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

• Synthesis and aqueous self-assembly of η5-CpMo(CO)2(PPh3)CO(CH2)5CH3.
• Highly integrated aqueous metal-carbonyl vesicles (MCsomes).
• Aggregation-enhanced IR absorption (AEIRA).

Molybdenum-carbonyl aqueous colloids are prepared from the self-assembly of η5-CpMo(CO)2(PPh3)CO(CH2)5CH3 (MpC6) in water. MpC6 is synthesized through a reaction of CpMo(CO)3 anion (Mp−) with Br(CH2)5CH3 in the presence of PPh3. The complex is characterized using IR, 1H NMR, 31P 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 (Rh) 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.

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