Graphical Abstract: Mixed-valent tetranuclear MnIIMnIII3 complex with 1,3-dimino-2-hydroxypropane-N,N’-N”-N”’-tetracetic acid, Ca2[Mn4{µ-OHO}(dhpta)2(CH3COO)2], where considerable antiferromagnetic interactions are operating, was synthesized and characterized by elemental analysis and IR and UV-vis spectroscopies, temperature dependence of magnetic susceptibilities (4.5—300K), and single-crystal X-ray crystallography.