Thallium Nuclear Magnetic Resonance in Thallous Iodide

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Abstract
Wide‐line nuclear magnetic resonance techniques have been used to investigate the electron coupled (or indirect) spin exchange interactions and chemical shifts of the two thalliumisotopes in thallous iodide. Thallous iodide undergoes a phase transition near 160°C from a layered orthorhombic structure to a cubic (CsCl) structure. An order‐of‐magnitude decrease in the estimated second moments of both thallium lines was observed in going from the orthorhombic to the cubic structure, and while the two thallium lines were the same width in the orthorhombic phase, the second moment of the 203Tl line was 50% greater than the second moment of the 205Tl line in the cubic phase. These results are interpreted in terms of a decrease in the “covalent character” of the bonding in the solid, with the transition to the cubic structure. This is consistent with the structural changes occurring at the orthorhombic to cubic transition which involve the lengthening of some unusually short thallium–iodine bonds to form a more symmetric solid with a higher density. The thalliumchemical shift in the cubic phase was found to be − 15 × 10−4 (relative to a saturated TlF solution). An analysis of the chemical shifts of the broad lines in the orthorhombic phase was not conclusive as the shifts were field dependent.