Two Structures Toward Understanding Evolution from Surfactant-Polyoxometalate Lamellae to Surfactant-Encapsulated Polyoxometalates

Surfactant-POM (polyoxometalate) phases are fascinating in both their self-assembly behavior and their utility as catalysts, probes, and photochromic, electrochroinic, and magnetic devices. Well-ordered lamellar phases are formed when the surfactant:POM ratio is 4:1 or 2:1, and these have been described in great detail from single-crystal X-ray diffraction Studies. However. the surfactant-encapsulated clusters (SECs) with much larger surfactant:POM ratios do not form single-crystals readily. Thus less is known about their structural detail, and the evolution from the well-ordered lamellar phases to the SECs with increasing surfactant: POM ratio has not been detailed. We present here two structures that have resulted from an investigation of understanding the evolution Of the surfactant-POM lamellar phase as the surfactant:POM ratio increases. [H2SiMo12O40][CH3CN](2)[C16H33N(CH3)(3)](4) (monoclinic #4, P2(1) a = 12.636(2) angstrom, b = 20.577(4) angstrom, c = 22.364(4) angstrom, beta = 93.394(4)degrees) holds true to the preference of 4:1 surfactant:POM ratio in well-ordered crystalline phases, whereas [HxSiMo12O40][C16H33N(CH3)(3)](5)[CH3CN](4) (triclinic No. 2, P (1) over bar, a = 12.513(7) angstrom, b = 23.370) angstrom, c = 2.44(1) angstrom, alpha = 93.418(8)degrees. beta = 92.046(8)degrees, gamma = 99.113(7)degrees) provides the first example of a surfactant-POM phase with a surfactant:POM ratio >4. This structure provides a glimpse of the structural evolution front ordered lamellar POM-surfactant phases to more disordered phases such as the SECs.