Molybdophosphonate clusters as building blocks in the oxomolybdate-organodiphosphonate/cobalt(II)-organoimine system: structural influences of secondary metal coordination preferences and diphosphonate tether lengths

Hydrothermal conditions have been used in the preparation of a series of organic-inorganic hybrid materials of the cobalt-molybdophosphonate family. The reactions of MoO(3), cobalt(II) acetate or cobalt(II) acetylacetonate, tetra-2-pyridylpyrazine (tpyprz), and organodiphosphonic acids H(2)O(3)P(CH(2))nPO(3)H(2) (n = 1-5 and 9) of varying tether lengths yielded compounds of the general type {Co(2)(tpyprz)(H(2)O)(m)}4+/MoxOy{O(3)P(CH(2))(n)PO(3)}z. The recurring theme of the structural chemistry is the incorporation of {Mo(5)O(15)(O(3)PR)(2)}(4-) clusters as molecular building blocks observed in the structures of nine phases (compounds 2-9 and 11). The structural consequences of variations in reaction conditions are most apparent in the series with propylene diphosphonate, where four unique structures 4-7 are observed, including two distinct three-dimensional architectures for compounds 5 and 6 whose formulations differ only in the number of water molecules of crystallization. With pentyldiphosphonate, a second phase 10 is obtained which exhibits a unique cluster building block, the hexamolybdate [Mo(6)O(18){O(3)P(CH(2))(5)PO(3)}](4-). In the case of methylenediphosphonic acid, a third structural motif, the trinuclear {(Mo(3)O(8))(O(3)PCH(2)PO(3))}2- subunit, is observed in compound 1. The structural chemistry of compounds 1-11 of this study is quite distinct from that of the {Ni(2)(tpyprz)(H(2)O)(m)}(4+)/Mo(x)O(y){O(3)P(CH(2))(n)PO(3)}z family, as well as that of the copper-based family. The structural diversity of this general class of materials reflects the coordination preferences of the M(II) sites, the extent of aqua ligation to the M(II) sites, the participation of both phosphate oxygen atoms and molybdate oxo-groups in linking to the M(II) sites, and the variability in the number of attachment sites at the molybdophosphonate clusters. Since the charge densities at the peripheral oxygen atoms of the clusters are quite uniform, the attachment of {M(2)(tpyprz)}(4+) subunits to the molybdophosphonates appears to be largely determined by steric, coulombic, and packing factors, as shown by extensive density functional theory calculations.     

A ladder based on paddlewheel diruthenium(II, II) rails connected by TCNQ rungs: a polymorph of the hexagonal 2-D network phase

The slow diffusion reaction of [Ru(2)(O(2)CCF(3))(4)(THF)(2)] with TCNQ in CH(2)Cl(2)/4-chlorotoluene, respectively, leads to the formation of ladder chain composed of [Ru(2)] rails and TCNQ rungs in a 2 : 1 ratio.     

气相VO（∑＋）与CH3OH（1^A′）分子自旋禁阻反应C—H，O—H键活化机理的理论研究

采用密度泛函理论（DFT）B3LYP与cCsD方法研究了二重态和四重态势能面自旋禁阻反应VO（∑’）活化cH30H（1^A′）分子c—H,0—H键的微观机理．通过自旋一轨道耦合的计算讨论了势能面交叉点和可能的自旋翻转过程．在MEcP处,四重态和二重态问的旋轨耦合常数为131．14cm^-1．自旋多重度发生改变,从四重态系间穿越到二重态势能面形成中间体2^IM1,导致反应势能面的势垒明显降低．     

Planar photonic crystals infiltrated with liquid crystals: optical characterization of molecule orientation

Nematic liquid crystals are infiltrated into InP-based planar photonic crystals. Optical measurements as a function of temperature and polarization are used to study the average director field configuration in the nanometer-size holes: a planar equilibrium state is found.     

A series of complexes of the phosphorus-based TTF ligand o-P2 with the metal ions Fe(II), Co(II), Ni(II), Pd(II), Pt(II), and Ag(I)

Reactions of 3,4-dimethyl-3',4'-bis(diphenylphosphino)tetrathiafulvalene, o-P2, with [BF(4)](-) salts of Fe(ii), Co(ii), Ni(II), Pd(II), and Pt(II) yield complexes of general formula [M(o-P2)(2)][BF(4)](2). Similar reactions between o-P2 and AgSbF(6) or AgPF(6) produced the salts [Ag(o-P2)(2)][X] where X = [SbF(6)](-) or [PF(6)](-). The resulting compounds were fully characterized by (1)H and (31)P{(1)H} NMR, infrared and electronic absorption spectroscopies, cyclic voltammetry, FAB-MS and single-crystal X-ray diffraction. The paramagnetic Co(II) compound exhibits an S = 3/2 state with large spin-orbit coupling contribution at higher temperatures and an effective S' = 1/2 state below 20 K. Electrochemical studies of the compounds indicate that the two functionalized TTF ligands are not in electronic communication and that they essentially behave as isolated redox centers.     

Coarse and fine tuning of the electronic energies of triimineplatinum(II) square-planar complexes

[Pt(tbtrpy)X]Y complexes (tbtrpy = 4,4',4' '-tBu3-2,2';6',2' '-terpyridine) exhibit charge-transfer absorption bands that can be drastically red-shifted to long-wavelength visible absorptions with arylthiolates as X. Further extension to the near-IR (NIR) region is achieved with 7,7,8,8-tetracyanoquinodimethane (TCNQ-) as Y-, resulting in black absorbers with continuous UV-vis-NIR absorptions and opening up potential applications in energy research.     

Infrared spectroscopy of phenylalanine Ag(I) and Zn(II) complexes in the gas phase

Infrared multiple-photon dissociation (IR-MPD) spectroscopy has been applied to singly-charged complexes involving the transition metals Ag(+) and Zn(2+) with the aromatic amino acid phenylalanine. These studies are complemented by DFT calculations. For [Phe+Ag](+) the calculations favor a tridentate charge solvation N/O/ring structure. The experimental spectrum strongly supports this as the predominant binding geometry and, in particular, rules out a significant presence of the salt-bridge conformation. Zn(2+) forms a deprotonated dimer complex with Phe, [Zn+Phe(2)-H](+), in which the +2 oxidation state serves as a useful biomimetic model for zinc protein sites. A number of low-energy conformations were located, of which the lowest-energy conformer predicted by the calculations involves a Phe ligand deprotonated on the carboxylic acid, while the other Phe ligand is in the tridentate charge solvation conformation. The calculated IR spectrum of this conformer gives a close fit to the experimental spectrum, strongly supporting this as the predominant binding geometry. This most stable calculated complex is characterized by N/ O/ring metal chelation with a tetrahedral-type coordination core of Zn(2+) to N and O of both ligands. Another similar tightly chelated structure shows a square-planar-type coordination core, but this structure is computed to be less stable and gives a less satisfactory match to the experimental spectrum. This preference for the tetrahedral geometry of the Lewis-basic atomic ligands parallels the common Zn(II) coordination geometry in proteins. The number of clearly identifiable peaks resolved in the IR-MPD spectra as well as the much-improved matches between the observed spectra and the DFT-calculated spectra of the most stable geometries compared to previous studies are noteworthy for systems of this size and complexity. These results demonstrate that IR spectroscopy of transition metal-amino acid complexes in combination with DFT calculations is a very powerful structural tool, readily applicable to biomimetic systems that model, for example, the reaction centers of proteins in the solvent-free environment. In addition, we present a novel ion-capturing method for Fourier transform ion cyclotron resonance mass spectrometry which removes the necessity of a buffer gas pulse, while allowing ion trapping at moderate voltages with apparently reduced collisional excitation of the ions.     

Broadcasts in graphs

We say that a function f:V→{0,1,…,diam(G)} is a broadcast if for every vertex v∈V, f(v)?e(v), where diam(G) denotes the diameter of G and e(v) denotes the eccentricity of v. The cost of a broadcast is the value . In this paper we introduce and study the minimum and maximum costs of several types of broadcasts in graphs, including dominating, independent and efficient broadcasts.     

Diameters of 3-sphere quotients

Let G⊂O(4) act isometrically on S³. In this article we calculate a lower bound for the diameter of the quotient spaces S³/G. We find it to be , which is exactly the value of the lower bound for diameters of the spherical space forms. In the process, we are also able to find a lower bound for diameters for the spherical Aleksandrov spaces, Sn/G, of cohomogeneities 1 and 2, as well as for cohomogeneity 3 (with some restrictions on the group type). This leads us to conjecture that the diameter of Sn/G is increasing as the cohomogeneity of the group G increases.