Structural and luminescence studies of the new nitridomagnesoaluminate CaMg2AlN3.

CaMg(2)AlN(3) was synthesized in a closed system by solid state reaction from binary nitrides. Structure refinements based on powder X-ray diffraction data suggested ambiguity about the occupancy of magnesium and aluminum tetrahedral sites. Solid-state (27)Al and (25)Mg NMR studies were used to adjudicate amongst possible space groups. With reference to projector augmented wave calculations of the quadrupolar coupling constants, the measured values of CQ and the numbers of crystallographically inequivalent Al and Mg sites indicate that CaMg(2)AlN(3) crystallizes in the space group P6(3)/mmc with partial occupancy of the distorted tetrahedral Al site and possibly also mixing of Mg(2+) and Al(3+) ions on opposite sites. The compound obtained by synthesis with a flux shows orange defect-related luminescence at room temperature.

New opportunities for high-resolution solid-state NMR spectroscopy of oxide materials at 21.1- and 18.8-T fields.

We present here high-resolution solid state NMR spectra of several oxide and silicate materials that illustrate the improvements obtainable with very high external fields (18.8 and 21.1 T), with probes capable of tuning to a wide frequency range that allow observations of nuclides from high to low magnetogyric ratio. We discuss 27Al MAS spectra for the zeolite scolecite (CaAl2Si3O10 x 3H2O), 17O MAS data for analcime (NaAlSi2O6 x H2O), calcium monoaluminate (CaAI2O4), and titanite (CaTiSiO5), 39K spin-echo spectra for leucite (KAlSi2O6), microline (KAlSiO8), muscovite (KAl2(AlSi3O10)(OH2) and a potassium aluminosolicate glass, and preliminary 73Ge spin-echo MAS spectra for crystalline and glassy germanium dioxide (GeO2).

Three-coordinated boron-11 chemical shifts in borates.

Despite the importance of (11)B nuclear magnetic resonance (NMR) in structural studies of borate glasses, no clear means of correlating NMR parameters with the number of nonbridging oxygens on three-coordinate boron has been demonstrated. In this work, a series of anhydrous, polycrystalline, binary borates has been examined by (11)B magic-angle spinning (MAS) NMR to obtain precise measurements of their three-coordinate boron isotropic chemical shifts. The shifts generally increase with the replacement of bridging oxygens by nonbridging oxygens, ranging from 14.6 ppm in crystalline B(2)O(3) to 22.5 ppm in magnesium orthoborate. The underlying physical basis for this trend is satisfactorily accounted for by considering second neighbor effects using bond valence sums. These data are supportive of a structural model for B(2)O(3) glass in which 72% of the boron atoms are in rings. High-field MAS NMR experiments (B(0) = 18.8 T) indicate that the boron shielding is anisotropic, with greater anisotropy measured for three-coordinate borons possessing one or two nonbridging oxygens, than for those with zero or three nonbridging oxygens.

Non-bridging oxygens in borate glasses: characterization by 11B and 17O MAS and 3QMAS NMR.

The concentrations of non-bridging oxygens (NBO) in oxide glasses has major effects on their properties and on those of their precursor glass melts. In borate and borosilicate glasses, the presence of NBO bonded to boron has generally been inferred from 11B NMR spectra and mass balance considerations. Here we report the direct observation of such NBO using 17O MAS and 3QMAS techniques, and compare estimates of their populations with those derived from high-resolution 11B MAS spectra. For the latter, two independent methods are used, based on the ratios of trigonal to tetrahedral boron and on the concentrations of trigonal boron sites with large quadrupolar asymmetry parameters. We include data on crystalline sodium pyroborate (Na4B2O5) and sodium metaborate (NaBO2), and several sodium and barium borate glasses. 17O chemical shifts and quadrupolar coupling constants for NBO bonded to boron vary considerably depending on their coordination environment. In borosilicates, peaks for this species may be hidden by overlap with B-O-Si or Si-O-Si resonances.

Anisotropy in the 31P, 63/65Cu indirect spin-spin coupling and 31P nuclear shielding tensors of linear copper(I) phosphines.

Phosphorus-31 CP/MAS NMR spectra of two linear bis(tribenzylphosphine)cuprate(I) salts reveal significant anisotropy in the one-bond 31P, 63,65Cu J tensors. The parallel and perpendicular components of 1J(31P, 63Cu), for example, are +2.0 and +1.3 kHz, respectively. The well-characterized space group and point symmetry in one of these compounds greatly simplifies the 31P lineshape analysis, thus dispensing with the need to make assumptions about the interaction tensors involved. This offers an unique opportunity to study DeltaJ by calculating dipolar coupling constants from known internuclear distances, and by using zero-field nuclear quadrupole resonance spectroscopy to obtain the magnitudes of the 63/65Cu nuclear quadrupole coupling constants, CQ. Copper-63 CQ values in these complexes exceed 80 MHz, proving to be the largest reported for copper(I) phosphines. Phosphorus-31 NMR spectra of non-spinning samples at three applied magnetic fields are also presented, along with lineshape calculations based on full-matrix Zeeman-quadrupolar Hamiltonian diagonalization. It is shown that exact 31P lineshape calculations provide the relative signs of CQ, the isotropic J-coupling, and the effective dipolar coupling constant. This appears to be the first unambiguous determination of Delta1J(31P, 63/65Cu).

Intentional iron overdose: an institutional review.

OBJECTIVE: To document the frequency of admissions and the outcome of patients with a diagnosis of intentional iron overdose to a large urban hospital. DESIGN: Retrospective review of hospital records. SETTING: Health Sciences Centre, Winnipeg, an 1100-bed primary and tertiary care centre serving a regional population of about 1.2 million. PATIENTS: All patients with a discharge diagnosis of iron overdose who were admitted from Jan. 1, 1979, to July 1, 1991. Of these 113 cases 66 (58%) represented an intentional iron overdose on the basis of information derived from the patient, family or friends. MAIN OUTCOME MEASURES: Frequency of admissions, length of hospital stay and survival rate. RESULTS: Most (53 [80%]) of the 66 patients were females. The mean age was 19.8 (standard deviation [SD] 6.1) years (range 9 to 48 years). One third of the cases were associated with excess alcohol intake. The frequency of hospital admissions increased during the study period (1.4 cases per year in the first 5 years and 9.8 cases per year in the last 5; 5.3 cases per year overall). The mean length of hospital stay was 6.8 (SD 12.1) days, and the mortality rate was 10%. CONCLUSIONS: Hospital admissions because of intentional iron overdose are becoming more frequent in this centre and are associated with appreciable morbidity and mortality rates. Prospective studies are required to delineate clearly the signs, symptoms and abnormal laboratory findings associated with this problem.