High-Pressure Synthesis of Cd(NH3)2[B3O5(NH3)]2: Pioneering the Way to the Substance Class of Ammine Borates.

To date, the access to the substance class of borates containing nitrogen, for example, nitridoborates, oxonitridoborates, or amine borates, was an extreme effort owing to the difficult starting materials and reaction conditions. Although a number of compounds containing boron and nitrogen are known, no adduct of ammonia to an inorganic borate has been observed so far. A new synthetic approach starting from the simple educts CdO, B2O3, and aqueous ammonia under conditions of 4.7 GPa and 800 °C led to the synthesis of Cd(NH3)2[B3O5(NH3)]2 as the first ammine borate. We thoroughly characterized this compound on the basis of low-temperature single-crystal and powder X-ray diffraction data, IR and Raman spectroscopy, and by quantum theoretical calculations. This contribution shows that the adduct of NH3 to the BO3 group of a complex B-O network can be stabilized, opening up a fundamentally new synthetic route to nitrogen-containing borates.

HP-CsB5O8 : synthesis and characterization of an outstanding borate exhibiting the simultaneous linkage of all structural units of borates.

The new cesium pentaborate HP-CsB5 O8 is synthesized under high-pressure/high-temperature conditions of 6 GPa and 900 °C in a Walker-type multianvil apparatus. The compound crystallizes in the orthorhombic space group Pnma (Z=4) with the parameters a=789.7(1), b=961.2(1), c=836.3(1) pm, V=0.6348(1) nm(3) , R1 =0.0359 and wR2 =0.0440 (all data). The new structure type of HP-CsB5 O8 exhibits the simultaneous linkage of trigonal BO3 groups, corner-sharing BO4 tetrahedra, and edge-sharing BO4 tetrahedra including the presence of threefold-coordinated oxygen atoms. With respect to the rich structural chemistry of borates, HP-CsB5 O8 is the second structure type possessing this outstanding combination of the main structural units of borates in one compound. The structure consists of corrugated chains of corner- and edge-sharing BO4 tetrahedra interconnected through BO3 groups forming octagonal channels. Inside these channels, cesium is 13+3-fold coordinated by oxygen atoms. (11) B MQMAS NMR spectra are analyzed to estimate the isotropic chemical shift values and quadrupolar parameters. IR and Raman spectra are obtained and compared to the calculated vibrational frequencies at the Γ-point. The high-temperature behavior is examined by means of temperature-programmed powder diffraction.

Oxonium ions substituting cesium ions in the structure of the new high-pressure borate HP-Cs(1-x)(H(3)O)(x)B(3)O(5) (x=0.5-0.7).

The new high-pressure borate HP-Cs1-x (H3 O)x B3 O5 (x=0.5-0.7) was synthesized under high-pressure/high-temperature conditions of 6 GPa/900 °C in a Walker-type multianvil apparatus. The compound crystallizes in the monoclinic space group C2/c (Z=8) with the parameters a=1000.6(2), b=887.8(2), c=926.3(2) pm, ß=103.1(1)°, V=0.8016(3) nm(3) , R1=0.0452, and wR2=0.0721 (all data). The boron-oxygen network is analogous to those of the compounds HP-MB3 O5 , (M=K, Rb) and exhibits all three structural motifs of borates-BO3 groups, corner-sharing BO4 tetrahedra, and edge-sharing BO4 tetrahedra-at the same time. Channels inside the boron-oxygen framework contain the cesium and oxonium ions, which are disordered on a specific site. Estimating the amount of hydrogen by solid-state NMR spectroscopy and X-ray diffraction led to the composition HP-Cs1-x (H3 O)x B3 O5 (x=0.5-0.7), which implies a nonzero phase width.

Experimental determinations and quantum-chemical calculations of the vibrational spectra of ß-ZnB4O7 and ß-CaB4O7.

The two oxoborates ß-ZnB4O7 and ß-CaB4O7 were synthesized and investigated by FTIR- and Raman spectroscopy and ab initio quantum chemical calculations. Maximum and mean deviations between experimentally determined bands and calculated modes ranged between 15-36 cm(-1) and 5-7 cm(-1), respectively, allowing band assignments to vibrational modes in most cases. The complex network structures with tetrahedral BO4 and planar OB3 groups are mirrored by the spectra and numerous vibrational modes, not assignable by standard borates classification schemes. It was confirmed that OB3 units, despite similar force constants and geometry, do not absorb in the same range as BO3 units. Bands in the high wavenumber range are rather caused by B-O-(Zn/Ca), O-B-O, B-O-B, and B-O stretching and bending vibrations. The experimental observation of inactive or Raman-active modes in the absorption spectra indicates defects or structural distortions in both compounds.