SYNTHESES, STRUCTURES AND SPECTROSCOPIC PROPERTIES OF NICKEL(II) CITRATO COMPLEXES, (NH4)2[Ni(Hcit)(H2O)2]2-2H2O AND (NH4)4[Ni(Hcit)2]-2H2O

• Published in: Journal of coordination chemistry 1997-07, Vol.42 (1-2), p.131-141
• Main Authors: Zhou, Zhao-Hui, Lin, Yi-Ji, Zhang, Hong-Bin, Lin, Guo-Dong, Tsai, Khi-Rui
• Format: Article
• Language: English
• Subjects: citrate; citric acid; Nickel; X-ray structure
• ISSN: 0095-8972; 1029-0389
• DOI: 10.1080/00958979708045286

Dimeric ammonium diaquocitratonickelate (II) dihydrate (NH 4 ) 2 [Ni(Hcit)(H,O) 2 ] 2 -2H 2 O, 1, and its sodium and potassium salts, as well as ammonium dicitratonickelate (II) dihydrate (NH 4 ) 4 [Ni(Hcit) 2 ] ·2H 2 O, 2, (H 4 cit = citric acid) have been synthesized and characterized by spectroscopic methods. The crystal structures of 1 and 2 were determined by X-ray methods. Compound 1 is triclinic. space group Pl with a = 6.4071(7), b = 9.4710(7), c = 9.6904(5) Å, α = 105.064(5), β = 91.992(7). γ = 89.334(8)°, V = 567.5(1) Å Z = 1, R = 0.037 for 1714 observed reflections. The structure consists of centrosymmetric dimers, [Ni(Hcit)(H 2 O) 2 ] 2 2- The principal Ni‒O dimensions are Ni‒O(hydroxy), 2.074(2)Å, Ni‒O(α-carboxy), 2.020(3)Å, Ni‒O(β-carboxy), 2.031(2). 2.037(2)Å, Ni‒O(water), 2.065(2), 2.072(3)Å. Compound 2 crystallizes in the monocliruc space group P 2 1 /a with a = 9.361(1), b= 13.496(1), c = 9.4238(7)Å, (3= 115.475(6)°, V= 1074.9(3)Å ; . Z= 2, R = 0.052 for 1507 observed reflections. The two terdentate citrato ligands coordinate symmetrically to one nickel via hydroxyl, α- and β-carboxylato oxygens and the remaining acetato groups are bonded through strong hydrogen bonds with the hydroxy group of another dicitrato nickel anion [2.526(6)Å]. The principal Ni‒O dimensions are: Ni‒O(hydroxy). 2.021(3)Å, Ni‒O (α-carboxy), 2.038(3)Å, Ni‒O(β-carboxy), 2.072(3)A. Nickel atoms in the two compounds have octahedral geometry. The two compounds can be transformed easily by reaction with ammonium citrate or nickel chloride.