Ian M. Walker

Single crystal electronic spectra, electron spin resonance and magnetic data for some high spin tetragonal cobalt(II) complexes at cryogenic temperatures

Abstract The electronic and esr spectra of a series of high spin cobalt(II) complexes of formula Co(EtNHCH2CH2NHEt)2Z2 (Z = Cl, Tr, NCS, NO3) and Co(MeNHCH2CH2NHMe)2(NO3)2 have been examined at R.T. and 10 K respectively. The single crystal polarised electronic spectra were analysed in terms of the Normalised Spherical Harmonic Hamiltonian and a good fit between observed and calculated band energies was obtained. All the complexes are trans, with the exception of Co(EtNHCH2CH2NHEt)2(NO3)2 which is cis. The data are consistent with the presence of a 4Eg ground term derived from the cubic 4T1g term under the influence of a tetragonal distortion for all but one of the complexes. Orbital angular overlap model parameters were derived for this series. These were compared with similar data for cobalt(II) and nickel(II) in the literature, with special reference to the corresponding nickel(II) ethylenediamine complexes. The chief difference between the cobalt and nickel complexes, in an analogous pair of ethylenediamine complexes, is a significantly larger axial repulsion energy in the nickel case. This is attributed to the presence of an extra anti-bonding electron in nickel(II) versus cobalt(II). The esr and magnetic data are fully consistent with the tetragonal model developed for these complexes but do not provide any additional characterisation.

Yttrium-89 magnetic resonance study of simple coordination complexes

Abstract 89 Y FT NMR studies of some simple salts and complex ions have been carried out on a Varian FT80A spectrometer at 3.895 MHz. Corresponding gadolinium salts with the matching counterion have been used as relaxation reagents. Shifts dependent on complexation equilibria have been observed for the carboxylate salts.

CONTACT VERSUS DIPOLAR NMR SHIFTS IN ION-PAIRED SYSTEMS

Abstract Proton NMR data for a series of unsymmetrically substituted ammonium and phosphonium cations in ion pairs with tetrahalocobaltate(II) and nickelate anions are compared with similar data for lanthanide containing systems. The data suggest that the dominant shift mechanism is the axial (through space) dipolar interaction in the cobalt complexes, and not the Fermi-Contact mechanism postulated in previous articles. The structural parameters for the ion-pairs which are obtained by comparison of theory and experiment are used to infer that the cation orientation with respect to the principal axis of magnetic susceptibility of the anion is roughly the same in both sets of complexes, as is the interionic distance, A.

Experimental Correlations of JNC With S-Character

Abstract Some quaternary ammonium salts and isonitriles are examined by 13C NMR. A Fermi-Contact type of correlation is suggested as a basis for estimation of the effect of lone pairs, alkyl substitution and π-bonding on JNC

Anomalous 13C Isotropic NMR Shifts in Tetraalkylammonium Tetrahalometallate(II) Ion Pairs. I. Organic Substituent Effects

13C isotropic NMR shifts have been recorded for a number of tetrahalocobaltate(II) salts containing various quaternary ammonium cations in dichloromethane and nitrobenzene solution. The isotropic shifts are a consequence of ion- aggregate formation, and show great sensitivity to changes in the organic substituents about the -onium centre. The 13C shifts appear to be due in large measure to a predominantly Fermi contact (through-bond) mechanism, unlike the more usual shifts encountered in lanthanide-containing systems. The observed shift patterns correlate well with steric effects induced by the presence or absence of bulky substituents near the central cation nitrogen atom.

NON-AXIAL MAGNETIC BEHAVIOUR OF LANTHANIDES IN ION PAIRS:— CHARACTERIZATION OF ANIONIC Ln(O2CCF3)4 AND Ln(NCS)6 COMPLEXES IN SOLUTION

Abstract Paramagnetic anions which posess formal cubic symmetry behave, in an NMR sense, as though they are rhombic to an approaching cation in an ion-pair complex. The two series of complexes Ln(O2CCF3)4 − and Ln(NCS)6 3- have been prepared in order to examine the underlying theory of dipolar shifts in ion-paired systems. Both series show non-axial behaviour. The former anions might, on the basis of IR studies, be expected to be non-cubic in solution, in disagreement with the NMR spectra. The latter exhibit cubic symmetry, as expected.

Water overtone and combination bands in the near-infrared spectrum of M2FeCl5.H2O (M = Cs, K) at cryogenic temperatures

Abstract Polarised crystal spectra of Cs 2 FeCl 5 .H 2 O have been measured at 10K in the range 3900–20000 cm −1 (2550-50Onm). The two ligand field spectra (8000–20000 cm −1 ) agree with those in the literature. Three distinct spectra were obtained in the 3900–7500 cm −1 range. The symmetry, intensity and energy of the bands permit their assignment pricipally as combination and overtone vibrations of the bound water. The plane of the water molecule is calculated to lie about 32° above or below the bc plane of the crystal. Limited assignments are offered for the more complex crystal system, K 2 FeCl 5 .H 2 O.

The Low Temperature Polarised Electronic Spectra of Some Tetragonal Nickel(II) Haloacetate Complexes

Abstract We have recently reported the single crystal electronic spectra of some substituted ethylenediamine complexes of nickel(II), discussing both cis (1) and trans (2) examples. We have also reported data for their cobalt(II) analogs (3). These were analysed using the Normalised Spherical Harmonic Hamiltonian (NSH) (4) and the Orbital Angular Overlap Model (OAM) (5) approaches. We have

13C and 14N isotropic NMR shifts in anionic nitratolanthanate(III) complexes with quaternary cations

The 14N NMR of nitrate ion coordinated to paramagnetic lanthanide cations in a series of penta- and hexanitratolanthanate(III) anions has been recorded in nitrobenzene- dichloromethane mixtures for all naturally occuring members of the lanthanide series except gadolinium. The nitrate 14N signals show large shifts from their normal values in diamagnetic environments. These isotropic shifts are analysed in terms of a mixture of Fermi contact and through-space dipolar effects. The nitrogen and carbon isotropic shifts from the ammonium cation were shown to be exclusively dipolar in nature. Estimation of the approximate relative amounts of contact and dipolar shift in the nitrate isotropic shifts was attempted. Mixtures of diamagnetic and paramagnetic complexes show separate nitrate 14N resonance signals under our operating conditions. A brief discussion of the kinetics of exchange of nitrate ion between different lanthanide environments is presented.