The compounds [La(H2O)3Cu3(Hmesox)3(H2O)5]·8H2O (1) and [La(H2O)2Cu3(Hmesox)3(H2O)3]·7H2O (2) have been prepared by the reaction of mesoxalic acid with basic copper(II) carbonate and lanthanum nitrate (H4mesox = mesoxalic acid, dihydroxymalonic acid). The compounds have been characterized by single crystal X-ray diffraction, magnetic susceptibility measurements and DFT calculations. The structure of both compounds is built up by [Cu3(Hmesox)3(H2O)5]3− and [Cu3(Hmesox)3(H2O)3]3− trinuclear entities (for 1 and 2, respectively) linked to La(III) ions to yield 2D sheets with the (6,3) topology if the lanthanum atom and the Cu3 centroids are considered as nodes. Due to the diamagnetic character of the La(III) ion the magnetic behaviour of both compounds is related to the copper(II) trinuclear entities, which display antiferromagnetic coupling making one of the S = 1/2 spin states to be the spin ground state. The magnetic coupling constants of the trinuclear units are determined by means of magnetic susceptibility measurements and they exhibit the expected trend showing strong antiferromagnetic couplings for large Cu–O–Cu bridging angles. Additionally, DFT calculations performed on these complexes agree with the experimental values obtained.
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