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Nb3Al crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. Nb is bonded in a 6-coordinate geometry to ten equivalent Nb and four equivalent Al atoms. There are two shorter (2.61 Å) and eight longer (3.19 Å) Nb–Nb bond lengths. All Nb–Al bond lengths are 2.92 Å. Al is bonded to twelve equivalent Nb atoms to form a mixture of edge and face-sharing AlNb12 cuboctahedra.
Nb3Al(PO4)6 crystallizes in the trigonal R3 space group. The structure is three-dimensional. there are three inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six PO4 tetrahedra. There is three shorter (1.98 Å) and three longer (2.01 Å) Nb–O bond length. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six PO4 tetrahedra. There is three shorter (1.97 Å) and three longer (2.00 Å) Nb–O bond length. In the third Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six PO4 tetrahedra. There is three shorter (1.96 Å) and three longer (2.01 Å) Nb–O bond length. Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six PO4 tetrahedra. There is three shorter (1.91 Å) and three longer (1.93 Å) Al–O bond length. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one AlO6 octahedra and corners with three NbO6 octahedra. The corner-sharing octahedra tilt angles range from 22–27°. There are a spread of P–O bond distances ranging from 1.50–1.56 Å. In the second P5+ site, P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share a cornercorner with one AlO6 octahedra and corners with three NbO6 octahedra. The corner-sharing octahedra tilt angles range from 25–29°. There are a spread of P–O bond distances ranging from 1.50–1.56 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Nb5+ and one P5+ atom. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Nb5+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a bent 150 degrees geometry to one Al3+ and one P5+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one Nb5+ and one P5+ atom. In the sixth O2- site, O2- is bonded in a bent 150 degrees geometry to one Nb5+ and one P5+ atom. In the seventh O2- site, O2- is bonded in a bent 150 degrees geometry to one Nb5+ and one P5+ atom. In the eighth O2- site, O2- is bonded in a bent 150 degrees geometry to one Nb5+ and one P5+ atom.