Efficient photodegradation of dyes by a new 3D Cd(II) MOF with rare fsh topology

Metal–organic frameworks (MOFs) can be regarded as 3D coordination polymers that adopt ordered porous structures and possess abundant active sites, which make them promising photocatalysts for the degradation of organic...

Synthesis and crystal structure of hexaaquacopper(II) 2,5-dicarboxyterephthalate, C10H16O14Cu

C 10 H 16 O 14 ${\text{C}}_{10}{\text{H}}_{16}{\text{O}}_{14}$ Cu, monoclinic, I2/a (no. 15), a = 7.2407(3) Å, b = 9.7565(4) Å, c = 21.1814(10) Å, β = 93.913(2)°, V = 1492.85(11) Å3, Z = 4, R g t ${R}_{gt}$ (F) = 0.0198, w R ref $w{R}_{\mathit{ref}}$ (F 2) = 0.0509, T = 200 K.

Crystal structure, vibrational frequencies and polarizability distribution in hydrogen-bonded salts of pyromellitic acid

Structural features of moderate-to-strong O—H...O hydrogen bonds are related to the frequencies of O—H stretching vibrations and to the electric polarizability distribution in the donor and acceptor functional groups for crystals synthesized from the 1,2,4,5-benzenetetracarboxylic (pyromellitic) acid, namely: bis(3-aminopyridinium) dihydrogen pyromellitate tetrahydrate, (1); bis(3-carboxypyridinium) dihydrogen pyromellitate, (2); bis(3-carboxyphenylammonium) dihydrogen pyromellitate dihydrate, (3); and bis(4-carboxyphenylammonium) dihydrogen pyromellitate, (4). A combination of single-crystal X-ray diffraction, powder Raman spectroscopy and first-principle calculations in both crystalline and gaseous phases has shown that changes in the O—H...O hydrogen-bond geometry can be followed by changes in the corresponding spectral modes. Vibrational properties of moderate hydrogen bonds can be estimated from correlations based on statistical analysis of several compounds [Novak (1974).Struct. Bond.18, 177–216]. However, frequencies related to very short O—H...O bonds can only be predicted by relationships built from a subset of structurally similar systems. Moreover, the way in which hydrogen bonds affect the polarizability of donor and acceptor groups depends on their strength. Moderate interactions enhance the polarizability and make it more anisotropic. Shorter hydrogen bonds may decrease the polarizability of a group as a consequence of the volume restraint implied by the neighbour molecule within a hydrogen-bonded aggregate. This is significant for evaluation of the electric susceptibility in crystals and, therefore, for estimation of refractive indices and birefringence.

Effect of carbon-skeleton isomerism on the dielectric properties and proton conduction of organic cocrystal compounds assembled from 1,2,4,5-benzenetetracarboxylic acid and piperazine derivatives

Two isostructural 2D supramolecular cocrystal compounds show different dielectric responses and proton conductivities due to the alteration of the carbon-skeleton of piperazine derivatives.

Copper pyromellitates: a complex story

Copper pyromellitate complexes range from unusual discrete molecular ions to 2- and 3-dimensional polymeric networks with considerable ligand structural versatility.

Role of the substituent effect over the squarate oxocarbonic ring: spectroscopy, crystal structure, and density functional theory calculations of 1,2-dianilinosquairane

This work presents the crystal structure and the investigation under a supramolecular perspective of a squaric acid derivative obtained from the replacement of the hydroxyl groups by anilines. The squaraine obtained (1,2-dianilinesquaraine) crystallizes in the Pbcn space group, in a unit cell with a = 26.5911(8) Å, b = 6.1445(10) Å, and c = 7.5515(5) Å. The bond lengths in the oxocarbon ring, squarate-N and C−O bonds present the character of double bonds. Also the difference between the longer and shorter C-C bond in the four-membered ring (ΔCC) is 0.0667 Å, showing a good degree of equalization of these bond lengths. The phenyl rings are slightly distorted in relation to the squarate ring, and the angle measured between the best plane fitted in each ring is 37.2(9)°. Each molecule is connected to the other through a hydrogen bond involving the N-H···O moieties, where the donor···acceptor distance is 2.826(1) Å, forming ribbons in a unidimensional arrangement C(5)R22(10) along the b axis. These structures are mutually connected by π-stacking interactions extending the supramolecular structure in a two-dimensional fashion. Besides, an interesting crossed structure can be easily identified in the formed sheets that are built through the C-H/π interactions. DFT calculations at the B3LYP/6-311++G(d,p) level of theory show an approximately planar molecular structure for the isolated molecule. However, when a dimer model built from hydrogen bonds is considered, the optimized structure presents considerable torsion between the phenyl and squarate rings, as observed in the experimental data. The electronic spectrum shows a strong absorption band at 341 nm that is red-shifted compared to the squarate maximum absorption (290 nm), indicating a more effective electronic delocalization. The most characteristic vibrational modes of the oxocarbon species were used as spectroscopic probe to understand how the substituent groups affect the oxocarbon moiety and, consequently, the vibrational spectra. The analysis shows that the modes associated with the C-Cox bonds are the most affected. Also the character of the double bond of squarate-N and the single bond for the phenyl-N are easily identified. In a general form, the calculated vibrational modes of the dimer model were in better accordance with the experimental data, mainly when the mode has a contribution from the acceptor molecule in the intermolecular interaction.

New insight on the investigation of the role of water in the solid-state structures of potassium croconate, K(2)C(5)O(5).2H(2)O, and its anhydrate

This work presents a comparative study of dihydrated and anhydrous forms of potassium croconate crystals by vibrational spectroscopy, X-ray powder diffraction, and thermogravimetry. These compounds have different colors (dihydrated is orange, and dehydrated is yellow) due to the presence of coordinated water molecules. X-ray diffraction patterns show that the unit cell of the yellow compound is smaller than that of the orange analogue, suggesting that the croconate ion layers are more closely bonded in this salt. The loss of water is reversible due to the potassium cation size which is intermediate between small (Li+ and Na+) and large (Rb+ and Cs+) alkaline metal ions. However, the hydrated compound (orange) is more stable, and with a small quantity of water the yellow compound is quickly converted to the orange compound. A diagnostic feature of the Raman spectrum for the orange (hydrated) and yellow (anhydrous) analogues is the singlet at 1240 cm(-1) in the former, assigned to a nu(CC) + delta(CCC) + nu(CO) + beta(CO) mode of E'2 symmetry, which splits in the yellow form to a doublet at 1256 and 1232 cm(-1).

A short hydrogen bond investigation by polarized Raman spectra of Co2+ and Zn2+ salts of pyromellitic acid

Cobalt and zinc salts of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), [C(6)H(2)(COO)(4)H(4)], have been synthesized and investigate by polarized Raman spectroscopy. These compounds present short intramolecular hydrogen bonds (SHB) between adjacent carboxyl groups. Raman spectra indicate the presence of this interaction in both salts. Three specific vibrational of SHB modes have been investigated: O-H-O symmetric [nu(sym)(OHO)] and asymmetric [nu(asym)(OHO)] stretching modes and O-H stretching mode [nu(O-H)], which they were observed around 300, 850 and 2500 cm(-1), respectively. In crystallographic point of view, the cobalt salt presents a symmetric SHB while the zinc salt presents an asymmetric SHB. In cobalt salt all three vibrational modes of O-H-O groups in polarized Raman spectra occur in A(g) orientation although in zinc salts two of them are observed in A(g) orientation and one in B(g). Spectra analysis indicate that nu(sym)(OHO) mode is observed as A(g) to cobalt salt and B(g) to zinc salt. This mode occurs in a crowded spectral region and its identification was made by deconvolution techniques. Comparing spectra of the two salts, it is observed a small difference in relative intensity and wavenumber shift of nu(sym)(OHO) (deviance of 43 cm(-1)) and nu(OH) (deviance of 21 cm(-1)) modes due probably to differences in O...O distance between salts and in orientation of pyromellitate anion in unit cell. The nu(asym)(OHO) mode does not present significant wavenumber shift due difference in SHB. The nu(OH) band presents a great potential for hydrogen bond studies due to the fact that in its vibrational region (around 2500 cm(-1)) it is not observed other vibrational modes of these compounds.

Vibrational spectra of Na, K, Mn2+, Ni2+ and Zn2+ salts of 1,2,4,5-benzenetetracarboxylic (pyromellitic) acid--a short hydrogen bond evidence

Five salts of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), [C6H2(COO)4H4], have been synthesized and investigated by infrared and Raman spectroscopy and by single crystal X-ray diffraction methods: sodium salt [Na2(H2O)2][C6H2(COO)4H2], potassium salt [K(H2O)3][C6H2(COO)4H3] and transition metal salts [M(H2O)6][C6H2(COO)4H2], which M = Mn, Ni and Zn. Crystal structures of all five compounds show short intramolecular asymmetric hydrogen bonds (SHB) between adjacent carboxyl groups with O...O distance average of 2.40 A. The Raman and infrared spectra reported indicate the presence of short hydrogen bonds in all salts, in agreement with the X-ray data. The O-H stretching mode [nu(OH)] had been observed at about 2500 cm(-1). Deuterated analogues were synthesized and their Raman spectra show that nu(OH)/nu(OD) ratio average is about unit. The symmetric [nu(sym)(O..H..O)] and asymmetric [nu(asym)(O..H..O)] stretching modes have been attributed about 300 and 870 cm(-1), respectively, in all salts, and for deuterated analogues, the ratio nu(OH)/nu(OD) to nu(sym)(O..H..O, O..D..O) is close to unit like it occurs in nu(OH). The vibrational modes, mainly SHB modes, are tentatively assigned by molecular orbital ab initio calculations of pyromellitic acid and anions [C6H2(COO)4H3]- and [C6H2(COO)4H2]2-. Geometry optimizations showed a good agreement with experimental data. Frequency calculation confirms the assignment of specific vibrational modes. Ab initio calculations show that nu(C=O) and nu(sym)(COO) are strongly coupled with in plane OH bending [delta(OH)]. In Raman spectra of deuterated analogues is observed a frequency shift of these bands.