Cobalt, Manganese, Nickel, and Vanadium Derivatives of the Cyclic 48-Tungsto-8-Phosphate [H7P8W48O184]33−
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Abstract
The cobalt(II) containing tungstophosphate [Co4(H2O)16P8W48O184]32− (1) has been synthesized by addition of Co2+ ions to an aqueous solution of [H7P8W48O184]33− (P8W48) and characterized by single-crystal XRD, IR, and UV−vis spectroscopy, elemental analysis, electrochemistry, and magnetochemistry. The novel polyanion 1 is a derivative of the superlacunary P8W48 with four cobalt(II) ions coordinated to the rim of the central cavity and two additional cobalt(II) ions linked on the outside bridging neighboring polyanions. Using similar synthetic procedures, but adding a few drops of H2O2, we isolated the manganese(II) derivative [Mn4(H2O)16(P8W48O184)(WO2(H2O)2)2]28− (2) and its nickel(II) analogue [Ni4(H2O)16(P8W48O184)(WO2(H2O)2)2]28− (3). Both polyanions have picked up two equivalents of tungsten resulting in the unprecedented {P8W50} host framework. We also made the vanadium(V) derivative [(VO2)4(P8W48O184)]36− (4), with four tetrahedral vanadate groups grafted to the P8W48 host. The voltammetric patterns associated with the W-centers in polyanions 1, 2, and 4 display enough distinct features allowing for a qualitative classification according to relative basicity of the reduced polyanions: 2 > P8W48 > 1 > 4. The electrochemistry of 1 offers a new example for detection of the Co2+ centers in a multicobalt containing polyanion. During a study of the Mn2+ centers of 2 at pH 5, a film deposition is observed. The vanadium(V) centers of 4 are well-behaved in a pH 0.33 medium. Temperature and magnetic field dependence of the magnetic moment of 1−3 were performed on a SQUID magnetometer over the temperature range 1.8−250 K and field range 0−7 T. The results are consistent with the model of noninteracting 3d metal ions. Variable temperature (4−295 K) and variable frequency (34−413 GHz) EPR measurements support the magnetic susceptibility results. The zero-field splitting D and g values obtained for 1−3 are in agreement with those reported for high-spin Co2+, Mn2+, and Ni2+ ions in axially distorted octahedral environments.
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