The Structure Chemistry of Boron-Rich Solids of the Alkali Metals

Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

“…XPS − and XANES measurements suggest that phosphorus in M 3 P, M 2 P, and MP holds the oxidation state P 1– , although the ionic character tends to increase as the P content increases. ,, Still, P-rich metal phosphides are valence compounds in the sense that valence electrons are essentially localized, so that MPs can be roughly described in the framework of the Zintl–Klemm formalism ,, in relative agreement with experimental crystal structures. , Consequently, the P center can be ascribed with a formal charge and can adopt several oxidation degrees ranging from 0 to −3 . Such a description, although valid for ionic MBs like alkali borides, usually fails for other metal borides . Indeed, the higher covalency of M–B bonds and the electron delocalization in the metal sublattice prevent an ionic description for B/M elemental ratio lower than 6.…”

Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

“…XPS − and XANES measurements suggest that phosphorus in M 3 P, M 2 P, and MP holds the oxidation state P 1– , although the ionic character tends to increase as the P content increases. ,, Still, P-rich metal phosphides are valence compounds in the sense that valence electrons are essentially localized, so that MPs can be roughly described in the framework of the Zintl–Klemm formalism ,, in relative agreement with experimental crystal structures. , Consequently, the P center can be ascribed with a formal charge and can adopt several oxidation degrees ranging from 0 to −3 . Such a description, although valid for ionic MBs like alkali borides, usually fails for other metal borides . Indeed, the higher covalency of M–B bonds and the electron delocalization in the metal sublattice prevent an ionic description for B/M elemental ratio lower than 6.…”

Nanodomains and local structure in ternary alkaline-earth hexaborides

“…The primary misfit is due to the first observed peak at approximately 1.9 Å , caused by the B-B bonds in the boron sub-lattice. In the majority of the literature, this bond length varies according to cation identity in the range 1.63-1.78 Å (Longuet-Higgins & Roberts, 1954;Schmitt et al, 2001;Chen et al, 2004;Albert, 2000;Albert & Hillebrecht, 2009), which is significantly shorter than that observed here. This apparently strained B-B bond is consistent with the large amount of micro-strain found by Cahill, Alberga et al (2017) in laboratory PXRD data collected from these samples.…”

New route toward nanosized crystalline metal borides with tuneable stoichiometry and variable morphologies

“…B-terminated facets are indeed expected from the excess of boron source introduced. Although the consideration of relative surface energies requires confirmation by first principle calculations, it is consistent with the high strength of the B-B bonds in such compounds and with the high stability of B 6 clusters in borides, 39 which suggest that the boron covalent framework should drive the relative surface energies, so that the role of the metal atoms would be secondary. Noteworthy, the largest facets in bulk tetraboride grown by a metal flux method are also {110}, 40 confirming their low surface energy.…”

Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

“…XPS − and XANES measurements suggest that phosphorus in M 3 P, M 2 P, and MP holds the oxidation state P 1– , although the ionic character tends to increase as the P content increases. ,, Still, P-rich metal phosphides are valence compounds in the sense that valence electrons are essentially localized, so that MPs can be roughly described in the framework of the Zintl–Klemm formalism ,, in relative agreement with experimental crystal structures. , Consequently, the P center can be ascribed with a formal charge and can adopt several oxidation degrees ranging from 0 to −3 . Such a description, although valid for ionic MBs like alkali borides, usually fails for other metal borides . Indeed, the higher covalency of M–B bonds and the electron delocalization in the metal sublattice prevent an ionic description for B/M elemental ratio lower than 6.…”

Nanodomains and local structure in ternary alkaline-earth hexaborides

“…The primary misfit is due to the first observed peak at approximately 1.9 Å , caused by the B-B bonds in the boron sub-lattice. In the majority of the literature, this bond length varies according to cation identity in the range 1.63-1.78 Å (Longuet-Higgins & Roberts, 1954;Schmitt et al, 2001;Chen et al, 2004;Albert, 2000;Albert & Hillebrecht, 2009), which is significantly shorter than that observed here. This apparently strained B-B bond is consistent with the large amount of micro-strain found by Cahill, Alberga et al (2017) in laboratory PXRD data collected from these samples.…”

New route toward nanosized crystalline metal borides with tuneable stoichiometry and variable morphologies

“…B-terminated facets are indeed expected from the excess of boron source introduced. Although the consideration of relative surface energies requires confirmation by first principle calculations, it is consistent with the high strength of the B-B bonds in such compounds and with the high stability of B 6 clusters in borides, 39 which suggest that the boron covalent framework should drive the relative surface energies, so that the role of the metal atoms would be secondary. Noteworthy, the largest facets in bulk tetraboride grown by a metal flux method are also {110}, 40 confirming their low surface energy.…”

Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

“…XPS − and XANES measurements suggest that phosphorus in M 3 P, M 2 P, and MP holds the oxidation state P 1– , although the ionic character tends to increase as the P content increases. ,, Still, P-rich metal phosphides are valence compounds in the sense that valence electrons are essentially localized, so that MPs can be roughly described in the framework of the Zintl–Klemm formalism ,, in relative agreement with experimental crystal structures. , Consequently, the P center can be ascribed with a formal charge and can adopt several oxidation degrees ranging from 0 to −3 . Such a description, although valid for ionic MBs like alkali borides, usually fails for other metal borides . Indeed, the higher covalency of M–B bonds and the electron delocalization in the metal sublattice prevent an ionic description for B/M elemental ratio lower than 6.…”

Nanodomains and local structure in ternary alkaline-earth hexaborides

“…The primary misfit is due to the first observed peak at approximately 1.9 Å , caused by the B-B bonds in the boron sub-lattice. In the majority of the literature, this bond length varies according to cation identity in the range 1.63-1.78 Å (Longuet-Higgins & Roberts, 1954;Schmitt et al, 2001;Chen et al, 2004;Albert, 2000;Albert & Hillebrecht, 2009), which is significantly shorter than that observed here. This apparently strained B-B bond is consistent with the large amount of micro-strain found by Cahill, Alberga et al (2017) in laboratory PXRD data collected from these samples.…”

New route toward nanosized crystalline metal borides with tuneable stoichiometry and variable morphologies

“…B-terminated facets are indeed expected from the excess of boron source introduced. Although the consideration of relative surface energies requires confirmation by first principle calculations, it is consistent with the high strength of the B-B bonds in such compounds and with the high stability of B 6 clusters in borides, 39 which suggest that the boron covalent framework should drive the relative surface energies, so that the role of the metal atoms would be secondary. Noteworthy, the largest facets in bulk tetraboride grown by a metal flux method are also {110}, 40 confirming their low surface energy.…”