The Weakly Coordinating Trichloromethanesulfonate Anion:  NQR Comparison of Its Coordinating Abilities via Oxygen with Those of the Chloroacetate Ions

Abstract

Ionic and covalent derivatives of the chlorine analogue of the nonbasic, weakly coordinating triflate ion, Cl3CSO3(-) or "trichlate" ion, have been prepared and compared with the corresponding more strongly coordinated chloroacetates, Cl(x)CH(3-x)CO(2)M (x = 1-3), using 35Cl NQR (nuclear quadrupole resonance) spectroscopy. The (35)Cl NQR frequencies of all types of derivatives are sensitive to the nature of the metal ion or Lewis acid and are most sensitive in the case of monochloroacetates. In covalent (including zirconocene) derivatives, the average NQR frequencies fall as the Pauling electronegativity of M falls. The results for ionic derivatives contrast with previous results for ionic hexachlorometalates: the average (35)Cl NQR frequencies drop sharply as the ionic radius of the group 1 cation increases. Ab initio Gaussian 98 computations at the B3LYP/6-311++G(3df,3pd) level on isolated XCH2CO2M (M = Li, Na, K; X = F, Cl) molecules duplicate this trend, showing increasing polarization of the C-Cl bond and smaller electric field gradients for larger group 1 ions; the relevance of this to the solid state polymerization of chloroacetates (Herzberg, O.; Epple, M. Eur. J. Inorg. Chem. 2001, 1395-1406) is discussed. We have prepared the dihydrate and monohydrate of trichlic acid, Cl3CSO3H. Although trichlates have the highest average NQR frequencies of any of these salts, the NQR frequencies of trichlic acid dihydrate are anomalously lower than those of trichloroacetic acid, which suggests that it is a strong acid, ionized in the solid state to H5O2+ and Cl3CSO3(-) ions.

35Cl NQR spectra of group 1 and silver dichloromethanesulfonates

“…With the exception of the silver salt, the spectral widths of the dichloromethanesulfonates do Signal-to-noise ratios are given in parentheses not exceed 1.0 MHz, and thus do not exceed the normal (small) spectral width ( ν between the highest and the lowest NQR frequency at 77 K) due to crystallographic inequivalence of chlorines of less than about 0.8 MHz for molecular compounds and less than perhaps 1.5 MHz in ionic chloroacetates [3]. This is in sharp contrast to the large spectral widths of 2.075 MHz found in Na…”

“…1 a Dichloromethanesulfonate ion (at left); b dichloromethanesulfonyl chloride synthesized earlier and was shown by X-ray crystallography and 35 Cl NQR (nuclear quadrupole resonance) spectroscopy to have Ag-Cl coordination (organochlorine coordination to Ag + produces a relatively large shift of 35 Cl NQR frequencies to lower values) [2]. Silver (I) trichloromethanesulfonate Ag + (Cl 3 CSO − 3 ) [3] was also synthesized; NQR indicated that it did not have such coordination [3]. Although silver dichloromethanesulfonate, Ag + (Cl 2 CHSO − 3 ), was synthesized by Senning et al [4], it was not structurally characterized; like CHCl 3 , it contains three strongly electron-withdrawing groups which may hinder coordination of the organochlorines to the silver ion.…”

“…Trichloromethanesulfonates were prepared using aqueous metal hydroxides and were easily separated from the metal chloride by recrystallization [3].…”

Nuclear Quadrupole Resonance (NQR) Spectroscopy

“…I bond in [Ag(I 2 CH 2 ) 2 ] (PF 6 ) is secondary, with no sp hybridization, substitution of the observed η in equation (6) gives a value for σ B2 of 0.162; this corresponds to the donation of the slight δ found in neutral CH 2 I 2 , 0.15 e − , to Ag + to give a neutral iodine atom in the complex. However, use of the quadrupole coupling constants of the free and complexed ligand in equations analogous to equations (8) or (9) give significantly different σ B2 values of 0.067 and 0.080.…”

“…The Schiff base formed from 2-chloroaniline and 2,6-dichlorobenzaldehyde undergoes oxidative addition to Mo(CO) 6 (8) and (9) allows us to estimate σ B2 = 0.134 -0.161. This large value can be justified by noting that Period 5 metal ions give larger crystal field stabilization energies than do Period 4 metal ions, especially when strongfield ligands such as CO are present.…”