Ring opening and extrusion of tellurium atoms in the reaction of benzo[b]tellurophene with trinuclear iron, ruthenium and osmium clusters: X-ray crystal structures of [Os 3 (μ-C 8 H 6 Te)(CO) 1 0 ], [Os 4 (μ-C 8 H 4 )(μ 3 -Te)(CO) 1 1 ], [Ru 2 (μ-C 8 H 6 Te)(CO) 6 ], [Ru 4 (μ 3 -Te)(μ-C 8 H 6 )(CO) 1 1 ] and [Fe 2 (μ-C 8 H 6 Te)(CO) 6 ]