Synthesis, molecular structures, and properties of the manganese chalcogenide complexes CpMn(CO)2SC(O)Ph, [CpMn(CO)2]2(μ-Se2), CpMn(CO)2SMe2, [CpMn(CO)2]2(μ-SMe2), and [CpMn(CO)2]2(μ-SeMe2)