The reaction of Mn(HCOO)(2)·2H(2)O, (t)BuSaoH(2) (3,5-di-tert-butyl-salicylaldoxime) and sodium azide in isopropanol leads to [NaMn(3)((t)BuSao)(6)] (1). Its structure can be described as a linear trinuclear cluster bridged by oximato ligands. Magnetic investigation revealed that the ferromagnetic coupling interaction is dominant in 1 leading to a ground-state spin S(T) = 5. 1 shows single-molecule magnet behaviour under zero or 1 kOe dc field with energy barrier U(eff) ~ 10 K.