The X-ray structures of the two monodimensional systems of formula [Mn(L)(2)(N-3)(2)](n) in which L = 3-ethylpyridine (1) or 2-hydroxypyridine (2) have been determined. Crystal data : 1, formula C14H18MnN8, monoclinic P2(1)/n, a = 10.210(5) Angstrom, b = 15.460(6) Angstrom, c = 10.880(4) Angstrom, beta = 95.86(3)degrees, Z = 4; 2, formula C10H18MnN8O2, triclinic P (1) over bar, a = 5.218(2) Angstrom, b = 6.841(3) Angstrom, c = 9.469(4) Angstrom, alpha = 79.30(4)degrees, beta = 87.85(4)degrees, gamma = 75.85(4)degrees, Z = 1. The two compounds consist of chains of manganese atoms bridged by double end-to-end azido bridges. 1 consists of a structurally and magnetically alternated chain whereas 2 is a homogeneous system. Magnetic measurements show antiferromagnetic interaction with J values -13.8/-11.7 and -7.0 cm(-1) for 1 and 2, respectively. The deformation of the Mn(N-3)(2) eight-membered lines from planarity to chair conformation has been correlated to the magnitude of the antiferromagnetic coupling constant by means of extended Huckel MO calculations.