Intramolecular ferro- and antiferromagnetic interactions in oxo-carboxylate bridged digadolinium(iii) complexes

Abstract

Two new digadolinium(III) complexes with monocarboxylate ligands, [Gd₂(pac)₆(H₂O)₄] (1) and [Gd₂(tpac)₆(H₂O)₄] (2) (Hpac = pentanoic acid and Htpac = 3-thiopheneacetic acid), have been prepared and their structures determined by X-ray diffraction on single crystals. Their structures consist of neutral and isolated digadolinium(III) units, containing six monocarboxylate ligands and four coordinated water molecules, the bridging skeleton being built by a μO(1):κ²O(1)O(2) framework. This structural pattern has already been observed in the parent acetate-containing compound [Gd₂(ac)₆(H₂O)₄]·4H₂O (3) whose structure and magnetic properties were reported elsewhere (L. Cañadillas-Delgado, O. Fabelo, J. Cano, J. Pasán, F. S. Delgado, M. Julve, F. Lloret and C. Ruiz-Pérez, CrystEngComm, 2009, 11, 2131). Each gadolinium(III) ion in 1 and 2 is nine-coordinated with seven carboxylate-oxygen atoms from four pac (1)/tpac (2) ligands and two water molecules (1 and 2) building a distorted monocapped square antiprism. The values of the intramolecular gadolinium–gadolinium separation are 4.1215(5) (1), 4.1255(6) (2) and 4.1589(3) Å (3) and those of the angle at the oxo-carboxylate bridge (θ) are 113.16(13) (1), 112.5(2) (2) and 115.47(7)° (3). Magnetic susceptibility measurements in the temperature range 1.9–300 K reveal the occurrence of a weak intramolecular antiferromagnetic interaction [J = −0.032(1) (1) and −0.012(1) cm⁻¹ (2), the Hamiltonian being defined as Ĥ = −JŜ_A·Ŝ_B] in contrast with the intramolecular ferromagnetic coupling which occurs in 3 (J = +0.031(1) cm⁻¹). The magneto–structural data of 1–3 show the relevance of the geometrical parameters at the μO(1):κ²O(1)O(2) bridge on the nature of the magnetic coupling between two gadolinium(III) ions.