Coordination of bistriflimide and triflate to the uranyl bis(diphenylphosphino)methane dication, {UO2(DPPMO2)2}2+

Abstract The {UO 2 (DPPMO 2 ) 2 } 2+ dication (where DPPMO 2  = bis(diphenylphosphino)methane) contains the linear uranyl group, {UO 2 } 2+ , with two bidentate P O donor ligands. Previously, we have shown that the weakly coordinating oxoanions [ReO 4 ] − and [TcO 4 ] − (as well as Cl − ) will fill a fifth equatorial coordination site yielding complexes of general formula [UO 2 (DPPMO 2 ) 2 X][X] (where X = [ReO 4 ] − , [TcO 4 ] − and Cl − ), with the X − anion acting in both monodentate coordinated and uncoordinated modes. Seven coordinate pentagonal bipyramidal uranyl complexes with the same general formula have now also been prepared with both the bistriflimide, ((CF 3 SO 2 ) 2 N − , NTf 2 - ) and triflate ( CF 3 SO 3 - OTf − ) anions and we report the structural characterisation of both [UO 2 (NTf 2 )(DPPMO 2 ) 2 ][NTf 2 ] ( 1 ) and [UO 2 (OTf)(DPPMO 2 ) 2 ][OTf] ( 2 ). In the case of 1 the anion is coordinated through a terminal oxygen, representing the first structural characterization of an actinide-bistriflimide complex. Both the solid state uranium-anion bond lengths (for O-donor ligands only) and 31 P{ 1 H} NMR solution competition studies indicate that the strength of the uranyl-anion bond decreases along the series Cl −  > [ReO 4 ] −  > [OTf] −  > [NTf 2 ] − . In addition, 31 P{ 1 H} NMR competition studies show that both nitrate and excess DPPMO 2 will readily displace the weakly coordinating X − anions.