Remarkable thermal stability of Eu(4-phosphonobenzoate): structure investigations and luminescence properties

International audienceA new 3D rare-earth hybrid material Eu(p-O(3)PC(6)H(4)COO) has been synthesised by a hydrothermal route from Eu(NO(3))(3) x 5 H(2)O and the rigid precursor, 4-phosphonobenzoic acid. The structure of Eu(p-O(3)PC(6)H(4)COO) has been solved by X-ray diffraction on a powder sample and is described as an inorganic network in which both carboxylic and phosphonic acid groups are linked to Eu ions forming a three-dimensional architecture. Thermal analysis performed on this compound has underlined its remarkable stability up to 510 degrees C and an optical study has been conducted to examine its luminescence properties that have been related to the structure of the material. The structural and luminescence properties have also been compared with the related material Eu phenylphosphonate

Structural Study of Hydrated/Dehydrated Manganese Thiophene-2,5-diphosphonate Metal Organic Frameworks, Mn₂(O₃P–C₄H₂S–PO₃)·2H₂O

Synthesis of thiophene-2,5-diphosphonic acid <b>2</b> is reported, and its use for synthesis of the original pristine materials Mn₂(O₃P–C₄H₂S–PO₃)·2H₂O <b>3</b> is reported. The structure of material <b>3</b> has been fully resolved from single-crystal X-ray diffraction. Mn₂(O₃P–C₄H₂S–PO₃)·2H₂O <b>3</b> crystallizes in a monoclinic cell (space group <i>P</i>2) with the following parameters: <i>a</i> = 11.60(1) Å, <i>b</i> = 4.943(5) Å, <i>c</i> = 19.614(13) Å, β = 107.22°. A noticeable feature of the structure of compound <b>3</b> is the orientation of the thiophene heterocycles that adopt two different orientations in two successive layers (along <i>c</i>). Thermal analysis of compound <b>3</b> indicates that the water molecules are easily removed from 160 to 230 °C while the dehydrated structure is stable up to 500 °C. The dehydrated compound obtained from <b>3</b> can be rehydrated to give the polymorphic compound Mn₂(O₃P–C₄H₂S–PO₃)·2H₂O <b>4</b>, which crystallizes in an orthorhombic cell (space group <i>Pnam</i>) with the following parameters: <i>a</i> = 7.5359(3) Å, <i>b</i> = 7.5524(3) Å, <i>c</i> = 18.3050(9) Å. The main difference between the structures of <b>3</b> and <b>4</b> arises from both the orientation of the thiophene rings (herringbone-type organization in <b>4</b>) and the structure of the inorganic layers. The thiophene-2,5-diphosphonic acid moieties engaged in materials <b>3</b> and <b>4</b> adopt a different orientation likely due to rotation around the P–C bonds and via the dehydrated state <b>5</b>, which is likely more flexible than the hydrated states. Study of the magnetic properties performed on compound <b>3</b> and <b>4</b> and on the dehydrated compounds Mn₂(O₃P–C₄H₂S–PO₃) <b>5</b> complemented by the structural study has permitted us to characterize the antiferromagnetic ground state of sample <b>3</b>, a weak ferromagnetic component in sample <b>4</b>, and complete paramagnetic behavior in sample <b>5</b>