Single crystals of Co4Fe3.33(VO4)(6) and Mn3Fe4(VO4)(6) were grown from equivalent CoO/Fe2O3/V2O5 and MnO/Fe2O3/V2O5 melts, respectively. The former crystallizes in the orthorhombic space group Pnma with parameters a = 4.965(1) Angstrom, b = 10.211(1) Angstrom, c = 17.188(3) Angstrom, and Z = 2 and is a homeotype of such catalysts as Mg-2.5-VMoO8. The lader crystallizes in the triclinic space group P (1) over bar with parameters a = 6.703(2) Angstrom, b = 8.137(1) Angstrom, c = 9.801(2) Angstrom, alpha = 105.56(1)degrees, beta = 105.58(2)degrees, gamma = 102.35(1)degrees, and Z = 1 and is a homeotype of beta-Cu3Fe4(VO4)(6), the low-pressure form of alpha-Cu3Fe4(VO4)(6). The cobalt analogue deviates in stoichiometry from the reactant melt to form the more dense alpha-Cu3Fe4(VO4)(6) structure type comprised of partially occupied face-sharing octahedral and trigonal prismatic coordination sites.