Rational synthesis, structural characterization and theoretical exploration on third-order nonlinear optical properties of isolated Agn (n = 5, 8, 12) alkynyl clusters

[Ag5(CCtBu)(CF3COO)7]3-, [Ag8(CCtBu)2(CF3COO)10]4- and [Ag12(CCtBu)6(CF3COO)8]2- clusters (Ag5, Ag8 and Ag12 for short) respectively in compounds 1-3 are potential NLO materials owing to their second hyperpolarizabilities γ values rising from 39.1 × 10−36, 60.3 × 10−36 to 97.7 × 10−36 esu with the growth of the number of Ag atoms and CC groups.