Vanadyl sulfates: molecular structure, magnetism and electrochemical activity

Reaction of differing amounts of vanadyl sulfate with p-tert-butylthiacalix[4]areneH(4) and base allows access to the vanadyl-sulfate species [NEt4](4)[(VO)(4)((3)-OH)(4)(SO4)(4)] 1/2H(2)O (1), [HNEt3](5)[(VO)(5)((3)-O)(4)(SO4)(4)] 4MeCN (2 4MeCN) and [NEt4](2)[(VO)(6)(O)(2)(SO4)(4)(OMe)(OH2)] MeCN (3 MeCN ). Similar use of p-tert-butylsulfonylcalix[4]areneH(4), p-tert-butylcalix[8]areneH(8) or p-tert-butylhexahomotrioxacalix[3]areneH(3) led to the isolation of [HNEt3](2)[H2NEt2](2){[VO(OMe)](2)p-tert-butylcalix[8-SO2]areneH(2)} (4), [HNEt3](2)[V(O)(2)p-tert-butylcalix[8]areneH(5)] (5) and [HNEt3](2)[VIV2VV4O(11)(OMe)(8)] (6), respectively. Dc magnetic susceptibility measurements were performed on powdered microcrystalline samples of 1-3 in the T = 300-2 K temperature range. Preliminary screening for electrochemical water oxidation revealed some activity for 2 with turnover frequency (TOF) and number (TON) of 2.2 x 10(-4) s(-1) and 6.44 x 10(-6) (mmol O-2/mmol cat.), respectively. The compound 3 showed an improved electrochemical activity in the presence of water. This is related to the increased number and the rate of electrons exchanged during oxidation of V4+ species, facilitated by protons generated in the water discharge process.