Two new compounds K-3[Cu-3(Hmesox)(3)(H2O)]center dot 4H(2)O (1) and [(PPh4)(2)[CoCu3(Hmesox)(3)Cl]} (2) [H(4)mesox = mesoxalic acid (2-dihydroxymalonic acid) and PPh4+ = tetraphenylphosphonium cation] have been prepared and magneto-structurally characterized. Compound 1 contains the [Cu-3(Hmesox)(3)](3-) entity which can be considered as a new precursor for molecular magnetism. In 1 the triangular arrangement of three copper(II) ions bridged by alkoxo groups are further connected to a symmetry-related tricopper(II) unit through a double oxo(carboxylate) bridge. The resulting hexacopper(II) entities are joined further through anti-syn carboxylate groups into an anionic threedimensional network of formula [Cu-3(Hmesox)(3)(H2O)(n)(3n-) whose charge is neutralized by univalent potassium cations. The strong decrease of the chi M T product [per three copper(II) ions] in the high temperature range with the occurrence of a plateau for a spin doublet at T < 65 K is as expected for the coexistence of two antiferromagnetic interactions within the quastisosceles tricopper(II),core of 1 [J = -194(1) cm(-1) and j = -3(4) cm(-1), the Hamiltonian being defined as H = -J(<(S)over cap>(1)center dot(S) over cap (2)center dot(S) over cap (3) - j((S) over cap (1)center dot(S) over cap (2))]. Compound 2 exhibits a chiral three-dimensional structure which is made up of an anionic [(CoCu3II)-Cu-II(mu(3)-Cl)(Hmesox)(3)(2n-) framework with a (10,3)-a topology whose cavities are filled by PPh4+ cations. The [Cu-3(II)(mu(3)-Cl)(Hmesox)(3)](3-) tricopper(II) unit in 2 acts as a tris-bidentate ligand through the Hmesox groups toward three cobalt(II) ions, these latter ones being tris-chelated. Alternating current (ac) and direct current (dc) magnetic susceptibility measurements of 2 show a ferrimagnetic behavior with a magnetic ordering at T-c = 18.5 K and a coercive field H-c = 5000 G. As shown by the magneto-structural study of 2, the use as a ligand of 1 versus metal ions other than cobalt(II) or preformed complexes whose coordination sphere is partially blocked represents a new and rational preparative route toward multifunctional heterometallic compounds.