Metal nitrosyls and their derivatives

Nitrosyl complexes, metal nitrosyls

1. Metal Nitrosyls and their derivatives: Subtitles: Definition. Classification Preparation Uses

2. Definition: Compounds that contain nitric oxide as NO+ ion, NO- ion or as neutral molecule are known as nitrosyl compounds. Coordination compounds containing coordinated NO+ group are called metal nitrosyls. metal nitrosyl compound.

3. Structure: Studies shows that NOCl molecule is bent with N-O and N-Cl bond distances equal to 1.14 A o and 1.95 A o respectively and ONCl bond angle is equal to 115 o . High value of dipole moment = 1.83 D measured in CCl 4 suggest that N-Cl bond has some iconic character. Covalent structure of NOCl have V- shape which results from sp 2 hybridization. N O Cl

4. Classification of Nitrosyl Compounds: It can be classified into three classes: Nitrosyl compounds containing NO+ group. e.g. Nitrosyl halides. Nitrosyl containing NO- group. e.g. Sodium nitrosyl Na[NO-]. Coordination compounds containing coordinated NO+ group: metal nitrosyls

5. Metal Nitrosyls: Coordination compounds containing coordinated NO+ group: metal nitrosyls. Metal nitrosyls are coordinated compounds in which NO molecule is attached as NO+ ion to a metal atom or ion. In these compounds NO+ ion which is known as nitrosonium or nitrosyl cation acts as a ligand. The coordination compounds of transition metal containing NO+ ion as ligand are called metal nitrosyls.

6. Examples of Metal Nitrosyls: Metal Nitrosyl carbonyls: Important examples of this class re as follow: {Co(NO+)(CO) 3 } , {Mn-(NO+)(CO) 4 } etc. Metal Nitrosyl Halides: These compounds are represented as: {Fe-(NO+) 2 I} 2 , {Fe(NO+)I}, {MI(NO+)X}, {Co-(NO+) 2 X} etc.

7. Metal Nitrosyl Thio-complexes: Coordinated compounds are given by only Fe, Co and Ni. Examples are M+{Fe-(NO+) 2 S}- etc. Metal Nitrosyl Cyano complexes: These complexes are as follow: [Mn+(NO+)(CN) 5 ] 2 -. Among these [Fe(NO+)(CN) 5 ] 2 - is most important. Miscallaneous Metal Nitrosyls: Nitrosyls like [Co+(NO+)(NH 3 ) 5 ] 2 +, [Fe+(NO+)] 2 + etc. are in this class.

8. Preparation: Metal Nitrosyl Carbonyls: It can be prepared by the action of NO on metal carbonyls. Fe(CO) 5 + 2NO Fe(CO) 2 (NO) 2 + 3CO Fe 3 (CO) 12 + 6NO 3Fe(CO) 2 (NO) 2 + 6CO Metal Nitrosyl Halides: Prepared by the action of NO on metal halides in the presence of suitable metal which acts as a halogen acceptor. 2NiI2 + 2NO + Zn 2[Ni(NO)I] + ZnI2

9. CoX2 + 4NO + Co 2[Co(NO)2X] Sodium Nitroprusside: It can be prepared by warming a solution of potassium ferrocyante with 50% HNO3 till a brown solution is obtained. K4[Fe(CN)6] + 4HNO3 H4[Fe(CN)6] + 4KNO3 H3[Fe(CN)6] + NO H2[Fe(NO)(CN)5] + HCN

10. USES: Metal nitrisyls are assumed to be intermediated in catalytic converters. In biology nitric oxide is an important signalling molecule in nature. Nitric oxide also attacks iron sulphur proteins giving dinitrosyl iron complexes.

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