Phosphaalkyne-Bridged Clusters: Synthesis, Characterization, and Nonlinear Optical Properties of Fe4Se2(μ-Se2PCBut)(CO)11

The reaction of Fe 2 (CO) 6 (μ-Se 2 ) with Bu t C ⋮P in THF solvent, in the presence of sodium hydride, yields the tetrairon cluster Fe 4 Se 2 (μ-Se 2 PCBu t )(CO) 11 . It has been characterized by IR and 1 H, 31 P, and 77 Se NMR spectroscopy, and its molecular structure has been established by single-crystal X-ray diffraction methods. The structure can be described as consisting of a bow-tie type Fe 3 Se 2 unit, one face of which is capped by an unusual FeSe 2 P unit, in which one Se is 3-coordinate and the other 2-coordinate. The second face is capped by a P C(CH 3 ) group such that the P atom is bonded to the middle Fe atom of the Fe 3 Se 2 bow tie and the C atom is attached to one Fe atom and one Se atom. Nonlinear optical properties of Fe 4 Se 2 (μ-Se 2 PCBu t )(CO) 11, measured by the Z-scan technique, indicate significant magnitudes for the third-order susceptibility.