Adduct formation between alkali metal ions and anionic LV(V)O(2)(-) (L(2-) = tridentate ONS ligands) species: syntheses, structural investigation, and photochemical studies

Syntheses of alkali metal adducts [LVO(2)M(H(2)O)(n)] (1-7) (M = Na(+), K(+), Rb(+), and Cs(+); L = L(1)(-)L(3)) of anionic cis-dioxovanadium(V) species (LVO(2)(-)) of tridentate dithiocarbazate-based Schiff base ligands H(2)L (S-methyl-3-((5-(R-2-hydroxyphenyl))methyl)dithiocarbazate, R = H, L = L(1); R = NO(2), L = L(2); R = Br, L = L(3)) have been reported. The LVO(2)(-) moieties here behave like an analogue of carboxylate group and have displayed interesting variations in their binding pattern with the change in size of the alkali metal ions as revealed in the solid state from the X-ray crystallographic analysis of 1, 3, 6, and 7. The compounds have extended chain structures, forming ion channels, and are stabilized by strong Coulombic and hydrogen-bonded interactions. The number of coordinated water molecules in [LVO(2)M(H(2)O)(n)] decreases as the charge density on the alkali metal ion decreases (n = 3.5 for Na(+) and 1 for K(+) and Rb(+), while, for Cs(+), no coordinated water molecule is present). In solution, compounds 1-7 are stable in water and methanol, while in aprotic solvents of higher donor strengths, viz. CH(3)CN, DMF and DMSO, they undergo photoinduced reduction when exposed to visible light, yielding green solutions from their initial yellow color. The putative product is a mixed-oxidation (mu-oxo)divanadium(IV/V) species as revealed from EPR, electronic spectroscopy, dynamic (1)H NMR, and redox studies.     

Complexation of metal ions, including alkali-earth and lanthanide(III) ions, in aqueous solution by the ligand 2,2',6',2'-terpyridyl

Some metal-ion-complexing properties of the ligand 2,2',6',2'-terpyridyl (terpy) in aqueous solution are determined by following the π-π* transitions of 2 × 10(-5) M terpy by UV-visible spectroscopy. It is found that terpy forms precipitates when present as the neutral ligand above pH ～5, in the presence of electrolytes such as NaClO(4) or NaCl added to control the ionic strength, as evidenced by large light-scattering peaks. The protonation constants of terpy are thus determined at the ionic strength (μ) = 0 to avoid precipitation and found to be 4.32(3) and 3.27(3). The log K(1) values were determined for terpy with alkali-earth metal ions Mg(II), Ca(II), Sr(II), and Ba(II) and Ln(III) (Ln = lanthanide) ions La(III), Gd(III), and Lu(III) by titration of 2 × 10(-5) M free terpy at pH >5.0 with solutions of the metal ion. Log K(1)(terpy) was determined for Zn(II), Cd(II), and Pb(II) by following the competition between the metal ions and protons as a function of the pH. Complex formation for all of these metal ions was accompanied by marked sharpening of the broad π-π* transitions of free terpy, which was attributed to complex formation affecting ligand vibrations, which in the free ligand are coupled to the π-π* transitions and thus broaden them. It is shown that log K(1)(terpy) for a wide variety of metal ions correlates well with log K(1)(NH(3)) values for the metal ions. The latter include both experimental log K(1)(NH(3)) values and log K(1)(NH(3)) values predicted previously by density functional theory calculation. The structure of [Ni(terpy)(2)][Ni(CN)(4)]·CH(3)CH(2)OH·H(2)O (1) is reported as follows: triclinic, P1, a = 8.644(3) ?, b = 9.840(3) ?, c = 20.162(6) ?, α = 97.355(5)°, β = 97.100(5)°, γ = 98.606(5)°, V = 1663.8(9) ?(3), Z = 4, and final R = 0.0319. The two Ni-N bonds to the central N donors of the terpy ligands in 1 average 1.990(2) ?, while the four peripheral Ni-N bonds average 2.107(10) ?. This difference in the M-N bond length for terpy complexes is typical of the complexes of smaller metal ions, while for larger metal ions, the difference is reversed. The significance of the metal-ion size dependence of the selectivity of polypyridyl ligands, and the greater rigidity of ligands based on aromatic groups such as pyridyl groups, is discussed.     

Low-temperature UV-visible and NMR spectroscopic investigations of O(2) binding to ((6)L)Fe(II), a ferrous heme bearing covalently tethered axial pyridine ligands

In this report, we describe the reversible dioxygen reactivity of ((6)L)Fe(II) (1) [(6)L = partially fluorinated tetraphenylporphyrin with covalently appended TMPA moiety; TMPA = tris(2-pyridylmethyl)amine] using a combination of low-temperature UV-vis and multinuclear ((1)H and (2)H) NMR spectroscopies. Complex 1, or its pyrrole-deuterated analogue ((6)L-d(8))Fe(II) (1-d(8)), exhibits downfield shifted pyrrole resonances (delta 28-60 ppm) in all solvents utilized [CH(2)Cl(2), (CH(3))(2)C(O), CH(3)CN, THF], indicative of a five-coordinate high-spin ferrous heme, even when there is no exogenous axial solvent ligand present (i.e., in methylene chloride). Furthermore, ((6)L)Fe(II) (1) exhibits non-pyrrolic upfield and downfield shifted peaks in CH(2)Cl(2), (CH(3))(2)C(O), and CH(3)CN solvents, which we ascribed to resonances arising from the intra- or intermolecular binding of a TMPA-pyridyl arm to the ferrous heme. Upon exposure to dioxygen at 193 K in methylene chloride, ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 433 (Soret), 529 (sh), 559 nm] reversibly forms a dioxygen adduct [UV-vis: lambda(max) = 422 (Soret), 542 nm], formulated as the six-coordinate low-spin [delta(pyrrole) 9.3 ppm, 193 K] heme-superoxo complex ((6)L)Fe(III)-(O(2)(-)) (2). The coordination of the tethered pyridyl arm to the heme-superoxo complex as axial base ligand is suggested. In coordinating solvents such as THF, reversible oxygenation (193 K) of ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 424 (Soret), 542 nm] also occurs to give a similar adduct ((6)L)Fe(III)-(O(2)(-)) (2) [UV-vis: lambda(max) = 418 (Soret), 537 nm. (2)H NMR: delta(pyrrole) 8.9 ppm, 193 K]. Here, we are unable to distinguish between a bound solvent ligand or tethered pyridyl arm as axial base ligand. In all solvents, the dioxygen adducts decompose (thermally) to the ferric-hydroxy complex ((6)L)Fe(III)-OH (3) [UV-vis: lambda(max) = 412-414 (Soret), 566-575 nm; approximately delta(pyrrole) 120 ppm at 193 K]. This study on the O(2)-binding chemistry of the heme-only homonuclear ((6)L)Fe(II) (1) system lays the foundation for a more complete understanding of the dioxygen reactivity of heterobinuclear heme-Cu complexes, such as [((6)L)Fe(II)Cu(I)](+), which are models for cytochrome c oxidase.     

Designing binuclear transition metal complexes: a new example of the versatility of N,N'-bis(2-aminobenzyl)-4,13-diaza-18-crown-6

N,N'-Bis(2-aminobenzyl)-4,13-diaza-18-crown-6 (L) is a versatile receptor able to adapt to the coordinative preferences of different metal cation guests. With first-row transition metal ions, L tends to form binuclear complexes but, depending on the nature of the particular metal ion, the structure of the binuclear complex may be very different. Herein we report a study of the structure and magnetic properties of the corresponding nickel(II) and cobalt(II) complexes. The X-ray crystal structure of the nickel complex (1), with formula [Ni2(L)(CH3CN)4](ClO4)4.CH3CN, shows that this compound presents a symmetric coordination environment with L adopting an anti arrangement. Each Ni(II) ion is six-coordinate in a distorted octahedral environment, and both metal ions are quite far from each other. On the other hand, the X-ray crystal structure of the cobalt complex (2), with formula [Co(L)(mu-OH)Co(CH3CN)](ClO4)3, reveals a rather different structure. Coordination number asymmetry is found: one of the Co(II) is five-coordinate in a distorted trigonal-bipyramidal coordination environment, while the second Co(II) ion is six-coordinate in a distorted octahedral arrangement. Now L adopts a syn arrangement and a hydroxide group acts as a bridge between both cobalt ions. This hydroxo-bridged Co(II) binuclear complex shows structural features that mimic the active site of methionine aminopeptidases. The magnetic properties of 1 and 2 have been investigated in the temperature range 2.0-300 K. Whereas 1 displays a Curie law except for temperatures below 50 K where zero-field splitting of the S= 1 ground state is observed, antiferromagnetic exchange in the singular asymmetric binuclear Co(II) complex 2 has been observed. This magnetic behaviour has been fitted considering first-order spin-orbit coupling in the assumed axially distorted octahedral site and totally quenched orbital contribution in the five-coordinate site in which zero-field splitting of the S= 3/2 ground state is operative.     

Platinum(II)-mediated coupling reactions of acetonitrile with the exocyclic nitrogen of 9-methyladenine and 1-methylcytosine. Synthesis, NMR characterization, and X-ray structures of new azametallacycle complexes

The hydroxo complex cis-[L2Pt(mu-OH)]2(NO3)2, (L = PMePh2, 1a), in CH3CN solution, deprotonates the NH2 group of 9-methyladenine (9-MeAd) to give the cyclic trinuclear species cis-[L2Pt[9-MeAd(-H)]]3(NO3)3, (L = PMePh2, 2a), in which the nucleobase binds the metal centers through the N(1), N(6) atoms. In solution at room temperature, 2a slowly reacts with the solvent to form quantitatively the mononuclear azametallacycle cis-[L2PtNH=C(Me)[9-MeAd(-2H)]]NO3 (L = PMePh2, 3a), containing as anionic ligand the deprotonated form of molecule N-(9-methyl-1,9-dihydro-purin-6-ylidene)-acetamidine. In the same experimental conditions, the hydroxo complex with PPh3 (1b) forms immediately the insertion product 3b. Single-crystal X-ray analyses of 3a and 3b show the coordination of the platinum cation at the N(1) site of the purine moiety and to the N atom of the inserted acetonitrile, whereas the exocyclic amino nitrogen binds the carbon atom of the same CN group. The resulting six-membered ring is slightly distorted from planarity, with carbon-nitrogen bond distances for the inserted nitrile typical of a double bond [C(3)-N(2) = 1.292(7) Angstroms in 3a and 1.279(11) Angstroms in 3b], while the remaining CN bonds of the metallocycle are in the range of 1.335(8)-1.397(10) Angstroms. A detailed multinuclear 1H, 31P, 13C, and 15N NMR study shows that the nitrogen atom of the inserted acetonitrile molecule binds a proton suggesting for 3a,b an imino structure in solution. In DMSO and chlorinated solvents, 3a slowly releases the nitrile reforming the trinuclear species 2a, whereas 3b forms the mononuclear derivative cis-[L2Pt[9-MeAd(-H)]]NO3 (L = PPh3, 4b), in which the adeninate ion chelates the metal center through the N(6) and N(7) atoms. Complex 4b is quantitatively obtained when 1b reacts with 9-MeAd in DMSO and can be easily isolated if the reaction is carried out in CH(2)Cl(2). In CH(3)CN solution, at room temperature, 4b slowly converts into 3b indicating that the insertion of acetonitrile is a reversible process. A similar metal-mediated coupling reaction occurs when 1a,b react with 1-methylcytosine (1-MeCy) in CH(3)CN. The resulting complexes, cis-[L(2)PtNH=C(Me)[1-MeCy(-2H)]]NO3, (L = PMePh2, 5a and PPh3, 5b), contain the deprotonated form of the ligand N-(1-methyl-2-oxo-2,3-dihydro-1H-pyrimidin-4-ylidene)-acetamidine. The X-ray analysis of 5a shows the coordination of the metal at the N(3) site of the pyrimidine cycle and to the nitrogen atom of the acetonitrile, with features of the six-membered metallocycle only slightly different from those found in 3a and 3b. In CD3CN/CH3(13)CN solution complexes 5a,b undergo exchange of the inserted nitrile, while in DMSO or chlorinated solvents they irreversibly release CH3CN to form species not yet fully characterized. No insertion of CH3CN occurs when the hydroxo complexes are stabilized by PMe3 and PMe2Ph.     

Synthesis, crystal structures, and magnetic properties of a new family of heterometallic cyanide-bridged Fe(III)2M(II)2 (M=Mn, Ni, and Co) square complexes

New heterobimetallic tetranuclear complexes of formula [Fe(III){B(pz)(4)}(CN)(2)(μ-CN)Mn(II)(bpy)(2)](2)(ClO(4))(2)·CH(3)CN (1), [Fe(III){HB(pz)(3)}(CN)(2)(μ-CN)Ni(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (2a), [Fe(III){B(pz)(4)}(CN)(2)(μ-CN)Ni(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (2b), [Fe(III){HB(pz)(3)}(CN)(2)(μ-CN)Co(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (3a), and [Fe(III){B(pz)(4)}(CN)(2)(μ-CN)Co(II)(dmphen)(2)](2)(ClO(4))(2)·2CH(3)OH (3b), [HB(pz)(3)(-) = hydrotris(1-pyrazolyl)borate, B(Pz)(4)(-) = tetrakis(1-pyrazolyl)borate, dmphen = 2,9-dimethyl-1,10-phenanthroline, bpy = 2,2'-bipyridine] have been synthesized and structurally and magnetically characterized. Complexes 1-3b have been prepared by following a rational route based on the self-assembly of the tricyanometalate precursor fac-[Fe(III)(L)(CN)(3)](-) (L = tridentate anionic ligand) and cationic preformed complexes [M(II)(L')(2)(H(2)O)(2)](2+) (L' = bidentate α-diimine type ligand), this last species having four blocked coordination sites and two labile ones located in cis positions. The structures of 1-3b consist of cationic tetranuclear Fe(III)(2)M(II)(2) square complexes [M = Mn (1), Ni (2a and 2b), Co (3a and 3b)] where corners are defined by the metal ions and the edges by the Fe-CN-M units. The charge is balanced by free perchlorate anions. The [Fe(L)(CN)(3)](-) complex in 1-3b acts as a ligand through two cyanide groups toward two divalent metal complexes. The magnetic properties of 1-3b have been investigated in the temperature range 2-300 K. A moderately strong antiferromagnetic interaction between the low-spin Fe(III) (S = 1/2) and high-spin Mn(II) (S = 5/2) ions has been found for 1 leading to an S = 4 ground state (J(1) = -6.2 and J(2) = -2.7 cm(-1)), whereas a moderately strong ferromagnetic interaction between the low-spin Fe(III) (S = 1/2) and high-spin Ni(II) (S = 1) and Co(II) (S = 3/2) ions has been found for complexes 2a-3b with S = 3 (2a and 2b) and S = 4 (3a and 3b) ground spin states [J(1) = +21.4 cm(-1) and J(2) = +19.4 cm(-1) (2a); J(1) = +17.0 cm(-1) and J(2) = +12.5 cm(-1) (2b); J(1) = +5.4 cm(-1) and J(2) = +11.1 cm(-1) (3a); J(1) = +8.1 cm(-1) and J(2) = +11.0 cm(-1) (3b)] [the exchange Hamiltonian being of the type H? = -J(S?(i)·S?(j))]. Density functional theory (DFT) calculations have been used to substantiate the nature and magnitude of the exchange magnetic coupling observed in 1-3b and also to analyze the dependence of the exchange magnetic coupling on the structural parameters of the Fe-C-N-M skeleton.     

A luminescent supermolecule with gold(I) quinoline-8-thiolate: crystal structure,spectroscopic and photophysical properties

The trinuclear complex [(8-QNS)(2)Au(AuPPh(3))(2)].BF(4) (8-QNS = quinoline-8-thiolate), with intramolecular gold(I)...gold(I) distances of 3.0952(4) and 3.0526(3) A, is aggregated to form a novel hexanuclear supermolecule, ([(8-QNS)2(Au(AuPPh3)2])2.(BF4)2, via a close intermolecular gold(I)...gold(I) contact of 3.1135(3) A. The beautiful hexanuclear supermolecule has an inversion center, and the six metal centers can be viewed as roughly coplanar. Six gold(I) ions are embedded in an ellipse and surrounded by 4 quinoline and 12 phenyl rings. The title compound shows interesting spectroscopic and luminescence properties dependent on the solvent polarity; i.e., it emits at ca. 440 and 636 nm in CH(2)Cl(2) and only at ca. 450 nm in CH(3)CN. The long-lived emission at ca. 636 nm (16.2 micros) in CH(2)Cl(2) is quenched by polar solvents such as CH(3)CN and CH(3)OH with quenching constants as 1.00 x 10(5) and 3.03 x 10(4) s(-1) M(-1), respectively, which is suggested to be related to the presence or absence of gold(I)...gold(I) interactions due to scrambling of the [AuPPh(3)]+ units, isolobal to H+.     

Synthesis and structures of a 3-sila-beta-diketiminatomagnesium bromide, ketenimide and triflate

The crystalline compounds [Mg(Br)(L)(thf)].0.5Et2O [L = {N(R)C(C6H3Me2-2,6)}2SiR, R = SiMe3] (1), [Mg(L){N=C=C(C(Me)=CH)2CH2}(D)2] [D = NCC6H3Me2-2,6 (2), thf (3)] and [{Mg(L)}2{mu-OSO(CF3)O-[mu}2] (4) were prepared from (a) Si(Br)(R){C(C6H3Me2-2,6)=NR}2 and Mg for (1), (b) [Mg(SiR3)2(thf)2] and 2,6-Me2C6H3CN (5 mol for (2), 3 mol for (3)), and (c) (2) + Me3SiOS(O)2CF3 for (4); a coproduct from (c) is believed to have been the trimethylsilyl ketenimide Me3SiN=C=C{C(Me)=CH}2CH2 (5).     

Coordination algorithms control molecular architecture: [CuI4(L2)4]4+ grid complex versus [MII2(L2)2X4]y+ side-by-side complexes (M=Mn,Co, Ni,Zn; X=solvent or anion) and [FeII(L2)3][Cl3FeIIIOFeIIICl3

The synthesis and characterisation of a pyridazine-containing two-armed grid ligand L2 (prepared from one equivalent of 3,6-diformylpyridazine and two equivalents of p-anisidine) and the resulting transition metal (Zn, Cu, Ni, Co, Fe, Mn) complexes (1-9) are reported. Single-crystal X-ray structure determinations revealed that the copper(I) complex had self-assembled as a [2 x 2] grid, [Cu(I) (4)(L2)(4)][PF(6)](4).(CH(3)CN)(H(2)O)(CH(3)CH(2)OCH(2)CH(3))(0.25) (2.(CH(3)CN)(H(2)O)(CH(3)CH(2)OCH(2)CH(3))(0.25)), whereas the [Zn(2)(L2)(2)(CH(3)CN)(2)(H(2)O)(2)][ClO(4)](4).CH(3)CN (1.CH(3)CN), [Ni(II) (2)(L2)(2)(CH(3)CN)(4)][BF(4)](4).(CH(3)CH(2)OCH(2)CH(3))(0.25) (5 a.(CH(3)CH(2)OCH(2)CH(3))(0.25)) and [Co(II) (2)(L2)(2)(H(2)O)(2)(CH(3)CN)(2)][ClO(4)](4).(H(2)O)(CH(3)CN)(0.5) (6 a.(H(2)O)(CH(3)CN)(0.5)) complexes adopt a side-by-side architecture; iron(II) forms a monometallic cation binding three L2 ligands, [Fe(II)(L2)(3)][Fe(III)Cl(3)OCl(3)Fe(III)].CH(3)CN (7.CH(3)CN). A more soluble salt of the cation of 7, the diamagnetic complex [Fe(II)(L2)(3)][BF(4)](2).2 H(2)O (8), was prepared, as well as two derivatives of 2, [Cu(I) (2)(L2)(2)(NCS)(2)].H(2)O (3) and [Cu(I) (2)(L2)(NCS)(2)] (4). The manganese complex, [Mn(II) (2)(L2)(2)Cl(4)].3 H(2)O (9), was not structurally characterised, but is proposed to adopt a side-by-side architecture. Variable temperature magnetic susceptibility studies yielded small negative J values for the side-by-side complexes: J=-21.6 cm(-1) and g=2.17 for S=1 dinickel(II) complex [Ni(II) (2)(L2)(2)(H(2)O)(4)][BF(4)](4) (5 b) (fraction monomer 0.02); J=-7.6 cm(-1) and g=2.44 for S= 3/2 dicobalt(II) complex [Co(II) (2)(L2)(2)(H(2)O)(4)][ClO(4)](4) (6 b) (fraction monomer 0.02); J=-3.2 cm(-1) and g=1.95 for S= 5/2 dimanganese(II) complex 9 (fraction monomer 0.02). The double salt, mixed valent iron complex 7.H(2)O gave J=-75 cm(-1) and g=1.81 for the S= 5/2 diiron(III) anion (fraction monomer=0.025). These parameters are lower than normal for Fe(III)OFe(III) species because of fitting of superimposed monomer and dimer susceptibilities arising from trace impurities. The iron(II) centre in 7.H(2)O is low spin and hence diamagnetic, a fact confirmed by the preparation and characterisation of the simple diamagnetic iron(II) complex 8. M?ssbauer measurements at 77 K confirmed that there are two iron sites in 7.H(2)O, a low-spin iron(II) site and a high-spin diiron(III) site. A full electrochemical investigation was undertaken for complexes 1, 2, 5 b, 6 b and 8 and this showed that multiple redox processes are a feature of all of them.     

A photometric study of the complexation reaction between Alizarin complexan and zinc(II), nickel(II), lead(II), cobalt(II) and copper(II)

The complexation reaction between Alizarin complexan ([3-N,N-di(carboxymethyl)aminomethyl]-1,2-dihydroxyanthraquinone; H(4)L) and zinc(II), nickel(II), lead(II), cobalt(II) and copper(II) has been studied by a spectrophotometric method. All these metal ions form 1:1 complexes with HL; 2:1 metal:ligand complex were found only for Pb(II) and Cu(II). The stability constants are (ionic strength I = 0.1, 20 degrees C): Zn(2+) + HL(3-) right harpoon over left harpoon ZnHL(-) log K +/- 3sigma(log K) = 12.19 +/- 0.09 (I = 0.5) Ni(2+) + HL(3-) right harpoon over left harpoon NiHL(-) log K +/- 3sigma(log K) = 12.23 +/- 0.21 Pb(2+) + HL(3-) right harpoon over left harpoon PbHL(-) log K +/- 3sigma(log K) = 11.69 +/- 0.06 PbHL(-) + Pb(2+) right harpoon over left harpoon Pb(2)L + H(+) log K approximately -0.8 Co(2+) + HL(3-) right harpoon over left harpoon CoHL(-) log K 3sigma(log K) = 12.25 + 0.13 Cu(2+) + HL(3-) right harpoon over left harpoon CuHL(-) log K 3sigma(log K) = 14.75 +/- 0.07 Cu(2+) + CuHL(-) right harpoon over left harpoon Cu(2)L + H(+) log K approximately 3.5 The solubility and stability of both the reagent and the complexes and the closenes of the values of the stability constants make this reagent suitable for the photometric detection of several metal ions in the eluate from an ion-exchange column.     

Stable enols of amides ArNHC(OH)=C(CN)CO(2)R. E/Z enols,equilibria with the amides,solvent effects,and hydrogen bonding

The structures of anilido cyano(fluoroalkoxycarbonyl)methanes ArNHCOCH(CN)CO(2)R, where R = CH(2)CF(3) or CH(CF(3))(2), Ar = p-XC(6)H(4), and X = MeO, Me, H, or Br, were investigated. In the solid state, all exist as the enols ArNHC(OH)=C(CN)CO(2)R 7 (R = CH(2)CF(3)) and 9 (R = CH(CF(3))(2)) with cis arrangement of the hydrogen-bonded ROC=O.HO moiety and a long C1=C2 bond. The product composition in solution is solvent dependent. In CDCl(3) solution, only a single enol is observed, whereas in THF-d(8) and CD(3)CN, two enols (E and Z) are the major products, and the amide is the minor product or not observed at all (K(Enol) 1.04-9 (CD(3)CN, 298 K) and 3 to >/=100 (THF, 300 K)). The percentage of the amide and the Z-enol increase upon an increase in temperature. In all solvents, the percent enol is higher for 9 than for 7. In CD(3)CN, more enol is observed when the aryl group is more electron-donating. The spectra in DMSO-d(6) and DMF-d(7) indicate the presence of mostly a single species, whose spectra do not change on addition of a base and is ascribed to the anion of the ionized carbon acid. Comparison with systems where the CN is replaced by a CO(2)R group (R = CH(2)CF(3), CH(CF(3))(2)) shows a higher percentage of enol for the CN-substituted system. Intramolecular (to CO(2)R) and intermolecular hydrogen bonds determine, to a significant extent, the stability of the enols, their Z/E ratios (e.g., Z/E (THF, 240 K) = 3.2-4.0 (7) and 0.9-1.3 (9)), and their delta(OH) in the (1)H spectra. The interconversion of Z- and E-enol by rotation around the C=C bond was studied by DNMR, and DeltaG() values of >/=15.3 and 14.1 +/- 0.4 kcal/mol for Z-7 and Z-9 were determined. Features of the NMR spectra of the enols and their anions are discussed.     

CuI complexes with N,N',S,S' scorpionate ligands: evidence for dimer-monomer equilibria

The heteroscorpionate N, N', S, S' donor ligands 4-methoxy-3,5-dimethyl-2-(3-(methylthio)-1-(3-(2-(methylthio)phenyl)-1H-pyrazol-1-yl)propyl)pyridine (L(a)) and 4-methoxy-3,5-dimethyl-2-(2-(methylthio)-1-(3-(2-(methylthio)phenyl)-1H-pyrazol-1-yl)ethyl)pyridine (L(b)) were prepared. The Cu(I) complexes [Cu(L(a))]2(BF4)2 (a2(BF4)2) and [Cu(L(b))]2(BF4)2 (b2(BF4)2) were synthesized and characterized by X-ray crystallography. Both compounds exhibit a dinuclear structure, presenting each Cu(I) center in a distorted N, N', S, S' tetrahedral environment. On the basis of nuclear magnetic resonance (NMR) and ESI-mass data, the presence of a mononuclear complex in equilibrium with the dimer was hypothesized for both complexes. The dimerization constants of the processes, 2a(+) = a2(2+) and 2b(+) = b2(2+) , were obtained by (1)H NMR dilution experiments (fast-exchange regime) in CD 3CN: log K(a2(2+)) = 3.55(6) and log K(b2(2+)) = 3.23(5) at 300 K. Thermodynamic parameters were determined by a van't Hoff analysis (280-310 K temperature range): DeltaH(0)(a2(2+)) = -12(1) kJ mol (-1), DeltaH(0)(b2(2+)) = -10(1) kJ mol(-1), DeltaS(0)(a2(2+)) = +27(4) kJ mol (-1), and DeltaS(0)(b2(2+)) = +28(4) kJ mol (-1). Pulsed gradient spin-echo (PGSE) NMR experiments provided the weighted-average hydrodynamic volume (VH) of the species present in CD 3CN solution at different copper concentrations (CCu). Nonlinear interpolation of VH as a function of C Cu for a dimer-monomer equilibrium led to the hydrodynamic volumes of both monomers (VH(0)(M)) and dimers (VH(0)(D)): VH(0)(a(+)) = 620(40) A(3), VH(0)(b(+)) = 550(10) A(3), VH(0)(a2(2+)) = 950(20) A(3), and VH(0)(b2(2+)) = 900(10) A(3). Cyclic voltammetry experiments performed in CH3CN and CH2Cl2 showed a quasi-reversible to irreversible behavior of the Cu(I)/Cu(II) redox couple for both complexes.     

Intracluster anionic oligomerization of acrylic ester molecules initiated by electron transfer from an alkali metal atom

Stabilities and intracluster reactions have been investigated by photoionization mass spectrometry for clusters composed of an alkali metal atom (M; Na and K) and acrylic ester molecules, CH(2)=CHCO(2)R, such as methyl acrylate (MA; R = CH(3)) and ethyl acrylate (EA; R = C(2)H(5)). The following two features are commonly observed in the photoionization mass spectra of M(CH(2)=CHCO(2)R)(n): (1) The ion with n = 3 is clearly observed as a magic number. (2) Fragmented cluster ions with the loss of ROH, [M(CH(2)=CHCO(2)R)(n) - ROH] are detected only for n = 3. These features are both explained by an intracluster oligomerization reaction initiated by electron transfer from the metal atoms. The magic number trimer is concluded to have the stable structure of cyclohexane derivatives as a result of oligomerization. The fragmentation reaction is explained by Dieckmann cyclization after anionic oligomerization to produce another isomer of the trimer. The intracluster electron transfer is also supported by theoretical calculation for Na(MA) based on density functional theory.     

A simple halide-to-anion exchange method for heteroaromatic salts and ionic liquids

A broad and simple method permitted halide ions in quaternary heteroaromatic and ammonium salts to be exchanged for a variety of anions using an anion exchange resin (A(-) form) in non-aqueous media. The anion loading of the AER (OH(-) form) was examined using two different anion sources, acids or ammonium salts, and changing the polarity of the solvents. The AER (A(-) form) method in organic solvents was then applied to several quaternary heteroaromatic salts and ILs, and the anion exchange proceeded in excellent to quantitative yields, concomitantly removing halide impurities. Relying on the hydrophobicity of the targeted ion pair for the counteranion swap, organic solvents with variable polarity were used, such as CH(3)OH, CH(3)CN and the dipolar nonhydroxylic solvent mixture CH(3)CN:CH(2)Cl(2) (3:7) and the anion exchange was equally successful with both lipophilic cations and anions.     

A novel bis tridentate bipyridine carboxamide ligand and its complexation to copper(II): synthesis, structure, and magnetism

A new bis tridentate ligand 2,2'-bipyridine-3,3'-[2-pyridinecarboxamide] H(2)L(1) which can bind transition metal ions has been synthesized via the condensation of 3,3'-diamino-2,2'-bipyridine together with 2-pyridine carbonyl chloride. Two copper(II) coordination compounds have been prepared and characterized: [Cu(2)(L(1))(hfac)(2)].3CH(3)CN.H(2)O (1) and [Cu(2)(L(1))Cl(2)].CH(3)CN (2). The single-crystal X-ray structures reveal that complex 1 crystallizes in the triclinic space group P1, with the unit cell parameters a = 12.7185(6) A, b = 17.3792(9) A, c = 19.4696(8) A, alpha = 110.827(2) degrees, beta = 99.890(3) degrees, gamma = 97.966(3) degrees, V = 3868.3(3) A3, Z = 4, R = 0.0321 and R(w) = 0.0826. Complex 2 crystallizes in the monoclinic space group P2(1)/n with the unit cell parameters a = 12.8622(12) A, b = 9.6100(10) A, c = 19.897(2) A, beta = 102.027(3) degrees, V = 2405.3(4) A(3), Z = 4, R = 0.0409 and R(w) = 0.1005. In both complexes the ligand is in the dianionic form and coordinates the divalent Cu(II) ions via one amido and two pyridine nitrogen donor atoms. In 1, the coordination geometry around both Cu(II) ions is best described as distorted trigonal bipyramidal where the remaining two coordination sites are satisfied by hexafluoroacetylacetonate counterions. In 2 both Cu(II )ions adopt a (4 + 1) distorted square pyramidal geometry. One copper forms a longer apical bond to an adjacent carbonyl oxygen atom, whereas the second copper is chelated to a neighboring Cu-Cl chloride ion to afford a mu-Cl-bridged dimerized [Cu(2)(L(1))Cl(2)](2) complex. The magnetic susceptibility data for 1 (2 -270 K), reveal the occurrence of weak antiferromagnetic interactions between the Cu(II) ions. In contrast, variable-temperature magnetic susceptibility measurements for 2 reveal more complex magnetic properties, with the presence of a weak antiferromagnetic exchange (J = -10.1 K) between the copper ions in each dinuclear copper complex and a stronger ferromagnetic exchange interaction (J = 32.9 K) between the Cu(II) ions of the Cu(mu-Cl)(2)Cu dimeric bridging units.     

Competing non-covalent interactions in alkali metal ion-acetonitrile-water clusters

Competitive ion-dipole, ion-water, and water-water interactions were investigated at the molecular level in M+ (CH3CN)n(H2O)m cluster ions for M = Na and K. Different [n,m] combinations for two different n + m cluster sizes were characterized with infrared predissociation spectroscopy in the O-H stretch region and MP2 calculations. In all cases, no differences were observed between the two alkali metal ions. The results showed that at the n + m = 4 cluster size, the solvent molecules interact only with the ion, and that the interaction between the ion and the large dipole moment of CH3CN decreases the ion-water electrostatic interactions. At the n + m = 5 cluster size, at least two different hydrogen-bonded structures were identified. In these structures, the ion-dipole interaction weakens the ability of the ion to polarize the hydrogen bonds and thus decreases the strength of the water-water interactions in the immediate vicinity of the alkali metal ion.     

Photodissociation of CO from [Ru3(mu3-O)(mu-OOCCH3)6(CO)L2] in acetonitrile, where L = pyridine, 4-cyanopyridine and methanol

Photodissociation of CO from oxo-centered trinuclear ruthenium clusters [Ru3(mu3-O)(mu-OOCCH3)6(CO)L2] (L = pyridine (py): 1; 4-cyanopyridine (cpy): 2; methanol: 3) dissolved in organic solvents has been examined. Upon photolysis (> or = 290 nm, a 450-W Xe lamp), an absorption peak at 585 nm observed for 1 in CH3CN decreases its intensity and a new absorption band appears and grows at 896 nm. This spectral change, presenting isosbestic points, corresponds to photosubstitution of CO in 1 to form [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)(py)2] 4. Photoexcitation of carbonyl complexes 2 and 3 in CH3CN also affords the corresponding CH3CN-coordinated complexes [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)(cpy)2] 6 and [Ru3(mu3-O)(mu-OOCCH3)6(CH3CN)3] 7, respectively. The photosubstitution reactions (excitation wavelength, > or = 290 nm) are well described by the first-order kinetics: k = 7.3 x 10(-4) s(-1) for 1, 4.9 x 10(-4) s(-1) for 2 and 5.1 x 10(-4) s(-1) for 3 (298 K). In the presence of a 100-fold excess of py, photolysis of 1 yields a tris(py) complex [Ru3(mu3-O)(mu-OOCCH3)6(py)3] 5 via photochemical loss of CO followed by coordination of py. The overall reaction (photochemical and thermal) is also confirmed by 1H NMR spectroscopy. The dissociative character of the photosubstitution is supported by negligible effects of the concentration of the entering pyridine molecule, the nature of solvents and the type of terminal monodentate ligands (other than CO) attached to the cluster. Quantum yield measurements with varied excitation wavelengths have shown that absorption bands located in the UV region (< 400 nm) play a principal role in photosubstitution, whereas an absorption band in the visible region (centered at approximately 580 nm), ascribed to an "intracluster" charge transfer, is not at all responsible for photosubstitution.     

The monoanionic pi-radical redox state of alpha-iminoketones in bis(ligand)metal complexes of nickel and cobalt

The electronic structures of nickel and cobalt centers coordinated by two alpha-iminoketone ligands have been elucidated using density functional theory calculations and a host of physical methods such as X-ray crystallography, cyclic voltammetry, UV-vis spectroscopy, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements. In principle, alpha-iminoketone ligands can exist in three oxidation levels: the closed-shell neutral form (L)0, the closed-shell dianion (L(red))(2-), and the open-shell monoanion (L*)(-). Herein, the monoanionic pi-radical form (L*)(-) of alpha-iminoketones is characterized in the compounds [(L*)2Ni] (1) and [(L*)2Co] (3), where (L*)(-) is the one-electron-reduced form of the neutral ligand (t-Bu)N=CH-C(Ph)=O. The metal centers in 1 and 3 are divalent, high-spin, and coupled antiferromagnetically to two ligand pi radicals. These bis(ligand)metal complexes can be chemically oxidized by two electrons to give the dications [trans-(L)2Ni(CH3CN)2](PF6)2 (2) and [trans-(L)2Co(CH3CN)2](PF6)2 (4), wherein the ligands are in the neutral form.     

Coordination site-dependent cation binding and multi-responsible redox properties of Janus-head metalloligand, [Mo(V)(1,2-mercaptophenolato)3

The redox-active fac-[Mo(V)(mp)(3)](-) (mp: o-mercaptophenolato) bearing asymmetric O- and S-cation binding sites can bind with several kinds of metal ions such as Na(+), Mn(II), Fe(II), Co(II), Ni(II), and Cu(I). The fac-[Mo(V)(mp)(3)](-) metalloligand coordinates to Na(+) to form the contact ion pair {Na(+)(THF)(3)[fac-Mo(V)(mp)(3)]} (1), while a separated ion pair, n-Bu(4)N[fac-Mo(V)(mp)(3)] (2), is obtained by exchanging Na(+) with n-Bu(4)N(+). In the presence of asymmetric binding-sites, the metalloligand reacts with Mn(II)Cl(2)·4H(2)O, Fe(II)Cl(2)·4H(2)O, Co(II)Cl(2)·6H(2)O, and Ni(II)Cl(2)·6H(2)O to afford UV-vis-NIR spectra, indicating binding of these guest metal cations. Especially, for the cases of the Mn(II) and Co(II) products, trinuclear complexes, {M(H(2)O)(MeOH)[fac-Mo(V)(mp)(3)](2)}·1.5CH(2)Cl(2) (3·1.5CH(2)Cl(2) (M = Mn(II)), 4·1.5CH(2)Cl(2) (M = Co(II))), are successfully isolated and structurally characterized where the M are selectively bound to the hard O-binding sites of the fac-[Mo(V)(mp)(3)](-). On the other hand, a coordination polymer, {Cu(I)(CH(3)CN)[mer-Mo(V)(mp)(3)]}(n) (5), is obtained by the reaction of fac-[Mo(V)(mp)(3)](-) with [Cu(I)(CH(3)CN)(4)]ClO(4). In sharp contrast to the cases of 1, 3·1.5CH(2)Cl(2), and 4·1.5CH(2)Cl(2), the Cu(I) in 5 are selectively bound to the soft S-binding sites, where each Cu(I) is shared by two [Mo(V)(mp)(3)](-) with bidentate or monodentate coordination modes. The second notable feature of 5 is found in the geometric change of the [Mo(V)(mp)(3)](-), where the original fac-form of 1 is isomerized to the mer-[Mo(V)(mp)(3)](-) in 5, which was structurally and spectroscopically characterized for the first time. Such isomerization demonstrates the structural flexibility of the [Mo(V)(mp)(3)](-). Spectroscopic studies strongly indicate that the association/dissociation between the guest metal ions and metalloligand can be modulated by solvent polarity. Furthermore, it was also found that such association/dissociation features are significantly influenced by coexisting anions such as ClO(4)(-) or B(C(6)F(5))(4)(-). This suggests that coordination bonds between the guest metal ions and metalloligand are not too static, but are sufficiently moderate to be responsive to external environments. Moreover, electrochemical data of 1 and 3·1.5CH(2)Cl(2) demonstrated that guest metal ion binding led to enhance electron-accepting properties of the metalloligand. Our results illustrate the use of a redox-active chalcogenolato complex with a simple mononuclear structure as a multifunctional metalloligand that is responsive to chemical and electrochemical stimuli.     

气相中碱金属离子与丝氨酸、亮氨酸和赖氨酸五肽复合物的裂解反应简

为了探索金属离子对含有不同侧链的多肽气相解离的影响,采用质谱法研究了碱金属离子Li+,Na+,K+,Rb+和Cs+分别与丝氨酸、亮氨酸和赖氨酸五肽(分别简写为S5,L5和K5)形成的复合物的裂解反应. 质谱定性结果表明,5种碱金属离子均可以在气相中与丝氨酸、亮氨酸和赖氨酸五肽形成配合比为1：1 和2：1的非共价复合物;竞争反应结果表明,随着碱金属离子半径的增加,它们与3种五肽的结合能力逐渐减弱. 质谱定量结果表明,K+与丝氨酸、亮氨酸和赖氨酸五肽复合物的结合常数分别为8.94×104,2.83×104和2.50×103 L/mol,表明K+与五肽复合物的结合强度按照丝氨酸、亮氨酸和赖氨酸的顺序依次减小. 含不同侧链碱金属离子-五肽复合物的碰撞诱导解离结果表明,复合物的碎裂主要发生在骨架上,丝氨酸五肽复合物最易碎裂,亮氨酸五肽复合物其次,赖氨酸五肽复合物则较难碎裂,且3种复合物的侧链断裂情况也呈现明显差异. 此外,研究了Na+与亮氨酸五肽复合物所产生的碎片离子,分析了不同离子之间的来源关系,并以Dunbar的复合物理论模型为依据,推测在碎裂过程中,碱金属离子可能向五肽的碳端或氮端偏移. 质谱碎片分析结果表明,在2：1的非共价复合物中,第一个碱金属离子与五肽上4个酰胺键的羰基结合,第二个碱金属离子与五肽的羧基氧原子结合.