Mer Isomers Research Articles

A DFT Analysis of Structural and Electronic Features of [Mo(CO)6‐n(SiX)n] (n=1, 2 and 3, and X=O, S, Se and Te) Complexes

AbstractDFT was used to analyze the molecular and electronic structures of the mono, di‐ and tri‐substituted isomers of [Mo(CO)6‐n(SiX)n] (where, X=O, S, Se, Te) and they were compared to the Mo(CO)6 complex. The total energy of all the complexes indicates that the trans isomer is slightly more stable than the cis isomer, but the stability of the fac and mer isomers is comparable. The HOMO‐LUMO energy gap of the complexes was determined and it indicated that the energy gap of the newly designed complexes is smaller than that of the parent complex Mo(CO)6 (1), ranging from 3.45–5.08 eV for the complexes 2–21. The FMO analysis of 2–21 showed that they are more reactive than complex 1. Insights on the bonding nature of these complexes are provided by the NPA, NBO, and EDA studies. The bond contribution from the Si atom in the Mo−Si bond is greater than that from the Mo atom, based on the NBO study. However, the C atom contributes more to the Mo−CO bond as well. Atomic charges on the Mo atom have a higher negative charge and the Si atom shows a positive charge in all the complexes. This study provides valuable information about the isolobal and isoelectronic nature of different substitutions of Si−X bonds at different positions instead of CO molecule in [Mo(CO)6].

A cobalt templated outer sphere hydrogen bond donor catalyst derived from 2-guanidinobenzimidazole: Synthesis, applications in carbon–carbon bond forming reactions, structure

A lipophilic tricationic cobalt tris(chelate) complex of 2-guanidinobenzimidazole (GBI), [Co(GBI)3]3+ 3BArf– (23+ 3BArf–; BArf = B(3,5-C6H3(CF3)2)4), is prepared from the corresponding hydrophilic trichloride salt and Na+ BArf– or Ag+ BArf– under aqueous/organic biphasic conditions. This racemic chiral complex, which is obtained as a mer isomer and a tetradecahydrate as assayed by NMR and TGA, is an excellent catalyst for additions of dimethyl malonate and indole to trans-ß-nitrostyrenes (10 mol%), and cycloadditions of CO2 to epoxides (1 mol%; solvent-free). Average yields (84 %, 91 %, 81 %) and rates are slightly greater than those obtained with a monocationic ruthenium GBI complex [(η5-C5H5)Ru(CO)(GBI)]+ BArf– prepared earlier. Attempted crystallization of 23+ 3Cl– gives a tetramethanol solvate of a salt derived from loss of two molecules of HCl. This can be represented as [Co(GBI)(GBI–H)2]+ Cl−, and bond lengths and hydrogen bonding motifs are carefully analyzed, especially in the context of dominant chelate resonance forms.

Spectroscopic and DFT study of tris(β-diketonato)cobalt(III) complexes

Nuclear magnetic resonance measurements confirm that, as expected, the mer isomer of tris(β-diketonato) cobalt(III) complexes is more stable ( mer isomers are more stable because they are less affected by steric hindrance and they have lower dipoles). An excess of the mer isomer or only the mer isomer is experimentally observed. The existence of both fac and mer isomers is predicted by density functional theory calculations. At room temperature, the nuclear magnetic resonance peaks of phenyl-containing mer complexes are broad due to the intermediate rotation of bulky phenyl groups resulting in only the average orientation of the non-equivalent protons in the mer complexes. However, upon heating to 55 °C (thus speeding up the rotation) or cooling to −50 °C (slowing down the rotation), this broad peak is resolved into three sets of carbon peaks appearing in the 13C NMR spectrum, as well as splitting of the 1H NMR peaks for the non-equivalent protons in the mer isomer. In solid-state 13C NMR the aromatic rings do not rotate, resulting in the splitting of all the 13C NMR peaks. Two sets of well-defined peaks are observed for the fluorine-containing compound [Co(CF3COCHCOCPh)3] in both the 13C and 19F NMR spectra, indicating that both the fac and mer isomers are present with a ratio of fac:mer = 0.1:1. The X-ray photoelectron spectroscopy measured binding energy of the Co 2p3/2 photoelectron lines are influenced by the subtle electronic (electron-donating or electron-withdrawing) properties of the R groups on the β-diketonato ligands. Various relationships are established between the binding energy of Co 2p3/2 and several physical and density functional theory–calculated properties, confirming good electronic communication (the measurable electronic effect that a molecular fragment has on the physical properties of another molecular fragment in the molecule) of the substituent groups through the pseudo aromatic system of the β-diketonato backbones to the metal.

A Series of Non-Oxido VIV Complexes of Dibasic ONS Donor Ligands: Solution Stability, Chemical Transformations, Protein Interactions, and Antiproliferative Activity.

A series of mononuclear non-oxido vanadium(IV) complexes, [VIV(L1-4)2] (1-4), featuring tridentate bi-negative ONS chelating S-alkyl/aryl-substituted dithiocarbazate ligands H2L1-4, are reported. All the synthesized non-oxido VIV compounds are characterized by elemental analysis, spectroscopy (IR, UV-vis, and EPR), ESI-MS, as well as electrochemical techniques (cyclic voltammetry). Single-crystal X-ray diffraction studies of 1-3 reveal that the mononuclear non-oxido VIV complexes show distorted octahedral (1 and 2) or trigonal prismatic (3) arrangement around the non-oxido VIV center. EPR and DFT data indicate the coexistence of mer and fac isomers in solution, and ESI-MS results suggest a partial oxidation of [VIV(L1-4)2] to [VV(L1-4)2]+ and [VVO2(L1-4)]-; therefore, all these three complexes are plausible active species. Complexes 1-4 interact with bovine serum albumin (BSA) with a moderate binding affinity, and docking calculations reveal non-covalent interactions with different regions of BSA, particularly with Tyr, Lys, Arg, and Thr residues. In vitro cytotoxic activity of all complexes is assayed against the HT-29 (colon cancer) and HeLa (cervical cancer) cells and compared with the NIH-3T3 (mouse embryonic fibroblast) normal cell line by MTT assay and DAPI staining. The results suggest that complexes 1-4 are cytotoxic in nature and induce cell death in the cancer cell lines by apoptosis and that a mixture of VIV, VV, and VVO2 species could be responsible for the biological activity.

DFT and electrochemical study on some iron(III) complexes with 2-hydroxybenzophenones

The synthesis, identification and electrochemical behaviour iron(III) complexes containing different 2-hydroxybenzophenone ligands are reported. The first reduction of the tris(2-hydroxybenzophenone)iron(III) complexes follow the same trend as that of the free, uncoordinated ligands and bis(2-hydroxybenzophenone)copper(II) complexes. The first reduction of the iron(III) complexes occur at a potential ca 1 V more positive than the reduction of the free ligands, but within 0.06 V of the reduction of bis(2-hydroxybenzophenone)copper(II) complexes. DFT calculations showed that [Fe(HBP)3] (where HBP = 2-hydroxybenzophenone) is high-spin. Calculations further showed that tris(2-hydroxybenzophenone)iron(III) complexes can exist as both the fac and mer isomers. DFT calculations further showed that the first reduction of the tris(2-hydroxybenzophenone)iron(III) complexes is iron based, while further reductions are ligand based.

The acid-mediated isomerization of iridium(III) complexes with cyclometalated NHC ligands: kinetic vs. thermodynamic control.

The isomerization of iridium(III) complexes with metalated N-heterocyclic carbene (NHC) ligands was studied. The fac isomers of complexes with 1-phenyl-3-methylbenzimidazolin-2-ylidene or 1-phenyl-3-benzylbenzimidazolin-2-ylidene ligands are transformed cleanly into the mer isomers when solutions of the complexes are treated with first HNTf2 and then NEt3. The transformation can be accomplished within a few minutes and the side product (NEt3H)(NTf2) is easy to separate. Spectroscopic and structural analyses indicate that the isomerization proceeds by protonation of the carbene ligand at the metalated phenyl group, accompanied by a fac → mer rearrangement of the carbene donors. An iridium complex with a 1-phenyl-1,2,4-triazolo[4,3-f]phenanthridine-based carbene ligand could not be isomerized under similar conditions, most likely because of its reduced conformational flexibility.

Towards Luminescent Vanadium(II) Complexes with Slow Magnetic Relaxation and Quantum Coherence.

Molecular entities with doublet or triplet ground states find increasing interest as potential molecular quantum bits (qubits). Complexes with higher multiplicity might even function as qudits and serve to encode further quantum bits. Vanadium(II) ions in octahedral ligand fields with quartet ground states and small zero-field splittings qualify as qubits with optical read out thanks to potentially luminescent spin-flip states. We identified two V2+ complexes [V(ddpd)2 ]2+ with the strong field ligand N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine (ddpd) in two isomeric forms (cis-fac and mer) as suitable candidates. The energy gaps between the two lowest Kramers doublets amount to 0.2 and 0.5 cm-1 allowing pulsed EPR experiments at conventional Q-band frequencies (35 GHz). Both isomers possess spin-lattice relaxation times T1 of around 300 μs and a phase memory time TM of around 1 μs at 5 K. Furthermore, the mer isomer displays slow magnetic relaxation in an applied field of 400 mT. While the vanadium(III) complexes [V(ddpd)2 ]3+ are emissive in the near-IR-II region, the [V(ddpd)2 ]2+ complexes are non-luminescent due to metal-to-ligand charge transfer admixture to the spin-flip states.

Crystallographic studies of fac- and mer-isomers of Cu[1,4,7,10,13,16-hexaazacyclooctadecane]2+. Influence of counterion and crystallization solvent on crystal structure and dynamic Jahn-Teller effects. Computational studies of structures, energetics, and mechanism of mer-fac isomerization

The syntheses and crystal structures of mer- and fac-isomers of [Cu(18N6)]2+(X−)2 are reported (18 N6 = 1,4,7,10,13,16-hexaazacyclooctadecane; X− = BF4−, ClO4−, NO3−) and compared to a previously reported example (X− = Cl−). Solution structures of the [Cu(18N6)]2+ dication in MeNO2 or MeOH are shown by FT-IR to be almost exclusively mer, and simple evaporation of these solutions or crystallization using Et2O co-solvent also afford the solid mer-salts. However, using C6H6 or CCl4 as crystallization co-solvents afforded the corresponding fac-isomers of the BF4− and ClO4− salts, in which the anions and the symmetrical solvent occupy locations on the crystallographic 3-fold axis. Similar treatment of the less symmetrical NO3− salts affords the mer-isomer without inclusion of C6H6. The solid-state structures of the mer-isomers each exhibit the anticipated tetragonal Jahn-Teller distortions, with two longer Cu-N bonds. In contrast the fac-isomers all show internally identical Cu-N distances, due to a dynamic exchange between Jahn-Teller distorted structures in the crystal. Density Functional Theory (DFT) is used to provide rationalizations of these observations and to elucidate an energetically feasible mechanistic pathway for the facile interconversion of mer and fac isomers in solution.

Fluoro-Germanium (IV) Cations with Neutral Co-Ligands—Synthesis, Properties and Comparison with Neutral GeF4 Adducts

The reaction of [GeF4L2], L = dmso (Me2SO), dmf (Me2NCHO), py (pyridine), pyNO (pyridine-N-oxide), OPPh3, OPMe3, with Me3SiO3SCF3 (TMSOTf) and monodentate ligands, L, in a 1:1:1 molar ratio in anhydrous CH2Cl2 formed the monocations [GeF3L3][OTf]. These rare trifluoro-germanium (IV) cations were characterised by microanalysis, IR, 1H, 19F{1H} and, where appropriate, 31P{1H} NMR spectroscopy. The 19F{1H} NMR data show that in CH3NO2 solution the complexes exist as a mixture of mer and fac isomers, with the mer isomer invariably having the higher abundance. The X-ray structure of mer-[GeF3(OPPh3)3][OTf] is also reported. The attempts to remove a second fluoride using a further equivalent of TMSOTf and L were mostly unsuccessful, although a mixture of [GeF2(OAsPh3)4][OTf]2 and [GeF3(OAsPh3)3][OTf] was obtained using excess TMSOTf and OAsPh3. The reaction of [GeF4(MeCN)2] with TMSOTf in CH2Cl2 solution, followed by the addition of 2,2′:6′,2”-terpyridine (terpy) formed mer-[GeF3(terpy)][OTf], whilst a similar reaction with 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3-tacn) in MeCN solution produced fac-[GeF3(Me3-tacn)][OTf]. Dicationic complexes bearing the GeF22+ fragment were isolated using the tetra-aza macrocycles, 1,4,7,10-tetramethyl-1,4,7,10-tetra-azacyclododecane (Me4-cyclen) and 1,4,8,11-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (Me4-cyclam), which reacted with [GeF4(MeCN)2] and two equivalents of TMSOTf to cleanly form the dicationic difluoride salts, cis-[GeF2(Me4-cyclen)][OTf]2 and trans-[GeF2(Me4-cyclam)][OTf]2. The 19F{1H} NMR spectroscopy shows that in CH3NO2 solution there are four stereoisomers present for trans-[GeF2(Me4-cyclam)][OTf]2, whereas the smaller ring-size of Me4-cyclen accounts for the formation of only cis-[GeF2(Me4-cyclen)][OTf], and is confirmed crystallographically. New spectroscopic data are also reported for [GeF4(L)2] (L = dmso, dmf and pyNO). Density functional theory calculations were used to probe the effect on the bonding as fluoride ligands were sequentially removed from the germanium centre in the OPMe3 complexes.

Covalent d-Block Organometallics: Teaching Lewis Structures and sd/sd2Hybridization Gives Students Additional Explanations and Powerful Predictive Tools

Despite tremendous efforts by instructors and textbook authors, students find it difficult to develop useful chemical intuitions about structures and key properties of the important d-block organometallic species that have a d6, d8, or d10 d-electron count. A full molecular orbital analysis is not always practical, and crystal field theory, while generally useful, is too limited here. It would be helpful to give students of organometallic chemistry an additional toolkit for understanding highly covalent d-block compounds. Hybridization arguments involving s and d orbitals (such as sd/sd2 hybridization for d8/d6 systems) provide useful insight, as is known from the research literature but rarely taught in undergraduate courses. This article makes descriptions of bonding that are based on s,d-hybridized orbitals more accessible, targeted toward undergraduate teaching. Geometries of unusual low-coordinate structures can be predicted. An in-depth physical explanation for the trans influence is provided. A clear explanation is given for the higher stability of the cis isomers versus the trans isomers in square-planar d8 complexes MR2L2 (R = alkyl/aryl, L = relatively weakly bonded neutral ligand) and for the fac versus mer isomers in octahedral d6 complexes MR3L3. Relevant to catalysis, it is explained why strongly donating ligands do not always facilitate oxidative addition and why 12-electron and 14-electron Pd(0) species are thermodynamically much more accessible than expected. The method capitalizes on first year knowledge, namely, the ability to write Lewis structures and to use hybridization arguments. It ties into the upper-year experience, including graduate school, where covalent d-block complexes may be encountered in research and where hybridization schemes will naturally emerge from using the natural bond orbital (NBO) formalism. It is discussed where the method might fit into the inorganic curriculum.

Separation of Isomers and Mechanisms of Inversion of Stereochemistry of Group 9 d6 Tris-Chelate Complexes of Hinokitiol.

Tris-chelate complexes of Co(III), Rh(III), and Ir(III) with 4-isopropyltropolone (hinokitiol or β-thujaplicin) form by the substitution of carbonate and chloride ligands from group 9 trivalent metal salts. The new complexes are neutral, are readily soluble in most organic solvents, and are brightly colored with strong charge transfer bands. The fac isomers of Co(hino)3 and Rh(hino)3 were isolated from the mixture by fractional recrystallization from ethanol. The remaining mixtures were respectively enriched by 5:3 and 4.4:3 for the mer isomer. The 1H NMR data show that the complexes exhibit remarkable stereochemical lability, which is unusual for diamagnetic d6 group 9 metals, with rotational barriers of 14.2 and 18.2 kcal/mol found for the inversion of stereochemistry of Co(hino)3 and Rh(hino)3. The low activation barriers, as well as the analysis of some key structural parameters, suggest that the inversion of stereochemistry occurs via a trigonal-twist (Bailar) mechanism. Facile substitution of a single hinokitiol ligand in the cobalt complex with ethylenediamine to form [Co(en)(hino)2]Cl also indicates that the tris-chelates are substitutionally and configurationally labile.

Isomerism, molecular structure, and vibrational assignment of tris(triflouroacetylacetonato)iron(III): An experimental and theoretical study

The isomerism, optimized molecular structure, UV spectrum, metal-ligand bond strength, and vibrational assignment of tris(triflouroacetylacetonato)iron(III), Fe(TFAA)3, were investigated by the aid of theoretical calculations (using DFT and Atoms-in-Molecules (AIM) at the B3LYP/6-311++G(d,p) level) and experimental methods (vibrational and UV spectroscopy). To explore the effect of the CF3 substituent in the β-position on the properties of complex, the above theoretical and experimental results of the titled complex compared with the corresponding data for tris(acetylacetonato) iron(III), Fe(AA)3. Both theoretical and experimental results confirmed that there is no significant difference in the strength of the Fe−O bond in these complexes. The effect of the CF3 group on the experimental vibrational bands of the chelated ring agrees with the calculated results. Comparing the observed and calculated vibrational spectra suggests that vibrational spectroscopy cannot be used to determine the type of isomer in the sample. However, due to the small difference of energy between the fac and mer isomers in the Fe(TFAA)3, the presence of both isomers in the sample is possible. The computed quantum chemical descriptors of Fe(TFAA)3 and Fe(AA)3 were also compared.

Solid-state nuclear magnetic resonance study of polymorphism in tris(8-hydroxyquinolinate)aluminium.

Tris(8-hydroxyquinolinate)aluminium (Alq3 ) is a metal-organic coordination complex, which is a widely used electroluminescent material in organic light-emitting diode technology. Crystalline Alq3 is known to occur in five polymorphic forms (denoted α, β, γ, δ, and ε), although the structures of some of these polymorphs have been the subject of considerable debate. In particular, the structure of α-Alq3 , which is a model for the local structure in amorphous films used in devices, is highly complex and has never been conclusively solved. In this work, we use solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations to investigate the local structure of four Alq3 samples. We find that the first structure proposed for α-Alq3 is inconsistent with all of the samples studied, and DFT calculations further suggest that this structure is energetically unfavourable. Instead, samples containing the meridional (mer) isomeric form are found to contain local structures consistent with ε-Alq3 , and a sample containing the facial (fac) isomeric form is consistent with a mixture of γ-Alq3 and δ-Alq3 . We also investigate the influence of different strategies for dispersion correction in DFT geometry optimisations. We find that a recently proposed modified semiempirical dispersion correction scheme gives good agreement with experiment. Furthermore, the DFT calculations also show that distinction between mer and fac isomers on the basis of ηQ that has been assumed in previous work is not always justified.

Compounds of the types Pn(pyS)3 (Pn = P, As, Bi; pyS: pyridine-2-thiolate) and Sb(pyS) x Ph3–x (x = 3–1); molecular structures and electronic situations of the Pn atoms

Abstract The compounds Pn(pyS)3 (Pn = P, As, Sb, Bi) were synthesized from the respective chloride (Pn = P, As, Sb) or nitrate (Bi), pyridine-2-thiol (pySH) and triethylamine (NEt3) as a supporting base in THF (P, Sb), CHCl3 (As) or methanol (Bi). Sb(pyS)3 was also obtained from the reaction of SbCl3 with LipyS (prepared in situ) in methanol. The compounds Sb(pyS)2Ph and Sb(pyS)Ph2 were prepared in a one-pot reaction starting from SbCl3 and SbPh3 (1:1 ratio). Upon Cl/pyS substitution, the resulting reaction mixture allows for a facile separation of the products in hot hexane. P(pyS)3 and As(pyS)3 crystallize isostructurally to the reported structure of Sb(pyS)3 with κ-S-bound pyS ligands. These crystal structures feature close Pn···Pn contacts which are most pronounced for the arsenic derivative. Bi(pyS)3 adopts a different molecular structure in the solid state, which features two chelating (κ 2-S,N-pyS) ligands and a κ-S-bound ligand. The presence of N→Bi interactions between the nitrogen atom of the κ-S-pyS ligand and the Bi atom of another molecule renders this structure a polymer chain along the crystallographic b axis with Bi⋅⋅⋅Bi van-der-Waals contacts. The structures of this set of Pn(pyS)3 compounds were also studied in solution using 1H NMR spectroscopy, revealing equivalent pyS ligands in discrete Pn(pyS)3 molecules. The molecular structure of Sb(pyS)Ph2 was optimized by quantum chemical methods, and a comparison with the structures reported for the other Sb/pyS/Ph combinations reveals Sb(pyS)2Ph to feature the strongest Sb···N interactions with the κ-S-pyS ligand. The results of 1H NMR spectroscopic investigations of the compounds Sb(pyS) x Ph3–x (x = 3–0) suggest the Ph protons in ortho position to be incorporated into intramolecular C–H···S contacts for x = 2 and 1. Natural localized molecular orbital (NLMO) calculations were employed in order to gain insights into the electronic situations of the Pn atoms and Pn–R bonds (R = S, C), especially for the effects caused by formal substitution of Pn in the compounds Pn(pyS)3 and the ligand patterns in the compounds Sb(pyS) x Ph3–x (x = 3–0). For the latter series of compounds, the electronic situation of the Sb atom was further studied by 121Sb Mössbauer spectroscopy, providing a correlation between the calculated electron density at Sb [ρ(0)] and the experimentally observed isomer shift δ. The missing link between group 15 and group 13 metal compounds of the type M(pyS)3, compound Al(pyS)3, was synthesized in this work. In the solid state (confirmed crystallographically), the mer isomer of this tris-chelate complex with distorted octahedral Al coordination sphere was found. This coordination mode was confirmed for the solution state (CDCl3) by 1H and 13C NMR spectroscopy at T = −40 °C.

Solvent-dependent fac/mer-isomerization and self-assembly of triply helical complexes bearing a pivot part.

Tris–chelate metal complexes of unsymmetrical bidentate ligands can form two geometric stereoisomers, facial (fac) and meridional (mer) isomers. Due to the small difference in their properties, the highly-selective synthesis of one of the isomers is challenging. We now designed a series of tripodal ligands with a tris(3-(2-(methyleneoxy)ethoxy)phenyl)methane pivot. Surprisingly, the ratio of the fac/mer isomers of the triply helical FeII complexes significantly changed depending on the solvents. To the best of our knowledge, this is the first example of fac/mer isomerism of a labile tris(2,2′-bipyridine) FeII complex governed by the solvent. Furthermore, well-defined self-assemblies were quantitatively produced by imine bond formation with a suitable diamine. The supramolecular assemblies contained only the fac isomer even though a mixture of the two isomers existed in solution before the condensation reaction. Namely, the self-assembly formation effectively adjusted the geometries of the building unit that results in the suitable supramolecular structure.

Antibacterial activity of a new class of tris homoleptic Ru (II)‐complexes with alkyl‐tetrazoles as diimine‐type ligands

Herein, we describe a new family of tris chelate homoleptic Ru (II) complexes, [Ru(N^N)3]2+, where the role of the diimine‐type ligands (N^N) was fulfilled by 2‐pyridyl (PTZ) or 2‐quinolyl tetrazole (QTZ) derivatives decorated with various alkyl substituents at the N‐2 position of the tetrazole ring. The new Ru (II) complexes with general formula [Ru (PTZ‐R)3]2+ and [Ru (QTZ‐R)3]2+, were obtained as mixtures of facial (fac) and meridional (mer) isomers, as suggested by NMR (1H, 13C) experiments, and confirmed in the case of mer‐[Ru (QTZ‐Me)3]2+, by X‐ray crystallography. The photophysical behavior of the tetrazole‐based [Ru(N^N)3]2+ type species was investigated by UV–vis absorption spectroscopy, providing trends typical of polypyridyl Ru (II) complexes. The new homoleptic complexes fac/mer‐[Ru (PTZ‐R)3]2+ and fac/mer‐[Ru (QTZ‐R)3]2+ have been assessed for any eventual antimicrobial activity towards two different bacteria such as Gram‐negative Escherichia coli and Gram‐positive Deinococcus radiodurans. Whereas being inactive toward E. coli, the response of agar disks diffusion tests suggested that some of the new fac/mer Ru (II) complexes could inhibit the growth of D. radiodurans. This effect was further investigated by determining the growth kinetics in liquid medium of D. radiodurans exposed to the fac/mer‐[Ru (PTZ‐R)3]2+ and fac/mer‐[Ru (QTZ‐R)3]2+ complexes at different concentrations. The outcome of these experiments highlighted that the turn‐on of the growth inhibitory effect took place as the linear hexyl chain was appended to the PTZ or QTZ scaffold, suggesting also how the inhibitory activity appeared more pronouncedly exerted by the facial isomers fac‐[Ru (PTZ‐Hex)3]2+ and fac‐[Ru (QTZ‐Hex)3]2+ (MIC = ca. 3.0 μg/ml) with respect to the corresponding meridional isomers (MIC = ca. 6.0 μg/ml).

Absorption and emission properties of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (M = Al, Ga, In) and correlations with molecular electrostatic potential.

Substituent effect for a series of 5-phenyl tris(8-hydroxyquinolinato) M(III) complexes (Mq3) of aluminum, gallium, and indium are investigated using density functional theory (DFT) for the ground state properties and the time-dependent version of DFT (TDDFT) for their absorption and emission properties. A comparison between the ground state energy of mer and fac isomers of all the complexes revealed that the mer configuration is always more stable than fac. The substituent effect is significantly reflected at the fluorescence maximum (λF ) values whereas the effect is moderate at the absorption maximum (λabs ) values. The molecular electrostatic potential (MESP) at the metal center (VM ) and the most electron rich region indicated by MESP minimum (Vmin ), located at the oxygen of phenoxide ring exhibit excellent correlations with the λF and Stokes shift (λF -λabs ) values. The study suggests the use of Stokes shift as an experimental quantity to measure the excited state substituent effect while the Vmin or VM emerge as theoretical quantities to measure the same.

Electronic effect of β‐diketonato ligands on the redox potential of fac and mer tris(β‐diketonato) iron(III) complexes: A density functional theory study and molecular electrostatic potential analysis

AbstractExperimental redox potentials of 16 derivatives of tris(β‐diketonato)iron(III) complexes (where β‐diketonato(R1COCHCOR2)─, with substituents R1 and R2 in different combinations of H, C4H3S, C4H3O, CH3, Ph, CF3, or C (CH3)3), and 11 additional isomers, were studied theoretically in terms of the electronic properties, substituent effects, electron affinity, and molecular electrostatic potential (MESP) analysis, using density functional theory methods. The computational methods reproduced the experimental reduction potential to a very high level of accuracy, especially when the M062X functional was used (with mean absolute deviation [MAD] = 0.054 and 0.093 and correlation R2 = 0.978 and 0.981 obtained by application of two slightly different free energy cycles, respectively). The most negative computed reduction potential corresponds to the most negative reported experimental reductions, which is indicative of the least favorable reduction potential, also in most cases the most stable molecules energetically. The calculated reduction potentials of the fac isomers of the molecules were generally higher (less negative) than that of the mer isomers when one of the ligand substituents R1 or R2 was CF3 (M062X results), indicating better ease of reduction, although in many cases, the experimental reduction potential agreed better with the calculated reduction potential of the mer isomer instead. The calculated reduction potentials were also affected by the substituents in the order of CF3 > H > C4H3S > C4H3O > Ph > CH3 > C(CH3)3 (the most negative value). The stronger the electron withdrawing tendency of the substituent, the more favorable (less negative value) the reduction potential becomes. In relation to the CH3‐substituted molecule 1 as a reference, the molecules with electron withdrawing substituents resulted in an electron‐deficient MESP iso‐surface, in both the neutral state and reduced state. All the molecules in their reduced state were characterized with an electron‐deficient MESP iso‐surface compared with the reduced CH3‐substituted molecule 1, with the deficiency increasing in mer compared with fac, for both the neutral and reduced molecules. The relative MESP values of ΔVFe in the reduced state of the molecules were able to predict the corresponding experimental reduction potential to a significant level of accuracy (with MAD = 0.091).

Tris(β-ketoiminato)ruthenium(III) complexes: Electrochemical and computational chemistry study

The electronic and electrochemical properties are reported here for the first time for a series of five tris(β-ketoiminato)ruthenium(III) complexes. Since the β-ketoiminato ligand is unsymmetrical, both fac and mer isomers are theoretically possible for these octahedral complexes. Density functional theory calculations show that for complexes containing an H on the imino position, both the fac and mer are energetically possible, while for complexes with a Ph on the imino position, the mer isomer is energetically favoured, due to the steric hindrance caused by the Ph group in the fac isomer. Electrochemistry, utilizing cyclic voltammetry, showed RuIII/IV oxidation, RuIII/II reduction, as well as ligand based reduction of the RuII complex. Different RuIII/IV and RuIII/II redox couples were observed for the different fac and mer isomers of the tris(β-ketoiminato)ruthenium(III) complexes.

A theoretical investigation of the fragment interaction and nonlinear optical and electronic properties of tris(β-diketonato)iron(III) complexes

This study presents the effects of substituent groups R1 and R2 of β-diketonato ligands (R1COCHCOR2)− in [Fe(β-diketonato)3] complexes, on the interaction energy between the ligand fragments and the central iron(III) atom, coupled with the nonlinear optical properties and electronic properties of the [Fe(β-diketonato)3] molecules. The results show that a CF3 group on the ligand reduces the nucleophilicity of the Fe atom and favours stability of the mer isomer above the fac isomer, contrary to what is observed in other unsymmetrically substituted molecules without a CF3 substituent group. The reduction of the molecules results in the weakening of the Fe–O coordination bonds, but increasing strength of the C–O covalent bonds of the ligands. The molecules that have favourable experimental reduction potentials (more positive values) are characterised by lower ionisation potential of the reduced iron(II), lower inductive effect and a lower energy of the lowest occupied molecular orbital (LUMO) before reduction (iron(III)), but by higher chemical potential and higher LUMO energy level after reduction (iron(II)). The experimental reduction potentials are found to correlate significantly with the inter-fragment total energy of interaction (ΔEtot) between the β-diketonato ligands and the iron(III) atom (R2 = 0.948), with a mean absolute deviation (MAD) of the predicted reduction potential of 0.073. Also, the contribution of electrical energy (EL) to the interaction energy (ΔEtot) correlates significantly with the experimental reduction potential (R2 = 0.951), resulting in an even better prediction of reduction potential (MAD = 0.067). It is observed that ring substituents (Ph, C4H3O, C4H3S), dipole moment and polarisability have a greater effect on the hyperpolarisability of the molecules, than merely the presence of a more withdrawing substituent, like CF3. Therefore, molecule [Fe(PhCOCHCOH)3] with a phenyl ring substituent is found to be the compound best suited for nonlinear optical (NLO) applications, extraordinarily higher than the other molecules of this study.