Three new gadolinium(III) complexes of formula [Gd4(bta) 3(H2O)16]n·12nH2O (1), [Gd4(bta)3(H2O)12] n·18nH2O (2) and [Gd2(H 2bta)(bta)(H2O)2]n·4nH 2O (3) (H4bta = 1,2,4,5-benzenetetracarboxylic acid) have been synthesized and their structures determined by X-ray diffraction. 1 and 3 are three-dimensional compounds whereas 2 exhibits a two-dimensional structure. The ability of the bta4- to adopt different coordination modes accounts for these high dimensionalities although it precludes a rational structural design. The structures of 1-3 have in common the double oxo-carboxylate bridge between gadolinium(III) ions (μ-O: κ2O,O′) either as a discrete units (1 and 2) or as a chain (3) and one (3) or two (2) syn-syn carboxylate bridges that reinforce this bridging pathway in 2 and 3. The values of the gadolinium-gadolinium separation through the double μ-O:κ2O,O′ skeleton are 4.1801(4) (1), 3.9345(7) (2) and 3.93279(13) Å (3) and those of the angle at the oxo-carboxylate bridge (θ) are 113.29(10) (1), 106.65 (2) and 104.42(6) and 108.22(6)° (3). The magnetic properties of 1 and 3 have been investigated in the temperature range 1.9-300 K and they show the occurrence of very weak ferro- (1) and weak antiferromagnetic (3) interactions [J = +0.00120(4) (1) and -0.0149(1) cm-1 (3), the Hamiltonians being defined as H = -JS1. S2 and H = -JΣ i=1 Si. Si+1, respectively]. The magneto-structural data of 1 and 3 show that the nature of the magnetic coupling between two gadolinium(III) ions is governed by the geometrical parameters at the μ-O:κ2O,O′ digadolinium(III) core. Although a quantitative magneto-structural correlation for this family cannot be established because the small number of reported examples nowadays, the present data do not follow the semi-empirical law proposed by Baggio et al.

Funding for this work is provided by the Ministerio de Economía y Competitividad through Projects MAT2010-16981, MAT2011-27233-C02-02, DPI2010-21103-C04-03, CTQ2010-15364 and “Factoría de Cristalización” (Consolider-Ingenio2010, CSD2006-00015), by the Generalitat Valenciana through Project ISIC/2012/002 and by the ACIISI (Gobierno de Canarias) through Project SolSub200801000389. J. P. also thanks the Universidad de La Laguna as part of the Campus de Excellence Project ‘CEI Canarias: Campus Atlántico Tricontinental’ for a research contract.

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