C h emIn fo rm 2 0 1 2 ,4 3 ,issu e 1 0 © 2 0 1 2 Wiley -VCH Verl ag G m b H & Co. K G a A , We i n he i m Vana dium I 500 0 DOI: 1 0.100 2/ch in.201 2100 15 Synthesis, Struc t ur e, and Solubility Studies of a New Ar se nato-Polyox ovana date C luster C ompo und: ( NH4)4[V 12As 8O 40(H 2O )]•4 H2O. -Th e title com poun d is prepare d by solv otherm al rea ction of NH4VO 3 and As 2O 3 in a 1:1 mixture of Et2O (o r Et O H) a n d H 2O (pH 6.5, 80 °C , closed glass tube , 7 d, 20% y ield). (N H4)4[V 12As 8O40(H 2O )]•4 H2O is cha rac terize d by sin gle c rysta l XRD, IR a nd solid sta te UV/VI S spe ctrosco py, and elec trospray io niza tion m ass spe ctrome try. It c rysta llize s in the o r th orhomb ic spa ce g roup Pn nn with Z = 2. T h e structure co ntains a n anionic c luste r shell, w hic h ca n be de rive d fr om the { V18O 42} c luste r by re plac ing VO5 polyh edra by As2O5 units a nd om itting two VO5 squa re p yramids. The c luste r an ion is best de sc ribed by th e formu la O40(H 2O) ] 4-. T h e c ompo und is a semic onductor w ith a band ga p of 2.8 eV. Its s olubility in H 2O, MeOH, a nd DM F is d isc usse d. -( W UT KO W SKI , A.