New complexes [ MOO(O,),L]~-[ L = malate, tartrate (tart), tartronate, quinate, or glycolate (glyc)], [WO(0,)2L]2-(L = citrate, tartrate, malate, or glycolate), and [W,O,(O,),(tart)]'-are reported, and modified preparations given for [MO(O,),LI2-and [M0,(0,)L(H,0)]2-( M = M o or W; L = oxalate). Raman and i.r. spectra of the solid complexes, and Raman, 13C and mMo n.m.r. spectra of their aqueous solutions, have been measured and are used to suggest the structures of the species in the solid state and solution. The X-ray crystal structure of K2[Mo0(0,),(glyc)]~2H,0 has been determined: triclinic, space group P i , with a = 7.222(4), b = 7.950(6), c = 10.450(5) A, a = 67.81 (4), p = 73.72(7), y = 64.84(4)O at 20 OC, and Z = 2; the structure has been refined to R = 0.035. We have previously prepared and characterised the oxalato (ox) peroxo complexes K,[MO(O,),(ox)], K,[MO,(O,)(ox)-(H,O)]-H,O (M = Mo or W),' the citrato (cit) (2-hydroxypropane-1,2,3-tricarboxylate) complex K,[MoO(O,),(cit)]-3H,0~0.5H,0,,Z and the tartrato (tart) complexes K4[M202-(O2),(tart)]4H2O (M = Mo or W)., X-Ray crystal structures of the complexes K2[MoO(02)2(ox)],4 K2[WO(02),(ox)],s K,[MoO(0,),(cit)]~3H20-0.5H202,2 and K4[Mo,O,(O,)4-(tart)]-4H,O have been reported.In this paper, we report a number of new, stable carboxylato peroxo complexes and present spectroscopic data for them in the solid state and for their aqueous solutions, as well as the first X-ray crystal structure of a glycolato (glyc) peroxo complex, namely K,[MoO(O2),(glyc)]~2H,O. The work has been undertaken in order to investigate further the chemistry of carboxylato peroxo complexes, as our earlier experiments on oxalato species indicate that carboxylates rival fluorides as coligands to impart chemical and thermal stability to peroxo complexes of the Group 4-6 transition metals.
Results and Discussion( a ) Formation of Complexes.-We find that carboxylato ligands capable of forming five-membered rings with the metal [e.g. oxalate, citrate, tartrate, malate, tartronate, glycolate, quinate (1,3,4,5-tetrahydroxycycIohexanecarboxylate)] generally give stable complexes with peroxo co-ligands. Using the same methods we find that carboxylates which do not form such rings (eg. acetate, adipate, succinate, salicylate, and thiosalicylate) do not form such complexes. Unsaturated acids
