X-ray powder structure of a new two-dimensional nickel(II) coordination polymer with pyrazine-2,3,5,6-tetracarboxylic acid.

The new nickel(II) coordination polymer poly[diaquanickel(II)-mu-(pyrazine-2,3,5,6-tetracarboxylato)-tetraaquanickel(II)], [[[Ni(C(8)N(2)O(8))(H(2)O)(2)]Ni(H(2)O)(4)]](n), has been synthesized and characterized both spectroscopically and crystallographically, by X-ray powder diffraction analysis. In this two-dimensional coordination polymer, Ni(II) ions are bridged by pyrazine-2,3,5,6-tetracarboxylic acid, coordinating in a bis-bidentate manner, so forming one-dimensional polymeric chains. The chains are linked by a second Ni(II) ion, via an O atom of the coordinated carboxylate group, resulting in the formation of a two-dimensional layer-like polymer. The remaining coordination sites of the two independent octahedral Ni(II) ions are occupied by water molecules. The layers are connected via hydrogen bonds involving all six coordinated water molecules.

Hydrogen bonding in the inner-salt zwitterion and in two different charged forms of 5,6-bis(2-pyridyl)pyrazine-2,3-dicarboxylic acid.

5,6-Bis(2-pyridyl)pyrazine-2,3-dicarboxylic acid exists as an inner-salt zwitterion, 3-carboxy-5-(2-pyridinio)-6-(2-pyridyl)pyrazine-2-carboxylate, (Ia), C(16)H(10)N(4)O(4). The adjacent pyridine and pyridinium rings are almost coplanar due to the presence of an intramolecular hydrogen bond involving the pyridine N atom and the NH H atom of the pyridinium group. In the crystal of (Ia), symmetry-related molecules are hydrogen bonded via the carboxylic acid OH group and one of the carboxylate O atoms to form a polymer, which exhibits a channel-type structure. In the HCl, HClO(4) and HPF(6) salts, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium chloride 2.25-hydrate, (II), C(16)H(11)N(4)O(4)(+).Cl(-).2.25H(2)O, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium perchlorate trihydrate, (IIIa), C(16)H(11)N(4)O(4)(+).ClO(4)(-).3H(2)O, and 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium hexafluorophosphate trihydrate, (IIIb), C(16)H(11)N(4)O(4)(+).PF(6)(-).3H(2)O, both pyridine rings are protonated. In the perchlorate form, and in the isomorphous hexafluorophosphate form, the molecule possesses C(2) symmetry, with has a symmetrical intramolecular hydrogen bond involving the adjacent carboxylate and carboxylic acid substituents. In the crystals of the chloride and perchlorate (or hexafluorophosphate) salts, hydrogen-bonded polymers are formed which are three-dimensional and one-dimensional, respectively.

Cyano-bridged bimetallic assemblies from hexacyanometalate, [M(CN)6](3-) (M = Mn(III) and Fe(III)), and [M(N4-macrocycle)]2+ (M=Fe(III), Ni(II) and Zn(II)) building blocks. Syntheses, multidimensional structures, and magnetic properties.

Reactions between [M(N(4)-macrocycle)](2+) (M = Zn(II) and Ni(II); macrocycle ligands are either CTH = d,l-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane or cyclam = 1,4, 8, 11-tetrazaazaciclotetradecane) and [M(CN)(6)](3-) (M = Fe(III) and Mn(III)) give rise to cyano-bridged assemblies with 1D linear chain and 2D honeycomblike structures. The magnetic measurements on the 1D linear chain complex [Fe(cyclam)][Fe(CN)(6)].6H(2)O 1 points out its metamagnetic behavior, where the ferromagnetic interaction operates within the chain and the antiferromagnetic one between chains. The Neel temperature, T(N), is 5.5 K and the critical field at 2 K is 1 T. The unexpected ferromagnetic intrachain interaction can be rationalized on the basis of the axially elongated octahedral geometry of the low spin Fe(III) ion of the [Fe(cyclam)](3+) unit. The isostructural substitution of [Fe(CN)(6)](3-) by [Mn(CN)(6)](3-) in the previously reported complex [Ni(cyclam)](3)[Fe(CN)(6)](2).12H(2)O 2 leads to [Ni(cyclam)](3)[Mn(CN)(6)](2).16 H(2)O 3, which exhibits a corrugated 2D honeycomblike structure and a metamagnetic behavior with T(N) = 16 K and a critical field of 1 T. In the ferromagnetic phase (H > 1 T) this compound shows a very important coercitive field of 2900 G at 2 K. Compound [Ni(CTH)](3)[Fe(CN)(6)](2).13H(2)O 4, C(60)H(116)Fe(2)N(24)Ni(3)O(13), monoclinic, A 2/n, a = 20.462(7), b = 16.292(4), c = 27.262(7) A, beta = 101.29(4) degrees, Z = 4, also has a corrugated 2D honeycomblike structure and a ferromagnetic intralayer interaction, but, in contrast to 2 and 3, does not exhibit any magnetic ordering. This fact is likely due to the increase of the interlayer separation in this compound. ([Zn(cyclam)Fe(CN)(6)Zn(cyclam)] [Zn(cyclam)Fe(CN)(6)].22H(2)O.EtOH) 5, C(44)H(122)Fe(2)N(24)O(23)Zn(3), monoclinic, A 2/n, a = 14.5474(11), b = 37.056(2), c = 14.7173(13) A, beta = 93.94(1) degrees, Z = 4, presents an unique structure made of anionic linear chains containing alternating [Zn(cyclam)](2+) and [Fe(CN)(6)](3)(-) units and cationic trinuclear units [Zn(cyclam)Fe(CN)(6)Zn(cyclam)](+). Their magnetic properties agree well with those expected for two [Fe(CN)(6)](3-) units with spin-orbit coupling effect of the low spin iron(III) ions.

Synthesis, structure, and redox and catalytic properties of a new family of ruthenium complexes containing the tridentate bpea ligand.

We have prepared a new family of ruthenium complexes containing the bpea ligand (where bpea stands for N,N-bis(2-pyridyl)ethylamine), with general formula [Ru(bpea)(bpy)(X)](n+) (2, X = Cl(-); 3, X = H(2)O; 4, X = OH(-)), and the trisaqua complex [Ru(bpea)(H2O)(3)](2+), 6. The complexes have been characterized through elemental analyses, UV-vis and (1)H NMR spectroscopy, and electrochemical studies. For complex 3, the X-ray diffraction structure has also been solved. The compound belongs to the monoclinic P2(1)/m space group, with Z = 2, a = 7.9298(6) A, b = 18.0226(19) A, c = 10.6911(8) A, and beta = 107.549(8) degrees. The Ru metal center has a distorted octahedral geometry, with the O atom of the aquo ligand placed in a trans position with regard to the aliphatic N atom of the bpea ligand so that the molecule possesses a symmetry plane. NMR spectra show that the complex maintains its structure in aqueous solution, and that the corresponding chloro complex also has a similar structural arrangement. The pH dependence of the redox potential for the complex [Ru(bpea)(bpy)(H2O)](PF(6))(2) is reported, as well as the ability of the corresponding oxo complex to catalyze the oxidation of benzylic alcohol to benzaldehyde in both chemical and electrochemical manners.

Chelate effect in the gas phase. The complexes of Ni(2,2,6,6-tetramethyl-3,5-heptanedionate)(2) with bidentate ligands.

When a bidentate ligand L-L is added to the square planar Ni(tmhd)(2) (tmhd = tetramethylhepanedionate), the octahedral complex Ni(tmhd)(2)L-L is formed. This reaction has been studied by vis spectroscopy in toluene at 25 degrees C and in the gas phase between 150 and 350 degrees C. It allows the comparison on one hand of the chelate effect of three ligands forming five-membered chelate rings: (i) the flexible N-N ligand tetramethylethylenediamine (TEME); (ii) the rigid N-N ligand 2,2-bipyridine (BPY); (iii) the flexible N-O ligand dimethylaminomethoxyethane (MAO). On the other hand, it allows the comparison of these ligands with the six-membered chelate ring-forming N-N ligand 1,3-tetramethylpropylenediamine (TEMP). From the temperature dependence of the gas-phase stability constants, enthalpies and entropies of the complex-forming reactions have been derived. As there are no solvation effects in the gas phase, the reaction enthalpies are the metal-ligand bond enthalpies. This is of particular interest for the hemilabile ligand MAO. For the N-N ligands, the stability of the metal-ligand bonds decreases in the order TEME > BPY > TEMP. The entropy of the complex formation with the two flexible ligands TEME and MAO is the same, while it is slightly more positive for the rigid BPY and a lot more positive for TEMP. Delta(form)G degrees (298) of the complexes is more negative in the gas phase than in solution because the solvation energy of the reactants is more negative than the solvation energy of the products. This is shown in detail for the formation of Ni(tmhd)(2)BPY where data of a complete thermodynamic cycle are presented.

Bis[4-(2-pyridylmethyleneamino)-phenyl] ether.

The title compound, C(24)H(18)N(4)O, is a bis-bidentate Schiff base ligand exhibiting pseudo-C(2) symmetry. The molecule is twisted about the central ether linkage and exhibits an imine E configuration. In the crystal, the molecules are linked by weak intermolecular C-H.N hydrogen bonds.

Synthesis, structure, and magnetic properties of three new one-dimensional nickel(II) complexes: new magnetic model for the first one-dimensional S = 1 complex with alternating ferro-ferromagnetic coupling.

Three new one-dimensional nickel(II) complexes with the formulas trans-[Ni(N-Eten)2(mu1.3-N3)]n(ClO4)n (1), trans-[Ni(N-Eten)2(mu1.3-N3)]n(PF6)n (2), and cis-[Ni(N-Eten)(mu1.1-N3)2]n (3) (N-Eten = N-Ethylethylenediamine) were synthesized and characterized. Complex 1 has the P2(1)/c space group and consists of a structurally and magnetically alternating one-dimensional antiferromagnetic system with end-to-end azido bridges. Compound 2 has the P1 space group and has alternate units in its structure but consists of a magnetically uniform one-dimensional antiferromagnetic system with end-to-end azido bridges. Complex 3 has the I2/a space group and may be described as a structurally and magnetically alternating one-dimensional ferromagnetic system with double azido bridged ligands in an end-on coordination mode. The chi(M)T versus T plots for compound 3 suggest an intramolecular ferromagnetic interaction between adjacent NiII ions and metamagnetism at low temperature (below 10 K). The magnetization measurements versus applied field confirm this metamagnetic ordering. In order to describe the magnetic data of this compound we developed a general formula for the magnetic susceptibility of the isotropic ferro-ferromagnetic S = 1 Heisenberg chain in terms of the alternation parameter alpha (= J2/J1); this assumed a variation of chi(M)T versus the length N.

Predetermined chirality at metal centers of various coordination geometries: a chiral cleft ligand for tetrahedral (T-4), square-planar (SP-4), trigonal-bipyramidal (TB-5), square-pyramidal (SPY-5), and octahedral (OC-6) complexes

Two tetradentate bispinene-bipyridine type ligands, each with six stereogenic carbon centers, were synthesized from (-)-alpha-pinene. Their ability to predetermine chiral configurations at metal centers was studied. The two diastereoisomers, L1 and L2, differ in their absolute configuration at the bridgehead position. These ligands form metal complexes with Ag(I), Pd(II), Zn(II), Cu(II), and Cd(II), with coordination numbers four, five, and six and with complete control of chirality at the metal centers. Using L1 rather than L2 leads to complexes of inverted absolute configuration at the metal centers. These diastereomeric coordination species can be obtained either as separate compounds or, in some cases, as solids containing them in a 1:1 ratio. Ligands L1 and L2 thus show that the pinene-bipyridines are versatile molecules for the formation of metal complexes with predetermined chirality. In all cases, absolute configurations were determined in the solid state by X-ray diffraction methods and in solution by CD spectroscopy. The sign of exciton couplets from the pi-pi* transitions always agrees with the expectations for a given local configuration at the metal center. The five-coordinate, inherently chiral species of Zn(II) and Cu(II) described in this article are the first examples of trigonal-bipyramidal metal complexes with predetermined absolute configuration containing topologically linear ligands.

A Metamagnetic Two-Dimensional Molecular Material with Nickel(II) and Azide.

Bridging azido ligands transmit both ferro- and antiferromagnetic interactions. The sheetlike structured complex [Ni(µ-N(3))(2)(N,N-Et(2)-N'-Me-en)](n) (see picture) exhibits a range of magnetic behaviors at low temperature. Short-range ferromagnetic and three-dimensional antiferromagnetic ordering compete, giving metamagnetic behaviors. N,N-Et(2)-N'-Me-en=N,N-diethyl-N'-methylethylenediamine.

Crystal structures and magnetic properties of metal complexes bearing four nitronyl nitroxide moieties in the same coordination sphere.

Mononuclear transition metal complexes of the type [M(2,6-NITpy)2](ClO4)2 x solvent (2,6-NITpy = 2,6-bis-(3'-oxide-1'-oxyl-4',4',5',5'-tetramethylimidazolin-2'-yl)pyridine; M = Ni (1), Co (2), Zn (3), Mn (4), Cu (5)) have been synthesized and characterized by single-crystal X-ray diffraction studies. Crystal data: 1, monoclinic, P2(1)/c, Z = 4, a = 20.946(2) A, b = 12.0633(2) A, c = 21.173(2) A, beta = 113.55(1) degrees; 2, monoclinic, P2(1)/c, Z = 4, a = 20.902(2) A, b = 12.0981(8) A, c = 21.215(2) A, beta = 113.130(9) degrees; 3, triclinic, P1, Z = 2, a = 11.410(1) A, b = 12.932(1) A, c = 21.609(2) A, alpha = 96.040(2) degrees, beta = 102.24(1) degrees, gamma = 114.98(1); 4, monoclinic, P2(1)/n, Z = 4, a = 11.5473(8) A, b = 19.212(1) A, c = 25.236(2) A, beta = 98.772(9) degrees; 5, triclinic, P1, Z = 2, a = 12.1604(9) A, b = 12.6961(9) A, c = 18.103(2) A, alpha = 84.191(8) degrees, beta = 73.392(8) degrees, gamma = 66.072(8). The two 2,6-NITpy biradicals behave as terdentate ligands and bind almost perpendicular to each other in meridional positions. In compounds 1-4, the pyridine rings are axially ligated and four different nitronyl nitroxide radicals bind to the metal center through their O(nitroxyl) atoms, forming the equatorial plane of a distorted octahedron. On the contrary, in the copper(II) complex (5), the two N(pyridyl) atoms are found in equatorial positions. Only two nitroxide groups are then bound to the copper(II) ion in the equatorial plane, the other two being axially ligated. The two axially bound nitronyl nitroxide radicals couple ferromagnetically to the copper center (JCu-rad(ax) = + 10 K), whereas a strong antiferromagnetic coupling between this metal ion and the equatorial nitroxide groups (JCu-rad(eq) = -460 K) is observed. The other complexes exhibit strong antiferromagnetic metal-radical interactions: JNi-rad = -240 K, for 1; JMn-rad = -120 K, for 4. Interestingly, the study of the diamagnetic zinc(II) compound (3) reveals a moderate intramolecular antiferromagnetic interaction between radicals coordinated to the same metal center (Jrad-rad = -27.7 K). This interaction is transmitted through space and is also present in the other complexes: Jrad-rad = -14 K, for 1; Jrad-rad = -10 K, for 4; Jrad-rad = -20.5 K, for 5. Antiferromagnetic intermolecular interactions are also present in all the complexes herein studied.

A thermal spin transition in [Co(bpy)3][LiCr(ox)3] (ox = C2O4(2-); bpy = 2,2'-bipyridine).

In the three-dimensional oxalate network structures [M(II)(bpy)3][M(I)-M(III)(ox)3] (ox= C2O4(2-); bpy = 2,2'-bipyridine) the negatively charged oxalate backbone provides perfect cavities for tris-bipyridyl complex cations. The size of the cavity can be adjusted by variation of the metal ions of the oxalate backbone. In [Co(bpy)3][NaCr(ox)3], the [Co(bpy)3]2 + complex is in its usual 4T1(t2g5e(g)2) high-spin ground state. Substituting Na+ by Li+ reduces the size of the cavity. The resulting chemical pressure destabilises the high-spin state of [Co(bpy)3]2+ to such an extent that the 2E(t2g6e(g)1) low-spin state becomes the actual ground state. As a result. [Co(bpy)3][LiCr(ox)3] becomes a spin-crossover system, as shown by temperature-dependent magnetic susceptibility measurements and single-crystal optical spectroscopy, as well as by an X-ray structure determination at 290 and 10 K.

Two 6-substituted 5,6-dihydro-alpha-pyrones from Ravensara anisata.

The leaves and bark dichloromethane extracts of Ravensara anisata showed antifungal activity against the yeast Candida albicans and the phytopathogenic fungus Cladosporium cucumerinum in bioautographic TLC assays. Activity-guided fractionation afforded two new alpha-pyrones: 6R*-(4R*-acetoxy-2S*-hydroxy- 8-phenyloctyl)-5,6-dihydro-2-H-pyran-2-one and 6R*-(2S*-acetoxy-4R*- hydroxy-8-phenyloctyl)-5,6-dihydro-2-H-pyran-2-one. Their structures have been established by NMR spectroscopy, chemical methods and X-ray crystallographic analysis. The antifungal activity against C. albicans and C. cucumerinum was determined for both compounds.

A new 2-hydroxyflavanone from Mosla soochouensis.

A new antifungal and radical scavenging 2-hydroxyflavanone, named mosloflavanone, was isolated from the dichloromethane extract of Mosla soochouensis together with the known mosloflavone and moslosooflavone. Structures were established by spectroscopic and chemical methods, as well as X-ray crystallography.

Inhibition of monoamine oxidase-B by condensed pyridazines and pyrimidines: effects of lipophilicity and structure-activity relationships.

A number of condensed pyridazines and pyrimidines were synthesized and tested for their monoamine oxidase-A (MAO-A) and MAO-B inhibitory activity. Their lipophilicity was examined by measuring partition coefficients and RP-HPLC capacity factors, revealing some peculiar electronic and conformational effects. Further insights were obtained by X-ray crystallography and a thermodynamic study of RP-HPLC retention. Structure-activity relations highlighted the main factors determining both selectivity and inhibitory potency. Thus, while most of the condensed pyridazines were reversible inhibitors of MAO-B with little or no MAO-A effects, the pyrimidine derivatives proved to be reversible and selective MAO-A inhibitors. Substituents on the diazine nucleus modulated enzyme inhibition. A QSAR analysis of X-substituted 3-X-phenyl-5H-indeno[1,2-c]pyridazin-5-ones showed lipophilicity to increase MAO-B and not MAO-A inhibitory activity.

Antifungal and antibacterial naphthoquinones from Newbouldia laevis roots.

From a dichloromethane extract of Newbouldia laevis roots, four new (6-hydroxydehydroiso-alpha-lapachone, 7-hydroxydehydroiso-alpha-lapachone, 5,7-dihydroxydehydroiso-alpha-lapachone and 3-hydroxy-5-methoxydehydroiso-alpha-lapachone) and six known naphthoquinones have been isolated. Their structures were established by spectroscopic methods (UV, EI mass spectrometry, 1H and 13C NMR) and that of 7-hydroxydehydroiso-alpha-lapachone was confirmed by X-ray crystallography. All naphthoquinones showed antifungal activity against Cladosporium cucumerinum and Candida albicans, and activity against the bacteria Bacillus subtilis and Escherichia coli.

Antibacterial phloroglucinols and flavonoids from Hypericum brasiliense.

Three known phloroglucinols (japonicine A, uliginosin A and isouliginosin B) and a new phloroglucinol (hyperbrasiol A) have been isolated from a petrol extract of the leaves and flowers of Hypericum brasiliense. Their structures were established by spectroscopic methods (UV, DCI-MS, 1H and 13CNMR, including SINEPT, HMBC, HSQC, DQFCOSY experiments). The substitution pattern of hyperbrasilol A was confirmed by X-ray crystallography. All four phloroglucinols were antibacterial against Bacillus subtilis in a TLC bioautographic assay. The flavonoids, kaempferol, luteolin, quercetin, quercitrin, isoquercitrin, hyperoside and guaijaverin, were isolated from a methanol extract of the same organs.

Polyphenols from Eriosema tuberosum.

A dichloromethane extract of the roots of Eriosema tuberosum exhibited antifungal activity against Cladosporium cucumerinum and Candida albicans using TLC bioautography. Bioassay-directed fractionation led to the isolation of four new compounds, eriosemaones A-D, together with a known compound, flemichin-D, as the active constituents. Three inactive polyphenols were also isolated after methylation, together with one new chromone, eriosematin. Structures were determined by spectroscopic analysis and from chemical evidence.

An antifungal gamma-pyrone and xanthones with monoamine oxidase inhibitory activity from Hypericum brasiliense.

A new gamma-pyrone (hyperbrasilone), three known xanthones (1,5-dihydroxyxanthone, 5-hydroxy-1-methoxyxanthone and 6-deoxyjacareubin) and betulinic acid have been isolated from a dichloromethane extract of stems and roots of Hypericum brasiliense. Their structures were established by spectroscopic methods (UV, EI-MS, 1H and 13C NMR) and that of the gamma-pyrone was confirmed by X-ray crystallography. Hyperbrasilone and the xanthones were all antifungal against Cladosporium cucumerinum, while the three xanthones showed differing degrees of inhibition of monoamine oxidase A and B.