Systematic Investigation of Zinc Aminoalkylphosphonates: Influence of the Alkyl Chain Lengths on the Structure Formation

With the high-throughput (HT) methodology, the bifunctional aminoalkylphosphonic acids (AAPA) linker molecules 2-aminoethyl- (AEPA), 3-aminopropyl- (APPA), and 4-aminobutylphosphonic acid (ABPA) [HO₃P–C_<i>n</i>H_2<i>n</i>–NH₂ (<i>n</i> = 2–4)] and zinc nitrate were used to synthesize new metal phosphonates in order to investigate the influence of the alkyl chain length on the structure formation. The systematic investigations led to one known (ZnO₃PC₂H₄NH₂) and six new compounds: one using AEPA, three using APPA, and two using ABPA. The crystal structures of five compounds were determined by single crystal X-ray diffraction, using X-ray powder diffraction (XRPD) data as well as structure modeling employing force field methods. For compound <b>1</b>, Zn­(O₃P–C₂H₄–NH₃)­(NO₃)­(H₂O) (monoclinic, <i>Cc</i>, <i>a</i> = 4.799(1) Å, <i>b</i> = 29.342(6) Å, <i>c</i> = 5.631(1) Å, β = 91.59(3)°, <i>V</i> = 792.7(3) ų, <i>Z</i> = 4), and compound <b>2</b>, Zn₂(OH)­(O₃P–C₃H₆–NH₃)­(NO₃) (monoclinic, <i>P</i>2/<i>c</i>, <i>a</i> = 12.158(2) Å, <i>b</i> = 5.0315(10) Å, <i>c</i> = 13.952(3) Å, β = 113.23(3)°, <i>V</i> = 784.3(3) ų, <i>Z</i> = 2), the structures were determined using single crystal X-ray diffraction data. The crystal structures of [Zn­(O₃P–C₃H₆–NH₂)]·H₂O (<b>3</b>) (monoclinic, <i>P</i>2₁/<i>c</i>, <i>a</i> = 9.094(2) Å, <i>b</i> = 5.0118(7) Å, <i>c</i> = 16.067(4) Å, β = 90.38(2)°, <i>V</i> = 732.3(2) ų, <i>Z</i> = 4) and Zn­(O₃P–C₄H₈–NH₂) (<b>5</b>) (monoclinic, <i>P</i>2₁/<i>c</i>, <i>a</i> = 8.570(7) Å, <i>b</i> = 8.378(4) Å, <i>c</i> = 9.902(6) Å, β = 90.94(5)°, <i>V</i> = 710.9(8) ų, <i>Z</i> = 4) were determined using XRPD data. The structural model for compound <b>6</b>, Zn­(O₃P–C₄H₈–NH₃)­(NO₃)­(H₂O), was established using lattice parameters from XRPD data and following crystal structure modeling employing force field methods. The structures depend strongly on the alkyl chain length <i>n</i>. For <i>n</i> = 2 and 4 isoreticular compounds are observed, while <i>n</i> = 3 leads to new structures. Larger amounts of all compounds were obtained employing scale-up syntheses in a conventional oven as well as in a microwave reactor system. In addition, in situ energy dispersive X-ray diffraction (EDXRD) experiments at 130 °C were performed at beamline F3 at HASYLAB, DESY, Hamburg, to investigate the formation of compounds <b>2</b> and <b>3</b> as well as the phase transformation of <b>2</b> into <b>3</b> upon addition of NaOH. All compounds were characterized in detail using X-ray powder diffraction, IR/Raman spectroscopy, and thermogravimetric and elemental analysis

Discovery of New Calcium Etidronates Employing Ultrasound Adapted High-Throughput Methods

The formation of calcium etidronates was investigated employing high-throughput ultrasonic synthesis. In the study of the system CaCl₂/H₂O₃P-C­(OH)­(CH₃)-PO₃H₂/H₂O/KOH three new crystalline products were obtained in dependence of the deprotonation degree of the bisphosphonic acid HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, H₂O₃P-C­(OH)­(CH₃)-PO₃H₂) and the sonication time. In a large region of the parameter space and at short reaction times [Ca­(HO₃P-C­(OH)­(CH₃)-PO₃H)­(H₂O)]·2.5H₂O (<b>1</b>) forms. At higher pH [KCa­(HO₃P-C­(OH)­(CH₃)-PO₃)­(H₂O)]·H₂O (<b>2</b>) containing the asymmetrically deprotonated HO₃P-C­(OH)­(CH₃)-PO₃^3– ion and [K₂Ca­(O₃P-C­(OH)­(CH₃)-PO₃)­(H₂O)₆] (<b>3</b>) with the fully deprotonated ligand are obtained. The crystal structures of <b>1</b> and <b>2</b> were solved and refined from X-ray powder diffraction data. The thermal decomposition of the compounds was investigated. If exposed to moderate temperatures 1.5 water molecules per formula unit are removed from the crystal structure of <b>1</b> and the pseudopolymorphic compound [Ca­(HO₃P-C­(OH)­(CH₃)-PO₃H)­(H₂O)₂] is formed [Uchtman J. Phys. Chem. 1972, 76, 1304−1310]

Discovery of New Calcium Etidronates Employing Ultrasound Adapted High-Throughput Methods

The formation of calcium etidronates was investigated employing high-throughput ultrasonic synthesis. In the study of the system CaCl₂/H₂O₃P-C­(OH)­(CH₃)-PO₃H₂/H₂O/KOH three new crystalline products were obtained in dependence of the deprotonation degree of the bisphosphonic acid HEDP (1-hydroxyethylidene-1,1-diphosphonic acid, H₂O₃P-C­(OH)­(CH₃)-PO₃H₂) and the sonication time. In a large region of the parameter space and at short reaction times [Ca­(HO₃P-C­(OH)­(CH₃)-PO₃H)­(H₂O)]·2.5H₂O (<b>1</b>) forms. At higher pH [KCa­(HO₃P-C­(OH)­(CH₃)-PO₃)­(H₂O)]·H₂O (<b>2</b>) containing the asymmetrically deprotonated HO₃P-C­(OH)­(CH₃)-PO₃^3– ion and [K₂Ca­(O₃P-C­(OH)­(CH₃)-PO₃)­(H₂O)₆] (<b>3</b>) with the fully deprotonated ligand are obtained. The crystal structures of <b>1</b> and <b>2</b> were solved and refined from X-ray powder diffraction data. The thermal decomposition of the compounds was investigated. If exposed to moderate temperatures 1.5 water molecules per formula unit are removed from the crystal structure of <b>1</b> and the pseudopolymorphic compound [Ca­(HO₃P-C­(OH)­(CH₃)-PO₃H)­(H₂O)₂] is formed [Uchtman J. Phys. Chem. 1972, 76, 1304−1310]

First Keto-Functionalized Microporous Al-Based Metal–Organic Framework: [Al(OH)(O₂C‑C₆H₄‑CO‑C₆H₄‑CO₂)]

Based on the V-shaped linker molecule 4,4′-benzophenonedicarboxylic acid, the new carbonyl-functionalized metal–organic framework (MOF) [Al­(OH)­(O₂C-C₆H₄-CO-C₆H₄-CO₂)], denoted as CAU-8, was discovered employing high-throughput methods. The compound is obtained from 4,4′-benzophenonedicarboxylic acid, Al₂(SO₄)₃·18H₂O in a mixture of <i>N</i>,<i>N</i>-dimethylformamide (DMF) and water under solvothermal conditions. The structure was determined from single-crystal X-ray diffraction data (<i>I</i>4₁/<i>a</i>, <i>a</i> = <i>b</i> = 13.0625(5), <i>c</i> = 52.565(2) Å). The framework is based on infinite inorganic building units of <i>trans</i>-connected, corner-sharing AlO₆-polyhedra. Parallel Al–O-chains are arranged in layers perpendicular to [001]. Within a layer an interchain distance of ∼1.1 nm is observed. The orientation of the Al–O-chains within neighboring layers is perpendicular to each other, along [100] and [010], respectively, and an ABCDA stacking of these layers is observed. The interconnection of these orthogonally oriented chains by the V-shaped dicarboxylate ions results in the formation a three-dimensional framework structure containing one-dimensional channels with a diameter of about 8 Å. The pore walls are lined by the keto-groups. CAU-8 was thoroughly characterized by X-ray powder diffraction (XRPD), thermogravimetric measurements, IR- and Raman-spectroscopy, elemental analysis, and gas sorption experiments using N₂ and H₂ as adsorptives. CAU-8 is stable up to 350 °C in air and exhibits a moderate porosity with a specific surface area of <i>S</i>_BET = 600 m²/g and a micropore volume of 0.23 cm³/g. Moreover, a detailed topological analysis of the framework was carried out, and an approach for the topological analysis of MOFs based on infinite 1-periodic building units is proposed

Synthesis and Characterization of New Ce(IV)-MOFs Exhibiting Various Framework Topologies

We report on the applicability of an easy general synthesis procedure for the formation of Ce­(IV)-MOFs which contain hexanuclear clusters. Thus, the series of Ce­(IV)-based MOFs isoreticular to their Zr analogues has been extended to <b>reo</b> and <b>spn</b> topologies. Four new MOFs denoted as Ce-UiO-66-BPyDC [Ce₆(μ₃-O)₄(μ₃-OH)₄(BPyDC)₆] (BPyDC^2– = 2,2′-bipyridine-5,5′-dicarboxylate), Ce-DUT-67-PZDC [Ce₆(μ₃-O)₄(μ₃-OH)₄(PZDC)₄(OH)₄(H₂O)₄] (PZDC^2– = 3,5-pyrazoledicarboxylate), Ce-DUT-67-TDC [Ce₆(μ₃-O)₄(μ₃-OH)₄(TDC)₄(OH)₄(H₂O)₄] (TDC^2– = 2,5-thiophenedicarboxylate), and Ce-MOF-808 [Ce₆(μ₃-O)₄(μ₃-OH)₄(BTC)₂(OH)₆(H₂O)₆] (BTC^3– = benzene-1,3,5-tricarboxylate) were obtained under mild reaction conditions (100 °C) and after short reaction times (15 min) using a modulated synthesis approach. The MOFs differ in their connectivity of the [Ce₆O₄(OH)₄(−CO₂)_<i>x</i>] (<i>x</i> = 12, 8, 6) cluster, the geometry of the organic linker molecules (linear and bent dicarboxylic acids, tricarboxylic acid), and the resulting topology (<b>fcu</b>, <b>reo</b>, <b>spn</b>). The structures of all Ce-MOFs were confirmed using PXRD data by Rietveld refinement and Le Bail fitting. The heterocyclic aromatic dicarboxylic acids H₂PZDC and H₂TDC lead to MOFs which are both isostructural to DUT-67 due to the similar linker geometries. Ce-UiO-66-BPyDC and Ce-MOF-808 are thermally stable up to 330 and 150 °C, respectively, as proven by VT-PXRD measurements. N₂ sorption experiments reveal large specific surface areas of 2120 m² g^–1 for Ce-UiO-66-BPyDC and 1725 m² g^–1 for Ce-MOF-808

Green Synthesis of Zr-CAU-28: Structure and Properties of the First Zr-MOF Based on 2,5-Furandicarboxylic Acid

A new Zr-based metal–organic framework denoted as Zr-CAU-28 with framework composition [Zr₆O₄(OH)₄(FDC)₄(OH)₄(H₂O)₄] (H₂FDC = 2,5-furandicarboxylic acid, CAU = Christian-Albrechts-University) was obtained under green synthesis conditions from a mixture of H₂O and acetic acid and employing microwave-assisted heating. Zr-CAU-28 is the first Zr-MOF based on H₂FDC, which is often considered a promising renewable alternative to terephthalic acid. The crystal structure was determined from powder X-ray diffraction data using a combination of direct methods, force field calculations, and Rietveld refinement. The compound crystallizes in the hexagonal crystal system (space group <i>P</i>6₃/<i>mmc</i>) with the cell parameters <i>a</i> = 24.9919(9) and <i>c</i> = 24.7688(9) Å. The framework structure adopts a kagome-like topology and hence contains large hexagonal channels with a pore diameter of approximately 16 Å and small trigonal channels with a size of 3 Å. Nitrogen sorption measurements were carried out at −196 °C and gave a specific surface area of <i>S</i>_BET = 1006 m²/g and a micropore volume of 0.42 cm³/g. Thermogravimetric analyses showed a stability up to 270 °C although temperature dependent PXRD measurements revealed a decrease in long-range order already above 150 °C. Furthermore, the Ce⁴⁺ based analogue Ce-CAU-28 could be obtained employing dimethylformamide/water mixtures as solvent. The structure and framework composition of this MOF are very similar to the ones of the Zr-based compound, but its thermal stability is clearly inferior. Thus, Ce-CAU-28 cannot be fully desolvated and exhibits a specific surface area of only <i>S</i>_BET = 360 m²/g and a micropore volume of 0.15 cm³/g

New Al-MOFs Based on Sulfonyldibenzoate Ions: A Rare Example of Intralayer Porosity

A new sulfone-functionalized metal–organic framework [Al­(OH)­(SDBA)]·0.25DMF, denoted CAU-11, was synthesized using a V-shaped linker molecule 4,4′-sulfonyldibenzoic acid (H₂SDBA). The crystal structure was solved from synchrotron X-ray powder diffraction data. Chains of trans corner-sharing AlO₆ octahedra are interconnected by the carboxylate groups to form layers (ABAB stacking). Within the layers, hydrophobic lozenge-shaped pores with a diameter of 6.4 × 7.1 Ų are present inducing permanent porosity (<i>a</i>_BET = 350 m² g^–1 and <i>V</i>_micro = 0.17 cm³ g^–1). With the application of HT-methods (HT = high throughput), the isoreticular carboxylate functionalized compound [Al­(OH)­(H₂DPSTC)]·0.5H₂O (CAU-11-COOH) was synthesized using the linker molecule 3,3′,4,4′-diphenylsulfone­tetracarboxylic dianhydride (DPSDA), which hydrolyzes under the reaction conditions. Due to the additional noncoordinating carboxylic acid groups the pores are hydrophilic. Changing the molar ratio of Al³⁺ to linker lead to the discovery of a second new compound [Al₂(OH)₂(DPSTC)­(H₂O)₂]·0.5H₂O (CAU-12). In CAU-12 the linker molecule is fully deprotonated which leads to different connectivity compared to the structure of CAU-11-COOH. Thermal activation of CAU-12 leads to dehydration and transformation of the structure to [Al₂(OH)₂­(DPSTC)]·<i>n</i>H₂O (CAU-12-dehy). Coordinated water molecules were removed, and the coordination site is replaced by the previously noncoordinating O atom of the adjacent carboxylate group. The SO₂-groups point into the pores resulting in a highly hydrophobic three-dimensional framework. The compounds exhibit high thermal stability in air at least up to 420 °C. Synthesis of CAU-11 can be easily scaled up in very high yields (98%)

Group 13 Metal Carboxylates: Using Molecular Clusters As Hybrid Building Units in a MIL-53 Type Framework

Systematic investigation of the reactions of the system AlCl₃·6H₂O/pyridine-2,4,6-tricarboxylic acid (H₃<b>PTC</b>)/pyridine in water yielded two new compounds, both containing the dimeric {Al<b>PTC</b>(μ-OH)­(H₂O)}₂^2– unit. With long reaction times, the framework compound [Al­(μ-OH)­{Al<b>PTC</b>(μ-OH)­(H₂O)}₂]·2H₂O (CAU-16, compound <b>1</b>) is obtained, the first example of a framework compound with a metal–organic cluster linker, and bearing the MIL-53 network. Although the compound does not breathe, as other MIL-53 compounds do, it has a maximum uptake of CO₂ of 1.76(2) mmol g^–1 at 196 K. With shorter reaction times, the molecular compound {Al­(H<b>PTC</b>)­(μ-OH)­(H₂O)}₂ (<b>2</b>) was prepared, leading to the proposal of a crystallization scheme for the Al³⁺-pyridine-2,4,6,-tricarboxylic acid system. To determine whether further framework compounds bearing hybrid metal cluster linkers could be prepared, systematic high-throughput investigations of pyridine-2,4,6-tricarboxylic acid in water with Ga³⁺ and In³⁺ were undertaken. These yielded two chain-type compounds, Ga<b>PTC</b>(H₂O)₂ (<b>3</b>) and In<b>PTC</b>(H₂O)₂ (<b>4</b>), with different coordination chemistries. Optimized syntheses for compounds <b>1</b>, <b>2</b>, and <b>4</b> are reported

Group 13 Metal Carboxylates: Using Molecular Clusters As Hybrid Building Units in a MIL-53 Type Framework

Systematic investigation of the reactions of the system AlCl₃·6H₂O/pyridine-2,4,6-tricarboxylic acid (H₃<b>PTC</b>)/pyridine in water yielded two new compounds, both containing the dimeric {Al<b>PTC</b>(μ-OH)­(H₂O)}₂^2– unit. With long reaction times, the framework compound [Al­(μ-OH)­{Al<b>PTC</b>(μ-OH)­(H₂O)}₂]·2H₂O (CAU-16, compound <b>1</b>) is obtained, the first example of a framework compound with a metal–organic cluster linker, and bearing the MIL-53 network. Although the compound does not breathe, as other MIL-53 compounds do, it has a maximum uptake of CO₂ of 1.76(2) mmol g^–1 at 196 K. With shorter reaction times, the molecular compound {Al­(H<b>PTC</b>)­(μ-OH)­(H₂O)}₂ (<b>2</b>) was prepared, leading to the proposal of a crystallization scheme for the Al³⁺-pyridine-2,4,6,-tricarboxylic acid system. To determine whether further framework compounds bearing hybrid metal cluster linkers could be prepared, systematic high-throughput investigations of pyridine-2,4,6-tricarboxylic acid in water with Ga³⁺ and In³⁺ were undertaken. These yielded two chain-type compounds, Ga<b>PTC</b>(H₂O)₂ (<b>3</b>) and In<b>PTC</b>(H₂O)₂ (<b>4</b>), with different coordination chemistries. Optimized syntheses for compounds <b>1</b>, <b>2</b>, and <b>4</b> are reported

Copper Phosphonatoethanesulfonates: Temperature Dependent in Situ Energy Dispersive X‑ray Diffraction Study and Influence of the pH on the Crystal Structures

The system Cu²⁺/H₂O₃P–C₂H₄–SO₃H/NaOH was investigated using in situ energy dispersive X-ray diffraction (EDXRD) to study the formation and temperature induced phase transformation of previously described copper phosphonosulfonates. Thus, the formation of [Cu₂(O₃P–C₂H₄–SO₃)­(OH)­(H₂O)]·3H₂O (<b>4</b>) at 90 °C is shown to proceed via a previously unknown intermediate [Cu₂(O₃P–C₂H₄–SO₃)­(OH)­(H₂O)]·4H₂O (<b>6</b>), which could be structurally characterized from high resolution powder diffraction data. Increase of the reaction temperature to 150 °C led to a rapid phase transformation to [Cu₂(O₃P–C₂H₄–SO₃)­(OH)­(H₂O)]·H₂O (<b>1</b>), which was also studied by in situ EDXRD. The comparison of the structures of <b>1</b>, <b>4</b>, and <b>6</b> allowed us to establish a possible reaction mechanism. In addition to the in situ crystallization studies, microwave assisted heating for the synthesis of the copper phosphonosulfonates was employed, which allowed the growth of larger crystals of [NaCu­(O₃P–C₂H₄–SO₃)­(H₂O)₂] (<b>5</b>) suitable for single crystal X-ray diffraction. Through the combination of force field calculations and Rietveld refinement we were able to determine the crystal structure of [Cu_1.5(O₃P–C₂H₄–SO₃)] 2H₂O (<b>3</b>) and thus structurally characterize all compounds known up to now in this well investigated system. With the additional structural data we are now able to describe the influence of the pH on the structure formation