[1,5-Bis(1-methyl-1H-imidazol-2-ylmethyl-κN³)-1,5-diazacyclooctane-N,N′]chlorocobalt(II) perchlorate

Abstract

The crystal structure of the title compound, H 26 N 6 )]ClO 4 , consists of discrete [CoCl(C 16 H 26 N 6 )] + cations and perchlorate anions. The ®ve-coordinate Co II atom has four nitrogen donors from the new mesocyclic ligand 1,5bis(1-methyl-1H-imidazol-2-ylmethyl)-1,5-diazacyclooctane [CoÐN 2.046 (3)±2.214 (4) A Ê ], and a chloride anion at the apical site [CoÐCl 2.3184 (13) A Ê ]. The coordination geometry of the complex is essentially square pyramidal. The mesocyclic ligand takes a boat±chair con®guration and the two imidazole pendants are not coplanar. The dihedral angle between the two imidazole planes is 15.97 . An H atom from the 1,5diazacyclooctane group effectively blocks the axial coordination site opposite the Cl ligand.Comment 1,5-Diazacyclooctane (DACO) derivatives bearing two additional functional donor pendants can strongly coordinate to transitional metal centers, forming square-pyramidal ®vecoordinate or square-planar four-coordinate complexes (Grapperhaus & Darensbourg, 1998;Nielson et al., 1971;Bu et al., 1999).The four donor atoms of such tetradentate ligands coordinate to the central metal ions nearly in a plane and the DACO backbone usually adopts a boat±chair con®guration. This con®guration will force a portion of the chelate framework across to the axial coordination position, and will sterically restrict further axial coordination to the metal center. Therefore, such DACO derivatives can be used as very good ligands for the construction of metal complexes with a squareplanar or square-pyramidal con®guration. The interesting chemistry of such DACO derivatives prompted us to create more such ligands by modifying DACO with heterocyclic donor pendants to obtain new complexes with functional properties. We synthesized a new mesocyclic ligand functionalized by two imidazole donor pendants, 1,5-bis(1-methyl-1H-imidazol-2-ylmethyl)-1,5-diazacyclooctane and its cobalt(II) complex, [CoCl(C 16 H 26 N 6 )]ClO 4 , (I). We report herein the crystal structure of this new complex.The structure of (I) comprises discrete [CoCl(C 16 H 26 N 6 )] + cations and perchlorate anions (Fig. 1). In the complex cation, the Co II atom is ®ve coordinate. 1,5-Bis(1-methyl-1H-imidazol-2-ylmethyl)-1,5-diazacyclooctane acts as a tetradentate ligand through one pair of nitrogen donors of the mesocyclic ring and the two N atoms of the imidazole pendants. The coordination geometry about the Co II atom can be described as square pyramidal. The four nitrogen donors of the ligand coordinate to the central Co II in one plane, with a chloride anion occupying an apical position. The ( value used to describe the degree of trigonal distortion is 0.006 (Addison et al., 1984), i.e. nearly zero, indicating that the distortion is very small. The Co atom is above the mean plane formed by atoms N1, N2, N3 and N5 by 0.549 A Ê towards the apical Cl ligand. The two imidazole pendants are not coplanar, their planes forming an angle of 15.97 .The six-membered CoNCH 2 CH 2 CH 2 N rings in H 26 N 6 )]ClO 4 adopt boat±chair con®gurations. ...