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NiS2 crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two NiS2 sheets oriented in the (0, 0, 1) direction. Ni4+ is bonded in a 6-coordinate geometry to six equivalent S2- atoms. All Ni–S bond lengths are 2.30 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Ni4+ atoms.
NiS2 is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three NiS2 sheets oriented in the (0, 0, 1) direction. Ni4+ is bonded to six equivalent S2- atoms to form edge-sharing NiS6 octahedra. All Ni–S bond lengths are 2.26 Å. S2- is bonded in a distorted T-shaped geometry to three equivalent Ni4+ atoms.
NiS2 crystallizes in the monoclinic P2_1 space group. The structure is two-dimensional and consists of one NiS2 sheet oriented in the (-1, 0, 1) direction. Ni4+ is bonded in a square co-planar geometry to four equivalent S2- atoms. There are two shorter (2.18 Å) and two longer (2.19 Å) Ni–S bond lengths. S2- is bonded in a distorted bent 120 degrees geometry to two equivalent Ni4+ atoms.
NiS2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ni4+ is bonded in a body-centered cubic geometry to eight equivalent S2- atoms. All Ni–S bond lengths are 2.47 Å. S2- is bonded to four equivalent Ni4+ atoms to form a mixture of edge and corner-sharing SNi4 tetrahedra.
NiS2 is Marcasite structured and crystallizes in the orthorhombic Pnnm space group. The structure is three-dimensional. Ni4+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with eight equivalent NiS6 octahedra, corners with six equivalent SNi3S tetrahedra, and edges with two equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 62°. There are two shorter (2.34 Å) and four longer (2.37 Å) Ni–S bond lengths. S2- is bonded to three equivalent Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three equivalent NiS6 octahedra, corners with thirteen equivalent SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 70–75°. The S–S bond length is 2.09 Å.
NiS2 crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. there are two inequivalent Ni4+ sites. In the first Ni4+ site, Ni4+ is bonded to twelve equivalent S2- atoms to form a mixture of edge and face-sharing NiS12 cuboctahedra. All Ni–S bond lengths are 2.83 Å. In the second Ni4+ site, Ni4+ is bonded to twelve equivalent S2- atoms to form a mixture of edge and face-sharing NiS12 cuboctahedra. All Ni–S bond lengths are 2.82 Å. S2- is bonded in a 11-coordinate geometry to six Ni4+ and five equivalent S2- atoms. There are a spread of S–S bond distances ranging from 2.52–2.58 Å.
NiS2 crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one NiS sheet oriented in the (0, 0, 1) direction and one S sheet oriented in the (0, 0, 1) direction. In the NiS sheet, Ni4+ is bonded to five equivalent S2- atoms to form a mixture of distorted corner and edge-sharing NiS5 trigonal bipyramids. There are one shorter (2.22 Å) and four longer (2.39 Å) Ni–S bond lengths. S2- is bonded in a distorted pentagonal planar geometry to five equivalent Ni4+ atoms. In the S sheet, S2- is bonded in a square co-planar geometry to four equivalent S2- atoms. All S–S bond lengths are 2.28 Å.
NiS2 is Marcasite-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Ni4+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with eight equivalent NiS6 octahedra, corners with six equivalent SNi3S tetrahedra, and edges with two equivalent NiS6 octahedra. The corner-sharing octahedra tilt angles range from 58–66°. There are a spread of Ni–S bond distances ranging from 2.32–2.40 Å. S2- is bonded to three equivalent Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three equivalent NiS6 octahedra, corners with thirteen equivalent SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 69–75°. The S–S bond length is 2.14 Å.
NiS2 is Skutterudite-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are two inequivalent Ni4+ sites. In the first Ni4+ site, Ni4+ is bonded to six S2- atoms to form NiS6 octahedra that share corners with eight equivalent NiS6 octahedra, corners with six SNi3S tetrahedra, and edges with two equivalent NiS6 octahedra. The corner-sharing octahedra tilt angles range from 62–63°. There are a spread of Ni–S bond distances ranging from 2.23–2.78 Å. In the second Ni4+ site, Ni4+ is bonded to six S2- atoms to form NiS6 octahedra that share corners with eight equivalent NiS6 octahedra, corners with six SNi3S tetrahedra, and edges with two equivalent NiS6 octahedra. The corner-sharing octahedra tilt angles range from 62–63°. There are a spread of Ni–S bond distances ranging from 2.23–2.78 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–77°. The S–S bond length is 2.10 Å. In the second S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–76°. The S–S bond length is 2.10 Å. In the third S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–76°. In the fourth S2- site, S2- is bonded to three Ni4+ and one S2- atom to form distorted SNi3S tetrahedra that share corners with three NiS6 octahedra, corners with thirteen SNi3S tetrahedra, and an edgeedge with one SNi3S tetrahedra. The corner-sharing octahedra tilt angles range from 66–77°.
NiS2 is trigonal omega-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Ni4+ sites. In the first Ni4+ site, Ni4+ is bonded to six S2- atoms to form edge-sharing NiS6 octahedra. All Ni–S bond lengths are 2.26 Å. In the second Ni4+ site, Ni4+ is bonded to six S2- atoms to form edge-sharing NiS6 octahedra. All Ni–S bond lengths are 2.26 Å. In the third Ni4+ site, Ni4+ is bonded to six S2- atoms to form edge-sharing NiS6 octahedra. All Ni–S bond lengths are 2.26 Å. In the fourth Ni4+ site, Ni4+ is bonded to six S2- atoms to form edge-sharing NiS6 octahedra. All Ni–S bond lengths are 2.26 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms. In the third S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms. In the fourth S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms. In the fifth S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms. In the sixth S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms. In the seventh S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms. In the eighth S2- site, S2- is bonded in a 3-coordinate geometry to three Ni4+ atoms.
Ca(NiS2)4 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent S2- atoms to form CaS6 octahedra that share corners with six equivalent NiS6 octahedra and edges with six equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 9°. All Ca–S bond lengths are 2.67 Å. There are two inequivalent Ni+3.50+ sites. In the first Ni+3.50+ site, Ni+3.50+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with six equivalent CaS6 octahedra and edges with six equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 9°. All Ni–S bond lengths are 2.26 Å. In the second Ni+3.50+ site, Ni+3.50+ is bonded to six S2- atoms to form NiS6 octahedra that share edges with two equivalent CaS6 octahedra and edges with six NiS6 octahedra. There are two shorter (2.32 Å) and four longer (2.33 Å) Ni–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a rectangular see-saw-like geometry to one Ca2+ and three Ni+3.50+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Ni+3.50+ atoms.
Ca(NiS2)4 is beta indium sulfide-derived structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ca2+ is bonded in a 6-coordinate geometry to six equivalent S2- atoms. All Ca–S bond lengths are 2.80 Å. There are two inequivalent Ni+3.50+ sites. In the first Ni+3.50+ site, Ni+3.50+ is bonded to six S2- atoms to form edge-sharing NiS6 octahedra. There are four shorter (2.27 Å) and two longer (2.28 Å) Ni–S bond lengths. In the second Ni+3.50+ site, Ni+3.50+ is bonded to six equivalent S2- atoms to form edge-sharing NiS6 octahedra. All Ni–S bond lengths are 2.29 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to one Ca2+ and three Ni+3.50+ atoms. In the second S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Ni+3.50+ atoms.
Ca(NiS2)2 is Spinel structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Ca2+ is bonded to four equivalent S2- atoms to form CaS4 tetrahedra that share corners with twelve equivalent NiS6 octahedra. The corner-sharing octahedra tilt angles range from 58–65°. All Ca–S bond lengths are 2.61 Å. Ni3+ is bonded to six equivalent S2- atoms to form distorted NiS6 octahedra that share corners with six equivalent CaS4 tetrahedra and edges with six equivalent NiS6 octahedra. There are four shorter (2.29 Å) and two longer (2.46 Å) Ni–S bond lengths. S2- is bonded to one Ca2+ and three equivalent Ni3+ atoms to form a mixture of distorted edge and corner-sharing SCaNi3 tetrahedra.
Zn(NiS2)2 is Spinel structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Ni3+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with six equivalent ZnS4 tetrahedra and edges with six equivalent NiS6 octahedra. There are four shorter (2.30 Å) and two longer (2.31 Å) Ni–S bond lengths. Zn2+ is bonded to four equivalent S2- atoms to form ZnS4 tetrahedra that share corners with twelve equivalent NiS6 octahedra. The corner-sharing octahedra tilt angles range from 58–60°. All Zn–S bond lengths are 2.34 Å. S2- is bonded to three equivalent Ni3+ and one Zn2+ atom to form a mixture of distorted edge and corner-sharing SZnNi3 trigonal pyramids.
Zn(NiS2)4 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Ni+3.50+ sites. In the first Ni+3.50+ site, Ni+3.50+ is bonded to six S2- atoms to form NiS6 octahedra that share edges with two equivalent ZnS6 octahedra and edges with six NiS6 octahedra. All Ni–S bond lengths are 2.27 Å. In the second Ni+3.50+ site, Ni+3.50+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with six equivalent ZnS6 octahedra and edges with six equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 10°. All Ni–S bond lengths are 2.33 Å. Zn2+ is bonded to six equivalent S2- atoms to form ZnS6 octahedra that share corners with six equivalent NiS6 octahedra and edges with six equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 10°. All Zn–S bond lengths are 2.53 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a rectangular see-saw-like geometry to three Ni+3.50+ and one Zn2+ atom. In the second S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Ni+3.50+ atoms.
NiS2 and NiS have been characterized as high energy density rechargeable positive electrodes for moderate-temperature Na batteries of the configuration, Na(1)/beta double prime-Al2O3/NaAlCl4(1), NiSx. The batteries operate in the temperature range 170 - 190 C. Positive electrode reactions during discharge/charge cycles have been characterized. Excellent rechargeability of the batteries has been demonstrated by extended cell cycling. A Na/NiS2 cell, operating at 190 C, exceeded 600 deep discharge/charge cycles with practically no capacity deterioration. The feasibility of secondary Na/NiSx batteries with specific energies equal to or greater than 50 Wh/lb and cycle lifes exceeding 1000 deep discharge/charge cycles has been demonstrated.
FeNi2S4 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Fe3+ is bonded to four equivalent S2- atoms to form FeS4 tetrahedra that share corners with twelve equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 56°. All Fe–S bond lengths are 2.12 Å. Ni+2.50+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with six equivalent FeS4 tetrahedra and edges with six equivalent NiS6 octahedra. All Ni–S bond lengths are 2.30 Å. S2- is bonded in a distorted rectangular see-saw-like geometry to one Fe3+ and three equivalent Ni+2.50+ atoms.
CoNi2S4 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Co4+ is bonded to four equivalent S2- atoms to form CoS4 tetrahedra that share corners with twelve equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 57°. All Co–S bond lengths are 2.13 Å. Ni2+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with six equivalent CoS4 tetrahedra and edges with six equivalent NiS6 octahedra. All Ni–S bond lengths are 2.29 Å. S2- is bonded in a distorted rectangular see-saw-like geometry to one Co4+ and three equivalent Ni2+ atoms.