Organometallic Oxides:  Oxidation of the Cubane [(η-C 5 R 5 )Cr(μ 3 -O)] 4 and the Structures and Magnetic Properties of the Salts {[(η-C 5 R 5 )Cr(μ 3 -O)] 4 }{tcnq} and {[(η-C 5 R 5 )Cr(μ 3 -O)] 4 }{BF 4 }