Vanadium Chemistry (3): The complexes

Oxalate

 V(V) forms a surprising complex: cis-[VO2(C2O4)2]3- whose ammonium salt (NH4)3[VO2(C2O4)2].2H2O is bright yellow and forms large, maybe even single crystals, but solution tends to be supersaturated till the end.

Preparation of this is quite hard to describe: Mixing same molar NH4VO3, H2C2O4 and (NH4)2C2O4 together in solution is OK, but then it darkens soon even if you are very precise. Use a few milliliter H2O2 to oxidize it back it turns red, and then in a few days it darkens and repeat H2O2 addition... finally it does not becomes dark but yellow, then go to vaporize at RT.

V(IV) forms a complex: cis-[VO(H2O)(C2O4)2]2- whose ammonium salt (NH4)2[VO(H2O)(C2O4)2].H2O can hardly be crystallized without ethanol.

todo;;;