Solvent dependent formation of Cu (II) complexes based on isonicotinamide ligand

Five solvent-dependent Cu(II) compounds have been synthesized with [Cu(μ-OAc)(μ-Pip)(MeOH)]2 (OAc = acetate; Pip = 1,3-benzodioxolecarboxylate) and isonicotinamide (Isn) as an auxiliary ligand in different solvents. In all the compounds, Pip units are displaced resulting in dimeric [Cu(μ-OAc)(OAc)(Isn)2(solvent)]2 (solvent = MeOH (2a), dmf and H2O (3) or H2O and HPip (4a)), paddle-wheel [Cu(μ-OAc)2(Isn)]2·2dmso (5) or monomeric compounds [Cu(OAc)2(HOAc)(Isn)2]·HOAc (6). All of them have been characterized by analytical and ATR-FTIR techniques and their X-ray crystal structures solved. The OAc anions construct different arrays and exhibit different coordination modes depending on the solvent used. The supramolecular expansion is constantly determined by the amide-amide pattern and the role of the occluded solvent molecules. This tendency is confirmed by Hirshfeld Surface analysis. Finally, the thermal stability of compound 4a has been analyzed

Isonicotinamide-Based Compounds: From Cocrystal to Polymer

The reaction between [Cu(μ-OAc)(μ-Pip)(MeOH)]2 (1) (OAc = acetate; Pip = 1,3-benzodioxole-5-carboxylate) and isonicotinamide (Isn) in MeOH as solvent yielded two mixture pairs of three compounds: {(HPip)2(Isn) (2), [Cu(Pip)2(Isn)2] (3)} and {(3), {[Cu3(Pip)2(OAc)2(μ-Isn)2(Isn)2(μ-OCH3)2(MeOH)2]·2MeOH}n (4)}. Modifying the reaction conditions (t, T, molar ratio), 2 and 3 have been successfully isolated, whereas 3 and 4 had to be mechanically separated. The recrystallization of 3 in pentanol yielded single crystals of compound [Cu(Pip)2(Isn)2]·C5H11OH (3a). The X-ray crystal structure of 2, 3a, and 4 has been elucidated showing a cocrystal, a monomer, and an unusual coordination polymer, respectively. The Pip ligand exhibited a chelate (3a) or a monodentate (4) coordination mode, but the Isonicotinamide (Isn) ligand is the one that promoted the arrangement of different structures and also mainly directs the formation of the 2D and 3D supramolecular assemblies. All the structures have been analyzed by Hirshfeld surface. In addition, the energy frameworks and lattice energy values of 2 and 3a have been calculated

Steric and Electronic Effects on the Structure and Photophysical Properties of Hg(II) Complexes

Since many factors influence the coordination around a metal center, steric and electronic effects of the ligands mainly determine the connectivity and, thus, the final arrangement. This is emphasized on Hg(II) centers, which have a zero point stabilization energy and, thus, a flexible coordination environment. Therefore, the unrestricted Hg(II) geometry facilitates the predominance of the ligands during the structural inception. Herein, we synthesized and characterized a series of six Hg(II) complexes with general formula (Hg(Pip)2(dPy)) (Pip = piperonylate, dPy = 3- phenylpyridine (3-phpy) (1), 4-phenylpyridine (4-phpy) (2), 2,2′- bipyridine (2,2′-bipy) (3), 1,10-phenanthroline (1,10-phen) (4), 2,2′:6′,2′-terpyridine (terpy) (5), or di(2-picolyl)amine (dpa) (6)). The elucidation of their crystal structures revealed the arrangement of three monomers (3, 5, and 6), one dimer (4), and two coordination polymers (1 and 2) depending on the steric requirements of the dPy and predominance of the ligands. Besides, the study of their photophysical properties in solution supported by TD-DFT calculations enabled us to understand their electronic effects and the influence of the structural arrangement on them

Diverse Structures and Dimensionalities in Zn(II), Cd(II), and Hg(II) Metal Complexes with Piperonylic Acid

Reaction of M(MeCO2)2 (M = Zn(II), Cd(II), and Hg(II)) with 1,3-benzodioxole-5-carboxylic acid (HPip) in methanol (MeOH) yields four piperonylate compounds, one of Zn(II) ([Zn(Pip)2(H2O)2] (1c)), two of Cd(II) ([Cd(μ-Pip)2(H2O)]n (2) and [Cd3(μ-Pip)6(MeOH)2]n (3)), and one of Hg(II) ([Hg(μ-Pip)2]n (4)). The obtention of compounds 1c and 4 was independent of the M/L ratio. These four compounds were characterized by analytical and spectroscopic techniques. In addition, the thermal stability of 1c, 2, and 4 has been studied, and the structure of all the complexes has been determined by the single crystal X-ray diffraction method. The Zn(II) compound displayed a monomeric structure, while Cd(II) and Hg(II) complexes exhibited three polymeric arrays. The Zn(II) (1c) and Hg(II) (4) centers are four- and eight-coordinated in a tetrahedral or squareantiprism geometry, respectively. Furthermore, the Cd(II) ions are either six- (2) or six- and seven- (3) coordinated in a octahedral or both octahedral and pentagonal bipyramid geometries, respectively. In these compounds, the Pip ligand presents different coordination modes: μ1-η1 (1c); μ2-η1:η1 and μ2-η2:η1 (2); μ2-η1:η1, μ2-η2:η1 and μ3-η2:η1:η1 (3); μ1-η2 and μ2-η2:η1 (4). The extended structures were also analyzed. Their photoluminescence properties have been examined, and the quantum yields have been calculated

Pyridine-driven assembly of Zn(II) and Cd(II) complexes with 2-furoic acid. The role of water in a structural transformation

Understanding the factors governing the self-assembly of organic ligands with metal ions is essential to engineering target molecular arrangements with the desired properties. Indeed, small modifications of the synthetic conditions lead to the obtention of different complexes, varying from discrete monomers to coordination polymers (CPs). Based on the potential coordinating ability of 2-furoic acid (2-FA), we prepared five Zn(II) and Cd(II) complexes to study the behavior of the furane O atom and the competitiveness of the M-O bond formation in methanol (MeOH). Reactions between M(OAc)(2 center dot)2H(2)O (M = Zn(II), Cd(II)), 2-FA, and two p-substituted pyridine ligands (isonicotinamide (Isn) and 4-acetylpyridine (4-Acpy)) in MeOH yielded the two dimers [Zn(mu-2-FA)(2-FA)(Isn)(2)](2) (1) and [Cd(mu-2-FA)(2-FA)(Isn)(2)](2) (2), the dimeric paddle-wheel [Zn(mu-2-FA)(2)(4-Acpy)](2) (3), and the monomer [Cd(2-FA)(2)(4-Acpy)(2)(OH2)] (4). Their crystal structures have been studied, observing diverse coordination numbers between five and seven and diverse coordination modes of the carboxylate groups. Interestingly, the recrystallization of 4 in acetonitrile (ACN) resulted in a dissolution-recrystallization structural transformation (DRST), leading to an intricate coordination polymer (CP) with the formula {[Cd(mu-2-FA)(2-FA)(OH2)(2)](n)[Cd(mu-2-FA)(2-FA)(4-Acpy)(OH2)](n)} (5) exhibiting coordination of the furane O atom. Within this collection of arrangements, 2-FA displayed a great diversity of coordination modes that were combined and interchanged in the DRST process. Their photophysical properties in solution have been analyzed and their quantum yields calculated. Likewise, further insight into the DRST process was obtained from fluorescence measurements. From these results, a pathway for the structural transformation highlighting the crucial role of solvents has been proposed

Synthesis and characterization of three new Cu(II) paddle-wheel compounds with 1,3-benzodioxole-5-carboxylic acid

Three different paddle wheel compounds have been synthesized, each one via a different synthetic pathway. The first method is the reaction of Cu(MeCO2)2 H2O with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) in a MeOH solution, yielding [Cu(m-Pip)2(MeOH)]2 (1). The second method is the transformation of the heteroleptic core paddle-wheel compound [Cu(m-MeCO2)(m-Pip)(MeOH)]2 into the homoleptic core paddle-wheel [Cu(m-Pip)2(DMSO)]2 2DMSO (2). Lastly, the third method is the substitution of the solvent molecule (DMF) present in the molecular array [Cu(m-Pip)2(DMF)]2 by 2-benzylpyridine (2-Bzpy) ligand, resulting in [Cu(m-Pip)2(2-Bzpy)]2 2.5MeOH H2O (3a). All compounds are characterized via EA, PXRD, ATR-FTIR, Far-IR and UV-Vis spectroscopy. For all three compounds, the X-ray crystal structure has been determined and their extended structures are discussed. Finally, TG/DTA measurements have been recorded

Tuning Photophysical Properties by p-Functional Groups in Zn(II) and Cd(II) Complexes with Piperonylic Acid

Aggregation between discrete molecules is an essential factor to prevent aggregation-caused quenching (ACQ). Indeed, functional groups capable of generating strong hydrogen bonds are likely to assemble and cause ACQ and photoinduced electron transfer processes. Thus, it is possible to compare absorption and emission properties by incorporating two ligands with a different bias toward intra- and intermolecular interactions that can induce a specific structural arrangement. In parallel, the π electron-donor or electron-withdrawing character of the functional groups could modify the Highest Ocuppied Molecular Orbital (HOMO)-Lowest Unocuppied Molecular Orbital (LUMO) energy gap. Reactions of M(OAc)2·2H2O (M = Zn(II) and Cd(II); OAc = acetate) with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) and 4-acetylpyridine (4-Acpy) or isonicotinamide (Isn) resulted in the formation of four complexes. The elucidation of their crystal structure showed the formation of one paddle-wheel [Zn(μ-Pip)2(4-Acpy)]2 (1); a mixture of one dimer and two monomers [Zn(µ-Pip)(Pip)(Isn)2]2·2[Zn(Pip)2(HPip)(Isn)]·2MeOH (2); and two dimers [Cd(μ-Pip)(Pip)(4-Acpy)2]2 (3) and [Cd(μ-Pip)(Pip)(Isn)2]2·MeOH (4). They exhibit bridged (1, µ2-η1:η1), bridged, chelated and monodentated (2, µ2-η1:η1, µ1-η1:η1 and µ1-η1), or simultaneously bridged and chelated (3 and 4, µ2-η2:η1) coordination modes. Zn(II) centers accommodate coordination numbers 5 and 6, whereas Cd(II) presents coordination number 7. We have related their photophysical properties and fluorescence quantum yields with their geometric variations and interactions supported by TD-DFT calculations

Reactivity of homoleptic and heteroleptic core paddle wheel Cu(II) compounds

The compound [Cu(μ-Pip)(μ-OAc)(MeOH)]2 (1) (Pip=Piperonylate, OAc=acetate, MeOH=methanol) has been obtained in high percentage yield. Its reactivity with pyridine/pyrazole derivative ligands (pyridine (py), 3-phenylpyridine (3-Phpy) and 4-acetylpyridine (4-Acpy)) and 3,5-dimethylpyrazole (3,5-dmpz) leads to four monomeric compounds: [Cu(Pip)2(dPy)2(H2O)] (dPy=py (2), 3-Phpy (3) and 4-Acpy (4a)) and [Cu(Pip)2(3,5-dmpz)2] (5). Furthermore, the reaction of 1 with HPip in MeOH:DMF solvent under reflux conditions yields the homoleptic core paddle-wheel compound [Cu(μ-Pip)2(DMF)]2·2DMF (6). The reaction between 6 and 2-benzylpyridine (2-Bzpy) yields the paddle-wheel core compound [Cu(Pip)2(2-Bzpy)]2 (7). All compounds have been fully characterized by analytical and spectroscopic techniques and their X-ray crystal structures have been determined. In this set of compounds, the carboxylate ligand (Pip) displays different coordination modes (monodentate (2-4), bidentate chelate (5) and bridged (1, 6 and 7)). Moreover, their extended structures are discussed: the crystal packing indicates hydrogen bond propagation, which defines 1D (2-5) or 2D (6 and 7) supramolecular networks

Kinetic energy bounds for particles confined in spherically-symmetric traps with non-standard dimensions

The kinetic energy of non-relativistic single-particle systems with arbitrary D-dimensional central potentials is found to be bounded from below by means of the orbital hyperangular quantum number, the dimensionality and some radial and logarithmic expectation values of the form langrkrang and langrk (ln r)mrang. Beyond the intrinsic physico-mathematical interest of this problem, we want to contribute to the current development of the theory of independent particles confined in spherically symmetric traps with non-standard dimensions. The latter has been motivated by the recent experimental achievements of the evaporative cooling of dilute (i.e. almost non-interacting) fermions in magnetic traps.We are very grateful for partial support from Junta de Andalucía (under the grants FQM-0207 and FQM-481), Ministerio de Educación y Ciencia (under the project FIS2005-00973), and the European Research Network NeCCA (under the project INTAS-03-51-6637). RGF acknowledges the support of Junta de Andalucía under the program of Retorno de Investigadores a Centros de Investigación Andaluces, and PSM the support of Ministerio de Educación y Ciencia under the program FPU

Cu(II) coordination polymers with 4,4 '-bipyridine. Synthesis and crystal structures

Extensively research has been devoted to the isolation and characterization of Cu(II) coordination polymers. Since many aspects can influence the final crystal structure, the effect of the solvent molecules through intermolecular interactions has been proven to be a determining factor. Herein, we elucidated the structure of two Cu(II) concomitant 1D polymers containing piperonylic acid (HPip) and 4,4 -bipyridine (4,4-bipy), which were simultaneously crystallized and subsequently isolated changing the synthetic conditions. Complex {[Cu(Pip)2(4,4-bipy)]}n (1) exhibits zig-zag polymeric chains while {[Cu(Pip)2(4,4 -bipy)(H2O)]¿ 1/2(4,4-bipy)¿(DMF)}n (2) displays linear polymeric chains stacked by water¿¿¿carboxylate intermolecular interactions, forming voids occupied by alternated guest 4,4-bipy and DMF molecules