Vanadium(V) complexes of 1,5,10-tris(2,3-dihydroxybenzoyl)-1,5,10-triazadecane and its analogs

Abstract

Vanadium(V) complexes of catechol and several polydentate analogs have been prepared and characterized in solution by optical and [sup 51]V NMR spectroscopies as well by solution thermodynamic measurements. The vanadium(V) catecholate species displayed relatively sharp [sup 51]V NMR signals in the range [minus]164 to [minus]268 ppm but in general were susceptible to decomposition by internal redox reactions yielding V(IV) and quinone, particularly in aqueous solution. The complexes of 1,5,10-tris(2,3-dihydroxybenzoyl)-1,5,10-triazadecane, and its sulfonated analog (3,4-LICAM and LICAMS) are an exception to this generalization and were quite stable. The sulfonated V(V)-LICAMS complex undergoes reversible protonations in aqueous solutions similar to those seen in the analogous Fe[sup 3+] complexes. The proton dependent formation constant for the reaction, K[sup *] = [V[sup V]LICAMS]/[VO[sub 2][sup +]][LICAMS][H[sup +]] has been measured, yielding a log K[sub ML] of 24.2 (1) at 0.5 M in KNO[sub 3] at 25[degrees]C and pH 5.50.