Synthesis and single crystal structures of ternary phosphides Li4SrP2 and AAeP (A=Li, Na; Ae=Sr, Ba)

Two new (NaSrP, Li4SrP2) 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 image (#189, a=7.6357(3) Å, c=4.4698(3) Å, V=225.69(2) Å3, Z=3, and R/wR=0.0173/0.0268). NaSrP adopts an ordered Fe2P structure type. PSr6 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 PNa6 face-sharing trigonal prisms. Li4SrP2 crystallizes in the rhombohedral space group image (#166, a=4.2813(2) Å, c=23.437(2) Å, V=372.04(4) Å3, Z=3, and R/wR=0.0142/0.0222). In contrast to previous reports, LiSrP and LiBaP crystallize in the centrosymmetric hexagonal space group P63/mmc (#194, a=4.3674(3) Å, c=7.9802(11) Å, V=131.82(2) Å3, Z=2, and R/wR=0.0099/0.0217 for LiSrP; a=4.5003(2) Å, c=8.6049(7) Å, V=150.92(2) Å3, Z=2, and R/wR=0.0098/0.0210 for LiBaP). Li4SrP2, LiSrP, and LiBaP can be described as Li3P derivatives. Li atoms and P atoms make a graphite-like hexagonal layer, image. In LiSrP and LiBaP, Sr or Ba atoms reside between image layers to substitute for two Li atoms of Li3P, while in Li4SrP2, Sr substitutes only between every other image layer.