Coordination chemistry of an amine-substituted bis(pyrazolyl)-pyridine ligand: interaction of a peripheral functional group on a coordination cage with the internal contents of the cavity

摘要

The ligand Lan contains two bidentate chelating pyrazolyl-pyridine termini connected to a central aminophenyl ring. In [ Ag 3 (Lan) 2](ClO 4) 3 each ligand coordinates in a pentadentate 2+ 1+ 2 manner, connecting all three Ag(I) ions. In contrast, in the octanuclear cubic coordination cage [ Co 8 (Lan) 12] [ BF 4] 16 each Lan coordinates as a bis(pyrazolyl-pyridine) tetradentate chelate, with the externallydirected amine groups not coordinated. From its 1H NMR spectrum this cage has the S 6 symmetric structure containing two fac and six mer tris-chelate Co(II) centres of other octanuclear cages. Slow crystallisation afforded [ Co 8 (Lan) 12 Na][ BF 4] 17, with S 4 symmetry arising from four fac and four mer tris-chelate Co(II) centres which alternate; the central cavity accommodates an Na+ cation and four fluoroborate anions which form a {Na(BF 4) 4} 3-guest. The {Na(BF 4) 4} 3-guest forms F HN hydrogen bonds through the cage windows with exterior amine groups. Rearrangement of the cage structure from S 6 to S 4 symmetry appears to facilitate inclusion of the fourfold symmetric guest.