The title polyanion is the first hybrid borophosphate-phenylphosphonate polyoxometalate. It was structurally characterized as its imidazolium salt, (C3N2H5)(5)[Mo12O30(BPO4)(2)(O3P-Ph)6].H2O (monoclinic, P2(1)/c, a = 22.120(3) Angstrom, b = 13.042(2) Angstrom, and c = 32.632(4) Angstrom, P = 101.293(3)degrees), which was synthesized hydrothermally from imidazole, molybdenum oxide and metal, and boric, phosphoric, and phenylphosphonic acids. The anion is the second example of a new class of polyoxometalates that resemble Dawson anions but where the two pole caps of three edge-sharing MoO6 octahedra in the latter are replaced by other units, in this case tetrahedral borate sharing corners with three phenylphosphonic groups, {(OB)(O3P-Ph)(3)}. The 12 molybdenum atoms forming the two equatorial belts of the cluster are of mixed-valence, five are Mov and seven are Mo-VI, and the resulting five electrons are delocalized. Four of these electrons are paired according to the temperature dependence of the magnetic susceptibility. The new compound is soluble in a mixture of water and pyridine (in equal volumes) as well as in nitromethane, and the anions are intact in these solutions.