A new heptadentate N6-O1 ligand, NN,N`,N-tetrakis(2-quinolylmethyl)-2-hydroxy-1,3-propanediamine (Htqhpn), was synthesized and used to generate compounds with linearly ordered Mn '' Mn ''' Mn ''' Mn '' tetranuclear cores. This is the lowest valent tetranuclear manganese complex that exhibits a (mu(2)-O)(2)Mn-2 core in the molecule. The electron paramagnetic resonance and magnetic measurements of these tetranuclear complexes suggest moderately strong antiferromagnetic coupling for the central Mn '''(2) core, with weak coupling between the Mn '' and Mn '' centers.