A series of novel mixed ligand dinickel complexes of the type [(Ni2L)-L-II(mu-L')](+), where L' is a tetrahedral oxo-alkoxo vanadate (L' = [O2VV(OR)(2)](-), R = H or alkyl) and L a macrocyclic N6S2 supporting ligand, have been prepared, and their esterification reactivity has been studied. The orthovanadate complex [Ni2L(mu-O2V(OH)(2))](+) (2), prepared by reaction between [Ni2L(mu-Cl)]ClO4 with Na3VO4 and a phase transfer reagent in CH3CN, reacts smoothly with MeOH and EtOH forming the vanadate diesters [Ni2L(mu-O2V(OMe)(2))](+) (3) and [Ni2L(mu-O2V(OEt)(2))](+) (4). The dialkyl orthovanadate esters in 3 and 4 are readily transesterified with mono- and difunctional alcohols. Complex 3 can also be generated from 4 by transesterification with MeOH. Complexes 3 and 4 react with diols (ethylene glycol, propylene glycol and diethylene glycol) as well to afford the complexes [Ni2L(mu-O2V(OH)(OCH2CH2OH))](+) (5), [Ni2L(mu-O2V(OCH2)(2)CH2)](+) (6), and [Ni2L(mu-O2V(OCH2CH2)(2)O)] (7). The crystal structures of the tetraphenylborate salts of complexes 3-7 reveal in each case four-coordinate O2VV(OR)(2)(-) groups bonded in a mu(1,3)-bridging mode to generate trinuclear complexes with a central N3Ni(mu-S)(2)(mu(1,3)-O2V(OR)(2))NiN3 core. The stabilization of the four-coordinate (VO2)-O-V(OR)(2)(-) moieties is a consequence of both the two-point coordinative fixation to and the steric protection of the bowl-shape binding pocket of the [Ni2L](2+) fragment. Cyclic voltammetry experiments reveal that the encapsulated vanadate esters are not reduced in a potential window of -2.0 to +2.5 V vs SCE. The spins of the nickel(II) (S-i = 1 ions) in 3 are weakly ferromagnetically coupled (J = +23 cm(-1), (H = -2JS(1)S(2))) to produce an S = 2 ground state.