Methanol Solvent Mol-ecule Research Articles

Synthesis, Spectroscopic Characterization, Crystal Structures and Antibacterial Activity of Vanadium(V) Complexes of Fluoro- and Chloro-Substituted Benzohydrazone Ligands

A new vanadium(V) complex, [VOL(OMe)(MeOH)]·MeOH (1·MeOH), was prepared by the reaction of VO(acac)2 with 2-chloro-N'-(5-fluoro-2-hydroxybenzylidene)benzohydrazide (H2L) in methanol. By addition of salicylhydroxamic acid (HSHA) to the methanolic solution of 1, a new salicylhydroxamate-coordinated vanadium(V) complex, [VOL(SHA)]·H2O (2·H2O), was obtained. Both complexes were characterized by elemental analysis, infrared spectroscopy, thermal analysis and single crystal X-ray diffraction. Complex 1 crystallizes with methanol molecule as a solvate, and complex 2 as a monohydrate. The V atoms in the complexes are in octahedral coordination. In the crystal structure of 1·MeOH, the vanadium complexes are linked by methanol solvate molecules through intermolecular O-H∙∙∙N and O-H∙∙∙O hydrogen bonds to form chains along the c axis. In the crystal structure of 2·H2O, the vanadium complexes are linked by water molecules through intermolecular O-H∙∙∙O hydrogen bonds, to form 1D chains along the a axis. The chains are further linked through intermolecular O-H∙∙∙N and O-H∙∙∙O hydrogen bonds in the c direction to form 2D layers. The antimicrobial activities of the complexes against K. pneumoniae, S. aureus, P. aeroginosa, E. coli, and B. subtilis were investigated.

Dinuclear lanthanoid(III) dithiocarbamato complexes bridged by (E)-N-benzylidenepicolinohydrazonate: Syntheses, crystal structures and spectroscopic properties

(E)-N-Benzylidenepicolinohydrazide (Hbphz) was used to synthesize a series of hydrazonato-bridged homodinuclear LnIII2 dithiocarbamato (RR′dtc−) complexes of the form [{Ln(RR′ dtc)2}2(µ-bphz)2] {Ln = La, Pr, Nd, Sm or Eu; RR′ = dimethyl-(Me2) or pyrrolidine-(pyr)}. X-ray crystallographic studies revealed that these complexes possessed a common head-to-tail type dinuclear structural motif in which two hydrazonato ligands bridged two LnIII centers in the μ − 1 κ2N(py),O:2 κ2O,N(imine) mode and two RR′dtc ligands coordinated to each LnIII center. Interestingly, while the SmIII and EuIII complexes crystallized as simple 8:8-coordinate dinuclear molecules, the lighter LnIII (i.e. LaIII, PrIII and NdIII) complexes afforded in some cases 9:9-coordinate molecules, where the ninth coordination site was occupied by a solvent ethanol or methanol molecule. Even for the lighter LnIII complexes, the complexes were solved in dichloromethane or chloroform as the 8:8-coordinate dimer, as revealed by 1H NMR spectroscopy. In the UV–visible absorption and magnetic circular dichroism (MCD) spectra of the complexes, similar spectral patterns for ligand-centered and Laporte forbidden f–f transitions were observed. The MCD spectral studies demonstrated the characteristic magneto-optical behavior of the complexes.

Palladium(II) complexes of a bridging amine bis-(phenolate) ligand featuring κ2 and κ3 coordination modes.

Bidentate and tridentate coordination of a 2,4-di-tert-butyl-substituted bridging amine bis-(phenolate) ligand to a palladium(II) center are observed within the same crystal structure, namely di-chlorido-({6,6'-[(ethane-1,2-diylbis(methyl-aza-nedi-yl)]bis-(methyl-ene)}bis-(2,4-di-tert-butyl-phenol))palladium(II) chlorido-(2,4-di-tert-butyl-6-{[(2-{[(3,5-di-tert-butyl-2-hy-droxy-phen-yl)meth-yl](meth-yl)amino}-eth-yl)(meth-yl)amino]-meth-yl}phenolato)palladium(II) methanol 1.685-solvate 0.315-hydrate, [PdCl2(C34H56N2O2)][PdCl(C34H55N2O2)]·1.685CH3OH·0.315H2O. Both complexes exhibit a square-planar geometry, with unbound phenol moieties participating in inter-molecular hydrogen bonding with co-crystallized water and methanol. The presence of both κ2 and κ3 coordination modes arising from the same solution suggest a dynamic process in which phenol donors may coordinate or dissociate from the metal center, and offers insight into catalyst speciation throughout Pd-mediated processes. The unit cell contains di-chlorido-({6,6'-[(ethane-1,2-diylbis(methyl-aza-nedi-yl)]bis-(methyl-ene)}bis-(2,4-di-tert-butyl-phenol))palladium(II), {(L 2)PdCl2}, and chlorido-(2,4-di-tert-butyl-6-{[(2-{[(3,5-di-tert-butyl-2-hy-droxy-phen-yl)meth-yl](methyl)amino}eth-yl)(meth-yl)amino]-meth-yl}phenolato)palladium(II), {(L 2 X)PdCl}, mol-ecules as well as fractional water and methanol solvent mol-ecules.

Crystal structure of hexa-μ-chlorido-μ4-oxido-tetra-kis-{[1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazole-κN 3]copper(II)} containing short NO2⋯NO2 contacts.

The title tetra-nuclear copper complex, [Cu4Cl6O(C6H9N3O3)4] or [Cu4Cl6O-(MET)4] [MET is 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazole or metronidazole], contains a tetra-hedral arrangement of copper(II) ions. Each copper atom is also linked to the other three copper atoms in the tetra-hedron via bridging chloride ions. A fifth coordination position on each metal atom is occupied by a nitro-gen atom of the monodentate MET ligand. The result is a distorted CuCl3NO trigonal-bipyramidal coordination polyhedron with the axial positions occupied by oxygen and nitro-gen atoms. The extended structure displays O-H⋯O hydrogen bonding, as well as unusual short O⋯N inter-actions [2.775 (4) Å] between the nitro groups of adjacent clusters that are oriented perpendicular to each other. The scattering contribution of disordered water and methanol solvent mol-ecules was removed using the SQUEEZE procedure [Spek (2015 ▸). Acta Cryst. C71, 9-16] in PLATON [Spek (2009 ▸). Acta Cryst. D65, 148-155].

Complexation of Lanthanides with N, N, N', N'-Tetramethylamide Derivatives of Bipyridinedicarboxylic Acid and Phenanthrolinedicarboxylic Acid: Thermodynamics and Coordination Modes.

The thermodynamics of Nd(III) and Eu(III) complexes with N, N, N', N'-tetramethyl-2,2'-bipyridine-6,6'-dicarboxamide (TMBiPDA) and N, N, N', N'-tetramethyl-1,10-phenanthroline-2,9-dicarboxamide (TMPhenDA) in CH3OH/10%(v)H2O solutions were studied. Stability constants and enthalpies of complexation were determined by absorption spectrophotometry, luminescence, and calorimetry. The stability constants of corresponding lanthanide complexes decrease in the order of TMPhenDA > TMBiPDA, while those of the corresponding ligand complexes with lanthanides decrease in the order of Nd(III) > Eu(III). The stepwise reactions for all 1:1 complexes as well as for the 1:2 Nd(III) complexes are driven by both enthalpy and entropy, while those for the 1:2 Eu(III) complexes are driven by entropy. The stronger affinity of TMPhenDA to Nd(III) and Eu(III) than that of TMBiPDA is predominantly arisen from its high preorganization. The spectra of the complexes in solutions are similar, implying that Nd(III) and Eu(III) coordinate with the two ligands in the same mode, which have been validated by 1H and 13C NMR titrations using La(III) as lanthanide tracer. The luminescence lifetimes of the Eu(III) complexes with TMBiPDA and TMPhenDA were evaluated by TRLFS. Structures of Nd(III)/TMPhenDA and Eu(III)/TMPhenDA complexes, identified by single-crystal X-ray diffractometry, show that ligand coordinates to metal in a tetradentate mode via two aromatic N-donors and two amide O-donors, and the central cation (Nd(III) or Eu(III)) is 10-coordinated by two whole TMPhenDA and two solvent (water or methanol) molecules. The M-O bond distances are almost identical, while the Nd-N bond distance is shorter than the Eu-O bond.

Structure and magnetic properties of two new lanthanide complexes with the 1-((E)-2-pyridinylmethylidene)semicarbazone ligand

Two novel semicarbazone-lanthanide(III) complexes were prepared and structurally characterized as [Ln (Hscpy)2 (NO3)2]NO3·MeOH (Ln = Gd and Tb; Hscpy = 1-((E)-2-pyridinylmethylidene)semicarbazone). The 4f metal ions experience deca-coordination geometry. Each molecular formula contains two neutral Hscpy molecules in the keto form coordinated through two nitrogen atoms and one oxygen atom, while two nitrate ligands are both coordinated in a chelate mode. The 1 + charge of the cation-complex is balanced by a nitrate anion. Extensive intermolecular hydrogen bonds are formed through the methanol solvate molecule, which acts both as a donor and an acceptor molecule. The chemical composition of the compounds was confirmed by high resolution mass spectra (ESI-MS); peaks at m/z = 122.07 and 148.05, assigned to the fragments C6H8N3+ and C7H6N3O+, respectively, are in agreement with the coordination of Hscpy. Alternating current magnetic susceptibility analysis was performed in the 10–10000 Hz range, and the terbium-complex showed slow relaxation of the magnetization when immersed in a static magnetic field of 1 kOe and 1.5 kOe, with an activation barrier to the relaxation (21.9(4) cm−1) among the highest found for ten-coordinated Tb(III) complexes. This behavior of slow relaxation of the magnetization is relevant as a memory effect regarding the development of Single Molecule Magnets (SMM).

(Methanol-κO)bis(thiocyanato-κN)[2,4,6-tris(pyridin-2-yl)-1,3,5-triazine-κ3N2,N1,N6]nickel(II) methanol monosolvate

In the structure of the title compound, [Ni(NCS)2(C18H12N6)(CH3OH)]·CH3OH, the NiIIion is six-coordinated in an octahedral coordination environment defined by three N atoms from a 2,4,6-tris(pyridin-2-yl)-1,3,5-triazine ligand, two N atoms from two mutuallycis-positioned SCN−anions and one O atom from a methanol ligand. The complex and methanol solvent molecules are linked by intermolecular hydrogen bonds. In the crystal, the complex molecules are stacked in columns parallel to thebaxis.

Crystal structure of 4-[(3-meth-oxy-2-oxidobenzyl-idene)azaniumyl]-benzoic acid methanol monosolvate.

In the crystal of the title compound, C15H13NO4·CH3OH, the Schiff base mol-ecule exists in the zwitterionic form; an intra-molecular N-H⋯O hydrogen bond stabilizes the mol-ecular structure. The benzene rings are nearly co-planar, subtending a dihedral angle of 5.34 (2)°. In the crystal, classical O-H⋯O and weak C-H⋯O hydrogen bonds link the Schiff base mol-ecules and methanol solvent mol-ecules into a three-dimensional supra-molecular architecture. The crystal studied was refined as an inversion twin.

Crystal structure of (methanol-κO)[5,10,15,20-tetra-kis-(2-amino-phen-yl)porphyrinato-κ4N]zinc(II)-chloro-form-methanol (1/1/1).

In the crystal structure of the title compound, [Zn(C44H32N8)(CH3OH)]·CHCl3·CH3OH, the ZnII cation is coordinated by four porphyrin N and one methanol O atom within a slightly distorted square-pyramidal environment and is shifted out of the porphyrin plane towards the direction of the methanol mol-ecule. The methyl group of the coordinating methanol mol-ecule is disordered over two sets of sites. The porphyrin backbone is nearly planar and the phenyl rings are almost perpendicular to the porphyrin plane. As is typical for picket-fence porphyrins, all four ortho substituents of the meso-phenyl groups (here the amino groups) are facing to the same side of the porphyrin mol-ecule. In the crystal structure, two neighbouring porphyrin complexes form centrosymmetric dimers that are connected via O-H⋯N hydrogen bonding. With the aid of additional N-H⋯N and C-H⋯N hydrogen bonding, these dimers are stacked into columns parallel to [010] that are finally arranged into layers parallel to (001). Between these layers channels are formed where chloro-form solvent mol-ecules are located that are connected to the porphyrin complexes by weak C-H⋯Cl hydrogen bonding. There are additional cavities in the structure where some small residual electron density is found, indicating the presence of disordered methanol mol-ecules, but a reasonable model could not be refined. Therefore the contribution of the electron density associated with the methanol solvent mol-ecule was removed with the SQUEEZE procedure [Spek (2015 ▸). Acta Cryst. C71, 9-18] in PLATON. Nevertheless, the given chemical formula and other crystal data take into account the methanol solvent mol-ecule.

The crystal structure of bis-[(E)-4-bromo-2-({[2-(pyridin-2-yl)eth-yl]imino}-meth-yl)phenol]nickel(II) bis-[(E)-4-bromo-2-({[2-(pyridin-2-yl)eth-yl]imino}-meth-yl)phenolato]nickel(II) bis(perchlorate) methanol monosolvate, a structure containing strong inter-species hydrogen bonds.

The title compound, [Ni(C14H12BrN2O)2][Ni(C14H13BrN2O)2](ClO4)2·CH3OH consists of two mononuclear ([Ni(HL)2]2+ and [NiL2]) complex mol-ecules linked by strong hydrogen bonding [O⋯O separations of only 2.430 (5) Å], which is the shortest reported to date for such species. In one of the complexes, both the coordinated phen-oxy groups retain their protons and thus this is the cationic equivalent species of the other complex where both coordinated phen-oxy groups are deprotonated. In addition, perchlorate anions are present for charge balance, as well as methanol solvate mol-ecules. For the neutral NiL2 complex, each 2-ethyl-amine-pyridine arm is disordered over two equivalent conformations with occupancies of 0.750 (8):0.250 (8). The perchlorate anion is disordered over two equivalent conformations with occupancies of 0.602 (8):0.398 (8). The perchlorate ions also link to the H atoms on the methanol methyl and hydroxyl groups. These inter-actions link the moieties into a complex three-dimensional array. The crystal studied was refined as a two-component twin.

Crystal structures of (aceto-nitrile-κN)tris-(pyridine-4-thio-amide-κN)bis-(thio-cyanate-κN)cobalt(II) aceto-nitrile disolvate and tetra-kis-(pyridine-4-thio-amide-κN)bis-(thio-cyanate-κN)nickel(II) methanol penta-solvate.

Reaction of Co(NCS)2 or Ni(NCS)2 with pyridine-4-thio-amide in different solvents led to the formation of two compounds with composition [Co(NCS)2(C2H3N)(C6H6N2S)3]·2CH3CN (1) and [Ni(NCS)2(C6H6N2S)4]·5CH3OH (2), respectively. The asymmetric unit of compound 1 consists of one cobalt(II) cation, two thio-cyanate anions, three pyridine-4-thio-amide ligands, one coordinating and two solvate aceto-nitrile mol-ecules. One of the two aceto-nitrile solvate mol-ecules is disordered over two sets of sites in a 0.62:0.38 ratio. The asymmetric unit of compound 2 comprises of one nickel(II) cation, two thio-cyanate anions, four N-bonding pyridine-4-thio-amide ligands and five methanol solvate mol-ecules. In compound 1, the cobalt(II) cations are octa-hedrally coordinated into discrete complexes by two terminal N-bonding thio-cyanate anions, the N atoms of three pyridine-4-thio-amide ligands and one aceto-nitrile mol-ecule. Additional aceto-nitrile solvate mol-ecules are located between the complexes,. The complexes and solvate mol-ecules are linked via inter-molecular hydrogen bonding into a three-dimensional framework. In compound 2, the nickel(II) cations are likewise octa-hedrally coordinated by two terminal N-bonded thio-cyanate anions and four N-bonding pyridine-4-thio-amide ligands into discrete complexes. From their arrangement cavities are formed, in which the methanol solvate mol-ecules are located. Again, the complexes and solvate mol-ecules are linked into a three-dimensional framework by inter-molecular hydrogen bonding.

Crystal structure of 2-{5-[2-(2-hy-droxy-phen-yl)diazen-1-yl]-1-methyl-pyrrol-2-yl}phenol methanol monosolvate.

In the title azo-pyrrole compound, C17H15N3O2·CH3OH, the azo N=N bond adopts a trans configuration and the pyrrole N and azo group are in an anti orientation. The dihedral angles between the pyrrole ring and the two phenyl rings are 6.7 (3) and 54.7 (3)°. In the crystal, a supra-molecular ring structure is formed between two azo-pyrrole and two methanol solvent mol-ecules through four O-H⋯O hydrogen bonds.

Crystal structures of 5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-decane cobalt(III) mono-phenyl-acetyl-ide and bis-phenyl-acetyl-ide.

Reported in this contribution are the synthesis and crystal structures of new mono- and bis-phenyl-acetyl-ides based on CoIII(DMC) (DMC is 5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne). Chlorido-(5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)(phenyl-ethyn-yl)cobalt(III) chloride-aceto-nitrile-methanol (1/1/1), [Co(C8H5)Cl(C12H28N4)]Cl·CH3CN·CH3OH, 1, and (5,12-dimethyl-1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)bis-(phenyl-ethyn-yl)cobalt(III) tri-fluoro-methane-sulfonate-di-chloro-methane (2/1), [Co(C8H5)2(C12H28N4)]2(CF3SO3)2·CH2Cl2, 2, were prepared under weak-base conditions in satisfactory yields. Single-crystal X-ray diffraction studies revealed that both 1 and 2 adopt a pseudo-octa-hedral symmetry in which the Cl-Co-C angles of 1 and C-Co-C of 2 range from 177.7 (2) to 178.0 (2)° and from 177.67 (9) to 179.67 (9)°, respectively. In both structures, the CoIII metal center is coordinated in the equatorial plane by four N atoms, in which the N-Co-N angles range from 85.6 (3) to 94.4 (3)°. The structure of 1 features two crystallographically independent mol-ecules in its triclinic cell (Z' = 2), which are related to each other by pseudo-monoclinic symmetry. The crystal investigated was twinned by a symmetry operator of the approximate double-volume C-centered cell (180° rotation around [201] of the actual triclinic cell), with a refined twin ratio of 0.798 (3) to 0.202 (3). Both methanol solvent mol-ecules in 1 are disordered, the major occupancy rates refined to 0.643 (16) and 0.357 (16). Compound 2 also contains two mol-ecules in the asymmetric unit, together with two tri-fluoro-methane-sulfonate anions [of which one is disordered; occupancy values of 0.503 (16) and 0.497 (16)] and a disordered di-chloro-methane [occupancy values of 0.545 (12) and 0.455 (12)].

Binuclear Triphenylantimony(V) Catecholate Based on Redox-Active Bis-o-Benzoquinone, a Bis-Catechol-Aldimine Derivative

The oxidative addition of bis-o-benzoquinone Q–(CH=N–N=CH)–Q (L), in which two 3,5-ditert-butyl-o-benzoquinones are linked to each other in positions 6 via the CH=N–N=CH group, to triphenylstibine gave a new binuclear triphenylantimony(V) bis-catecholate complex, Ph3Sb(Cat–(CH=N–N=CH)–Cat)SbPh3 (I). Recrystallization of I from a methanol–trichloromethane mixture resulted in an additional coordination of a methanol molecule to each antimony atom to give the binuclear complex, (CH3OH)Ph3Sb(Cat–(CH=N–N=CH)–Cat)SbPh3(CH3OH) (I · 2CH3OH), the crystals of which (I · 2CH3OH) · 2CH3OH · CHCl3 (II) contain additionally two methanol solvate molecules, which fix the geometry of the nitrogen-containing bridging group, and a trichloromethane molecule. The molecular structure of compound II in the crystalline state was determined by X-ray diffraction (CIF file CCDC no. 1560840).

Bis(4-aminophenylhydroxamato-κ2 O,O′)copper(II) methanol disolvate

In the title complex, [Cu(C7H7N2O2)2]·2CH3OH, the metal centre is coordinated by two 4-aminophenylhydroxamate bidentate ligands, in a distorted square-planar geometry. The asymmetric unit is completed by two methanol solvent molecules, which are involved in hydrogen bonding with N—H functionalities of the free hydroxamate groups. The crystal structure also features N—H...O bonds formed by the NH2 groups, and O—H...O hydrogen bonds with the methanol solvent molecules as donors.

Crystal structure of bis-(pyridine-4-carbo-thio-amide-κN1)bis-(thio-cyanato-κN)cobalt(II) methanol monosolvate.

The asymmetric unit of the title compound, [Co(NCS)2(C6H6NS)4]·CH3OH, consists of one cobalt(II) cation, two thio-cyanate anions, four pyridine-4-carbo-thio-amide ligands and one methanol mol-ecule that are located in general positions. The CoII cations are coordinated by two terminal N-bonding thio-cyanate anions and four N-bonding pyridine-4-carbo-thio-amide ligands, resulting in discrete and slightly distorted octa-hedral complexes. These complexes are linked into a three-dimensional network via inter-molecular N-H⋯S hydrogen bonding between the amino H atoms and the thio-cyanate and pyridine-4-carbo-thio-amide S atoms. From this arrangement, channels are formed in which the methanol solvate mol-ecules are embedded and linked to the host structure by inter-molecular O-H⋯S and N-H⋯O hydrogen bonding.

Elaborating the excited state behavior of 2‐(4′‐N,N‐dimethylaminophenyl)‐imidazo[4,5‐c]pyridine coupling with methanol solvent

AbstractWe present a theoretical investigation about the excited state dynamical mechanism of 2‐(4′‐N,N‐dimethylaminophenyl)‐imidazo[4,5‐c]pyridine (DMAPIP‐c). Within the framework of density functional theory and time‐dependent density functional theory methods, we reasonably repeat the experimental electronic spectra, which further confirm the theoretical level used in this work is feasible. Given the best complex model, 3 methanol (MeOH) solvent molecules should be connected with DMAPIP‐c forming DMAPIP‐c‐MeOH complex in both ground state and excited state. Exploring the changes about bond lengths and bond angles involved in hydrogen bond wires, we find the O7‐H8···N9 one should be largely strengthened in the S1 state, which plays an important role in facilitating the excited state intermolecular proton transfer (ESIPT) process. In addition, the analyses about infrared vibrational spectra also confirm this conclusion. The redistribution about charges distinguished via frontier molecular orbitals based on the photoexcitation, we do find tendency of ESIPT reaction due to the most charges located around N9 atom in the lowest unoccupied molecular orbital. Based on constructing the potential energy curves of both S0 and S1 states, we not only confirm that the ESIPT process should firstly occur along with hydrogen bond wire O7‐H8···N9, but also find a low potential energy barrier 8.898 kcal/mol supports the ESIPT reaction in the S1 state forming DMAPIP‐c‐MeOH‐PT configuration. Subsequently, DMAPIP‐c‐MeOH‐PT could twist its dimethylamino moiety with a lower barrier 3.475 kcal/mol forming DMAPIP‐c‐MeOH‐PT‐TICT structure. Our work not only successfully explains previous experimental work but also paves the way for the further applications about DMAPIP‐c sensor in future.

Bis(3,5-dimeth-oxy-2-{[2-(pyridin-2-yl)ethyl-imino-κN]-meth-yl}phenolato-κO)bis-(dimethyl sulfoxide)-manganese(III) perchlorate methanol 0.774-solvate.

The title compound, [Mn(C16H17N2O3)2(C2H6OS)2]ClO4·0.774CH3OH, comprises a central octa-hedrally coordinated MnIII cation, with two bidentate Schiff base ligands occupying the equatorial positions and two dimethyl sulfoxide (DMSO) ligands occupying the axial positions. There are two independant cations in the asymmetric unit, with the MnIII atoms of both cations being positioned on crystallographic centers of inversion. The perchlorate anion is disordered over two equivalent conformations, with occupancies of 0.744 (3) and 0.226 (3). In addition, there is a methanol solvent mol-ecule in the crystal lattice that is too close to the minor component of the perchlorate anion to be present simultaneously and thus it was refined to have the same occupancy as the major component of this anion. There is a Jahn-Teller distortion which results in Mn-ODMSO axial bond lengths of 2.2365 (12) and 2.2368 (12) Å in the two cations. In the crystal, inter-molecular π-π stacking between the non-coordinating pyridine rings of each cation is observed. This π-π stacking, along with extensive O-H⋯O hydrogen bonding and C-H⋯O inter-actions, link the components into a complex three-dimensional array.

Exploring the excited state behavior for 2-(phenyl)imidazo[4,5-c]pyridine in methanol solvent

In this present work, we theoretically investigate the excited state mechanism for the 2-(phenyl)imidazo[4,5-c]pyridine (PIP-C) molecule combined with methanol (MeOH) solvent molecules. Three MeOH molecules should be connected with PIP-C forming stable PIP-C-MeOH complex in the S0 state. Upon the photo-excitation, the hydrogen bonded wires are strengthened in the S1 state. Particularly the deprotonation process of PIP-C facilitates the excited state intermolecular proton transfer (ESIPT) process. In our work, we do verify that the ESIPT reaction should occur due to the low potential energy barrier 8.785 kcal/mol in the S1 state. While the intersection of potential energy curves of S0 and S1 states result in the nonradiation transition from S1 to S0 state, which successfully explain why the emission peak of the proton-transfer PIP-C-MeOH-PT form could not be reported in previous experiment. As a whole, this work not only put forward a new excited state mechanism for PIP-C system, but also compensates for the defects about mechanism in previous experiment.

Explaining the excited state behavior of t-DMASIP-b sensor: A theoretical study

In this present work, we theoretically investigate the excited state dynamical mechanism of a novel sensor trans-2-[4′-(N,N-dimethylamino)styryl]imidazo[4,5-b]pyridine (t-DMASIP-b). Within the framework of density functional theory (DFT) and time dependent DFT (TDDFT) methods, we reasonably repeat the experimental electronic spectra, which further confirm the theoretical level used in this work is feasible. Given the best complex model, two methanol (MeOH) solvent molecules should be connected with t-DMASIP-b forming t-DMASIP-b-MeOH complex in both ground state and excited state. Exploring the changes about bond lengths and bond angles involved in hydrogen bond wires, we find the O5-H6⋯N7 one should be largely strengthened in the S1 state, which might facilitate the excited state intermolecular proton transfer (ESIPT) process. In addition, the analyses about infrared (IR) vibrational spectra also confirm this conclusion. The redistribution about charges distinguished via frontier molecular orbitals (MOs) based on the photo-excitation, we do find tendency of ESIPT reaction due to the most charges located around N7 atom in the LUMO orbital. Even though some indications reveal the ESIPT, we find the moderate potential energy barriers in the S1-state potential energy curves. The moderate potential energy barrier 12.89kcal/mol along with O5-H6⋯N7 hydrogen bonding wire indeed hinders the proceeding of ESIPT, so only one fluorescence peak was reported in previous experiment, which has been reasonably explained in our work. As a whole, we deem our work not only successfully explains previous experimental work, but also paves the way for the further applications about t-DMASIP-b sensor in future.