This study describes the strain geometry, crystal‐plastic deformational features, isotopic age of metamorphism, and calculated seismic properties of two medium‐temperature eclogite types from the Malpica‐Tui Allochthonous Complex of Variscan NW Iberia. The eclogite types are eclogites with coronitic garnets and eclogites with a planolinear fabric. Both of them were buried, deformed and recrystallized under maximum pressure and temperature of 2.6 GPa and 610–640°C, and subsequently exhumed in a late Devonian subduction channel. The metamorphic peak of the subduction‐exhumation cycle occurred ~375 Ma ago. Omphacite petrofabric ties eclogites with coronitic garnet to noncoaxial constrictional strain and eclogites with planolinear fabrics to noncoaxial flattening strain and stretching along the lineation. We also used omphacite crystallographic preferred orientations to calculate and constrain the seismic properties of the eclogites. The slight variations in petrophysical properties observed are interpreted to result from variations in the strain regime recorded by pristine eclogites, or from variations in the modal proportions of the constituent high‐pressure minerals. We foresee that eclogite in subduction metamorphic complexes might be either seismically undetectable or detected as planar features with high impedance contrasts relative to their host rocks.

Site insights: The title compound has been synthesized by mild hydrothermal conditions. The iron(II) and iron(III) cations are trapped in two different crystallographic positions, whereas the phosphite and hydrogenphosphate–phosphate oxoanions are disordered in two phosphorus sites (see structure). The compound has antiferromagnetic interactions and the nature of the iron centers is investigated by Mössbauer spectroscopy.

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A new iron(III) phosphite templated by ethylenediamine has been synthesized using solvothermal conditions under autogenous pressure. The (C2N2H10)[Fe(HPO3)F3] compound has been characterized by single-crystal X-ray diffraction data and spectroscopic and magnetic techniques. The crystal structure is formed by chains extended along the c axis and surrounded by ethylenediammonium cations. A study by diffuse-reflectance spectroscopy has been performed, and the calculated Dq, B, and C parameters for the Fe(III) cations are 1030, 720, and 3080 cm(-1), respectively. The Mössbauer spectrum at room temperature is characteristic of Fe(III) ions. The electron spin resonance (ESR) spectra carried out at different temperatures show isotropic signals with a g value of 2.00(1). The thermal evolution of the intensity of the ESR signals indicates the existence of antiferromagnetic interactions for the Fe(III) phase. The magnetic susceptibility data of the Cr(III) and V(III) compounds show antiferromagnetic couplings. The J-exchange parameters of the Fe(III) and Cr(III) compounds have been calculated by using a model for a triangular spin ladder chain. The values are J1 = -1.63(1) K and J2 = -0.87(2) K with g = 2.02 for the Fe(III) phase and J(1) = -0.56(2) K and J2 = -0.40(2) K with g = 1.99 for the Cr(III) compound. In the case of the V(III) phase, the fit has been performed considering a linear chain with the magnetic parameters D = 2.5 cm(-1) and J = -1.15(1) K.