Investigations on the synthesis, structures, and properties of new copper(I) 2,3-dimethylpyrazine coordination compounds

Five new coordination compounds were prepared, structurally characterized, and investigated for their thermal properties. In the structure of the ligand-rich 4:9 compound, tetra(mu2-chloro)bis(mu2-2,3-dimethylpyrazine-N,N')tetrakis(2,3-dimethylpyrazine-N)tetracopper(I) tris(2,3-dimethylpyrazine)solvate (I), discrete complexes are formed by build up of two [(CuCl-(2,3-dimethylpyrazine)2]2 dimers, which are connected by two 2,3-dimethylpyrazine ligands via mu-N,N' coordination. In the 1:1 compound poly[mu2-chloro-mu2-2,3-dimethylpyrazine-N,N'-copper(I)] (II), (CuCl)2 dimers are found, which are connected by the 2,3-dimethylpyrazine ligands into layers. For this composition, a second polymorphic modification was found (III), which exhibits a different topology of the coordination network and a different packing of the layers. In the most stable 3:2 compound catena[tri(mu2-chloro)bis(mu2-2,3-dimethylpyrazine-N,N')tricopper(I)] (IV), six-membered rings of (CuCl)3 are found, which are connected by the 2,3-dimethylpyrazine ligands into chains. In the ligand-deficient 2:1 compound, poly[di(mu3-chloro)(mu2-2,3-dimethylpyrazine-N,N')dicopper(I)] (V), CuCl double chains are found, which are connected by the 2,3-dimethylpyrazine ligands into layers. On heating, compound I transforms quantitatively into the 3:2 compound IV without the formation of II or III as intermediates. Compound IV is also obtained by heating either the 1:1 compound II or III. On further heating, the 3:2 compound IV loses additional ligands, forming the ligand-deficient 2:1 compound V, which then decomposes into CuCl. The stability, thermal reactivity, and the transition behavior of all compounds were investigated using different thermoanalytical methods. These results are compared with those previously reported for the structurally similar CuCl(2-ethylpyrazine) coordination compounds. The formation and the stability of the different compounds in solution were also investigated.     

Polynuclear palladium complexes with 3,5-dimethylpyrazolate exhibiting three different coordination modes

The characterisation of dinuclear pyrazolato-bridged Pd(II) complexes, [(Pd(mu-dmpz)Cl(Hdmpz))2] (1) and [(Pd(mu-dmpz)(dmpz)(Hdmpz))2] (2) (Hdmpz=dimethylpyrazole), has been carried out. An X-ray study of compound 2 reveals the existence of intramolecular N-H...N hydrogen bonds between neighbouring dmpz groups. Compound 2 has been deprotonated and both acidic hydrogen atoms substituted by two metal atoms of Cu(I), Ag(I) or Au(I) to give the tetranuclear compounds [Pd2M2(mu(2)-dmpz-kappaN,N')6] (M=Cu, Ag, Au). The structure of these compounds resembles a box with a small cavity inside. There are also three pi-electron-rich clefts between each of the three pairs of azolato rings, capable of further complexation. The reactions of [Pd2M2(mu(2)-dmpz-kappaN,N')6] (M=Cu, Ag, Au) with AgClO4 render compounds of the type [(Pd2M2(mu(2)-dmpz-kappaN,N')2(-)(mu(3)-dmpz-kappaN,N',C4)4Ag2(mu(2)-O2ClO2))2] (M=Cu, Ag, Au). The X-ray structures of crystals obtained from a solution of compounds [(Pd2M2(mu(2)-dmpz-kappaN,N')2(mu(3)-dmpz-kappaN,N',C4)4Ag2(mu(2)-O(2)ClO2))2] (M=Ag, Au) in acetone reveals a [(Pd2M2(mu(2)-dmpz-kappaN,N')2(mu(3)-dmpz-kappaN,N',C4)4Ag(OCMe2)(OClO3)Ag(mu(2)-O2ClO2))2] stoichiometry, indicating that only two of the three pi-electron-rich clefts have been used to accommodate Ag+ ions. Each of the silver atoms are located in between two 3,5-dmpz rings and are eta(1)-bonded to the C4 atom of each group.     

Synthesis,Crystal Structures,and Thermal Properties of New Zinc(II) Thiocyanato Coordination Compounds

Reaction of zinc(II) thiocyanate with pyrazine, pyrimidine, pyridazine, and pyridine leads to the formation of new zinc(II) thiocyanato coordination compounds. In bis(isothiocyanato‐N)‐bis(μ₂‐pyrazine‐N,N) zinc(II) ( 1 ) and bis(isothiocyanato‐N)‐bis(μ₂‐pyrimidine‐N,N) zinc(II) ( 2 ) the zinc atoms are coordinated by four nitrogen atoms of the diazine ligands and two nitrogen atoms of the isothiocyanato anions within slightly distorted octahedra. The zinc atoms are connected by the diazine ligands into layers, which are further linked by weak intermolecular S ··· S interactions in 1 and by weak intermolecular C–H ··· S hydrogen bonding in 2 . In bis(isothiocyanato‐N)‐bis(pyridazine‐N) ( 3 ) discrete complexes are found, in which the zinc atoms are coordinated by two nitrogen atoms of the isothiocyanato ligands and two nitrogen atoms of the pyridazine ligands. The crystal structure of bis(isothiocyanato‐N)‐tetrakis(pyridine‐N) ( 4 ) is known and consists of discrete complexes, in which the zinc atoms are octahedrally coordinated by two thiocyanato anions and four pyridine molecules. Investigations using simultaneous differential thermoanalysis and thermogravimetry, X‐ray powder diffraction and IR spectroscopy prove that on heating, the ligand‐rich compounds 1 , 2 , and 3 decompose without the formation of ligand‐deficient intermediate phases. In contrast, compound 4 looses the pyridine ligands in two different steps, leading to the formation of the literature known ligand‐deficient compound bis(isothiocyanato‐N)‐bis(pyridine‐N) ( 5 ) as an intermediate. The crystal structure of compound 5 consists of tetrahedrally coordinated zinc atoms which are surrounded by two isothiocyanato anions and two pyridine ligands. The structures and the thermal reactivity are discussed and compared with this of related transition metal isothiocyanates with pyrazine, pyrimidine, pyridazine, and pyridine.     

Synthesis,crystal structures,and thermal and thermodynamic properties of dimorphic copper(I) coordination polymers

A second modification of the literature-known copper(I) coordination polymer CuCl(pyridazine) was prepared by the reaction of CuCl with pyridazine in acetonitrile. The crystal structure of catena[CuCl(mu(2)-pyridazine-N,N)] is built up of CuCl chains of which each two are connected by the pyridazine ligands to form double chains that are directed parallel to the crystallographic a-axis. In the literature known form LI (CuCl)(2) dimers occur that are connected to chains by the pyridazine ligand. On heating, compound I and LI lose half of the pyridazine ligands and transform to the new 2:1 coordination polymer poly[(CuCl)(2)(pyridazine-N,N)] (II), which transforms at higher temperatures to CuCl. The crystal structure of II is composed of discrete CuCl tetra-chains that are linked by the pyridazine ligands to sheets parallel to (010). The same thermal reactivity is found for the literature-known compound CuBr(pyridazine) (LII), which is isotypic to LI. On heating LII a transformation into the new 2:1 compound poly[(CuBr)(2)(pyridazine-N,N)] (III) is observed, which is isotypic to II. The thermal reactivity of all compounds and the transformation behavior as well as the range of thermodynamic stability of the dimorphic modifications were studied using DTA-TG-MS and DSC measurements, temperature dependent X-ray powder investigations, and crystallization experiments.     

1D and 2D end-to-end azide-bridged cobalt(II) complexes: syntheses, crystal structures, and magnetic properties

Two new polynuclear azido-bridged Co(II) compounds with formulas catena-[Co(mu1,3-N3)(N3)(py)2(H2O)]n (1) and [Co(mu1,3-N3)2(4-acpy)2]n (2) (py=pyridine, 4-acpy=4-acetylpyridine) have been structurally and magnetically characterized. Compound 1 crystallizes in the orthorhombic system Fddd space group and consists of a single end-to-end azido-bridged chain with the Co(II) atoms in a CoN5O slightly distorted octahedron. Compound 2 crystallizes in the monoclinic system P21/a space group and shows 2D sheets built up through end-to-end azido bridges with the Co(II) atoms in a CoN6 environment. The magnetic properties of 1 and 2 are reported. In the high-temperature region, the plots of chiM or chiMT vs T for 1 and 2 compounds can be fitted by using the Curie-Weiss law, and the best-fit values are -69.1 and -22.6 K, respectively. For 2 magnetic ordering and spontaneous magnetization is achieved below Tc=25 K.     

Spectroscopic investigations of new binuclear transition metal complexes of Schiff bases derived from 4,6-diacetylresorcinol and 3-amino-1-propanol or 1,3-diamino-propane

The bifunctional carbonyl compound; 4,6-diacetylresorcinol (DAR) serves as precursor for the formation of different Schiff base ligands, which are either di- or tetra-basic with two symmetrical sets of either O2N or N2O tridentate chelating sites. The condensation of 4,6-diacetylresorcinol with 3-amino-1-propanol (3-AP) or 1,3-diaminopropane (DAP), yields the corresponding hexadentate Schiff base ligands, abbreviated as H4La and H2Lb, respectively. The structures of these ligands were elucidated by elemental analyses, IR, mass, 1H NMR and electronic spectra. Reaction of the Schiff base ligands with copper(II), nickel(II), cobalt(II), zinc(II), cadmium(II), iron(III), chromium(III), vanadyl(IV) and uranyl(VI) ions in 1:2 molar ratio afforded the corresponding transition metal complexes. A variety of binuclear complexes for the metal complexes were obtained with the ligands in its di- or tetra-deprotonated forms. The structures of the newly prepared complexes were identified by elemental analyses, infrared, electronic, mass, 1H NMR and ESR spectra as well as magnetic susceptibility measurements and thermal gravimetric analysis (TGA). The bonding sites are the azomethine and amino nitrogen atoms, and phenolic and alcoholic oxygen atoms. The metal complexes exhibit different geometrical arrangements such as square planar, tetrahedral, square pyramid and octahedral arrangement.     

Syntheses, spectroscopic characterization and thermal behavior on novel binuclear transition metal complexes of hydrazones derived from 4,6-diacetylresorcinol and oxalyldihydrazine

4,6-Diacetylresorcinol (DAR) serves as precursor for the formation of different hydrazone ligands, which are di-, tetra- or hexa-basic with two symmetrical sets of O(2)N tridentate, O(2)N(2) tetradentate or O(4)N(2) hexadentate chelating sites. The condensation of 4,6-diacetylresorcinol (DAR) with oxalyldihydrazine (ODH), in the molar ratio 1:1 and 1:2, yields the corresponding hydrazone, H(6)L(a) and H(4)L(b), ligands, respectively. The structures of these ligands were elucidated by elemental analyses and IR, mass, (1)H NMR and UV-vis spectra. Reactions of the hydrazone ligands with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), iron(III) and chromium(III) ions in 1:2 molar ratio afforded the corresponding transition metal complexes. A variety of binuclear transition metal complexes were obtained in its di-, tetra- or hexa-deprotonated forms. The structures of the newly prepared complexes were identified by elemental analyses and IR, UV-vis, mass, (1)H NMR and ESR spectra, as well as, magnetic susceptibility measurements and thermal gravimetric analysis (TGA). The bonding sites are the azomethine and CO oxygen atoms in either keto or enol forms and amino nitrogen atoms, and phenolic oxygen atoms. The metal complexes exhibit different geometrical structures such as tetrahedral and octahedral arrangements.     

Phosphonate- and ester-substituted 2-cyanoethylene-1,1-dithiolate clusters of zinc: aerial CO2 fixation and unusual binding patterns

Treatment of [Zn(tmeda)Cl2] (tmeda = N, N, N', N'-tetramethylethylenediamine) with a phosphonate-substituted 2-cyanoethylene-1,1-dithiolato ligand in air yields a tetranuclear zinc-carbonate complex 1 having the formula of [Zn4(tmeda)3(mu3-CO3){S2CC(CN)P(O)(OEt)2}3] in which four zinc atoms form a trigonal pyramid with the apical zinc atom in a hitherto unknown S3O3 coordination sphere. It is the first example of aerial CO2 fixation to afford a metal-carbonato compound incorporating 1,1-ethenedithiolate ligands. In sharp contrast, reaction with an isobutyl ester-substituted 2-cyanoethylene-1,1-dithiolate forms a trimeric zinc complex [Zn(tmeda){S2CC(CN)(CO2(i)Bu)}]3, 2, which does not contain the metal-bound carbonate. Compound 2 is the first example of a trinuclear zinc complex composed of four-, five-, and six-coordinated Zn atoms. The unsymmetrical ligand orientation around three zinc centers in 2 suggests that the other structural isomer, which would have an idealized C3 axis, may exist. The reaction of the ethyl ester derivative of 2-cyanoethylene-1,1-dithiolate with [Zn(tmeda)Cl2] affords [{Zn(tmeda)Cl}2{S2CC(CN)(CO2Et)}], 3. The ester-functionalized 1,1-dithiolate ligands in compounds 2 and 3 display a bimetallic, triconnective coordination mode, which is rare for these types of ligands. Some probable intermediates generated from the formation of compound 1 have also been proposed.     

Synthesis and characterization of f-element iodate architectures with variable dimensionality, alpha- and beta-Am(IO3)3

Two americium(III) iodates, beta-Am(IO3)3 (I) and alpha-Am(IO3)3 (II), have been prepared from the aqueous reactions of Am(III) with KIO(4) at 180 degrees C and have been characterized by single-crystal X-ray diffraction, diffuse reflectance, and Raman spectroscopy. The alpha-form is consistent with the known structure type I of anhydrous lanthanide iodates. It consists of a three-dimensional network of pyramidal iodate groups bridging [AmO8] polyhedra where each of the americium ions are coordinated to eight iodate ligands. The beta-form reveals a novel architecture that is unknown within the f-element iodate series. beta-Am(IO3)3 exhibits a two-dimensional layered structure with nine-coordinate Am(III) atoms. Three crystallographically unique pyramidal iodate anions link the Am atoms into corrugated sheets that interact with one another through intermolecular IO3-...IO3- interactions forming dimeric I2O10 units. One of these anions utilizes all three O atoms to simultaneously bridge three Am atoms. The other two iodate ligands bridge only two Am atoms and have one terminal O atom. In contrast to alpha-Am(IO3)3, where the [IO3] ligands are solely corner-sharing with [AmO8] polyhedra, a complex arrangement of corner- and edge-sharing mu2- and mu3-[IO3] pyramids can be found in beta-Am(IO3)3. Crystallographic data: I, monoclinic, space group P2(1)/n, a = 8.871(3) A, b = 5.933(2) A, c = 15.315(4) A, beta = 96.948(4) degrees , V = 800.1(4) A(3), Z = 4; II, monoclinic, space group P2(1)/c, a = 7.243(2) A, b = 8.538(3) A, c = 13.513(5) A, beta = 100.123(6) degrees , V = 822.7(5) A(3), Z = 4.     

Silver(I) coordination chemistry of 2,6-diarylpyrazines. Pi-stacking,anion coordination,and steric control

The silver(I) coordination chemistry of 2,6-diarylpyrazines is reported. Discrete coordination complexes and two-dimensional coordination networks were characterized. The substitution pattern on the pendant aryl groups controlled the type of coordination chemistry involved. Thus, o-methyl-substituted aryl groups held the aryl groups orthogonal to the central pyrazine ring, opening the "hindered" nitrogen atoms to complexation, and polymeric networks were characterized. In the absence of the o-methyl groups, discrete coordination complexes were characterized. Thus, a dimeric 2:1 ligand-silver(I) complex was isolated and characterized on reaction of 2,6-bis(3',5'-dimethylphenyl)pyrazine with silver(I) trifluoroacetate in acetonitrile solvent, while a 2:2 complex was isolated from dichloromethane solvent. Two trifluoroacetate ligands bridge two silver cations in both complexes. Reaction of the same pyrazine ligand with silver(I) tetrafluoroborate yielded a discrete 2:1 complex. A 2:1 complex was isolated on reaction of 2,6-diphenylpyrazine with silver(I) nitrate. These complexes were interlinked by weakly coordinating nitrate anions to form interwoven one-dimensional ribbons. Two-dimensional networks were obtained on reaction of silver(I) trifluoroacetate with either 2,6-bis(2',6'-dimethylphenyl)pyrazine or 2-(2',6'-dimethylphenyl)-6-(3',5'-dimethylphenyl)pyrazine. The networks comprised pyrazine-silver(I) strands cross-linked with complex bridged silver(I) trifluoroacetates.     

Structures, photoluminescence, up-conversion, and magnetism of 2D and 3D rare-earth coordination polymers with multicarboxylate linkages

Four new rare-earth compounds, [Eu(NDC)1.5(DMF)2] (1), [Nd2(NDC)3(DMF)4].H2O (2), [La2(NDC)3(DMF)4].0.5H2O (3), and [Eu(BTC)(H2O)] (4), where NDC = 1,4-naphthalenedicarboxylate, BTC = 1,3,5-benzenetricarboxylate, and DMF = N,N-dimethylformamide, have been synthesized through preheating and cooling-down crystallization. Compounds 1-3 possess similar 2D structures, in which the NDC ligands link M(III) (M = La, Nd, and Eu) ions of two adjacent double chains constructed by NDC ligands and dinuclear M(III) building units. In compound 4, the Eu(III) ion is seven-coordinated by O atoms from six BTC ligands and one terminal water molecule in a distorted pentagonal-bipyramidal coordination environment. If the BTC ligand and the Eu(III) ion are regarded as six-connected nodes, respectively, the structure of compound 4 can be well described as a 3D six-connected net. Furthermore, compounds 1 and 4 exhibit strong red luminescence upon 355-nm excitation. Compound 2 displays interesting emissions in the near-IR region, and yellow (580 nm) pumping of this compound results in UV and intense blue emissions through an up-conversion process. The magnetic properties of compounds 1, 2, and 4 have been studied through measurement of their magnetic susceptibilities over the temperature range of 4-300 K.     

Systematic investigations on magneto-structural correlations of copper(II) coordination polymers based on organic ligands with mixed carboxylic and nitrogen-based moieties

Reaction of copper(II) tetrazolate-5-carboxylate with different neutral N-donor spacer ligands under hydrothermal conditions leads to the formation of five new coordination polymers, [Cu(tzc)(pyz)(0.5)(H(2)O)(2)](n)·H(2)O (1), [Cu(tzc)(pyz)](n) (2), [Cu(tzc)(pym)(H(2)O)](n) (3), [Cu(tzc)(dpe)(0.5)(H(2)O)](n) (4) and [Cu(tzc)(azpy)(0.5)(H(2)O)](n) (5) (tzc = tetrazolate-5-carboxylate, pyz = pyrazine, pym = pyrimidine, dpe = 1,2-di(4-pyridyl)ethylene and azpy = 4,4'-azopyridine). All five structures were characterized by X-ray single-crystal measurements and bulk material can be prepared phase pure in high yields. The crystal structures of the hydrates 1, 3, 4 and 5 show dimeric [Cu(2)(N(tzc)-N(tzc))(2)] building units formed by μ(2)-N1,O1:N2 bridging tzc ligands as the characteristic structural motif. These six-membered entities in 1, 4 and 5 are connected by μ(2)-N,N' bridging N-donor ligands into 1D chains and in 3 into 2D layers. In the crystal structure of compound 2 adjacent Cu(II) cations are connected by μ(2)-N1,O1:N4,O2 bridging tzc ligands into chains, which are further connected by μ(2)-N,N' bridging pyz ligands forming 2D layers. Extensive hydrogen bonds in all compounds play an important role in the construction of their supramolecular networks. Investigations of their thermal properties reveal water release upon heating according to the formation of anhydrates before starting decomposing above 220 °C. Furthermore, the magnetic properties have been studied leading to consistent global antiferromagnetic exchange interactions with coupling constants of J = 3 ± 1 cm(-1) and long-range antiferromagnetic ordering states at lower temperatures.     

Structure and properties of bivalent nickel and copper complexes with pyrazine-amide-thioether coordination: stabilization of trivalent nickel

Acyclic pyrazine-2-carboxamide and thioether containing hexadentate ligand 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpzctb), in its deprotonated form, has afforded light brown [Ni(II)(bpzctb)](1)(S=1) and green [Cu(II)(bpzctb)](2)(S=1/2) complexes. The crystal structures of 1.CH(3)OH and 2.CH(2)Cl(2) revealed that in these complexes the ligand coordinates in a hexadentate mode, affording examples of distorted octahedral M(II)N(2)(pyrazine)N'(2)(amide)S(2)(thioether) coordination. Each complex exhibits in CH(2)Cl(2) a reversible to quasireversible cyclic voltammetric response, corresponding to the Ni(III)/Ni(II)(1) and Cu(II)/Cu(I)(2) redox process. The E(1/2) values reveal that the complexes of bpzctb(2-) are uniformly more anodic by approximately 0.2 V than those of the corresponding complexes with the analogous pyridine ligand, 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpctb), attesting that compared to pyridine, pyrazine is a better stabilizer of the Ni(ii) or Cu(i) state. Coulometric oxidation of the previously reported complex [Ni(II)(bpctb)] and 1 generates [Ni(III)(bpctb)](+) and [Ni(III)(bpzctb)](+) species, which exhibit a LMCT transition in the 470--480 nm region and axial EPR spectra corresponding to a tetragonally elongated octahedral geometry. Complex 2 exhibits EPR spectra characteristic of the d(z(2)) ground state.     

Chelate ring size variations and their effects on coordination chemistry and catechol dioxygenase reactivity of iron(III) complexes

The catechol dioxygenase reactivity of iron(III) complexes using tripodal ligands was investigated. Increasing, as well as decreasing, chelate ring sizes in the highly active complex [Fe(tmpa)(dbc)]B(C6H5)4 (tmpa = tris[(2-pyridyl)methyl]amine; dbc = 3,5-di-tert-butylcatecholate dianion), using related ligands, only resulted in decreased reactivity of the investigated compounds. A detailed low-temperature stopped-flow investigation of the reaction of dioxygen with [Fe(tmpa)(dbc)]B(C6H5)4 was performed, and activation parameters of DeltaH++ = 23 +/- 1 kJ mol(-1) and DeltaS++ = -199 +/- 4 J mol(-1) K(-1) were obtained. Crystal structures of bromo-(tetrachlorocatecholato-O,O')(bis((2-pyridyl)methyl)-2-pyridylamine-N,N',N')-iron(III), (mu-oxo)-bis(bromo)(bis((2-pyridyl)methyl)-2-pyridylamine-N,N',N' ',N')-diiron(III), dichloro-((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N' ',N')-iron(III) and (tetrachlorocatecholato-O,O')((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N' ',N')-iron(III) are reported.     

Reaction of Sulfur with Ga-C Bonds: Synthesis and Characterization of [PyRGaS](3) Formed from Ga(S(2)R)(3) (R = Et, Me)

The reactions of Ga(CH(2)CH(3))(3) with variable amounts of elemental sulfur, S(8), in toluene or benzene at different temperatures result in the insertion of sulfur into the Ga-C bonds to form the compounds Ga[(S-S)CH(2)CH(3)](3) (I) and Ga[(S-S-S)CH(2)CH(3)](3) (II). Compound I was isolated from the reaction at low temperature while at room temperature; compound II was the major product. Compound II exhibited the maximum extent of sulfur insertion even when the reactions were carried out with more than 9.0 equiv of sulfur. The reactions of Ga(CH(3))(3) with various amounts of sulfur in toluene or benzene only result in the formation of compound III, Ga[(S-S)CH(3)](3). In pyridine at -30 degrees C, deinsertion of the sulfur atoms from Ga-S-S-C bonds was observed for the first time from compounds I and III resulting in formation of the six-membered Ga-S ring compounds IV, [PyEtGaS](3), and V, [PyMeGaS](3), respectively. Compounds IV and V were characterized by (1)H NMR, (13)C NMR, elemental analyses, thermogravimetric analysis, and single-crystal X-ray diffraction. Compound IV crystallized in the monoclinic space group P2(1)/n, with a = 9.288(2) ?, b = 14.966(2) ?, c = 19.588(3) ?, beta = 90.690(10) degrees, and Z = 4. Compound V crystallized in the monoclinic space group P2(1)/c, with a = 10.385(1) ?, b = 15.300(2) ?, c = 15.949(2) ?, beta = 107.01(1) degrees, Z = 4, unit cell volume = 2423.5(5) ?(3), R = 0.030, and R(w) = 0.026. The sulfur insertion reaction pathway was investigated by time-dependent and variable-temperature (1)H NMR spectroscopy.     

Synthesis,Crystal Structures,Thermal and Magnetic Properties of New Selenocyanato Coordination Polymers with Pyrazine as Co‐Ligand

Reaction of iron(II), cobalt(II) and nickel(II) selenocyanate with pyrazine in water at room temperature leads to the formation of the isotypic new ligand‐rich 1:2 (1:2 = ratio between metal and co‐ligand) compounds [M(NCSe)₂(pyrazine)₂]_n (M = Fe ( 1 ), Co ( 2 ), Ni ( 3 )). The crystal structure of 2 was determined by X‐ray single crystal analysis and those of 1 and 3 were refined from X‐ray powder data with the Rietveld method. In their crystal structure the metal(II) cations are coordinated by four pyrazine co‐ligands, which connect them into layers, and two terminally N‐bonded selenocyanato anions in a distorted octahedral arrangement. The terminal coordination mode of the selenocyanato anions was further emphasized by IR spectroscopic investigations. On heating, all compounds decompose in a single heating step without the formation of ligand‐deficient intermediates like previously reported for related thiocyanato compounds. Magnetic measurements of compound 1 show a long‐range antiferromagnetic ordering with an ordering temperature of T_N = 6.7 K, which must be mediated by the aromatic π‐system of the pyrazine ligand, whereas 2 and 3 show only Curie–Weiss behavior with antiferromagnetic exchange interactions.     

Synthesis and coordination chemistry of two N2-donor chelating di(indazolyl)methane ligands: structural characterization and comparison of their metal chelation aptitudes

The N(2)-donor bidentate ligands di(1H-indazol-1-yl)methane (L(1)) and di(2H-indazol-2-yl)methane (L(2)) (L in general) have been synthesized, and their coordination behavior toward Zn(II), Cd(II), and Hg(II) salts has been studied. Reaction of L(1) and L(2) with ZnX(2) (X = Cl, Br, or I) yields [ZnX(2)L] species (1-6), that, in the solid state, show a tetrahedral structure with dihapto ligand coordination via the pyrazolyl arms. The reaction of L(1) and L(2) with Zn(NO(3))(2)·6H(2)O is strongly dependent on the reaction conditions and on the ligand employed. Reaction of L(1) with equimolar quantities of Zn(NO(3))(2)·6H(2)O yields the neutral six-coordinate species [Zn(NO(3))(2)(L(1))], 7. On the other hand the use of L(1) excess gives the 2:1 adduct [Zn(NO(3))(2)(L(1))(2)], 8 where both nitrates act as a unidentate coordinating ligand. Analogous stoichiometry is found in the compound obtained from the reaction of L(2) with Zn(NO(3))(2)·6H(2)O which gives the ionic [Zn(NO(3))(L(2))(2)](NO(3)), 10. Complete displacement of both nitrates from the zinc coordination sphere is observed when the reaction between L(1) excess and the zinc salt was carried out in hydrothermal conditions. The metal ion type is also determining structure and stoichiometry: the reaction of L(2) with CdCl(2) gave the 2:1 adduct [CdCl(2)(L(2))(2)] 11 where both chlorides complete the coordination sphere of the six-coordinate cadmium center; on the other hand from the reaction of L(1) with CdBr(2) the polynuclear [CdBr(2)(L(1))](n) 12 is obtained, the Br(-) anion acting as bridging ligands in a six-coordinate cadmium coordination environment. The reaction of L(1) and L(2) with HgX(2) (X = Cl, I, SCN) is also dependent on the reaction conditions and the nature of X, two different types of adducts being formed [HgX(L)] (14: L = L(1), 16, 17: L = L(1) or L(2), X = I, 19: L = L(2), X = SCN) and [HgX(L)(2)] (15: L = L(2), X = Cl, 18: L = L(1), X = SCN). The X-ray diffraction analyses of compounds 1, 2, 4, 5, 7, 8, 10-12, 14, 15, and 19 are also reported. The variations of the coordination geometry parameters in the complexes are compared and discussed.     

The fragmentation of some alkyl thio-phosphate esters by electron-impact

The mass spectra of the following compounds have been studied: and the fragmentation pathways established with the aid of accurate mass measurements, metastable transition and appearance potential determination. The mass spectra show that the sulphur-containing compounds (II to IV) give a stronger molecular ion that that of compound I. A further significant difference is the low intensity, in the mass spectra of II to IV, of the fragments relative to the processes that occur in I, probably because the electron removed upon ionisation belongs to the sulpher atom in compounds II to IV and to the oxygen in compound I. The isomeric compounds, (III and IV) show quite different mass spectra, The radicals containing only Phosphorus and oxygen have an ionisation potential close to 9 eV and the presence of sulphur considerably lowes this value. The measured ionisation potentials of compounds I to IV are respectively, 10·7₀, 9·5₅, 9·2₀ and 9·0₀eV. The heats of formation of compounds II and III have been estimated as ?176 and ?118 Kcal mole^?1, respectively.     

Holo- and hemidirected lead(II) in the polymeric [Pb(4)(mu-3,4-TDTA)2(H2O)2]*4H2O complex. N,N,N',N'-tetraacetate ligands derived from o-phenylenediamines as sequestering agents for lead(II)

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N',N'-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25 degrees C, I = 0.5 mol x dm(-3) in NaClO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(mu-3,4-TDTA)4(H2O)2]*4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants K(Pb)eff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media.     

Highly selective ferric ion sorption and exchange by crystalline metal phosphonates constructed from tetraphosphonic acids

With the motivation of searching for highly selective ferric ion sorbents, two open-framework and microporous materials, {[Pb7(HEDTP)2(H2O)] x 7H2O}n (1) and {[Zn2(H4EDTP)] x 2H2O}n (2) [H8EDTP = N,N,N',N'-ethylenediaminetetrakis(methylenephosphonic acid)], have been synthesized and structurally characterized. The structure of compound 1 results from the seven crystallographically different lead atoms that are bridged by two HEDTP(7-) ligands to yield a three-dimensional microporous framework with tunnels along the a and b axes. Compound 2 features a layer architecture built of square waves along the a axis. The layers are connected by hydrogen bonds between uncoordinated phosphonate oxygen atoms to form a three-dimensional supramolecular network, with one-dimensional tunnels along the a axis. Both compounds 1 and 2 exhibited high ion sorption and exchange capacities for millimolar concentrations of Fe(III). Specifically, when 0.01 g of 1 (or 2) was added to 5 mL of a 1 mM metallic chloride aqueous solution and the mixture was allowed to stand for 2 days at room temperature, compound 1 adsorbed nearly 100% of Fe(III) and compound 2 adsorbed 96.8% of Fe(III). They were also found to adsorb ferric ions selectively over other metal ions, such as Ca(II), Cr(II), Mn(II), Cu(II), Zn(II), Cd(II), etc. Their special ferric ion uptake capacities may be attributed to the cation exchange, coordination bonding, and electrostatic attraction between ferric ions and metal phosphonates.