Constructing chiral MOFs by functionalizing 4,2′:6′,4″-terpyridine with long-chain alkoxy domains: rare examples of neb nets

Reactions of 4′-(4- n alkyloxyphenyl)-4,2′:6′,4″-terpyridines (alkyl = hexyl or nonyl) with CoIJNCS) 2 lead to three structurally characterized chiral 3D assemblies which adopt rare neb topologies. For the n hexyl-functionalized ligands, both enantiomorphic lattices of the neb nets (crystallizing in the tetragonal space groups P4 1 2 1 2 and P4 3 2 1 2, respectively) are presente

Effect of high-pressure on molecular magnetism

The effect of pressure on a number of magnetically interesting compounds such as single-molecule magnets and dimeric copper and manganese molecules has been investigated to probe the validity of ambient magneto-structural correlations. The first chapter is an introduction to the equipment and methodologies that have been adopted to carry out the experimental high-pressure work. The second chapter reports the first combined high-pressure single crystal X-ray diffraction and high pressure magnetism study of four single-molecule magnets (SMMs). At 1.5 GPa the structures [Mn6O2(Et-sao)6(O2CPh(Me)2)2(EtOH)6] (1) – an SMM with a record effective anisotropy barrier of ~86 K – and [Mn6O2(Etsao) 6(O2C-naphth)2(EtOH)4(H2O)2] (2) both undergo significant structural distortions of their metallic skeletons which has a direct effect upon the observed magnetic response. Up to 1.5 GPa pressure the effect is to flatten the Mn-N-O-Mn torsion angles weakening the magnetic exchange between the metal centres. In both compounds one pairwise interaction switches from ferro- to antiferromagnetic, with the Jahn-Teller (JT) axes compressing (on average) and re-aligning differently with respect to the plane of the three metal centres. High pressure dc χMT plots display a gradual decrease in the low temperature peak value and slope, simulations showing a decrease in |J| with increasing pressure with a second antiferromagnetic J value required to simulate the data. The “ground states” change from S = 12 to S = 11 for 1 and to S = 10 for 2. Magnetisation data for both 1 and 2 suggest a small decrease in |D|, while out-of-phase (χM //) ac data show a large decrease in the effective energy barrier for magnetisation reversal. The third SMM is the complex [Mn3(Hcht)2(bpy)4](ClO4)3·Et2O·2MeCN (3·Et2O·2MeCN) that at 0.16 GPa loses all associated solvent in the crystal lattice, becoming 3. At higher pressures structural distortions occur changing the distances between the metal centres and the bridging oxygen atoms making |J| between the manganese ions weaker. No significant variations are observed in the JT axis of the only MnIII present in the structure. Highpressure dc χMT plots display a gradual decrease in the low temperature peak value and slope. Simulations show a decrease in J with increasing pressure although the ground state is preserved. Magnetisation data do not show any change in |D|. The fourth SMM, [(tacn)6Fe8O2(OH)12](ClO4)3.9Br4.1⋅6H2O, (4) is the largest inorganic compound ever studied at high-pressure. Up to 2.0 GPa the conformation of the complex remains largely unaffected, with the counter ions and water molecules moving around to accommodate a compression of the unit cell volume. High pressure magnetic susceptibility data collected up to 0.93 GPa confirm minimal changes in the intra-molecular exchange interactions. The third chapter focuses on three hydroxo-bridged CuII dimers: [Cu2(OH)2(H2O)2(tmen)2](ClO4)2 (5), [Cu2(OH)2(tben)2](ClO4)2 (6) and [Cu2(OH)2(bpy)2](BF4)2 (7) have been structurally determined up to 2.5, 0.9 and 4.7 GPa, respectively. 6 and 7 have never been reported before. Pressure imposes important distortions in the structures of all three complexes, particularly on the bond distances and angles between the metal centres and the bridging hydroxo groups. 5 undergoes a phase transition between 1.2 and 2.5 GPa caused by the loss of a coordinated water molecule. This leads to a loss of symmetry and dramatic changes in the molecular structure of the complex. The structural changes are manifested in different magnetic behaviours of the complexes as seen in dc susceptibility measurements up to ~0.9 GPa: J becomes less antiferromagnetic in 5 and 6 and more ferromagnetic in 7. The fourth chapter shows the compression of two oxo-bridged MnII/MnIII mixed valence dimers: [Mn2O2(bpy)4](ClO4)3⋅3CH3CN, (8) has been squeezed up to 2.0 GPa whilst [Mn2O2(bpy)4](PF6)3⋅2CH3CN⋅1H2O, (9) could be measured crystallographically up to 4.55 GPa. 9 has never been reported before, while 8 has been reported in a different crystallographic space group. The application of pressure imposes significant alterations in the structures of both complexes. In particular, in 8 the Mn-Mn separation is reduced by the contraction of some of the Mn-O bond distances, 9 shows essentially analogous behaviour: the Mn-Mn distance and nearly all the Mn-N bonds shrink significantly. The magnetic behaviour of the complexes has been measured up to 0.87 GPa for 8 and 0.84 GPa for 9, but neither display any significant differences with respect to their ambient data

Induced axial chirality by a tight belt: naphthalene chromophores fixed in a 2,5-substituted cofacial para-phenylene-ethynylene framework

We report the design of a synthetically easy accessible axial chirality-inducing framework for a chromophore of choice. The scaffold consists of two basic para-phenylene-ethynylene backbones separated by laterally placed corner units. Substitution with an inherently achiral chromophore at the 2 and 5 positions of the central phenylene excitonically couples the chromophore associated transition and thereby results in chiroptical properties. Using 6-methoxynaphthalene as a model chromophore, we present the synthesis, structural analysis and spectroscopic investigation of the framework. The chiral framework was synthesized in three straightforward synthetic steps and fully characterized. The obtained racemic compounds were resolved using HPLC and assignment of the absolute configuration was performed using the exciton chirality method, crystallography and DFT calculations. This simple yet potent framework might prove useful to enrich the structural diversity of chiral materials

Xanthene[n]arenes: Exceptionally Large, Bowl-Shaped Macrocyclic Building Blocks Suitable for Self-Assembly

A new class of macrocycles denoted as "xanthene[ n ]arenes" was synthesized. In contrast to most other macrocycles, they feature a conformationally restricted bowl shape due to the attached alkyl groups at the linking methylene units. This facilitates the synthesis of cavitands and the self-assembly to molecular capsules via noncovalent interactions. The derivatization potential of the novel macrocycles was demonstrated on the xanthene[3]arene scaffold. Besides a deep cavitand and an oxygen-embedded zigzag hydrocarbon belt[12]arene, a modified macrocycle was synthesized that self-assembles into a hydrogen-bonded tetrameric capsule, demonstrating the potential of xanthene[ n ]arenes as a new set of macrocyclic building blocks

X-Ray Crystallographic Studies of Quasi-Racemates for Absolute Configuration Determinations

The determination of the absolute configuration of chiral molecular entities by means of X-ray crystallography is overall of central importance in stereochemistry. However, the growth of enantiopure single crystals often represents an unsurmountable and frustrating hurdle. Quasi-racemic crystals of biomacromolecules, for which the absolute configuration is predetermined by the chiral monomers, allowed the X-ray crystallographic analysis of systems that are difficult to crystallize as pure enantiomers, with aims other than the determination of the absolute structure. Taking advantage of the greater propensity of quasi-racemic mixtures to co-crystallize compared to growing enantiomerically pure crystals of a single compound, we herein describe the use of X-ray crystallography of quasi-racemates for the absolute configuration determination. We expect that this approach is particularly useful to establish the sense of selectivity in the development of stereoselective methods by simplified crystallizations, while confirming the consistent selectivity with a second molecular structure within the same measurement

Megalo-Cavitands: Synthesis of Acridane[4]arenes and Formation of Large, Deep Cavitands for Selective C70 Uptake

Deep cavitands, concave molecular containers, represent an important supramolecular host class that has been explored for a variety of applications ranging from sensing, switching, purification and adsorption to catalysis. A major limitation in the field has been the cavitand volume that is restricted by the size of the structural platform utilized (diameter approx. 7 Å). We here report the synthesis of a novel, unprecedentedly large structural platform, named acridane[4]arene (diameter approx. 14 Å), suitable for the construction of cavitands with volumes of up to 814 Å3. These megalo-cavitands serve as size-selective hosts for fullerenes with mM to sub-μM binding affinity for C60 and C70. Furthermore, the selective binding of fullerene C70 in the presence of C60 was demonstrated

An Ortho-Tetraphenylene-Based “Geländer” Architecture Consisting Exclusively of 52 sp2^{2}-Hybridized C Atoms

A new type of “Geländer” molecule based on a ortho-tetraphenylene core is presented. The central para-quaterphenyl backbone is wrapped by a 4,4’-di((Z)-styryl)-1,1’-biphenyl banister, with its aryl rings covalently attached to all four phenyl rings of the backbone. The resulting helical chiral bicyclic architecture consists exclusively of sp2-hybridized carbon atoms. The target structure was assembled by expanding the central ortho-tetraphenylene subunit with the required additional phenyl rings followed by a twofold macrocyclization. The first macrocyclization attempts based on a twofold McMurry coupling were successful but low yielding; the second strategy, profiting from olefin metathesis, provided satisfying yields. Hydrogenation of the olefins resulted in a saturated derivative of similar topology, thereby allowing the interdependence between saturation and physico-chemical properties to be studied. The target structures, including their solid-state structures, were fully characterized. The helical chiral bicycle was synthesized as a racemate and separated into pure enantiomers by HPLC on a chiral stationary phase. Comparison of recorded and simulated chiroptical properties allowed the enantiomers to be assigned

Positional Isomerism in the N^N Ligand: How Much Difference Does a Methyl Group Make in [Cu(P^P)(N^N)]+ Complexes?

The synthesis and structural characterization of 5,60-dimethyl-2,20-bipyridine (5,60-Me2bpy) are reported, along with the preparations and characterizations of [Cu(POP)(5,60-Me2bpy)][PF6] and [Cu(xantphos)(5,60-Me2bpy)][PF6] (POP = bis(2-(diphenylphosphanyl)phenyl)ether, xantphos = 4,5- bis(diphenylphosphanyl)-9,9-dimethyl-9H-xanthene). Single-crystal X-ray structure determinations of [Cu(POP)(5,60-Me2bpy)][PF6] and [Cu(xantphos)(5,60-Me2bpy)][PF6] confirmed distorted tetrahedral copper(I) coordination environments with the 5-methylpyridine ring of 5,60-Me2bpy directed towards the (C6H4)2O unit of POP or the xanthene unit of xantphos. In the xantphos case, this preference may be attributed to C-H : : : interactions involving both the 6-CH unit and the 5-methyl substituent in the 5-methylpyridine ring and the arene rings of the xanthene unit. 1H NMR spectroscopic data indicate that this ligand orientation is also preferred in solution. In solution and the solid state, [Cu(POP)(5,60-Me2bpy)][PF6] and [Cu(xantphos)(5,60-Me2bpy)][PF6] are yellow emitters, and, for powdered samples, photoluminescence quantum yields (PLQYs) are 12 and 11%, respectively, and excited-state lifetimes are 5 and 6 s, respectively. These values are lower than PLQY and values for [Cu(POP)(6,60-Me2bpy)][PF6] and [Cu(xantphos)(6,60-Me2bpy)][PF6], and the investigation points to the 6,60-dimethyl substitution pattern in the bpy ligand being critical for enhancement of the PLQY