The repulsive Coulomb barrier along a dissociation path of the BeC(2-)(4) dianion

We present ab initio calculations of the repulsive Coulomb barrier for several geometrically stable isomers of the BeC(2-)(4) dianion. We describe how the deformation of certain isomers can account for the experimental Coulomb explosion images of the dianion. For the most stable linear isomer, C(-)(2)BeC(-)(2), we examined the electron tunneling process along the dissociation path to obtain C(-)(2) plus BeC(-)(2). We found the crossing point for autodetachment to be R(c)(dis)= 3.25 A. R(dis) is the bond length between C(-)(2) and BeC(-)(2); at this point, the electron tunneling energy is equal to the maximum of the repulsive Coulomb barrier. In the framework of the Wenzel-Kramer-Brioullin theory, the electron-loss lifetime of the metastable C(-)(2)BeC(-)(2) dianion at the equilibrium geometry, R(dis) = 1.64 A, was estimated to be about 5 ms. This lower limit is in agreement with the experimental results in which the BeC(2-)(4) dianion has a lifetime much longer than 5 micros.     

Study of ion specific interactions of alkali cations with dicarboxylate dianions

Alkali metal cations often show pronounced ion-specific interactions and selectivity with macromolecules in biological processes, colloids, and interfacial sciences, but a fundamental understanding about the underlying microscopic mechanism is still very limited. Here we report a direct probe of interactions between alkali metal cations (M(+)) and dicarboxylate dianions, (-)O(2)C(CH(2))(n)CO(2)(-) (D(n)(2-)) in the gas phase by combined photoelectron spectroscopy (PES) and ab initio electronic structure calculations on nine M(+)-D(n)(2-) complexes (M = Li, Na, K; n = 2, 4, 6). PES spectra show that the electron binding energy (EBE) decreases from Li(+) to Na(+) to K(+) for complexes of M(+)-D(2)(2-), whereas the order is Li(+) < Na(+) ≈ K(+) when M(+) interacts with a more flexible D(6)(2-) dianion. Theoretical modeling suggests that M(+) prefers to interact with both ends of the carboxylate -COO(-) groups by bending the flexible aliphatic backbone, and the local binding environments are found to depend upon backbone length n, carboxylate orientation, and the specific cation M(+). The observed variance of EBEs reflects how well each specific dicarboxylate dianion accommodates each M(+). This work demonstrates the delicate interplay among several factors (electrostatic interaction, size matching, and strain energy) that play critical roles in determining the structures and energetics of gaseous clusters as well as ion specificity and selectivity in solutions and biological systems.     

The dianion of 5-cyanoiminotetrazoline: C2N62-

Several salts (alkali, Pd(NH(3))(3), and (i)PrNH(2)) of 5-cyanoiminotetrazoline (C(2)N(6)(2-), 5-cyanoiminotetrazolinediide, CIT) were investigated. A full characterization by means of X-ray, Raman, NMR techniques, mass spectrometry, and elemental analysis is presented for the (i)()PrNH(2) (4), Cs (5), and Pd(NH(3))(3) (6) salts. The CIT dianion represents a nitrogen-rich binary CN dianion, and 5 forms monoclinic crystals (a = 7.345(2) Angstroms, b = 9.505(2) Angstroms, c = 10.198(2) Angstroms, beta = 92.12(3) degrees, space group P2(1)/n, Z = 4). DSC and in situ temperature-dependent X-ray diffraction measurements of the cesium salt 5 revealed an astonishing thermal stability accompanied by a reversible phase transition from the low-temperature alpha modification to the metastable beta modification at 253 degrees C. Above the melting point (334 degrees C), the cesium salt decomposes yielding cesium azide and cesium dicyanamide, which decomposes under further heating under release of nitrogen. The reaction of Cs(2)CIT with SO(2) resulted in the surprising formation of a new cesium salt with the 5-cyaniminotetrazoline-1-sulfonate dianion (Cs(2)CITSO(3).SO(2) (7)). 7 crystallizes in the monoclinic space group P2(1) with one SO(2) solvent molecule (a = 8.0080(2) Angstroms, b = 8.0183(2) Angstroms, c = 9.8986(3) Angstroms, beta = 108.619(1) degrees, Z = 2). The structure and bonding of the 10pi dianion are discussed on the basis B3LYP/aug-cc-pvTZ computations (MO, NBO), and the three-dimensional array of the cesium salts with respect to the Cs(delta) (+)-N(delta)(-) in 5 compared to the Cs(delta)(+)-N(delta)(-) and Cs(delta)(+)-O(delta)(-) in 7 is discussed. Due to the expected rich bonding modes of the CIT anions, the coordination chemistry with palladium was also studied, yielding monoclinic crystals of [Pd(CIT)(NH(3))(3)].H(2)O (6, a = 7.988(2) Angstroms, b = 8.375(2) Angstroms, c = 13.541(3) Angstroms, beta = 104.56 degrees, space group P2(1)/n, Z = 4). In the solid state, the complex is composed of dimers, showing two agostic interactions and an unusual close interplanar pi-pi stacking of the tetrazole moiety of the CIT ligand.     

Periodic trends in hexanuclear actinide clusters

Four new Th(IV), U(IV), and Np(IV) hexanuclear clusters with 1,2-phenylenediphosphonate as the bridging ligand have been prepared by self-assembly at room temperature. The structures of Th(6)Tl(3)[C(6)H(4)(PO(3))(PO(3)H)](6)(NO(3))(7)(H(2)O)(6)·(NO(3))(2)·4H(2)O (Th6-3), (NH(4))(8.11)Np(12)Rb(3.89)[C(6)H(4)(PO(3))(PO(3)H)](12)(NO(3))(24)·15H(2)O (Np6-1), (NH(4))(4)U(12)Cs(8)[C(6)H(4)(PO(3))(PO(3)H)](12)(NO(3))(24)·18H(2)O (U6-1), and (NH(4))(4)U(12)Cs(2)[C(6)H(4)(PO(3))(PO(3)H)](12)(NO(3))(18)·40H(2)O (U6-2) are described and compared with other clusters of containing An(IV) or Ce(IV). All of the clusters share the common formula M(6)(H(2)O)(m)[C(6)H(3)(PO(3))(PO(3)H)](6)(NO(3))(n)((6-n)) (M = Ce, Th, U, Np, Pu). The metal centers are normally nine-coordinate, with five oxygen atoms from the ligand and an additional four either occupied by NO(3)(-) or H(2)O. It was found that the Ce, U, and Pu clusters favor both C(3i) and C(i) point groups, while Th only yields in C(i), and Np only C(3i). In the C(3i) clusters, there are two NO(3)(-) anions bonded to the metal centers. In the C(i) clusters, the number of NO(3)(-) anions varies from 0 to 2. The change in the ionic radius of the actinide ions tunes the cavity size of the clusters. The thorium clusters were found to accept larger ions including Cs(+) and Tl(+), whereas with uranium and later elements, only NH(4)(+) and/or Rb(+) reside in the center of the clusters.     

Cyclic carbon cluster dianions and their aromaticity

Cyclic carbon cluster dianions (CC(2))(2-)(n)(n = 3-6) are investigated by ab initio methods with regard to their geometric properties, electronic stability, and aromaticity. The unique wheel-like structures of these dianions consist of a n-membered carbon ring, where a C(2) unit is attached to each carbon atom. All investigated dianions represent stable gas-phase dianions. While the smallest member of this family (CC(2))(2-)(3) is clearly aromatic, the aromatic character decreases rapidly with increasing ring size. The geometries and the aromaticity of the cyclic clusters (CC(2))(2-)(n)(n = 3-6) can be nicely explained using resonance structure arguments.     

Geometry and stability of BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters

Density functional theory B3PW91/6-31+G* calculations on BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters have been carried out to examine the effect of cluster size, relative composition, binding energy per atom, HOMO-LUMO gap, vertical ionization potential, and electron affinity on their relative stabilities. The most stable planar cyclic conformations of these clusters always show at least a set of two carbon atoms between two beryllium atoms, while structures where beryllium atoms cluster together, or allow the intercalation of one carbon atom between two of them, generally seem to be the least stable ones. Clusters containing 1, 2, and 3 beryllium atoms (Be2C8, Be3C6, Be2C6, BeC6, Be2C4, BeC4, Be2C2, and BeC2) are identified as clusters of "magic numbers" in terms of their high binding energy per atom, high HOMO-LUMO gap, vertical ionization potential, and second difference in energy per beryllium atom.     

Study of the Lithiated Phenylacetonitrile Monoanions and Dianions Formed According to the Lithiated Base Used (LHMDS, LDA, or n-BuLi). 2. Alkylation and Deuteriation Mechanism Study by Vibrational and NMR Spectroscopy and Quantum Chemistry Calculations

Mechanisms of alkylation by PhCH(2)Cl or CH(3)I in THF and of deuteriation by DCl (4 N in D(2)O) in THF or THF-toluene of lithiated phenylacetonitrile monoanions and dianions obtained with LHMDS, LDA, or n-BuLi are studied by vibrational and NMR spectroscopy and quantum chemistry calculations. Dialkylation of the three dilithio dianions generated with n-BuLi (2.0-2.7 equiv, THF-hexane) depends on their structure: N-lithio (PhCCNLi)(-)Li(+) and (C,N)-dilithio PhCLiCNLi dianions afford PhCR(2)CN (R = PhCH(2), CH(3)) from the intermediate N-lithio monoalkylated monoanion PhCRCNLi 10; C-lithio dianion (PhCLiCN)(-)Li(+) leads to a carbenoid species, the C-lithio monoalkylated nitrile PhCLiRCN 11, which either eliminates carbene Ph-C?-R and different LiCN species or isomerizes to PhCRCNLi in the presence of LiX (X = Cl, I). Dialkylation or dideuteriation of monoanions (monomers, dimers, and heterodimers [PhCHCNLi·LiR'], R' = (SiMe(3))(2)N, (i-Pr)(2)N) obtained with LHMDS or LDA (2.4 equiv, THF) proceeds via a sequential mechanism involving monometalation-monoalkylation (or monodeuteriation) reactions. Some carbene and (LiCNLi)(+) are also observed, and explained by another mechanism implying the C-lithio monoalkylated monoanion PhCLiRCN 9 in the presence of LiX. These results show the ambiphilic behavior of PhCLiRCN as a carbenoid (11) or a carbanion (9) and the importance of LiX formed in situ in the first alkylation step.     

Gas-phase stability of derivatives of the closo-hexaborate dianion B(6)H(6)(2-)

B(6)H(6)(2-) does not represent a stable gas-phase dianion, but emits spontaneously one of its excess electrons in the gas phase. In this work we address the question whether small stable gas-phase dianions can be constructed from the parent B(6)H(6)(2-) dianion by substitution of the hydrogens with appropriate ligands. Various hexa-, tetra-, and disubstituted derivatives B(6)L(6)(2-), B(6)H(2)L(4)(2-), and B(6)H(4)L(2)(2-) (L = F, Cl, CN, NC, or BO) are investigated with ab initio methods in detail. Four stable hexasubstituted B(6)L(6)(2-) (L = Cl, CN, NC, or BO) and three stable B(6)H(2)L(4)(2-) (L = CN, NC, or BO) gas-phase dianions could be identified and predicted to be observable in the gas phase. The trends in the electron-detachment energies depending on various ligands are discussed and understood in the underlying electrostatic pattern and the electronegativities of the involved elements.     

Small gas-phase dianions of Zn3O(4)(2-), Zn4O(5)(2-), CuZn2O(4)(2-), Si2GeO(6)(2-), Ti2O(5)(2-) and Ti3O(7)(2-)

We have searched for new species of small oxygen-containing gas-phase dianions produced in a secondary ion mass spectrometer by Cs+ ion bombardment of solid samples with simultaneous exposure of their surfaces to O2 gas. The targets were a pure zinc metal foil, a copper-contaminated zinc-based coin, two silicon-germanium samples (Si(1-x)Ge(x)(with x= 6.5% or 27%)) and a piece of titanium metal. The novel dianions Zn3O(4)(2-), Zn4O(5)(2-), CuZn2O(4)(2-), Si2GeO(6)(2-), Ti2O(5)(2-) and Ti3O(7)(2-) have been observed at half-integer m/z values in the negative ion mass spectra. The heptamer dianions Zn3O(4)(2-) and Ti2O(5)(2-) have been unambiguously identified by their isotopic abundances. Their flight times through the mass spectrometer are approximately 20 micros and approximately 17 micros, respectively. The geometrical structures of the two heptamer dianions Ti2O(5)(2-), and Zn3O(4)(2-) are investigated using ab initio methods, and the identified isomers are compared to those of the novel Ge2O(5)(2-) and the known Si2O(5)(2-) and Be3O(4)(2-) dianions.     

The first example of macrocycles containing butterfly transition metal cluster cores via novel tandem reactions

A novel type of double butterfly, two mu-CO-containing dianions {[(mu-CO)Fe2(CO)6]2[mu-SCH2(CH2OCH2)nCH2S-mu]}2- (m1, n = 2, 3), has been synthesized from dithiol HSCH2(CH2OCH2)nCH2SH (n = 2, 3), Fe3(CO)12, and Et3N in THF at room temperature. While dianions m1 react in situ with CS2 followed by treatment with dihalide 1,4-(BrCH2)2C6H4 or 1,4-I(CH2)4I to give macrocyclic clusters [mu-SCH2(CH2OCH2)nCH2S-mu](mu-CS2ZCS2-mu)[Fe2(CO)6]2 (1a, n = 2, Z = 1,4-(CH2)2C6H4; 1b, n = 3, Z = (CH2)4), reactions of dianions m1 with (mu-S2)Fe2(CO)6 followed by treatment with dihalide 1,4-I(CH2)4I afford macrocyclic clusters [mu-SCH2(CH2OCH2)nCH2S-mu]{[Fe2(CO)6]2(mu4-S)}2[mu-S(CH2)4S-mu] (2a, n = 2; 2b, n = 3). The crystal structures of 1a and 2b are described.     

Formation and chemical reactivities of a new type of double-butterfly [[Fe2(mu-CO)(CO)6]2(mu-SZS-mu)]2-: synthetic and structural studies on novel linear and macrocyclic butterfly Fe/E (E=S,Se) cluster complexes

A new type of double-butterfly [[Fe(2)(mu-CO)(CO)(6)](2)(mu-SZS-mu)](2-) (3), a dianion that has two mu-CO ligands, has been synthesized from dithiol HSZSH (Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2)), [Fe(3)(CO)(12)], and Et(3)N in a molar ratio of 1:2:2 at room temperature. Interestingly, the in situ reactions of dianions 3 with various electrophiles affords a series of novel linear and macrocyclic butterfly Fe/E (E=S, Se) cluster complexes. For instance, while reactions of 3 with PhC(O)Cl and Ph(2)PCl give linear clusters [[Fe(2)(mu-PhCO)(CO)(6)](2)(mu-SZS-mu)] (4 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2)) and [[Fe(2)(mu-Ph(2)P)(CO)(6)](2)(mu-SZS-mu)] (5 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2)), reactions with CS(2) followed by treatment with monohalides RX or dihalides X-Y-X give both linear clusters [[Fe(2)(mu-RCS(2))(CO)(6)](2)(mu-SZS-mu)] (6 a-e: Z=CH(2)(CH(2)OCH(2))(1,2)CH(2); R=Me, PhCH(2), FeCp(CO)(2)) and macrocyclic clusters [[Fe(2)(CO)(6)](2)(mu-SZS-mu)(mu-CS(2)YCS(2)-mu)] (7 a-e: Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2); Y=(CH(2))(2-4), 1,3,5-Me(CH(2))(2)C(6)H(3), 1,4-(CH(2))(2)C(6)H(4)). In addition, reactions of dianions 3 with [Fe(2)(mu-S(2))(CO)(6)] followed by treatment with RX or X-Y-X give linear clusters [[[Fe(2)(CO)(6)](2)(mu-RS)(mu(4)-S)](2)(mu-SZS-mu)] (8 a-c: Z=CH(2)(CH(2)OCH(2))(1,2)CH(2); R=Me, PhCH(2)) and macrocyclic clusters [[[Fe(2)(CO)(6)](2)(mu(4)-S)](2)(mu-SYS-mu)(mu-SZS-mu)] (9 a,b: Z=CH(2)(CH(2)OCH(2))(2,3)CH(2); Y=(CH(2))(4)), and reactions with SeCl(2) afford macrocycles [[Fe(2)(CO)(6)](2)(mu(4)-Se)(mu-SZS-mu)] (10 d: Z=CH(2)(CH(2)OCH(2))(3)CH(2)) and [[[Fe(2)(CO)(6)](2)(mu(4)-Se)](2)(mu-SZS-mu)(2)] (11 a-d: Z=(CH(2))(4), CH(2)(CH(2)OCH(2))(1-3)CH(2)). Production pathways have been suggested; these involve initial nucleophilic attacks by the Fe-centered dianions 3 at the corresponding electrophiles. All the products are new and have been characterized by combustion analysis and spectroscopy, and by X-ray diffraction techniques for 6 c, 7 d, 9 b, 10 d, and 11 c in particular. X-ray diffraction analyses revealed that the double-butterfly cluster core Fe(4)S(2)Se in 10 d is severely distorted in comparison to that in 11 c. In view of the Z chains in 10 a-c being shorter than the chain in 10 d, the double cluster core Fe(4)S(2)Se in 10 a-c would be expected to be even more severely distorted, a possible reason for why 10 a-c could not be formed.     

Formation of aluminium, aluminium nitride and nitrogen clusters via laser ablation of nano aluminium nitride. Laser Desorption Ionisation and Matrix-Assisted Laser Desorption Ionisation Time-of-Flight Mass Spectrometry

Laser Desorption Ionisation (LDI) and Matrix-Assisted Laser Desorption Ionisation (MALDI) Time-of-Flight Mass Spectrometry (TOFMS) were used to study the pulsed laser ablation of aluminium nitride (AlN) nano powder. The formation of Al(m)(+) (m=1-3), N(n)(+) (n=4, 5), AlN(n)(+) (n=1-5, 19, 21), Al(m)N(+) (m=2-3), Al(3)N(2)(+), Al(9)N(n)(+) (n=5, 7, 9, 11 and 15), Al(11)N(n)(+) (n=4, 6, 10, 12, 19, 21, 23, and 25), and Al(13)N(n)(+) (n=25, 31, 32, 33, 34, 35, and 36) clusters was detected in positive ion mode. Similarly, Al(m)(-) (m=1-3), AlN(n)(-) (n=1-3, 5), Al(m)N(-) (n=2, 3), Al(2)N(n)(-) (n=2-4, 28, 30), N(n)(-) (n=2, 3), Al(4)N(7)(-) Al(8)N(n)(-) (n=1-6), and Al(13)N(n)(-) (n=9, 18, 20, 22, 24, 26, 28, 33, 35, 37, 39, 41 and 43) clusters were observed in negative ion mode. The formation of the stoichiometric Al(10) N(10) cluster was shown to be of low abundance. On the contrary, the laser ablation of nano-AlN led mainly to the formation of nitrogen-rich Al(m)N(n) clusters in both negative and positive ion mode. The stoichiometry of the Al(m)N(n) clusters was determined via isotopic envelope analysis and computer modelling.     

Laser ablation synthesis of new phosphorus nitride clusters from α-P3N5 via Laser Desorption Ionization and Matrix Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry

Phosphorus nitride clusters generated during Laser Desorption Ionization (LDI) and Matrix-Assisted Laser Desorption Ionization (MALDI) of solid P(3) N(5) were analyzed via Time-of-Flight Mass Spectrometry (TOF MS). The LDI TOF mass spectra show the formation of series of clusters: P(m)N(n)(+) {(m=1; n=8-11), (m=4; n=3-4), (m=5; n=1-5), (m=6; n=1-3, 5-8), (m=2-7; n=1), (m=5-10; n=2), (m=4-6; n=3), (m=4,5; n=4), (m=5,6; n=5)}, and P(m)N(n)(-) (m=4,5; n=1). Using 3-hydroxypicolinic acid (HPA) as a matrix the P(m)N(n)(+) species (m=1-4, 6, 8) with a high nitrogen content (n=4, 5, 8, 10-12, 20) were identified. The formation of a N(6)(-) cluster was also detected using a C(60) matrix. Under various conditions singly charged P(m)(+) (m=2-7, 9, 13), P(m)(-) (m=3-11, 13, 15, 17), N(n)(+) (n=5, 9, 10, 12, 13), and N(n)(-) (n=6, 10-15) clusters were identified in the mass spectra. Such high nitrogen content clusters (up to N(15)(-)) generated by laser desorption from a solid material are described for the first time. The stoichiometry of the P(m)N(n) clusters was determined via isotopic envelope analysis and computer modelling. The composition of the clusters with respect to the crystalline structure of α-P(3)N(5) is discussed.     

Chiral recognition between a substituted cyclooctatetraene dianion and a half crown ether substituted with ibuprofen

(S)-Verbenol was substituted onto cyclooctatetraene (COT) via an ether linkage. In tetrahydrofuran (THF), Cs(+) or Na(+) counterions are tightly ion associated with the verbenoxy-COT dianion. A cosolvent, consisting of an ibuprofen unit connected to a half crown ether, was added to the verbenoxy-COT(2)(-),M(+)(2) solutions. The intimate interaction between the chiral cosolvent (ibuprofoxymethoxyethoxyethane) and the ion-associated counterion (either Na(+) or Cs(+)) forces a chiral recognition between the verbenoxy moiety and the ibuprofoxy moiety. When a molar excess of the cosolvent is present in the dianion THF solution, separation of the cosolvent associated with the verbenoxy-COT(2)(-),M(+)(2) complex from the uncomplexed cosolvent allows partial resolution of the enantiomers of ibuprofoxymethoxyethoxyethane.     

Germanium and tin analogues of alkynes and their reduction products

The reduction of terphenylgermanium(II) or terphenyltin(II) chlorides with alkali metals was investigated. Treatment of Ar'GeCl or ArGeCl (Ar' = C(6)H(3)-2,6-Dipp(2), Dipp = C(6)H(3)-2,6-Pr(i)(2); Ar = C(6)H(3)-2,6-Trip(2), Trip = C(6)H(2)-2,4,6-Pr(i)(3)) with lithium, sodium, or potassium afforded the neutral alkyne analogues Ar'GeGeAr', 1, ArGeGeAr, 2, the singly reduced radical species NaArGeGeAr, 3, or KAr'GeGeAr', 4, or the doubly reduced compounds Li(2)Ar'GeGeAr', 5, Na(2)ArGeGeAr, 6, or K(2)ArGeGeAr, 7. Similarly, reduction of Ar'SnCl or ArSnCl afforded the neutral Ar'SnSnAr', 8, or ArSnSnAr, 9, the radical anions [(THF)(3)Na[rSnSnAr]], 10, [K(THF)(6)][Ar'SnSnAr'], 11, [K(THF)(6)][ArSnSnAr], 12, [K(18-crown-6)(THF)(2)] [ArSnSnAr], 13, or the doubly reduced Na(2)ArSnSnAr, 14, K(2)Ar'SnSnAr', 15, or K(2)ArSnSnAr, 16. The compounds were characterized by UV-vis, (1)H and (13)C NMR or EPR spectroscopy. The X-ray crystal structures of all compounds were determined except those of 2 and 9. The neutral 1 and 8 displayed planar, trans-bent CMMC (M = Ge and Sn) cores with M-M-C angles of 128.67(8) and 125.24(7) degrees, respectively. The M-M bond lengths, 2.2850(6) and 2.6675(4)A, indicated considerable multiple character and a bond order approaching two. Single and double reduction of the neutral species resulted in the narrowing of the M-M-C angles by ca. 12-32 degrees and changes in the Ge-Ge and Sn-Sn bond lengths. One-electron reduction afforded a slight (ca. 0.03-0.05A) lengthening of the Ge-Ge bonds in the case of germanium species 3 and 4 and a greater lengthening (ca. 0.13-0.15A) for the Sn-Sn bonds in the tin compounds 10-13. The addition of another electron yielded salts of the formal dianions [Ar'MMAr'](2)(-) and [ArMMAr](2)(-) which are isoelectronic to the corresponding doubly bonded, neutral arsenic and antimony derivatives. All the dianion salts were obtained as contact ion triples with two alkali metal cations complexed between aryl rings. The Ge-Ge bonds in the dianions of 5-7 were longer, whereas the Sn-Sn distances in the dianions in 14, 15, and 16 were shorter than those in the monoanions. Unusually, the Li(2)Ar'GeGeAr' salt, 5, displayed a longer Ge-Ge bond (by ca. 0.06A) than those of its Na(+) or K(+) analogue salts which was attributed to the greater polarizing power of Li(+). It was concluded that the M-M bond lengths in 3-7 and 10-16 are dependent on several factors that include M-M-C angle, Coulombic repulsion, alkali metal cation size, and the character of the molecular energy levels. The M-M bonding in the neutral compounds was accounted for in terms of a second-order Jahn-Teller mixing of sigma- and a pi-orbital which afforded bond orders near two for the neutral compounds, 1, 2, 8, and 9. Calculations on MeMMMe (M = Ge or Sn) model species showed that the LUMO corresponded to an orbital that had n(+) lone pair character. The slight Ge-Ge bond length increase upon one-electron reduction is consistent with these results, and the further bond lengthening upon double reduction is consistent with increased Coulombic repulsion. The greater Sn-Sn bond length increase seen for one-electron reduction of the tin species is probably due to the increased p-character of orbitals comprising the Sn-Sn sigma-bond when the Sn-Sn-C angle is decreased by ca. 30 degrees. Upon further reduction, the slight decrease in the Sn-Sn bond is probably a result of the reduced importance of Coulombic repulsion due to the larger size of tin and a widening of the Sn-Sn-C angles which may shorten the Sn-Sn sigma-bond.     

Synthesis, molecular structure and properties of the [H6-nNi30C4(CO)34(CdCl)2]n- (n=3-6) bimetallic carbide carbonyl cluster: a model for the growth of noncompact interstitial metal carbides

Reaction of the [Ni(9)C(CO)(17)](2-) dianion with CdCl(2)2.5 H(2)O in THF affords the novel bimetallic Ni--Cd carbide carbonyl clusters [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-) (n=3-6), which undergo several protonation-deprotonation equilibria in solution depending on the basicity of the solvent or upon addition of acids or bases. Although the occurrence in solution of these equilibria complicates the pertinent electrochemical studies on their electron-transfer activity, they clearly indicate that the clusters [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-) (n=3-6), as well as the structurally related [H(6-n)Ni(34)C(4)(CO)(38)](n-) (n=4-6), undergo reversible or partially reversible redox processes and provide circumstantial and unambiguous evidence for the presence of hydrides for n=3, 4 and 5. Three of the [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-) anions (n=4-6) have been structurally characterized in their [NMe(3)(CH(2)Ph)](4)[H(2)Ni(30)C(4)(CO)(34)(CdCl)(2)]2 COMe(2), [NEt(4)](5)[HNi(30)C(4)(CO)(34)(CdCl)(2)]2 MeCN and [NMe(4)](6)[Ni(30)C(4)(CO)(34)(CdCl)(2)]6 MeCN salts, respectively. All three anions display almost identical geometries and bonding parameters, probably because charge effects are minimized by delocalization over such a large metal carbonyl anion. Moreover, the Ni(30)C(4) core in these Ni-Cd carbide clusters is identical within experimental error to those present in the [HNi(34)C(4)(CO)(38)](5-) and [Ni(35)C(4)(CO)(39)](6-) species, suggesting that the stepwise assembly of their nickel carbide cores may represent a general pathway of growth of nickel polycarbide clusters. The fact that the [H(6-n)Ni(30)C(4)(CO)(34)(micro(5)-CdCl)(2)](n-)(n=4-6) anions display two valence electrons more than the structurally related [H(6-n)Ni(34)C(4)(CO)(38)](n-) (n=4-6) species has been rationalized by extended Hückel molecular orbital (EHMO) analysis.     

An experimental and theoretical vibrational spectroscopic study of [AsPh(4)](2)[Sn(dmit)(3)] x Me(2)CO

As shown previously by X-ray structure determinations, [tris(1,3-dithiole-2-thione-4,5-dithiolato)stannate(IV)](2-) salts, [Q](2)[Sn(dmit)(3)], contain isolated cations and dianions. While the tin centres generally having octahedral geometries, the overall shapes of the dianions of these complexes in the solid state can differ with conformations varying from T, Y to asymmetrical arrangements. We now report, as a follow up to our earlier study on the Y-shaped complex, [NEt(4)](2)[Sn(dmit)(3)], an experimental and theoretical study of the vibrational spectra of solid solvated {[AsPh(4)](2)[Sn(dmit)(3)] x Me(2)CO}, in which the dianion has a T-shaped conformation. The infrared and Raman spectra, recorded from 4000 to 150 cm(-1), have been analysed by different ab initio calculations based on restricted Hartree-Fock (RHF) and density functional theory (DFT-Beck3LYP). The calculations were carried out on isolated dianions and cations with the 6-31G and 6-31G(d) basis sets and effective core potentials of Steven, Bash and Krauss (SBK). Fundamentals, overtones and combinations have been assigned. Generally, the Y- and T-shaped dianions exhibit similar infrared/Raman spectra, apart from differences in the C=C and the symmetrical M-S stretching frequencies: such differences can be used diagnostically to distinguish the overall shape of the tris(chelated)metallate dianion.     

Formation and emission of gold and silver carbide cluster ions in a single C60- surface impact at keV energies: experiment and calculations

Impact of fullerene ions (C(60)(-)) on a metallic surface at keV kinetic energies and under single collision conditions is used as an efficient way for generating gas phase carbide cluster ions of gold and silver, which were rarely explored before. Positively and negatively charged cluster ions, Au(n)C(m)(+) (n = 1-5, 1 ≤ m ≤ 12), Ag(n)C(m)(+) (n = 1-7, 1 ≤ m ≤ 7), Au(n)C(m)(-) (n = 1-5, 1 ≤ m ≤ 10), and Ag(n)C(m)(-) (n = 1-3, 1 ≤ m ≤ 6), were observed. The Au(3)C(2)(+) and Ag(3)C(2)(+) clusters are the most abundant cations in the corresponding mass spectra. Pronounced odd/even intensity alternations were observed for nearly all Au(n)C(m)(+/-) and Ag(n)C(m)(+/-) series. The time dependence of signal intensity for selected positive ions was measured over a broad range of C(60)(-) impact energies and fluxes. A few orders of magnitude immediate signal jump instantaneous with the C(60)(-) ion beam opening was observed, followed by a nearly constant plateau. It is concluded that the overall process of the fullerene collision and formation∕ejection of the carbidic species can be described as a single impact event where the shattering of the incoming C(60)(-) ion into small C(m) fragments occurs nearly instantaneously with the (multiple) pickup of metal atoms and resulting emission of the carbide clusters. Density functional theory calculations showed that the most stable configuration of the Au(n)C(m)(+) (n = 1, 2) clusters is a linear carbon chain with one or two terminal gold atoms correspondingly (except for a bent configuration of Au(2)C(+)). The calculated AuC(m) adiabatic ionization energies showed parity alternations in agreement with the measured intensity alternations of the corresponding ions. The Au(3)C(2)(+) ion possesses a basic Au(2)C(2) acetylide structure with a π-coordinated third gold atom, forming a π-complex structure of the type [Au(π-Au(2)C(2))](+). The calculation shows meaningful contributions of direct gold-gold bonding to the overall stability of the Au(3)C(2)(+) complex.     

Photoelectron spectroscopy of doubly and singly charged group VIB dimetalate anions: M2O72-, MM'O72-, and M2O7- (M, M' = Cr, Mo, W)

We produced both doubly and singly charged Group VIB dimetalate species-M(2)O(7)(2-), MM'O(7)(2-), and M(2)O(7)(-) (M, M' = Cr, Mo, W)-using two different experimental techniques (electrospray ionization for the doubly charged anions and laser vaporization for the singly charged anions) and investigated their electronic and geometric structures using photoelectron spectroscopy and density functional calculations. Distinct changes in the electronic and geometric structures were observed as a function of the metal and charge state. The electron binding energies of the heteronuclear dianions MM'O(7)(2-) were observed to be roughly the average of those of their homonuclear counterparts (M(2)O(7)(2-) and M'(2)O(7)(2-)). Density functional calculations indicated that W(2)O(7)(2-), W(2)O(7)(-), and W(2)O(7) possess different ground-state structures: the dianion is highly symmetric (D(3d),(1)A(1g)) with a single bridging oxo ligand, the monoanion is a doublet (C(1), (2)A) with two bridging oxo ligands and a radical terminal oxo ligand, whereas the neutral is a singlet (C(1), (1)A) with two bridging oxo ligands and a terminal peroxo ligand. The combined experimental and theoretical study provides insights into the evolution of geometric and electronic structures as a function of charge state. The clusters identified might provide insights into the possible structures of reactive species present in early transition-metal oxide catalysts that are relevant to their reactivity and catalytic function.     

Investigations of cluster ions formed between cesium cations and benzoic, salicylic and phthalic acids by electrospray mass spectrometry and density-functional theory calculations. Toward a modeling of the interaction of Cs+ with humic substances

A concerted theoretical (density-functional theory) and experimental electrospray mass spectrometry study was conducted on the formation of cesium cation adducts with small molecules taken as models of specific interactions sites in humic substances. Electrospray experiments with phenol, benzoic acid, salicylic acid, and phthalic acid, in methanolic solution containing cesium nitrate, were performed using a quadrupole ion trap. The formation of positively charged mixed clusters, [Cs(CsNO3)(n)(CsA1)(m)(Cs2A2)(p)]+ (A1 = benzoate, salicylate, and hydrogenophthalate, A2 = phthalate), was observed. Calculations of structures and bonding energetics of Cs+ in simple adducts formed with NO3-, CsNO3, A-, AH, and CsA are reported. The observation of variable cluster stoichiometry (n, m and p values) was interpreted in terms of more or less favorable interaction energies between Cs+ and the neutral species constituting the clusters. Phenol did not form clusters in significant abundances, despite a strong calculated interaction between Cs+ and cesium phenolate. This was attributed to its weak acid dissociation in the electrospray solution.