Solvation of copper(II) sulfate in binary water/N,N-dimethylformamide mixtures: from the solution to the gas phase

The solvation of copper(II) sulfate in binary mixtures of water and N,N-dimethylformamide (DMF) is studied by a combined approach using electrochemical studies in solution and a mass spectrometric assay of the solvated ions formed from these solutions upon electrospray ionization (ESI). In the condensed phase, the limiting transference numbers (t(+/-)(o)) and the apparent ion association constants (K(A)'s) of CuSO(4) have been determined in water/DMF solutions at 20 degrees C. The t(+)(o) values decrease with increasing DMF content, demonstrating a gradual solvation of Cu(2+) by DMF molecules. The association constants indicate that aggregation becomes more pronounced as the DMF content increases. In order to achieve complementary insight, the intrinsic interactions among the ions and solvent molecules are investigated in gas-phase experiments of the CuSO(4)/water/DMF system using ESI mass spectrometry. Under the conditions used, the dications [Cu(DMF)(n)](2+) (n = 3-6), [Cu(2)(DMF)(n)SO(4)](2+) (n = 2-7), and [Cu(3)(DMF)(n)(SO(4))(2)](2+) (n = 2-7), and the monocations [Cu(OH)(DMF)(n)](+), [Cu(DMF)(n)(HSO(4))](+) (both, n = 1-3), and [Cu(DMF)(n)](+) (n = 1, 2), are formed as the leading copper-containing cations. Likewise, polynuclear copper clusters observed in the anion ESI spectra support partial aggregation occurring in solution. The gas-phase studies clearly support the conclusions that (i) DMF is a highly preferred ligand for CuII in comparison to water and that (ii) DMF supports ion association for which the mass spectrometric data suggest the formation of polynuclear copper clusters.     

Mono- and dinuclear complexes of chiral tri- and tetradentate Schiff-base ligands derived from 1,1'-binaphthyl-2,2'-diamine

The synthesis and characterization of the bis(bidentate) Schiff-base ligand [(R)-2] formed by the condensation reaction of (R)-1,1'-binaphthyl-2,2'-diamine [(R)-BINAM] with pyridine-2-carboxaldehyde is presented. The coordination chemistry of (R)-2 with Ni(ClO(4))(2).6H(2)O, Co(ClO(4))(2).6H(2)O, CuCl(2), and CuSO(4) has been investigated. Reaction of (R)-2 with the first two metal salts leads to complexes of the type [M((R)-4)(2)](ClO(4))(2) (M = Ni(II), Co(II)), where (R)-4 is a tridentate ligand resulting from the hydrolytic cleavage of one of the pyridyl groups from (R)-2. Both complexes were characterized by X-ray crystallography, which showed that the Lambda absolute configuration of the metal center is favored in both cases. (1)H NMR spectroscopy suggests that the high diastereoselectivity of Lambda-[Co((R)-4)(2)](ClO(4))(2) is maintained in solution. The reaction of (R)-2 with CuCl(2) leads to the dinuclear complex [Cu(2)((R)-2)Cl(4)], which has a [Cu(2)(mu(2)-Cl(2))] core. The reaction of CuSO(4) with (R)-2 gives a dimeric complex, [Cu((R)-4)SO(4)](2), which features a [Cu(2)(mu(2)-(SO(4))(2))] core. This complex can be prepared directly by the reaction of (R)-BINAM with pyridine-2-carboxaldehyde and CuSO(4). The use of rac-BINAM in this synthetic procedure leads to the heterochiral dimer [Cu(2)((R)-4)((S)-4)(SO(4))(2)]; that is, the ligands undergo a self-sorting (self/nonself discrimination) process based on chirality. The reaction of rac-BINAM, pyridine-2-carboxaldehyde, and Co(ClO(4))(2).6H(2)O proceeds via a homochiral self-sorting pathway to produce a racemic mixture of [Co((R)-4)(2)](2+) and [Co((S)-4)(2)](2+). The variable-temperature magnetic susceptibilities of the bimetallic complexes [Cu(2)((R)-2)Cl(4)], [Cu((R)-4)(mu(2)-SO(4))](2), and [Cu(2)((R)-4)((S)-4)(mu(2)-SO(4))(2)] all show weak antiferromagnetic coupling with J = -1.0, -0.40, and -0.67 cm(-)(1), respectively.     

Diastereoselective fragmentation of chiral alpha-aminophosphonic acids/metal ion aggregates

Diastereomeric clusters of general formula [MAB(2)](+) and [MA(2)B](+) (M = Li(I), Na(I), Ag(I), Ni(II)-H, or Cu(II)-H; A = (R)-(-)- and (S)-(+)-(1-aminopropyl)phosphonic acid; B = (1R)-(-)- and (1S)-(+)-(1-aminohexyl)phosphonic acid) have been readily generated in the electrospray ionization (ESI) source of a triple-quadrupole mass spectrometer and their collision-induced dissociation (CID) investigated. CID of diastereomeric complexes, e.g. [MA(S)(B(S))(2)](+) and [MA(R)(B(S))(2)](+), leads to fragmentation patterns characterized by R(homo) = [MA(S)B(S)](+)/[M(B(S))(2)](+) and R(hetero) = [MA(R)B(S)](+)/[M(B(S))(2)](+) abundance ratios, which depend upon the relative stability of the diastereomeric [MA(S)B(S)](+) and [MA(R)B(S)](+) complexes in the gas phase. The chiral resolution factor R(chiral) = R(homo)/R(hetero) is found to depend not only on the nature of the M ion but also on that of the fragmenting species, whether [MAB(2)](+) or [MA(2)B](+). The origin of this behavior is discussed.     

Structure and dissociation characteristics of metal chloride anion clusters containing redox-active metal ions studied by laser desorption and electrospray ionization mass spectrometry and ab initio calculations

Copper chloride anion clusters with both copper oxidation states can be made by laser desorption of CuCl(2) crystals. We have used this method to study the dissociation characteristics of such cluster ions. The stability and the structure of the observed complexes were probed by ab initio calculations. These calculations show that many of these complexes are bridged structures. Thus, for the Cu(2)Cl(4) dimer anion, formally [ClCu-Cl-CuCl(2)](-) , with putative mixed copper oxidation states, the two copper ions become equivalent through bridging. Such bridging does not occur when redox inactive metal ions are present as in [ClCu-Cl-CaCl(2)](-) . By observing the dissociation characteristics of a variety of metal chloride cluster anions produced from binary mixtures, the following Cl(-) affinity order is obtained: FeCl(3) > CuCl > CaCl(2) > FeCl(2) > AgCl ≈ CuCl(2) ≈ ZnCl(2) > LiCl. Ab initio calculations on the Cl(-) affinity of selected chlorides confirm this order as do Cl(-) affinity estimates from the experimentally known vertical electron detachment energies of the superhalogens CaCl(3)(-) and LiCl(2)(-) . An equimolar mixture of CuCl(2) and FeCl(3) produces an intense cluster ion, which, from (65)Cu labeling experiments, is best described as FeCl(4)(-)···Cu(+)···(-)Cl(4) Fe, a Cu(+) bound superhalogen FeCl(4)(-) dimer. The Cu(+) ion can be replaced by the redox inactive alkali cations and by Ag(+) but these metal ion bound FeCl(4)(-) dimers show an entirely different fragmentation behavior which is attributed to the absence of bridging. Electrospray ionization (ESI) of CuCl(2) produces an extended series of (CuCl(2))(n) Cl(-) anions (n = 1-11) and so in ESI very limited reduction of Cu(2+) takes place. The (CuCl(2))(n) Cl(-) anions show an abundant dissociation via loss of neutral Cu(2)Cl(4) which according to our ab initio calculations is 9 kcal/mol more stable than two CuCl(2).     

Spectroelectrochemical Studies of Copper(I) Complexes with Binaphthyridine and Biquinoline Ligands. Crystal Structure Determination of Bis(6,7-dihydrodipyrido[2,3-b:3',2'-j][1,10]phenanthroline)copper(I) Tetrafluoroborate

The electrochemical and spectral properties of some copper(I) polypyridyl complexes based on 6,7-dihydrodibenzo[b,j][1,10]phenanthroline, dmbiq, and 6,7-dihydrodipyrido[2,3-b:3',2'-j][1,10]phenanthroline, dmbinap, are reported. These complexes are [Cu(dmbiq)(2)](+), 1; [Cu(dmbiq)(PPh(3))(2)](+), 2; [Cu(dmbinap)(2)](+), 3; and [Cu(dmbinap)(PPh(3))(2)](+), 4. 3 and 4 may be reduced to form ligand-based radical anion species. The resonance Raman spectra of 3(*)()(-)() and 4(*)()(-)() are almost identical and correspond closely to the spectrum of dmbinap(*)()(-)() and the reported spectra of complexes containing 2,2'-biquinoline radical anion moieties. Reduction processes for 1 and 2 are irreversible. For 1 the electronic spectral changes arising from reduction suggest demetallation of the complex. The structure of [Cu(C(18)H(12)N(4))(2)][BF(4)].CH(2)Cl(2) (3[BF(4)].CH(2)Cl(2)) was determined by single-crystal X-ray diffraction. It crystallized in the monoclinic space group P2(1)/c with cell dimensions a = 14.059(7) ?, b = 15.058(6) ?, c = 16.834(9) ?, beta = 111.56(5) degrees, Z = 4, rho(calcd) = 1.611 g/cm(3), and R(F(o)) = 0.0497.     

Comparative study of mono- and dinuclear complexes of late 3d-metal chlorides with N,N-dimethylformamide in the gas phase

Mono- and binuclear complexes of N,N-dimethylformamide (DMF) with chlorides of the divalent, late 3d metals M = Co, Ni, Cu, and Zn are investigated by means of electrospray ionization (ESI). Specifically, ESI leads to monocations of the type [(DMF)(n)MCl](+) and [(DMF)(n)M(2)Cl(3)](+), of which the species with n = 2 and 3 were selected for in-depth studies. The latter include collision-induced dissociation experiments, gas-phase infrared spectroscopy, and calculations using density functional theory. The mononuclear complexes [(DMF)(n)MCl](+) almost exclusively lose neutral DMF upon collisional activation with the notable exception of the copper complex, for which also a reduction from Cu(II) to Cu(I) concomitant with the release of atomic chlorine is observed. For the dinuclear clusters, there exists a competition between loss of a DMF ligand and cluster degradation via loss of neutral MCl(2) with decreasing cluster stability from cobalt to zinc. For the specific case of [(DMF)(n)ZnCl](+) and [(DMF)(n)Zn(2)Cl(3)](+), ion-mobility mass spectrometry indicates the existence of two isomeric cluster ions in the case of [(DMF)(2)Zn(2)Cl(3)](+) which corroborates parallel theoretical predictions.     

Electrodeposition of copper on a Pt(111) electrode in sulfuric acid containing poly(ethylene glycol) and chloride ions as probed by in situ STM

This study employed real-time in situ STM imaging to examine the adsorption of PEG molecules on Pt(111) modified by a monolayer of copper adatoms and the subsequent bulk Cu deposition in 1 M H(2)SO(4) + 1 mM CuSO(4)+ 1 mM KCl + 88 μM PEG. At the end of Cu underpotential deposition (~0.35 V vs Ag/AgCl), a highly ordered Pt(111)-(√3 × √7)-Cu + HSO(4)(-) structure was observed in 1 M H(2)SO(4) + 1 mM CuSO(4). This adlattice restructured upon the introduction of poly(ethylene glycol) (PEG, molecular weight 200) and chloride anions. At the onset potential for bulk Cu deposition (~0 V), a Pt(111)-(√3 × √3)R30°-Cu + Cl(-) structure was imaged with a tunneling current of 0.5 nA and a bias voltage of 100 mV. Lowering the tunneling current to 0.2 nA yielded a (4 × 4) structure, presumably because of adsorbed PEG200 molecules. The subsequent nucleation and deposition processes of Cu in solution containing PEG and Cl(-) were examined, revealing the nucleation of 2- to 3-nm-wide CuCl clusters on an atomically smooth Pt(111) surface at overpotentials of less than 50 mV. With larger overpotential (η > 150 mV), Cu deposition seemed to bypass the production of CuCl species, leading to layered Cu deposition, starting preferentially at step defects, followed by lateral growth to cover the entire Pt electrode surface. These processes were observed with both PEG200 and 4000, although the former tended to produce more CuCl nanoclusters. Raising [H(2)SO(4)] to 1 M substantiates the suppressing effect of PEG on Cu deposition. This STM study provided atomic- or molecular-level insight into the effect of PEG additives on the deposition of Cu.     

Structural, spectroscopic, and electrochemical properties of tri- and tetradentate N3 and N3S copper complexes with mixed benzimidazole/thioether donors

Cupric and cuprous complexes of bis(2-methylbenzimidazolyl)(2-methylthiophene)amine (L(1)), bis(2-methylbenzimidazolyl)benzylamine (L(2)), bis(2-methylbenzimidazolyl)(2,4-dimethylphenylthioethyl)amine (L(3)), bis(1-methyl-2-methylbenzimidazolyl)benzylamine (Me(2)L(2)), and bis(1-methyl-2-methylbenzimidazolyl)(2,4-dimethylphenylthioethyl)amine (Me(2)L(3)) have been spectroscopically, structurally, and electrochemically characterised. The thioether-containing ligands L(3) and Me(2)L(3) give rise to complexes with Cu-S bonds in solution and in the solid state, as evidenced by UV-vis spectroscopy and X-ray crystallography. The Cu(2+) complexes [L(1)CuCl(2)] (1), [L(2)CuCl(2)] (2) and [Me(2)L(3)CuCl]ClO(4) (3(Me,ClO4)) are monomeric in solution according to ESI mass spectrometry data, as well as in the solid state. Their Cu(+) analogues [L(1)Cu]ClO(4), [L(2)Cu]ClO(4), [L(3)Cu]ClO(4) (4-6), [BOC(2)L(1)Cu(NCCH(3))]ClO(4) (4(BOC)), [Me(2)L(2)Cu(NCCH(3))(2)]PF(6) (5(Me)) and [Me(2)L(3)Cu](2)(ClO(4))(2) (6(Me)) are also monomeric in acetonitrile solution, as confirmed crystallographically for 4(BOC) and 5(Me). In contrast, 6(Me) is dimeric in the solid state, with the thioether group of one of the ligands bound to a symmetry-related Cu(+) ion. Cyclic voltammetry studies revealed that the bis(2-methylbenzimidazolyl)amine-Cu(2+)/Cu(+) systems possess half-wave potentials in the range -0.16 to -0.08 V (referenced to the ferrocenium-ferrocene couple); these values are nearly 0.23 V less negative than those reported for related bis(picolyl)amine-derived ligands. Based on these observations, the N(3) or N(3)S donor set of the benzimidazole-derived ligands is analogous to previously reported chelating systems, but the electronic environment they provide is unique, and may have relevance to histidine and methionine-containing metalloenzymes. This is also reflected in the reactivity of [Me(2)L(2)Cu(NCCH(3))(2)](+) (5(Me)) and [Me(2)L(3)Cu](+) (6(Me)) towards dioxygen, which results in the production of the superoxide anion in both cases. The thioether-bound Cu(+) centre in 6(Me) appears to be more selective in the generation of O(2)˙(-) than 5(Me), lending evidence to the hypothesis of the modulating properties of thioether ligands in Cu-O(2) reactions.     

Synthesis, characterization, and reactivity of Fe complexes containing cyclic diazadiphosphine ligands: the role of the pendant base in heterolytic cleavage of H2

The iron complexes CpFe(P(Ph)(2)N(Bn)(2))Cl (1-Cl), CpFe(P(Ph)(2)N(Ph)(2))Cl (2-Cl), and CpFe(P(Ph)(2)C(5))Cl (3-Cl)(where P(Ph)(2)N(Bn)(2) is 1,5-dibenzyl-1,5-diaza-3,7-diphenyl-3,7-diphosphacyclooctane, P(Ph)(2)N(Ph)(2) is 1,3,5,7-tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane, and P(Ph)(2)C(5) is 1,4-diphenyl-1,4-diphosphacycloheptane) have been synthesized and characterized by NMR spectroscopy, electrochemical studies, and X-ray diffraction. These chloride derivatives are readily converted to the corresponding hydride complexes [CpFe(P(Ph)(2)N(Bn)(2))H (1-H), CpFe(P(Ph)(2)N(Ph)(2))H (2-H), CpFe(P(Ph)(2)C(5))H (3-H)] and H(2) complexes [CpFe(P(Ph)(2)N(Bn)(2))(H(2))]BAr(F)(4), [1-H(2)]BAr(F)(4), (where BAr(F)(4) is B[(3,5-(CF(3))(2)C(6)H(3))(4)](-)), [CpFe(P(Ph)(2)N(Ph)(2))(H(2))]BAr(F)(4), [2-H(2)]BAr(F)(4), and [CpFe(P(Ph)(2)C(5))(H(2))]BAr(F)(4), [3-H(2)]BAr(F)(4), as well as [CpFe(P(Ph)(2)N(Bn)(2))(CO)]BAr(F)(4), [1-CO]Cl. Structural studies are reported for [1-H(2)]BAr(F)(4), 1-H, 2-H, and [1-CO]Cl. The conformations adopted by the chelate rings of the P(Ph)(2)N(Bn)(2) ligand in the different complexes are determined by attractive or repulsive interactions between the sixth ligand of these pseudo-octahedral complexes and the pendant N atom of the ring adjacent to the sixth ligand. An example of an attractive interaction is the observation that the distance between the N atom of the pendant amine and the C atom of the coordinated CO ligand for [1-CO]BAr(F)(4) is 2.848 ?, considerably shorter than the sum of the van der Waals radii of N and C atoms. Studies of H/D exchange by the complexes [1-H(2)](+), [2-H(2)](+), and [3-H(2)](+) carried out using H(2) and D(2) indicate that the relatively rapid H/D exchange observed for [1-H(2)](+) and [2-H(2)](+) compared to [3-H(2)](+) is consistent with intramolecular heterolytic cleavage of H(2) mediated by the pendant amine. Computational studies indicate a low barrier for heterolytic cleavage of H(2). These mononuclear Fe(II) dihydrogen complexes containing pendant amines in the ligands mimic crucial features of the distal Fe site of the active site of the [FeFe]-hydrogenase required for H-H bond formation and cleavage.     

Dithiocarboxylate complexes of ruthenium(II) and osmium(II)

The ruthenium(II) complexes [Ru(R)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh) are formed on reaction of IPr·CS(2) with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] (BTD = 2,1,3-benzothiadiazole) or [Ru(C(C≡CPh)=CHPh)Cl(CO)(PPh(3))(2)] in the presence of ammonium hexafluorophosphate. Similarly, the complexes [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)](+) are formed in the same manner when ICy·CS(2) is employed. The ligand IMes·CS(2) reacts with [Ru(R)Cl(CO)(BTD)(PPh(3))(2)] to form the compounds [Ru(R)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C≡CPh)=CHPh). Two osmium analogues, [Os(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) and [Os(C(C≡CPh)=CHPh)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+) were also prepared. When the more bulky diisopropylphenyl derivative IDip·CS(2) is used, an unusual product, [Ru(κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IDip)Cl(CO)(PPh(3))(2)](+), with a migrated vinyl group, is obtained. Over extended reaction times, [Ru(CH=CHC(6)H(4)Me-4)Cl(BTD)(CO)(PPh(3))(2)] also reacts with IMes·CS(2) and NH(4)PF(6) to yield the analogous product [Ru{κ(2)-SC(H)S(CH=CHC(6)H(4)Me-4)·IMes}Cl(CO)(PPh(3))(2)](+)via the intermediate [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IMes)(CO)(PPh(3))(2)](+). Structural studies are reported for [Ru(CH=CHC(6)H(4)Me-4)(κ(2)-S(2)C·IPr)(CO)(PPh(3))(2)]PF(6) and [Ru(C(C≡CPh)=CHPh)(κ(2)-S(2)C·ICy)(CO)(PPh(3))(2)]PF(6).     

Analysis of triacylglycerols with non-aqueous reversed-phase liquid chromatography and positive ion electrospray tandem mass spectrometry

A non-aqueous reversed-phase liquid chromatographic method coupled to electrospray ionisation (ESI) tandem mass spectrometry was developed for the analysis of triacylglycerols (TGs). The synthetic TGs studied were separated according to their equivalent carbon number with a gradient of methanol (containing 0.01% (v/v) formate adjusted to pH 5.3 with ammonia) and chloroform. ESI mass spectra of TGs yielded positive ion current signals for [M + NH(4)](+) and [M + NH(4)-RCOONH(4)](+). The mass spectra also showed signals believed to arise from [M + K](+). Collision-induced dissociation (CID) of the [M + NH(4)](+) precursor ion yielded [M + NH(4) - RCOONH(4)](+), [RCO + 74](+) and [RCO](+) product ions as aids for the structural elucidation of the TGs. In addition, [RCO - 18](+) and small amounts of [RCO - 2](+) product ions were also found. The latter ions were observed only for TGs containing unsaturated fatty acids. CID of ammoniated 1-stearoyl-2-oleoyl-3-linoleoyl-glycerol (18:0/18:1/18:2) indicated that neutral loss of the sn-2 fatty acid was energetically less favourable than loss of the fatty acid from the sn-1 or sn-3 position.     

Anion selectivity in zwitterionic amide-functionalised metal salt extractants

Amide-functionalised salen ligands capable of extracting metal salts have been synthesised and characterised. Single-crystal X-ray structure determinations of complexes of NiSO4, [Ni(L)(SO4)], confirm that the ionophores are in a zwitterionic form with Ni(II) bound in the deprotonated salen moiety and the SO4(2-) ion associated with protonated pendant N'-amidopiperazine groups. Treatment of [Ni(L)(SO4)] with base removes the protons from the pendant amido-amine group resulting in loss of the SO4(2-) ion and formation of metal-only complexes of type [Ni(L-2H)], which have been characterized by single-crystal X-ray diffraction. Three of the ligands with solubilities suitable for solvent extraction studies show loading and stripping pH-profiles that are suitable for the recovery of CuSO4 or CuCl2 from industrial leach solutions. The copper-only complexes, [Cu(L-2H)], are selective for Cl- over SO4(2-) in both solvent extraction and bulk liquid membrane transport experiments and were found to bind Cl- in two steps via the formation of a 1:1:1 [Cu(L-H)Cl] assembly, followed by a 1:1:2 [Cu(L)Cl2] assembly as the pH of the aqueous phase is lowered. The anion transport selectivity was evaluated for a number of other mono-charged anions and interestingly the ligands were found to display a preference for the Br- ion. To probe the influence of the Hofmeister bias on the selectivity of anion complexation, single-phase potentiometric titration experiments were employed to investigate the binding of SO4(2-) and Cl- by one of the copper only complexes, [Cu(L-2H)] in 95 %/5 % MeOH/water. Under these conditions selectivity was reversed (SO4(2-)>Cl-) confirming that the Hofmeister bias, which reflects the relative hydration energies of the anions, dominates the selectivity of anion extraction from aqueous media into CHCl3.     

Tetraphosphinitoresorcinarene complexes: dynamic clusters with silver(I) and copper(I) halides

Silver(I) and copper(I) halide derivatives of several tetrakis(diphenylphosphinito)resorcinarene ligands are reported. The complexes [resorcinarene(O(2)CR)(4)(OPPh(2))(4)(M(5)X(5))], with resorcinarene = (PhCH(2)CH(2)CHC(6)H(2))(4), R = C(6)H(11), 4-C(6)H(4)Me, C(4)H(3)S, OCH(2)CCH, or OCH(2)Ph, M = Ag, X = Cl, Br, or I, M = Cu, and X = Cl or I, contain a crownlike [P(4)M(5)X(5)] metal halide cluster. These crown clusters were found to be dynamic in solution, as studied by variable-temperature NMR, and easily fragment to give the corresponding complexes containing [P(4)M(4)X(5)](-) and [P(4)M(2)(micro-X)](+) units. Reaction of pentasilver crown clusters with triflic acid gave the corresponding disilver complexes [resorcinarene(O(2)CR)(4)(OPPh(2))(4)]Ag(2)(micro-Cl)]]CF(3)SO(3). Thus, these resorcinarene-based ligands act as a platform for the easy and reversible assembly of copper(I) and silver(I) clusters with novel structures.     

Influence of solvent and counter ion on copper complexes with N-alkyl-pyridine-2-carboxamides as studied by electrospray ionization mass spectrometry

The interactions of copper(II) with N-alkyl-pyridine-2-carboxamides (M) were studied by electrospray ionization mass spectrometry. The influence of solvent and counter ion (Cl-, ClO4-) on the type of ions (complexes) observed was discussed. By cone voltage increase, the fragmentation "in source" of the ions discussed was achieved. In methanol solution containing N-alkyl-pyridine-2-carboxamide (M) and CuCl2 the singly- and doubly charged-ions [M+CuCl]+ and [M2+Cu]+2 were detected. In acetonitrile solution containing N-alkyl-pyridine-2-carboxamide and CuCl2, the copper(I)-containing ions [M+CH3CN+Cu]+ were formed. The use of Cu(ClO4)2 instead of CuCl2 resulted in more abundant doubly-charged ions in both methanol and acetonitrlile solutions and, for the former solution, the ions containing methoxyl anion, namely [M+CuOCH3]+, were observed. When water was used as a solvent, the abundant ions corresponding to the protonated ligands were formed, while the ions corresponding to copper complexes were characterised by low abundances.     

Mass spectrometric studies on pyridine-piperazine-containing ligands and their complexes with transition metals formed in solution

Electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) methods were used to study open-chain piperazine-containing ligands (L) and their complexes formed with transition-metal salts. ESI and MALDI measurements were performed with a Fourier transform ion cyclotron resonance (FT-ICR) and a time-of-flight (TOF) mass spectrometer, respectively. Only singly charged complexes, between one ligand and one or several metal ions, were formed in the ESI measurements. Because the net charge was always one, one or several counterions were attached to the complex. Under ESI conditions, the complexes formed between the ligands and metal (Co, Ni, Cu, and Cd) salts were [L + M + X](+), [L + H + M + X(2)](+) and [L + M(2) + X(3)](+) (M = metal ion, X = counterion). In collision induced dissociation reactions the [L + H + M + X(2)](+) complexes easily eliminated one proton and one counterion. Fragmentation pathways were more dependent on the metal ion than the ligand, and elimination of the second counterion occurred with one proton from copper and nickel complexes and with one proton and one hydrogen from cobalt complexes. Differences in the fragmentation of the complexes could be due to electronic configuration of the metal ion. In the MALDI measurements the ratio between the [L + H](+) and [L - H](+) ions varied with the matrix. Fragmentation of the ligands through elimination of 2-methylpyridine end groups occurred with the aromatic matrices containing carboxylic acid and hydroxyl substituents. Ionization of the complexes was not successful with MALDI as the matrix molecules were also attached to the complexes.     

Tri- and tetracoordinate copper(I) complexes bearing bidentate soft/hard SN and SeN ligands based on 2-aminopyridine

The coordination properties of the EN ligands N-(2-pyridinyl)amino-diphenylphosphine sulfide, N-(2-pyridinyl)amino-diisopropylphosphine sulfide, N-(2-pyridinyl)amino-diphenylphosphine selenide, N-(2-pyridinyl)amino-diisopropylphosphine selenide towards copper(I) precursors CuX (X = Br, I), [Cu(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), and [Cu(CH(3)CN)(4)]PF(6) were studied. Treatment of CuX with EN ligands resulted in the formation of tricoordinate complexes of the type [Cu(κ(2)(E,N)-EN)X]. The reaction of [Cu(IPr)Cl] with EN ligands, followed by halide abstraction with AgSbF(6), afforded cationic tricoordinate complexes [Cu(κ(2)(S,N)-EN)(IPr)](+), while the reaction of [Cu(CH(3)CN)(4)](+) with two equivalents of EN ligands yielded tetrahedral complexes [Cu(κ(2)(E,N)-EN)(2)](+). Halide removal from [Cu(κ(2)(S,N)-SN)I] with silver salts in the presence of L = CH(3)CN and CNtBu afforded dinuclear complexes of the type [Cu(κ(2)(S,N),μ(S)-SN)(L)](2)(2+) containing bridging SN ligands. With the terminal alkynes HC≡CC(6)H(4)Me and HC≡CC(6)H(4)OMe, complexes of the formula [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)Me)](+) and [Cu(κ(2)(S,N)-SN-iPr)(η(2)-HC≡CC(6)H(4)OMe)](+) were obtained. The mononuclear nature of these compounds was supported by DFT calculations. Most complexes were also characterized by X-ray crystallography.     

Crystal structures of Au2 complex and Au25 nanocluster and mechanistic insight into the conversion of polydisperse nanoparticles into monodisperse Au25 nanoclusters

We previously reported a size-focusing conversion of polydisperse gold nanoparticles capped by phosphine into monodisperse [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) nanoclusters in the presence of phenylethylthiol. Herein, we have determined the crystal structure of [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) nanoclusters and also identified an important side-product-a Au(I) complex formed in the size focusing process. The [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)Cl(2)](2+) cluster features a vertex-sharing bi-icosahedral core, resembling a rod. The formula of the Au(I) complex is determined to be [Au(2)(PPh(3))(2)(SC(2)H(4)Ph)](+) by electrospray ionization (ESI) mass spectrometry, and its crystal structure (with SbF(6)(-) counterion) reveals Au-Au bridged by -SC(2)H(4)Ph and with terminal bonds to two PPh(3) ligands. Unlike previously reported [Au(2)(PR(3))(2)(SC(2)H(4)Ph)](+) complexes in the solid state, which exist as tetranuclear complexes (i.e., dimers of [Au(2)(PR(3))(2)(SC(2)H(4)Ph)](+) units) through a Au···Au aurophilic interaction, in our case we found that the [Au(2)(PPh(3))(2)(SC(2)H(4)Ph)](+) complex exists as a single entity, rather than being dimerized to form a tetranuclear complex. The observation of this Au(I) complex allows us to gain insight into the intriguing conversion process from polydisperse Au nanoparticles to monodisperse Au(25) nanoclusters.     

Approaching the gas-phase structures of [AgS8]+ and [AgS16]+ in the solid state

Upon treating elemental sulfur with [AgSbF(6)], [AgAl(hfip)(4)], [AgAl(pftb)(4)] (hfip=OCH(CF(3))(2), pftb =OC(CF(3))(3)) the compounds [Ag(S(8))(2)][SbF(6)] (1), [AgS(8)][Al(hfip)(4)] (2), and [Ag(S(8))(2)](+)[[Al(pftb)(4)](-) (3) formed in SO(2) (1), CS(2) (2), or CH(2)Cl(2) (3). Compounds 1-3 were characterized by single-crystal X-ray structure determinations: 1 by Raman spectroscopy, 2 and 3 by solution NMR spectroscopy and elemental analyses. Single crystals of [Ag(S(8))(2)](+)[Sb(OTeF(5))(6)](-) 4 were obtained from a disproportionation reaction and only characterized by X-ray crystal structure analysis. The Ag(+) ion in 1 coordinates two monodentate SbF(6) (-) anions and two bidentate S(8) rings in the 1,3-position. Compound 2 contains an almost C(4v)-symmetric [AgS(8)](+) moiety; this is the first example of an eta(4)-coordinated S(8) ring (d(Agbond;S)=2.84-3.00 A). Compounds 3 and 4, with the least basic anions, contain undistorted, approximately centrosymmetric Ag(eta(4)-S(8))(2) (+) cations with less symmetric eta(4)-coordinated S(8) rings (d(Agbond;S)=2.68-3.35 A). The thermochemical radius and volume of the undistorted Ag(S(8))(2) (+) cation was deduced as r(therm)(Ag(S(8))(2) (+))=3.378+ 0.076/-0.120 A and V(therm)(Ag(S(8))(2) (+))=417+4/-6 A(3). AgS(8) (+) and several isomers of the Ag(S(8))(2) (+) cation were optimized at the BP86, B3LYP, and MP2 levels by using the SVP and TZVPP basis sets. An analysis of the calculated geometries showed the MP2/TZVPP level to give geometries closest to the experimental data. Neither BP86 nor B3LYP reproduced the longer weak dispersive Agbond;S interactions in Ag(eta(4)-S(8))(2) (+) but led to Ag(eta(3)-S(8))(2) (+) geometries. With the most accurate MP2/TZVPP level, the enthalpies of formation of the gaseous [AgS(8)](+) and [Ag(S(8))(2)](+) cations were established as Delta(f)H(298)([Ag(S(8))(2)](+), g)=856 kJ mol(-1) and Delta(f)H(298)([AgS(8)](+), g)=902 kJ mol(-1). It is shown that the [AgS(8)](+) moiety in 2 and the [AgS(8)](2) (+) cations in 3 and 4 are the best approximation of these ions, which were earlier observed by MS methods. Both cations reside in shallow potential-energy wells where larger structural changes only lead to small increases in the overall energy. It is shown that the covalent Agbond;S bonding contributions in both cations may be described by two components: i) the interaction of the spherical empty Ag 5s(0) acceptor orbital with the filled S 3p(2) lone-pair donor orbitals and ii) the interaction of the empty Ag 5p(0) acceptor orbitals with the filled S 3p(2) lone-pair donor orbitals. This latter contribution is responsible for the observed low symmetry of the centrosymmetric Ag(eta(4)-S(8))(2) (+) cation. The positive charge transferred from the Ag(+) ion in 1-4 to the coordinated sulfur atoms is delocalized over all the atoms in the S(8) ring by multiple 3p(2)-->3sigma* interactions that result in a small long-short-long-short Sbond;S bond-length alternation starting from S1 with the shortest Agbond;S length. The driving force for all these weak bonding interactions is positive charge delocalization from the formally fully localized charge of the Ag(+) ion.     

Formation of diclofenac molecular ions as the effect of Cu(2+)-π interaction under electrospray ionization mass spectrometry conditions

Solutions containing diclofenac (M) and a copper salt [CuCl2, Cu(ClO4)2, Cu(NO3)2, CuSO4) were analysed by electrospray ionisation mass spectrometry (ESI-MS). Because of the cation-pi interactions in diclofenac-Cu(II) complexes, the diclofenac molecular ion M+* at m/z 295 was formed. It was found that the solvent composition (methanol versus water/methanol) and counter ion strongly affect the M+* ion formation. Formation pathways of ion M+* are discussed.     

Can metal ions be used as gas‐phase disulfide bond cleavage reagents? A survey of coinage metal complexes of model peptides containing an intermolecular disulfide bond

The role that a metal ion can have in promoting disulfide bond cleavage has been assessed by surveying the tandem mass spectra of the following metal complexes of model peptides containing an intermolecular disulfide bond: [M--H+Cu(II)](+); [M--H+Cu(II)(bipy)](+); [M+Ag(I)](+); and [M+Au(I)(PMe(3))](+). In comparison to previously studied protonated peptides, these binary and ternary metal complexes generally yield more abundant S--S and/or C--S bond cleavage. In general, [M--H+Cu(II)](+) ions cleave the adjacent C--S bond more readily, while the [M+Au(I)(PMe(3))](+) ion cleaves the S--S bond more readily. The ternary metal complex [M--H+Cu(II)(bipy)](+), on the other hand, fragments by exclusive loss of the bipyridyl ligand for the larger model peptides studied. Of all coinage metal systems studied, Me(3)PAu(+) is superior in promoting disulfide bond cleavage.