Begoña Bazán

Organically templated open-framework phosphites

Here we present a summary of the work carried out in the last few years on the synthesis and characterization of a new type of organically templated inorganic–organic solid based on the (HPO3)2−phosphite oxoanion, with special focus on the magnetostructural properties of those systems containing open d-shell transition metal ions. As a result of the inherent connectivity of the metal-phosphite framework, the magnetic behaviour of the great majority of these materials is characterized by weak antiferromagnetic interactions that become relevant only at low temperature.

Solid-state transformation of the MOF [Ni2(bipy)1.5(PDC)2(H2O)2]·3.5H2O

The combination of non-centrosymmetric ligands and dipyridyl spacers produces a MOF that potentially can be porous with formula [Ni2(bipy)1.5(PDC)2(H2O)2]·3.5H2O (bipy = 4,4′-bipyridine and PDC = pyridine-2,5-dicarboxylate). Dehydration of this compound results in a new MOF in which the formation of additional bonds between the carboxylate groups of PDC and the metal ion has occurred. This solid-state transformation takes place with no significant changes in the coordination sphere of the metal ion, which is unusual for coordination polymers. Both compounds exhibit the same unprecedented topology where the connectivity between nodes is remarkably high.

Thermal stability and crystallochemical analysis for CoII-based coordination polymers with TPP and TPPS porphyrins

Two new CoP–bipy compounds have been synthesised and characterised, where P is TPP for compound 1 (TPP = meso-tetraphenylporphyrin) and TPPS for compound 2 (TPPS = meso-tetraphenylporphine-tetrasulfonic acid tetrasodium salt), and bipy is 4,4′-bipyridine. Compound 1 consists of 1D polymers packed in a network where isolated porphyrin units are immobilized by an extended π-bond system. On the other hand, as we are aware, compound 2 is the first Co–TPPS compound in literature. It also consists of 1D polymers that are formed by the alternation of two distinct metal centres. These unprecedented polymers are packed forming cavities where crystallization molecules of water are located. The robustness of the hydrogen bond system and a topology based on interpenetrated nets are responsible for the high thermal stability of compound 2. Additionally, a crystallochemical study confirmed the existence of a correlation between the degree of ruffled distortion of the porphyrin macrocycle and some selected dihedral angles and distances for CoII porphyrins in literature.

Hydrothermal synthesis, crystal structure, and spectroscopic and magnetic properties of a new organically templated mixed-anion fluoro-arsenate-phosphate iron(III) compound, (C6H14N2)[Fe3(HAsO4)1.33(HPO4)0.67(AsO4)0.84(PO4)0.16F4]0.5(H2O)

Abstract The new organically templated mixed-anion fluoro-arsenate–phosphate iron(III) compound, with formula (C6H14N2)[Fe3(HAsO4)1.33(HPO4)0.67(AsO4)0.84(PO4)0.16F4]0.5(H2O), has been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure has been solved from X-ray single crystal data. The unit-cell parameters are a=18.267(1), b=10.085(1), c=20.436(2) A, β=105.97(1)°. Monoclinic, C2/c with Z=8. The structure consists of a three-dimensional inorganic framework formed by [Fe3(HAsO4)1.33(HPO4)0.67(AsO4)0.84(PO4)0.16F4]2− inorganic layers linked by hydrogen-arsenate/phosphate anions. There are three iron atoms crystallographically independent per unit-formula. The sheets are constructed from Fe(1)Fe(3)O6F4 and Fe(2)2O8F2 dimeric units with edge-sharing octahedra. The 1,4-diazabicyclooctane dications are located inside the cavities of the inorganic skeleton. The IR and Raman spectroscopies confirm the simultaneously existence of both the arsenate/hydrogenarsenate and phosphate/hydrogenphosphate anions. From the diffuse reflectance spectrum the Dq=1080 and Racah parameters B=1040 and C=2620 cm−1 for the d5-high spin iron(III) cation in octahedral geometry have been calculated. The Mossbauer spectrum at room temperature is characteristic of high spin iron(III) cations. The ESR spectra are isotropic with a g-value of 1.99(1), which remains unchanged with variation in temperature. Magnetic measurements indicate the presence of antiferromagnetic interactions with a maximum in the susceptibility at around 6.0 K.

Host–guest chemistry of NiII coordination compounds with PDC and (py)2CO: reversible crystal-to-amorphous transformations induced by solvent exchange

The host-chemistry of four coordination networks has been studied by means of X-ray diffractometry (XRD), thermogravimetry (TG) and X-ray thermodiffractometry (TDX). The four compounds exhibit the general formula [Ni(PDC)((py)2C(OH)2)(ROH)]·xROH, where PDC is pyridine-2,5-dicarboxylate(2−), ((py)2C(OH)2) is the gem-diol of di-2-pyridyl ketone ((py)2CO), and R = H (1a), Me (3m), Et (3e), iPr (3p), and x = 2 when R = H, and x = 1 when R = Me, Et, iPr. The compounds are monomers packed through hydrogen bonds and π interactions. Dehydration of compound 1a produces an amorphous compound (2) that recovers crystallinity by re-adsorption of water, and also by adsorption of alcohols (methanol, ethanol, and isopropanol). Desorption of those alcohols can also be produced, yielding again the amorphous compound, which can be used again as host framework. This is, adsorption–desorption has been observed to be completely reversible not only for a particular guest molecule but also for the exchange of different guests. Compound 2 becomes, therefore, a host framework for at least four exchangeable molecules of solvent. This host–guest chemistry is based on the synergic effect of three simple processes: the exchange of crystallisation molecules, the labile coordination of the solvent molecules to the octahedral coordination sphere, and the sp2 → sp3 rehybridization of the carbonyl group in (py)2CO in the presence of different solvents.

CuII–PDC-bpe frameworks (PDC = 2,5-pyridinedicarboxylate, bpe = 1,2-di(4-pyridyl)ethylene): mapping of herringbone-type structures

Solid coordination frameworks (SCF) are crystalline materials based on connections between metal ions through organic ligands. In this sense, combination of polycarboxylate anions and dipyridyl ligands is an effective strategy to produce extended structures. In this context, this work is focused on two novel CuII-based SCFs incorporating PDC (2,5-pyridinedicarboxylate) and bpe (1,2-di(4-pyridyl)ethylene): Cu2[(PDC)2(bpe)(H2O)2]·3H2O·DMF (1), and Cu[(PDC)(bpe)0.5(H2O)]·2H2O (2), where DMF is dimethylformamide. Both compounds were synthesized by slow evaporation, and their crystal structures were determined by X-ray diffraction. Further structural, thermal and magnetic characterization was carried out by means of IR, TG/DTG, DTA analysis, EPR, and measurements of the magnetic susceptibility. The crystallographic analysis revealed that compounds 1 and 2 can be described as herringbone-type layers formed by helicoidal Cu–PDC–Cu chains connected through bpe ligands. Solvent molecules are crystallized between the layers, providing the inter-layer connections through hydrogen bonds. Differences between the two compounds are attributable to these solvent molecules, being indicative of the flexibility of this type of SCFs. On the other hand, due to the variety of structures found in the literature that have been described as “herringbone arrays”, this work also presents a crystallochemical study based on them. The study considers stoichiometry and structural parameters leading to the identification of two types of herringbone arrays, depending on the number of connections for the metal nodes (i.e. 3- and 4-connected).

Unprecedented coordination modes for PDC (pyridine-2,5-dicarboxylate) in polymorphic 3D heterobimetallic compounds α- and β-[MNa2(PDC)2(H2O)4], with M = Ni, Co

Four 3D coordination polymers have been hydrothermally synthesized using PDC (PDC = pyridine-2,5-dicarboxylate), and subsequently characterised. The four compounds are heterobimetallic, their formula being [MNa2(PDC)2(H2O)4], with M = Ni, Co. Two polymorphous compounds having the formula [NiNa2(PDC)2(H2O)4] have been obtained: polymorph α is monoclinic, and β is triclinic. Similarly, two phases have been characterised for the [CoNa2(PDC)2(H2O)4] formula, which are isostructural with the nickel compounds. All the studied compounds are 3D by covalent bonding. The four of them exhibit sodium octahedral chains whose extension allows the presence of perpendicular nickel octahedral chains for the monoclinic phases (α polymorphs). However, for the triclinic phases (β polymorphs) the connections between nickel ions just extend to trimers. The interest of these compounds lies on several aspects: two new coordination modes have been detected for PDC and all compounds exhibit a novel 3D complex multi-nodal topology. Density functional calculations have been carried out to analyse the crystallographic and chemical relationships between these phases.

CuII-based metal–organic nanoballs for very rapid adsorption of dyes and iodine

CuII nanoballs have been determined to be among the best MOPs (Metal–Organic Polyhedra) reported so far for the adsorption of small molecules, with the highlighting advantage of rapid kinetics, which focuses on their applicability to the removal of emerging pollutants.

Coordination and crystallization molecules: their interactions affecting the dimensionality of metalloporphyrinic SCFs.

Synthetic metalloporphyrin complexes are often used as analogues of natural systems, and they can be used for the preparation of new Solid Coordination Frameworks (SCFs). In this work, a series of six metalloporphyrinic compounds constructed from different meso substituted metalloporphyrins (phenyl, carboxyphenyl and sulfonatophenyl) have been structurally characterized by means of single crystal X-ray diffraction, IR spectroscopy and elemental analysis. The compounds were classified considering the dimensionality of the crystal array, referred just to coordination bonds, into 0D, 1D and 2D compounds. This way, the structural features and relationships of those crystal structures were analyzed, in order to extract conclusions not only about the dimensionality of the networks but also about possible applications of the as-obtained compounds, focusing the interest on the interactions of coordination and crystallization molecules. These interactions provide the coordination bonds and the cohesion forces which produce SCFs with different dimensionalities.

Mother structures related to the hexagonal and cubic close packing in Cu24 clusters: solvent-influenced derivatives

Compound 1 [Cu24(m-BDC)24(DMF)20(H2O)4]·24DMF·40H2O (m-BDC is 1,3-benzenedicarboxylate and DMF is N,N-dimethylformamide) has been synthesized and structurally characterized by X-ray diffraction. It consists of Cu24 clusters arranged in such a way that 12 dimers are connected through m-BDC ligands. The clusters exhibit an internal cavity where crystallization molecules of DMF and water are located. Additionally, there are guest DMF and water molecules in the voids generated by the 3D packing of the Cu24 clusters. The thermal stability of compound 1 has also been characterized, concluding that hydrogen bonds between solvent molecules are responsible for the robustness of the network. Compound 1 is similar to seven other compounds found in the literature. This work is focused on the crystallochemical comparison of these compounds, which concludes that there are two mother structures related to the hexagonal and cubic close packing of polyhedra. Derivative compounds are produced in the presence of different solvent molecules (differences affecting both the nature and the number of the guest molecules).