this protonated complex has been determined by X-ray analysis. The crystals of composition [Cu H 2 (LH 2 )(CH 3 CN) 4 ][ClO 4 ] 6 ·2H 2 O·3CH 3 CN belong to the monoclinic system. space group P 2 1 /n with cell parametrs a = 10.661 (3), b = 23.014(3), c = 17.217(4)A, β = 96.58(2)°, Z = 2. The citation is arranged on a crystallographic symmetry centre, which is located at the middle of the protonated piperazine ring. The protonation at the piperazine N atoms is supported by the total charge of the cation and by the analysis of the difference Fourier map. The copper ions are five-coordinated, with ligation of the two benzimidazole residues and the tertiary N donor in the basal plane of a distorted square pyramid. Two CH 3 CN molecules, one at the basal, the other at the apical position, complete the coordination polyhedron. The centrosymmetric spacer, between the tertiary N atoms, deviates from the higher C 2h symmetry, so that the two approximately planar N (CH 2 ) 3 groupings lie in two parallel planes. Complexes containing reduced copper ions, [Cu H 2 L 2+ and [Cu H 2 Cu II L] 4+ , have also been obtained, but these ions do not bind to the piperazine B site which can only be used to coordinate divalent metal ions. The complexes containing Cu(II) centres exhibit EPR signals indicative of mononuclear species with tetragonal symmetry. The different coordination environment of [Cu H 2 L] 4+ with respect to [Cu H 2 Zn H L] 6+ , [Cu H 2 Co H L] 6+ or [Cu H 2 (LH 2 ] 6+ is reflected by a difference in the magnetic parameters of the complexes. The EPR spectrum of [Cu H 3 L] 6+ is very similar to those of [Cu H 2 Zn H L] 6+ , typical for Cu(II)-A sites, but the integrated intensity accounts for only about 2.2 paramagnetic centres per molecule. It is likely that a dipolar interaction between one of the Cu(II)-A centres and the Cu(II)-B centre produces severe broadening of the corersponding signals and apparent reduction in the overall EPR intensity. Voltammetric data in acetonitrile solution exhibit quasi-reversible electron transfer for the Cu(II)/Cu(II) couples with estimated reduction potentials in the range 0.39–0.56 V versus NHE. The voltammogram of [Cu H 3 L] 6+ run at low concentration and sweep rate shows that the three-electron transfer in split into one-electron and two-electron steps. Binding experiments show that the complexes bind azide molecules in the terminal mode to the copper (II) centres with affinity constants decreasing in the series: [Cu H 3 L] 6+ > [Cu H 2 L] 4+ . The complexes derived from L are catalytically active in the air oxidation of di-tert-butylcatechol (DTBC). The oxidations are biphasic, with a fast initial stoichiometric phae corresponding to reduction of a pair of copper(II) centres and oxidation of DTBC to quinone followed by the catalytic reaction. The catalytic reaction follows substrate saturation behaviour, with kinetic constants decreasing in the order: [Cu H 3 L 6+ > [Cu H 2 Co H L] 6+ > [Cu H 2 Zn H L] 6+ ≈ [Cu H 2 L] 4+ . Anaerobic experiments show that the two-electron oxidation of DTBC involves reduction of one Cu(II)-A site and the Cu(II)-B site for [Cu H 3 L] 6+ , both the Cu(II)-A sites of Cu H 2 Zn H L] 6+ and [Cu H 2 K] 4+ , but one Cu(II)-A and Co(III) in the case of the mixed [Cu H 2 Co 11 L] 6+ complex, since the Co(II) ion is rapidly oxidised to Co(III) in the conditions in which the catalytic reaction is carried out.

Cation site location in hydrated chabazites. Crystal structure of barium- and cadmium- exchanged chabazites

Chabazite from N.E. Azerbaijan, Iran, was ion-exchanged with barium and cadmium to give Ba 1.8 Al 3.8 Si 8.2 O 24 , 9.7 H 2 O and Ca 0.31 Sr 0.13 Cd 1.4 Al 3.8 Si 8.2 O 24 , 11.6 H 2 O respectively. Both structures were determined at room temperature in the R3m space group with cell dimensions a = 9.420(9) A, α = 94.21(7)° and a = 9.435(9) A, α = 94.66(6)° for the Ba- and Cd-exchanged chabazites. The final R index is 0.097 for (Ba-chab and 0.072 for (Cd)-chab using 685 and 555 independent reflections respectively in the least squares refinement. Comparison of the electron distribution in the cages after ion-exchange with that of the parent chabazite indicates the presence of three chief cation sites: two in the large cage alone the [1 1 1] diagonal and one located near the 8-ring window. The site at the centre of the hexagonal prism, present in the natural chabazite, is not occupied since it may only accommodate small ions such as calcium.

Crystal structures of the hydrated and dehydrated forms of a partially cesium-exchanged chabazite

Crystal structures of a partially cesium-exchanged chabazite h-Cs-CHA, Cs 3.0 Ca 0.4 Al 3.8 Si 8.3 O 24 .9.5H 2 O and its dehydrated form d-Cs-CHA were determined in the rhombohedral space group R ¯3 m . Unit cell parameters and R -indexes were a =9.441 (1)A, α=94.23(2)° and 0.049 for h-Cs-CHA, and a =9.397(2)A, α=93.74(2)° and 0.046 for d-Cs-CHA, respectively. In both h-Cs-CHA and d-Cs-CHA, site IV, at the centre of the S 8 R window, is nearly fully occupied by the Cs + ions. In h-Cs-CHA, a small number of Cs + ions are located in site 1′, along the [111] direction. The Ca 2+ ions occupy site 1″, along the [111] direction, in h-Cs-CHA and site III, at the centre of the D 6 R cage, in d-Cs-CHA. Only minor distortions of the framework geometry occur upon dehydration, in contrast with the results found for chabazites exchanged with other monovalent cations. The framework stability is discussed and related to the dimensions of the Cs + ion.