Nitridogermanate

The nitridogermanates are chemical compounds containing germanium atoms bound to nitrogen. The simplest anion is GeN₄⁸⁻, but these are often condensed, with the elimination of nitrogen.

Nitridogermanates can form quite a few structures. Germanium can be in three different oxidation states. In the +2 oxidation state there is [Ge^IIN₂]⁴⁻ which has a boomerang shape. The most common is the +4 state with [Ge^IVN₃]⁵⁻ is a planar three pointed star, and [Ge^IVN₄]⁸⁻ as tetrahedra. Condensation of the tetrahedra yields [Ge₂ ^IVN₆]¹⁰⁻. The +3 state is rare, and represented by [Ge^III ₂N₆]¹²⁻ with a covalent bond between the two germanium atoms.^[1] A few compounds also contain germanium in negative oxidation states −2 and −4 and so can be considered germanides as well.

Synthesis

Reduced compounds may be produced by using a flux of molten sodium. Nitrogen may be introduced by using sodium azide. Alkaline earth elements increase the solubility of nitrogen in molten sodium. Containers can be made from sealed tubes of niobium or tantalum. The sodium can be evaporated by heating to over 300°C in a vacuum.^[2]

Properties

Nitridogermanates tend to be unstable in air, as they react with water vapour to form ammonia.

Related

Nitridogermanates are in the category of nitridotetralates, or more generally nitridometallates, tetrel pnictides or pnictidometallates. Related compounds include the nitridosilicates, and rare nitridostannates. By varying the pnictogen, there are also the phosphidogermanates. Other similar compounds are the nitridogallates and nitridomanganates.

Subtypes may be termed nitridoalumogermanates or nitridomagnesogermanates, if they contain aluminium or magnesium.

List

name	formula	formula weight	crystal system	space group	unit cell Å	volume	density	comments	ref
	α-Ge3N4
phenacite phase of germanium nitride	β-Ge3N4
spinel germanium nitride	γ-Ge3N4			Fd3m	a 8.2125Å b 8.2125Å c 8.2125				[3]
	Ca2GeN2		tetragonal	P42/mbc	a = 11.2004, c = 5.0482, Z = 8			black	[2][4]
	Ca4GeN4		monoclinic	P21/c	a = 9.2823, b = 6.0429, c = 11.1612, β = 116.498°, Z = 4			orange	[2]
pentacalcium nitridodigermanate	Ca5[Ge2N6]			C2/c	a 9.836 b 6.0519 c 12.757 β 100.2°			colourless	[5][6]
	Ca6[Ge2N6]		trigonal	R3	a=9.2078 c=9.2679	680.5	3.439	grey; band gap 1.1 eV	[1]
	Ca7[GeN6]		orthorhombic	Pbcn	a = 10.826, b = 6.194, c = 13.121 Z=4	879.8	3.301	yellow with N3−	[7]
	Ca0.8Li0.2Al0.8Ge1.2N3				a = 9.9822, b = 5.7763, c = 5.1484, Z = 4				[8]
	Li4Ca13Ge6N18		monoclinic	C2/c	a = 12.328 b = 12.662 c = 14.711 β = 108.688°	2175.2	3.776	clear	[9]
	Mg5Ca2GeN6			P63/mmc	a = 3.453, c = 17.51	180.8			[2][10]
	Mg5Ca4Ge3N10		monoclinic	C2/m	a = 11.269, b = 3.327, c = 8.008, β = 109.80° Z=4	282.4		colourless; layered	[2][11]
	ZnGeN2
strontium gallium germanium subnitirde	Sr2GeGaN		monoclinic	P21/c	a=6.885 b=4.0432 c=8.680 β =108.454 Z=2	229.21	4.804	black glossy	[12]
	Li3Ca4(Ga3Ge)N8								[13]
	α-Sr2[GeN2]	275.85	tetragonal	P42/mbc	a=11.773 c=5.409 Z=8	749.7		black	[1][14]
	β-Sr2[GeN2]	275.85	orthorhombic	Cmac	a=5.441 b=11.377 c=12.229 Z=8	756.9	4.841	black with blue sheen	[14][15]
	Sr3Ge2N2	436.1	monoclinic	P21/m	a = 9.032, b = 3.883, c = 9.648, β = 112.42°, Z=2	312.9	4.630	dark blue-grey	[16]
	Sr4[GeN4]		monoclinic	P21/c	a = 9.7923, b = 6.3990, c = 11.6924 β = 115.966°			dark red	[17]
	Sr5[Ge2N6]	667.36	monoclinic	C2/c	a = 10.408, b = 6.521, c = 13.565, β = 100.29° Z = 4	905.8	4.893	yellow/ orange	[1][5]
	Sr7[GeN6]		orthorhombic	Pbcn	a = 11.526, b = 6.587, c = 13.836 Z=4	1050.5	4.869	red with N3−; Sr in 4-fold coordination	[1][7]
	Sr6[Ge2N6]		trigonal	R3	a=9.6655 c=9.6655	790.91	4.755	black; band gap 0.2 eV	[1]
	Sr8Ge2[GeN4]		monoclinic	Cc	a = 10.1117, b = 17.1073, c = 10.0473, β = 115.966°			black	[17]
pentastrontium nitridodigermanate	Sr6Ge5N2	916.69	orthorhombic	Pmmn	a = 4.0007, b = 17.954, c = 9.089 Z=2	652.8	4.663	black; unstable in air	[18]
Strontium Germanium Nitride	Sr11Ge4N6	1338.24	tetragonal	P4nbm	a=7.278 c=18.681 Z=2	989.5	4.491	black; contains Ge4−	[19]
	Sr17Ge6N14		triclinic	P1	a = 7.5392, b = 9.7502, c = 11.6761, α = 103.308°, β = 94.651°, γ = 110.248°			black; contains Ge4−	[17]
	Li4Sr3Ge2N6		monoclinic	C2/m	a=6.1398, b=10.021, c=6.3130, β=91.279°, Z=2				[20]
	Mg3SrGeN4		tetragonal	I4/m	a = 8.316, c = 3.398, Z = 2				[2][21]
	MgSr3GeN4		orthorhombic	Pnna	a=5.939, b=10.320, c=9.618, Z=6			yellow	[2][22][15]
	Ba3Ge2N2		monoclinic	P21/m	a = 9.61196, b = 4.0466, c = 10.1337 β = 113.55° Z=2	361.61	5.375	metallic; contains Ge2−	[23]
	Ba6Ge5N2	1215.01	orthorhombic	Pmmn	a = 4.1620, b = 18.841, c = 9.6116 Z=2	753.7	5.354	black; unstable in air	[18]
	Ba9Ge3N10		rhombohedral	R3c	a=7.9399 c=17.282 Z=2	943.53	5.610	black	[24]
	MgBa3GeN4		orthorhombic	Pnma	a=6.159 b=10.558 c=10.048 Z=4	653.4	5.743	yellow	[2][25]
	Mg3BaGeN4		tetragonal	I4/m	a = 8.392, c = 3.4813, Z = 2				[26]
barium gallium germanium subnitirde	Ba2GeGaN		monoclinic	P21/c	a 7.249 b 4.21 c 9.314 β 108.87°			black glossy	[27]