Two new polymeric manganese-azido systems with formula Cs(n)-[[Mn(N3)3]n] (1) and [[N(C2H5)4]n][[Mn2-(N3)5(H2O)]n] (2) were synthesised and structurally characterised. Compound 1 crystallises in the P2(1)/n group and consists of a three-dimensional system with end-to-end and end-on azido bridges with the caesium atoms in the holes of the net. Magnetically, compound 1 is a rare case of a three-dimensional network with alternate ferro-antiferromagnetic interactions. Compound 2 crystallises in the P1 group and consists of double chains of manganese atoms bridged by end-on and, the exceptional, (mu-1,1,1)-azido bridges. Magnetically, compound 2 shows net ferromagnetic behaviour. Exact fit of the magnetic data was performed for the two compounds by means of Monte Carlo simulations based on the Metropolis algorithm on sets of 10 x 10 x 10 (1) and 1 x 1 x 320 (2) S = 5/2 classical spin centres.