Nowadays the laboratory synthesis of an artificial oxygen-evolving complex (OEC) has been the objective of many synthetic chemists. Particular attention has been given to mixed manganese-calcium compounds aimed to shed light on the tetranuclear arrangement of the manganese centers in the oxygen-evolving complex (OEC) of photosystem II [1, 2].   The employment of 2-pyridinemethanol (PM) for the synthesis of hetero-nuclear Mn/Ca complexes, has afforded a range of coordination compounds including cuboid-like Mn2Ca2 core. Two of them: [Mn2Ca2(PM)6(CHCl2COO)2(NO3)2(H2O)2] (a) and [Mn2Ca2(PM)6(CH3CN)2(H2O)4](ClO4)4 (b) are built up from molecular and cationic tetranuclear units, respectively. The structure of compound {[MnCa(PM)3(3ClPhCOO)(H2O)]ClO4}n (c) is characterized as a cationic coordination polymer, where the Mn2Ca2 units are linked to each other via the calcium ions with two carboxylic acid moieties (Fig.1). The calcium ion is seven coordinated (distorted pentagonal bipyramid) in a and b whereas 8coordinated in c. For all complexes, each manganese (III) ion has Jahn-Teller-like distorted octahedral environment.   Magnetic measurements established that (b) exhibits an unique Mn(III) valence state. Manganese ions in (b) are coupled ferromagnetically forming a dimer at low temperature with a S=4 ground state. Ac magnetization in addition shows the slow relaxation characteristics of a Single Molecule Magnet below 4K with two relaxation processes