Search

Abstract Background Some patients have noted a foul odor during radiation therapy sessions, but the cause of the odor remains unknown. Since we suspected that this phenomenon is due to ozone generated by ionizing radiation, this experimental study measured ozone concentrations in the treatment room and in a coiled polyvinyl chloride (PVC) tube placed within the radiation field. Methods We measured ozone concentrations using an ultraviolet absorption method and an ozone monitor. A PVC tube (inner diameter 7 mm, outer diameter 10 mm) was used to mimic the environment of the nasal cavity. The tube (790 cm) was coiled and set between two 4-cm-thick (for X-rays) or 2-cm-thick (for electron beams) water-equivalent solid phantoms. The sampling tube of the ozone monitor was inserted into the PVC tube, and the joint was sealed to prevent environmental air contamination. To measure ozone concentrations in the atmosphere, the sampling tube supplied with the unit was used. A linac was used on a full-sized treatment field (40 cm × 40 cm at a source-to-axis distance of 100 cm). The effect of an electron beam on ozone concentrations was also evaluated with a full-sized treatment field (40 cm × 40 cm at a source-to-surface distance of 100 cm). Results Ozone levels in the treatment room were undetectable before the start of daily treatment but reached 0.008 parts per million (ppm) or more at 1 h after the start of treatment. Concentrations then remained nearly constant at 0.010–0.015 ppm throughout the day. The maximum ozone concentration in the PVC tube was only 0.006 ppm, even when it was irradiated at 2400 monitor units/min. Depending on the X-ray dose rate, the concentration increased to a maximum of 0.010 ppm with oxygen flowing into the other end of the tube at 1.5 L/min. Ozone concentrations in the PVC tube did not differ significantly between X-ray and electron-beam irradiation. Conclusions Only traces of ozone were found in the PVC tube that was used to mimic the nasal passages during radiation, these concentrations were too low for human perception. However, ozone concentrations did reach potentially detectable levels in the treatment room.

The synthesis, characterization, and solid-state structure of bulky alkoxy- and aryloxy-supported yttrium polynuclear hydrides are reported. Hydrogenolysis of the supertrityl alkoxy anchored yttrium dialkyl, Y(OTr*)(CH 2 SiMe 3 ) 2 (THF) 2 ( 1 ) (Tr* = tris(3,5-di- tert -butylphenyl)methyl), resulted in the clean conversion to the tetranuclear dihydride, [Y(OTr*)H 2 (THF)] 4 ( 1a ). X-ray analysis revealed a highly symmetrical structure ( 4 ̅ site symmetry) with the four Y atoms located on the corners of a compressed tetrahedron, each bonded to an OTr* and tetrahydrofuran (THF) ligand and the cluster held together by four face-capping, μ 3 -H, and four edge-bridging, μ 2 -H, hydrides. DFT calculations on the full system with and without THF, but also on model systems, clearly show that the structural preference for complex 1a is controlled by the presence and coordination of THF molecules. Contrary to the exclusive formation of the tetranuclear dihydride, hydrogenolysis of the bulky aryloxy yttrium dialkyl, Y(OAr*)(CH 2 SiMe 3 ) 2 (THF) 2 ( 2 ) (Ar* = 3,5-di- tert -butylphenyl) gave a mixture of the analogous tetranuclear 2a and trinuclear, [Y 3 (OAr*) 4 H 5 (THF) 4 ], polyhydride, 2b . Similar results, i.e., a mixture of tetra-/tri-nuclear products, were obtained from hydrogenolysis of the even bulkier Y(OAr Ad2,Me )(CH 2 SiMe 3 ) 2 (THF) 2 compound. Experimental conditions were established to optimize the production of either the tetra- or trinuclear products. X-ray structure of 2b revealed a triangular array of three yttrium atoms with two face-capping μ 3 -H and three edge-bridging μ 2 -H hydrides, with one yttrium bonded to two aryloxy ligands while the other two have a complement of one aryloxy and two THF ligands; the solid-state structure is close to being C 2 symmetric, with the C 2 axis running through the unique Y and unique μ 2 -H hydride. As opposed to 2a , which shows distinct 1 H NMR resonances for μ 3 / μ 2 -H (δ = 5.83/6.35 ppm, respectively), no hydride signals for 2b were observed at room temperature, indicating hydride exchange on the NMR time scale. Their presence and assignment were secured at -40 °C from 1 H SST (spin saturation) experiment.

The synthesis and structural characterization of Ae(Tp iPr2 ) 2 (Ae = Mg, Ca, Sr, Ba; Tp iPr2 = hydrido-tris(3,5-diisopropyl-pyrazol-1-yl)borate) are reported. In the crystalline state, the alkaline earth metal centers are six-coordinate, even the small Mg 2+ ion, with two κ 3 - N , N ', N ''-Tp i Pr2 ligands, disposed in a bent arrangement (B···Ae···B < 180°). However, contrary to the analogous Ln(Tp iPr2 ) 2 (Ln = Sm, Eu, Tm, Yb) compounds, which all exhibit a bent-metallocene structure close to C s symmetry, the Ae(Tp iPr2 ) 2 compounds exhibit a greater structural variation. The smallest Mg(Tp iPr2 ) 2 has crystallographically imposed C 2 symmetry, requiring both bending and twisting of the two Tp i Pr2 ligands, while with the similarly sized Ca 2+ and Sr 2+ , the structures are back toward the bent-metallocene C s symmetry. Despite the structural variations, the B···M···B bending angle follows a linear size-dependence for all divalent metal ions going from Mg 2+ to Sm 2+ , decreasing with increasing metal ion size. The complex of the largest metal ion, Ba 2+ , forms an almost linear structure, B···Ba···B 167.5°. However, the "linearity" is not due to the compound approaching the linear metallocene-like geometry, but is the result of the pyrazolyl groups significantly tipping toward the metal center, approaching "side-on" coordination. An attempt to rationalize the observed structural variations is made.

In the title compound, [Lu(C 7 H 7 ) 3 (C 4 H 8 O) 2 ] ( 1 ), the Lu ion is coordinated by three benzyl and two tetra-hydro-furan ligands. Two of the benzyl groups are bonded in a classical η 1 -fashion through the methyl-ene via the ipso -carbon atom of the benzyl ligand in addition to bonding through the methyl-ene C atom, resulting in a modified trigonal-bipyramidal coordination geometry about the Lu center.

The reaction of EuI 2 (THF) 2 with potassium hydro-tris-(3,5-diiso-propyl-pyrazol-yl)borate (K[HB(3,5- i Pr2 pz) 3 ] (= KTp i Pr2 , pz = pyrazol-yl) in a molar ratio of 1:1.5 resulted in extensive ligand fragmentation and formation of the europium(II) mono(scorpionate) complex bis-(3,5-diisopropyl-1 H -pyrazole)[hydro-tris-(3,5-diiso-propyl-pyrazol-yl)borato]iodido-europium(II), [Eu(C 27 H 46 BN 6 )I(C 9 H 16 N 2 ) 2 ] or (Tp i Pr2 )(3,5- i Pr2 pzH) 2 Eu II I, 1 , in high yield (78%). As a typical by-product, small amounts of the sterically crowded pyraza-bole derivative trans -4,8-bis-(3,5-diiso-propyl-pyrazol-1-yl)-1,3,5,7-tetra-iso-propyl-pyraza-bole, C 36 H 62 B 2 H 8 or trans -{(3,5- i Pr2 pz)HB(μ-3,5- i Pr2 pz)} 2 , 2 , were formed. Both title compounds have been structurally characterized through single-crystal X-ray diffraction. In 1 , two isopropyl groups are each disordered over two orientations with occupancy ratios of 0.574 (10):0.426 (10) and 0.719 (16):0.281 (16). In 2 , one isopropyl group is similarly disordered, occupancy ratio 0.649 (9):0.351 (9).

Well-defined lanthanide polysulfide complexes containing S4(2-) and S5(2-) ligands, the samarium(iii) pentasulfide complex Sm(Tp(iPr2))(κ(1)-3,5-(i)Pr2Hpz)(S5) and the tetrasulfide-bridged binuclear ytterbium(iii) complex (μ-S4)[Yb(Tp(iPr2))(κ(1)-3,5-(i)Pr2Hpz)(κ(2)-3,5-(i)Pr2pz)]2 (Tp(iPr2) = hydro-tris(3,5-diisopropylpyrazolyl)borate), have been synthesized and structurally characterized by single-crystal X-ray diffraction.

The synthesis and characterization of Ln(Tp(iPr2))2 (Ln = Sm, 3Sm; Tm, 3Tm) are reported. While the simple (1)H NMR spectra of the compounds indicate a symmetrical solution structure, with equivalent pyrazolyl groups, the solid-state structure revealed an unexpected, "bent sandwich-like" geometry. By contrast, the structure of the less sterically congested Tm(Tp(Me2,4Et))2 (4) adopts the expected symmetrical structure with a linear B-Tm-B arrangement. Computational studies to investigate the origin of the unexpected bent structure of the former compounds indicate that steric repulsion between the isopropyl groups forces the Tp ligands apart and permits the development of unusual interligand C-H···N hydrogen-bonding interactions that help stabilize the structure. These results find support in the similar geometry of the Tm(III) analogue [Tm(Tp(iPr2))2]I, 3Tm(+), and confirm that the low symmetry is not the result of a metal-ligand interaction. The relevance of these results to the general question of the coordination geometry of MX2 and M(C5R5)2 (M = heavy alkaline earth and Ln(II), X = halide, and C5R5 = bulky persubstituted cyclopentadienyl) complexes and the importance of secondary H-bonding and nonbonding interactions on the structure are highlighted.

The new divalent thulium compound [Tm(BH(4))(2)(DME)(2)] could be prepared by reduction of [Tm(BH(4))(3)(THF)(3)] or from TmI(2) and KBH(4). It was used as a precursor to the divalent [(Tp(tBu,Me))Tm(BH(4))(THF)] by reaction with potassium tris(2-tBu-4-Me)pyrazolylborate (KTp(tBu,Me)). Both Tm(II) compounds were found active as ε-caprolactone polymerisation catalysts.

The reaction of YbI(2) with KTp(Me2) gives (Tp(Me2))YbI(THF)(2) (1-Yb) as a thermally unstable product. Use of the more hindered KTp(tBu,Me) gave (Tp(tBu,Me))LnI(THF)(n) (Ln = Sm, n = 2, 2-Sm; Ln = Yb, n = 1, 2-Yb). The crystal structures of both these compounds are reported. Adducts with neutral ligands such as pyridines and isonitriles can be prepared and the crystal structures of [(Tp(tBu,Me))YbIL(n)] (L = CN(t)Bu, n = 1; L = 3,5-lutidine, n = 2) are described. 2-Sm can be oxidized using AgBPh(4) to give [(Tp(tBu,Me))SmI(THF)(2)]BPh(4). Compounds 2-Sm and 2-Yb are useful starting materials for the preparation of heteroleptic compounds by metathesis with appropriate potassium reagents. The preparations and characterization of the hydrocarbyls (Tp(tBu,Me))Ln{CH(SiMe(3))(2)} (Ln = Sm, 5-Sm; Yb, 5-Yb) and [(Tp(tBu,Me))Ln{CH(2)(SiMe(3))}(THF)] (Ln = Yb, 6a-Yb) and the triethylborohydrides [(Tp(tBu,Me))Ln(HBEt(3))(THF)(n)] (Ln = Sm, n = 0, 7-Sm; Yb, n = 1, 7-Yb) are reported, as well as the crystal structures of 5-Sm and 5-Yb, and the THF adducts 6a-Yb and [(Tp(tBu,Me))Sm{CH(SiMe(3))(2)}(THF)], 5a-Sm.

The use of the Tp(iPr(2)) ligand led to the straightforward and high-yield synthesis of rare examples of trinuclear monoligand lanthanide dihydrides, [(Tp(iPr(2)))LnH(2)](3) (Ln = Y, Lu). The Y complex was found to mediate the hydrogenation and coupling of carbon monoxide with exclusive formation of propene via the intermediacy of a cluster-bound propenolate ligand.

In the title compound, [Yb(C(24)H(40)BN(6))(2)]·C(7)H(8), the Yb atom is coordinated by two tris(3-tert-butyl-5-methyl-pyrazol-1-yl)hydridoborate [Tp(tBu,Me)] ligands. One ligand binds in the κ(3) mode, throuh three N atoms of the pyrazolyl rings, the other ligand coordinates through two N atoms of the pyrazolyl rings and the H atom attached to the central B via an agostic-type inter-action through the B-H group of the second Tp(tBu,Me) ligand, giving an overall distorted octa-hedral geometry. One of the tert-butyl groups is disordered over two sites, with occupancies of 0.65 and 0.35.

The reaction of Ln(AlMe(4))(3) with bulky hydrotris(pyrazolyl)borate (Tp(t)(Bu,Me))H proceeds via a sequence of methane elimination and C-H bond activation, affording unprecedented rare-earth metal ligand moieties including Ln(Me)[(micro-Me)AlMe(3)] and X-ray structurally characterized "Tebbe-like" Ln[(micro-CH(2))(2)AlMe(2)].

Stoichiometric reaction of [ Sm(Tp(Me2))2 ], 1, with a variety of reducible ketone- and quinone-type substrates gave thermally stable, isolable radical anions/ketyls in moderate to good yields. Thus reaction with benzophenone gave [Sm(Tp(Me2))2(OCPh2)], 2, with fluorenone [Sm(Tp(Me2))2(eta1-OC13H8)], 3, and di-tert-butylparaquinone [Sm(Tp(Me2))2(eta1-OC6H2(tBu)2O)], 4, each of which was structurally characterized. In the case of the less-hindered benzoquinone, an unimetallic semiquinone [Sm(Tp(Me2))2(OC6H4O)], 5, could be isolated, although it was unstable with respect to formation of the dimetallic complex [Sm(Tp(Me2))2]2(mu-OC6H4O), 6. Compound 6 was structurally characterized, as was its anthraquinone analogue [Sm(Tp(Me2))2]2(mu-OC14H8O), 7. When the analogous reaction was carried out between the less-reducing [Eu(Tp(Me2))2] and benzoquinone, only the europium analogue of the semiquinone 5, [Eu(Tp(Me2))2(OC6H4O)], 8, could be isolated. The use of the sterically hindered 3,5-di-tert-butyl-o-benzoquinone allowed isolation of [Sm(Tp(Me2))2(DTBSQ)], 9.

Reaction of [(Tp(Me)2)(2)UI] with KNR(2) (R = C(6)H(5), SiMe(3)) in tetrahydrofuran (THF) afforded the monomeric trivalent actinide amide complexes [(Tp(Me)2)(2)U[N(C(6)H(5))(2)]], 1, and [(Tp(Me)2)(2)U[N(SiMe(3))(2)]], 2. The complexes have been fully characterized by spectroscopic methods and their structures were confirmed by X-ray crystallographic studies. In the solid state 1 and 2 exhibit distorted pentagonal bipyramidal geometries. The U-NR(2) bond lengths in both complexes are the same but in complex 2 the greater steric demands of the N(SiMe(3))(2) ligand led to elongated U-N(pz) bonds, especially those opposite the amido ligand.

Adventitious hydrolysis of a number of different complexes with the molecular formula Ln(Tp(Me2))(2)X [Tp(Me2) = (HB(dmpz)(3)), where X is a basic anionic ligand] in various solvents, yielded crystals of highly insoluble dimers of the general formula [Ln(Tp(Me2))(mu-BOp(Me2))](2) (1) [Ln = La, Ce, Sm; BOp(Me2) = (HBO(dmpz)(2))(2)(-); dmpzH = 3,5-dimethylpyrazole]. The results of several single-crystal X-ray determinations are reported. One metal nitrogen distance, that lying across from the two negatively charged bridging oxygen atoms, is 0.06 A longer than the others, suggesting an unusual trans influence at a lanthanide center. The formation of 1 is proposed to involve the intermediacy of Ln(Tp(Me2))(2)OH formed by protonolysis with adventitious water.

Reaction of LnI2 (Ln = Sm, Yb) with two equivalents of NaTp(Me2) or reduction of Eu(Tp(Me2))2OTf gives good yields of the highly insoluble homoleptic Ln(II) complexes, Ln(Tp(Me2))2 (Ln = Sm (1a), Yb (2a), Eu (3a)). Use of the additionally 4-ethyl substituted Tp(Me2,4Et) ligand produces the analogous, but soluble Ln(Tp(Me2,4Et))2 (1-3b) complexes. Soluble compounds are also obtained with the Tp(Ph) and Tp(Tn) ligands (Tn = thienyl), Ln(Tp(Ph))2 (Ln = Sm, 1c; Yb, 2c) and Ln(Tp(Tn))2 (Ln = Sm, 1d; Yb, 2d). To provide benchmark parameters for structural comparison the series of Sm(Tp(Me2))2X complexes (X = F, 1e; Cl, 1f; Br, 1g; I, 1h; BPh4, 1j) were prepared either via oxidation of the Sm(Tp(Me2))2 or salt metathesis from SmX3 (X = Cl, Br, I). The solid-state structures of 1-3a, 1b, 1-2c and 1e, 1f, 1h, and 1j were determined by single-crystal X-ray diffraction. The homoleptic bis-Tp complexes are all six-coordinate with trigonal antiprismatic geometries, planes of the kappa(3)-Tp ligands are parallel to one another. In the series of Sm(Tp(Me2))2X complexes the structure changes from seven-coordinate molecular compounds, with intact Sm-X bonds, for X = F, Cl, to six-coordinate ionic structures [Sm(Tp(Me2))2]X (X = I, BPh4), suitable crystals of the bromide compound could not be obtained. The dependence of the structures on the size of X is understandable in terms of the interplay between the size of the cleft that the [Sm(Tp(Me2))2](+) fragment can make available and the donor ability of the anionic group toward the hard Sm(III) center.

Divalent and solvent-free: the ytterbium hydrido complex 1 was obtained by the hydrogenolysis of [(Tp(tBu,Me))Yb(CH(2)SiMe(3))(thf)]. The steric demand of the bulky hydrotris(3-tert-butyl-5-methylpyrazolyl)borate ligand, Tp(tBu,Me), is sufficient to stabilize the dimer, yet facile room-temperature reactions with amines, alkynes, diynes, and CO indicate a rich chemistry of 1.