Aluminum 1,4‐benzenedicarboxylate Al(OH)O2CC6H4CO2⋅ HO2CC6H4CO2H0.70 or MIL‐53 as (Al) has been hydrothermally synthesized by heating a mixture of aluminum nitrate, 1,4‐benzenedicarboxylic acid, ...and water, for three days at 220 °C. Its 3 D framework is built up of infinite trans chains of corner‐sharing AlO4(OH)2 octahedra. The chains are interconnected by the 1,4‐benzenedicarboxylate groups, creating 1 D rhombic‐shaped tunnels. Disordered 1,4‐benzenedicarboxylic acid molecules are trapped inside these tunnels. Their evacuation upon heating, between 275 and 420 °C, leads to a nanoporous open‐framework (MIL‐53 ht (Al) or Al(OH)O2CC6H4CO2) with empty pores of diameter 8.5 Å. This solid exhibits a Langmuir surface area of 1590(1) m2 g−1 together with a remarkable thermal stability, since it starts to decompose only at 500 °C. At room temperature, the solid reversibly absorbs water in its tunnels, causing a very large breathing effect and shrinkage of the pores. Analysis of the hydration process by solid‐state NMR (1H, 13C, 27Al) has clearly indicated that the trapped water molecules interact with the carboxylate groups through hydrogen bonds, but do not affect the hydroxyl species bridging the aluminum atoms. The hydrogen bonds between water and the oxygen atoms of the framework are responsible for the contraction of the rhombic channels. The structures of the three forms have been determined by means of powder X‐ray diffraction analysis. Crystal data for MIL‐53 as (Al) are as follows: orthorhombic system, Pnma (no. 62), a = 17.129(2), b = 6.628(1), c = 12.182(1) Å; for MIL‐53 ht (Al), orthorhombic system, Imma (no. 74), a = 6.608(1), b = 16.675(3), c = 12.813(2) Å; for MIL‐53 lt (Al), monoclinic system, Cc (no. 9), a = 19.513(2), b = 7.612(1), c = 6.576(1) Å, β = 104.24(1)°.
Breathing under water! The porous aluminum terephthalate (MIL‐53) exhibits a remarkable amplitude of breathing upon hydration (see scheme). XRD, NMR, and PACHA modeling have been applied to rationalize this high degree of structural flexibility.
The spontaneous self‐assembly of a neutral circular trinuclear TiIV‐based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The ...trimeric ring helicate was obtained after diffusion of n‐pentane into a solution with dichloromethane. The circular helicate has been characterized by using single‐crystal X‐ray diffraction study, 13C CP‐MAS NMR and 1H NMR DOSY solution spectroscopic, and positive electrospray ionization mass‐spectrometric analysis. These analytical data were compared with those obtained from a previously reported double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double‐stranded helicates was characterized by ΔH(toluene)=−30 kJ mol−1 and ΔS(toluene)=+357 J K−1 mol−1, whereas these values were ΔH(CH2Cl2)=−75 kJ mol−1 and ΔS(CH2Cl2)=−37 J K−1 mol−1 for the ring helicate. The transformation of the ring helicate into the double‐stranded helicate was a strongly endothermic process characterized by ΔH(CH2Cl2)=+127 kJ mol−1 and ΔH(n‐pentane)=+644 kJ mol−1 associated with a large positive entropy change ΔS=+1115 J K−1⋅mol−1. Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to n‐pentane. Suggestions for increasing the stability of the ring helicate are given.
The spontaneous self‐assembly of a neutral circular trinuclear TiIV‐based helicate is described. Crystals of this trimeric ring helicate were obtained after diffusion of n‐pentane into a solution of the sample in dichloromethane. This architecture contrasts with the double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate (see picture).
A binuclear Ti(IV)-based helicate synthesized from a symmetric tetrahydroxyheptaphenylene strand was self-assembled in solution and shown to undergo a spontaneous head-to-tail differentiation ...according to single-crystal X-ray diffraction.
A new class of organic crystalline 2,2'-biphenol-based H-bonded material displaying 1D-channels encapsulating solvent molecules is described. A reversible guest-induced crystal-to-crystal conversion ...between the solvated H-bonded phase and a compact H-bonded non-solvated phase was observed. The energy competition between intramolecular H-bonds formation and solvation of organic pores has been characterized using PACHA calculations.
We report the synthesis and structural characterisation of two titanium(IV) complexes. A new titanium(IV) complex bearing four picolinato ligands, denoted as Ti(pic)4, has been prepared under ...solvothermal conditions. This complex identified by single‐crystal diffraction is a new example of an octacoordinated environment for titanium(IV) and is close to an ideal triangular dodecahedron. A second synthesis of a hexaprismatric carboxylato titanium complex formulated as Ti6(μ3‐O)6(OiPr)6(μ‐O2CC5H3NCOOiPr)6 starting from a dissymmetric anhydride pyridine carboxylic precursor is described. The solid‐state analysis shows the presence of a single compound among 13 possible species. Calculations gave evidence of a highly selective mechanism leading to the formation of the final product.
The structural characterisation of two titanium(IV) complexes bearing pyridinecarboxylato ligands is reported. An uncommon octacoordinated complex was obtained by treating picolinic acid with titanium isopropoxide. A second complex formulated as Ti6(μ3‐O)6(OiPr)6(μ‐O2CC5H3NCOOiPr)6 was prepared from titanium isopropoxide and a dissymmetric anhydride pyridine carboxylic precursor.
A new mixed zinc-aluminum phosphate Zn(3)Al(6)(PO(4))(12), 4tren, 17H(2)O (MIL-74) has been hydrothermally synthesized with the tris(2-aminoethyl)amine (tren) as a structure-directing agent (453 K, ...36 h, autogenous pressure). The solid was characterized by a nonclassical method combining single-crystal X-ray diffraction and several solid-state NMR experiments, RFDR, C7 double quantum ((31)P), and 3QMAS ((27)Al). Its crystal structure is cubic, a = 16.7942(1) A, but the choice of the space group does not follow usual routes of structure determination, due to some "disorder" between Zn and Al. It can be assigned as well to I-43m or to P-43n. The open-framework is built up from an enneameric unit (T = Zn, Al) containing five TO(4) and four PO(4) tetrahedra (one of the P-O bonds is terminal). A central TO(4) tetrahedral unit shares all of the corners with four phosphates groups. Two phosphate groups are connected to two other peripheral TO(4) units. It results in the formation of a "pseudo" planar building block T(5)P(4) consisting of four square 4-rings. The connection of the T(5)P(4) units generates a three-dimensional framework, which defines a super-sodalite topology. The resulting cavities (diameter of 10 A) are bound by 12-ring windows in which are located the tren species in interaction with the phosphate groups (mainly terminal P-O bonds) through hydrogen bonds. A cluster of 17 water molecules occupies the center of the super-sodalite cage. The cationic (Zn, Al) occupancy is discussed for this specific topology.
The 3,3'-diphenyl-2,2'-biphenol (dpbpolH(2)) ligand is shown to react with Ti(OPr(i))(4) in a 2:1 ratio to yield a novel C(2)-symmetric mononuclear octahedral Ti(IV) bis-biphenolate complex, ...cis-Ti(dpbpol)(2)(HOPr(i))(2).
