The π-acidity/basicity of cyclic trinuclear units (CTUs): from theoretical perspective to potential applications
Cyclic trinuclear units (CTUs) based on Au(I), Ag(I) and Cu(I) cations, featuring near planar nine-membered coordination rings, represent an improtant class of metal-organic π-acids/bases with highly adjustable π-acidity/basicity. Their superior π-acidity/basicity coupling with Lewis-acidic and metal···metal bonding sites provids excellent attration with a wide range of acidic/basic species, and usully followed by noticeable changes of luminescent or charge transfer behaviors. A series of representative cases have been selected herein for such cyclic trinuclear units in both olgomeric and polymeric sysytems during the past two decades. Their facinating and profound potential applictions related to π-acidity/basicity are highlighted, including molecular absorption and separation, luminescent sensing and detection, organic light-emitting diode (OLED), metal-organic field-effect transistor (MOFET), molecular wire, and catalysis. The challenges in improving the performance in practical application will also be discussed.