Synthesis and structure of multicomponent crystals of fullerenes and metal tetraarylporphyrins

The preparation of fullerene complexes with metal tetraarylporphyrins in the presence of excess ferrocene (Cp(2)Fe) results in the formation of new solvent-free and multicomponent molecular crystals. New isomorphous complexes of C(60) with PyZnTPP (ZnTPP identical with zinc 5,10,15,20-tetraphenyl-21H,23H-porphyrinate) and PyCoTPP (CoTPP identical with cobalt(II) 5,10,15,20-tetraphenyl-21H,23H-porphyrinate) containing Cp(2)Fe and the isostructural C(70) complex with PyZnTPP have been prepared. The crystal structures of the new layered C(60) complexes CoTMPP x C(60) (obtained in the presence of Cp(2)Fe) and CoTMPP x 2C(60) x 3C(7)H(8) (obtained in the absence of Cp(2)Fe) have been described (CoTMPP identical with cobalt(II) 5,10,15,20-tetrakis(p-methoxyphenyl)-21H,23H-porphyrinate). Cobalt atoms of the PyCoTPP and CoTMPP molecules are weakly coordinated to C(60) with Co...C(C(60)) distances in the 2.64-2.82 A range, whereas zinc atoms of PyZnTPP, as well as cobalt atoms of the CoTMPP molecules in the solvent-free phase, form only van der Waals contacts with fullerenes. Different packing arrangements in the crystals of fullerene-porphyrin complexes have been discussed.     

Ligand‐Tuning of the Excitation Wavelength of a Solid state E/Z Isomerization: [Zn(TA)2(2,2′‐Bipyridyl)] in a Supramolecular Framework

The single‐crystal‐to‐single‐crystal (SCSC) E?Z photoisomerization of TA in the supramolecular solid CECR‐[Zn(TA)₂(bpy)]·H₂O (CECR = C‐ethylcalixresorcinarene, HTA = tiglic acid, and bpy = 2,2′‐bipyridine, is induced by 458 nm light, indicating a red‐shift of the photo‐active wavelength on introduction of the aromatic bpy ligand compared with the previously studied reaction of CECR‐[Zn(TA)₂(H₂O)₂] 4H₂O. Theoretical calculations show that the initial excitation involves the bipyridyl ligand, which acts as an intramolecular photosensitizer for the isomerization process. The reaction is topotactic and illustrated by photodifference maps.     

The New Photocrystallography

Shine your light : Recent work in photocrystallography demonstrates a large photoinduced increase in the magnetic susceptibility of a solid, which is accompanied by significant changes in the bond lengths of the Nd? NC? Fe moiety (see picture; black are ground‐state bond lengths in Å, red are photoinduced bond lengths).

     

Transformation of a C-methylcalix[4]resorcinarene-based host-guest complex from a wave-like to a novel triangular brick-wall architecture

A novel 2D triangular brick-wall framework based on CMCR and bpe with included ruthenocene guest molecules is formed with time by conversion of a 1D wave-like polymer structure with an accompanying bowl-to-boat conformational change of the CMCR molecules.     

On the photochemical behavior of the [Ru(NH3)4(NO)nicotinamide]3+ cation and the relative stability of light-induced metastable isonitrosyl isomers of Ru complexes

Low-temperature IR experiments on crystalline samples of trans-[Ru(NH3)4(NO) nicotinamide]3+ salts show a light-induced absorption band typical for MS1 NO linkage isomers upon exposure to 300-500 nm light from a Xe source. The formation of a metastable species is confirmed by DSC measurement on a sample irradiated at low temperature with 457 nm light from an Ar+ laser. The light-induced species decays between 250 and 260 K according to both IR and DSC results. This decay temperature (Td) is somewhat below that observed for other high-Td linkage isomers, even though the NO-stretching frequency of the of [Ru(NH3)4(NO) nicotinamide]3+ ion is above that of the other isomers, demonstrating a lack of precise correlation between the two physical properties. The 90 K crystal structure of trans-[Ru(NH3)4(NO)nicotinamide](SiF6)(NO3).H2O is reported. The geometry from theoretical DFT calculations of the ground-state structure agrees well with the experimental results, except for the orientation of the CONH2 substituent in the pyridine ring, which is rotated by 180 degrees in the crystal due to packing effects. The MS1 and MS2 linkage isomers are found to correspond to local minima on the ground-state potential energy surface, and their geometries and energies are reported.     

Syntheses, structures, photoluminescence and theoretical studies of xanthone in crystalline resorcinarene-based inclusion complexes

Two new crystalline resorcinarene-based xanthone inclusion complexes, CECRxanthoneMeOH (1), and HECR2 xanthone6 MeOH (2) (CECR = C-ethylcalix[4]resorcinarene, HECR = hexaethylresorcin[6]arene) have been prepared to study the relation between photophysical properties and solid-state structure. Compared with the neat crystals, the xanthone phosphorescence is severely quenched in both solids, but the lifetime is an order of magnitude larger in 2, in which xanthone occurs as a dimer, than in 1, in which it occurs as a monomer. The electronic transitions involved in the photoluminescent process, and the relation between the energy levels of host and guest and emission quenching of the guest in the supramolecular solid have been investigated by means of time-dependent density functional theory (TDDFT) calculations.     

Calculation of electrostatic interaction energies in molecular dimers from atomic multipole moments obtained by different methods of electron density partitioning

Accurate and fast evaluation of electrostatic interactions in molecular systems is still one of the most challenging tasks in the rapidly advancing field of macromolecular chemistry, including molecular recognition, protein modeling and drug design. One of the most convenient and accurate approaches is based on a Buckingham-type approximation that uses the multipole moment expansion of molecular/atomic charge distributions. In the mid-1980s it was shown that the pseudoatom model commonly used in experimental X-ray charge density studies can be easily combined with the Buckingham-type approach for calculation of electrostatic interactions, plus atom-atom potentials for evaluation of the total interaction energies in molecular systems. While many such studies have been reported, little attention has been paid to the accuracy of evaluation of the purely electrostatic interactions as errors may be absorbed in the semiempirical atom-atom potentials that have to be used to account for exchange repulsion and dispersion forces. This study is aimed at the evaluation of the accuracy of the calculation of electrostatic interaction energies with the Buckingham approach. To eliminate experimental uncertainties, the atomic moments are based on theoretical single-molecule electron densities calculated at various levels of theory. The electrostatic interaction energies for a total of 11 dimers of alpha-glycine, N-acetylglycine and L-(+)-lactic acid structures calculated according to Buckingham with pseudoatom, stockholder and atoms-in-molecules moments are compared with those evaluated with the Morokuma-Ziegler energy decomposition scheme. For alpha-glycine a comparison with direct "pixel-by-pixel" integration method, recently developed Gavezzotti, is also made. It is found that the theoretical pseudoatom moments combined with the Buckingham model do predict the correct relative electrostatic interactions energies, although the absolute interaction energies are underestimated in some cases. The good agreement between electrostatic interaction energies computed with Morokuma-Ziegler partitioning, Gavezzotti's method, and the Buckingham approach with atoms-in-molecules moments demonstrates that reliable and accurate evaluation of electrostatic interactions in molecular systems of considerable complexity is now feasible.