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 OEC [1]. The discovery of a rational synthetic route to accurate structural/electronic analogues of the OEC will be an important scientific breakthrough, hopefully leading to a deeper understanding of the PSII function. As a part of our systematic study here we describe results of synthesis and investigation of two heterometallic coordination compounds with general formula {[Mn2Ca2(hmp)6(L)2(H2O)2](ClO4)2}n, where L = 3-Cl-benzoic (1) or benzoic (2) acids. In efforts to construct them our attention focussed on using pre-organised [Mn3O(L)6Py2(H2O)] complexes [2] with the intention of forming clusters with Ca(ClO4)2 and 2-(hydroxymethyl)pyridine (hmp). Cluster 1 represents a polymer that crystallizes in the monoclinic space group P-1.figureStructure of {[Mn2Ca2(hmp)6(3-ClPh)2(H2O)2](ClO4)2}n (1). Methyl groups are omitted for clarity. The manganese and calcium ions of the [Mn2IICa2]8+ core are bridged by six moieties of 2-(hydroxymethyl)pyridine and two acid moieties. The coordination of each Ca atom is completed by one water molecule. The Ca and Mn atoms are seven and six coordinate, respectively. The distance Mn….Mn is 3,2967 Å but Mn….Ca – 3,403 Å. Complexes were characterised by different physical-chemical methods: IR, cyclic voltammetry, UV-visible spectroscopy.