- Abstract We report a study of the 203 Tl and 205 Tl Nuclear Magnetic Resonance of the ternary semiconductor TlTaS 3 that shows a chain structure. Our measurements show noticeable intra-chain (Tl–Tl) and inter-chain (Tl–Ta) indirect nuclear spin–spin interactions. These couplings result from the overlap of the Tl and Ta electron wave functions across the intervening S atom, in contrast with the expected 1D-behavior of the compound. The experimental results are in good agreement with the calculated electronic band structure. The role of the 6s 2 electron pair of Tl in interatomic interactions is discussed.