Vitaly E. Matulis

Azide Binding Controlled by Steric Interactions in Second Sphere. Synthesis, Crystal Structure, and Magnetic Properties of [NiII2(L)(μ1,1-N3)][ClO4] (L = Macrocyclic N6S2 Ligand)

The dinuclear Ni(II) complex [Ni2(L(2))][ClO4]2 (3) supported by the 28-membered hexaaza-dithiophenolate macrocycle (L(2))(2-) binds the N3(-) ion specifically end-on yielding [Ni2(L(2))(μ(1,1)-N3)][ClO4] (7) or [Ni2(L(2))(μ(1,1)-N3)][BPh4] (8), while the previously reported complex [Ni2L(1)(μ(1,3)-N3)][ClO4] (2) of the 24-membered macrocycle (L(1))(2-) coordinates it in the end-to-end fashion. A comparison of the X-ray structures of 2, 3, and 7 reveals the form-selective binding of complex 3 to be a consequence of its preorganized, channel-like binding pocket, which accommodates the azide anion via repulsive CH···π interactions in the end-on mode. In contrast to [Ni2L(1)(μ(1,3)-N3)][ClO4] (2), which features a S = 0 ground state, [Ni2(L(2))(μ(1,1)-N3)][BPh4] (8) has a S = 2 ground state that is attained by competing antiferromagnetic and ferromagnetic exchange interactions via the thiolato and azido bridges with a value for the magnetic exchange coupling constant J of 13 cm(-1) (H = -2JS1S2). These results are further substantiated by density functional theory calculations. The stability of the azido-bridged complex determined by isothermal titration calorimetry in MeCN/MeOH 1/1 v/v (log K11 = 4.88(4) at I = 0.1 M) lies in between those of the fluorido- (log K11 = 6.84(7)) and chlorido-bridged complexes (log K11 = 3.52(5)). These values were found to compare favorably well with the equilibrium constants derived at lower ionic strength (I = 0.01 M) by absorption spectrophotometry (log K11 = 5.20(1), 7.77(9), and 4.13(3) for N3(-), F(-), and Cl(-) respectively).

Aqueous-based synthesis of atomic gold clusters: Geometry and optical properties

Gold clusters synthesized by the solution-based growth technique have exhibited ultraviolet (UV) light emission with nearly zero Stokes shift. Atomic arrangement decided optical properties of the Au microclusters have been studied extensively. In addition to the time-of-flight mass spectra, the comparison of experimental and theoretical emission and absorption spectra confirms the presence of Au8 clusters with the planar hexagon+1-shaped geometry. The observed UV emission is attributed to the transition from the highest occupied to the lowest unoccupied molecular orbitals of the hexagon+1 structured Au8 clusters.

Cavitands incorporating a Lewis acid dinickel chelate function as receptors for halide anions.

The halide binding properties of the cavitand [Ni2(L(Me2H4))](2+) (4) are reported. Cavitand 4 exhibits a chelating N3Ni(μ-S)2NiN3 moiety with two square-pyramidal Ni(II)N3S2 units situated in an anion binding pocket of ∼4 Å diameter formed by the organic backbone of the (L(Me2H4))(2-) macrocycle. The receptor reacts with fluoride, chloride (in MeCN/MeOH), and bromide (in MeCN) ions to afford an isostructural series of halogenido-bridged complexes [Ni2(L(Me2H4))(μ-Hal)](+) (Hal = F(-) (5), Cl(-) (6), and Br(-) (7)) featuring a N3Ni(μ-S)2(μ-Hal)NiN3 core structure. No reaction occurs with iodide or other polyatomic anions (ClO4(-), NO3(-), HCO3(-), H2PO4(-), HSO4(-), SO4(2-)). The binding events are accompanied by discrete UV-vis spectral changes, due to a switch of the coordination geometry from square-pyramidal (N3S2 donor set in 4) to octahedral in the halogenido-bridged complexes (N3S2Hal donor environment in 5-7). In MeCN/MeOH (1/1 v/v) the log K11 values for the 1:1 complexes are 7.77(9) (F(-)), 4.06(7) (Cl(-)), and 2.0(1) (Br(-)). X-ray crystallographic analyses for 4(ClO4)2, 4(I)2, 5(F), 6(ClO4), and 7(Br) and computational studies reveal a significant increase of the intramolecular distance between two propylene groups at the cavity entrance upon going from F(-) to I(-) (for the DFT computed structure). In case of the receptor 4 and fluorido-bridged complex 5, the corresponding distances are nearly identical. This indicates a high degree of preorganization of the [Ni2(L(Me2H4))](2+) receptor and a size fit mismatch of the receptor binding cavity for anions larger than F(-).

Symmetry-adapted-cluster configuration interaction study of the doublet states of HCl+: potential energy curves, dipole moments, and transition dipole moments.

The electronic structure of the HCl(+) molecular ion has been calculated using the general-R symmetry-adapted-cluster configuration interaction (SAC-CI) method. The authors present the potential energy curves, dipole moments, and transition dipole moments for a series of doublet states. The data are compared with the previous CASSCF and MCSCF calculations. The SAC-CI results reproduce quite well the data available in literature and extend the knowledge on the HCl(+) electronic structure for several higher states. The calculated R-dependent behavior of both dipole moments and transition dipole moments for a series of bound and unbound states reveals an intricate dissociation process at intermediate distances (R>R(e)). The pronounced maxima in transition dipole moment (TDM) describing transitions into high electronic states (X (2)Pi-->3 (2)Pi, X (2)Pi-->3 (2)Sigma, 2 (2)Pi-->3 (2)Pi, 3 (2)Pi-->4 (2)Pi) occur at different interatomic separations. Such TDM features are promising for selection of excitation pathways and, consequently, for an optimal control of the dissociation products.

Theoretical study of optical properties of gold clusters

Characteristics of photoelectron spectrum of Au2− and Au4− clusters were calculated using different functionals and basis sets, and the results were compared with experimental data. The TD-B3LYP/LANL2Z method was shown to provide for calculation of these characteristics with good accuracy. Based on these results we suggested the methods and carried out appropriate calculations of the absorption and emission for different isomers of Au8 clusters. It was shown that the best agreement with the experimental data is observed for the planar C2ν “hexagon+1” structure, therefore, this is the structure observed experimentally. The calculated value of the Stokes shift for the specified structure does not exceed 12 nm, which is also in good agreement with experimental results.

catena-Poly[[tetrakis(2-allyltetrazole-κN4)-tetra-μ-chloro-tricopper(II)]-di-μ-chloro]

In the crystal structure of the title compound, [Cu(3)Cl(6)(C(4)H(6)N(4))(4)](n), there are three Cu atoms, six Cl atoms and four 2-allyltetrazole ligands in the asymmetric unit. The polyhedron of one Cu atom adopts a flattened octahedral geometry, with two 2-allyltetrazole ligands in the axial positions [Cu-N4 = 1.990 (2) and 1.991 (2) A] and four Cl atoms in the equatorial positions [Cu-Cl = 2.4331 (9)-2.5426 (9) A]. The polyhedra of the other two Cu atoms have a square-pyramidal geometry, with three basal sites occupied by Cl atoms [Cu-Cl = 2.2487 (9)-2.3163 (8) and 2.2569 (9)-2.3034 (9) A] and one basal site occupied by a 2-allyltetrazole ligand [Cu-N4 = 2.028 (2) and 2.013 (2) A]. A Cl atom lies in the apical position of either pyramid [Cu-Cl = 2.8360 (10) and 2.8046 (9) A]. The possibility of including the tetrazole N3 atoms in the coordination sphere of the two Cu atoms is discussed. Neighbouring copper polyhedra share their edges with Cl atoms to form one-dimensional polymeric chains running along the a axis.

Interaction of Nitric Oxide and Nitric Oxide Dimer with Silver Clusters

Study of interaction of NO and (NO)2 molecules with silver clusters has been carried out using the hybrid method S2LYP based on density functional theory (DFT). The role of cluster charge and site of adsorption on N–O stretch frequency, adsorption energy and geometry has been investigated. Four cluster models of different size have been used for simulation of (NO)2 adsorption on Ag{111} surface. The pronounced effect of N–N bond shortening in comparison with gaseous (NO)2 has been found due to adsorption of (NO)2 on silver cluster. This phenomenon is important as possible pathway of N–N bond formation in catalytic fragmentation of NO molecule. The calculations showed that the silver octamer is the best candidate for simulation of formation and fragmentation of (NO)2 on Ag{111} surface within the cluster model.

5-MERCAPTOTETRAZOLE-1-ACETIC ACID AS A NOVEL CAPPING LIGAND FOR STABILIZATION OF METAL NANOPARTICLES IN WATER

Tetrazole derivatives are an intriguing type of capping ligands for stabilization nanoparticles (NPs). The presence of four nitrogen atoms in the tetrazole ring determines its unique thermal behavior, hydrophilicity as well as strong coordination ability towards different metal ions (Fig. 1). Recently, 5-mercaptomethyltetrazole (1) was found to be a substitute for thioglycolic acid which is widely used as a capping agent in the aqueous synthesis of colloidal semiconductor NPs [1]. The employment of this tetrazole results in stable watersoluble CdTe, ZnSe and Au NPs which possess the unique ability to reversibly form hydrogels upon addition of transition metal salts [1-3]. The formation of hydrogels occurs owing to the cross-linking of capping ligands through complexation by metal ions. Spherical and nearly monodispersed noble metal NPs were synthesized by the reduction of metal precursors in a biphasic toluenewater system in the presence of 1-R-tetrazole-5-thiols (2) [4].

DFT Study of Gold Clusters Luminescence Spectrum

Methods of calculation of optical absorption and emission spectra for Au8 cluster has been suggested and corresponding calculations has been carried out. It has been shown that the best agreement with experiment is observed in case of planar C2v hexagon+1 shaped structure. The comparison of calculated absorption and emission spectra reveals that Stokes shift is small (about 11.5 nm) which agrees well with experimental results.