Basicity of some aliphatic amines in mixed H2O?CH3CN solvents

The values of pK_a^ms (K_a^ms represents ionization constant of conjugate acid of amine base in mixed water–acetonitrile solvent) for all amines, except for charged amine bases, show a mild decrease (ca. 0.1–0.4 pK units) with the increase in CH₃CN content from 2 to ∼60% v/v. However, the pK_a^ms values at 70% v/v CH₃CN become nearly equal or slightly larger (by ≤0.7 pK units) than the corresponding pK_a^ms at 2% v/v CH₃CN for all neutral and charged amines. The values of pK_a^ms for phenol increase from 10.17 to 13.38 with the increase in the content of CH₃CN from 2 to 70% v/v in mixed aqueous solvent. Taft reaction constants, ρ*, obtained from the plots of pK_a^ms against ∑σ* for primary and secondary amines decrease by ca. 0.8 ρ* units with the increase in the CH₃CN content from 2 to 70% v/v. The values of pK_a^ms show an empirical linear relationship with the corresponding values of pK_a^w (where pK_a^w represents the pK_a obtained in aqueous solvent containing 2% v/v CH₃CN), which allows the estimation of a pK_a in mixed H₂O CH₃CN solvents from that in water. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 146–152, 2000     

Concentrations of Active Species in the Flowing Afterglow of a Nitrogen Microwave Plasma

Measurements of nitrogen atom density, by means of NO chemical titration, along with an evaluation of the densities of some excited species N ₂ (B, v=11), N ₂ (B, v=2), N ₂ (C, v=0), and N ₂ ⁺ (B,v=0), by means of a spectroscopic study of some bands of dinitrogen, are achieved along the flowing afterglow of a dinitrogen microwave plasma (2450 MHz) for several pressures. The concentrations obtained are in the following range: [N]10 ⁺¹⁵ , [N ₂ (B, 2)]10 ⁺⁹ –10 ⁺¹⁰ , [N ₂ (B, 11)]10 ⁺⁸ –10 ⁺⁹ , [N ₂ (C, 0)]10 ⁺⁶ –10 ⁺⁷ , [N ₂ ⁺ (B,0)]10 ⁺⁶ -10 ⁺⁸ (cm^-3). From a kinetic study of the formation and decay of excited and charged species, an estimation of N ₂ (A, v), N ₂ (X, v, and N ₂ ⁺ (X) densities can be derived: [N ₂ (A, v)]10 ⁺¹² , [N ₂ (X, v6)]10 ⁺¹⁵ –10 ⁺¹⁶ , [N ₂ (X, v12)]10 ⁺¹⁴ –10 ⁺¹⁵ , [N ₂ ⁺ (X)]10 ⁺¹⁰ (cm ^-3 ).     

The Ionization Energies of Di-n-Alkyl Diacetylenes

The He(Iα) photoelectron spectra and the ionization energies of symmetrically substituted di-n-alkyl-diacetylenes R-(C?C)₂-R (with R ? CH₃, C₂H₅, n-C₃H₇, n-C₄H₉) are presented. The effect of the alkyl substitutents is that the two acetylenic ionization energies, I_v,1 and I_v,2, shift by the same amount, i.e. their difference I_v,2 – I_v,1 remains constant (2.45 ± 0.05 eV). Between 12.5 eV and 17 eV the band system in the photoelectron spectrum of R-(C?C)₂-R is superimposable with that in the spectrum of the corresponding alkane, RH, with the exception of a uniformly small shift of all the bands to higher ionization energy.     

Accurate electrical and spectroscopic properties ofX 1Σ+ BeO from coupled-cluster methods

Summary This paper reports a series of coupled-cluster (CC) calculations through CCSDT on the theoretically challenging ground state of the BeO molecule. Along with CC methods, quadratic configuration interaction (QCI) approximations to CC theory have been used (QCISD and QCISD(T)), which show several dramatic failings. Equilibrium electrical properties (, _xx , and _zz ) and basic spectroscopic properties (r _e, _e,D _e, and infrared intensity (I)) have been computed. Basis set and electron correlation effects are analyzed in order to arrive at accurate values of the dipole moment and polarizability, which are not known experimentally. For the dipole moment, we obtain a value of 6.25 D, with an uncertainty of about 0.1 D. For _xx and _zz , we suggest respective values of 32 and 36 atomic units (a.u.) and error bars of about 1 and 2 a.u. With extended basis sets, the spectroscopic propertiesr _e, _e, andD _e are reproduced to high accuracy, which is the first time this has been achieved for this species byab initio methods. At the highest calculation levels,I is predicted to be very small. AlthoughI has not been measured, some support for this prediction comes from a recent infrared study of BeO-rare gas complexes. The QCI methods are shown to be much more sensitive to basis set, and even with large basis sets yield values of _zz andI which differ from CC results by an order of magnitude and three orders of magnitude, respectively. These differences doubtless arise from the importance of single excitations (T ₁) for this molecule, as several terms involvingT ₁ are neglected in the QCISD approximation compared with CCSD. We also report CC calculations with Brueckner orbitals, which yield results similar to those obtained with restricted Hartree-Fock orbitals.     

Synthesis and magnetism of μ-1,3,5-benzenetricarboxylatocopper(II) trinuclear complexes

Summary Three new Cu^II trinuclear complexes, namely [Cu₃(BZT)(phen)₃(ClO₄)₃]·6H₂O (1), [Cu₃(BZT)(Nphen)₃ (ClO₄)₃]·6H₂O (2) and [Cu₃(BZT)(bipy)₃ (ClO₄)₃]·3H₂O (3) (BZT) = 1,3,5-benzenetricarboxylato, phen = 1,10-phenanthroline, Nphen = 5-nitro-1,10-phenanthroline, bipy = 2,2-bipyridyl, have been synthesized, with 1,3,5-benzenetricarboxylato as the bridged ligand, and characterized by elemental analysis, and i.r. and electronic reflection spectra. We propose that the complexes have an extended 1,3,5-benzenetricarboxylatobridged structure containing three Cu^II atoms. The variable-temperature magnetic susceptibilities of the complexes were measured in the 77–300 K range. The magnetic coupling parameters are consistent with an antiferromagnetic exchange model based on the Hamiltonian operator [=–2J( _{1 2}+ _{1 3}+ _{2 3}, where S ₁=S ₂=S ₃=1/2, giving the antiferromagnetic coupling parameters of 2J = – 18.6 cm^-1 for (1)–(3).     

Intramolecular carboxylic group‐assisted cleavage of N‐(2‐hydroxyphenyl)phthalamic acid (7) and N‐(2‐methoxyphenyl)phthalamic acid (8): Absence of intramolecular general acid catalysis due to 2‐OH in 7

The values of pseudo first‐order rate constants (k_obs) for the cleavage of N‐(2‐hydroxyphenyl)phthalamic acid ( 7 ), obtained at 4.9 × 10^?2 M HCl, 35°C, and within CH₃CN content range 2–80% (v/v) in mixed aqueous solvent are smaller than k_obs for the cleavage of N‐(2‐methoxyphenyl)phthalamic acid ( 8 ), obtained under almost similar experimental conditions, by nearly 1.5‐ to 2‐fold. These observations show the absence of expected intramolecular general acid catalysis due to 2‐OH group in 7 . The values of k_obs for the cleavage of 7 and 8 decrease by more than 20‐fold with the increase in the content of CH₃CN from 2 to 80–82% (v/v) in mixed aqueous solvent. The kinetic data reveal that in acidic aqueous cleavage of 7 , N‐cyclization (leading to the formation of imide) and O‐cyclization (leading to the formation of phthalic anhydride) vary from ～10 to 15% and ～90 to 85%, respectively, with the increase in CH₃CN content from 2 to 80% (v/v). Similar increase in CH₃CN content causes increase in N‐cyclization from ～0 to 5% and decrease in O‐cyclization from ～100 to 95% in the acidic aqueous cleavage of 8 . Some speculative, yet conceivable, reasons for nearly 10 and 0% N‐cyclization in the cleavage of respective 7 and 8 at low content of CH₃CN have been described. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 746–758, 2006     

Preparation and structural characterization of a hexanuclear molybdenum (II) cluster containing carboxylate ligands (Bu4N)2[Mo6(μ3-Cl)8(O2CMe)6]

The hexamolybdenum cluster complex [Mo₆(₃-Cl)₈(O₂CMe)₆]^2–, 1 was isolated as the Bu₄N⁺ salt in 71% yield from the reaction of (Bu₄N)₂[Mo₆(₃-Cl)₈Cl₆] with AgO₂CMe in CH₂Cl₂ solvent. The compound was characterized by single crystal X-ray diffraction analysis. The cluster contains an octahedral arrangement of six molybdenum atoms with eight chloride ligands bridging the eight trianglar faces and six carboxylate ligands terminally coordinated through one oxygen atom to each of the six molybdenum atoms. Crystal data: space group =P2₁/n,a=10.713(3)Å,b=14.43(1)Å,c=21.919(4)Å, =94.37(2)°,Z=2, 1965 reflections,R=0.036.     

Effects of solvents on the reactions of coordination complexes: Part 20. Kinetics and mechanism of base hydrolysis of (αβS) (Salicylato) (Tetraethylenepentamine) Cobalt(III) in aquo-organic solvent media

The kinetics of base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine) cobalt(III) have been investigated in aquo-organic solvent media at 15.0 < t, °C < 40.0, and I = 0.10 mol dm (ClO₄^?) using propane-2-ol (?70% v/v), t-butanol (?60% v/v), acetone (?70% v/v), acetonitrile (?50% v/v), and ethylene glycol (?70% v/v) as cosolvents. Both the spontaneous and base-catalyzed hydrolysis of the phenoxide species [(tetren)CoO₂CC₆H₄O]⁺ were appreciably accelerated by the cosolvents PrⁱOH, Bu^tOH, Me₂CO, and MeCN. On the contrary the base hydroylsis (k₂) was retarded while spontaneous aquation (k₁) was accelerated to a small extent with increased EG content. Variation of log k₁ and log k (k = k₂ at I = 0) with mole fraction (_X0.S) or reciprocal of the relative permitivity (D_s^?1) of the media were nonlinear. The transfer free energy of the transition state relative to that of the initial state of the substrate for transfer of species from water to mixed solvents also varied nonlinearly with _X0.S, or D_s^?1 indicating solvent specificity. The activation parameters, ΔH^≠ and ΔS^≠ varied nonlinearly with solvent composition exhibiting extrema. The preferential solvation and solvent structural effects mediated the kinetics and energetics of the reaction. © 1995 John Wiley & Sons, Inc.     

Allowance for polarization of atomic electron shells in MO LCAO calculations

The application of MO LCAO methods to molecules containing elements in the higher periods is discussed, especially compounds containing two phenyl rings linked via an oxygen atom. The calculated -electron density is found to agree with the observed electronic absorption spectra, dipole moment, effects of polarity on reactivity, and so on, provided that the wave function used for the heteroatom with n>2 is =c₁ npz+ +c_{2 nd}+...; the terms c_{2 nd}... provide correction for the change in the atomic function _npz produced by the surrounding atoms. This effect is not important for O, N, and C (first period). The effects of surrounding atoms on _npz for the halogen atom have evidently to be considered in computations on the -electron density for any molecule containing such an atom.     

Der Einfluß von methyl- und dimethylsubstituierten Pyridinen als Liganden auf die Struktur und den Elektronentransfer bei Thiocyanat-Kupfer(II)-Komplexen

Complexes of the type Cu(NCS)₂ L ₂ whereL are all isomeric picolines and lutidines, as well as those of the type Cu(NCS)₂ L ₃ forL=-, -picoline, 3,4-, and 3,5-lutidine were prepared. The complexes were studied by means of thermal decomposition, and by electronic andESR spectroscopy. The results obtained have been brought into correlation with the effect of the ligandsL being caused by the methyl groups on the pyridine ring. It has been found that the differences in the properties studied which appear between Cu(NCS)₂ L ₂ and Cu(NCS)₂(pyridine)₂ are conditioned especially by the steric effect of the ligandsL with the methyl group in -position. The other ligandsL, however, show also an influence on some properties of the respective complexes.

---

---

Mit 2 Abbildungen     

Characteristic Features of the Formation of Copper(I) π-Complexes with N-Allyl Derivatives of Piperazinium Sulfamate

The crystals of two copper(I) complexes and piperazinium sulfamate were synthesized by ac electrochemical technique from Cu(NH₂SO₃)₂· xH₂O and N,N-diallylpiperazine, N-allylpiperazine, or piperazine titrated by sulfamic acid in aqueous methanol to pH 4. The crystal structures of the complexes were determined (DARCh diffractometer, MoK radiation, /2 scan mode). The crystal data: [C₃H₅NH(CH₂)₄NHC₃H₅]_0.5[Cu(NH₂SO₃)₂] · H₂O (I), space group P1¯, a = 8.053(1) Å, b = 10.247(2) Å, c = 8.918(2) Å, = 113.03(1)°, = 107.14(2)°, = 95.15(1)°, Z = 2; [NH₂(CH₂)₄NH₂]_0.5NH₂SO₃ (II), space group P2₁/a, a = 8.468(7) Å, b = 5.92(1) Å, c = 10.890(9) Å, = 100.40(9)°, Z = 4; {[C₃H₅NH(CH₂)₄NHC₃H₅][NH₂(CH₂)₄NH₂]}_0.5[Cu(NH₂SO₃)₃] · H₂O (III), space group P1¯, a = 11.729(3) Å, b = 8.266(2) Å, c = 10.611(3) Å, = 82.13(2)°, = 65.73(2)°, = 74.86(2)°, Z = 2. Structure III is a hybrid of elements of structures I and II and contains the -coordinated Cu(I) atom surrounded by three -donor sulfamate nitrogen atoms, which was found for the first time.     

Synthesis and Structural Features of Copper(I) Chloride and Bromide Complexes with the N,N,N′,N′-Tetraallylpiperasinium Cation (L2+) of Compositions L2+[CuCl2]– 2 and L2+[CuBr3]2–

Crystals of the -complex [C₄H₈N₂(C₃H₅)₄]²⁺[CuCl₂]^– ₂ (I) were prepared by ac electrochemical synthesis from copper and N,N,N,N-tetraallylpiperasinium chlorides in alcohol solution. Similar synthesis with the use of the metal and N,N,N,N-tetraallylpiperasinium bromides yielded the complex [C₄H₈N₂(C₃H₅)₄]²⁺[CuBr₃]^2– (II). Structures I and II were studied by X-ray diffraction (DARCh automated single-crystal diffractometer, MoK radiation). Crystals of I are triclinic, space group P1¯, a = 8.650(3) Å, b = 7.572(2) Å, c = 8.095(3) Å, = 100.45(2)°, = 83.91(2)°, = 99.89(2)°, V = 512.1(6) ų, Z = 1. Crystals of II are orthorhombic, space group Pn2₁ a, a = 17.673(3) Å, b = 14.369(6) Å, c = 8.244(2) Å, V = 2093(2) ų, Z = 4. In structure I, the potentially tetradentate N,N,N,N-tetraallylpiperasinium cation uses two centrosymmetric allyl groups for bonding with copper atoms, whose environment is completed to the trigonal-planar coordination with the chlorine atoms. The [C₄H₈N₂(C₃H₅)₄]²⁺[CuCl₂]^– ₂ groups are joined into a three-dimensional framework by weak hydrogen bonds. The inorganic fragment CuCl^– ₂ is partially disordered, which appears as splitting of the positions of the copper atom and one of the chlorine atom. In compound II, the inorganic fragment occurs as an unusual trigonal-planar CuBr^2– ₃ anion; the N,N,N,N-tetraallylpiperasinium cation is not involved in metal coordination.     

Crystal structures and hydrogen bonding schemes in four benzamide derivatives (2-hydroxy-benzamide, 2-hydroxy-thiobenzamide, 2-hydroxy-N,N-dimethyl-benzamide,and 2-Hydroxy-N,N-dimethyl-thiobenzamide)

Summary 2-Hydroxy-benzamide, C₇H₇NO₂; monoclinic; I2/a-C _2h ⁶ ;a=12.901 (2),b=4.982 (1),c=20.987 (3) Å; =91.50 (2)°;Z=8. 2-Hydroxy-thiobenzamide, C₇H₇NOS; monoclinic; P2₁/n-C _2h ⁵ ;a=13.508 (5),b=6.780 (2),c=15.878 (6) Å; =93.74 (5)°;Z=8. 2-Hydroxy-N,N-dimethyl-benzamide, C₉H₁₁NO₂; orthorhombic; Pbca-D _2h ¹⁵ ;a=11.752 (2),b=16.680 (3),c=9.079 (2) Å;Z=8. 2-Hydroxy-N,N-dimethyl-thiobenzamide, C₉H₁₁NOS; monoclinic; P2₁/c-C _2h ⁵ ;a=6.983 (1),b=11.652 (3),c=11.704 (3) Å; =100.02 (2)°;Z=4. The crystal structures of these four compounds were determined (respectively refined: 2-hydroxy-benzamide) by single crystal X-ray data. The refinements of the structure parameters by least squares methods yielded in all casesR<0.056. The hydrogen atoms were located by means of difference Fourier summations. The O-H ... O distances are 2.513 (1) Å in 2-hydroxy-benzamide (intramolecular) and 2.625 (1) Å in 2-hydroxy-N,N-dimethyl-benzamide (intermolecular). The two O-H ... S distances in 2-hydroxy-thiobenzamide are 2.904 (2) Å and 2.918 (2) Å (intramolecular, two molecules in the asymmetric unit) and 3.228 (2) Å in 2-hydroxy-N,N-dimethyl-thiobenzamide (intermolecular). Clear N-H ... O hydrogen bonds with 2.926 (1) Å and 3.006 (1) Å occur only in the structure of 2-hydroxy-benzamide (intermolecular).

---

Die Kristallstrukturen und Wasserstoffbrücken-Bindungsschemata in vier Benzamid-Derivaten

Zusammenfassung 2-Hydroxy-benzamid, C₇H₇NO₂; monoklin; I2/a-C _2h ⁶ ;a=12.901 (2),b=4.982 (1),c=20.987 (3) Å; =91.50 (2)°;Z=8. 2-Hydroxy-thiobenzamid, C₇H₇NOS; monoklin; P2₁/n-C _2h ⁵ ;a=13.508 (5),b=6.780 (2),c=15.878 (6) Å; =93.74 (5)°;Z=8. 2-Hydroxy-N,N-dimethyl-benzamid, C₉H₁₁NO₂; orthorhombisch; Pbca-D _2h ¹⁵ ;a=11.752 (2),b=16.680 (3),c=9.079 (2) Å;Z=8. 2-Hydroxy-N,N-dimethyl-thiobenzamid, C₉H₁₁NOS; monoklin; P2₁/c-C _2h ⁵ ;a=6.983 (1),b=11.652 (3),c=11.704 (3) Å; =100.02 (2)°;Z=4. Die Kristallstrukturen dieser vier Verbindungen wurden mittels Röntgen-Einkristalldaten bestimmt (bzw. verfeinert: 2-Hydroxy-benzamid). Die Verfeinerungen der Strukturparameter nach der Methode der kleinsten Quadrate ergab in allen FällenR<0.056. Die Wasserstoffatome konnten anhand von Differenz-Fourier-Summationen belegt werden. Die O-H ... O-Abstände haben folgende Werte: 2.513(1)Å in 2-Hydroxy-benzamid (intramolekular) und 2.625(1) Å in 2-Hydroxy-N,N-dimethyl-benzamid (intermolekular). Die zwei O-H ... S-Abstände sind in 2-Hydroxy-thiobenzamid 2.904(2)Å und 2.918(2)Å (intramolekular, zwei moleküle in der asymmetrischen Einheit) und 3.228(2)Å in 2-Hydroxy-N,N-dimethyl-thiobenzamid(intermollekular). Klar zuzuordnende N-H ... O-Wasserstoffbrücken mit 2.926(1)Å und 3.006(1)Å treten lediglich in der Struktur des 2-Hydroxy-benzamid auf (intermolekular).

     

Chemical Bonding in Molecules and Complexes Containing d-Elements Based on DFT

Summary. Metal–ligand bonding in transition metal halide molecules and complexes with different central ions, oxidations states, and coordination numbers: Cr^IIIX₆^3–, Cr^IVX₄, Cr^IIX₂ (X = F,Cl,Br,I), M^IIICl₆^3–(M = Mo,W), M^III(H₂O)₆³⁺(M = Cr,Co) and Re₂Cl₈^2– has been studied in terms of the Extended Transition State (ETS) energy patitioning scheme within the DFT and electron density analysis (the Laplacian of the electron density and the electronic localization function). Bonding is found to be dominated by ionicity in all cases, especially so for complexes with higher coordination numbers. Covalent contributions to the metal–ligand bond are found to be mainly due to the nd-electrons and to lesser extent due to the metal (n+1)s and (n+1)p-orbitals, contributions from (n+1)s increasing when going to lower coordination numbers. Metal–ligand bonding analysis have been used in order to check some concepts emerging from ligand field theory when applied to the spectroscopy and magnetism of transition metal complexes. It is pointed out that for complexes of high symmetry (MX₆, O_h, MX₄, T_d, and MX₂, D_h) electron density analyses gain interpretative power when partitioned into contributions from occupied orbitals of different symmetry.     

Two Modifications of the Mixed-Ligand Complex ZnPhen(i-C3H7OCS2)2 with Monodentate and Bidentate Ligands i-C3H7OCS 2 -

Two crystal modifications (m-1 and m-2) of the mixed-ligand complex ZnPhen(i-PrOCS₂)₂ have been isolated. Their crystal structures were solved using X-ray diffraction data (CAD-4 diffractometer, MoK radiation, 3141 and 3532 F_hkl, R = 0.0363 and 0.0304). For both modifications, the crystals are monoclinic with unit cell parameters a = 10.543(2), b = 13.494(3), c = 16.875(3) , = 102.08(3)°, V = 2347.6(8) ³, Z = 4, space group P2₁/n (m-1) and a = 10.931(2), b = 12.996(3), c = 16.288(3) , = 92.69(3)°, V = 2311.3(8) ³, Z = 4, space group P2₁/n (m-2). The structures basically consist of discrete monomer molecules in which the Zn atom has a tetragonal pyramidal (m-1: ZnN₂S₃, c.n. 5, bidentate and monodentate i-PrOCS ₂ ^- ligands) or distorted octahedral (m-2: ZnN₂S₄, c.n. 6, bidentate i-PrOCS ₂ ^- ligands) environment. Molecular packings and their interactions in the structures are discussed.     

Effects of mixed CH3CN(SINGLEBOND)H2O solvents on rate of intramolecular general base-catalyzed cleavage of ionized phenyl salicylate in the presence of 3-aminopropan-1-ol, 1,2-diaminoethane,and glycine

The effects of mixed CH₃CN(SINGLEBOND)H₂O solvents on rates of aminolysis of ionized phenyl salicylate, PS⁻, reveal a nonlinear decrease in the nucleophilic second-order rate constants, k_n^ms, (for aminolysis) with increase in the content of CH₃CN until it becomes ∼50%, v/v. The values of k_n^ms remain almost unchanged with change in the CH₃CN content within 50 to 70 or 80%, v/v. The effects of mixed CH₃CN(SINGLEBOND)H₂O solvents on pK_a of leaving group, phenol, and protonated amine nucleophile have been concluded to be the major source for the observed mixed solvent effects on k_n^ms. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 301–307, 1998.     

Steric structure and thermodynamic aspects of the complexes of dysprosium(iii) with aminobenzoic acids in aqueous solutions

Steric structures of dysprosium(III) aminobenzoate complexes with the 11 and 12 molar ratio in aqueous solutions were determined on the basis of pH-metric and paramagnetic birefringence data. An increase in conjugation observed for the series of the acids,viz., benzoic,meta-, ortho-, andpara-aminobenzoic acids, results in the increased stability of the complexes with the 11 and 12 composition. In the case ofpara-aminobenzoic acid, the polyhedra [DyL(H₂O)₆]²⁺ and [DyL₂(H₂O)₄]⁺ are cubes with the ligands coordinated to one and two edges, respectively. In the case ofmeta-aminobenzoic acid, the polyhedra [DyL(H₂O)₆]²⁺ and [DyL₂(H₂O)₄]⁺ are a dodecahedron with the ligand coordinated to one edge and a square anti-prism with the ligands coordinated to two edges, respectively. In the case ofortho-aminobenzoic acid, both the 11 and 12 complexes have structures that are intermediate between the structures ofmeta- andpara-aminobenzoic acids.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1767–1770, October, 1994.     

Ionization potentials of halides. Substituent effects in Cl-, Br-, and I-centered radical cations

The first vertical ionization potentials (I) of halides HalX (Hal = Cl, Br, I; X is an inorganic or organic substituent) are linearly related to the inductive (_I), resonance (_R ⁺), and polarizability () constants of the substituents X (I = a + b_I + c_R ⁺ + d). As the atomic number of the Hal element in the Hal^·+X radical cations increases, the inductive interaction is strengthened while the polarizability interaction is weakened. Conjugation remains virtually independent of the Hal atom. The resonance _R ⁺-constants of the MX₃ (M = Si, Ge, Sn, Pb) substituents bound to the Hal^·+ radical cation centers were first calculated.     

Synthesis and characterization of β-diketonato- and phenoxoderivatives of mono(dizirconium-ennea-isopropoxy)copper(II)

Summary -Diketonato- and phenoxo-derivatives of mono(dizirconium-ennea-isopropoxy) copper(II), [Cu{Zr₂(OPr-i)₉}-(RCOCHCOR)] and [Cu{Zr₂(OPr-i)₉}(-OAr)], have been prepared by the interaction of K(RCOCHCOR) or KOAr (1 mol) [R = R = Me (1a); R = R = CF₃ (1b); R = Me, R = CF₃ (1c); OAr = 2,6-Me₂C₆H₃O (2a), 3,5-Me₂C₆H₃O (2b), p-ClC₆H₄O (2c)] with [Cu{Zr₂-(OPr-i) ₉}(-Cl)] (1 mol) in PhH. Alcohol interchanges of the derivative [Cu{Zr₂(OPr-i)₉}(-Cl)] have also been studied. These new compounds have been characterized by elemental analyses, i.r., electronic and e.s.r. spectra, and magnetic susceptibility measurements. The studies indicate a distorted octahedral geometry around Cu^II.     

Kinetics and mechanism of nucleophilic substitution of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II) by pyridine bases

The reaction of dichloro{1-methyl-2-(arylazo)imidazole}palladium(II), Pd(RaaiMe)Cl₂ where RaaiMe = p-R–C₆H₄N=N–C₃H₂N₂-1-Me; R = H(1), Me(2), Cl(3), with pyridine bases [RPY: R = H (a), 4-Me (b), 4-Cl (c), 2-Me (d), 2,6-Me₂ (e), 2,4,6-Me₃ (f)] has been studied spectrophotometrically in MeCN at 451 nm. The products (4) have been isolated and characterised as trans-Pd(RPy)₂Cl₂. The kinetics of the nucleophilic substitution has been examined under pseudo-first-order conditions at 298 K. A single phase reaction step has been observed for bases such as Hpy (a), 4-MePy (b) and 4-ClPy (c) and follows the rate law: rate = (a + k[RPy]²[Pd(RaaiMe)Cl₂]). The bases 2-MePy (d), 2,6-Me₂Py (e) and 2,4,6-Me₃Py (f) exhibits a bi-phasic reaction and follows the rate laws: rate–1 = (a + k[RPy][Pd(RaaiMe)Cl₂]) and rate–2 = (a + k[RPy][Pd(RaaiMe)-Cl₂]), where k is the third-order rate constant; k is the second-order first phase rate constant, k is the second-order second phase rate constant and a/a/a correspond to the solvent dependent constant of the respective reaction path. The rate data supports a nucleophilic association path. External addition of Cl^– (LiCl) suppresses the rate, which follows the order: k/k/k (3) > k/k,k (1) > k/k,k (2). The k values are linearly related to the Hammett constants. The 2-substituted pyridines (d–f) remarkably reduce the rate and show a bi-phasic reaction behaviour as compared with 4-Rpy (a–c). This is attributed to the steric effect that destabilises the transition state. The rate decreases with increasing steric crowding at the ortho-position and follows the order: (d) > (f) > (e). The 4-substituted pyridines control the rate via an inductive effect and follow the order: (b) > (a) > (c).