Dore A. Clemente

Synthesis, molecular structure and reactivity of sodium 5-sulfosalicylate dihydrate and sodium[triaqua(5-sulfosalicylato)copper(II)] 2 hemihydrate

Abstract The crystal and molecular structure of sodium 5-sulfosalicylate dihydrate, Na[(H2Ssal)(H2O)2], (1) (H3Ssal=5-sulfosalicylic acid) has been determined through X-ray diffraction analysis. The 5-sulfosalicylate anion has lost the proton at the SO3H group but retains the usual intermolecular hydrogen bond between phenolic and carboxylic oxygen. The reaction in water of 1 with [Cu(II)(H2O)4]SO4·H2O, gives rise to the green sodium[triaqua(5-sulfosalicylato)copper(II)] 2 hemihydrate, Na[(H2O)3(Ssal)Cu(II)]·2×0.5H2O, (2). The 5-sulfosalicylate anion, (Ssal3−), coordinates rather unusually in the syn–syn coordination mode since it binds bidentately the Cu(II) ion through the carboxylic and the phenolic oxygens, with Cu(II)Ocarboxylic=1.909(4) A and Cu(II)Ophenolic=1.885(4) A distances. Copper(II) completes its square-planar coordination with two water molecules and in addition, perpendicularly to the square-planar coordination plane, another two water molecules with long bonds are present (Cu(II)O=2.518 and 2.912 A). The green complex 2 reacts easily with adenine in water at pH 7 giving rise to the violet tetraadeninato(diaqua)-bis(copper(II)) dihydrate, [Cu2(Ade)4(H2O)2])]·2H2O, (3) (Ade−=adeninato monoanion). This complex, that geometrically resembles copper(II) acetate monohydrate, was already described by Sletten. Finally, on the basis of the present results a possible mechanism for the anticancer activity of complex 2 and of other Cu(II)–salicylate complexes is proposed and discussed.

Some palladium(II) and platinum(II) lead bonded complexes

Abstract Complexes of the type M(PPh 3 ) 2 (PbPh 3 ) 2 [M = Pd, (Ia) and Pt, (Ib)] have been prepared by oxidative addition of hexaphenyldilead to M(PPh 3 ) 4 . The compound Pt(PPh 3 ) 2 (PbPh 3 ) 2 , (Ib), slowly decomposes in dichloromethane to give cis -Pt(PPh 3 ) 2 (PbPh 3 )Ph, (II). which can also be obtained by treating (Ib) with the stoichiometric amount of LiPh. Reaction of Pt(PPh 3 ) 4 with hexamethyldidead gives the complex Pt(PPh 3 ) 2 (PbMe 3 )Me directly. The MPb bonds are easily cleaved by bromine, iodine and hydrogen bromide. The X-ray structure of (II) has been determined using three-dimensional counter data and refined by the least-square method ( R = 0.07). The crystals are monoclinic a = 22.501, b = 10.502, c = 24.120 A, β = 113.43°, space group P 2 1 / c with Z = 4. The complex exhibits a cis configuration, with the coordination around the platinum atom essentially square-planar: the PtPb and PtC(phenyl)bond lengths are 2.698(1) and 2.055(3)A, respectively.

Crystal and molecular structure of [NN′-ethylenebis(salicylideneiminato)](methanol)dioxouranium

The crystal and molecular structure of the title compound has been determined by three-dimensional X-ray methods. Crystals are monoclinic, space group P21/n with cell dimensions: a= 18·695(15), b= 9·012(9), c= 10·652(10)A, γ= 97·52°(5), and Z= 4. The structure was solved by the heavy-atom method from 2239 reflections collected by counter, and refined by least-squares methods to R 0·055.Four atoms of the Schiff base and the oxygen of the methanol are co-ordinated in a plane, forming a slightly irregular pentagon, with the uranyl group perpendicular to this plane. Equatorial U–O(3) and U–O(4) distances are 2·25(2) and 2·33(3)A, while U–O(MeOH) is 2·45(3)A U–N(1) and U–N(2) are 2·57(2) and 2·54(5)A. The only short intermolecular distance, O(4)⋯ O(5) of two neighbouring molecules 2·58A, suggests the presence of a hydrogen bond. The N(1)–CH2–CH2–N(2) group is in a near-gauche conformation (torsion angle 51·8°) and the complex exhibits an overall ‘stepped’ geometry. The stereochemistry and chemical properties of 3dtransition-metal compounds of such ligands are compared.

Structure of two polymorphs of the TTF-TCNE charge-transfer complex and the degree of ionicity

Charge-transfer (CT)π complexes between tetrathiafulvalene (TTF, donor) and tetracyanoethylene (TCNE, acceptor) have been studied. Two polymorphs (α and β) were obtained depending on the solvent used. X-Ray analysis has shown that both polymorphs are monoclinic with space group P21/n, are present in dimeric form [(TTF)2(TCNE)2] and possess very similar molecular dimensions. The crystal structure of both polymorphs is composed of mixed stacks of [TTF]2 and [TCNE]2 dimers in a (TTF)2—(TCNE)2—(TTF)2—(TCNE)2 one-dimensional arrangement. The interaction between TTF and TCNE is very strong in both polymorphs, as indicated by the low interplanar spacing (α phase = 3.13 A, β phase = 3.15 A) and low dihedral angle (α phase = 1.26°, β phase = 2.20°) but they differ for the hydrogen-bonding network and lamellar sheets. A method based on the C—S bond lengths provides for these two CT complexes a degree of ionicity or charge transfer (δ) of 0.54 e, in good agreement with that obtained using IR frequencies (δ= 0.5 ± 0.1 e) and very similar to that of TTF–TCNQ (δ= 0.59 e). Nevertheless, in contrast with TTF–TCNQ, these polymorphs exhibit a very high resistivity (≈ 109Ω cm) that may be explained by the dimerization process and by the mixed-stack formation.

Co-ordination chemistry of adenine (HAde): synthesis and characterization of [CuII(tren)(nucleobase)]X2[tren = tris-(2-aminoethyl)amine, X = Cl or NO3] complexes and crystal structure of [CuII(tren)(Ade)]Cl·2H2O

The five-co-ordinate complexes [CuII(tren)(H2O)]Cl21, [CuII(tren)(HAde)]Cl22, [CuII(tren)(HAde)]-[NO3]23 and [CuII(tren)(Ade)]Cl·2H2O 4[tren = tris(2-aminoethyl)amine and HAde = neutral adenine] have been synthesized and characterized. The geometry and structures of the complexes were studied by electronic and IR spectra and, in addition, the structure of complex 4 has been determined by X-ray crystallography. The physicochemical data for complexes 2 and 3 support the presence of neutral adenine co-ordinated to CuII, whereas in complex 4 the adenine molecule is bound in its monoanionic form, as confirmed by the X-ray analysis [monoclinic, space group P21/a, a= 15.001(2), b= 8.422(1), c= 15.039(2)A, β= 105.90(6)°, Z= 4; R= 0.065 for 2596 unique diffraction data]. The co-ordination polyhedron around the Cu2+ ion is approximately trigonal bipyramidal, with the equatorial sites occupied by the three primary amino nitrogen atoms and the axial positions occupied by the tertiary amino nitrogen and the imidazole N9 nitrogen from the adenine monoanion. The Cu–N(9) distance is rather short at 1.965(9)A. Such selective metal bonding in adenine is very probably promoted by the trigonal-bipyramidal geometry around CuII and by the relatively low steric hindrance of the CuII(tren) moiety.

Structure of trans-chloro-1,4-bis(ϱ-methoxyphenyl)-1,4-diaza-3methylbutadiene-2-yl-bis(triphenylphosphine)-palladium(II)

Abstract The structure of the compound trans-[PdCl { C(N-ϱ-C 6 H 4 OMe)C (Me)N-ϱ-C 6 H 4 OMe} (PPh 3 ) 2 ] was solved, using a conventional combination of Patterson and Fourier functions, least-squares refinements and electron density difference maps, to a reliability index R of 0.069 for the 2923 observed reflections collected by four-circle diffractometer. The palladium arom is surrounded in a roughly planar fashion by two trans phosphorus atoms, a chlorine atom, and a σ-bonded carbon atom of the diazabutadienyl group. This group assumes a trans configuration, the NCCN fragment being virtually planar and nearly normal to the mean coordination plane. The Pdligand bond lengths are: PdC 1.98(1), PdCl 2.41(1),PDP(1) 2.33(1) and PdP(2) 2.35(1) A.

Centrosymmetric and pseudo-centrosymmetric structures refined as non-centrosymmetric

The behaviour of the Flack parameter for centrosymmetric and pseudo-centrosymmetric crystal structures based on crystal structures published as being non-centrosymmetric is presented. It is confirmed for centrosymmetric structures that the value obtained for the Flack parameter is critically dependent on the Friedel coverage of the intensity data, approaching 0.5 for a coverage of 100% and sticking near the starting value for a coverage of 0%. For pseudo-centrosymmetric structures, even those very close to being centrosymmetric, it is found that it is often possible to obtain significant values of the Flack parameter. A theoretical basis for this surprising result is established. It has also been possible to establish an a priori estimate of the standard uncertainty of the Flack parameter based only on the chemical composition of the compound and the wavelength of the radiation. The paper concludes with preliminary presentations of bias in the Flack parameter and of inconsistent chemical and crystallographic data.

Piperazine (and derivatives) Copper(II) compounds: 1,4-dimethylpiperazin-1,4-ium tetrachlorocuprate(II) and CuN bond formation in trichloro(1-methylpiperazin-1-ium-N4)copper(II) and trichloro(1,4-dimethylpiperazin-1-ium-N4)copper(II).

Abstract The ionic salt (H2Me2ppz)2+ [CuCl4]2− (1), the pseudotetrahedral zwitterionic [CuCl3(HMe2ppz)] (2) and [CuCl3(H2Meppz)] (3) complexes of copper(II) have been synthesized and characterized, [(H2Me2ppz)2+=1,4-dimethyl-piperazin-1,4-ium; (HMe2ppz)+=1,4-dimethylpiperazin-1-ium; (H2Meppz)+=1-methylpiperazin-1-ium]. The X-ray diffraction analysis of compound (1) shows that the [CuCl4]2− anion possesses a flattened tetrahedral geometry with the two largest ClCuCl angles being 125.90(5) and 131.41(5)°. The CuCl distances range from 2.215(1) to 2.267(1) A and all the chlorine atoms are involved in bifurcated hydrogen bonds. Physico-chemical measurements, UV–Vis, IR and especially X-ray analysis, prove that complex 2 is the first example of a Cu(II) ion bonded to one nitrogen atom of the piperazinium ring which is not constrained into a macrocyclic ligand. In fact, the CuCl3 group is coordinated to the (HMe2ppz)+ cation in the unusual axial position similar to the Co(II) derivative. The CuCl3N coordination polyhedron exhibits a pseudotetrahedral geometry with the two largest ClCuCl angles being 132.17(12) and 135.38(7)°. Complex 3 shows the same physico-chemical behaviour as complex 2 confirming that this complex also contains a Cu(II)N bond in a pseudo-tetrahedral environment.

Boat versus chair conformation in N-methyl- and N,N′-dimethylpiperazine platinum(II) complexes studied by X-ray analysis. A rare example of metal chelate piperazine: cis-[PtCl2(Me2ppz)] Part I

Abstract The square-planar platinum(II) complexes [PtCl3(H2Meppz)] (1), trans-[PtCl2(H2Meppz)2]2+2Cl−·2H2O (2), and cis-[PtCl2-(Me2ppz)] (3) (HMeppz=N-methylpiperazine, Me2ppz=N,N′-dimethylpiperazine) have been synthesized and characterized by IR, 1H NMR and X-ray diffraction analysis. In complexes 1 and 2 the hexaatomic ring of N-methylpiperazine adopts a chair conformation with the NCH3 and NPt bonds in equatorial position and the two NH bonds in axial position. The coordination to platinum(II) always occurs through the unmethylated nitrogen atom while the methylated nitrogen is protonated, producing a positive charge on the outside surface of the molecule. In addition, complex 1 is present as an amphilonic species since N+HCH3 is balanced by -PtCl3−. In contrast, in complex 3N,N′-dimethylpiperazine adopts a boat conformation stabilized by chelation of the nitrogen donors to platinum(II) so that complex 3 represents a rare example of piperazine chelated to platinum(II). An attempt is also made to correlate the biological activity of chair and boat piperazine complexes with their structural parameters.

30 Space-group corrections: two examples of false polymorphism and one of incorrect interpretation of the fine details of an IR spectrum

Revised structures are reported for 30 crystalline compounds, based on space groups of higher symmetry than originally reported. In 18 cases the Laue class is revised, in seven cases the center of symmetry is added, in two cases the Laue class change is coupled with the addition of the center of symmetry, in two cases the addition of the center of symmetry also requires the addition of systematic absences and, finally, one case of the addition of systematic absences without changing the Laue group is reported. Two examples (CSD refcodes: DAMLIM and ABPZCU01) of false polymorphism and one (PAVJUR) of the erroneous interpretation of the fine details of IR spectra, owing to incorrect space-group determination, have been detected.