Coadsorption of Cu(II) and glyphosate at the water-goethite (alpha-FeOOH) interface: molecular structures from FTIR and EXAFS measurements

The coadsorption of Cu(II) and glyphosate (N-(phosphonomethyl)glycine, abbreviated to PMG) at the water-goethite interface was studied by means of batch adsorption experiments, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and extended X-ray absorption fine structure (EXAFS) spectroscopy. The system was investigated over the pH range 3--9 and at total concentrations of 0.9 micromol and 2.2 micromol Cu(II) and PMG per m(2) of goethite. The collective quantitative and spectroscopic results show that Cu(II) and PMG directly interact at the water-goethite interface to form ternary surface complexes. Two predominating complexes have been identified. At pH 4 the IR and CuK-edge EXAFS data indicate a molecular structure where the phosphonate group of PMG bonds monodentately to the surface in an inner sphere mode, while carboxylate and amine groups coordinate to Cu(II) to form a 5-membered chelate ring. Hence, at pH 4, Cu(II) and PMG form a ternary surface complex on goethite with the general structure goethite-PMG-Cu(II). At the highest pH investigated (pH 9), the carboxylate group is still coordinated to Cu(II) but the phosphonate group is present in a relatively free, non-coordinated and/or disordered state. Although the spectroscopic data are not conclusive they indicate the formation of ternary surface complexes with the molecular architecture goethite-Cu(II)-PMG at high pH.     

Co-adsorption of cadmium(II) and glyphosate at the water-manganite (gamma-MnOOH) interface

The co-adsorption of Cd(II) and glyphosate (N-(phosphonomethyl)glycine, PMG) at the manganite (gamma-MnOOH) surface has been studied in the pH range 6-10 at 25 degrees C and with 0.1 M Na(Cl) as ionic medium. Batch adsorption experiments, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used for the quantitative analysis and the determination of the molecular structure of the surface complexes. The adsorption of Cd(II) and PMG in the ternary Cd(II)-PMG-manganite system was compared with the adsorption in the binary Cd(II)-manganite and PMG-manganite systems. The formation of three inner sphere surface complexes was observed, a ternary Cd(II)-PMG-manganite complex, a binary Cd(II)-manganite complex and a binary PMG-manganite complex. The surface concentration of the ternary complex and the Cd(II)-manganite complex was more or less constant throughout the pH range studied. However, the surface concentration of the binary PMG-manganite complex decreased with increasing pH. The major part of the binary PMG-surface complex was protonated. The ternary surface complex displayed a type B structure (Cd(II)-PMG-manganite). The average Cd-Mn distance obtained from EXAFS (3.26 A) indicates that the binary and ternary Cd(II)-surface complexes are formed by edge-sharing of Mn and Cd octahedra on the (010) plane of the manganite crystals.     

An electron paramagnetic resonance study of copper(II)-beta-substituted beta-amino acid systems by the two-dimensional simulation method: first evidence of primarily steric effects of substituents on equilibria of metal complexes

We have studied the complex equilibria of copper(II) with a series of beta-substituted beta-amino acids (R: H, Me, Et, iBu, iPr, cHex, 1-EtPr, and tBu) in aqueous solution by pH potentiometry and electron paramagnetic resonace (EPR) spectroscopy in the range pH = 2-8 at various metal and ligand concentrations. The basicities of the corresponding donor groups differed only slightly in the series of ligands. A purely mathematical method, the matrix rank analysis carried out on the EPR spectrum package recorded in the presence of copper(II), indicated the formation of 6 independent paramagnetic species. Accordingly, Cu(2+) (aqua complex) and the complexes [CuLH](2+), [CuL](+), [CuL(2)H(2)](2+), [CuL(2)H](+), and [CuL(2)] were considered in the subsequent analysis of series of spectra, and also two isomers of [CuL(2)] were identified. The formation constants and the EPR parameters, e.g. the isotropic g-factors and the copper and nitrogen hyperfine couplings for the above species, were determined in the same optimization procedure by the simultaneous evaluation of spectra. The ligands "LH" are suggested to bind in equatorial positions through their carboxylate groups, while the amino acids in the L protonation state are likely to occupy two equatorial sites via the amino and carboxylate groups. For the isomers of [CuL(2)], the donors of the same kind are in the cis or trans position. As far as we know, this is the first reported case in which a strong correlation has been found between the steric effects of substituents characterized by Meyer's steric parameter V(a) and the protonation constants of metal complexes. The observed trend for the preference for nonprotonated complexes [CuL](+) and [CuL(2)] to increase with the steric demand of the substituent was explained by the increasing shielding effect of the substituent hindering protonation of the nonprotonated complex.     

Copper(II) complexes of N-(phosphonomethyl)glycine in aqueous solution: a thermodynamic and spectrophotometric study

Copper(II) complexes with the herbicide N-(phosphonomethyl)glycine (glyphosate) have been investigated in aqueous solution by means of pH-metric measurements at different temperatures, 5 相似文献   

Zn6[MeN(CH2CO2)(CH2PO3)](6)(Zn)]4- anion: the first example of the oxo-bridged Zn6 octahedron with a centered Zn(II) cation

Hydrothermal reactions of N-(phosphonomethyl)-N-methylglycine, MeN(CH(2)CO(2)H)(CH(2)PO(3)H(2)) (H(3)L), with zinc(II) acetate resulted in the formation of a novel zinc carboxylate-phosphonate, [Zn(6)L(6)(Zn)][Zn(H(2)O)(6)](2) x 22H(2)O (1). The structure of 1 contains a heptanuclear zinc phosphonate cluster anion, [Zn(6)L(6)(Zn)](4-), in which seven zinc(II) cations form an unusual Zn(6)(Zn) centered octahedron with six of its Zn(3) triangle faces each further capped by a phosphonate group. The Zn(II) cations of the Zn(6) octahedron are five-coordinated whereas the centered Zn(II) cation is octahedrally coordinated. Packing of these cluster anions creates micropores occupied by the hydrated zinc(II) cations as well as lattice water molecules. The structural skeleton of 1 is retained after the removal of the lattice water molecules.     

Metal carboxylate-phosphonate hybrid layered compounds: synthesis and single crystal structures of novel divalent metal complexes with N-(phosphonomethyl)iminodiacetic acid

Two novel divalent metal complexes with N-(phosphonomethyl)iminodiacetic acid, H(2)O(3)PCH(2)N(CH(2)CO(2)H)(2) (H(4)PMIDA), [Co(2)(PMIDA)(H(2)O)(5)] x H(2)O, 1, and [Zn(2)(PMIDA)(CH(3)CO(2)H)] x 2H(2)O, 2, have been synthesized and structurally characterized. The structure of complex 1 features two different kinds of Co(II) layers, namely, a cobalt phosphonate layer along the <100> plane and a cobalt carboxylate layer along the <300> plane. The Co(II) atoms in the phosphonate layer are octahedrally coordinated by 4 aqua ligands and 2 oxygen atoms from two phosphonic acid groups. Two Co(II) octahedra are bridged by a pair of phosphonic groups into a dimeric unit, and such dimers are interconnected into a layer through hydrogen bonding between aqua ligands. The Co(II) atoms in the carboxylate layer are octahedrally coordinated by a chelating PMIDA ligand, one aqua ligand, and one phosphonic oxygen atom from the neighboring PMIDA ligand. These Co(II) octahedra are interlinked by bridging carboxylic groups into a one-dimensional chain along the c-axis; such chains are held together by hydrogen bonds formed between carboxylic oxygen atoms and lattice water molecules, in such a way as to form a layer along the <300> direction. Two such layers are interconnected into a double layer via hydrogen bonding. These double layers are further interconnected with the Co(II) phosphonate layers through phosphonate tetrahedra along the a direction, resulting in the formation of a complicated three-dimensional network. The crystal structure of 2 contains a metal phosphonate and metal carboxylate hybrid layer along the <202> plane. One of the two zinc atoms in the asymmetric unit is tetrahedrally coordinated by four oxygen atoms from two phosphonic acid groups and two carboxylic groups; the other zinc atom is 5-coordinated by three oxygen atoms and a nitrogen atom from a chelating PMIDA ligand and one oxygen atom from the acetic acid. The above two types of zinc metal ions are interconnected by bridging carboxylic and phosphonic groups, resulting in the formation of a layered structure.     

Thermodynamics of the Protonation of an Analogue of Glyphosate, <Emphasis Type="Italic">N</Emphasis>-(phosphonomethyl)-<Emphasis Type="SmallCaps">l</Emphasis>-proline,in Aqueous Solutions

N-(phosphonomethyl)-l-proline is an analogue of glyphosate. The protonation for N-(phosphonomethyl)-l-proline was studied by potentiometry, calorimetry, ³¹P NMR spectroscopy and quantum chemical calculations to further understand the protonation process of glyphosate. The results confirmed that the order of successive protonation sites of totally deprotonated N-(phosphonomethyl)-l-proline are a phosphonate oxygen, amino nitrogen, and finally the carboxylate oxygen. The results can improve the understanding of the biological activity of these types of molecules in solution.     

Photophysical and ab Initio Studies of Mononuclear Copper(I) Complexes

Described are the photophysical properties of the mononuclear copper(I) complexes CuL(4)(+) (L = pyridine (py), 4-methylpyridine, 4-phenylpyridine, or acetonitrile), Cu(lut)(3)(+) (lut = 2,6-lutidine), and Cu(lut)(2)(+). Each of these compounds as their solid PF(6)(-) salts display a relatively long-lived (>1 &mgr;s), visible range emission at both ambient temperature and at 77 K but not in fluid solutions. Also reported are the results for ab initio calculations at the restricted Hartree-Fock self-consistent field level to probe the natures of lower energy excited states of the hypothetical species CuL(n)()(+) (L = NH(3), CH(3)CN, or py; n = 1-4). These results point to an assignment of the lowest energy, luminactive excited states as being largely metal centered, d --> s in character for each of the above complexes with the possible exception of the CuL(4)(+) species where L is py or a substituted analogue. In the case of Cu(py)(4)(+) the ab initiocalculations indicate a metal-to-ligand charge transfer to be the lowest energy Franck-Condon state, although the similarities of emission band shapes, energies, and lifetimes among the various complexes suggest a common d --> s assignment.     

Crystal structure and physico-chemical characterization of the nitrato complexes of copper(II) with 1-ethoxymethylimidazole

Nitrato complexes of copper(II) with 1-ethoxymethyl- imiazole (L), of general formulae CuL2(NO3)2 (1) and CuL4(NO3)2 (2) have been prepared and characterized by elemental analysis and by i.r., f.i.r., vis-n.i.r. spectral evidence, conductivity, magnetochemical measurements and single crystal X-ray analysis. Compound (1) has two 1-ethoxymethylimidazole molecules and two bidentate nitrato groups in the copper(II) co-ordination sphere. In complex (2) the immediate surroundings of copper(II) is described by a tetragonally elongated octahedron with the difference the horizontal and equatorial bond lengths of 0.462 Å.     

Cooperative pull and push effects on the O-O bond cleavage in acylperoxo complexes of [(Salen)MnIIIL]: ensuring formation of manganese(V) oxo species

The acidity (pull) and the axial ligand (push) effects on the O-O bond cleavage in the [(Salen)Mn(III)(RCO(3))L] acylperoxo complexes, with model L = none, NH(3), and HCO(2)(-) (1), have been studied with B3LYP density functional calculations. The acidic conditions have been mimicked by explicit protonation of 1 to afford a variety of [(Salen)Mn(III)(RCO(3)H)L] (2) and [(SalenH)Mn(III)(RCO(3))L] (3) complexes in ground quintet states. The protonation assists the O-O bond heterolysis, thus primarily forming highly reactive Mn(V)(O) species, and consequently suppresses formation of the less reactive Mn(IV)(O) species through homolytic channel described earlier in 1 [Khavrutskii, I. V.; Rahim, R. R.; Musaev, D. G.; Morokuma, K. J. Phys. Chem. B 2004, 108, 3845-3854]. In addition to the qualitative change of the O-O bond cleavage mode, the protonation affects the rate of the O-O bond cleavage. Therefore, varying the acidity of the reaction media helps control the O-O bond cleavage mode and rate.     

Microspeciation in the copper(II)-L-histidylglycine system. An ESR study by the two-dimensional computer simulation method

Twelve ESR-active (and one inactive) copper(II) complexes of L-histidylglycine (HL) were characterized via their formation (micro)constants and ESR parameters obtained by two-dimensional ESR spectroscopic evaluation in aqueous solution. In strongly acidic media, the ligand is coordinated through its N-terminal donor groups: the complex [CuLH(2)](3+) involves monodentate imidazole binding, whereas [CuLH](2+) involves bidentate ligation through the amino and imidazole N atoms. This histamine-like bonding mode also predominates in the isomers of [CuL(2)], formed at ligand excess near pH 7: in the major 4N isomer, both ligands occupy two equatorial sites, while in the 3N isomer, the second dipeptide is coordinated equatorially by the amino and axially by the imidazole groups. At above pH 3-4, deprotonation of the peptide group also starts: in approximately 60% of the molecules of [CuL](+), the peptide group is deprotonated, while in the minor isomer histamine-like coordination occurs. At higher pH, the active dimer [Cu(2)L(2)H(-2)], the mixed hydroxo complexes (the inactive [Cu(2)L(2)H(-3)](-) and the active [CuLH(-2)](-)), and the bis complexes [CuL(2)H](+) and [CuL(2)H(-1)](-) all involve tridentate equatorial ligation of the backbone by the amino and deprotonated peptide N and the carboxylate O atoms. In the active dimer, the neutral imidazole groups form bridges between CuLH(-1) units. In [CuL(2)H](+), the second ligand is bound equatorially via its imidazole group; in [CuL(2)H(-1)](-), the L ligand occupies the fourth equatorial site and an axial site through its amino and imidazole N atoms, respectively.     

Tunability of the M(II)M(III)/M(II)(2) and M(III)(2)/M(II)M(III) (M=Mn, Co) couples in bis-μ-O,O'-carboxylato-μ-OR bridged complexes

A comparison of the electrochemical properties of a series of dinuclear complexes [M(2)(L)(RCO(2))(2)](+) with M = Mn or Co, L = 2,6-bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolato (bpsmp(-)) or 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato (bpbp(-)) and R = H, CH(3), CF(3) or 3,4-dimethoxybenzoate demonstrates: (i) The electron-withdrawing sulfonyl groups in the backbone of bpsmp(-) stabilize the [M(2)(bpsmp)(RCO(2))(2)](+) complexes in their M(II)(2) oxidation state compared to their [M(2)(bpbp)(RCO(2))(2)](+) analogues. Manganese complexes are stabilised by approximately 550 mV and cobalt complexes by 650 mV. (ii) The auxiliary bridging carboxylato ligands further attenuate the metal-based redox chemistry. Substitution of two acetato for two trifluoroacetato ligands shifts redox couples by 300-400 mV. Within the working potential window, reversible or quasi-reversible M(II)M(III)? M(II)(2) processes range from 0.31 to 1.41 V for the [Co(2)(L)(RCO(2))(2)](+/2+) complexes and from 0.54 to 1.41 V for the [Mn(2)(L)(RCO(2))(2)](+/2+) complexes versus Ag/AgCl for E(M(II)M(III)/M(II)(2)). The extreme limits are defined by the complexes [M(2)(bpbp)(CH(3)CO(2))(2)](+) and [M(2)(bpsmp)(CF(3)CO(2))(2)](+) for both metal ions. Thus, tuning the ligand field in these dinuclear complexes makes possible a range of around 0.9 V and 1.49 V for the one-electron E(M(II)M(III)/M(II)(2)) couple of the Mn and Co complexes, respectively. The second one-electron process, M(II)M(III)? M(III)(2) was also observed in some cases. The lowest potential recorded for the E°(M(III)(2)/M(II)M(III)) couple was 0.63 V for [Co(2)(bpbp)(CH(3)CO(2))(2)](2+) and the highest measurable potential was 2.23 V versus Ag/AgCl for [Co(2)(bpsmp)(CF(3)CO(2))(2)](2+).     

Study of intramolecular competition between carboxylate and phosphonate for Pt(II) with the aid of a novel tridentate carboxylato-thioether-phosphonato ligand

The tridentate dianionic ligand 2-[2'-(hydroxyisopropoxyphosphoryl)phenylsulfanyl]benzoate (L(2-)) reacts with cis-[Pt(NH(3))(2)(H(2)O)(2)](2+) to form an S,O-chelate in which the O-coordinated group is either carboxylate or phosphonate, depending on the degree of protonation of the complex. Carboxylate appears to be the stronger ligand, and the stoichiometric reaction between cis-[Pt(NH(3))(2)(H(2)O)(2)](2+) and L(2-) yields the neutral species [Pt(L)(NH(3))(2)], with L bound by sulfanyl and carboxylate groups, both in solution and in the solid state. Upon protonation of [Pt(L)(NH(3))(2)], the stronger basicity of the carboxylate causes the Pt coordination to switch from carboxylate to phosphonate, and the uncoordinated carboxylate group becomes protonated. In methanolic solution, the first-order kinetics of this rearrangement could be observed by (31)P NMR spectroscopy. Both complexes-the carboxylate-bound neutral complex [Pt(L)(NH(3))(2)].H(2)O (triclinic, P1 (no. 2), a=9.529(6), b=9.766(6), c=12.299(7) angstroms, alpha=106.91(2), beta=101.71(2), gamma=102.05(2) degrees, Z=2) and the perchlorate salt of the phosphonate-bound complex [Pt(LH)(NH(3))(2)]ClO(4).H(2)O (monoclinic, P2(1)/c (no. 14), a=12.095(2), b=14.046(2), c=14.448(2) angstroms, beta=95.55(2) degrees, Z=4)-were characterized by X-ray crystallography.     

Rational assembly of soluble copper(II) phosphonates: synthesis, structure and magnetism of molecular tetranuclear copper(II) phosphonates

The reactions of the dinuclear copper complexes [Cu(2)(L)(OAc)] [H(3)L = N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) or [Cu(2)(L')(OAc)] (H(3)L' = N,N'-(2-hydroxypropane-1,3-diyl)bis(4,5-dimethylsalicylaldimine)] with various phosphonic acids, RPO(3)H(2) (R = t-Bu, Ph, c-C(5)H(9), c-C(6)H(11) or 2,4,6-i-Pr(3)-C(6)H(2)), leads to the replacement of the acetate bridge affording tetranuclear copper(II) phosphonates, [Cu(4)(L)(2)(t-BuPO(3))](CH(3)OH)(2)(C(6)H(6)) (1), [Cu(4)(L)(2)(PhPO(3))(H(2)O)(2)(NMe(2)CHO)](H(2)O)(2) (2), [Cu(4)(L')(2)(C(5)H(9)PO(3))](CH(3)OH)(2) (3), [Cu(4)(L')(2)(C(6)H(11)PO(3)](MeOH)(4)(H(2)O)(2) (4) and [Cu(4)(L')(2)(C(30)H(46)P(2)O(5))](PhCH(3)) (5). The molecular structures of 1-4 reveal that a [RPO(3)](2-) ligand is involved in holding the four copper atoms together by a 4.211 coordination mode. In 5, an in situ formed [(RPO(2))(2)O](4-) ligand bridges two pairs of the dinuclear subunits. Magnetic studies on these complexes reveal that the phosphonate ligand is an effective conduit for magnetic interaction among the four copper centers present; a predominantly antiferromagnetic interaction is observed at low temperatures.     

水合双邻羟基苄氨乙酸铜配位结构的EXAFS研究

用参数化经验公式, 从已知晶体结构的无水双邻羟基苄胺铜(II)[Cu(o-OC6H4CH2NH2)2, 1]的EXAFS数据中分离出振幅和相移, 拟合另一已知晶体结构的水合双邻羟基苄胺铜(II){[Cu(o-OC6H4CH2NH2)2.H2O].1/2.H2O, 2}的结构参数并进行检验后, 代入未知结构的水合双邻羟基苄氨乙酸铜(II)[Cu(o-HOC6H4CH2NHCH2CO2)2.H2O, 3]中进行曲线拟合, 得到配位原子、键长和配位数等结构信息. 结合红外光谱, 推断标题化合物中, Cu(II)与两个苄基氮和两个羧基氧形成一个平面四边形的配位结构.铜与羧基氧键长2.00A, Cu-N键长1.99A, 另有一个较远的配位水分子, 铜与水的氧距离2.95A. 配体上的酚基氧没有与Cu(II)配合. 因此, 邻羟基苄氨乙酸(HBG)与Cu(II)配位时表现为二啮形式.     

Rare example of mu-nitrito-1kappa2O,O':2kappaO coordinating mode in copper(II) nitrite complexes with monoanionic tridentate Schiff base ligands: structure, magnetic, and electrochemical properties

Three new copper(II) complexes, [CuL(1)(NO(2))](n) (1), [CuL(2)(NO(2))] (2), and [CuL(3)(NO(2))] (3), with three similar tridentate Schiff base ligands [HL(1) = 6-amino-3-methyl-1-phenyl-4-azahept-2-en-1-one, HL(2) = 6-amino-3-methyl-1-phenyl-4-azahex-2-en-1-one, and HL(3) = 6-diethylamino-3-methyl-1-phenyl-4-azahex-2-en-1-one] have been synthesized and characterized structurally and magnetically. In all three complexes, the tridentate Schiff base ligand and one oxygen atom of the nitrite ion constitute the equatorial plane around Cu(II), whereas the second oxygen atom of the nitrite ligand coordinates to one of the axial positions. In 1, this axially coordinated oxygen atom of the nitrite ligand also coordinates weakly to the other axial position of a Cu(II) ion of another unit to form a one-dimensional chain with the mu-nitrito-1kappa(2)O,O':2kappaO bridging mode. Complexes 2 and 3 are discrete monomers that are joined together by intermolecular H bonds and C-H....pi interactions in 2 and by only C-H....pi interactions in 3. A weak antiferromagnetism (J = -1.96(2) cm(-1)) is observed in complex 1 due to its asymmetric nitrite bridging. Complexes 2 and 3 show very weak antiferromagnetic interactions (J = -0.089 and -0.096 cm(-1), respectively) attributed to the presence of intermolecular H-bonding and C-H....pi interactions. The corresponding Cu(I) species produced by the electrochemical reduction of complexes 1 and 2 disproportionate to Cu(0) and Cu(2+,) whereas the reduced Cu(I) species of complex 3 seems to be stable presumably due to a higher tetrahedral distortion of the equatorial plane in 3 compared to that in 1 and 2.     

Synthesis of the first heterometalic star-shaped oxido-bridged MnCu3 complex and its conversion into trinuclear species modulated by pseudohalides (N3(-), NCS- and NCO-): structural analyses and magnetic properties

A tetra-nuclear, star-shaped hetero-metallic copper(II)-manganese(II) complex, [{CuL(H(2)O)}(2)(CuL)Mn](ClO(4))(2) (1) has been synthesized by reacting the "complex as ligand" [CuL] with Mn(ClO(4))(2) where H(2)L is the tetradentate di-Schiff base derived from 1,3-propanediamine and 2-hydroxyacetophenone. Upon treatment with the polyatomic anions azide, cyanate, or thiocyanate in methanol medium, complex 1 transforms into the corresponding trinuclear species [(CuL)(2)Mn(N(3))(2)] (2), [(CuL)(2)Mn(NCO)(2)] (3) and [(CuL)(2)Mn(NCS)(2)] (4). All four complexes have been structurally and magnetically characterized. In complex 1 the central Mn(II) ion is encapsulated by three terminal [CuL] units through the formation of double phenoxido bridges between Mn(II) and each Cu(II). In complexes 2-4 one of the CuL units is replaced by a couple of terminal azide, N-bonded cyanate or N-bonded thiocyanate ions respectively and the central Mn(II) ion is connected to two terminal Cu(II) ions through a double asymmetric phenoxido bridge. Variable temperature magnetic susceptibility measurements show the presence of moderate ferrimagnetic exchange interactions in all the cases mediated through the double phenoxido bridges with J values (H = -JS(i)S(i + 1)) of -41.2, -39.8 and -12.6 cm(-1) (or -40.5 and -12.7 cm(-1) if we use a model with two different exchange coupling constants) for the tetranuclear MnCu(3) cluster in compound 1 and -20.0, -17.3 and -32.5 cm(-1) for the symmetric trinuclear MnCu(2) compounds 2-4. These ferrimagnetic interactions lead to spin ground states of 1 (5/2 - 3*1/2) for compound 1 and 3/2 (5/2 - 2*1/2) for compounds 2-4.     

Chromotropism studies on copper(II) compounds. Part II. Dinuclear copper(II) complexes with triply-bridged hydroxo,acetate, and halo ligands

Abstract

Two triply-bridged dinuclear copper(II) complexes of formula [LCu(μ-OH)(μ-OAc)(μ-X)CuL]X?0.5H₂O where L is a bidentate ligand of N-(pyridine-2-ylmethyl)propane-2-amine and X=Cl, 1 and Br, 2 were synthesized and characterized by elemental analyses, spectroscopic techniques (IR, UV–Vis, EPR), thermal analysis, conductance measurements, and single-crystal X-ray structure determination. The structures of both complexes are similar. The complexes show a distorted square-pyramidal arrangement around each copper(II) ion with a CuN₂O₂X chromophore in which both copper(II) ions are connected by a hydroxo bridge and a triatomic syn-syn carboxylato bridge in equatorial positions and a halide ion bridge at the axial site. The chromotropism behavior of the complexes, including solvato-, thermo-, and halochromism, were investigated in detail. Their halochromism was investigated in the pH range of 2.0–11.0 by visible absorption spectroscopy. The reversible color variations from blue to colorless are attributable to deprotonation and protonation of the ligands. The complexes show reversible thermochromism in solution due to dissociation and recombination of ligands to copper ions.     

Unexpected selectivities in C-H activations of toluene and p-xylene at cationic platinum(II) diimine complexes. New mechanistic insight into product-determining factors.

The C-H activation of toluene and p-xylene at cationic Pt(II) diimine complexes (N-N)Pt(CH(3))(H(2)O)(+)BF(4)(-) (N-N = Ar-N=CMe-CMe=N-Ar; 1(BF(4)(-)), N(f)-N(f), Ar = 3,5-(CF(3))(2)C(6)H(3)); 2(BF(4)(-)), N'-N', Ar = 2,6-(CH(3))(2)C(6)H(3)) has been investigated. The reactions were performed at ambient temperature in 2,2,2-trifluoroethanol (TFE), and after complete conversion of the starting material to mixtures of Pt-aryl/Pt-benzyl complexes and methane, acetonitrile was added to trap the products as more stable acetonitrile adducts. In the reactions with toluene, the relative amounts of products resulting from aromatic C-H activation were found to decrease in the order (N-N)Pt(m-tolyl)(NCMe)(+) > (N-N)Pt(p-tolyl)(NCMe)(+) > (N-N)Pt(o-tolyl)(NCMe)(+) for both 1 and 2. Unlike the reaction at 1, significant amounts of the benzylic activation product (N'-N')Pt(benzyl)(NCMe)(+) were concurrently formed in the C-H activation of toluene at 2. The C-H activation of p-xylene revealed an even more remarkable difference between 1 and 2. Here, the product ratios of (N-N)Pt(xylyl)(NCMe)(+) and (N-N)Pt(p-methylbenzyl)(NCMe)(+) were found to be 90:10 and 7:93 for reactions at 1 and 2, respectively. The elimination of toluene from (N(f)-N(f))Pt(Tol)(2) species (3a-c; a, Tol = o-tolyl; b, Tol = m-tolyl; c, Tol = p-tolyl) after protonolysis with 1 equiv of HBF(4) was investigated. Most notably, protonation in neat TFE followed by addition of acetonitrile gave a 77:23 mixture of (N(f)-N(f))Pt(m-tolyl)(NCMe)(+) (4b) and (N(f)-N(f))Pt(p-tolyl)(NCMe)(+) (4c) from all three isomeric bis(tolyl) complexes 3a-c. The presence of acetonitrile during the protonation reactions resulted in considerably less isomerization. This behavior is explained by an associative mechanism for the product-determining displacement of toluene by the solvent. For the C-H activation reactions, our findings suggest the existence of a dynamic equilibrium between the isomeric intermediates (N-N)Pt(aryl)(CH(4))(+) (aryl = tolyl/benzyl from 1; xylyl/p-methylbenzyl from 2). The observed selectivities might then be explained by steric and electronic effects in the pentacoordinate transition-state structures for the solvent-induced associative elimination of methane from these intermediates.