Three-coordinated boron-11 chemical shifts in borates.

نویسندگان

  • S Kroeker
  • J F Stebbins
چکیده

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.

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

High-pressure Syntheses and Characterization of the Rare Earth Borates RE5(BO3)2F9 (RE=Dy, Ho)

The new rare earth fluoride borates RE5(BO3)2F9 (RE = Ho, Dy) were synthesized under highpressure/high-temperature conditions of 1.5 GPa, 1250 ◦C for Dy5(BO3)2F9 and 2.5 GPa, 1200 ◦C for Ho5(BO3)2F9 in a Walker-type multianvil apparatus from the corresponding rare earth oxides, rare earth fluorides, and boron oxide. The single-crystal structure determinations have revealed that both compounds a...

متن کامل

Synthesis of glucaminium-based ionic liquids and their application in the removal of boron from water.

A novel class of ionic liquids (ILs), exhibiting high selectivity towards boron species as well as the ability to phase separate from water, were synthesized from N-methyl-D-glucamine. The complexation of boric acid/borate with the ILs was confirmed using (11)B NMR.

متن کامل

Boric Acid and Borates

Boric acid and its chemical relatives are pesticides that are derived from the element boron. Boron rarely occurs alone and is typically found in combination with other elements; common combinations are boric acid or borates.1 Unlike many pesticides which are synthetic compounds,2 boric acid and related pesticides are naturally occurring compounds.1 Boron compounds are widely found in rivers, s...

متن کامل

Dependence of N4 upon alkali modifier in binary borate glasses

In this paper we re-examine the alkali dependence of the fraction of four-coordinated borons (N4) in two series of glasses: alkali borates (0·4M2O.B2O3) and mixed lithium caesium borates (0·4(xLi2O+(1-x)Cs2O). B2O3). High field B MAS-NMR experiments were performed to maximise the accuracy of the present results. We found no evidence for an alkali dependence on N4 in either system. In each case ...

متن کامل

11B solid-state NMR investigation of the rhamnogalacturonan II-borate complex in plant cell walls.

The boron in plant cell walls, which is water-insoluble and in the solid state, is solubilized by pectinase digestion to give a dimeric rhamnogalacturonan II-borate (dRG-II-B) complex. To clarify the nondestructive structure of boron present in plant cell walls (as represented by sugar beet fiber), we performed 192- and 96-MHz 11B solid state NMR measurements. The use of a high field magnet fre...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:
  • Inorganic chemistry

دوره 40 24  شماره 

صفحات  -

تاریخ انتشار 2001