Crystal structure of dimethylammonium triaquabis(4-hydroxypyridine- 2,6-dicarboxylato)samarium(III) dihydrate, [C2H8N][Sm(H2O)3(C7H3NO5)2] · 2H2O

Abstract

Source of materialThe mixture of Sm(NO 3 ) 3 · 6H 2 O( 0.085 g, 0.2 mmol) and 4-hydroxypyridine-2,6-dicarboxylic acid (H 3 CAM, 0.074 g, 0.4 mmol) was stirred into 15 ml aqueous solution and the pH value was adjusted to approx. 5with 1.0 Mammonia. Then 5mL ethanol solution of N,N-dimethylformamide (DMF, 1.0 mL) was added. The reaction mixture was heated on awater bath for 10 hat 70°C, then filtered. The resulting clear solution was diffused with diethyl ether vapor at room temperature for two weeks, blockshaped colourless crystals insoluble in water were obtained (yield 0.049 g, 36 %). Elemental analysis -found: C, 32.67 %; H, 3.19 %; N, 6.17 %; calculated: C, 32.95 %; H, 3.20 %; N, 6.06 %. IR data are available in the CIF. DiscussionDuring the past two decades, there has been growing interest in lanthanoids and their compounds because of the emergence of novel structure features and functional properties in different application fields [1][2][3]. The current attention is focused on the construction of rear earth metal-organic frameworks (MOFs) with novel topology and on the crystal engineering of molecular architectures organized by coordination bonds and supramolecular contacts (such as hydrogen bonding, p-p stack interactions, etc.) [4,5]. In this work, 4-hydroxypyridine-2,6-dicarboxylic acid (H 3 CAM) was employed as the major ligand because it has a unique configuration, which can potentially provide more coordination features [6,7]. The title crystal structure is composed of one Sm(III) ion, two HCAM 2-ligands, three coordinating water molecules, and two lattice water molecules as well as one dimethylammonium cation (DMA), which is in situ generated through the DMF solvent under the hydrothermal condition [8,9]. Each Sm(III) is ninecoordinated and exhibits atricapped trigonal prismatic environment formed by four oxygen atoms from the two carboxylate groups of HCAM 2-ligands, two nitrogen atoms from two pyridine rings, and three oxygen atoms from water molecules. Each HCAM 2-ligand adopts at ri-dentate coordination mode, employing one nitrogen and two oxygen atoms to chelate Sm(III) ion. The dimethylamine does not participate in the coordination due to its protonation under the acidic condition. This coordination mode can also be observed in the analogous lanthanide complexes [10]. The [Sm(HCAM) 2]unit carries one negative charge, while DMA bears one positive charge, thus maintaining the charge balance. The d(Sm-O) range from 2.416(4) to 2.624(2) Å,and d(Sm-N) range from 2.555(3) to 2.594(5) Å,which are within normal ranges [12]. The dihedral angle between the two pyridyl rings attached to the central Sm ion is 70.20°,and the angle of N1-Sm-N2 is 118.25°.B oth the pyridine ring and the dicarboxylate group of HCAM ligands are almost coplanar, and the atoms in the pyridine deviate from the least square plane defined by the pyridine ring by less than 0. 020 Å.Deviation from the mean plane defined by the pyridine ring are observed for both of carboxylic groups with values ranging from O2 -0.156(7) to O1 +0.153...