The novel gadolinium(III) complex of formula [Gd(2)(mal)(3)(H(2)O)(6)] (1) (H(2)mal = 1,3-propanedioic acid) has been prepared and characterized by X-ray diffraction analysis. Crystal data for 1: monoclinic, space group I2/a, a = 11.1064(10) A, b = 12.2524(10) A, c =13.6098(2) A, beta = 92.925(10) degrees, U = 1849.5(3) A(3), Z = 4. Compound 1 is a three-dimensional network made up of malonate-bridged gadolinium(III) ions where the malonate exhibits two bridging modes, eta(5)-bidentate + unidentate and eta(3):eta(3) + bis(unidentate). The gadolinium atom is nine-coordinate with three water molecules and six malonate oxygen atoms from three malonate ligands forming a distorted monocapped square antiprism. The shortest metal-metal separations are 4.2763(3) A [through the oxo-carboxylate bridge] and 6.541(3) A [through the carboxylate in the anti-syn coordination mode]. The value of the angle at the oxo-carboxylate atom is 116.8(2) degrees. Variable-temperature magnetic susceptibility measurements reveal the occurrence of a significant ferromagnetic interaction through the oxo-carboxylate pathway (J = +0.048(1) cm(-1), H = -JS(Gd(1)) x S(Gd(1a))).
Polycrystalline samples of dimeric cadmium tartrate, [(Cd,C4H4O6)2H2O)]3H2O [labeled CdT(I)], were studied using impedance measurements and x-ray powder diffraction. The dependence of the real part of the dielectric constant on temperature showed a sharp peak at about 65 °C, revealing a structural phase transition, while the other broad peak in the temperature range (70<T<85 °C) was due to the loss of water molecules. The x-ray powder diffraction patterns at three temperatures (25, 60, and 70 °C) are consistent with three nonequivalent space groups. According to these results, it seems that this compound undergoes two successive phase transitions: P212121→P21→Pnmn, suggesting an intermediate ferroelectric behavior, labeled CdT(II) between a paraelectric CdT(I) and an anhydrous phase, labeled CdT(III).
2); H 2 mal ~malonic acid] have been synthesised and characterized by X-ray diffraction. Their structure consists of corrugated layers of trans-diaquabismalonatemetalate(II) and trans-diaquametal(II) units bridged by carboxylate-malonate groups in the anti-syn conformation. Two crystallographycally independent metal atoms occur in 1 and 2. The malonate anion acts simultaneously as a bidentate and bis-monodentate ligand. Variabletemperature (1.9-295 K) magnetic susceptibility measurements indicate the occurrence of weak antiferro-(1) and ferromagnetic (2) interactions between the cobalt(II) (1) and nickel(II) ions (2) through the anti-syn caboxylate-malonate bridge. A brief discussion on the structural diversity and crystal engineering possibilities of the malonate complexes with divalent first-row transition metal ions other than copper(II) is carried out.
Slow diffusion of aqueous solutions of europium() chloride into gel of sodium metasilicate containing malonic acid (H 2 mal) yields single crystals of the three-dimensional compound of formula [Eu 2 (mal) 3 (H 2 O) 6 ] whose structure was determined by X-ray diffraction methods at 293 and 173 K. It crystallizes in the monoclinic system but the spatial group changes from I2/a in the high temperature range (293 ≥ T ≥ 236 K) to Ia in the low temperature range (T < 236 K). In both cases, nine oxygen atoms forming a distorted monocapped square antiprism surround the Eu 3ϩ ions. The structure at 293 K consists of a three-dimensional arrangement of triaquaeuropium() units bridged by malonate groups which result from cross-linking of the single chains running parallel to the c axis and the double zigzag chains which grow in the ab plane. At low temperature the structure of the compound can be visualised as chains of europium() ions linked through two of the three crystallographically independent malonate ligands, whose chains run parallel to the b axis and a second family of chains (along the c axis) through the third independent malonate ligand forming a three-dimensional network. In both the crystal structure is stabilised through extensive hydrogen bonding involving carboxylate and water molecules. Studies of the magnetic behaviour, spectroscopic, thermogravimetric and calorimetric characteristics of [Eu 2 (mal) 3 (H 2 O) 6 ] are reported. Laser-excited site selective spectroscopy shows a unique crystal-field site for Eu III ions in the crystal at room temperature and down to 236 K. However, below this temperature, two different sites are clearly identified, in agreement with a change in the crystal structure.
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