The synthesis and full characterization of [(tmc)MnCl].X (where tine is 1,4,8,11-tetramethyl-1,4,8,1 1-tetraazacyclotetradecane and X is BPh4- or BF4-) are reported. The complex is of type I geometry. The manganese ion is pentacoordinated by the four tertiary nitrogen atoms of the macrocycle and one axial chloride. Variable-temperature magnetic susceptibility da ta indicate that the oxidation state of the manganese ion is +II with S = 5/2. The EPR spectrum exhibits unusual signals, with the main derivative line at g = 3.7 and transitions at more than 900 mT. The cyclic voltammogram of this derivative consists of two reversible systems at +1.14 and +1.36 V vs SCE related by a chemical equilibrium attributed to an isomerization process.