Nuclear Quadrupole Resonance in TiCl4, ThCl4, NbCl5, and TaCl5

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Abstract
The chlorine resonance in titanium tetrachloride has been re‐examined, confirming the existence of four resonances. A chlorine‐35 resonance at about 6 Mc has been discovered in thorium tetrachloride. The frequency suggests highly ionic bonding, which contradicts earlier conclusions from x‐ray studies. Some double‐bond character may be present in the Th–Cl bond. Niobium and chlorine resonances have been discovered in niobium pentachloride. The niobium resonances are described by a single set of parameters, the coupling constant eqQ being approximately 78 Mc, and the asymmetry parameter, η=0.32. Because of the large asymmetry parameter, it was possible to observe two ΔM=2 and one ΔM=3 transitions. Only a single Cl35 resonance was found at about 13 Mc, although two more chlorine resonances would be expected on the basis of crystal structure. The frequency of the chlorine resonance suggests appreciable covalency in the niobium‐chlorine bond in niobium pentachloride. A single resonance has been found in tantalum pentachloride at about 13 Mc. It is believed to be a chlorine‐35 resonance. A fairly simple method is outlined for determining the asymmetry parameter of the electric‐field gradient from the observed transition frequencies without directly solving the secular equations.

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