Gary Wulfsberg

A 35Cl NQR study of coordination of Orthochlorines in cobalt(II) 4-substituted-2,6-dichlorophenolates

Abstract The 35Cl NQR spectra of some cobalt(II) 2,4,6-trichlorophenolates, 2,6-dichlorophenolates, and 4-bromo-2,6-dichlorophenolates, including two of known crystal structures, have been investigated to study the nature of organochlorine-to-cobalt coordinate covalent bonding. As expected, the difference in frequency of the coordinated and the non-coordinated ortho chlorines increases (to as high as 3 MHz, corresponding to thedonation of about 0.1 electron by the coordinated organochlorine) as the metal-chlorine bond distance decreases (to as short a distance as 262 pm). The frequency difference is found to be temperature-dependent (less at higher temperatures) if the difference at 77K exceeds about 1.3 MHz.

Weakly Coordinating Ligands: Nuclear Quadrupole Coupling Constants and Asymmetry Parameters of Iodocarbons Coordinated to Metal Ions

NQR (nuclear quadrupole resonance) spectroscopy is potentially one of the best ways of characterizing the bonding of metal cations such as zirconocene cations and Ag+ to halogen donor atoms in weakly coordinating anions and neutral ligands such as halocarbons. Known coordination of organoiodine atoms to silver ions was studied by 127I NQR spectroscopy in [Ag(p-C6H4I2)](PO2F2), [Ag(o-C6H4I2)]N03 , [Ag(CH2I2)2]PF6, and the explosive [Ag(CH2I2)]NO3 ; a possible case of iodocarbon coordination to a mercury atom in C5Cl5HgCl ·CH2I2 was also investigated. Both the low-frequency (ca. 300 MHz) and the high-frequency (ca. 500 MHz) NQR signals were detected for each compound, and, for the first time, the quadrupole coupling constants e2Qqzz/h and asymmetry parameters ηof coordinated organohalogen atoms were obtained. As compared to the free iodocarbons, substantial (4 - 12%) reductions of e2Qqzz/h and substantial increases in η (to about 20 - 40%) were found in the iodocarbon complexes of silver, but not of mercury. From approximate theoretical analysis of the data, it appears that the electronic interaction of silver and iodine is quite substantial.

Coordination of Ortho-Chlorines in Copper (I) and Silver (I) 2,6-Di- and 2,4,6-Trichlorophenolates

Abstract The crystal structure of (Ph3P)2AgOC6H2Cl3 (I) is reported along with the syntheses and 35Cl and 63Cu NQR spectra of I and several related silver (I) and copper (I) 2,6-di- and 2,4,6-trichlorophenolates containing phosphines, phosphites, and pyridine as co-ligands. I crystallizes in space group P21/cc with a= 16.692(4) Å, b= 17.942 (4) A, c = 12.857 (3) Å, β = 97.60 (1)°, F = 3816.68 Å3, and Z = 4. The final R (F) = 0.0475 and R (W) = 0.0396. Ag is coordinated in a trigonal planar geometry by the P atoms of the two triphenylphosphine ligands and the O atom of the chlorophenolate; Ag is then capped by one ortho-chlorine of the trichlorophenolate ligand at a distance of 3.160 (2) Å. In the 35Cl NQR spectrum of this compound the two ortho-chlorines of the trichlorophenolate ligand have a large frequency difference of 1.500 MHz, indicating that one ortho-chlorine is coordinated to the silver; 35Cl NQR spectra of related complexes are also presented and discussed. The 35Cl NQR frequency differences of coordinated and non-coordinated ortho-chlorines in metal chlorophenolates correlate well with the metal-chlorine distances but not with the metal-chlorine-carbon bond angles. A different correlation is found for the silver complexes of dichloroalkanes; possible reasons for this are discussed.

Crystallographic and spectroscopic assessment of chelate-stabilized aryl halide complexes at a seven-coordinate d4 molybdenum centre

A new series of chelate stabilized aryl halide coordination complexes of molybdenum are prepared by a novel oxidative addition strategy; quantitative equilibrium measurements suggest that the structure of the chelate ring, rather than the identity of the halide (X = Cl, Br, I), controls the strength of aryl halide binding in these complexes.

Investigation of the C−Cl bonds in trichloroacrylic acid, Cl2C=CClCOOH, by single crystal Zeeman split NQR

Abstract The 35Cl NQR spectrum of trichloroacrylic acid, Cl2C = CClCOOH, was studied by single crystal Zeeman NQR spectroscopy at 303 K (high temperature phase I) and at 275 K (low temperature phase II). At 303 K for the = CCl2 group chlorines it was found eQΦzz h-1(35Cl(2)) = 76.179 MHz, η (35Cl) = 0.1597; eQΦzz h -1 (35Cl(3))= 74.693 MHz, η(35Cl) = 0.1868 and for the = CClC - group chlorine eQΦzz h -1(35Cl(1)) = 75.145 MHz, η (35Cl) = 0.1568. The difference in the electric field gradients at the stereochemically inequivalent chlorines Cl(2) and Cl(3) is rather large. The asymmetry parameter η (35Cl(1)) shows an unusual temperature dependence which probably originates from the change of the hydrogen dynamics and position within the dimeric H-bonded unit (Cl2C = CClCOOH)2 during the phase transition

Activation Energies for Fluxional Behavior in Aryl(pentachlorocyclopentadienyl)mercurials, η1 -C5Cl5 HgR, from 35Cl NQR Relaxation Times

Abstract Solid-state activation energies for fluxional behavior in three aryl-subsituted (pentachlorocyclo-pentadienyl)phenylmercury compounds RHgC5 Cl5 : (pentachlorocyclopentadienyl)(pentamethyl-phenyl)mercury (I, R = C6 (CH3)5 , Eact = 19.3 kJ mol-1); (pentachlorocyclopentadienyl)(2,4,6-tris-(terf-butyl)phenyl)mercury (II, R = 2,4,6-C 6 H 2 (C(CH3)3)3 , Eact = 59.5 kJ mol-1); and (pentachloro-cyclopentadienyl)(phenyl)mercury (III, R = C6H5 , E act = 62.8 kJ mol-1) have beeb obtained from 35Cl NQR spin-lattice relaxation-time measurements. II has also been shown to be fluxional in solution by 13C NMR spectra. II was prepared by an exchange reaction between Hg(C5Cl5)2 and Hg(2,4,6-C6H2(C(CH3)3)3)2 , which reacted readily despite the great steric hindrance present in the latter reagent.

Studies of Fluxionality in Pentachlorocyclopentadienylmercurials RHgC5Cl5 by Solution and Solid State 13C NMR and by 35Cl NQR Spectroscopy

Solution and magic-angle-spinning solid-state 13C NMR spectra are reported for η1-(pentachlorocyclopentadienyl)( pentamethylphenyl) mercury, C6Me5HgC5Cl5 (II). The latter suggests that II is fluxional in the solid state. Some expected consequences of fluxional behavior also appear in the 35Cl NQR spectra of II and several related pentachlorocyclopentadienylmercurials.