Three compounds with formula [Mn(L)(2)(N-3)(2)](n), in which L is 4-acpy = 4-acetylpyridine (1), Etinc = ethyl isonicotinate (2), and py = pyridine (3), have been studied from the magnetic point of view. The new compound [Mn(L)(2)(N-3)(2)](n) (2) crystallizes in the monoclinic system, space group P2(1)/a (No. 14), formula [C16H18MnN8O4], with a = 15.176(5) Angstrom, b = 9.060(3) Angstrom, c = 15.760(6) Angstrom, beta = 111.62(3)degrees, and Z = 4. Compounds 1 and 2 are two-dimensional systems, whereas 3 is a 3-D compound. Compound 2 shows ferromagnetic Mn-2(N-3)(2) dimeric entities linked antiferromagnetically to the four neighboring dimeric entities by four end-to-end azido bridges, leading to an alternate ferromagnetic-antiferromagnetic two-dimensional compound. MO calculations have been performed to study the superexchange pathway for the manganese 1,3-azido system.