Complexes of molybdenum(V) and lanthanum(III) with 2′,2′′′-(2,6-pyridinediyldiethylidene)-dioxamohydrazide (H2dapsox)

In a template synthesis from ethanolic solution of MoOCl3, 2,6-diacetylpyridine (dap), and semioxamazide (sox), in the molar ratio 1:1:2, a dimeric molybdenum(V) complex [Mo2O2(H(2)dapsox)(2)]Cl-6 . 4H(2)O (where H(2)dapsox= 2 ' ,2 ' ' '-(2,6-pyridinediyldiethylidenedioxamohydrazide) was obtained. In a similar reaction, starting from La(NO3)(3) . 6H(2)O, the complex [La(H(2)dapsox)(NO3)x](NO3)(3-x).1/2EtOH (x=1,2), having coordination number 9, was obtained. In the latter complex two NO3 groups were bidentately coordinated in the solid state, but only one in the solution. Besides [Mo2O2(TPP)(2)] (TPP = tetraphenylporphyrin), the molybdenum(v) complex [Mo2O2 (H(2)dapsox)(2)]Cl-6 . 4H(2)O is the only other known example of a dimeric mu -oxodimolybdenum(V) species that is paramagnetic (mu = 0.95 BM). One of the Mo atoms has pentagonal bipyramidal coordination, and the other pentagonal pyramidal coordination. In aqueous solution a rare example of a pentagonal pyramidal ion [MoO(dapsox)](+) is presumably present. Solution EPR spectra (at 77 K) cannot be related to either of the two known types of Mo(V) species based on the extent of g anisotropy. The substances also were characterized by IR and electronic spectroscopy, and by thermal analysis.