Synthesis and single crystal structures of ternary phosphides Li 4SrP 2 and AAeP ( A=Li, Na; Ae=Sr, Ba)

Abstract

Two new (NaSrP, Li 4SrP 2) and two known (LiSrP, LiBaP) ternary phosphides have been synthesized and characterized using single crystal X-ray diffraction studies. NaSrP crystallizes in the non-centrosymmetric hexagonal space group P 6 ¯ 2 m (#189, a=7.6357(3) Å, c=4.4698(3) Å, V=225.69(2) Å 3, Z=3, and R/w R=0.0173/0.0268). NaSrP adopts an ordered Fe 2P structure type. PSr 6 trigonal prisms share trigonal (pinacoid) faces to form 1D chains. Those chains define large channels along the [001] direction through edge-sharing. The channels are filled by chains of PNa 6 face-sharing trigonal prisms. Li 4SrP 2 crystallizes in the rhombohedral space group R 3 ¯ m (#166, a=4.2813(2) Å, c=23.437(2) Å, V=372.04(4) Å 3, Z=3, and R/w R=0.0142/0.0222). In contrast to previous reports, LiSrP and LiBaP crystallize in the centrosymmetric hexagonal space group P6 3/ mmc (#194, a=4.3674(3) Å, c=7.9802(11) Å, V=131.82(2) Å 3, Z=2, and R/w R=0.0099/0.0217 for LiSrP; a=4.5003(2) Å, c=8.6049(7) Å, V=150.92(2) Å 3, Z=2, and R/w R=0.0098/0.0210 for LiBaP). Li 4SrP 2, LiSrP, and LiBaP can be described as Li 3P derivatives. Li atoms and P atoms make a graphite-like hexagonal layer, ∞ 2 [ LiP ] 2 - . In LiSrP and LiBaP, Sr or Ba atoms reside between ∞ 2 [ LiP ] 2 - layers to substitute for two Li atoms of Li 3P, while in Li 4SrP 2, Sr substitutes only between every other ∞ 2 [ LiP ] 2 - layer.