Aggregation-enhanced IR absorption (AEIRA) of molybdenum-carbonyl organometallic aqueous colloids

Abstract Molybdenum-carbonyl aqueous colloids are prepared from the self-assembly of η 5 -CpMo(CO) 2 (PPh 3 )CO(CH 2 ) 5 CH 3 (MpC6) in water. MpC6 is synthesized through a reaction of CpMo(CO) 3 anion (Mp − ) with Br(CH 2 ) 5 CH 3 in the presence of PPh 3 . The complex is characterized using IR, 1 H NMR, 31 P NMR spectroscopies and confirmed by X-ray crystallography. MpC6 is hydrophobic, non-surface active, but capable of assembling in water without critical aggregation concentration (CAC) via water carbonyl interactions (WCIs). The assembly generates vesicles with a zeta potential of −69.6 mV and the resultant colloids possess a highly integrated structure upon dilution. The hydrodynamic radius (R h ) of the colloids is ca. 60 nm with a narrow size distribution (PDI = 0.07). The IR absorption of the CO groups for the aggregates in THF/water (40/60 v/v) solution is ∼70-fold stronger than that for the MpC6 molecules in THF. This aggregation-enhanced IR absorption (AEIRA) is attributed to the association of the polarizable metal carbonyl groups on the surface of the colloids.