We synthesized two surfactant-encapsulated polyoxometalate (POM) clusters (SECs), (DODA)(15)[H3Mo57V6(NO)(6)O-189(H2O)(12)(VO)(6)](.)13H(2)O (SEC-2, DODA: dimethyldioctadecyl ammonium) and (DODA)(12)[Eu(H2O)P5W30O110](.)28H(2)O (SEC-3). SECs were characterized in detail by elemental analysis, UV-Vis absorption spectroscopy, FTIR, H-1 NMR, thermogravimetric analysis, Langmuir isotherms, and powdered X-ray diffractions. SEC-2 can form a stable monolayer at the air-water interface. SEC-2 and SEC-3 possess a layered structure with periodicities of 3.8 and 5.05 nm, respectively. Alkyl chains in SEC-2 are disordered, but SEC-3 is indicative of well-ordered alkyl chains. According to the simplified structural analysis for SEC-2 and SEC-3, DODAs occupy areas of 1.12 and 0.589 nm(2) on the surface of the POMs, which are characteristic of the liquid-like and crystalline-like phases for DODA, respectively. The different conformations of DODAs then lead to the different packing structures of SECs. This work is aiming to control the organizational structures of the POM-based materials by selecting the appropriate POMs. (C) 2003 Elsevier Inc. All rights reserved.