Returns to Schooling in Spain. How Reliable Are IV Estimates?

This paper studies the Ordinary Least-Squared (OLS) and Instrumental Variables (IV) estimates of the returns to schooling for male workers in Spain. OLS estimates are often biased due to the endogeneity of schooling, measurement errors or omitted variables. Proper IV estimates correct this bias. The reliability of family background, natural experiments (based on changes in the education system and season of birth) and the availability of a college in the province is checked using Spanish data. The results suggest that background and college availability are valid instruments and that the IV estimates of the returns to schooling are higher than OLS estimates. These results are in line with the majority of previous results in the literature.Returns to schooling, Instrumental Variables, Spanish schooling system

Cerca bibliogràfica sobre complicacions de l'ortoqueratologia, comparació amb altres modalitats d'ús de lents de contacte

Actualment notem un gran increment de miopia arreu del món, per tant s’han posat en pràctica tractaments per resoldre aquesta pandèmia. Un d’ells és l’ortoqueratologia, aquesta tècnica permet la compensació total o parcial de l’error refractiu durant el dia, fent ús d’una lent de contacte rígida durant la nit, adaptada amb la finalitat de moldejar la còrnia i prescindir de compensació durant el dia. En aquest treball s’explica en que tracta l’ortoqueratologia i l’evolució, així com les complicacions més comunes de les lents de contacte en general. Es fa una recerca bibliogràfica d’estudis realitzats en grups de pacients portadors de lents de contacte de diferents tipus i diferents reemplaçaments. A partir d’això s’obté unes conclusions de la prevalença de complicacions en totes elles, amb la finalitat de veure quines són les complicacions més comunes de l’ortoqueratologia i amb major incidència respecte a les altres modalitats de lents de contacte

Influence of a series of pyridine ligands on the structure and photophysical properties of Cd(II) complexes

Among the group 12 metal ions, the Cd(II) ion presents an ionic radius comparable to that of Hg(II), while its electronegativity resembles that of Zn(II). Thus, these characteristics make it a suitable candidate for the synthesis of fluorescent coordination complexes given that it tends to maximize the chelation enhanced effect (CHEF), while its electronegativity helps to prevent the quenching of fluorescence generated by the heavy atom effect. Accordingly, herein, we performed a systematic study using Cd(II) compounds bearing α-acetamidocinnamic acid (HACA) and different N-, N^N- and N^N^N-pyridine ligands (dPy), namely pyridine (py) (1), 3-phenylpyridine (3-phpy) (2), 2,2′-bipyridine (2,2′-bipy) (3), 1,10-phenantroline (1,10-phen) (4) and 2,2′:6′,2′′-terpyridine (terpy) (5). The elucidation of their crystal structures revealed the formation of one coordination polymer (1), one dimer (3) and three monomers (2, 4, and 5). All the synthesized compounds were characterized via analytical and spectroscopic techniques, and their molecular and supramolecular structures were discussed. The photophysical properties of 1–5 in MeOH were studied and their quantum yields (Φ) were calculated, revealing an enhancement in the Φ value of the complexes generated by the CHEF of dPy

Structural influence of the length and functionality of NN-donor spacers in Cd(II) ladder-type coordination polymers

The understanding of the effect generated by small differences of the organic ligands on the molecular and supramolecular arrangement of coordination polymers (CPs) is a key factor to control their properties. Therefore, the study of structurally related ligands differing in some factors inter alia functional group orientation, length, or functionality is a crucial task for crystal engineers. In this contribution, the reactions between Cd(OAc)2·2H2O, α-acetamidocinnamic acid (HACA) and different N,N-donor spacers with increasing length (pyrazine, pyz; 4,4’-bipyridine, 4,4’-bipy; 1,2-bis(4-pyridyl)ethylene, 1,2-bpe), as well as additional functionalities (4,4’-azopyridine, 4,4’-azpy) have been successfully performed. Their crystal structures have been elucidated revealing a family of ladder-type 1D CPs showing molecular arrays with single pillars for {[Cd2(μ-ACA)2(ACA)2(pyz)(H2O)2]·2EtOH}n (1), and double pillars for [Cd2(μ-ACA)2(ACA)2(4,4’-bipy)2]n (2), [Cd2(μ-ACA)2(ACA)2(1,2-bpe)2]n (3) and {[Cd2(μ-ACA)2(ACA)2(4,4’-azpy)2]·4,4’-azpy·9H2O}n (4). Remarkably, the effect of the addition of the azo group in 4 compared with 2 and 3 has led to a CP with the same molecular arrangement but different crystal packing, allowing the introduction of one non-coordinated 4,4’-azpy and nine water molecules. Finally, their solid-state UV-Vis and photoluminescence have been measured observing their blue-emitting properties

Amide-Driven Secondary Building Unit Structural Transformations between Zn(II) Coordination Polymers

The behavior of coordination polymers (CPs) against external stimuli has witnessed remarkable attention, especially when the resulting CPs present reversible molecular arrays. Accordingly, CPs with these characteristics can lead to differences in their properties owing to these structural differences, being promising for their use as potential molecular switches with diverse applications. Herein, we have synthesized four Zn(II) CPs bearing α-acetamidocinnamic acid (HACA) and 4,4′-bipyridine (4,4′-bipy). The reaction between Zn(OAc)2·2H2O, HACA, and 4,4′-bipy yields {[Zn(ACA)2(4,4′-bipy)]·EtOH}n (1), which was used for the formation of three CPs through dissolution–recrystallization structural transformations (DRSTs): {[Zn(ACA)2(4,4′-bipy)]·2MeOH}n (2), {[Zn2(μ-ACA)2(ACA)2(4,4′-bipy)]·2H2O}n (3), and {[Zn3(μ-ACA)6(4,4′-bipy)]·0.75CHCl3}n (4). The study of the four crystal structures revealed that their secondary building units (SBUs) comprise monomeric, dimeric, and trimeric arrangements linked by 4,4′-bipy ligands. The fundamental role of the utilized solvent and/or temperature, as well as their effect on the orientation of the amide moieties driving the formation of the different SBUs is discussed. Furthermore, the reversibility and interconversion between the four CPs have been assayed. Finally, their solid-state photoluminescence has evinced that the effect of the amide moieties not only predetermine a different SBU but also lead to a different emission in 4 compared with 1–3

Synthesis and characterization of Pd(II), Pt(II), Cu(I), Ag(I) and Cu(II) complexes with N,O-hybrid pyrazole ligand

The coordination behavior of N,O-hybrid pyrazole-based metal-organic frameworks are described. 2- (3,5-Pyridyl-1H-pyrazol-1-yl)ethanol (L) and its Pd(II), Pt(II), Cu(I), Ag(I) and Cu(II) complexes with different anions have been synthesized and characterized by elemental analysis, conductivity, mass spectrometry, IR, 1H, 13C{1H} and 195Pt{1H} NMR spectroscopies. Complex 1 was also characterized by single crystal X-ray diffraction. For complex 7 has also been possible to perform the UV-Vis and magnetic susceptibility measurements. All complexes are monomers, except the complexes obtained by reaction of the ligand (L) with M(MeCO2)2 (M = Pd(II), Pt(II)) or CuBr2, which are dimers

Virtual assessment achieved two binary cocrystals based on a liquid and a solid pyridine derivative with modulated thermal stabilities

The rational design of cocrystals triggered by the control of recurrent H-bonded patterns referred to as supramolecular synthons enabled the correlation between their structure and properties, which has been a topic of interest owing to the possibility to modulate them depending on the selected components. Accordingly, melting point has been one of the most studied properties, providing materials with enhanced thermal stability for specific applications. Within this frame, in this work we have selected a liquid and a solid pyridine derivative (dPy), namely 4-acetylpyridine (4-Acpy) and 2-hydroxypyridine (2-OHpy) to combine with carboxylic acids to obtain a pair of cocrystals. An initial virtual screening of some carboxylic acids based on the positive and negative critical points of the molecular electrostatic potential (MEP) surfaces was performed to evaluate the feasibility of cocrystal formation. This enabled us to select 1,3-benzodioxole-5-carboxylic acid (piperonylic acid, HPip) to combine with 4-Acpy and a-acetamidocinnamic acid (HACA) with 2-OHpy. Then, we have obtained the corresponding cocrystal experimentally by means of liquid-assisted grinding (LAG), and their crystal structures were elucidated, revealing the formation of (HPip)(4-Acpy) (1) and (HACA)(Pdon) (2) (Pdon = 2-pyridone), observing the tautomerization of 2-OHpy to Pdon. Both cocrystals were characterized by analytical and spectroscopic techniques. In addition, a Cambridge Structural Database (CSD) survey of 4-Acpy and Pdon in cocrystal systems was performed and the observed preferences regarding their preferable synthons and dimensionalities were shown. Finally, their melting points have been determined, and the resulting values have been correlated with the crystal packing of the compounds, supported by Hirshfeld surface analysis and energy frameworks

Synthesis of a Heterometallic [Zn2Ca] Pinwheel Array Stabilized by Amide-Amide Synthons

The rational design of heterometallic compounds bearing s-block metal ions have been a difficult task for chemists owing to their lack of preferential geometries. However, some strategies, such as the design of coordinating pockets with different sizes and/or donor atoms, have offered great results. In this work, this strategy has been tested using Ca(II) as an s-block metal ion and a compound previously obtained by our group with the formula [Zn3(μ-ACA)6(4-phpy)2], which contains tetrahedral N,O- and octahedral O-coordinating pockets as a model structure. From this work, the corresponding heterometallic compound with the formula [Zn2Ca(μ-ACA)6(4-phpy)2]·EtOH (1) has been successfully synthesized, and fully characterized, and its crystal structure has been elucidated. Furthermore, we have compiled all the crystal structures containing [Zn2M] pinwheel secondary building units (SBUs), where M stands for an s-block metal ion, and the observed tendencies, as well as the promising applications as template SBUs for the preparation of 1D–3D coordination polymers, have been discussed. Finally, solid-state UV-Vis and photoluminescence have been recorded and compared with the homometallic [Zn3(μ-ACA)6(4-phpy)2] compound

Construction of Zn(II) Linear Trinuclear Secondary Building Units from A Coordination Polymer Based on α-Acetamidocinnamic Acid and 4-Phenylpyridine

The synthesis and characterization of one coordination polymer and two trinuclear complexes are presented. The coordination polymer [Zn2( -O,O'-ACA)2(ACA)2(4-Phpy)2]n (1) has been obtained by the reaction between Zn(OAc)2 2H2O, -acetamidocinnamic acid (HACA), and 4-phenylpyridine (4-Phpy) using EtOH as solvent. Its recrystallization in CH3CN or EtOH yields two trinuclear complexes, both having pinwheel arrays with formulas [Zn3( -ACA)6(4-Phpy)2] 4CH3CN (2 4CH3CN) and [Zn3( -ACA)6(EtOH)2] 4EtOH (3 4EtOH), respectively. These trinuclear species, unavoidably lose their solvent co-crystallized molecules at RT yielding the complexes [Zn3( -ACA)6(4-Phpy)2] (2) and [Zn3( -ACA)6(EtOH)2] (3). In addition, compound 2 has also been obtained reacting Zn(OAc)2 2H2O, HACA, and 4-Phpy in a 1:2:2 ratio using CH3CN as solvent. Compounds 1-3 have been characterized by analytical and spectroscopic techniques. Furthermore, single crystals suitable for X-ray di raction method for compounds 1, 2 4CH3CN, and 3 4EtOH were obtained and their supramolecular interactions have been studied and discussed, showing 2D supramolecular planes for the trinuclear complexes and a 3D supramolecular network for the coordination polymer. Finally, the supramolecular interactions of 2 4CH3CN and 3 4EtOH have been compared using Hirshfeld surface analysis and electrostatic potential calculations

Cocrystals Based on 4,4'-bipyridine: Influence of Crystal Packing on Melting Point

The reactions of piperonylic acid (HPip) and cinnamic acid (HCinn) with 4,4'-bipyridine (4,4'-bipy) have been assayed using the same synthetic methodology, yielding two binary cocrystals with different acid:4,4'-bipy molar ratios, (HPip)(4,4'-bipy) (1) and (HCinn)2(4,4'-bipy) (2). The melting point (m.p.) of these cocrystals have been measured and a remarkable difference (DT 78 C) between them was observed. Moreover, the two cocrystals have been characterized by powder X-ray diffraction (PXRD), elemental analysis (EA), FTIR-ATR, 1H NMR spectroscopies, and single-crystal X-ray diffraction. The study of their structural packings via Hirshfeld surface analysis and energy frameworks revealed the important contribution of the pi..pi and C-H...pi interactions to the formation of different structural packing motifs, this being the main reason for the difference of m.p. between them. Moreover, it has been observed that 1 and 2 presented the same packing motifs as the crystal structure of their corresponding carboxylic acids, but 1 and 2 showed lower m.p. than those of the carboxylic acids, which could be related to the lower strength of the acid-pyridine heterosynthons respect to the acid-acid homosynthons in the crystal structures