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Synthesis and Structural Determination of Early Transition-Metal Compounds:

Research Project with Dr. Charles H. Mahler

Student Researchers: Brian L. Belz, Joseph M. Keane, Matthew L. Barr, Edward R. Slavin III, Zachary J. Shiffler, Stacy L. Howerter, and Matthew C. Zarzyczny.

Although the chalcogenides (O, S, Se, Te) have well known chemistry, most of their compounds with transition-metals are insoluble; indeed many metals are found as chalcogenide ores. Recently, though, a growing number of soluble transition-metal chalcogenides have been synthesized and studied.(1) This project involves the synthesis of new, soluble compounds of the early transition-metal chalcogenides, their characterization, growth of single-crystals of the compounds, and the determination of their structures by single-crystal X-ray diffraction studies.

The building blocks used to synthesize the new compounds are the soluble tetraselenometalate ions, MSe42-, where the metal is either tungsten or molybdenum. These anions are synthesized in the following reaction: (M = Mo, W; solvent = DMF)

M(CO)6 + 2 Na2Se3 + 2 P(C6H5)4Cl -----> [P(C6H5)4]2MSe4 + 6 CO + 2 NaCl + Na2Se2

These MSe42- anions can then be reacted with organic compounds, selenium and sulfur containing compounds, and a variety of divalent transition-metal salts. Mixed-metal selenides form on reaction of MSe42- and divalent metal salts.(2) The following reaction is typical:

2 MoSe42- + Pd2+ -----> Pd(MoSe4)22-

The anion has the following structure (determined by single-crystal X-ray diffraction in collaboration with Dr. Marj Kastner at Bucknell University):

All of these compounds are air-sensitive, decomposing on exposure to moisture and/or oxygen. They are therefore synthesized and isolated under a non-reactive, inert-gas atmosphere using Schlenk line techniques. This also eliminates any odors associated with selenium chemistry.

The compounds can be characterized using infrared, ultraviolet-visible, and nuclear magnetic resonance spectroscopies, as well as by X-ray structure determination. Crystals of these compounds can generally be grown by solvent layering or slow cooling methods. We have used these crystals to determine the structures of our compounds using X-ray diffraction techniques.

References:

(1)Ansari, M.A.; Ibers, J.A. Coord. Chem. Rev., 1990, 100, 223 - 266.
(2)Ansari, M.A.; Chau, C.-N.; Mahler, C.H.: Ibers, J.A. Inorg. Chem., 1989, 28, 650 - 654.

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Last updated October 3, 2003.
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