Topological ferrimagnetic behavior of two new [Mn(L)(2)(N-3)(2)](n) chainswith the new AF/AF/F alternating sequence (L=3-methylpyridine or 3,4-dimethylpyridine)

The reaction of manganese(II) and pyridine derivatives such as 3-methylpyri dine (S-Mepy) and 3,4-dimethylpyridine (3,3-Dmepy) led to the new one-dimen sional systems trans-[Mn(3-Mepy)(2)(N-3)(2)](n) (1) and trans-[Mn(3,4-Dmepy )(2)(N-3)(2)](n) (2). Compound 1 crystallizes in the monoclinic system, spa ce group P2(1)/n, a = 11.201(3) Angstrom, b = 14.499(4) Angstrom, c = 14.30 8(4) Angstrom, Z = 6, and compound 2 crystallizes in the triclinic system, space group P (1) over bar, a = 11.502(4) Angstrom, b = 14.246(5) Angstrom, c = 16.200(8) Angstrom, Z = 6. The two compounds show the same general one -dimensional arrangement of double azido bridges between neighboring mangan ese atoms with the unprecedented -Mn-(mu (1,3)-N-3)(2)-Mn-(mu (1,3)-N-3)(2) -Mn-(mu (1,1)-N-3)(2)-Mn- sequence. Susceptibility and magnetization measur ements reveal a ferrimagnetic-like behavior derived from the topology of th e chain. A model of the Heisenberg chain, comprising classical spins couple d through alternating exchange interactions J(1)J(1)J(2)... is proposed to describe the magnetic behavior.