New cluster compounds [H3O(Ph3PO)3]2[Mo6Cl14] (I) and [H(Ph3PO)2]2[Re6S6Br8] (II) have been prepared by the reaction of a acetonitrile solution of triphenylphosphane oxide Ph3PO with octahedral cluster complexes of molybdenum (H3O)2Mo6Cl14·6H2O and rhenium K2Re6S6Br8, respectively, (with addition of several drops of HBr). The structures and properties of the products were studied by single‐crystalX‐ray diffraction and NMR and luminescence spectroscopic methods. The compounds studied are characterized by strong hydrogen bonds with O–O distances of 2.45–2.51 Å (I) and 2.34–2.41 Å (II); unusual H‐bonded cationic trimers, [H3O(Ph3PO)3]+, were found in compound I. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)