How do phosphoramides compete with phosphine oxides in lanthanide complexation? Structural, electronic and energy aspects at ab initio and DFT levels

Novel comparison of the structural, electronic and energy aspects of lanthanide complexes of model phosphoramides (PAs) with those of phosphine oxides (POs), phosphate esters (PEs) and phosphoryl trihalides (PHs) has been carried out by ab initio and DFT calculations. Atoms in Molecules (AIM) and Natural Bonding Orbital (NBO) analyses were performed to understand the electronic structure of ligands L and related complexes, L–Ln³⁺. NBO analysis indicates that the negative charge on phosphoryl oxygen (O_P) and the p character of the phosphoryl lone pair, Lp(O_P), increase in the order PH < PE < PO < PA. Positive charge of the lanthanide cation in PA complexes is less than those of PH, PE and PO complexes, due to the more intense ligand to metal charge transfer (LMCT). The metal–ligand distance decreases in the order PH > PE > PO > PA, which is confirmed by the results of AIM analysis. Charge density at the bond critical point of L–Ln³⁺ follows the sequence PH < PE < PO < PA. The results of the Energy Decomposition Analysis (EDA) indicate that the donative interaction and LMCT increases in order PH < PO < PE < PA. The effect of basis set superposition error (BSSE) on the L···Ln³⁺ interaction energies was also studied in detail at DFT, MP2 and CCSD(T) levels using the counterpoise (CP) method. Trends in the CP-corrected L–Ln³⁺ bond energies are in good accordance with the optimized O_P···Ln³⁺ distances. The results show that the difference between CP-corrected and uncorrected interaction energies in PA complexes is larger than those in the others, because PAs are more deformable. It is depicted that PAs are comparable with POs in lanthanide complexation.     

Mononuclear copper(II) complexes of bis-triazole-based macrocyclic Schiff base hydrazones: direct synthesis,EPR studies,magnetic and thermal properties

Mononuclear copper(II) complexes of 1,2,4-triazole-based Schiff base macrocyclic hydrazones, III and IV, have been reported. The prepared amorphous complexes have been characterized by spectroscopic methods, electron spray ionization mass spectrometry, and elemental analysis data. Electrochemical studies of the complexes in DMSO show only one quasi-reversible reduction wave at +0.43 V (ΔE = 70 mV) and +0.42 V (ΔE = 310 mV) for III and IV, respectively, which is assigned to the Cu(II) → Cu(I) reduction process. Temperature dependence of magnetic susceptibilities of III and IV has been measured within an interval of 2–290 K. The values of χ_M at 290 K are 1.72 × 10^?3 cm³ mol^?1 and 1.71 × 10^?3 for III and IV, respectively, which increases continuously upon cooling to 2 K. EPR spectra of III and IV in frozen DMSO and DMF were also reported. The trend g_|| > g⊥ > g_e suggests the presence of an unpaired electron in the d_x2?y2 orbital of the Cu(II) in both complexes. Furthermore, spectral and antimicrobial properties of the prepared complexes were also investigated.     

Further studies on the properties and effect of high energetic ionizing radiation on copper(II) complexes: 1H NMR,electronic absorption,ESR spectra and solid electrical conductivity

The effect of energetic γ-radiation on ¹H NMR, electronic absorption, ESR spectra, differential thermal analysis (DTA) and solid state dc electrical conductivity of the ligand N-phenyl-2-(2-(phenylamino)acetyl)hydrazine carbothioamide (H₂L) and its copper(II) complexes; Cu(HL)(OAc)H₂O, Cu(HL)BrH₂O and Cu(H₂L)₂(NO₃)₂?3H₂O before and after γ-irradiation (hereafter referred to as (B), (B ₁ ), (B ₂ ), (B ₃ ) and (A), (A ₁ ), (A ₂ ), (A ₃ ), respectively) has been studied. Electronic spectral bands of the complexes after irradiation exhibited some better resolved shapes with a remarkably higher absorbance, ESR spectrum of complex Cu(HL)BrH₂O (B ₂ ) before irradiation showed isotropic spectrum with g _iso = 2.075 however, after irradiation (A ₂ ) displayed axial ESR spectrum with g _∥ > g _⊥ > 2.0023 and d _(x2?y2) ground state. DTA of the compounds reveals that γ-irradiation induced generation of new peaks as well as changes in the peak intensities. Solid state dc electrical conductivity for complexes was investigated before and after γ-irradiation. Complexes were found to be semiconductors, the activation energies (E _a) were calculated for the complexes by using the Arrhenius plot.     

Synthesis, crystal structures and electrochemical properties of CoIII complexes with hexadentate ligand containing thioether-amidopyridyl donor set

Two new cobalt(III) complexes of the hexadentate ligand [1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane] (H₂bpctb) with N₄S₂ donor set atoms have been synthesized. A reaction of Co(CH₃COO)₂·4H₂O with (H₂bpctb) leads to the formation of [Co^III(bpctb)]PF₆ (1) having a CoN₂(pyridine)N′₂(amide)S₂(thioether) coordination by symmetric bpctb^2? ligand. A similar reaction under slightly different conditions, however, gives [Co^III(L ^a )(L ^b )] (2), resulting from a C–S bond cleavage reaction triggered by an acetate ion as a base, having CoN₂(pyridine)N′₂(amide)S(thioether)S′(thiolate) coordination. These two Co(III) complexes have been characterized by elemental analyses and spectroscopic methods, and the crystal and molecular structures of [Co^III(bpctb)]PF₆ (1) in the form of the solvate (1·MeOH·H₂O) and of [Co^III(L ^a )(L ^b )] (2) have been determined by X-ray crystallography. The Co atoms of both complexes exhibit distorted octahedral geometry. The electrochemical investigation of [Co(bpctb)]PF₆·MeOH·H₂O (1·MeOH·H₂O) and [Co^III(L ^a )(L ^b )] (2) by cyclic voltammetry reveals a reversible Co^III–Co^II redox process at E _1/2 = ?0.32 V (ΔE _p = 80 mV); for 1, and E _1/2 = ?0. 87 V (ΔE _p = 70 mV) for 2.     

Synthesis and thermal behavior study of complexes of the type [Pd(μ-X)(4-eb-p-phen)]2 (X = Cl,Br, I,N3, NCO,SCN) and 4-eb-p-phen [bis(4-ethylbenzyl)p-phenylenediimine]

The Schiff base bis(4-ethylbenzyl) p-phenylenediimine, 4-eb-p-phen (1), and six new dimeric Pd(II) complexes of the type [Pd(μ-X)(4-eb-p-phen)]₂ {X = Cl (2), Br (3), I (4), N₃ (5), NCO (6), SCN (7)} have been synthesized and characterized by elemental analysis, IR spectroscopy, and ¹H and ¹³C{¹H}-NMR experiments. The thermal behavior of the complexes 2–7 has been investigated by means of thermogravimetry and differential thermal analysis. From the final decomposition temperatures, the thermal stability of the complexes can be ordered in the following sequence: 3 > 4 > 7 > 2 ≈ 5 > 6. The final products of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction (XRD).     

fac-Cobalt(III)-azido complexes derived from substituted pyridyl-based tridentate amines

Four new mononuclear triazido-cobalt(III) complexes [Co(L ^1/2/4 )(N₃)₃] and [Co(L ³ )(N₃)₃]·CH₃CN where L ¹  = [(2-pyridyl)-2-ethyl]-(2-pyridylmethyl)-N-methylamine, L ²  = [(2-pyridyl)-2-ethyl]-[6-methyl-(2-pyridylmethyl)]-N-methylamine, L ³  = [(2-pyridyl)-2-ethyl]-[3,5-dimethyl-4-methoxy-(2-pyridylmethyl)]-N-methylamine, and L ⁴  = [(2-pyridyl)-2-ethyl]-[3,4-dimethoxy-(2-pyridylmethyl)]-N-methylamine, respectively, were synthesized and structurally characterized. The four complexes were characterized by elemental microanalyses, IR and UV–VIS spectroscopy and X-ray single crystal crystallography. The complexes display two strong IR bands over the frequency region 2,020–2,050 cm^?1 assigned for the asymmetric stretching frequency, ν_a(N₃) of the coordinated azides indicating facial geometry. The molecular structure determinations of the complexes were in complete agreement with fac-[Co(L)(N₃)₃] conformation in distorted octahedral Co(III) environment.     

Copper complexes of two isomeric NS2-macrocycles

Two isomeric NS₂-macrocycles incorporating a xylyl group at ortho (o -L) and meta (m -L) positions were employed and their copper complexes (1?C5) were prepared and structurally characterized. The copper(II) nitrate complexes [Cu(L)(NO₃)₂] (1: L = o -L, 2: L = m -L) for both ligands were isolated. In each case, the copper center is five-coordinated with a distorted square pyramidal geometry. Despite the overall geometrical similarity, 1 and 2 show the different ligand conformation due to the discriminated packing pattern. Reaction of o -L with copper(II) perchlorate afforded complex 3 containing two independent complex cations [Cu(o -L)(H₂O)(DMF)(ClO₄)]⁺ and [Cu(o -L)(H₂O)(DMF)]²⁺; the coordination geometry of the former is a distorted octahedron while the latter shows a distorted square pyramidal arrangement. In the reactions of copper(I) halides (I or Br), o -L gave a mononuclear complex [Cu(o-L)I] (4) with a distorted tetrahedral geometry, while m -L afforded a unique exodentate 2:1 (ligand-to-metal) complex [trans-Br₂Cu(m-L)₂] (5) adopting a trans-type square-planar arrangement.     

Synthesis and characterization of palladium(II) complexes [PdX2(p-diben)] (X = Cl,Br, I,N3, or NCO; p-diben = N,N′-bis(4-dimethylaminobenzylidene)ethane-1,2-diamine): crystal structure of [Pd(N3)2(p-diben)]

Five new complexes of general formula [PdX₂(p-diben)], where p-diben = N,N′-bis(4-dimethylaminobenzylidene)ethane-1,2-diamine) (1) and X = Cl (2), Br (3), I (4), N₃ (5), or CNO (6), were synthesized and characterized by physicochemical and spectroscopic methods. The crystal structure of compound (5) was determined by single-crystal X-ray diffraction. Complexes 2–6 were characterized as N,N-chelated products. The crystal structure confirmed this formulation for [Pd(N₃)₂(p-diben)], besides showing the isomerism inversion of one of the C=N bonds, caused by Pd(II) coordination.     

Cis–trans isomerization and spin multiplicity dependences on the static first hyperpolarizability for the two-alkali-metal-doped saddle[4]pyrrole compounds

Doping two alkali-metal atoms (Li and Na) into the saddle-shaped saddle[4]pyrrole forms four new two-alkali-metal-doped compounds with alkalide or electride characteristic. They are cis-LiNa(saddle[4]pyrrole) isomers 1(singlet) and 2(triplet), and trans-Li(saddle[4]pyrrole)Na isomers 3(singlet) and 4(triplet). The four structures with all-real frequencies are obtained at the density functional theory (DFT) B3LYP/6-311+G(d) level. All calculations of electric properties have been carried out at the second order Møller–Plesset perturbation theory (MP2) level. The order of the β ₀ values is 3.54 × 10³ for trans-4(triplet) <1.51 × 10⁴ for cis-1(singlet) <3.57 × 10⁴ for cis-2(triplet) <2.34 × 10⁵ a.u. for trans-3(singlet). The static first hyperpolarizability (β ₀) depends on the cis–trans isomerization and spin multiplicity. The result demonstrates that the cis–trans isomerization and spin multiplicity controls of the second-order NLO response are possible.     

Syntheses, crystal structures and fluorescent properties of two d 10-metal coordination polymers based on 1,5-naphthalenedisulfonic acid

The first examples of two d ¹⁰ metal coordination polymers based on 1,5-naphthalenedisulfonic acid and benzimidazole, namely, [Cd(bim)₄(1,5-nds)] 1 and [Ag(bim)₂]·½1,5-nds 2 (bim = benzimidazole, 1,5-nds = 1,5-naphthalenedisulfonic acid) were synthesized successfully under solvothermal conditions. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR, TG-DSC, PXRD, UV–Vis, and DFT. 1 exhibits a 3D supramolecular structure which started from 1D helical chain. 2 also shows a 3D architecture which was assembled via π–π interactions and hydrogen bonds. The hydrogen bonds formed by 1,5-nds play an important role in increasing the dimensionality of architectures of 1 (from 1D to 3D) and 2 (from 0D to 1D). Moreover, both 1 and 2 show excellent luminescent properties, 335 nm for 1 (λ _ex = 286 nm) and 341 nm and 389 nm for 2 (λ _ex = 234 nm), and may be the suitable candidates of fluorescent materials. From UV–Vis spectra, the remarkable absorption peaks can be found at 276 nm for 1 and 271 nm for 2. The simulated UV–Vis spectra (290.30 nm for 1 and 271.64 nm for 2) by Gaussian 09 DFT correspond well with the experimental results. From the electron density distribution of frontier molecular orbitals, it is known that the two absorption bands are attributed to the intra-ligand electron transition from HOMO?26 to LUMO and from HOMO?3 to LUMO+1 for 1, from HOMO?1 to LUMO+18 and LUMO+19 for 2.     

Selective complexation of alkali metal ions and nanotubular cyclopeptides: a DFT study

A density functional theory based on interaction of alkali metal cations (Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) with cyclic peptides constructed from 3 or 4 alanine molecule (CyAla3 and CyAla4), has been investigated using mixed basis set (C, H, O, Li⁺, Na⁺ and K⁺ using 6-31+G(d), and the heavier cations: Rb⁺ and Cs⁺ using LANL2DZ). The minimum energy structures, binding energies, and various thermodynamic parameters of free ligands and their metal cations complexes have been determined with B3LYP and CAM-B3LYP functionals. The order of interaction energies were found to be Li⁺ > K⁺ > Na⁺ > Rb⁺ > Cs⁺ and Li⁺ > Na⁺ > K⁺ ? Rb⁺ > Cs⁺, calculated at CAM-B3LYP level for the M/CyAla3 and M/CyAla4 complexes, respectively. Their selectivity trend shows that the highest cation selectivity for Li⁺ over other alkali metal ions has been achieved on the basis of thermodynamic analysis. The main types of driving force host–guest interactions are investigated, the electron-donating O offers lone pair electrons to the contacting LP* of alkali metal cations.     

Complexation of the cesium cation with lithium ionophore VIII: extraction and DFT study

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs⁺(aq) + 1·Na ⁺ (nb) = 1·Cs⁺(nb) + Na⁺(aq) taking place in the two-phase water-nitrobenzene system (1 = lithium ionophore VIII; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (Cs⁺, 1·Na⁺) = ?0.5 ± 0.1. Further, the stability constant of the 1·Cs⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Cs⁺) = 4.8 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1·Cs⁺ was derived. In the resulting complex, the “central” cation Cs⁺ is bound by six bond interactions to the corresponding six oxygen atoms of the parent ligand 1.     

Iron carbonyl cluster complexes with monophosphine ligands: synthesis,characterization, and crystal structure

Three new monophosphine-substituted iron carbonyl cluster complexes [(μ-PDT)Fe₂(CO)₅L] [(PDT = SCH₂CH₂CH₂S, L = P(CH₂Ph)₃, 1; P(C₆H₁₁)₃, 2; PPh₂(PhMe-p), 3)], which can be regarded as active site mimics for [FeFe]-hydrogenase, have been prepared in 40–70 % yields by reactions of the parent complex (μ-PDT)Fe₂(CO)₆ (A) with monophosphine ligands in the presence of the decarbonylating agent Me₃NO·2H₂O. All three complexes were characterized by elemental analysis and spectroscopic techniques, as well as by X-ray crystallography for complex 1. The IR spectra of the complexes reveal that the electron-donating abilities of the different monophosphine ligands follow the order PPh₂(PhMe-p) > P(C₆H₁₁)₃ > P(CH₂Ph)₃.     

Sulfonyl-bridged oligo(benzoic acid)s: synthesis, X-ray structures, and properties as metal extractants

Sulfonyl-bridged oligo(benzoic acid)s 7 _n (n = 2–4) are prepared from the corresponding triflate esters (8 _n ) of sulfur-bridged oligophenols by palladium-catalyzed methoxycarbonylation of the triflate moieties, followed by hydrolysis of the resulting methyl esters, and subsequent oxidation of the sulfur bridges. X-ray analysis reveals that dimer 7 ₂ forms supramolecular zig-zag chains through intermolecular hydrogen bonds between the carboxy groups. As for the crystal of trimer 7 ₃ , two molecules are associated through two couples of intermolecular hydrogen bonds between terminal and central carboxy groups to form a cyclic dimer, which connects with two adjacent dimers with the remaining carboxy groups to construct an infinite columnar structure. Tetramer 7 ₄ adopts a monomolecular cyclic structure through intramolecular hydrogen bonds between the terminal carboxy groups, and a molecule connects with each of two adjacent molecules through two couples of intermolecular hydrogen bonds between inner carboxy and sulfonyl groups. Solvent extraction experiments reveal that the oligo(benzoic acid)s exhibit high extractability toward lanthanoid ions (Ln³⁺); the performance follows the order 7 ₄  ≈ 7 ₃  > 7 ₂ . Moderate extraction selectivity is observed for the extraction of Pr³⁺, Gd³⁺, and Yb³⁺ with 7 ₂ . X-ray crystallographic analysis of cluster [Tb₄L₄(H₂O)₆](Et₃NH)₄, which was prepared from 7 ₄ (H₄L) and Tb(NO₃)₃·6H₂O in the presence of Et₃N, reveals that no sulfonyl oxygens coordinate to the metal centers. This indicates that the high extractability of 7 ₄ originates from the electron-withdrawing nature of the sulfonyl function, which increases the acidity of two adjacent carboxy groups.     

Synthesis, crystal structures and properties of four manganese coordination polymers with 4,4-bipyridine-derived ligands

Four new coordination polymers, namely Mn₂(4,4-bpy)₂(o-tol)₄ 1, Mn₂(4,4-bpy)₂(m-tol)₄ 2, Mn₂(bpp)₂(m-tol)₄ 3 and {[Mn₂(4,4-bpy)₂(p-tol)₄][Mn(4,4-bpy)₂(H₂O)₂(p-tol)₂]}·6H₂O 4 have been synthesized from 4,4′-bipyridine (4,4-bpy), 1,3-bis(4-pyridyl)-propane (bpp), o-toluic acid (o-Htol), m-toluic acid (m-Htol) and p-toluic acid (p-Htol). All four complexes feature dinuclear Mn₂(tol)₄ moieties, which are bridged by 4,4-bpy or bpp ligands to form 1D double-chain structures. The resulted 1D double-chains are assembled via hydrogen bonding or π···π stacking into 2D supramolecular layers. The complexes were characterized by physico-chemical (thermal behavior) and infrared spectroscopy. Variable temperature magnetic characterization suggest weak antiferromagnetic coupling exchange between dimeric Mn(II) centers (J = ?0.46 cm^?1 for 1, ?0.56 cm^?1 for 2, ?1.28 cm^?1 for 3 and ?0.59 cm^?1 for 4).     

Synthesis and characterization of palladium(II) and platinum(II) metal complexes with iminophosphine ligands: X-ray crystal structures of platinum(II) complexes and use of palladium(II) complexes as pre-catalysts in Heck and Suzuki cross-coupling reactions

The reactions of N-(2(diphenylphosphino) benzylidene) (phenyl) methanamine, Ph₂PPhNHCH₂-C₅H₄N, 1 and N-(2-(diphenylphosphino) (benzylidene) (thiophen-2-yl) methanamine, Ph₂PPhNHCH₂-C₄H₃S, 2 with MCl₂(cod) and MCl(cod)Me (M = Pd, Pt; cod = 1,5-cyclooctadiene) yield the new complexes [M(Ph₂PPhNHCH₂-C₅H₄N)Cl₂], M = Pd1a, Pt1b, [M(Ph₂PPhNHCH₂-C₅H₄N)ClMe], M = Pd1c, Pt 1d, [M(Ph₂PPhNHCH₂-C₄H₃S)Cl₂], M = Pd2a, Pt 2b, and [M(Ph₂PPhNHCH₂-C₄H₃S)ClMe], M = Pd2c, Pt 2d, respectively. The new compounds were isolated as analytically pure crystalline solids and characterized by ³¹P-, ¹H-NMR, IR spectroscopy, electro spray ionization-mass spectrometry (ESI-MS) and elemental analysis. The representative solid-state molecular structures of the platinum complexes 1b and 2b were determined using single crystal X-ray diffraction analysis and revealed that the complexes exhibit a slightly distorted square-planar geometry. Furthermore, the palladium complexes were tested as potential catalysts in the Heck and Suzuki cross-coupling reactions.     

Hetero-heptanuclear (Fe–Na) complexes of salicylaldehydes: crystal and molecular structure of [Fe2(3-OCH3-salo)8 · Νa5] · 3OH · 8H2Ο

The reaction of Fe(III) with the substituted salicylaldehydes [X-saloH, where X = 3-OCH₃ (L ¹ ), 5-CH₃ (L ² ), 5-Cl (L ³ ), 5-NO₂ (L ⁴ )] led to the formation of four new iron(III) hetero-heptanuclear complexes (Fe–Na) under the general formula [Fe₂(X-salo)₈Νa₅] · 3OH · zH₂Ο. The two different coordination modes of the ligand, as well as the geometry around the metal ions were deduced by X-ray structure analysis of compound 1, [Fe₂(3-OCH₃-salo)₈Νa₅] · 3OH · 8H₂Ο. The complexes have also been characterized by physicochemical and spectroscopic (IR, UV–Vis, Mössbauer) methods.     

Chiral resolution of l- and d-alanine and a racemic macrocyclic nickel(II) complex: synthesis and crystal structures

The reactions of a racemic four-coordinate Ni(II) complex [Ni(rac-L)](ClO₄)₂ with l- and d-alanine in acetonitrile/water gave two six-coordinate enantiomers formulated as [Ni(RR-L)(l-Ala)](ClO₄)·2CH₃CN (1) and [Ni(SS-L)(d-Ala)](ClO4) (2) (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-tetradecane, Ala^? = alanine anion), respectively. Evaporation from the remaining solutions gave two four-coordinate enantiomers characterized as [Ni(SS-L)](ClO₄)₂ (S-3) and [Ni(RR-L)](ClO₄)₂ (R-3), respectively. Single-crystal X-ray diffraction analyses of complexes 1 and 2 revealed that the Ni(II) atom has a distorted octahedral coordination geometry, being coordinated by four nitrogen atoms of L in a folded configuration, plus one carboxylate oxygen atom and one nitrogen atom of l- or d-Ala^? in mutually cis-positions. Complexes 1 and 2 are supramolecular stereoisomers, constructed via hydrogen bonding between [Ni(RR-L)(l-Ala)]⁺ or [Ni(SS-L)(d-Ala)]⁺ monomers to form 1D hydrogen-bonded zigzag chains. The homochiral natures of complexes 1 and 2 have been confirmed by CD spectroscopy.     

The unimolecular thermal decomposition of oxetane and its methyl derivatives: An Ab initio and RRKM calculations

Quantum mechanical and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations are carried out to study the thermal unimolecular decomposition of oxetane (1), 2-methyloxetane (2), and 2,2-dimethyloxetane (3) at the MPW1PW91/6-311 + G** level of theory. The results of the calculations reveal that decomposition reaction of compounds 1?C3 yields formaldehyde and the corresponding substituted olefin. The predicted high-pressure-limit rate constants for the decomposition compounds 1?C3 are represented as 6.61 × 10¹³exp(?32472/T), 9.33 × 10¹³exp(?29873/T), and 4.79 × 10¹³exp(?27055/T) s^?1, respectively. The fall-off pressures for the decomposition of compounds 1?C3 are found to be 9.42 × 10^?2, 3.67 × 10^?3, and 7.26 × 10^?4 mm Hg, respectively. As the fall-off pressure of the decomposition process of compounds 1?C3 are in the following order: P _1/2(1) > P _1/2(2) > P _1/2(3); therefore the decomposition rates are as follow: rate(1) < rate(2) < (3).