Due to 2nd-order Jahn-Teller effect, some M cations such as Ti4+, Sn4+, In3+, Nb5+, Cu2+ and W6+ are allowed to enter the MO 6 octahedral site while maintaining the high-symmetry structure of MTe 3 O 8. Therefore, the series of MTe 3 O 8 compounds when M = Sn, Ti, In 0·5 Nb 0·45 V 0.05 and In 0·4 Cu 0·1 Nb 0·4 W 0.1 were successfully synthesized. Rietveld refinement is utilized to visualize the crystal structures. M − O bonds are expanded because of the larger M cations while the O-M-O angles are distorted slightly. As a result of stereoactive 5 s 2 lone-pair electron of Te4+ in TeO 4 E unit, the structure is flexible as reflected by the small variation of Te–O bond lengths and O–Te–O angles. XANES reveal that the local structures of all compounds are preserved. However, different M cations affect their color and electronic band structures, which can be explained differently by the simple band-to-band transition, the VB-V 3 d electronic transition and the d-d electronic transition. [Display omitted] • In 0·5 Nb 0·45 V 0·05 Te 3 O 8 and In 0·4 Cu 0·1 Nb 0·4 W 0·1 Te 3 O 8 were first studied. • Both short-range and long-range orderings are preserved in all compounds. • XANES and XPS spectra are investigated in detail. • The effects of M cations on electronic structures and optical properties are discussed. [ABSTRACT FROM AUTHOR]