The rational synthesis of the new sandwich-type arsenotungstocerate [As2W18Ce3O71(H2O)3]122 is reported for the first time by reaction of the trivacant lacunary species A-a-[AsW9O34]92 with appropriate CeIV. The single crystal structure analysis was carried out on K7(H3O)5[As2W18Ce3O71(H2O)3]·9H2O; H39As2Ce3K7O88W18; (2) which crystallizes in triclinic system, space group P1 with a ¼ 11:615ð5Þ A ° , b ¼ 17:638ð7Þ A ° , c ¼ 19:448ð8Þ A ° , a ¼ 73:643ð7Þ8; b ¼ 88:799ð7Þ8; g ¼ 88:078ð7Þ8 and Z ¼ 2: The anion consists on two lacunary A-a-[AsW9O34]92 Keggin moieties linked via a (H2OCeO)3 belt leading to a sandwich-type structure. Each cerium atom adopts tri-capped trigonal-prismatic coordination achieved by two terminal oxygen of an edge shared paired of WO6 octahedra to each A-a-AsW9O34 92 moiety and two oxygen from the belt and the cap by one m3 2 O (As, W2) to each A-a-AsW9O34 92 moiety and one external water ligand. The Ce–O bond lengths average in CeO6 group, Ce–O(As, W2) and Ce–O(nW) are 2.300(9), 2.887(3) and 2.682(5) A° , respectively. The acid/base titration curve reveals that the anion has two different titrable protons.
