International Journal of Inorganic Materials 3 (2001) 901–906 Urea hydrolysis of cobalt(II) nitrate melts: synthesis of novel hydroxides and hydroxynitrates * Michael Rajamathi, P. Vishnu Kamath Department of Chemistry, Central College, Bangalore University, Bangalore 560 001, India Accepted 23 July 2001 Abstract Urea hydrolysis of Co(II) nitrate melts in an open vessel yields different phases at different temperatures. While at 808Ca hydrotalcite-like mixed-valent Co(II,III) hydroxide of formula Co(OH) (NO ) ?2/3H O is obtained, at 1008C we obtain a modification 2 3 0.27 2 of Co(II) hydroxide with formula Co(OH) (NO ) ?2 / 3H O. At higher temperatures, two different basic salts of composition 1.75 3 0.25 2 Co (OH) (NO ) ?5H O (1208C) and Co (OH) (NO ) (1608C) are obtained.  2001 Elsevier Science Ltd. All rights reserved. 7 12 3 2 2 3 4 3 2 Keywords: Urea hydrolysis; Cobalt(II) nitrate melts; Novel hydroxides; Hydroxynitrates ( x50.67) [8] and Ni(OH)(NO ) ?HO( x51) [9], all ob- 3 2 1. Introduction tained by urea hydrolysis of nickel nitrate melts at different temperatures, have been reported. Compositionally, these Layered hydroxynitrates of divalent metals having the represent a series of solid solutions, the end members of formula M(OH) (NO ) ?mH O (M5Co, Ni, Cu, Zn) 22x 3 x 2 which are Ni(OH) and Ni(NO ) . Structurally, the hy- 2 3 2 and their mixed metal analogues (also called hydroxy droxide-rich phases ( x50.5, 0.67) are hexagonal and double salts, HDSs) derive their structure from that of the isotypic with Ni(OH) , while the nitrate-rich phases ( x51) mineral brucite, Mg(OH) [1]. Brucite consists of hexa- 2 2 are of lower (monoclinic) symmetry, nickel nitrate itself gonally close packed hydroxyl ions in which alternate 21 21 being a triclinic phase. In all of these compounds, Ni layers of octahedral sites are occupied by Mg . This occupies octahedral sites. results in an ordered stacking of charge-neutral slabs of ˚ The Co(II) system is potentially of greater interest as composition [Mg(OH) ] having a c-parameter of 4.8 A 2 21 Co can occupy both octahedral and tetrahedral sites in [2]. The hydroxynitrates, on the other hand, comprise x 1 varying proportions. Markov et al. [10] prepared positively charged layers of composition [M(OH) ] 22x Co (OH) (NO ) ?0.25H O and Co (OH) (NO ) ?5H O which incorporate nitrate ions to restore charge neutrality. 2 3 3 2 7 12 3 2 2 by controlled alkali precipitation from Co(II) nitrate The nitrate ions can be bound directly to the metal ion (a solutions. Co (OH) (NO ) ?0.25H O is a hexagonal form of bonding known as grafting) or loosely intercalated 2 3 3 2 ˚ ˚ layered material ( a53.17 A, c56.95 A) in which all the in the van der Waal’s gap, with water molecules providing 21 Co occupy octahedral sites in brucite-derived layers. In for coordinative saturation of the metal ion. Nitrate inser- ˚ ˚ Co (OH) (NO ) ?5H O ( a53.13 A, c59.18 A), five of tion causes an increase in the interlayer distance, and the 7 12 3 2 2 21 ˚ the seven Co occupy octahedral sites in brucite-derived c-parameter varies in the range 6.9–9.2 A depending on layers of composition [Co h(OH) ], while the remaining the nature of nitrate incorporation and the position of the 5 12 two occupy tetrahedral sites above and below the layer, metal ions. Many of these hydroxy salts exhibit interesting leading to an increased c-parameter. Petrov et al. [11] interlayer chemistry [3,4] and they are also used as synthesized both ordered and disordered forms of precursors to oxides [5,6]. Co(OH)(NO ) ?H O by hydrolysis of Co(II) nitrate melts Among the hydroxynitrates of Ni(II), three phases, 3 2 with NaHCO ?NH OCONH in a sealed tube. This com- Ni (OH) (NO ) ?0.25H O ( x50.5) [7], Ni (OH) (NO ) 3 4 2 2 3 3 2 3 4 3 2 ˚ ˚ pound is monoclinic ( a517.757 A, b53.142 A, c514.188 ˚ * A, b 5113.558 ), isostructural with Zn(OH)(NO ) ?HO Corresponding author. Tel.: 191-80-221-1679. 3 2 1466-6049 / 01 / $ – see front matter  2001 Elsevier Science Ltd. All rights reserved. PII: S1466-6049(01)00090-3