Coordination of {Mo(142)} Ring to La(3+) Provides Elliptical {Mo(134)La(10)} Ring with a Variety of Coordination Modes

A 28-electron reduced C(2h)-Mo-blue 34Ǻ outer ring diameter circular ring, [Mo(142)O(429)H(10)(H(2)O)(49)(CH(3)CO(2))(5)(C(2)H(5)CO(2))](30-) (≡{Mo(142)(CH(3)CO(2))(5)(C(2)H(5)CO(2))}) comprising eight carboxylate-coordinated (with disorder) {Mo(2)} linkers and six defect pockets in two inner rings (four and three for each, respectively), reacts with La(3+) in aqueous solutions at pH 3.5 to yield a 28-electron reduced elliptical C(i)-Mo-blue ring of formula [Mo(134)O(416)H(20)(H(2)O)(46){La(H(2)O)(5)}(4){La(H(2)O)(7)}(4){LaCl(2)(H(2)O)(5)}(2)](10-) (≡{Mo(134)La(10)}), isolated as the Na(10)[Mo(134)O(416)H(20)(H(2)O)(46){La(H(2)O)(5)}(4){La(H(2)O)(7)}(4){LaCl(2)(H(2)O)(5)}(2)]·144 H(2)O Na(+) salt. The elliptical structure of {Mo(134)La(10)} showing 36 and 31 Å long and short axes for the outer ring diameters is attributed to four (A-D) modes of LaO(9)/LaO(7)Cl(2 )tricapped-trigonal-prismatic coordination (TTP) geometries. Two different LaO(2)(H(2)O)(7) and one LaO(2)(H(2)O)(2)Cl(2) 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 {Mo(142)(CH(3)CO(2))(5)(C(2)H(5)CO(2))}, and two LaO(4)(H(2)O)(5) TTP geometries (as D mode) result from the displacement of two (acetate/propionate-coordinated) binuclear {Mo(2)} linkers with La(3+) in each inner ring. The isothermal titration calorimetry (ITC) of the ring modification from circle to ellipsoid, showing the endothermic reaction of [La(3+)]/[{Mo(142)(CH(3)CO(2))(5)(C(2)H(5)CO(2))}] = 6/1 with ΔH = 22 kJ⋅mol(-1), ΔS = 172 J⋅K(-1)⋅mol(-1), ΔG = −28 kJ⋅mol(-1), and K = 9.9 × 10(4) M(-1) at 293 K, leads to the conclusion that the coordination of the defect pockets to La(3+) precedes the replacement of the {Mo(2)} linkers with La(3+). (139)La- NMR spectrometry of the coordination of {Mo(142)(CH(3)CO(2))(5)(C(2)H(5)CO(2))} ring to La(3+) is also discussed.