María Hernández-Molina

This paper investigates the effect of nozzle temperature, from 180 to 260 °C, on properties of polylactic acid (PLA) samples manufactured by fused deposition modeling (FDM) technology. The main objective of this research is to determinate an optimum nozzle temperature relative to tensile, flexural and compressive properties of printed specimens. After manufacturing, the samples exhibit an amorphous structure, without crystallization effects, independently of the fabrication temperature. In order to determine the influence of printing temperature on mechanical properties, uniaxial tensile, three-point flexural and compression strength tests were carried out. The obtained results suggest that a relative low printing temperature could reduce the material flow and decrease the density of the final prototype, with a negative effect on both the quality and the mechanical properties of the pieces. If temperature increases up to 260 °C, an excess of material can be deposited, but with no significant negative effect on mechanical parameters. There is an optimum nozzle temperature interval, depending on the considered piece and test, for which mechanical values can be optimized. Taking into account all tests, a recommended extruder temperature interval may be identified as 220–240 °C. This range encompasses all mechanical parameters, avoiding the highest temperature where an excess of material was observed. For this printing temperature interval, no significant mechanical variations were appreciated, which corresponds to a stable behavior of the manufactured specimens.

Four gadolinium(III) complexes with dicarboxylate ligands of formulas [Gd₂(mal)₃(H₂O)₅]_n·2nH₂O (1), [Gd₂(mal)₃(H₂O)₆]_n (2), [NaGd(mal)(ox)(H₂O)₃]_n (3), and [Gd₂(ox)₃(H₂O)₆]_n·2.5nH₂O (4) (mal = malonate; ox = oxalate) have been prepared, and their magnetic properties have been investigated as a function of the temperature. The structures of 1−3 have been determined by X-ray diffraction methods. The crystal structure of 4 was already known, and it is made of hexagonal layers of Gd atoms that are bridged by bis-bidentate oxalate. Compound 1 is isostructural with the europium(III) malonate complex [Eu₂(mal)₃(H₂O)₅]_n·2nH₂O,¹ whose structure was reported elsewhere. The Gd atoms in 1 define a two-dimensional network where a terminal bidentate and bridging bidentate/bis-monodentate and tris-bidentate coordination modes of malonate occur. Compound 2 has a three-dimensional structure with a structural phase transition at 226 K, which involves a change of the space group from I2/a to Ia. Although its structure at room temperature was already known, that below 226 K was not. Pairs of Gd atoms with a double oxo−carboxylate bridge occur in both phases, and the main differences between both structures deal with the Gd environment and the H-bond pattern. 3 is also a three-dimensional compound, and it was obtained by reacting Gd(III) ions with malonic acid in a silica gel medium. Oxalic acid results as an oxidized product of the malonic acid, and single crystals of the heteroleptic complex were produced. The Gd atoms in 3 are connected through bis-bidentate oxalate and carboxylate−malonate bridges in the anti−anti and anti−syn coordination modes. Compounds 1 and 2 exhibit weak but significant ferromagnetic couplings between the Gd(III) ions through the single (1) and double (2) oxo−carboxylate bridges, whereas antiferromagnetic interactions across the bis-bidentate oxalate account for the overall antiferromagnetic behavior observed in 3 and 4.

The molecular and crystal structures of the title compound are reported. The molecular structure shows an oxalate-linked copper(II) two-dimensional coordination polymer where the knots are occupied by the [Cu(oxalate)₂]_n units and the edges by the [Cu(ethylenediamine)₂]_2n units which grow in the (011) plane. The compound crystallizes in the monoclinic system, space group P2₁/n, with a⊕=⊕15.579(3), b⊕=⊕8.073(2) and c⊕=⊕12.980(3) Å, β⊕=⊕118.67(2)°, Z⊕=⊕4, V⊕=⊕1432.3(6) ų. The crystal structure is formed by a three-dimensional network via an extensive hydrogen-bonding network involving water molecules, nitrogen atoms from the ethylenediamine ligand and oxygen atoms from the perchlorate anions.