(C5Me5)2Sm(THF)2 reacts with Te and Se in a 2:1 ratio at room temperature in THF to form [(C5Me5)2Sm-((THF)]2(mu-Te), 1, and [(C5Me5)2Sm(THF)]2(mu-Se), 2, respectively. (C5Me5)2Sm(THF)2 reacts with Ph3P=Se and Ph3P=S in a 2:1 ratio at room temperature in THF to form 2 and [(C5Me5)2Sm(THF)]2(mu-S), 3, respectively. (C5Me5)2Sm(THF)2 reacts with excess Te and Se at room temperature in THF to form [(C5Me5)2Sm]2(Te3)(THF), 4, and [(C5Me5)2Sm]2(mu-eta1:eta3-Se3)(THF), 5. The sulfur analog, [(C5Me5)2Sm]2(Se)(THF), 6, can be prepared from (C5Me5)2Sm(THF)2 and S8 in a 2:3 ratio. Triselenide 5 can also be prepared from monoselenide 2 and 2 equiv of Se and monotelluride 1 reacts with excess Te to form tritelluride 4. Both of these reactions occur in THF but not in toluene. Selenium reacts with monotelluride 1 to form a mixture containing a mixed chalcogen complex 7, but this product is not generated from complex 2 by reaction with excess Te. The trichalcogenides 5 and 6 can be converted back to the monochalcogenides 2 and 3, respectively, with 2 equiv of PPh3. 4 reacts with PMe3 in THF to form [(C5Me5)2Sm]2(mu-eta2:eta2-Te2), 8. X-ray crystallographic studies revealed that 2 and 3 are isostructural and differ from 1 only in that 1 has benzene in the lattice instead of toluene. In each complex, a bent metallocene moiety is attached to one THF ligand and a bridging E group. The Sm-E distances are 2.988(2)/2.987(2) (Te), 2.782(1)/2.779(1) (Se), and 2.663(1)/2.665(1) angstrom (S) and the Sm-E-Sm angles are 170.2(1) (Te), 169.7(1) (Se), and 170.0(1)(S). The(Se-Se-Se)2- unit in [(C5Me5)2Sm]2(mu-eta1:Se3)(THF), 5, contains Se-Se distances of 2.377(1) angstrom and 2.326(1) angstrom with an angle of 107.7(1)degrees. The samarium of one of the bent metallocene units in 5 is attached to THF and a bridging selenium atom with a Sm-Se(1) distance of 2.963(1) angstrom. The other (C5Me5)2Sm unit is 3.007(1) angstrom from Se(1) and 3.198(1) and 2.917(1) angstrom, respectively, from Se(2) and Se(3), which are sequentially connected to Se(1). The plane of three selenium atoms forms an angle of 57.9-degrees with the Sm2Se(1) plane. A mixed Se/Te complex, 7, was isolated from the reaction of 1 with Se. 7 is analogous to and isostructural with 5 and contains some Te distributed over at least two of the three chalcogen sites in the molecule. In 8, two bent metallocene units are side on coordinated to a Te2 unit with a 2.773(1) angstrom Te-Te bond such that the four C5Me5 rings define a square plane.