Cyclopentadienyl chromium and tungsten complexes with halide, methyl and σ-phenylethynyl ligands: Structures of (η5-C5H5)Cr(NO)2(–C≡C–C6H5), (η5-C5H5)Cr(NO)2I and [(η5-C5H4)-COOCH3]W(CO)3Cl