Heterobimetallic coordination polymers incorporating [M(CN)(2)](-) (M = Cu,Ag) and [Ag(2)(CN)(3)](-) units: increasing structural dimensionality via M-M' and M...NC interactions

A series of new heterometallic coordination polymers has been prepared from the reaction of metal-ligand cations and KAg(CN)(2) units. Many of these contain silver-silver (argentophilic) interactions, analogous to gold-gold interactions, which serve to increase supramolecular structural dimensionality. Compared to [Au(CN)(2)](-) analogues, these polymers display new trends specific to [Ag(CN)(2)](-), including the formation of [Ag(2)(CN)(3)](-) and the presence of Ag...N interactions. [Cu(en)(2)][Ag(2)(CN)(3)][Ag(CN)(2)] (1, en = ethylenediamine) forms 1-D chains of alternating [Ag(CN)(2)](-) and [Ag(2)(CN)(3)](-) units via argentophilic interactions of 3.102(1) A. These chains are connected into a 2-D array by strong cyano(N)-Ag interactions of 2.572(3) A. [Cu(dien)Ag(CN)(2)](2)[Ag(2)(CN)(3)][Ag(CN)(2)] (2, dien = diethylenetriamine) forms a 1-D chain of alternating [Cu(dien)](2+) and [Ag(CN)(2)](-) ions with the Cu(II) atoms connected in an apical/equatorial fashion. These chains are cross-linked by [Ag(2)(CN)(3)](-) units via argentophilic interactions of 3.1718(8) A and held weakly in a 3-D array by argentophilic interactions of 3.2889(5) A between the [Ag(CN)(2)](-) in the 2-D array and the remaining free [Ag(CN)(2)](-). [Ni(en)][Ni(CN)(4)].2.5H(2)O (4) was identified as a byproduct in the reaction to prepare the previously reported [Ni(en)(2)Ag(2)(CN)(3)][Ag(CN)(2)] (3). In [Ni(tren)Ag(CN)(2)][Ag(CN)(2)] (5, tren = tris(2-aminoethyl)amine), [Ni(tren)](2+) cations are linked in a cis fashion by [Ag(CN)(2)](-) anions to form a 1-D chain similar to the [Au(CN)(2)](-) analogue. [Cu(en)Cu(CN)(2)Ag(CN)(2)] (6) is a trimetallic polymer consisting of interpenetrating (6,3) nets stabilized by d(10)-d(10) interactions between Cu(I)-Ag(I) (3.1000(4) A). Weak antiferromagnetic coupling has been observed in 2, and a slightly stronger exchange has been observed in 6. The Ni(II) complexes, 4 and 5, display weak antiferromagnetic interactions as indicated by their relatively larger D values compared to that of 3. Magnetic measurements on isostructural [Ni(tren)M(CN)(2)][M(CN)(2)] (M = Ag, Au) show that Ag(I) is a more efficient mediator of magnetic exchange as compared to Au(I). The formation of [Ni(CN)(4)](2)(-), [Ag(2)(CN)(3)](-), and [Cu(CN)(2)](-) are all attributed to secondary reactions of the dissociation products of the labile KAg(CN)(2).     

Microsolvation of the dicyanamide anion: [N(CN)(2)(-)](H(2)O)n (n = 0-12)

Photoelectron spectroscopy is combined with ab initio calculations to study the microsolvation of the dicyanamide anion, N(CN)(2)(-). Photoelectron spectra of [N(CN)(2)(-)](H2O)n (n = 0-12) have been measured at room temperature and also at low temperature for n = 0-4. Vibrationally resolved photoelectron spectra are obtained for N(CN)(2)(-), allowing the electron affinity of the N(CN)2 radical to be determined accurately as 4.135 +/- 0.010 eV. The electron binding energies and the spectral width of the hydrated clusters are observed to increase with the number of water molecules. The first five waters are observed to provide significant stabilization to the solute, whereas the stabilization becomes weaker for n > 5. The spectral width, which carries information about the solvent reorganization upon electron detachment in [N(CN)(2)(-)](H2O)n, levels off for n > 6. Theoretical calculations reveal several close-lying isomers for n = 1 and 2 due to the fact that the N(CN)(2)(-) anion possesses three almost equivalent hydration sites. In all the hydrated clusters, the most stable structures consist of a water cluster solvating one end of the N(CN)(2)(-) anion.     

Metallophilic interactions in closed-shell d10 metal-metal dicyanide bonded luminescent systems Eu[Ag(x)Au(1-x)(CN)2]3 and their tunability for excited state energy transfer

We report on the heterobimetallic system, Eu[Ag(x)Au(1-x)(CN)(2)](3) (x = 0-1) in which sensitization of europium luminescence occurs by energy transfer from [Ag(x)Au(1-x)(CN)(2)](-) donor excited states. The donor states have energies which are tunable and dependent on the Ag/Au stoichiometric ratio. These layered systems exhibit interesting properties, one of which is their emission energy tunability when excited at different excitation wavelengths. In this paper, we report on their use as donor systems with Eu(III) ions as acceptor ions in energy transfer studies. Luminescence results show that the mixed metal dicyanides with the higher silver loading have a better energy transfer efficiency than the pure Ag(CN)(2)(-) and Au(CN)(2)(-) donors. The better energy transfer efficiency is due to the greater overlap between the donor emission and acceptor excitation. Additionally, more acceptor states are available in the high silver loading mixed metal Eu(III) complexes. The results from a crystal structure determination and Raman experiments are also presented in this paper and provide information about metallophilic interactions in the closed-shell d(10) metal-metal [Ag(x)Au(1-x)(CN(2)](-) dicyanide clusters.     

Cyanide-limited complexation of molybdenum(III): synthesis of octahedral [Mo(CN)(6)](3-) and cyano-bridged [Mo(2)(CN)(11)](5-)

Octahedral coordination of molybdenum(III) is achieved by limiting the amount of cyanide available upon complex formation. Reaction of Mo(CF(3)SO(3))(3) with LiCN in DMF affords Li(3)[Mo(CN)(6)] x 6DMF (1), featuring the previously unknown octahedral complex [Mo(CN)(6)](3-). The complex exhibits a room-temperature moment of mu(eff) = 3.80 mu(B), and assignment of its absorption bands leads to the ligand field parameters Delta(o) = 24800 cm(-1) and B = 247 cm(-1). Further restricting the available cyanide in a reaction between Mo(CF(3)SO(3))(3) and (Et(4)N)CN in DMF, followed by recrystallization from DMF/MeOH, yields (Et(4)N)(5)[Mo(2)(CN)(11)] x 2DMF x 2MeOH (2). The dinuclear [Mo(2)(CN)(11)](5-) complex featured therein contains two octahedrally coordinated Mo(III) centers spanned by a bridging cyanide ligand. A fit to the magnetic susceptibility data for 2, gives J = -113 cm(-1) and g = 2.33, representing the strongest antiferromagnetic coupling yet observed through a cyanide bridge. Efforts to incorporate these new complexes in magnetic Prussian blue-type solids are ongoing.     

Assignment of the electronic spectra of [Mo(CN)(8)](4)(-) and [W(CN)(8)](4)(-) by Ab initio calculations

CASPT2 calculations are performed on the dodecahedral and square antiprismatic isomers of the [Mo(CN)(8)](4)(-) and [W(CN)(8)](4)(-) complexes. The high-energy experimental bands above 40000 cm(-)(1) are assigned to MLCT transitions. The experimental observed trend of the extinction coefficients for the molybdenum and tungsten complex is reproduced by our CASSCF oscillator strengths. All bands below 40000 cm(-)(1) can be ascribed to ligand-field transitions, although small contributions from forbidden MLCT transitions cannot be excluded. In order to account for all experimental bands in the electronic spectrum of these octacyanocomplexes, a dynamic equilibrium in solution between the two isomeric forms must be hypothesized. Spin-orbit coupling effects are found to be more important for the square antiprismatic isomers; in particular, large singlet-triplet mixings are calculated for this isomer of [W(CN)(8)](4)(-). Ligand-field and Racah parameters as well as spin-orbit coupling constants are determined on the basis of the calculated transition energies. The obtained values for these parameters support the recently proposed model for exchange interactions in magnetic clusters and networks containing pentavalent octocyanometalates of molybdenum and tungsten.     

Characterization of the [Ag(dmb)(2)(+)](n) oligomers (dmb = 1,8-diisocyano-p-menthane) in solution

The crystallographically characterized polymers [[Ag(dmb)(2)]Y](n) (Y = BF(4)(-), NO(3)(-), ClO(4)(-)) extensively dissociate in solution, contrarily to the Cu analogue, and common molecular weight determination techniques such as light scattering, osmometric, and intrinsic viscosity measurements fail to provide data allowing full characterization. Using pulsed NMR experiments, notably (13)C NMR T(1) (spin lattice relaxation time) and NOE (nuclear Overhauser enhancement) measurements on various ionic [[Ag(dmb)(2)]Y](n) materials (Y = BF(4)(-), NO(3)(-), ClO(4)(-)) and their related mononuclear [Ag (CN-t-Bu)(4)]Y salts in acetonitrile-d(3) (as comparative standards), the dipole-dipole spin lattice relaxation times (T(1)(DD)) of a selected quaternary (13)C probe are measured. These data allow us to extract the correlation times (tau(c)), which in turn permit us to estimate the volume of the tumbling species in solution. The comparison of the data between the [Ag(dmb)(2)(+)](n) and Ag(CN-t-Bu)(4)(+) species indicates the oligomeric nature of the former species, where the average number of Ag(dmb)(2)(+) approximately 8 (M(n) approximately 4000-5000).     

Synthesis, structural, and photoluminescence studies of Gd(terpy)(H2O)(NO3)2M(CN)2 (M = Au, Ag) complexes: multiple emissions from intra- and intermolecular excimers and exciplexes

The highly luminescent bimetallic cyanide materials, Gd(terpy)(H(2)O)(NO(3))(2)M(CN)(2) (M = Au, Ag; GdAu and GdAg, respectively) are quick and easy to synthesize under ambient conditions. A characteristic feature exhibited by both solid-state compounds is an intense red emission when excited with UV light. Additionally, GdAu exhibits a broad-band green emission upon excitation in the near UV region. A combination of structural and spectroscopic results for the compounds helps explain the underlying conditions responsible for their unique properties. Single-crystal X-ray diffraction experiments expose their structural features, including the fact that they are isostructural. Crystallographic data for the representative GdAu compound (Mo K(α), λ = 0.71073 ?, T = 290 K): triclinic, space group P ?1, a = 7.5707(3) ?, b = 10.0671(4) ?, c = 15.1260(4) ?, α = 74.923(3)°, β = 78.151(3)°, γ = 88.401(3)°, V = 1089.04(7) ?(3), and Z = 2. Although the compounds crystallize as dimers containing M···M distances smaller than the sum of their van der Waals radii, the Au···Au (3.5054(4) ?) and/or the Ag···Ag (3.6553(5) ?) interactions are relatively weak and are not responsible for the low energy red emission. Rather, the green emission in GdAu presumably originates from the [Au(CN)(2)(-)](2) dimeric excimer, while the [Ag(CN)(2)(-)](2) dimers in GdAg do not display visible emission at either 290 or 77 K. The unusual red emission exhibited by both compounds likely originates from the formation of an excited state exciplex that involves intermolecular π-stacking of 2,2':6',2"-terpyridine ligands. The room-temperature and low-temperature steady-state photoluminescent properties, along with detailed time-dependent, lifetime, and quantum yield spectroscopic data provide evidence regarding the sources of the multiple visible emissions exhibited by these complexes.     

Electronic and Geometric Structure of Bimetallic Clusters: Density Functional Calculations on [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and [Ag(13){Fe(CO)(4)}(8)](n)(-) (n = 0-5)

The results of all-electron density functional calculations on the bimetallic cluster compounds [M(4){Fe(CO)(4)}(4)](4-) (M = Cu, Ag, Au) and on the corresponding naked species M(4)Fe(4) are reported. The trends within the triad have been investigated. The bare metal clusters exhibit a strong magnetization which is quenched on addition of CO ligands. The bonding in the bare clusters is different for the silver derivative compared to that of copper and gold, resulting in comparatively weaker Ag-Fe and Ag-Ag bonds. This can be rationalized in terms of the different d-sp mixing, which for Cu and Au is larger than for Ag. Relativistic effects act to increase the 4d-5s mixing in Ag and to strengthen the intermetallic bond with Fe. In the carbonylated clusters a charge transfer from the metal M (M = Cu, Ag, or Au) to the Fe(CO)(4) groups occurs so that the atoms M can be considered in a formal +I oxidation state, rationalizing the nearly square-planar geometry of the metal frame. In fact, the local coordination of the M atoms is almost linear, as expected for complexes of M(I). The addition of extra electrons results in a stabilization of the clusters, indicating the electron-deficient nature of these compounds. Similar features have been found for the largest cluster synthesized so far for this class of compounds, [Ag(13){Fe(CO)(4)}(8)](n)(-), (n = 0-5). The nature and localization of the unpaired electron in the tetraanion is also discussed.     

Preparation and Structures of the 2.2.2-Cryptand(1+) Salts of the [Sb(2)Se(4)](2)(-), [As(2)S(4)](2)(-), [As(10)S(3)](2)(-), and [As(4)Se(6)](2)(-) Anions

2.2.2-Cryptand(1+) salts of the [Sb(2)Se(4)](2)(-), [As(2)S(4)](2)(-), [As(10)S(3)](2)(-), and [As(4)Se(6)](2)(-) anions have been synthesized from the reduction of binary chalcogenide compounds by K in NH(3)(l) in the presence of the alkali-metal-encapsulating ligand 2.2.2-cryptand (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane), followed by recrystallization from CH(3)CN. The [Sb(2)Se(4)](2)(-) anion, which has crystallographically imposed symmetry 2, consists of two discrete edge-sharing SbSe(3) pyramids with terminal Se atoms cis to each other. The Sb-Se(t) bond distance is 2.443(1) ?, whereas the Sb-Se(b) distance is 2.615(1) ? (t = terminal; b = bridge). The Se(b)-Sb-Se(t) angles range from 104.78(4) to 105.18(5) degrees, whereas the Se(b)-Sb-Se(b) angles are 88.09(4) and 88.99(4) degrees. The (77)Se NMR data for this anion in solution are consistent with its X-ray structure (delta 337 and 124 ppm, 1:1 intensity, -30 degrees C, CH(3)CN/CD(3)CN). Similar to this [Sb(2)Se(4)](2)(-) anion, the [As(2)S(4)](2)(-) anion consists of two discrete edge-sharing AsS(3) pyramidal units. The As-S(t) bond distances are 2.136(7) and 2.120(7) ?, whereas the As-S(b) distances range from 2.306(7) to 2.325(7) ?. The S(b)-As-S(t) angles range from 106.2(3) to 108.2(3) degrees, and the S(b)-As-S(b) angles are 88.3(2) and 88.9(2) degrees. The [As(10)S(3)](2)(-) anion has an 11-atom As(10)S center composed of six five-membered edge-sharing rings. One of the three waist positions is occupied by a S atom, and the other two waist positions feature As atoms with exocyclic S atoms attached, making each As atom in the structure three-coordinate. The As-As bond distances range from 2.388(3) to 2.474(3) ?. The As-S(t) bond distances are 2.181(5) and 2.175(4) ?, and the As-S(b) bond distance is 2.284(6) ?. The [As(4)Se(6)](2)(-) anion features two AsSe(3) units joined by Se-Se bonds with the two exocyclic Se atoms trans to each other. The average As-Se(t) bond distance is 2.273(2) ?, whereas the As-Se(b) bond distances range from 2.357(3) to 2.462(2) ?. The Se(b)-As-Se(t) angles range from 101.52(8) to 105.95(9) degrees, and the Se(b)-As-Se(b) angles range from 91.82(7) to 102.97(9) degrees. The (77)Se NMR data for this anion in solution are consistent with its X-ray structure (delta 564 and 317 ppm, 3:1 intensity, 25 degrees C, DMF/CD(3)CN).     

Preparation and characterization of the argentates: [Ag[P(CF(3))(2)](2)](-), [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-) (M = Cr, W), and [Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)](-): X-ray crystal structure of [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)

The first example of a mononuclear diphosphanidoargentate, bis[bis(trifluoromethyl)phosphanido]argentate, [Ag[P(CF(3))(2)](2)](-), is obtained via the reaction of HP(CF(3))(2) with [Ag(CN)(2)](-) and isolated as its [K(18-crown-6)] salt. When the cyclic phosphane (PCF(3))(4) is reacted with a slight excess of [K(18-crown-6)][Ag[P(CF(3))(2)](2)], selective insertion of one PCF(3) unit into each silver phosphorus bond is observed, which on the basis of NMR spectroscopic evidence suggests the [Ag[P(CF(3))P(CF(3))(2)](2)](-) ion. On treatment of the phosphane complexes [M(CO)(5)PH(CF(3))(2)] (M = Cr, W) with [K(18-crown-6)][Ag(CN)(2)], the analogous trinuclear argentates, [Ag[(micro-P(CF(3))(2))M(CO)(5)](2)](-), are formed. The chromium compound [K(18-crown-6)][Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)] crystallizes in a noncentrosymmetric space group Fdd2 (No. 43), a = 2970.2(6) pm, b = 1584.5(3) pm, c = 1787.0(4), V = 8.410(3) nm(3), Z = 8. The C(2) symmetric anion, [Ag[(micro-P(CF(3))(2))Cr(CO)(5)](2)](-), shows a nearly linear arrangement of the P-Ag-P unit. Although the bis(pentafluorophenyl)phosphanido compound [Ag[P(C(6)F(5))(2)](2)](-) has not been obtained so far, the synthesis of its trinuclear counterpart, [K(18-crown-6)][Ag[(micro-P(C(6)F(5))(2))W(CO)(5)](2)], was successful.     

A study of structural and bonding variations in the homologous series [Mo(2)(CN)(6)(dppm)(2)](n-) (n = 2, 1, 0)

Reaction of Mo(2)Cl(4)(dppm)(2) (dppm = bis(diphenylphosphino)methane) with 6 equiv of [n-Bu(4)N][CN] or [Et(4)N][CN] in dichloromethane yields [n-Bu(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (1) and [Et(4)N](2)[Mo(2)(CN)(6)(dppm)(2)] (2), respectively. The corresponding one- and two-electron oxidation products [n-Bu(4)N][Mo(2)(CN)(6)(dppm)(2)] (3) and Mo(2)(CN)(6)(dppm)(2) (4)were prepared by reactions of 1 with the oxidant NOBF(4). Single-crystal X-ray structures of 2.2CH(3)CN, 3.2CH(3)CN.2H(2)O, and 4.2CH(3)NO(2) were performed, and the results confirmed that all three complexes contain identical ligand sets with trans dppm ligands bisecting the Mo(2)(mu-CN)(2)(CN)(4) equatorial plane. The binding of the bridging cyanide ligands is affected by the oxidation state of the dimolybdenum core as evidenced by an increase in side-on pi-bonding overlap of the mu-CN in going from 1 to 4. The greater extent of pi-donation into Mo orbitals is accompanied by a lengthening of the Mo-Mo distance (2.736(1) A in Mo(2)(II,II) (2), 2.830(1) A in Mo(2)(II,III) (3), and 2.936(1) A in Mo(2)(III,III) (4)). A computational study of the closed-shell members of this homologous series, [Mo(2)(CN)(6)(dppm)(2)](n)() (n = 2-, 0), indicates that the more pronounced side-on pi-donation evident in the X-ray structure of 4 leads to significant destabilization of the delta orbital and marginal stabilization of the delta() orbitals with respect to nearly degenerate delta and delta orbitals in the parent compound, 2. The loss of delta contributions combined with the reduced orbital overlap due to higher charges on molybdenum centers in oxidized complexes 3 and 4 is responsible for the observed increase in the length of the Mo-Mo bond.     

Solvent coordination in gas-phase [Mn.(H(2)O)(n)](2+) and [Mn.(ROH)(n)](2+) complexes: theory and experiment

An experimental gas-phase study of the intensities and fragmentation patterns of [Mn.(H(2)O)(n)](2+) and [Mn.(ROH)(n)](2+) complexes shows the combinations [Mn.(H(2)O)(4)](2+) and [Mn.(ROH)(4)](2+) to be stable. Evidence in complexes involving the alcohols methanol, ethanol, 1-propanol, and 2-propanol favors preferential fragmentation to [Mn.(ROH)(4)](2+), whereas the fragmentation data for water is less clear. Supporting density functional calculations show that both [Mn.(H(2)O)(4)](2+) and [Mn.(MeOH)(4)](2+) adopt stable tetrahedral configurations, similar to those proposed for biochemical systems where solvent availability and coordination is restricted. Calculated incremental binding energies show a gradual decline on going from one to six solvent molecules, with a step occurring between four and five molecules. The addition of further solvent molecules to the stable [Mn.(MeOH)(4)](2+) unit shows a preference for [Mn.(MeOH)(4)(MeOH)(1,2)](2+) structures, where the extra molecules occupy hydrogen-bonded sites in the form of a secondary solvation shell. Very similar behavior is seen on the part of water. As part of an analysis of the experimental data, the calculations have explored the influence different spins states of Mn(2+) have on solvent geometry. It is concluded that the experimental observations are best reproduced when the central Mn(2+) ion is in the high-spin (6)S ground state. The results are also considered in terms of the biochemical activity of Mn(2+) where the ion is capable of isomorphous substitution with Zn(2+), which itself exhibits a preference for tetrahedral coordination.     

The mechanism for water exchange in [UO(2)(H(2)O)(5)](2+) and [UO(2)(oxalate)(2)(H(2)O)](2-), as studied by quantum chemical methods.

The mechanisms for the exchange of water between [UO(2)(H(2)O)(5)](2+), [UO(2)(oxalate)(2)(H(2)O)](2)(-)(,) and water solvent along dissociative (D), associative (A) and interchange (I) pathways have been investigated with quantum chemical methods. The choice of exchange mechanism is based on the computed activation energy and the geometry of the identified transition states and intermediates. These quantities were calculated both in the gas phase and with a polarizable continuum model for the solvent. There is a significant and predictable difference between the activation energy of the gas phase and solvent models: the energy barrier for the D-mechanism increases in the solvent as compared to the gas phase, while it decreases for the A- and I-mechanisms. The calculated activation energy, Delta U(++), for the water exchange in [UO(2)(H(2)O)(5)](2+) is 74, 19, and 21 kJ/mol, respectively, for the D-, A-, and I-mechanisms in the solvent, as compared to the experimental value Delta H(++) = 26 +/- 1 kJ/mol. This indicates that the D-mechanism for this system can be ruled out. The energy barrier between the intermediates and the transition states is small, indicating a lifetime for the intermediate approximately 10(-10) s, making it very difficult to distinguish between the A- and I-mechanisms experimentally. There is no direct experimental information on the rate and mechanism of water exchange in [UO(2)(oxalate)(2)(H(2)O)](2-) containing two bidentate oxalate ions. The activation energy and the geometry of transition states and intermediates along the D-, A-, and I-pathways were calculated both in the gas phase and in a water solvent model, using a single-point MP2 calculation with the gas phase geometry. The activation energy, Delta U(++), in the solvent for the D-, A-, and I-mechanisms is 56, 12, and 53 kJ/mol, respectively. This indicates that the water exchange follows an associative reaction mechanism. The geometry of the A- and I-transition states for both [UO(2)(H(2)O)(5)](2+) and [UO(2)(oxalate)(2)(H(2)O)](2-) indicates that the entering/leaving water molecules are located outside the plane formed by the spectator ligands.     

A theoretical study of the NMR spin-spin coupling constants of the complexes [(NC)(5)Pt-Tl(CN)(n)](n-) (n = 0-3) and [(NC)(5)Pt-Tl-Pt(CN)(5)](3-): a lesson on environmental effects

The molecular geometries and the nuclear spin-spin coupling constants of the complexes [(NC)(5)Pt-Tl(CN)(n)](n-), n = 0-3, and the related system [(NC)(5)Pt-Tl-Pt(CN)(5)](3-) are studied. These complexes have received considerable interest since the first characterization of the n = 1 system by Glaser and co-workers in 1995 [J. Am. Chem. Soc. 1995, 117, 7550-7551]. For instance, these systems exhibit outstanding NMR properties, such as extremely large Pt-Tl spin-spin coupling constants. For the present work, all nuclear spin-spin coupling constants J(Pt-Tl), J(Pt-C), and J(Tl-C) have been computed by means of a two-component relativistic density functional approach. It is demonstrated by the application of increasingly accurate computational models that both the huge J(Pt-Tl) for the complex (NC)(5)Pt-Tl and the whole experimental trend among the series are entirely due to solvent effects. An approximate inclusion of the bulk solvent effects by means of a continuum model, in addition to the direct coordination, proves to be crucial. Similarly drastic effects are reported for the coupling constants between the heavy atoms and the carbon nuclei. A computational model employing the statistical average of orbital-dependent model potentials (SAOP) in addition to the solvent effects allows to accurately reproduce the experimental coupling constants within reasonable limits.     

Mechanistic studies on the reactions of PhS(-) or [MoS(4)](2)(-) with [M(4)(SPh)(10)](2)(-) (M = Fe or Co)

Kinetic studies, using stopped-flow spectrophotometry, on the reactions of [M(4)(SPh)(10)](2)(-) (M = Fe or Co) with PhS(-) to form [M(SPh)(4)](2)(-) are described, as are the reactions between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) to form [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). The kinetics of the reactions with PhS(-) are consistent with an initial associative substitution mechanism involving attack of PhS(-) at one of the tetrahedral M sites of [M(4)(SPh)(10)](2)(-) to form [M(4)(SPh)(11)](3)(-). Subsequent or concomitant cleavage of a micro-SPh ligand, at the same M, initiates a cascade of rapid reactions which result ultimately in the complete rupture of the cluster and formation of [M(SPh)(4)](2)(-). The kinetics of the reaction between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) indicate an initial dissociative substitution mechanism at low concentrations of [MoS(4)](2)(-), in which rate-limiting dissociation of a terminal thiolate from [M(4)(SPh)(10)](2)(-) produces [M(4)(SPh)(9)](-) and the coordinatively unsaturated M site is rapidly attacked by a sulfido group of [MoS(4)](2)(-). It is proposed that subsequent chelation of the MoS(4) ligand results in cleavage of an M-micro-SPh bond, initiating a cascade of reactions which lead to the ultimate break-up of the cluster and formation of the products, [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). With [Co(4)(SPh)(10)](2)(-), at higher concentrations of [MoS(4)](2)(-), a further substitution pathway is evident which exhibits a second order dependence on the concentration of [MoS(4)](2)(-). The mechanistic picture of cluster disruption which emerges from these studies rationalizes the "all or nothing" reactivity of [M(4)(SPh)(10)](2)(-).     

Synthesis and properties of [Ru(2)(acac)(4)(bptz)](n+) (n=0,1) and crystal structure of [Ru(2)(acac)(4)(bptz)

The neutral complex [Ru(2)(acac)(4)(bptz)] (I) has been prepared by the reaction of Ru(acac)(2)(CH(3)CN)(2) with bptz (bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine) in acetone. The diruthenium(II,II) complex (I) is green and exhibits an intense metal-ligand charge-transfer band at 700 nm. Complex I is diamagnetic and has been characterized by NMR, optical spectroscopy, IR, and single-crystal X-ray diffraction. Crystal structure data for I are as follows: triclinic, P1, a = 11.709(2) A, b = 13.487(3) A, c = 15.151(3) A, alpha = 65.701(14) degrees, beta = 70.610(14) degrees, gamma = 75.50(2) degrees, V = 2038.8(6) A(3), Z = 2, R = 0.0610, for 4397 reflections with F(o) > 4sigmaF(o). Complex I shows reversible Ru(2)(II,II)-Ru(2)(II,III) and Ru(2)(II,III)-Ru(2)(III,III) couples at 0.17 and 0.97 V, respectively; the 800 mV separation indicates considerable stabilization of the mixed-valence species (K(com) > 10(13)). The diruthenium(II,III) complex, [Ru(2)(acac)(4)(bptz)](PF(6)) (II) is prepared quantitatively by one-electron oxidation of I with cerium(IV) ammonium nitrate in methanol followed by precipitation with NH(4)PF(6). Complex II is blue and shows an intense MLCT band at 575 nm and a weak band at 1220 nm in CHCl(3), which is assigned as the intervalence CT band. The mixed valence complex is paramagnetic, and an isotropic EPR signal at g = 2.17 is observed at 77 and 4 K. The solvent independence and narrowness of the 1200 nm band show that complex II is a Robin and Day class III mixed-valence complex.     

Site-differentiated hexanuclear rhenium(III) cyanide clusters [Re(6)Se(8)(PEt(3))(n)()(CN)(6)(-)(n)()](n)()(-)(4) (n = 4, 5) and kinetics of solvate ligand exchange on the cubic [Re(6)Se(8)](2+) Core

The site-differentiated, cyanide-substituted hexanuclear rhenium(III) selenide clusters cis- and trans-[Re(6)Se(8)(PEt(3))(4)(CN)(2)] and [Re(6)Se(8)(PEt(3))(5)(CN)](+) have been prepared from heterogeneous reactions of the corresponding iodo clusters with AgCN in refluxing chloroform. Isolated yields are 68%, 46%, and 64% for cis-[Re(6)Se(8)(PEt(3))(4)(CN)(2)], trans-[Re(6)Se(8)(PEt(3))(4)(CN)(2)], and [Re(6)Se(8)(PEt(3))(5)(CN)](+), respectively. The new compounds are air- and water-stable and are characterized by X-ray diffraction crystallography, (31)P NMR and IR spectroscopies, and FAB mass spectrometry. In related work, the solvent exchange rates of two site-differentiated monosolvate clusters, [Re(6)Se(8)(PEt(3))(5)(MeCN)](SbF(6))(2) and [Re(6)Se(8)(PEt(3))(5)(Me(2)SO)](SbF(6))(2), in neat solvents were measured by (1)H NMR. These clusters are substitutionally inert; k approximately 10(-)(5)-10(-)(6) s(-)(1) at 318 K. Activation parameters indicate a dissociative ligand exchange mechanism; DeltaH() values obtained from least-squares fitting of temperature-dependent kinetics data exceed RT by a factor of ca. 50 over the temperature range studied. These results demonstrate that the substitutional lability encountered in a previous study of cluster photophysics (Gray, T. G.; Rudzinski, C. M.; Nocera, D. G.; Holm, R. H. Inorg. Chem. 1999, 38, 5932) cannot result from ground-state thermal reactions.