Bis(2-acetylpyridine-κ2 N,O)silver(I) tetrafluoridoborate: a complex with silver in a seesaw coordination geometry

The reaction of 2-acetylpyridine with silver(I) tetrafluoridoborate leads to the discrete title complex, [Ag(C7H7NO)2]BF4, in the cation of which the Ag atom is coordinated by two 2-acetylpyridine ligands, each of which is N,O-bidentate, albeit with stronger bonding to the N atoms [Ag—N = 2.2018 (15) and 2.2088 (14) Å; Ag—O = 2.5380 (13) and 2.5454 (13) Å]. The four-coordinate Ag atom has a seesaw coordination geometry with a τ4 index of 0.51. The tetrafluoridoborate anion is disordered over two orientations with 0.568 (10):0.432 (10) occupancies.

The reaction of 2-acetylpyridine with silver(I) tetrafluoridoborate leads to the discrete title complex, [Ag(C 7 H 7 NO) 2 ]BF 4 , in the cation of which the Ag atom is coordinated by two 2-acetylpyridine ligands, each of which is N,O-bidentate, albeit with stronger bonding to the N atoms [Ag-N = 2.2018 (15) and 2.2088 (14) Å ; Ag-O = 2.5380 (13) and 2.5454 (13) Å ]. The four-coordinate Ag atom has a seesaw coordination geometry with a 4 index of 0.51. The tetrafluoridoborate anion is disordered over two orientations with 0.568 (10):0.432 (10) occupancies.
Bis(2-acetylpyridine-2 N,O)silver(I) tetrafluoridoborate: a complex with silver in a seesaw coordination geometry M. A. O'Donnell and P. J. Steel

Comment
For some time we have been involved in the study of silver complexes of chelating and bridging heterocyclic ligands (Steel, 2005;Fitchett & Steel, 2006;O'Keefe & Steel, 2007;Steel & Fitchett, 2008;Golder et al., 2010). 2-acetylpyridine coordinates to a variety of transition metals, usually as an N,O-chelating ligand, although it has been reported to act as an O-monodentate donor to a zinc porphyrin (Byrn et al., 1993). X-ray crystal structures have been reported for complexes of 2-acetylpyridine with silver(I) perchlorate (Bowmaker et al., 2005;Drew et al., 2005), trifluoroacetate (Bowmaker et al., 2005), trifluoromethanesulfonate (Di Nicola et al., 2010) and nitrate (Bowmaker et al., 2005). The latter has a single 2-acetylpyridine bound to the silver with a chelating nitrate anion, while the others have two chelating 2-acetylpyridine ligands. We now report the structure of its complex with silver(I) tetrafluoridoborate, the title compound [Ag(C 7 H 7 NO) 2 ] BF 4 (I).
In (I), the asymmetric unit contains a complex cation comprising a silver(I) atom bound to two bidentate N,O-chelated 2-acetylpyridine ligands [Ag-N, 2.2018 (15), 2.2088 (14) Å; Ag-O, 2.5380 (13), 2.5454 (13) Å], and a tetrafluoridoborate counter-anion (Fig. 1). The tetrafluoridoborate anion is disordered over two orientations with relative F occupancies of 57:43% about a common central B. Since the silver atom makes no other contacts less than 2.72 Å it should be classified as four-coordinate (Young & Hanton, 2008). Calculation of the τ 4 index (Yang et al., 2007) produces a value of 0.51 which means that the geometry around the silver should be described as seesaw.

Experimental
The title compound was prepared by diffusion of pentane into a methanol solution of a mixture of 2-acetylpyridine and silver(I) tetrafluoridoborate.