Metal-organic frameworks in cadmium(II) complexes with 5-methoxyindole-2-carboxylic acid: structure, vibrational spectra and DFT calculations

Power of Infrared and Raman Spectroscopies to Characterize Metal-Organic Frameworks and Investigate Their Interaction with Guest Molecules

“…The value of the spectral split between the (COO – ) modes, Δν exp , is widely used to conclude on the coordination mode of different carboxylates and the observations were reviewed by Deacon and Phillips . However, it was underlined that this criterion should be taken with care . The split typical of the ionic form (sodium salts) is usually used as a reference value ( ca .…”

“…76 However, it was underlined that this criterion should be taken with care. 77 The split typical of the ionic form (sodium salts) is usually used as a reference value (ca. 200 cm −1 for formates and 164−171 cm −1 for acetates).…”

Synthesis, Structural Diversity, and Properties of Cd Metal–Organic Frameworks Based on 2-(5-Bromo-pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate and N-Heterocyclic Ancillary Ligands

“…Compounds 1 – 5 all exhibited one emission band centered at 421, 448, 449, 444, and 400 nm upon excitation at 366, 365, 383, 362, and 345 nm, respectively (Figure ). In combination with the emission spectra of free ligands H 3 L, phen, bpy, and pbim (Figures S13 and S14), the emission bands of 1 – 5 that slightly blue- or red-shift from the 425 nm emission of free ligand H 3 L can be mainly attributed to the intraligand π–π* transitions of (HL) 2– ligands, which can be compared with those emissions reported for cadmium­(II) complexes with other N-donor ligands. − ,− The differences in the excitation and emission energies for 1 – 5 are dependent on metal–ligand perturbations and thereby on the coordination geometries of Cd II in every compound. Additionally, the relatively broad emission bands for 3 – 5 indicate some contribution from the intraligand π–π* transitions of the auxiliary ligands phen, bpy, and pbim.…”

“…Cd4 is five-coordinated by two N and three O atoms from two trans -chelating imidazoledicarboxylates of two (HL) 2– ligands and a water molecule and thereby form a distorted trigonal bipyramid geometry with the three coordinated O atoms in the equatorial plane and the two N atoms at the apical sites (the bond lengths of Cd–N and Cd–O range from 2.184(10) to 2.278(5) Å). Notably, the bond lengths of Cd–N and Cd–O in 2 comparatively shorten with the decrease of coordination number of Cd II ions from 7 to 5 but fall in the normal ranges. − As for the four crystallographically independent (HL) 2– ligands, two of them adopt μ 3 - k N,O: k N′,O′: k N″ coordination mode observed in 1 to connect Cd1, Cd3 (Cd3E), and Cd4 (Cd4C), one adopts μ 3 - k N,O: k N′,O′: k O″ coordination mode to bridge Cd1, Cd2, and Cd2D, and the other adopts μ- k N,O: k N′,O′ coordination mode to chelate Cd2 and Cd3 (Figure ). In 2 , the four crystallographically independent (HL) 2– ligands vary the dihedral angles between their imidazole and pyridyl groups from 21.1(3) to 32.7(3)°, matching the coordination requirements in different conformers.…”

“…In this context, as well as further pursuing our work in this area, we designed and synthesized 2-(5-bromo-pyridin-3-yl)-1 H -imidazole-4,5-dicarboxylic acid (H 3 L), another compound analogous to our previously reported pyridyl-containing H 3 IDC derivatives (Scheme ). , In contrast with 2-(pyridine-3-yl)-1 H -4,5-imidazoledicarboxylic acid ligand, the additional halogen atom Br in H 3 L not only provides halogen-related interactions to extend the dimensions of the resulting MOFs but also influences the photoelectric properties and chemical environment of the MOFs, which has become quite attractive in recent crystal engineering. , In this paper, cadmium­(II) ion, one of currently used metal ions for the construction of functional MOFs, has been selected as a metal center to incorporate into our H 3 L-based MOFs due to its labile coordination number and the interesting fluorescence of its complexes. − As is well-known, the combination of different ligands may result in greater tunability than that present with only a single ligand to construct MOFs, − and thus, a series of N-heterocyclic ligands such as planar chelating ligand 1,10-phenanthroline (phen), rodlike bridge 4,4′-bipyridine (bpy), and V-shaped bridge 1,1′-(5-methyl-1,3-phenylene)­bis­(1 H -imidazole) (pbim) are chosen as auxiliary ligands in our present work (Scheme ). By doing so, we hope to modulate the structures and properties of H 3 L-based Cd–MOFs through the different structure types and coordination tendencies of the additional ligands and to further understand the assembly principles in a mixed ligand system as well.…”