“…However, the distance remains significantly greater than the distance between two BaO 3 layers (about 2.4 Å ). For M 3+ , Ba 3 MRu 2 O 9 compounds have been reported for all the other lanthanide ions [35][36][37][38] and for M=Y, In [35,37,39], the MOD of Ru is +4.5 and the metal-metal bond remains strong, the Ru-Ru distance is in the range 2.52-2.56 Å . For M 2+ cations (M=Ni, Co, Zn, Cu [36,39,40] and M=Mg, Ca, Cd, Sr [41][42][43]), the ruthenium is Ru(V), the metalmetal bond, although weaker, remains strong (the RuRu distance is in the range 2.65-2.70 Å ).…”