Pendant cyclodicarbaphosphazatriene-containing monomers and polymers: synthesis,crystal structures and polymerization behavior of [NC(NMe2)]2[NP(O-C6H4-p-C6H4-p-CH=CH2)(X)], X = Cl,OCH2CF3, OC6H5, OC6H4-m-CH3, OC6H4-p-Br

The reaction of the dicarbaphosphazene, [NC(NMe(2))](2)[NPCl(2)] (2), with the sodium salt of 4-hydroxy-4'-vinylbiphenyl afforded the vinyl group containing monomer [NC(NMe(2))](2)[NP(Cl)(O-C(6)H(4)-p-C(6)H(4)-p-CH=CH(2))] (3). Replacement of the lone chlorine atom of 3 by oxygen nucleophiles gave [NC(NMe(2))](2)[NP(OR)(O-C(6)H(4)-p-C(6)H(4)-p-CH=CH(2))] [R = CH(2)CF(3) (4); C(6)H(5) (5); C(6)H(4)-m-CH(3) (6); C(6)H(4)-p-Br(7)]. The X-ray crystal structures of 3-7 reveal that all the cyclodicarbaphosphazenes have a planar N(3)PC(2) ring; the ring carbons are completely planar, while the geometry around phosphorus is pseudotetrahedral. The presence of weak intermolecular hydrogen bonding [C-H---X(Cl or Br), C-H---N, or C-H---pi] interactions in 3-7 leads to the formation of polymeric architectures in the solid-state. The monomers 4-7 can be polymerized by a free-radical initiator to afford the corresponding air-stable homopolymers 8-11. These have moderate molecular weights with polydispersity indices ranging from 1.33 to 1.58. All of these polymers have high glass transition temperatures and have excellent thermal stability.     

Fragmentation of transition metal carbonyl cluster anions: structural insights from mass spectrometry

The anionic clusters [HOs(5)(CO)(15)](-), [PtRu(5)C(CO)(15)](2-), [Os(10)C(CO)(24)](2-), [Os(17)(CO)(36)](2-), [Os(20)(CO)(40)](3-), [Co(6)C(CO)(15)](2-), [Pt(3)Ru(10)C(2)(CO)(32)](2-) and [Pd(6)Ru(6)(CO)(24)](2-) have been analysed by energy-dependent electrospray ionisation mass spectrometry (EDESI-MS). Three main features have emerged. Firstly, carbonyl ligands are fragmented from clusters with compact metal cores in an orderly fashion, with each of the ions generated by CO loss having approximately equal intensity. Secondly, electron autodetachment takes place in multiply charged anionic clusters, but only after elimination of a large proportion of their carbonyl ligands. Thirdly, clusters with open metal cores do not undergo CO loss in an orderly fashion, but certain peaks are considerably less intense. The appearance of these low-intensity peaks is believed to signify polyhedral core rearrangements, with open clusters folding to form more compact geometries. In some cases, the gas-phase transformations observed by EDESI-MS mirror those that are known to take place in solution.     

Network hydrogen bonding: the crystal and molecular structure of cubane-1,3,5,7-tetracarboxylic acid dihydrate

The structure of cubane-1,3,5,7-tetracarboxylic acid dihydrate (1) has been determined. It crystallizes in the space groupP2₁/c with cell dimensionsa=6.503(1),b=19.173(1),c=10.527(1) Å, β=101.60(1). The details of this structure have reaffirmed the fact that the cubane skeleton is a flexible entity which reflects its steric and electronic environment. Of the four carboxylic acid groups three adopt asyn conformation while the fourth adopts ananti conformation. The orientation of these groups with respect to the cubane skeleton is reflected in the C?C bond lengths. Those C?C bonds which are perpendicular to the carboxylic acid groups are the longest and those which are most nearly eclipsed are the shortest in the cubane skeleton. In all cases it is the C=O rather than the C?O bond which is most nearly eclipsed with a C?C bond. The tetrahedral orientation of the substitutents does not express itself in a three dimensional supramolecular assembly; however, all four carboxylic acid groups are involved in very strong donor hydrogen bonds which result in a two dimensional array parallel to (100). An additional surprising results is the fact that none of the four substituents participate in traditional hydrogen bonded carboxylic acid dimeric moieties.     

Small cluster models of the surface electronic structure and bonding properties of titanium carbide, vanadium carbide, and titanium nitride

Density functional theory (DFT) calculations on stoichiometric, high-symmetry clusters have been performed to model the (100) and (111) surface electronic structure and bonding properties of titanium carbide (TiC), vanadium carbide (VC), and titanium nitride (TiN). The interactions of ideal surface sites on these clusters with three adsorbates, carbon monoxide, ammonia, and the oxygen atom, have been pursued theoretically to compare with experimental studies. New experimental results using valence band photoemission of the interaction of O(2) with TiC and VC are presented, and comparisons to previously published experimental studies of CO and NH(3) chemistry are provided. In general, we find that the electronic structure of the bare clusters is entirely consistent with published valence band photoemission work and with straightforward molecular orbital theory. Specifically, V(9)C(9) and Ti(9)N(9) clusters used to model the nonpolar (100) surface possess nine electrons in virtually pure metal 3d orbitals, while Ti(9)C(9) has no occupation of similar orbitals. The covalent mixing of the valence bonding levels for both VC and TiC is very high, containing virtually 50% carbon and 50% metal character. As expected, the predicted mixing for the Ti(9)N(9) cluster is somewhat less. The Ti(8)C(8) and Ti(13)C(13) clusters used to model the TiC(111) surface accurately predict the presence of Ti 3d-based surface states in the region of the highest occupied levels. The bonding of the adsorbate species depends critically on the unique electronic structure features present in the three different materials. CO bonds more strongly with the V(9)C(9) and Ti(9)N(9) clusters than with Ti(9)C(9) as the added metal electron density enables an important pi-back-bonding interaction, as has been observed experimentally. NH(3) bonding with Ti(9)N(9) is predicted to be somewhat enhanced relative to VC and TiC due to greater Coulombic interactions on the nitride. Finally, the interaction with oxygen is predicted to be stronger with the carbon atom of Ti(9)C(9) and with the metal atom for both V(9)C(9) and Ti(9)N(9). In sum, these results are consistent with labeling TiC(100) as effectively having a d(0) electron configuration, while VC- and TiN(100) can be considered to be d(1) species to explain surface chemical properties.     

Pentafluorosulfanylnitramide salts

The synthesis and properties of a new class of inorganic salts, named pentafluorosulfanylnitramide salts (or pentafluorosulfanylnitraminic acid salts) [Z+SF5NNO2-], are described. A number of SF5-nitramide salts (Z+SF5NNO2-) were successfully prepared via nucleophilic displacements from carbamates and/or ion exchange techniques, but some salts [M(SF5NNO2)x; M = Li, Mg, Al] decomposed during isolation procedures and appear to be unstable in the solid state. Single-crystal X-ray diffraction was used to fully characterize the Z+SF5NNO2-, and their properties/structures are compared with those of the corresponding dinitramide salts (or dinitraminic acid salts), Z+N(NO2)2-. X-ray crystallography revealed major structural differences between N(NO2)2- and SF5N(NO2)- salts concerning the N-N distances and the angles subtended at the central nitrogen atom. In the N(NO2)2- salts, there are two nonequivalent N-N (average lengths 1.372(2) and 1.354(2) A) distances and an average N-N-N angle of 115.8(3) degrees (falls between sp3 and sp2 hybridization). In the SFsNNO2- salts, the average N-N distance is much shorter, 1.308(9) A, and the average N-N-S angle is 120.0(5) degrees (closely fits sp2 hybridization). The SF5NNO2- salts show a remarkable metrical similarity for the SF5 moiety in all structures, indicating a lack of sensitivity to its steric and electronic environment. This is in marked contrast to N(NO2)2-, where there is a wide variation in conformations adopted by these anions which can be related to their environment.     

Synthesis, structure, and catalytic properties of V(IV), Mn(III), Mo(VI), and U(VI) complexes containing bidentate (N, O) oxazine and oxazoline ligands

Synthesis of seven complexes containing oxazoline ([(L(1))(2)V=O] (4), [(L(1))(2)MoO(2)] (5), [(L(1))(2)UO(2)] (6); HL(1) (1) [HL(1) = 2-(4',4'-dimethyl-3'-4'-dihydroxazol-2'-yl)phenol]), chiral oxazoline ([(L(2))(2)UO(2)] (7); HL(2) (2) [HL(2) = (4'R)-2-(4'-ethyl-3'4'-dihyroxazol-2'-yl)phenol]), and oxazine ([(L(3))(2)V=O] (8), [(L(3))(2)Mn(CH(3)COO(-))] (9), [(L(3))(2)Co] (10); HL(3) (3) [HL(3) = 2-(5,6-dihydro-4H-1,3-oxazolinyl)phenol]) and their characterization by various techniques such as UV-vis, IR, and EPR spectroscopy, mass spectrometry, cyclic voltammetry, and elemental analysis are reported. The novel oxazine (3) and complexes 4, 5, 8 and 9 were also characterized by X-ray crystallography. Oxazine 3 crystallizes in the monoclinic system with the P2(1)/n space group, complexes 4 and 9 crystallize in the monoclinic system with the P2(1)/c space group, and complexes 5 and 8 crystallize in the orthorhombic system with the C222(1) space group and the P2(1)2(1)2(1) chiral space group, respectively. The representative synthetic procedure involves the reaction of metal acetate or acetylacetonate derivatives with corresponding ligand in ethanol. Addition of Mn(OAc)(2).4H(2)O to an ethanol solution of 3 gave the unexpected complex Mn(L(3))(2).(CH(3)COO(-)) (9) where the acetate group is coordinated with the metal center in a bidentate fashion. The catalytic activity of complexes 4-9 for oxidation of styrene with tert-butyl hydroperoxide was tested. In all cases, benzaldehyde formed exclusively as the oxidation product.     

Chemically induced cyclometalation of 2-(arylazo)phenols. Synthesis,characterization, and redox properties of a family of organoosmium complexes

Reaction of 2-(arylazo)phenols (H(2)ap-R; R = OCH(3), CH(3), H, Cl, and NO(2)) with [Os(PPh(3))(2)(CO)(2)(HCOO)(2)] affords a family of organometallic complexes of osmium(II) of type [Os(PPh(3))(2)(CO)(ap-R)] where the 2-(arylazo)phenolate ligand is coordinated to the metal center as a tridentate C,N,O-donor. Structure of the [Os(PPh(3))(2)(CO)(ap-H)] complex has been determined by X-ray crystallography. All the [Os(PPh(3))(2)(CO)(ap-R)] complexes are diamagnetic and show characteristic (1)H NMR signals and intense MLCT transitions in the visible region. They also show emission in the visible region at ambient temperature. Cyclic voltammetry on the [Os(PPh(3))(2)(CO)(ap-R)] complexes shows a reversible Os(II)-Os(III) oxidation within 0.39-0.73 V vs SCE, followed by a reversible Os(III)-Os(IV) oxidation within 1.06-1.61 V vs SCE. Coulometric oxidation of the [Os(PPh(3))(2)(CO)(ap-R)] complexes generates the [Os(III)(PPh(3))(2)(CO)(ap-R)](+) complexes, which have been isolated as the hexafluorophosphate salts. The [Os(III)(PPh(3))(2)(CO)(ap-R)]PF(6) complexes are one-electron paramagnetic and show axial ESR spectra. In solution they behave as 1:1 electrolytes and show intense LMCT transitions in the visible region. The [Os(III)(PPh(3))(2)(CO)(ap-R)]PF(6) complexes have been observed to serve as mild one-electron oxidants in a nonaqueous medium.     

Dioxo-bridged dinuclear manganese(III) and -(IV) complexes of pyridyl donor tripod ligands: combined effects of steric substitution and chelate ring size variations on structural,spectroscopic, and electrochemical properties

The syntheses and structural, spectral, and electrochemical characterization of the dioxo-bridged dinuclear Mn(III) complexes [LMn(mo-O)(2)MnL](ClO(4))(2), of the tripodal ligands tris(6-methyl-2-pyridylmethyl)amine (L(1)) and bis(6-methyl-2-pyridylmethyl)(2-(2-pyridyl)ethyl)amine (L(2)), and the Mn(II) complex of bis(2-(2-pyridyl)ethyl)(6-methyl-2-pyridylmethyl)amine (L(3)) are described. Addition of aqueous H(2)O(2) to methanol solutions of the Mn(II) complexes of L(1) and L(2) produced green solutions in a fast reaction from which subsequently precipitated brown solids of the dioxo-bridged dinuclear complexes 1 and 2, respectively, which have the general formula [LMn(III)(mu-O)(2)Mn(III)L](ClO(4))(2). Addition of 30% aqueous H(2)O(2) to the methanol solution of the Mn(II) complex of L(3) ([Mn(II)L(3)(CH(3)CN)(H(2)O)](ClO(4))(2) (3)) showed a very sluggish change gradually precipitating an insoluble black gummy solid, but no dioxo-bridged manganese complex is produced. By contrast, the Mn(II) complex of the ligand bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine (L(3a)) has been reported to react with aqueous H(2)O(2) to form the dioxo-bridged Mn(III)Mn(IV) complex. In cyclic voltammetric experiments in acetonitrile solution, complex 1 shows two reversible peaks at E(1/2) = 0.87 and 1.70 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and the Mn(III)Mn(IV) <--> Mn(IV)(2) processes, respectively. Complex 2 also shows two reversible peaks, one at E(1/2) = 0.78 V and a second peak at E(1/2) = 1.58 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and Mn(III)Mn(IV) <--> Mn(IV)(2) redox processes, respectively. These potentials are the highest so far observed for the dioxo-bridged dinuclear manganese complexes of the type of tripodal ligands used here. The bulk electrolytic oxidation of complexes 1 and 2, at a controlled anodic potential of 1.98 V (vs Ag/AgCl), produced the green Mn(IV)(2) complexes that have been spectrally characterized. The Mn(II) complex of L(3) shows a quasi reversible peak at an anodic potential of E(p,a) of 1.96 V (vs Ag/AgCl) assigned to the oxidation Mn(II) to Mn(III) complex. It is about 0.17 V higher than the E(p,a) of the Mn(II) complex of L(3a). The higher oxidation potential is attributable to the steric effect of the methyl substituent at the 6-position of the pyridyl donor of L(3).     

Nickel(II) and copper(II) complexes of ONS ligands formed from 2-hydroxyacetophenone and S-alkyldithiocarbazates and the X-ray crystal structure of the [Ni(Ap-SMe)py] complex (Ap-SMe = anion of the 2-hydroxyacetophenone Schiff base of S-methyl-dithiocarbazate)

Summary New nickel(II) and copper(II) complexes of general formulae [M(Ap-SR)] and [Ap-SR)B] (Ap-SR = dianionic forms of the Schiff bases of 2-hydroxyacetophenone and S-alkyl esters of dithiocarbazic acid; M = Ni^II or Cu^II; R = Me or CH₂Ph; B = py, phen or dipy have been synthesized and characterized by a variety of physicochemical techniques. Magnetic and spectroscopic data support an oxygen-bridged binuclear structure for the [M(Ap-SR)] complexes. The [M(Ap-SR)py] complexes are four-coordinate and square planar, whereas the [M(Ap-SR)B] complexes (B = phen or dipy) are five-coordinate and probably trigonal bipyramidal. The [Cu(Ap-SR)B] complexes (B = py, phen or dipy) obey the Curie-Weiss law over the 298-93 K range.The structure of the [Ni(Ap-SMe)py] complex has been determined by X-ray crystallography. It has an approximately square-planar structure in which the doubly-deprotonated Schiff base is coordinated to the Ni^II ion via the azomethine N atom, the phenolic O atom and the thiolato S atom. The fourth coordination position around the Ni^II ion is occupied by the N of the pyridine ligand.     

Sterically demanding multidentate ligand tris[(2-(6-methylpyridyl))methyl]amine slows exchange and enhances solution state ligand proton NMR coupling to (199)Hg(II)

The solution state coordination chemistry of Hg(ClO(4))(2) with tris[(2-(6-methylpyridyl))methyl]amine (TLA) was investigated in acetonitrile-d(3) by proton NMR. Although Hg(II) is a d(10) metal ion commonly associated with notoriously rapid exchange between coordination environments, as many as six ligand environments were observed to be in slow exchange on the chemical shift time scale at select metal-to-ligand ratios. One of these ligand environments was associated with extensive heteronuclear coupling between protons and (199)Hg and was assigned to the complex [Hg(TLA)](2+). The (5)J((1)H(199)Hg) = 8 Hz associated with this complex is the first example of five-bond coupling in a nitrogen coordination compound of Hg(II). The spectral complexity of related studies conducted in acetone-d(6) precluded analysis of coordination equilibria. Crystallographic characterization of the T-shaped complex [Hg(TLAH)(CH(2)COCH(3))](ClO(4))(2) (1) in which two pyridyl rings are pendant suggested that the acidity of acetone combined with the poor coordinating abilities of the neutral solvent adds additional complexity to solution equilibria. The complex crystallizes in the triclinic space group P1 macro with a = 9.352(2) A, b = 12.956(2) A, c = 14.199(2) A, alpha = 115.458(10) degrees, beta = 90.286(11) degrees, gamma = 108.445(11) degrees, and Z = 2. The Hg-N(amine), Hg-N(pyridyl), and Hg-C bond lengths in the complex are 2.614(4), 2.159(4), and 2.080(6) A, respectively. Relevance to development of (199)Hg NMR as a metallobioprobe is discussed.