Chemistry and Nh3
Introduction
The linkage isomers may arise when one or more of the ligand ca coordinate to the metal in more then one way, e.g. in NO2 two oxygen atoms are potential donor site. Such a ligand is ambidentate. The following reactions show how linkage isomers can be prepared.
[Co(NH3)5Cl]Cl2(s) + dilNH3(aq) → [Co(NH3)5(OH2)]Cl2
[Co(NH3)5Cl]Cl2 + NaNO2 + conc. HCl → [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown)
[Co(NH3)5Cl]Cl2 + NaNO2 → [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal)
[Co(NH3)5(NO2-O)]Cl2 + warm HCl → [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown)
[Co(NH3)5(NO2-N)]Cl2 + UV → [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal)
The complexes [Co(NH3)5(NO2-N)]Cl2 and [Co(NH3)5(NO2-O)]Cl2 can be distinguished by using IR-spectroscopy. The hypothesis was these complexes can be differ by the color of there crystals, e.g. [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown) and [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal).
For the O-bonded ligand, characteristic absorption bands at 1065 and 1470 cm-1 are observed, while for the N-bonded ligand, the corresponding vibration wave number are 1310 and 1430 cm-1.
Structures of the two linkage isomers of [Co(NH3)5(NO2)]2+.
Procedure
Preparation for isomer [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown) * 1.5g of Cobalt(III)penta-amine, chloride was dissolved into a 15mL of water with ammonia (5mL) on a 100mL beaker. * The complex solution was boiled completely, filtered, cooled and acidify with diluted HCl, (orange litmus paper was used). * NaNO2 (2g) was added and heat to the solution until the red precipitation get dissolve. * The solution was cooled and concentrated HCl (20mL) was added carefully. * The solution was cooled and the yellow or orange-brown crystals were filtered, washed with alcohol and finally with ether.
Preparation for isomer [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal) part(II) * 1.5g of Cobalt(III)penta-amine, chloride was dissolved in a 100mL beaker
The linkage isomers may arise when one or more of the ligand ca coordinate to the metal in more then one way, e.g. in NO2 two oxygen atoms are potential donor site. Such a ligand is ambidentate. The following reactions show how linkage isomers can be prepared.
[Co(NH3)5Cl]Cl2(s) + dilNH3(aq) → [Co(NH3)5(OH2)]Cl2
[Co(NH3)5Cl]Cl2 + NaNO2 + conc. HCl → [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown)
[Co(NH3)5Cl]Cl2 + NaNO2 → [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal)
[Co(NH3)5(NO2-O)]Cl2 + warm HCl → [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown)
[Co(NH3)5(NO2-N)]Cl2 + UV → [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal)
The complexes [Co(NH3)5(NO2-N)]Cl2 and [Co(NH3)5(NO2-O)]Cl2 can be distinguished by using IR-spectroscopy. The hypothesis was these complexes can be differ by the color of there crystals, e.g. [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown) and [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal).
For the O-bonded ligand, characteristic absorption bands at 1065 and 1470 cm-1 are observed, while for the N-bonded ligand, the corresponding vibration wave number are 1310 and 1430 cm-1.
Structures of the two linkage isomers of [Co(NH3)5(NO2)]2+.
Procedure
Preparation for isomer [Co(NH3)5(NO2-N)]Cl2 (yellow or orange-brown) * 1.5g of Cobalt(III)penta-amine, chloride was dissolved into a 15mL of water with ammonia (5mL) on a 100mL beaker. * The complex solution was boiled completely, filtered, cooled and acidify with diluted HCl, (orange litmus paper was used). * NaNO2 (2g) was added and heat to the solution until the red precipitation get dissolve. * The solution was cooled and concentrated HCl (20mL) was added carefully. * The solution was cooled and the yellow or orange-brown crystals were filtered, washed with alcohol and finally with ether.
Preparation for isomer [Co(NH3)5(NO2-O)]Cl2 (red/ salmon-pink crystal) part(II) * 1.5g of Cobalt(III)penta-amine, chloride was dissolved in a 100mL beaker
References: 1. Dr. G. Maguire, 2009, Inorganic Chemistry (Chem. 210) Practical Manual, UKZN Durban. 2. Werner, A. “Über strukturisomere Salze der Rhodanwasserstoffsäure und der salpetrigen Säure” Berichte der deutschen chemischen Gesellschaft 1907, volume 40, 765-788. DOI: 10.1002/cber.190704001117