Stern-Gerlach experiments of one-dimensional metal-benzene sandwich clusters: M_n(C₆H₆)_m (M = Al, Sc, Ti, and V)

A molecular beam of multilayer metal-benzene organometallic clusters M _n(C₆H₆)_m (M = Al, Sc, Ti, and V) was produced by a laser vaporization synthesis method, and their magnetic deflections were measured. Multidecker sandwich clusters of transition-metal atoms and benzene Sc_n(C₆H₆)_n+1 (n = 1, 2) and V_n(C₆H₆)_n+1 (n = 1-4) possess magnetic moments that increase monotonously with n. The magnetic moments of Al(C₆H₆), Sc_n(C₆H ₆)_n+1, and V_n(C₆H₆) _n+1 are smaller than that of their spin-only values as a result of intracluster spin relaxation, an effect that depends on the orbital angular momenta and bonding characters of the orbitals containing electron spin. While Ti(C₆H₆)₂ was found to be nonmagnetic, Ti _n(C₆H₆)_n+1 (n = 2, 3) possess nonzero magnetic moments. The mechanism of ferromagnetic spin ordering in M ₂(C₆H₆)₃ (M = Sc, Ti, V) is discussed qualitatively in terms of molecular orbital analysis. These sandwich species represent a new class of one-dimensional molecular magnets in which the transition-metal atoms are formally zerovalent.