Solid-state 93Nb and 13C NMR investigations of half-sandwich niobium(I) and niobium(V) cyclopentadienyl complexes

Solid-state 93Nb and 13C NMR experiments, in combination with theoretical calculations of NMR tensors, and single-crystal and powder X-ray diffraction experiments, are applied for the comprehensive characterization of structure and dynamics in a series of organometallic niobium complexes. Half-sandwich niobium metallocenes of the forms Cp'Nb(I)(CO)4 and CpNb(V)Cl4 are investigated, where Cp = C5H5- and Cp' = C5H4R- with R = COMe, CO2Me, CO2Et, and COCH2Ph. Anisotropic quadrupolar and chemical shielding (CS) parameters are extracted from 93Nb MAS and static NMR spectra for seven different complexes. It is demonstrated that 93Nb NMR parameters are sensitive to changes in temperature and Cp' ring substitution in the Cp'Nb(I)(CO)4 complexes. There are dramatic differences in the 93Nb quadrupolar coupling constants (C(Q)) between the Nb(I) and Nb(V) complexes, with C(Q) between 1.0 and 12.0 MHz for Cp'Nb(CO)4 and C(Q) = 54.5 MHz for CpNbCl4. The quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequence is applied to rapidly acquire, in a piecewise fashion, a high signal-to-noise ultra-wide-line 93Nb NMR spectrum of CpNbCl4, which has a breadth of ca. 400 kHz. Solid-state 93Nb and 13C NMR spectra and powder XRD data are used to identify a new metallocene adduct coordinated at the axial position of the metal site by a THF molecule: CpNb(V)Cl4.THF. 13C MAS and CP/MAS NMR experiments are used to assess the purity of samples, as well as for measuring carbon CS tensors and the rare instance of one-bond 93Nb, 13C J-coupling, 1J(93Nb,13C). Theoretically calculated CS and electric field gradient (EFG) tensors are utilized to determine relationships between tensor orientations, the principal components, and molecular structures.     

Formation of {Cu6[S2P(OC2H5)2]6} on Cu2S surfaces from aqueous solutions of the KS2P(OC2H5)2 collector: scanning electron microscopy and solid-state 31P cross-polarization/magic angle spinning and static 65Cu NMR studies

The interactions of synthetic chalcocite surfaces with diethyldithiophosphate, potassium salt, K[S2P(OC2H5)2], were studied by means of 31P cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy and scanning electron microscopy (SEM). To identify the species formed on the Cu2S surfaces, a polycrystalline {CuI6[S2P(OC2H5)2]6} cluster was synthesized and analyzed by SEM, powder X-ray diffraction techniques and solid-state 31P CP/MAS NMR and static 65Cu NMR spectroscopy. 31P chemical shift anisotropy (CSA) parameters, delta(cs) and eta(cs), were estimated and used for assigning the bridging type of diethyldithiophosphate ligands in the {CuI6[S2P(OC2H5)2]6} cluster. The latter data were compared to 31P CSA parameters estimated from the spinning sideband patterns in 31P NMR spectra of the collector-treated mineral surfaces: formation of polycrystalline {CuI6[S2P(OC2H5)2]6} on the Cu2S surfaces is suggested. The second-order quadrupolar line shape of 65Cu was simulated, and the NMR interaction parameters, CQ and etaQ, for the copper(I) diethyldithiophosphate cluster were obtained.     

Solid-state (63)Cu and (65)Cu NMR spectroscopy of inorganic and organometallic copper(I) complexes

Solid-state 63Cu and 65Cu NMR experiments have been conducted on a series of inorganic and organometallic copper(I) complexes possessing a variety of spherically asymmetric two-, three-, and four-coordinate Cu coordination environments. Variations in structure and symmetry, and corresponding changes in the electric field gradient (EFG) tensors, yield 63/65Cu quadrupolar coupling constants (CQ) ranging from 22.0 to 71.0 MHz for spherically asymmetric Cu sites. These large quadrupolar interactions result in spectra featuring quadrupolar-dominated central transition patterns with breadths ranging from 760 kHz to 6.7 MHz. Accordingly, Hahn-echo and/or QCPMG pulse sequences were applied in a frequency-stepped manner to rapidly acquire high S/N powder patterns. Significant copper chemical shielding anisotropies (CSAs) are also observed in some cases, ranging from 1000 to 1500 ppm. 31P CP/MAS NMR spectra for complexes featuring 63/65Cu-31P spin pairs exhibit residual dipolar coupling and are simulated to determine both the sign of CQ and the EFG tensor orientations relative to the Cu-P bond axes. X-ray crystallographic data and theoretical (Hartree-Fock and density functional theory) calculations of 63/65Cu EFG and CS tensors are utilized to examine the relationships between NMR interaction tensor parameters, the magnitudes and orientations of the principal components, and molecular structure and symmetry.     

A solid-state 53Cr NMR study of chromate and dichromate salts

Solid-state (53)Cr NMR spectra of a series of chromate (CrO4(2-)) and dichromate (Cr2O7(2-)) salts have been examined by employing the stepped-frequency quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) experiment and high applied magnetic field strengths, 11.75 and 18.8 T. Cr-53 nuclear quadrupolar coupling constants, CQ(53Cr), ranging from 1.23 to 5.01 MHz for the Cr(4(2-) salts and 7.25 to 8.14 MHz for the Cr2O7(2-) salts have been measured. For the dichromate salts, this corresponds to central transition 53Cr NMR lineshapes of 200-250 kHz at 18.8 T. The use of hyperbolic secant (HS) pulses in combination with the Hahn-echo (HE) or QCPMG experiment results in significant sensitivity enhancements when acquiring 53Cr NMR spectra of magic-angle spinning (MAS) samples, provided the MAS rate is fast with respect to the second-order quadrupolar interaction. For the CrO4(2-) and Cr2O7(2-) salts, the anisotropic chromium magnetic shielding interaction is generally negligible compared to the second-order 53Cr nuclear quadrupolar interaction. No simple correlation between the structure of the CrO4(2-) and Cr2O7(2-) anions and the observed CQ(53Cr) values has been found.     

(39)K NMR of solid potassium salts at 21 T: effect of quadrupolar and chemical shift tensors

39K Solid State NMR spectra (static and magic angle spinning (MAS)) on a set of potassium salts measured at 21.14 T show that the chemical shift range for K(+) ions in diamagnetic salts is well in excess of 100 ppm contrary to previous assumptions that it was quite small. Inequivalent potassium sites in crystals can be resolved through differences in chemical shifts, with chemically similar sites showing differences of over 10 ppm. The quadrupolar coupling constants obtained from MAS and solid echo experiments on powders cover the range from zero for potassium in cubic environments in halides to over 3 MHz for the highly asymmetric sites in K2CO3. Although the quadrupolar effects generally dominate the 39K spectra, in several instances, we have observed subtle but significant contributions of chemical shift anisotropy with values up to 45 ppm, a first such observation. Careful analysis of static and MAS spectra allows the observation of the various chemical shift and quadrupole coupling tensor components as well as their relative orientations, thereby demonstrating that high-field 39K NMR spectroscopy in the solid state has a substantial sensitivity to the local environment with parameters that will be of considerable value in materials characterization and electronic structure studies.     

Ultrahigh-field NMR spectroscopy of quadrupolar transition metals: 55Mn NMR of several solid manganese carbonyls

55Mn NMR spectra acquired at 21.14 T (nu(L)(55Mn) = 223.1 MHz) are presented and demonstrate the advantages of using ultrahigh magnetic fields for characterizing the chemical shift tensors of several manganese carbonyls: eta5-CpMn(CO)3, Mn2(CO)10, and (CO)5MnMPh3 (M = Ge, Sn, Pb). For the compounds investigated, the anisotropies of the manganese chemical shift tensors are less than 250 ppm except for eta5-CpMn(CO)3, which has an anisotropy of 920 ppm. At 21.14 T, one can excite the entire m(I) = 1/2 <--> m(I) = -1/2 central transition of eta5-CpMn(CO)3, which has a breadth of approximately 700 kHz. The breadth arises from second-order quadrupolar broadening due to the 55Mn quadrupolar coupling constant of 64.3 MHz, as well as the anisotropic shielding. Subtle variations in the electric field gradient tensors at the manganese are observed for crystallographically unique sites in two of the solid pentacarbonyls, resulting in measurably different C(Q) values. MQMAS experiments are able to distinguish four magnetically unique Mn sites in (CO)(5)MnPbPh3, each with slightly different values of delta(iso), C(Q), and eta(Q).     

Synthesis and characterization of a novel cyclic aluminophosphinate: structure and solid-state NMR study

We present the structure and a multinuclear solid-state NMR study of a new cyclic aluminophosphinate. The crystallographic structure of [Al(2)(HC(6)H(5)PO(2))(2)(C(4)H(9)OH)(8)]Cl(4) (compound 1) was obtained at low temperature (a = 11.830(7) A, b = 14.216(6) A, c = 17.790(6) A, beta = 91.25(4) degrees, monoclinic, P21/c, Z = 2). (13)C IRCP (inversion recovery cross polarization) and NQS (non quaternary suppression) NMR experiments allowed the complete assignment of the quaternary carbon atom of the phenyl ring and the precise determination of the isotropic /(1)J(P-C)/ coupling constant. (31)P CP MAS dynamics was carefully studied by varying the contact time. Dipolar oscillations even at slow MAS were observed. Up to 11 kHz, these oscillations were more pronounced, and the P-H distance was easily extracted. (27)Al NMR quadrupolar parameters for 1 were obtained with very good accuracy, and unusual satellite transition splitting was observed. Furthermore, the isotropic lines of the inner and outer transitions were clearly observable, leading to the unambiguous determination of the quadrupolar parameters.     

113Cd Shielding Tensors of Monomeric Cadmium Compounds Containing Nitrogen Donor Atoms. 3. CP/MAS Studies on Five-Coordinate Cadmium Complexes Having N(3)X(2) (X = H, N, O, and S) Donor Atoms

The principal elements of the (113)Cd shielding tensor for a set of five- coordinate compounds having mixed donor atoms coordinating to the cadmium were determined via CP/MAS NMR experiments. The first complex, [HB(3,5-Me(2)pz)(3)]CdBH(4) (where pz = pyrazolyl), has a CdN(3)H(2) inner coordination sphere. The isotropic chemical shift in the solid state is 355.1 ppm, and its chemical shift anisotropy (CSA, Deltasigma) is -596 ppm with an asymmetry parameter (eta) of 0.64. The second complex, [HB(3,5-Me(2)pz)(3)]Cd[H(2)B(pz)(2)], has five nitrogen donor atoms bonded to the cadmium. This N(5) or N(3)N(2) compound was the only material of this study to manifest dipolar splitting of the cadmium resonance from the quadrupolar (14)N. The isotropic chemical shift, CSA, and the value of eta for this material were therefore determined at higher field where the dipolar splitting was less than the linewidth, yielding values of 226.6 ppm, -247 ppm, and 0.32, respectively. A second N(5) material, [HB(3-Phpz)(3)]Cd[H(2)B(3,5-Me(2)pz)(2)], was also investigated and has an isotropic shift of 190.2 ppm, a CSA of 254 ppm, and an eta of 0.86. Also studied was [HB(3-Phpz)(3)]Cd[(Bu(t)CO)(2)CH], which has an CdN(3)O(2) inner core. The isotropic chemical shift of this complex is 173.6 ppm, and the values of Deltasigma and eta were determined to be -258 ppm and 0.38, respectively. The final compound, [HB(3,5-Me(2)pz)(3)]Cd[S(2)CNEt(2)], with N(3)S(2) donor atoms, has an isotropic shift of 275.8 ppm, an eta of 0.51, and a CSA of +375 ppm. Utilizing previous assignments, the most shielded tensor element was determined to be oriented normal to the plane of the tridentate ligand. The shielding tensor information is used to speculate on the coordination geometry of the CdN(3)O(2) inner core complex.     

29Si chemical shift anisotropies in calcium silicates from high-field 29Si MAS NMR spectroscopy

29Si chemical shift anisotropy (CSA) data have been determined from (29)Si MAS NMR spectra recorded at 14.1 T for a number of synthetic calcium silicates and calcium silicate hydrates. These are beta- and gamma-Ca(2)SiO(4), Ca(3)SiO(4)Cl(2), alpha-dicalcium silicate hydrate (alpha-Ca(2)(SiO(3)OH)OH), rankinite (Ca(3)Si(2)O(7)), cuspidine (Ca(4)Si(2)O(7)F(2)), wollastonite (beta-Ca(3)Si(3)O(9)), pseudowollastonite (alpha-Ca(3)Si(3)O(9)), scawtite (Ca(7)(Si(6)O(18))CO(3).2H(2)O), hillebrandite (Ca(2)SiO(3)(OH)(2)), and xonotlite (Ca(6)Si(6)O(17)(OH)(2)). The (29)Si MAS NMR spectra of rankinite and wollastonite clearly resolve manifolds of spinning sidebands from two and three Si sites, respectively, allowing the CSA parameters to be obtained with high precision for each site. For the (29)Si Q(1) sites in rankinite and cuspidine, the CSA asymmetry parameters (eta(sigma) approximately 0.6) contrast the general expectation that sorosilicates should possess small eta(sigma) values as a result of the nearly axially symmetric environments of the SiO(4) tetrahedra. The (29)Si CSA parameters provide an improved insight into the electronic and geometric environments for the SiO(4) tetrahedra as compared to the values solely for the isotropic chemical shift. It is shown that the shift anisotropy (delta(sigma)) and the CSA asymmetry parameter (eta(sigma)) allow a clear distinction of the different types of condensation of SiO(4) tetrahedra in calcium silicates. This relationship may in general be valid for neso-, soro-, and inosilicates. The CSA data determined in this work may form a valuable basis for (29)Si MAS NMR studies of the structures for tobermorites and calcium silicate hydrate phases resulting from hydration of Portland cements.     

Solid-state (14)N MAS NMR of ammonium ions as a spy to structural insights for ammonium salts

The high resolution offered by magic-angle spinning (MAS), when compared to the static condition in solid-state NMR of powders, has been used to full advantage in a (14)N MAS NMR study of some ammonium salts: CH(3)NH(3)Cl, (NH(4))(2)(COO)(2) x H(2)O, (CH(3))(3)(C(6)H(5)CH(2))NCl, (CH(3))(3)(C(6)H(5))NI, [(n-C(4)H(9))(4)N](2)Mo(2)O(7), (NH(4))(2)HPO(4), and NH(4)H(2)PO(4). It is shown that the high-quality (14)N MAS NMR spectra, which can be obtained for these salts, allow determination of the (14)N quadrupole coupling parameters, i.e. C(Q) (the quadrupole coupling constant) and eta(Q) (the asymmetry parameter), with very high precision. In particular, it is shown that precise C(Q), eta(Q) parameters can be determined for at least two different (14)N sites in case the individual spinning-sideband (ssb) intensities arise from a single manifold of ssbs, i.e. the ssbs for the two sites cannot be resolved. This feature of (14)N MAS NMR, which is the first demonstration for manifolds of ssb in MAS NMR without the potential information from a central transition, becomes especially useful at the slow spinning frequencies (nu(r) = 1000-1500 Hz) applied to some of the ammonium salts studied here. The detection of the number of sites has been confirmed by the corresponding crystal structures determined from single-crystal X-ray diffraction (XRD), either in this work for the unknown structure of benzyl trimethylammonium chloride or from reports in the literature. The magnitudes of the (14)N quadrupole coupling constants for the ammonium salts studied here are in the range from C(Q) approximately 20 kHz to 1 MHz while the asymmetry parameters span the full range 0 < or = eta(Q) < or = 1. Clearly, the (14)N quadrupole coupling parameters (C(Q), eta(Q)) for ammonium ions appear highly sensitive toward crystal structure and therefore appreciably more informative for the characterization of ammonium salts in comparison to the isotropic (14)N (or (15)N) chemical shifts.     

Ten-electron coordination and reactivity of an arylphosphinidene ligand

Photochemical decarbonylation of [Mo2Cp2(mu-PR*)(CO)4] (Cp = eta5-C5H5; R* = 2,4,6-C6H2tBu3) gives [Mo2Cp2(mu-kappa1:kappa1,eta6-PR*)(CO)2], which shows the first example of a remarkable 10-electron donor arylphosphinidene ligand which bridges two Mo atoms through its phosphorus atom while being pi-bonded to one Mo center through the six carbon atoms of the aryl ring. This causes a severe pyramidal distortion of the P-bound C atom. The complex adds CO to give [Mo2Cp2(mu-kappa1:kappa1,eta4-PR*)(CO)3], which has an 8-electron donor PR* ligand, and then the parent complex [Mo2Cp2(mu-PR*)(CO)4]. Protonation of [Mo2Cp2(mu-kappa1:kappa1,eta6-PR*)(CO)2] gives the hydride [Mo2Cp2(H)(mu-kappa1:kappa1,eta6-PR*)(CO)2]+, which undergoes P-C bond cleavage and hydride migration, affording the phosphido cation [Mo2Cp2(mu-P)(eta6-R*H)(CO)2]+.     

液晶型聚氨酯弹性体的固体高分辨核磁共振研究

采用固体高分辨＾１３Ｃ核磁共振谱以及溶液碳谱、氢谱的方法对以聚四氢呋喃（ＰＴＭＯ）为软段、４，４＇－二苯基甲烷二异氰酸酯（ＭＤＩ）为硬段、４，４＇－二羟已氧基联苯（ＨＢ６）为扩链剂的液晶型聚氨酯弹性体的相态结构、分子运动、氢键相互作用等问题进行了研究。探讨了样品的化学结构与上述问题间的关系。     

Dihydrogen to dihydride isomerization mechanism in [(C5Me5)FeH2(Ph2PCH2CH2PPh2)]+ through the experimental and theoretical analysis of kinetic isotope effects

The isomerization of complex [Cp*Fe(dppe)(eta2-H2)]+, generated in situ by low-temperature protonation of Cp*Fe(dppe)H with either HBF4 or CF3COOH, to the dihydride tautomer trans-[Cp*Fe(dppe)(H)2]+ is irreversible and follows first-order kinetics in the -10 to +15 degrees C range with Delta H double dagger = 21.6 +/- 0.8 kcal mol(-1) and DeltaS double dagger = 5 +/- 3 eu. The isomerization rate constant is essentially independent of the nature and quantity of a strong acid. Density functional theory (DFT) calculations on various models, including the complete system at both the quantum mechanics/molecular mechanics (QM/MM) and full QM levels, probe the relative importance of steric and electronic effects for the relative stability of the nonclassical and classical isomers and identify two likely isomerization mechanisms: a "direct" pathway involving simultaneous H-H bond breaking and cis-trans isomerization and a "via Cp" pathway involving agostic C5Me5H intermediates. Both pathways are characterized by activation energies in close correspondence with the experimental value (21.3 and 22.2 kcal mol(-1), respectively). Further kinetic studies were carried out for the Cp*Fe(dppe)H + CF3COOD and Cp*Fe(dppe)D + CF3COOD systems at 273 K. The [Cp*Fe(dppe)(eta2-HD)]+ complex establishes a very rapid isotope redistribution equilibrium with the eta2-H2 and eta2-D2 analogues. The equilibrium constant value (K = 3.3 +/- 0.3) indicates a significant equilibrium isotope effect. Simulation of the rate data provides access to the individual isomerization rate constants kHH, kHD, and kDD for the three isotopomers, yielding kinetic isotope effects: kHH/kHD = 1.24 +/- 0.01 and kHD/kDD = 1.58 +/- 0.01 (and, consequently, kHH/kDD = 1.96 +/- 0.02). The analysis of the DFT-calculated frequencies, using the [Cp*Fe(dhpe)H2]+ model system, for the [Cp*Fe(dhpe)(eta2-XY)]+ isotopomers as well as transition states for the "direct" (TSdir) and "via Cp" (TSrot) pathways (X = H, D) allowed the computation of the expected isotope effects. A comparison with the experiment strongly suggests that the mechanism occurs via the "direct" pathway for the present system, although the small difference in the calculated energy barriers suggests that the "via Cp" pathway may be preferred in other cases.     

Solid-state natural abundance 25Mg NMR studies of Na2MgEDTA x 4 H2O--a possible new reference compound for 25Mg NMR spectroscopy

Natural abundance solid-state (25)Mg NMR measurements were made of the disodium salt of magnesium ethylenediaminetetraacetate tetrahydrate (Na(2)MgEDTA x 4 H(2)O). Both magic angle spinning (MAS) and static experiments were employed to determine the quadrupole coupling constant (C(q)) and the asymmetry parameter (eta(q)) of the electric field gradient (EFG) tensor associated with (25)Mg in this compound, giving the values C(q) = 1.675(5) MHz and eta(q) = 0.15(1). The isotropic chemical shift was determined to be delta(iso) = 0.25(10) ppm (relative to 11 M MgCl(2) aqueous solution) and a small chemical shift anisotropy (CSA) contribution (approximately -13 ppm) was detected, one of the first CSA reports in (25)Mg NMR. This compound exhibited remarkably good (25)Mg NMR sensitivity, due to its fast spin-lattice relaxation and modest quadrupole coupling, which allowed its use as a secondary shift reference and as a test sample for the implementation and optimisation of signal-enhancement methods in (25)Mg NMR spectroscopy, such as double frequency sweeps (DFS) and the use of adiabatic hyperbolic secant (HS) and WURST pulses.     

Structure and dynamics of homoleptic beryllocenes: a solid-state 9Be and 13C NMR study

The correlation between anisotropic 9Be NMR (quadrupolar and chemical shielding) interactions and the structure and dynamics in [Cp2Be], [Cp2*Be], and [(C5Me4H)2Be] is examined by solid-state 9Be NMR spectroscopy, as well as by ab initio and hybrid density functional theory calculations. The 9Be quadrupole coupling constants in the three compounds correspond well to the relative degrees of spherical ground-state electronic symmetry of the environment about beryllium. Theoretical computations of NMR interaction tensors are in excellent agreement with experimental values and aid in understanding the origins of NMR interaction tensors and their correlation to molecular symmetry. Variable-temperature (VT) 9Be and 13C NMR experiments reveal a highly fluxional structure in the condensed phase of [Cp2Be]. In particular, the pathway by which the Cp rings of [Cp2Be] 'invert' coordination modes is examined in detail using hybrid density functional theory in order to inspect variations of the 9Be NMR interaction tensors. The activation energy for the 'inversion' process is found to be 36.9 kJ mol(-1) from chemical exchange analysis of 13C VT CP/MAS NMR spectra. The low-temperature (ca. -100 degrees C) X-ray crystal structures of all three compounds have been collected and refined, and are in agreement with previously reported structures. In addition, the structure of the same Cp2Be crystal was determined at 20 degrees C and displays features consistent with increased intramolecular motion, supporting observations by 9Be VT NMR spectroscopy.     

Parallel modes of C-H bond activation initiated by CpMo(NO)(CH2CMe3)(C6H5) at ambient temperatures

The molybdenum nitrosyl complex Cp*Mo(NO)(CH2CMe3)(C6H5) reacts at room temperature via elimination of neopentane or benzene to form the transient species Cp*Mo(NO)(=CHCMe3) and Cp*Mo(NO)(eta2-C6H4). These reactive intermediates effect the intermolecular activation of hydrocarbon C-H bonds via the reverse of the transformations by which they are generated. Thermolysis of Cp*Mo(NO)(CH2CMe3)(C6H5) in pyridine yields the adducts Cp*Mo(NO)(=CHCMe3)(NC5H5) and Cp*Mo(NO)(eta2-C6H4)(NC5H5), and the benzyne complex has been characterized by X-ray diffraction.     

Incorporation of aluminum in the calcium silicate hydrate (C-S-H) of hydrated portland cements: a high-field 27Al and 29Si MAS NMR investigation

The calcium silicate hydrate (C-S-H) phase resulting from hydration of a white Portland cement (wPc) in water and in a 0.3 M NaAlO(2) solution has been investigated at 14 and 11 hydration times, respectively, ranging from 6 h to 1 year by (27)Al and (29)Si MAS NMR spectroscopy. (27)Al MAS NMR spectra recorded at 7.05, 9.39, 14.09, and 21.15 T have allowed a determination of the (27)Al isotropic chemical shift (delta(iso)) and quadrupolar product parameter (P(Q) = C(Q)) for tetrahedrally coordinated Al incorporated in the C-S-H phase and for a pentacoordinated Al site. The latter site may originate from Al(3+) substituting for Ca(2+) ions situated in the interlayers of the C-S-H structure. The spectral region for octahedrally coordinated Al displays resonances from ettringite, monosulfate, and a third aluminate hydrate phase (delta(iso) = 5.0 ppm and P(Q) = 1.20 MHz). The latter phase is tentatively ascribed to a less-crystalline aluminate gel or calcium aluminate hydrate. The tetrahedral Al incorporated in the C-S-H phase has been quantitatively determined from (27)Al MAS spectra at 14.09 T and indirectly observed quantitatively in (29)Si MAS NMR spectra by the Q(2)(1Al) resonance at -81.0 ppm. A linear correlation is observed between the (29)Si MAS NMR intensity for the Q(2)(1Al) resonance and the quantity of Al incorporated in the C-S-H phase from (27)Al MAS NMR for the different samples of hydrated wPc. This correlation supports the assignment of the resonance at delta(iso)((29)Si) = -81.0 ppm to a Q(2)(1Al) site in the C-S-H phase and the assignment of the (27)Al resonance at delta(iso)((27)Al) = 74.6 ppm, characterized by P(Q)((27)Al) = 4.5 MHz, to tetrahedrally coordinated Al in the C-S-H. Finally, it is shown that hydration of wPc in a NaAlO(2) solution results in a C-S-H phase with a longer mean chain length of SiO(4) tetrahedra and an increased quantity of Al incorporated in the chain structure as compared to the C-S-H phase resulting from hydration of wPc in water.     

Use of dipotassium cyanamide for the synthesis of cyanoimido (NCN2-) complexes of tungsten and cobalt

Three transition metal cyanoimido (NCN2-) complexes, (Cp*WS2)2(mu-NCN) (1) (Cp* = eta 5-C5Me5), K[(Cp*WS2)2(NCN)] (2) and ([bipy)2Co]2(mu-NCN)2)(ClO4)2 (3), were synthesized from dipotassium cyanamide, and their structures were determined.     

Transition metal complexes of the chelating phosphine borane ligand Ph2PCH2Ph2P.BH3

Chromium and ruthenium complexes of the chelating phosphine borane H(3)B.dppm are reported. Addition of H(3)B.dppm to [Cr(CO)(4)(nbd)](nbd = norbornadiene) affords [Cr(CO)(4)(eta1-H(3)B.dppm)] in which the borane is linked to the metal through a single B-H-Cr interaction. Addition of H(3)B.dppm to [CpRu(PR(3))(NCMe)(2)](+)(Cp =eta5)-C(5)H(5)) results in [CpRu(PR(3))(eta1-H(3)B.dppm)][PF(6)](R = Me, OMe) which also show a single B-H-Ru interaction. Reaction with [CpRu(NCMe)(3)](+) only resulted in a mixture of products. In contrast, with [Cp*Ru(NCMe)(3)](+)(Cp*=eta5)-C(5)Me(5)) a single product is isolated in high yield: [Cp*Ru(eta2-H(3)B.dppm)][PF(6)]. This complex shows two B-H-Ru interactions. Reaction with L = PMe(3) or CO breaks one of these and the complexes [Cp*Ru(L)(eta1-H(3)B.dppm)][PF(6)] are formed in good yield. With L = MeCN an equilibrium is established between [Cp*Ru(eta2-H(3)B.dppm)][PF(6)] and the acetonitrile adduct. [Cp*Ru (eta2-H(3)B.dppm)][PF(6)] can be considered as being "operationally unsaturated", effectively acting as a source of 16-electron [Cp*Ru (eta1-H(3)B.dppm)][PF(6)]. All the new compounds (apart from the CO and MeCN adducts) have been characterised by X-ray crystallography. The solid-state structure of H(3)B.dppm is also reported.     

Low-temperature NMR studies of Zn tautomerism and hindered rotations in solid zincocene derivatives

Using a combination of NMR methods we have detected and studied fluxional motions in the slip-sandwich structure of solid decamethylzincocene (I, [(eta5-C5Me5)Zn(eta1-C5Me5)]). For comparison, we have also studied the solid iminoacyl derivative [(eta5-C5Me5)Zn(eta1-C(NXyl)C5Me5)] (II). The variable temperature 13C CPMAS NMR spectra of I indicate fast rotations of both Cp* rings in the molecule down to 156 K as well as the presence of an order-disorder phase transition around 210 K. The disorder is shown to be dynamic arising from a fast combined Zn tautomerism and eta1/eta5 reorganization of the Cp* rings between two degenerate states A and B related by a molecular inversion. In the ordered phase, the degeneracy of A and B is lifted; that is, the two rings X and Y are inequivalent, where X exhibits a larger fraction of time in the eta5 state than Y. However, the interconversion is still fast and characterized by a reaction enthalpy of DeltaH = 2.4 kJ mol-1 and a reaction entropy of DeltaS = 4.9 J K-1 mol-1. In order to obtain quantitative kinetic information, variable temperature 2H NMR experiments were performed on static samples of I-d6 and II-d6 between 300 and 100 K, where in each ring one CH3 is replaced by one CD3 group. For II-d6, the 2H NMR line shapes indicate fast CD3 group rotations and a fast "eta5 rotation", corresponding to 72 degrees rotational jumps of the eta5 coordinated Cp* ring. The latter motion becomes slow around 130 K. By line shape analysis, an activation energy of the eta5 rotation of about 21 kJ mol-1 was obtained. 2H NMR line shapes analysis of I-d6 indicates fast CD3 group rotations at all temperatures. Moreover, between 100 and 150 K, a transition from the slow to the fast exchange regime is observed for the 5-fold rotational jumps of both Cp* rings, exhibiting an activation energy of 18 kJ mol-1. This value was corroborated by 2H NMR relaxometry from which additionally the activation energies 6.3 kJ mol-1 and 11.2 kJ mol-1 for the CD3 rotation and the molecular inversion process were determined.