Synthesis and characterization of new five-coordinate platinum nitrosyl derivatives: density functional theory study of their electronic structure

The neutral, five-coordinate platinum nitrosyl compounds [Pt(C(6)F(5))(3)(L)(NO)] (2) [L=CNtBu (2 a), NC(5)H(4)Me-4 (2 b), PPhMe(2) (2 c), PPh(3) (2 d) and tht (2 e)] have been prepared by the reaction of [NBu(4)][Pt(C(6)F(5))(3)(L)] (1) with NOClO(4) in CH(2)Cl(2). The ionic compound [N(PPh(3))(2)][Pt(C(6)F(5))(4)(NO)] (4) has been prepared in a similar way starting from the homoleptic species [N(PPh(3))(2)](2)[Pt(C(6)F(5))(4)] (3). Compounds 2 and 4 are all diamagnetic with [PtNO](8) electronic configuration and show nu(NO) stretching frequencies at around 1800 cm(-1). The crystal and molecular structures of 2 c and 4 have been established by X-ray diffraction methods. The coordination environment for the Pt center in both compounds can be described as square pyramidal (SPY-5). Bent nitrosyl coordination is observed in both cases with Pt-N-O angles of 120.1(6) and 130.2(7) degrees for 2 c and 4, respectively. The bonding mechanism of the nitrosyl ligand coordinated to various model [Pt(II)R(4)](2-) (R=H, Me, Cl, CN, C(6)F(5) or C(6)Cl(5)) and [Pt(C(6)F(5))(3)(L)](-) (L=CNMe, PH(3)) systems has been studied by density functional calculations at the B3LYP level of theory, using the SDD basis set. The R(4)Pt-NO and (C(6)F(5))(3)(L)Pt-NO interactions generally involve two components: i) a direct Pt-NO bonding interaction and ii) multicenter-bonding interactions between the N atom of the NO ligand and the donor atoms of the R and L ligands. Moreover, with the more complex R groups, C(6)F(5) or C(6)Cl(5), a third component has been found to arise, which involves multicenter electrostatic interactions between the positively charged NO ligand and the negatively charged halo-substituents in the ortho-position of the C(6)X(5) groups (X=F, Cl). The contribution of each component to the Pt-NO bonding in R(4)Pt-NO and (C(6)F(5))(3)(L)Pt-NO compounds seems to be modulated by the electronic and steric effects of the R and L ligands.     

Insights into the Intramolecular Donor Stabilisation of Organostannylene Palladium and Platinum Complexes: Syntheses,Structures and DFT Calculations

The syntheses of the transition metal complexes cis‐[(4‐tBu‐2,6‐{P(O)(OiPr)₂}₂C₆H₂SnCl)₂MX₂] ( 1 , M=Pd, X=Cl; 2 , M=Pd, X=Br; 3 , M=Pd, X=I; 4 , M=Pt, X=Cl), cis‐[{2,6‐(Me₂NCH₂)₂C₆H₃SnCl}₂MX₂] ( 5 , M=Pd, X=I; 6 , M=Pt, X=Cl), trans‐[{2,6‐(Me₂NCH₂)₂C₆H₃SnI}₂PtI₂] ( 7 ) and trans‐[(4‐tBu‐2,6‐{P(O)(OiPr)₂}₂ C₆H₂SnCl)PdI₂]₂ ( 8 ) are reported. Also reported is the serendipitous formation of the unprecedented complexes trans‐[(4‐tBu‐2,6‐{P(O)(OiPr)₂}₂C₆H₂SnCl)₂ Pt(SnCl₃)₂] ( 10 ) and [(4‐tBu‐2,6‐{P(O) (OiPr)₂}₂C₆H₂SnCl)₃Pt(SnCl₃)₂] ( 11 ). The compounds were characterised by elemental analyses, ¹H, ¹³C, ³¹P, ¹¹⁹Sn and ¹⁹⁵Pt NMR spectroscopy, single‐crystal X‐ray diffraction analysis, UV/Vis spectroscopy and, in the cases of compounds 1 , 3 and 4 , also by Mössbauer spectroscopy. All the compounds show the tin atoms in a distorted trigonal‐bipyramidal environment. The Mössbauer spectra suggest the tin atoms to be present in the oxidation state III. The kinetic lability of the complexes was studied by redistribution reactions between compounds 1 and 3 as well as between 1 and cis‐[{2,6‐(Me₂NCH₂)₂C₆H₃SnCl}₂PdCl₂]. DFT calculations provided insights into both the bonding situation of the compounds and the energy difference between the cis and trans isomers. The latter is influenced by the donor strength of the pincer‐type ligands.     

Vibrational corrections to geometries of transition metal complexes from density functional theory

Zero-point vibrational corrections are computed at the BP86/AE1 level for the set of 50 transition-metal/ligand bonds that have recently been proposed as testing ground for DFT methods, because of the availability of precise experimental gas-phase geometries (Bühl and Kabrede, J Chem Theory Comput 2006, 2, 1282). These corrections are indicated to be transferable to a large extent between various density-functional/basis-set combinations, so that they can be used to estimate zero-point averaged r0g distances from re values optimized at other theoretical levels. Applying this approach to a number of popular DFT levels does not, in general, improve their overall accuracy in terms of mean and standard deviations from experiment. The hybrid variant of the meta-functional TPSS is confirmed as promising choice for computing structures of transition-metal complexes.     

Oligonuclear Molecular Models of Intermetallic Phases: A Case Study on [Pd2Zn6Ga2(Cp*)5(CH3)3]

The synthesis, characterization, and theoretical investigation by means of quantum‐chemical calculations of an oligonuclear metal‐rich compound are presented. The reaction of homoleptic dinuclear palladium compound [Pd₂(μ‐GaCp*)₃(GaCp*)₂] with ZnMe₂ resulted in the formation of unprecedented ternary Pd/Ga/Zn compound [Pd₂Zn₆Ga₂(Cp*)₅(CH₃)₃] ( 1 ), which was analyzed by ¹H and ¹³C NMR spectroscopy, MS, elemental analysis, and single‐crystal X‐ray diffraction. Compound 1 consisted of two C_s‐symmetric molecular isomers, as revealed by NMR spectroscopy, at which distinct site‐preferences related to the Ga and Zn positions were observed by quantum‐chemical calculations. Structural characterization of compound 1 showed significantly different coordination environments for both palladium centers. Whilst one Pd atom sat in the central of a bi‐capped trigonal prism, thereby resulting in a formal 18‐valence electron fragment, {Pd(ZnMe)₂(ZnCp*)₄(GaMe)}, the other Pd atom occupied one capping unit, thereby resulting in a highly unsaturated 12‐valence electron fragment, {Pd(GaCp*)}. The bonding situation, as determined by atoms‐in‐molecules analysis (AIM), NBO partial charges, and molecular orbital (MO) analysis, pointed out that significant Pd? Pd interactions had a large stake in the stabilization of this unusual molecule. The characterization and quantum‐chemical calculations of compound 1 revealed distinct similarities to related M/Zn/Ga Hume–Rothery intermetallic solid‐state compounds, such as Ga/Zn‐exchange reactions, the site‐preferences of the Zn/Ga positions, and direct M? M bonding, which contributes to the overall stability of the metal‐rich compound.     

Synthetic, structural, and theoretical investigations of alkali metal germanium hydrides--contact molecules and separated ions

The preparation of a series of crown ether ligated alkali metal (M=K, Rb, Cs) germyl derivatives M(crown ether)_nGeH₃ through the hydrolysis of the respective tris(trimethylsilyl)germanides is reported. Depending on the alkali metal and the crown ether diameter, the hydrides display either contact molecules or separated ions in the solid state, providing a unique structural insight into the geometry of the obscure GeH₃^? ion. Germyl derivatives displaying M? Ge bonds in the solid state are of the general formula [M([18]crown‐6)(thf)GeH₃] with M=K ( 1 ) and M=Rb ( 4 ). The compounds display an unexpected geometry with two of the GeH₃ hydrogen atoms closely approaching the metal center, resulting in a partially inverted structure. Interestingly, the lone pair at germanium is not pointed towards the alkali metal, rather two of the three hydrides are approaching the alkali metal center to display M? H interactions. Separated ions display alkali metal cations bound to two crown ethers in a sandwich‐type arrangement and non‐coordinated GeH₃^? ions to afford complexes of the type [M(crown ether)₂][GeH₃] with M=K, crown ether=[15]crown‐5 ( 2 ); M=K, crown ether=[12]crown‐4 ( 3 ); and M=Cs, crown ether=[18]crown‐6 ( 5 ). The highly reactive germyl derivatives were characterized by using X‐ray crystallography, ¹H and ¹³C NMR, and IR spectroscopy. Density functional theory (DFT) and second‐order Møller–Plesset perturbation theory (MP2) calculations were performed to analyze the geometry of the GeH₃^? ion in the contact molecules 1 and 4 .     

Synthesis,Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(22) Fullerene

Trifluoromethylation of higher fullerene mixtures with CF₃I was performed in ampoules at 400 to 420 and 550 to 560 °C. HPLC separation followed by crystal growth and X‐ray diffraction studies allowed the structure elucidation of nine CF₃ derivatives of D₂‐C₈₄ (isomer 22). Molecular structures of two isomers of C₈₄(22)(CF₃)₁₂, two isomers of C₈₄(22)(CF₃)₁₄, four isomers of C₈₄(22)(CF₃)₁₆, and one isomer of C₈₄(22)(CF₃)₂₀ were discussed in terms of their addition patterns and relative formation energies. DFT calculations were also used to predict the most stable molecular structures of lower CF₃ derivatives, C₈₄(22)(CF₃)_2–10. It was found that the addition of CF₃ groups to C₈₄(22) is governed by two rules: additions can only occur at para positions of C₆(CF₃)₂ hexagons and no additions can occur at triple‐hexagon‐junction positions on the fullerene cage.     

Synthesis,Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(23) Fullerene

Trifluoromethylation of a higher fullerene mixture with CF₃I was performed in ampoules at 550 °C. HPLC separation followed by crystal growth and X‐ray diffraction study resulted in the structure elucidation of nine CF₃ derivatives of D_2d‐C₈₄ (isomer 23). The molecular structures of C₈₄(23)(CF₃)₄, C₈₄(23)(CF₃)₈, C₈₄(23)(CF₃)₁₀, C₈₄(23)(CF₃)₁₂, two isomers of C₈₄(23)(CF₃)₁₄, two isomers of C₈₄(23)(CF₃)₁₆, and C₈₄(23)(CF₃)₁₈ were discussed in terms of their addition patterns and the relative formation energies. Extensive theoretical DFT calculations were performed to identify the most stable molecular structures. It was found that the addition of CF₃ groups to the C₈₄(23) fullerene is governed by two main rules: no additions in positions of triple hexagon junctions and predominantly para additions in C₆(CF₃)₂ hexagons on the fullerene cage. The only exception with an isolated CF₃ group in C₈₄(23)(CF₃)₁₂ is discussed in more detail.     

Synthesis and Bonding in Carbene Complexes of an Unsymmetrical Dilithio Methandiide: A Combined Experimental and Theoretical Study

Herein, we report the preparation of a new unsymmetrical, bis(thiophosphinoyl)‐substituted dilithio methandiide and its application for the synthesis of zirconium‐ and palladium‐carbene complexes. These complexes were found to exhibit remarkably shielded ¹³C NMR shifts, which are much more highfield‐shifted than those of “normal” carbene complexes. DFT calculations were performed to determine the origin of these observations and to distinguish the electronic structure of these and related carbene complexes compared with the classical Fischer and Schrock‐type complexes. Various methods show that these systems are best described as highly polarized Schrock‐type complexes, in which the metal–carbon bond possesses more electrostatic contributions than in the prototype Schrock systems, or even as “masked” methandiides. As such, geminal dianions represent a kind of “extreme” Schrock‐type ligands favoring the ionic resonance structure M⁺? CR₂^? as often used in textbooks to explain the nucleophilic nature of Schrock complexes.     

The Effect of Guest Metal Ions on the Reduction Potentials of Uranium(VI) Complexes: Experimental and Theoretical Investigations

Two mononuclear uranyl complexes, [UO₂L¹] ( 1 ) and [UO₂L²] ⋅ 0.5 CH₃CN ⋅ 0.25 CH₃OH ( 2 ), have been synthesized from two multidentate N₃O₄ donor ligands, N,N′-bis(5-methoxysalicylidene)diethylenetriamine (H₂L¹) and N,N′-bis(3-methoxysalicylidene)diethylenetriamine (H₂L²), respectively, and have been structurally characterized. Both complexes 1 and 2 showed a reversible U^VI/U^V couple at −1.571 and −1.519 V, respectively, in cyclic voltammetry. The reduction potential of the U^VI/U^V couple shifted towards more positive potential on addition of Li⁺, Na⁺, K⁺, and Ag⁺ metal ions to acetonitrile solutions of complex 2 , and the resulting potential was correlated with the Lewis acidity of the metal ions and was also justified by theoretical DFT calculations. No such shift in reduction potential was observed for complex 1 . All four bimetallic products, [UO₂L²Li_0.5](ClO₄)_0.5 ( 3 ), [UO₂L²Na(ClO₄)]₂ ( 4 ), [UO₂L²Ag(NO₃)(H₂O)] ( 5 ), and [(UO₂L²)₂K(H₂O)₂]PF₆ ( 6 ), formed on addition of the Li⁺, Na⁺, Ag⁺, and K⁺ metal ions, respectively, to acetonitrile solutions of complex 2 , were isolated in the solid state and structurally characterized by single-crystal X-ray diffraction. In all the species, the inner N₃O₂ donor set of the ligand encompasses the equatorial plane of the uranyl ion and the outer open compartment with O₂O′₂ donor sites hosts the second metal ion.     

A Magnetic Ionic Liquid Based on Tetrachloroferrate Exhibits Three‐Dimensional Magnetic Ordering: A Combined Experimental and Theoretical Study of the Magnetic Interaction Mechanism

A new magnetic ionic liquid (MIL) with 3D antiferromagnetic ordering has been synthetized and characterized. The information obtained from magnetic characterization was supplemented by analysis of DFT calculations and the magneto‐structural correlations. The result gives no evidence for direct iron‐iron interactions, corroborating that the 3D magnetic ordering in MILs takes place via super‐exchange coupling containing two diamagnetic atoms intermediaries.     

Theoretical study of the magnetic behavior of ferric wheels.

Calculations of exchange coupling constants (J) based on density functional theory for eight complete, nonmodeled ferric wheels have been performed, and a comparison with the values obtained from magnetic susceptibility data is presented. The calculated J values obtained with a generalized-gradient approximation (GGA) functional are in good agreement with the experiment probably because the inclusion of pseudopotentials partially compensates the overestimation of the spin delocalization. The magnetostructural correlation obtained shows a strong dependence of the exchange coupling on both the Fe-O-Fe bond angle and the Fe-O bond distance. This correlation holds for both the ferric wheels and the alkoxo-bridged Fe(III) dinuclear complexes reported in the literature.     

A structural and computational study of synthetically important alkali-metal/tetramethylpiperidide (TMP) amine solvates

Two heavy alkali-metal salts of the sterically demanding amine, 2,2,6,6-tetramethylpiperidine (TMPH), have been prepared using different methodologies. Complex 1, [((tmeda)Na(tmp))2] (TMEDA=N,N, N',N'-tetramethylethylenediamine), can be synthesized by a deprotonative route. This is achieved by reacting butylsodium with TMPH in the presence of excess TMEDA in hexane. The potassium congener [((tmeda)K(tmp))2] (2), can be prepared by treating KTMP (made using a metathesis reaction between LiTMP and potassium tert-butoxide) with an excess of TMEDA in hexane. In the solid state, 1 and 2 are essentially isostructural. They are discretely dimeric and their framework consists of a four-membered M-N-M-N ring (M=Na or K, N=TMP). Due to the high steric demand of the TMP ligand, the TMEDA molecules bind to the metal centers in an asymmetric manner. In 2, each of the coordination spheres of the metals is completed by an agostic K...CH3(TMP) interaction. DFT calculations at the B3 LYP/6-311G** level give an insight into why 1 and 2 adopt dramatically different structures from their previously reported, "open-dimeric", lithium counterpart. The theoretical work also focuses on the TMEDA-free parent amide complexes and reveals that the energy difference for the formation of [(M(tmp))x] (in which, M=Li or Na, x=3 or 4; and M=K, x=2, 3 or 4) are small.     

Alkali metal diphenylmethanides: synthetic, computational and structural studies

In search of new synthetic precursors for the preparation of alkaline earth organometallic compounds, we investigated the application of a powerful desilylation reaction to cleanly afford a variety of contact and charge-separated alkali metal derivatives without the difficulties commonly encountered in other methods. The resulting diphenylmethanides display both contact molecules and separated ion pairs. Analysis of the structural data demonstrates that simple electrostatic models are insufficient for predicting and explaining the solid-state structures of these complexes. Detailed computational investigations were performed to probe the nature of the metal-anion and metal-donor interactions and determine the contributions of each to the observed solid-state structures.     

The effect of the functional,basis set,and solvent in the simulation of the geometry and spectroscopic properties of VIVO2+ complexes. chemical and biological applications

The geometry of 32 V^IVO²⁺ complexes with different donor set, electric charge, geometry, arrangement of the ligands with respect to the V?O bond and type of ligand was calculated by density functional theory methods. 32 V?O, 45 V? O, 16 V? OH, 40 V? N, 24 V? S, and 14 V? Cl bonds were examined. The performance of several functionals (B3LYP, B3P86, B3PW91, HCTH, TPSS, PBE0, and MPW1PW91), keeping constant the Pople triple‐zeta basis sets 6‐311g, was tested. The order of accuracy of the functional in the prediction of the bond distances, expressed in terms of mean of the deviation Δd (Δd = d^calcd ? d^exptl) and absolute deviation |Δd| (|Δd| = |d^calcd ? d^exptl|) from the experimental values and of the corresponding standard deviations (SD(Δd) and SD(|Δd|)), is: B3P86 ～ PBE0 ～ MPW1PW91 > B3PW91 ? TPSS > B3LYP ? HCTH. In the gas phase the prediction of V?O, V? O, V? N bond lengths is rather good, but that of V? OH, V? S and V? Cl distances is by far worse. An improvement in the optimization of V? S and V? Cl lengths is reached by adding polarization and diffuse functions on the sulfur and chlorine atoms. Finally, a general improvement in the prediction of all the calculated bond lengths and angles is obtained by simulating the structures in the solvent where they are isolated within the framework of the polarizable continuum model. The last choice allows also to improve the prediction of structural (the deviation of a penta‐coordinate geometry toward the trigonal bipyramid) and spectroscopic parameters (⁵¹V and ¹⁴N hyperfine coupling constants and ¹⁴N nuclear quadrupolar coupling constant). In most of the cases, the structures optimized in solution closely approach the experimental ones and this can be of great help in the simulations of naturally occurring vanadium compounds and metal site of V‐proteins, like amavadin and the reduced form of vanadium bromoperoxidase (VBrPO). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Quantum Chemical Study of the Reactions between Pd+/Pt+ and H2O/H2S

The study of the reactions of water and hydrogen sulfide with palladium and platinum cations has been completed in this work, in both low‐ and high‐spin states. Our calculations predict that only the formation of platinum sulfide is exothermic (in both spin states), whereas for the remaining species the oxides and sulfides are found to be more reactive than their corresponding bare metal cations. An in‐depth analysis of the reaction paths leading to metal oxide and sulfide species is given, including various minima, and several important transition states. All results have been compared with existing experimental and theoretical data, and earlier works covering the reaction of nickel cation with water and hydrogen sulfide to observe the trends for the group 10 transition metals.