Mild pyrolysis of arachno-(Cp*RuCO) 2 B 2 H 6 , 1 (Cp* = η 5 -C 5 Me 5 ), with Fe 2 (CO) 9 leads to the isolation of a mixed-metal tetrahedral cluster, [Cp*Ru(CO) 2 (μ-H)-{RuFe 3 (CO) 9 }], 2, in which [Cp*RuH(CO) 2 ] is attached to the tetrahedral cluster in an exopolyhedral manner. Cluster 2 can be viewed as 52-cve (cluster valence electron) tetrahedral cluster, in which the Ru fragment occupies the low connectivity cluster vertexes and participates in an exopolyhedral hydrogenbridged ruthenium-ruthenium double bond. Cluster 2 has been characterized by mass spectrometry, IR, and 1 H, 11 B, and 13 C NMR spectroscopy, and the geometric structure was unequivocally established by crystallographic analysis.