Oxalatonickelate Explained

The oxalatonickelates are a class of compounds that contain nickel complexed by oxalate groups. They form a series of double salts, and include clusters with multiple nickel atoms. Since oxalate functions as a bidentate ligand it can satisfy two coordinate positions around the nickel atom, or it can bridge two nickel atoms together.

The shape around the nickel atom is octahedral for diaquabis(oxalato)nickelate. The colour of this is green due to the Ni(–O–)₆ chromophore. The absorption in infrared is at 8,300 9,060 13,400, 15,260, and 26,160 cm⁻¹.^[1] The ligand field parameters are 10 Dq=8800 cm⁻¹ and B=1000 cm⁻¹.^[1]

formula	name	other names	structure	colour or decomposition	CAS Number	references
[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni]²⁻	bis(oxalato)nickelate (2−)					^[2]
Li₂[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni]•6H₂O	dilithium bis(oxalato)nickelate (2−)			dehydrate 80° decompose 345°	112678-94-1	^[3]
Na₂[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni]•3H₂O	disodium bis(oxalato)nickelate (2−)			dehydrates at 85°, decompose over 320°	107996-66-5	^[4] ^[5]
[NH<sub>4</sub>]₂[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni]•3H₂O	diammonium bis(oxalato)nickelate (2−)			dehydrate 180-262° deaminate 262-338 °C	108559-31-5	^[6]
K₂[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni•2H<sub>2</sub>O]•4H₂O	dipotassium trans-diaquabis(oxalato-O,O')nickelate(II)-water (1/4)	potassium bis oxalate nickel(II) tetrahydrate	monoclinic a=8.647 b=6.627 c=12.118 β=101.58° V=680.3 Z=2 density=2.05 / 2.04	green	14244-63-4	^[7] ^[8] ^[9] ^[10]
Co[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni]•5H₂O	cobalt(II)bis(oxalato)nickelate(II)pentahydrate			light pink		^[11]
Mn[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni]•4H₂O	manganese(II)bis(oxalato)nickelate(II)tetrahydrate			light blue		^[12]
Cd[(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>Ni]•4H₂O	cadmium(II)bis(oxalato)nickelate(II)tetrahydrate			blue

Because the Ni²⁺ ion resembles many other divalent metal ions, it can be substituted by them, or substitute for them in other oxalate compounds to form mixed oxalates where the proportions can vary continuously. For example, magnesium nickel oxalate dihydrate.^[13]

Notes and References

Morrison. J.T.. Baker. W.A.. Nickel(II) complexes with oxygen and sulfur donors. Inorganica Chimica Acta. January 1969. 3. 463–467. 10.1016/S0020-1693(00)92534-9.
Book: Macintyre. Jane E.. Dictionary of Inorganic Compounds, Supplement 4. 1997. CRC Press. 9780412750205. 453. 21 April 2016. en.
Saha. H.L.. Mitra. S.. Thermal decomposition reactions of metal carboxylato complexes in the solid state. III. Thermographic and differential thermal studies of metal oxalato, malonato and succinato complexes. Thermochimica Acta. June 1987. 116. 53–64. 10.1016/0040-6031(87)88164-9.
Book: Macintyre. Jane E.. Dictionary of Inorganic Compounds, Supplement 4. 1997. CRC Press. 9780412750205. 251. 21 April 2016. en.
Saha. H.L.. Mitra. S.. Thermal decomposition reactions of metal carboxylato complexes in the solid state. I. Thermographic and differential thermal studies of metal oxalato, malonato and succinato complexes. Thermochimica Acta. January 1987. 109. 2. 331–342. 10.1016/0040-6031(87)80029-1.
Saha. H.L.. Mitra. S.. Thermal decomposition reactions of metal carboxylato complexes in the solid state. II. Thermographic and differential thermal studies of metal oxalato, malonato and succinato complexes. Thermochimica Acta. March 1987. 112. 2. 275–287. 10.1016/0040-6031(87)88284-9.
Román. P.. Guzmán-Miralles. C.. Luque. A.. Structure of dipotassium trans-diaquabis(oxalato-O,O')nickelate(II)–water (1/4). Acta Crystallographica Section C. 15 July 1993. 49. 7. 1336–1339. 10.1107/S0108270193000940. 1993AcCrC..49.1336R .
Narsimhulu. M.. Raju. B.. Saritha. A.. Narayana Rao. D.. Hussain. K.A.. A new room-temperature ultraviolet emission material: $\ce$ . Physica B: Condensed Matter. September 2015. 472. 45–48. 10.1016/j.physb.2015.05.019. 2015PhyB..472...45N.
Book: Macintyre. Jane E.. Dictionary of Inorganic Compounds, Supplement 1. CRC Press. 9780412490903. 45. 25 April 2016. en. 1993-07-15.
Book: Macintyre. Jane E.. Dictionary of Inorganic Compounds, Supplement 4. 1997. CRC Press. 9780412750205. 222. 21 April 2016. en.
Deb. Nidhuban. Baruah. S. D.. Dass. N. N.. Synthesis, Characterization and Thermal Decomposition of $\ce$ ( $x=5\text\ce$ and $x=4\text\ce$ ). Journal of Thermal Analysis and Calorimetry. 2000. 59. 3. 791–797. 10.1023/A:1010153720786. 94453246.
Deb. Nidhuban. Thermal decomposition of manganese(II)bis(oxalato)nickelate(II)tetrahydrate. Journal of Thermal Analysis and Calorimetry. July 2005. 81. 1. 61–65. 10.1007/s10973-005-0746-y. 94799986.
Packter. A.. Omomo. A.. The coprecipitation of Magnesium Nickel Oxalate Dihydrate Powders (solid solutions) from aqueous solution: Precipitate compositions and Coprecipitate Mechanisms. Crystal Research and Technology. 1984. 19. 4. 467–476. 10.1002/crat.2170190406. 1984CryRT..19..467P .