Crystalline thallium(I) alkylxanthate complexes [Tl{S(S)COR}]n (R = C2H5, i-C3H7, i-C 4H9, s-C4H9, and C5H 11) and isotope-substituted heteropolynuclear Cu(II)Tl(I) complexes [63(65)CuTl6(S2COR)8] (R= i-C 4H9 and C5H11) were obtained and studied by ESR and high-resolution solid-state 13C CP/MAS NMR spectroscopy. According to the 13C NMR data, polynuclear thallium(I) complexes contain structurally equivalent alkylxanthate ligands. The ESR study revealed the Jahn-Teller dynamic effect in Cu(II)Tl(I) complexes; the nuclei of six Tl atoms are involved in the hyperfine interaction