Abstract
The reaction of [Mo(CO)~3~(MeCN)~3~] with K~4~Pb~9~ in the presence of 2.2.2‐cryptand (2.2.2‐crypt) has been investigated. The transition metal complex [K(2.2.2‐crypt)]~4~[(η^5^__‐Pb~9~)Mo(CO)~3~] (1), which contains a Pb~9~^4–^ Zintl anion coordinated by Mo in an η^5^‐fashion, is isolated for the first time and characterized by single‐crystal X‐ray structure analysis. The 10 metal atoms in the [(η^5^‐Pb~9~)Mo(CO)~3~]^4–^ anion form a bicapped square antiprism, with the Mo(CO)~3~ unit occupying a waist vertex position. The IR spectra of single crystals, as well as of the crude product, show clearly that only the [(η^5^‐Pb~9~)Mo(CO)~3~]^4–^ ion is formed. In contrast, the reaction of [Mo(CO)~3~(Mes)] with K~4~Pb~9~ under the same reaction conditions gives a mixture of compound 1 and its isomer [K(2.2.2‐crypt)]~4~[(η^4^‐__Pb~9~)Mo(CO)~3~] (2). Compounds 1 and 2 were isolated without additional solvent molecules. The Pb–Mo, Pb–Pb, and Mo–C bond lengths and Mo–C–O bond angles in the η^4^‐ and η^5^‐isomers are compared and the packing of compounds 1 and 2 is discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)