Arsenic-Sulfur Heterocycle Formation via Metal Coordination. Synthesis and Molecular Structure of cyclo-(CH3AsS)n (n = 3, 4), ((CO)3Mo)(η3-cyclo-(CH3As)6S3), and the Triple-Decker-Sandwich Complex (η5-(C5H5)2Mo2(η2,μ-As3)(η2,μ-AsS)).