The photochemical behavior of free CO(CN) ~a~n-d of the adducts obtained from the association of CO(CN) ~w~it-h diethylammonium ion (Et2NH2+)a, linear plyammonium ion (L-21- N6H2+),a nd three plyammonium macrocycles (24-N6H66+, 32-C9-N6H66+a,n d 32-N8HSs+F, igure 1) has been studied in aqueous solution at room temperature. In all cases a simple photoaquation reaction takes place, with substitution of one CN- ligand by HzO. The quantum yield of the photoaquation reaction (a = 0.30 for the free CO(CN) ~c~om- plex) is not affected by the presence of Et2NHz+b ut decreases when Co(CN):- is associated with polyammonium ions. Specifically, the photoaquation quantum yield drops to 0.15, 0.1 1, and 0.10 when CO(CN)63- is associated with 24-N6H66+3, 2-C9-N6H66+a,n d 32-N8HB8+re, spectively. The reduction of the quantum yield is interpreted by assuming that only a discrete number of CN- are allowed to dissociate in the adducts. This agrees with the formation of adducts of defined molecular structure, in which some of the CN- ligands are bound to the plyammonium receptor and are thus prevented from escaping when the Co-CN bonds are temporarily broken as a consequence of light excitation. These adducts may be considered as complexes of complexes (or supercomplexes) since the ligands coordinated in the first coordination sphere of the metal in their turn coordinate a macrocyclic ligand. The results obtained indicate that it is possible to protect coordination compounds against ligand photodissociation by using appropriate receptors and they are also promising for other applications related to the control of photochemical reactions.
Control of the Photochemical Reactivity of Coordination Compounds by Formation of Supramolecular Structures: the Case of Hexacyanocobaltate (III) Anion Associated with Polyammonium Macrocyclic Receptors
CASTELVETRO, VALTER;
1985-01-01
Abstract
The photochemical behavior of free CO(CN) ~a~n-d of the adducts obtained from the association of CO(CN) ~w~it-h diethylammonium ion (Et2NH2+)a, linear plyammonium ion (L-21- N6H2+),a nd three plyammonium macrocycles (24-N6H66+, 32-C9-N6H66+a,n d 32-N8HSs+F, igure 1) has been studied in aqueous solution at room temperature. In all cases a simple photoaquation reaction takes place, with substitution of one CN- ligand by HzO. The quantum yield of the photoaquation reaction (a = 0.30 for the free CO(CN) ~c~om- plex) is not affected by the presence of Et2NHz+b ut decreases when Co(CN):- is associated with polyammonium ions. Specifically, the photoaquation quantum yield drops to 0.15, 0.1 1, and 0.10 when CO(CN)63- is associated with 24-N6H66+3, 2-C9-N6H66+a,n d 32-N8HB8+re, spectively. The reduction of the quantum yield is interpreted by assuming that only a discrete number of CN- are allowed to dissociate in the adducts. This agrees with the formation of adducts of defined molecular structure, in which some of the CN- ligands are bound to the plyammonium receptor and are thus prevented from escaping when the Co-CN bonds are temporarily broken as a consequence of light excitation. These adducts may be considered as complexes of complexes (or supercomplexes) since the ligands coordinated in the first coordination sphere of the metal in their turn coordinate a macrocyclic ligand. The results obtained indicate that it is possible to protect coordination compounds against ligand photodissociation by using appropriate receptors and they are also promising for other applications related to the control of photochemical reactions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
