5d TM di-tellurides: cationic vs. anionic polymerization

Layered 5d transition metal (TM) di-tellurides with light transition metals (Hf – Re) crystalline in a structure with the layer stacking of …Te-TM-Te-Te-TM-Te…, and in these tellurides, there exists a very weak van der Waals coupling between Te-Te lyaers with the c/a ratio of 1.6-2. It turns out that in these van der Waals compounds, various polymerization of TM cations occurs, and the number of 5d electrons is essential for the determination of the self-organized pattern of cationic polymers. On the other hand, layered 5d transition metal d-tellurides with heavy transition metals (Pt, Au) tend to have a small c/a ratio of 1.2-1.3. AuTe2 forms in an incommensurate structure based of Te-Te dimers, and in PtTe2, there exists a significant covalent bonding between Te-Te layers. IrTe2 with the c/a ratio of 1.38 turns out to be a unique system at the verge of cationic vs. anisonic polymerization, exhibiting various phase transitions with different Ir-dimer patterns.