EDTA COMPLEX CONTAINING 2 TRIANGULAR TRIMOLYBDENUM CLUSTERS WITH MO-MO SINGLE BONDS

From a solution of molybdenum(IV) in aqueous acetate buffer to which Na2H2EDTA is added, red crystals are obtained upon slow evaporation. This product has the composition Na4[Mo6O8(EDTA)3]-14H2O. The crystals belong to the space group P21/c with unit cell dimensions a = 18.157 (6) Å, b = 16.903 (5) Å, c = 19.101 (4) Å, β= 91.38 (2)°, V = 5861 (3) Å3; the cell contains four formula units. The structure has been solved and refined and found to be built of anions consisting of two equivalent trinuclear units connected by EDTA groups. Each trinuclear unit consists of an equilateral triangle of Mo atoms (mean Mo-Mo = 2.51 ± 0.01 Å) capped by one triply bridging oxygen atom (mean Mo-O = 2.04 ± 0.02 Å) and three oxygen atoms that bridge pairs of molybdenum atoms (mean Mo-O = 1.93 ± 0.01 Å). Each Mo atom is then coordinated by two carboxyl oxygen atoms and a nitrogen atom from one end of an EDTA4- ion; each end of each EDTA4- ion is attached to a different Mo3 cluster, so that two such clusters are connected by three EDTA units to form a prolate spheroid. The Mo3(μ3-O)(μ2-O)3O6N3 groups have the same geometric structure that has recently been found for the [Mo3O4(C2O4)3-(H2O)3]2- ion. © 1979, American Chemical Society. All rights reserved.