Coordination of {Mo142} Ring to La3+ Provides Elliptical {Mo134La10} Ring with a Variety of Coordination Modes

A 28-electron reduced C2h-Mo-blue 34Ǻ outer ring diameter circular ring, [Mo142O429H10(H2O)49(CH3CO2)5(C2H5CO2)] (≡{Mo142(CH3CO2)5(C2H5CO2)}) comprising eight carboxylate-coordinated (with disorder) {Mo2} linkers and six defect pockets in two inner rings (four and three for each, respectively), reacts with La in aqueous solutions at pH 3.5 to yield a 28-electron reduced elliptical Ci-Mo-blue ring of formula [Mo134O416H20(H2O)46{La(H2O)5}4{La(H2O)7}4{LaCl2(H2O)5}2] (≡{Mo134La10}), isolated as the Na10[Mo134O416H20(H2O)46{La(H2O)5}4{La(H2O)7}4{LaCl2(H2O)5}2]·144 H2O Na salt. The elliptical structure of {Mo134La10} showing 36 and 31 Å long and short axes for the outer ring diameters is attributed to four (A-D) modes of LaO9/LaO7Cl2 tricapped-trigonal-prismatic coordination (TTP) geometries. Two different LaO2(H2O)7 and one LaO2(H2O)2Cl2 TTP geometries (as A-C modes) for each of two inner rings result from the coordination of all three defect pockets of the inner ring for {Mo142(CH3CO2)5(C2H5CO2)}, and two LaO4(H2O)5 TTP geometries (as D mode) result from the displacement of two (acetate/propionate-coordinated) binuclear {Mo2} linkers with La in each inner ring. The isothermal titration calorimetry (ITC) of the ring modification from circle to ellipsoid, showing the endothermic reaction of [La]/[{Mo142(CH3CO2)5(C2H5CO2)}] = 6/1 with ΔH = 22 kJ⋅mol, ΔS = 172 J⋅K⋅mol, OPEN ACCESS Materials 2010, 3 65 ΔG = −28 kJ⋅mol, and K = 9.9 × 10 M at 293 K, leads to the conclusion that the coordination of the defect pockets to La precedes the replacement of the {Mo2} linkers with La. LaNMR spectrometry of the coordination of {Mo142(CH3CO2)5(C2H5CO2)} ring to La is also discussed.