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The reduction of BODIPYs and dipyrrins to dipyrromethanes, via a reaction involving ethylene glycol and sodium methoxide, is reported. When benzyl alcohol is used in place of ethylene glycol, the addition of 2,4-dinitrophenylhydrazine to the reaction mixture after microwave irradiation results in the production of 1-benzylidene-2- (2,4dinitrophenyl)hydrazone, indicating concomitant production of aldehyde alongside the dipyrromethane. Key words: F-BODIPY, dipyrrin reduction, dipyrromethane formation, microwave-assisted. On decrit la reduction de BODIPYs et de dipyrrines en dipyrromethanes par une reaction faisant intervenir de l'ethylene glycol et du methanolate de sodium. Si l'on remplace l'ethylene glycol par l'alcool benzylique, l'ajout de 2,4dinitrophenylhydrazine au melange reactionnel apres irradiation par micro-ondes donne de la 1-benzylidene-2-(2,4-dinitrophenyl) hydrazone, ce qui indique la production concomitante d'un aldehyde et du dipyrromethane. [Traduit par la Redaction] Mots-cles : reduction des dipyrrines, F-BODIPY, formation de dipyrromethane, assistee par mico-ondes., Introduction Dipyrrins present a useful ligand scaffold, with significant interest being devoted to dipyrrinato complexes of transition metals and boron. (1,2) There are limited reports regarding the chemical manipulation of [...]

The synthesis and characterization of the first heteroleptic pyrrolide/2,2'-bipyridyl complexes of ruthenium(II) are reported. Pyrroles substituted at the 2-position with X = O functionality react with Ru[(bipy).sub.2][Cl.sub.2]- 2[H.sub.2]O to form complexes in which the pyrrolide ligands chelate to Ru(II). The library of pyrroles includes 2-formyl, 2-keto, 2-carboxylato, 2- sulfinyl, and 2-sulfonyl derivatives. Key words: ruthenium complexation, formyl pyrrole, keto pyrrole, chelation. On a effectue la synthese et caracterise les premiers complexes heteroleptiques pyrrolidure/2,2'-bipyridyle du ruthenium(II). Les pyrroles substitues en position 2 par une fonctionnalite X = O reagissent avec le Ru[(bipy).sub.2][Cl.sub.2]- 2[H.sub.2]O pour former des complexes dans lesquels les ligands pyrrolidures se chelatent au Ru(II). La bibliotheque de pyrroles comprend les derives 2-formyle, 2-ceto, 2-carboxylato, 2-sulfinyle et 2-sulfonyle. Mots-cles : complexation du ruthenium, formylpyrrole, cetopyrrole, chelation., Introduction The chemistry of the cyclopentadienyl unit as a ligand in transition metal chemistry is well-established. (1,2) However, the ability of isoelectronic and geometrically comparable pyrrolide ligands to coordinate to [...]

X-ray crystallographic studies of two axial glycosyl sulfoxides having [R.sub.S] configurations (derivatives of phenyl 2-azido-2-deoxy-1-thio-α-D-galactopyranoside S-oxide) show that they adopt anti conformations in the solid state, in contrast to previous observations and assumptions. Density functional theory (DFT) calculations at the B3lYP6-311G+(d,p)/ 6-31G(d) level confirm that anti conformations of both phenyl and methyl [R.sub.S] glycosyl sulfoxides of 2-azido-2-deoxy-α-D-pyranosides are more stable than exo-anomeric conformations in the gas phase. 1D NOE measurements indicate that the more polar exo-anomeric conformers are only populated to a slight extent in solution. The anti conformations are distorted so that the glycosyl substituents are closer to being eclipsed with H1. This distortion allows S n → [σ.sup.*] overlap if the sulfur lone pair is a p-type lone pair. Evidence for this overlap comes from short C1-S bond distances, as short as the comparable bond distances in the X-ray crystal structure and in the results from DFT calculations for the [S.sub.S] glycoside, which does adopt the expected exo-anomeric conformation, both in the solid state and in solution, and has normal n → [σ.sup.*] overlap. For 2-deoxy derivatives not bearing a 2-azido group, gas-phase DFT calculations at the same level indicate that the anti- and exo-anomeric conformers have comparable stabilities. Comparison of the results of the two series shows that electronegative substituents in equatorial orientations at C2 destabilize conformations with parallel S-O arrangements, the conformation favored by having an endocyclic C-O dipole antiparallel to the S-O dipole, by about 2.5 kcal [mol.sup.-1] (1 cal = 4.184 J). An equatorial glycosyl sulfoxide, ([S.sub.S]) phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-β- D-glucopyranoside S-oxide, also adopts an anti conformation in the solid state as shown by X-ray diffraction. It also adopts this conformation in solution, in contrast to studies of other equatorial glycosyl sulfoxides. Key words: sulfoxide configurations, glycosyl sulfoxides, conformational analysis, density functional theory (DFT) calculations, 1D NOE measurements, X-ray crystallography. Des etudes de cristallographie par diffraction des rayons-X de deux glycosyles sulfoxydes axiaux de configurations [R.sub.S], des derives du S-oxyde de 2-azido-2-desoxy-1-thio-a-galactopyranoside de phenyle, montrent qu'ils adoptent des conformations anti a l'etat solide, contrairement aux observations anterieures et aux hypotheses. Des calculs selon la theorie de la fonctionnelle de la densite; (TFD) au niveau B31YP6-311G+(d,p)/6-31G(d) confirment que les conformations anti que, en phase gazeuse, chacun des [R.sub.S] glycosyles sulfoxydes, 2-azido-2-desoxy-1-thio-α- galactopyranoside tant de methyle que de phenyle sont plus stable dans les conformations anomeres exo. Des mesures d'effet Overhauser nucleaire (eOn) 1D indiquent que, en solution, les conformeres anomeres les plus polaires ne forment qu'une faible partie de la population. Les conformations anti sont deformees de facon a ce que les substituants glycolyses soient dans une position pratiquement eclipsee avec le H1. Cette distorsion permet un recouvrement S n → [σ.sup.*] sur la paire libre du soufre est une paire libre de type p. Un support pour ce recouvrement vient des courtes longueurs de liaison C1-S, pratiquement aussi courtes que les longueurs mesurees par diffraction des rayons-X dans la structure cristalline et en accord avec les resultats des calculs TFD pour le [S.sub.S] glycoside qui adopte la conformation anomere exo attendue, tant a l'etat solide qu'en solution, et pour le recouvrement n → [σ.sup.*] normal. Pour les derives 2-desoxy ne portant pas de groupe azido, les calculs de TFD en phase gazeuse, au meme niveau, indiquent que les conformeres anomeres anti et exo ont des stabilites comparables. Une comparaison des resultats des deux series montre que les substituants electronegatifs en orientations equatoriales en C2 destabilisent les conformations avec des arrangements S-O paralleles, la conformation favorisee par un dipole C-O endocyclique antiparallele au dipole S-O par environ 2,5 kcal [mol.sup.-1] (1 cal = 4.184 J). La diffraction des rayons-X montre aussi que, a l'etat solide, un glycosyle sulfoxyde equatorial, le S-oxyde du [S.sub.S] 3,4,6-tri-O-acetyl-2-desoxy-2- phtalimido-1-thio-β-D-glucopyranoside de phenyle, adopte aussi une conformation anti. Il adopte aussi cette conformation en solution, en opposition a ce qui a ete observe dans les etudes sur glycosyles sulfoxydes equatoriaux. Mots-cles: configurations de sulfoxydes, glycosyles sulfoxydes, analyse conformationnelle, calculs selon la theorie de la fonctionnelle de la densite (TFD), mesures d'effet Overhauser nucleaire (eOn) 1D, cristallographie., Introduction One of the most important techniques for the formation of glycosides employs glycosyl sulfoxides activated by electrophiles as leaving groups. (1) This method has been used to form glycosides [...]

The first series of alkali dipyrrinato complexes is reported, encompassing lithium, sodium, and potassium salts of meso-unsubstituted and meso-aryl-substituted derivatives. By varying the substituents at the meso position, the intermolecular distance between the two nitrogen atoms and thus the [κ.sup.2]-N,N-bidentate bite angle was altered, as confirmed by comparison of crystallographic structures of dipyrrin free-bases in the solid-state. The mode of bonding varies as the ionic radius of the metal ion increases: solid-state structures reveal lithium to be accommodated in the plane of the dipyrrinato unit, whilst sodium is accommodated out of plane. The reactivity of analogous lithium, sodium, and potassium dipyrrinato complexes increases as the ionic radius of the metal ion increases, in keeping with the concept that the complexes tend towards an increasingly ionic nature as the size of the alkali metal increases. Key words: dipyrrin, dipyrrinato, alkali salts, monoanionic bidentate, N,N-chelation, pyrrolic. On rapporte la preparation de la premiere serie de complexes dipyrrinato alcalins comportant les sels de lithium, de sodium et de potassium de derives meso non substitueeset meso substituees par des groupes aryles. En faisant varier la nature des substituants en position meso, on modifie la distance intermoleculaire entre les deux atomes d'azote et, en consequence, l'angle de morsure [κ.sup.2]-N,N du bidentate, tel que confirmee par une comparaison des structures cristallographiques des bases libres dipyrrines a l'etat solide. Le mode de liaison varie avec une augmentation du rayon ionique de l'ion metallique; les structures a l'etat solide revelent que le lithium s'accommode dans le plan de l'unite dipyrrinato alors que le sodium est accommode hors du plan. La reactivite des complexes analogues du lithium, du sodium et du potassium augmente avec une augmentation du rayon ionique du metal ionique, en accord avec le concept que les complexes tendent vers une nature de plus en plus ionique avec une augmentation de la taille des metaux alcalins. Mots-cles: dipyrrine, dipyrrinato, sels alcalins, bidentate monoanionique, N,N-cheelation, pyrrolique. [Traduit par la Redaction], Introduction The N-H hydrogen atom of dipyrrins (Fig. 1), best-known for their presence in 4,4-difluoro-4-bora-3a,4a-diaza-s-indacenes (BODIPYs), (1) can be formally deprotonated to give the monoionic conjugated dipyrrinato species that can [...]

The electron density of 4-methyl-[4]helicene is analyzed with an emphasis on the fjord region as metabolic activation is initiation in this region. The analysis has shown that the highly twisted nature of helicenes have entailed the appearance of a weak closed-shell hydrogen-hydrogen (H-H) bonding interaction in the fjord region of the molecule.

Abstract: Several molecular organic crystals [tetraphenylphosphonium squarate, bianthrone, and bis(benzophenone) azine] have been analyzed topologically following a multipole refinement of each compound. This has resulted in the complete characterization of [...]

Abstract: The synthesis of an 'unknown' Fe(II) complex originally reported in 1973 and formulated then as [Fe(DMSO)5C1] [Sn[Cl.sub.4]] was thoroughly reproduced and the compound reformulated as the novel [Fe[(DMSO).sub.6]] [Sn[Cl.sub.6]] [...]

Abstract: The stepwise symmetry-allowed cycloaddition reactions of [[SNS].sup.+] with the dinitriles NC-X-CN (X = C[Cl.sub.2], CO) were investigated. The reaction of [[SNS].sup.+] and dinitrile in 2:1 ratio yielded the dicycloaddition [...]

The inter/intramolecular interactions (S...I, S...S, I...I, and I...H) present in the iodoform octasulfur molecule are investigated based on the properties of the electron density at the bond critical point (BCP). The results have shown that these interactions play an important role in the stability of the crystalline state of iodoform octasulfur.

The 50 weak intramolecular interactions ranging from C-H...O hydrogen bonds to H-H bonds for three molecular crystals are considered and a correlation is obtained using properties of electron density at bond critical point. The correlations of the three types of interactions helped better understanding of the differences and similarities between them and allow H-H bonds to be distinguished from other types of weak interactions such as hydrogen bonds.

Abstract: A novel two-step procedure involving the formation of 1-arylidene-2-tetralones from 2-tetralone and subsequent Michael addition of a cyclic secondary amine on the alkenone followed by in situ aerial oxidation [...]

Abstract: The tetraiphenylphosphonium squarate salt crystallizes with a number of diverse interactions, which all have the potential to be classified as hydrogen bonds. The squarate anions are found as dimers [...]

The nature of the structure and bonding in S(sub 2)I(sub 4)(super 2+) is clarified by carrying out infrared and FT-Raman spectra for S2I4(MF6)2, and by carrying out a normal-coordinate analysis of the vibrational spectra. The experimental evidence for the high S-S and I-I bond orders in S(sub 2)I(sub 4)(super 2+) is described.

We report the synthesis, using an organic-template-free hydrothermal crystallization method, and catalysis of a new type of nanocomposite material, 1.3 nm-sized Ru[O.sub.2] particles confined in faujasite zeolite. The zeolite-confined Ru[O.sub.2] composites were fully characterized with X-ray powder diffraction, Ru K-edge X-ray absorption, and high-resolution transmission electron microscopy. XRD and X-ray fluorescence analysis indicate that the framework is faujasite zeolite with a Si:A1 ratio of 1.25. Ru K-edge X-ray absorption near-edge structures indicate that the ruthenium species in the zeolite is Ru(IV) with nearest-neighbor octahedral environments similar to hydrous Ru[O.sub.2], i.e., distorted "Ru[O.sub.6]". The [k.sup.2]-weighted extended X-ray absorption fine structure indicates that the Ru(IV) species anchored in the zeolite likely form amorphous Ru[O.sub.2] with a 2D-chain structure, in which Ru[O.sub.6] units are connected together by two shared oxygen atoms. TEM shows that the particle size of Ru[O.sub.2] encapsulated inside the supercages of FAU is about 1.3 nm. The Ru[O.sub.2]-FAU composites display significant catalytic activity in the oxidation of cyclohexane with BHP under mild (room temperature and 1 atm (1 atm [equivalent]101.325 kPa)) conditions. The ketone and alcohol concentration can be as high as 0.26 mol [L.sup.-1] in 5 h with 48% peroxide efficiency. The catalyst is stable and reusable. Possible oxidation mechanisms are also discussed. Key words: nanocomposite, ruthenium oxide, catalysis, oxidation, zeolite.

The crystal structures of the tetraphenylborates of the dabco[H.sup.+], guanidinium (MeCN solvate), and biguanidiniun cations are shown to contain a variety of C-H ... H-C dihydrogen (DB) bonds of nominally zero polarity, as well as a variety of N-H ... N, C-H ... N, N-H ... Ph, and C-H ... Ph hydrogen (HB) bonds. These intermolecular bonds have been characterized topologically after multipole refinement of the structures. The coexistence of the DBs and HBs in each of the structures makes it possible to establish their relative strength hierarchy. It also illustrates the importance of the DBs in satisfying the tendency of these structures to maximize the total intermolecular bonding engagement. To compare the above DBs with other DBs, the results of an extensive set of MP2/6-31G(d,p) calculations (supplied by I. Alkorta) were analyzed for reference correlations between the bond-critical parameters. Thus, for an X-H ... H-Y bond, the difference [Delta][epsilon][(H).sub.m] between the Mulliken charges on the H atoms in the uncomplexed X-H and H-Y components correlates quite well with the X-H ... H-Y parameters and can be used for predicting the topological strength of an X-H ... H-Y bond. The use of the difference [Delta][epsilon][(H).sub.c] in the bond does not appear to change the correlation significantly; closer correlations are observed when the amount of charge transferred on formation of the H ... H bond is used instead of [Delta][epsilon][(H).sub.m] or [Delta][epsilon][(H).sub.c]. Bonding interactions are obtained even between like or symmetry-related H atoms as a consequence of induced-dipole interactions, which accounts for the existence of the above intermolecular C-H ... H-C bonds with d(H ... H) = 2.18-2.57 [Angstrom] electron density at the bond-critical point of [Tilde]0.05-0.08 e/[Angstrom .sup.3], and a rough estimate of the H ... H binding energy of [Tilde]1-5 kcal/mol. Examination of the bond-critical parameters of X-H ... H-Y bonds also suggests a criterion of stability of these bonds with respect to the transition from non-shared (closed-shell) X-H ... H-Y interaction to covalent (shared-shell) X ... H-H ... Y interaction. This transition appears to be discontinuous. Key words: bond-critical parameters, bond topology, dihydrogen bonds, hydrogen bonds, organoammonium tetraphenylborates.

As part of a systematic development of bismuth coordination chemistry, we are exploiting the thermodynamic and hydrolytic stability of Bi--S bonds. A series of heteroleptic thiolate bismuth complexes have been isolated and characterized. The generally applicable synthetic methodology involves the use of hetero-bifunctional ligands containing a thiolate moiety as an anchor to facilitate coordinate interaction of weak donors (carbonyls, amines, hydroxyls) with bismuth. The bifunctional nature of the ligands is manifested in chelating roles. Important comparisons with established thiolate complexes of bismuth are discussed. Key words: bismuth, thiolate, heteroleptic, crystallography.

Pyridine, when allowed to react with chromic anhydride under strictly anhydrous conditions, gives the known, very air-sensitive, crystalline 2:1 Lewis acid-base complex 1. The crystal structure has now been successfully determined. When benzimidazole and three 2-alkyl-1H-benzimidazoles were treated with chromium trioxide in aqueous acetic acid, crystalline dichromate salts (2-5) were readily formed. These salts consist of dichromate anions linked to the cations by hydrogen bonds of the type N--H ... O. The chromium atoms have distorted tetrahedral environments, with the Cr--O distances being typical for dichromate anions. In the cases of the 2-methyl and 2-ethyl salts, the anions are disordered about a centre of inversion. The hydrogen bonding arrangements are discussed and the structures are compared with other oxygenated chromium(VI) species. The dichromate salts are useful selective oxidants for a range of primary and secondary alcohols; examples of these reactions are reported. Key words: chromium(VI), pyridine--chromium trioxide complex, benzimidazolinium dichromate salts, controlled oxidation of alcohols.

Methods were developed to convert dipentaerythritol efficiently into di-[OMICRON]-benzylidene, di-[OMICRON]-cyclohexylidene, di-[OMICRON]-l-ethylpropylidene, and di-[OMICRON]-methylene diacetals. The known di-[OMICRON]-benzylidene acetal, considered to be a single isomer, was shown to be close to a statistical mixture of the cis, cis-,cis,trans-, and trans,trans-isomers. Structures were established by a combination of NMR spectroscopy and X-ray crystallography. Reaction of the di-[OMICRON]-benzylidene acetals with benzyl chloride and potassium hydroxide surprisingly gave good to excellent yields of the monobenzyl ethers. An explanation for this observation was advanced. The dibenzyl derivatives of the di-[OMICRON]-benzylidene acetals were formed by reaction of their dianions with benzyl bromide in DMF. Selective reduction of the di-[OMICRON]-benzylidene acetals with triethylsilane and boron trifluoride etherate gave 2',6'-di-[OMICRON]-benzyldipentaerythritol. A crown ether was formed in modest yield (12%) by reaction of the dianion of the di-[OMICRON]-methylene acetal with [alpha],[alpha]'-dibromo-m-xylene in DMF. Key words: dipentaerythritol, pentaerythritol, acetals, dendrimer, selective benzylation, crown ether.

Reduction of [[(CNSNS).sub.2]][As [[F.sub.6]].sub.2] with triphenylantimony and tetrabutylammonium chloride produced the diradical 5,5'-bis(1,3,2,4-dithiadiazolyl) [SNSNC-CNSNS] in high yield as a black solid with widely ranging magnetic susceptibilities (e.g., 0.6 to 2.6 [micro][sub.B]), which on oxidation with As[F.sub.5] regenerated [[(CNSNS).sub.2]][As[[F.sub.6]].sub.2]. The identity of [SNSNC-CNSNS] was established from EPR, vibrational, and mass spectra. Ab initio molecular orbital [MPW1PW91/6-311G(2df)] calculations show the lowest energy structure to consist of two coplanar rings separated by a C--C single bond (1.444 [Angstrom]), reflected in the comparison of the vibrational spectra of the diradical with that of [[(CNSNS).sub.2]][As[[F.sub.6]].sub.2] and the calculated spectra. Confidence in the calculated [MPW1PW91/6-311G(2df)] structure of the diradical is supported by the excellent agreement between the calculated and X-ray single crystal structure geometries of [[CNSSN].sub.2] and [[[(CNSNS).sub.2].sup.2+]] in [[(CNSNS).sub.2]][[As[F.sub.6]].sub.2]. The molecular orbitals indicate the diradical is essentially disjoint, confirmed by a very small (0.07 kJ [mol.sup.1]) GVB-PP(TC-SCF)/6-311G* calculated singlet-triplet energy gap. Accordingly, the EPR spectrum of the diradical (in tetrahydrofuran, 293 K) shows a simple 3-line pattern (g = 2.0043, a([14.sup]N) = 1.11 mT) with no observable exchange coupling between the two radical centers. Mechanical grinding of the diradical results in a large increase in paramagnetism (e.g., from 1.03 to 2.55 [micro][sub.B]) that is unprecedented in main group chemistry. The X-ray diffraction data of the ground and unground powder are consistent with a second order phase change on grinding. Attempts to obtain crystals of the diradical by sublimation led instead to numerous decomposition and rearrangement products, including 4-cyano-l,2,3,5-dithiadiazolyl [NC-CNSSN], monoclinic space group C2/c, a = 9.46(2) [Angstrom], b = 7.625(5) [Angstrom], c = 13.17(2) [Angstrom], [beta] = 107.94(4)[degrees], Z = 8. The structure consists of axially symmetric, co-facial, cis dimers linked to form strands through two sets of C[equivalent to][N.sup.[delta]] ... [S.sup.[delta]] contacts. More efficient and larger scale preparations of [SNS][As[F.sub.6] and [[(CNSNS).sub.2]][Asp[[F.sub.6].sub.2]] are reported. Key words: 5,5'-bis(1,3,2,4-dithiadiazolyl), diradical, paramagnetism, mechanical grinding, second order phase change, 4-cyano- 1,2,3,5-dithiadiazolyl.

Various stoichiometric combinations of P[Cl.sub.3] with DippN[H.sub.2] (Dipp = 2,6-di-isopropylphenyl) have been examined using [sup.31]P NMR spectroscopy. The dehydrochloride coupling reaction is mediated by the moderate steric bulk of the Dipp substituent. Isolation procedures and characterization data are reported for the aminodichlorophosphine (1), the aminotetrachlorodiphosphine (4), and the dichlorophosphetidine (7). The observations offer new appreciation of dehydrochloride coupling products of halophosphines with primary amines. Key words: phosphorus, nitrogen, phosphazanes, phosphetidines, iminophosphine.

The equilibrium geometries of the isoelectronic Z[Ph.sup.0, [+ or -] 1.sub.4] (Z = B, C, N) molecules have been optimized, in [S.sub.4] and [D.sub.2d] symmetries, at the HF/6-31G(d,p) and B3LYP/6-31G(d,p) levels, with the phenyl rings constrained to be planar. The ground-state conformations of all three species are shown to be of [S.sub.4] symmetry, but the difference of the energies of the [S.sub.4] and the [D.sub.2d] conformations is estimated to amount to only ~1 kcal [mol.sup.-1], with a barrier to concerted rotational reorientation of the phenyl rings of ~5.0 kcal [mol.sup.-1] for B[Ph.sup.1.sub.4], ~6.4 kcal [mol.sup.-1] for C[Ph.sub.4], and ~7.9 kcal [mol.sup.-1] for N[Ph.sup.+.sub.4]. A redetermination of the crystal structure of C[Ph.sub.4] from -60[degrees]C X-ray data agrees with the results of previous determinations at ambient temperature; the C[Ph.sub.4] molecule in the crystal is slightly compressed along the [S.sub.4] axis relative to the free molecule, otherwise the geometries of the two are essentially the same. Correlations between the optimized geometric parameters of the Z[Ph.sup.0, [+ or -] 1.sub.4] molecules have been examined and analyzed in detail, as have the substitution-induced changes in the geometry of the phenyl ring. The results confirm and strengthen the conclusions from the statistical studies by Domenicano et al. on the geometry of benzene rings monosubstituted by atoms of elements from the first row of the Periodic system. Key words: tetraphenylborate, tetraphenylmethane, tetraphenylammonium, ab initio molecular geometries.

Research has been conducted on the nucleophilic carbene. The reactions of this compound with diazofluorene, diphenyldiazomethane and azidotrimethylsilane have been investigated via single-crystal X-ray crystallography and the results are discussed.

Phosphorus-31 1D NMR spectra of a stationary powder sample of a phosphole tetramer containing two phosphorus spin pairs have been obtained at 4.7 T and 9.4 T. In order to separate [sup.31]P--[sup.31]P spin-spin coupling from anisotropic chemical shielding, 2D spin--echo NMR spectra have been acquired. Phosphorus-31 CPMAS NMR experiments indicate that the two spin pairs of the tetramer are equivalent and each may be treated as an isolated spin pair. Within a given spin pair, the difference between the isotropic chemical shifts of two directly bonded phosphorus nuclei is 1.7 ppm. As well, they are spin-spin coupled by both the indirect and direct interactions, [sup.1]J. ([sup.31]P,[sup.31]P = -362 Hz and [R.sub.DD] = 1.80 kHz, respectively. The principal components and relative orientation of the two phosphorus chemical shielding tensors have been determined using the dipolar-chemical shift technique; however, since the dipolar tensor is axially symmetric, ambiguities in the chemical shielding tensor orientation relative to the molecular framework result. Using ab initio calculations and simulations of the 2D spin-echo spectra, many of these ambiguities have been resolved. The spans and skews of the phosphorus shielding tensors for all four three-coordinate phosphorus nuclei are the same within experimental error, 115 ppm and 0.70, respectively. Combined experimental and theoretical results indicate that the phosphorus shielding tensor orientations are dictated by the local environment. For both shielding tensors, the most shielded component, [[Delta].sub.33], is approximately 78[degrees] from the P--P bond and in the phosphole ring plane. The relative orientation of the [[Delta].sub.33] components is described by a dihedral angle of 82[degrees], similar to the dihedral angle of approximately 76[degrees] defining the twist of the phosphole rings about the bridging P--P bond. Key words: solid-state [sup.31]P NMR, phosphorus chemical shielding tensors, phosphole tetramer, [sup.31]P--[sup.31]P spin pairs, ab initio calculations.

Nitrate, acetate, chloride and bromide salts of the bicyclic cation [Bi(SCH2CHOH)2]+ reveal a substantial thermodynamic preference for the thiolate-alcohol chelate in a 2:1 stoichiometry. The conformational features of the cation were drammatically different in each of the the resulting molecular structures. The changes in the molecular structure of the bicyclic bis(2-hydroxyethanediol)bismuth(III) complexes were also dependent on the relative donor capabilities of the anion.

The phosphadiazonium cation (Mes*NP)+ undergoes nucleophilic additions with fluorenylidine anion Mes*NH2 and Mes*OH, where Mes* = 2,4,6-tri-tert-butylphenyl, to yield phosphaalkenes and phosphenium cations which show the insertion of the N-P moiety into the H-Y, where Y = C, N, O bonds. A general reaction mechanism is experimentally supported by the separation and characterization of a sigma-complex model of the trapped intermediate, (Mes*NP-PPh3)(SO3CF3), for the insertion mechanism.

Sterically burdened Sb N(H)(C6H2Bu3)3 and Bi N(H)(C6H2Bu3)3 are isolated and studied for their spectroscopic and structural properties. Nuclear magnetic resonance spectroscopy and x-ray crystallography are used in the experiments. Results indicate that substantial steric crowding occurs in the complexes due to the C6H2Bu3 substituents. This phenomenon causes a severe distortion from a pyramidal geometry at the pnictogen center.

Vibrational spectroscopic and x-ray crystallographic observations of two classes dithiabismuth heterocycles synthesized via quantitative metathesis were carried out. The heterocycles were chloro-substituted monocycles and tethered bicyclic derivatives. The observations revealed the occurence of monocyclic bismuthenium cations as the dominant dissociation product in their synthesis.

Evaporation of a solution of SNSAsF6 and SNAsF6 in SO2 produces SNSNS(AsF6)2 heterocycle in good yield. Vibrational spectroscopy and X-ray crystallography reveal the presence of 6pi, electron rich aromatic SNSNS2+ in the heterocycle and the aromatic species dissociate into SN+ and SNS+ in SO2 solution. Synthesis of SNSNS2+ from SN+ and SNS+ involves a lattice-enforced symmetry-allowed cycloaddition, and the dication is stabilized by lattice.

Single crystal x-ray diffraction experiments analyze the crystal structure and electron density of 3-((p-nitrophenoxy)methyl)-3-chlorodiazirine. The phenyl portions of the compound exhibit the expected deformation density. The dynamic deformation density reveals that the bonding in the ring is a combination of a strained sigma bonding system with a pi donation from the N double bond N of an sp(2) carbon.

Studies of tetrachlorogallate and tetraphenylborate salts of the phosphenium cations ((iPr2N)2P)+ and (MeNCH2CH2N-(Me)P)+ reveals that the latter is monomeric in the solid state unlike the arsenic analogue. The compound with (Bph4) present is a covalent structure indicating the steric-feature-induced ionic formulation. The stability of the gallate salts in solution reveals the crucial nature of electrostatic interactions or ion-pairing.

An analysis of hexaaziridinylcyclotriphosphazone benzene solvate crystal structure and electron density reveals the deformation densities of a benzene ring, two azidirinyl rings and a phosphazene ring. The observed values correspond well with theoretical predictions for phosphazene and azidirinyl rings. The deformation density observations are similar to pi/pi model densities with phosphone atom conjugation.

Salts containing the first arsolidinium cations were prepared, isolated and structurally characterized. The chloride ion abstraction reaction efficiently yielded the nonmetal ion as tetrachloroaluminate and gallate salts. A centrosymmetric dimeric arrangement consisting of relatively weak As-N or As-S interactions for three derivatives was revealed by X--ray crystallography. In addition, formal examples of stable carbene analogues without the presence of of steric protection of pi-delocalization aided by Huckel destabilization.

CF3CN reacted with S4(AsF6)2 and S8(AsF6)2 in SO2 at room temperature to form 5-(trifluoromethyl)-1,2,3,4-trithiazolium hexafluoroarsenate. The product contained a planar 7pi CNSSS.+ radical cation. Spectroscopic and magnetic susceptibility measurements were conducted to fully determine the structure and magnetic properties of the compound.