Clarifying the Electronic Structure of Anion-Templated Silver Nanoclusters by Optical Absorption Spectroscopy and Theoretical Calculation.

Electronic structures of anion-templated silver nanoclusters (Ag NCs) are not well understood compared to conventional, template-free Ag NCs. In this study, we synthesized three new anion-templated Ag NCs, namely [S@Ag 17 (S-4CBM) 15 (PPh 3 ) 5 ] 0 , [S@Ag 18 (S-4CBM) 16 (PPh 3 ) 8 ] 0 , and [Cl@Ag 18 (S-4CBM) 16 (PPh 3 ) 8 ][PPh 4 ], where S-4CBM = 4-chlorobenzene methanethiolate, and single-crystal X-ray crystallography revealed that they have S@Ag 6 , S@Ag 10 , and Cl@Ag 10 cores, respectively. Investigation of their electronic structures by optical spectroscopy and theoretical calculations elucidated the following unique features: (1) their electronic structures are different from those of template-free Ag NCs described by the superatomic concept; (2) optical absorption in the range of 550-400 nm for S 2- -templated Ag NCs is attributed to the charge transitions from S 2- -templated Ag-cage orbitals to the s-shaped orbital in the S 2- moiety; (3) the Cl - -templated Ag NCs can be viewed as [Cl@Ag 18 (S-4CBM) 16 (PPh 3 ) 8 ] 0 [PPh 4 ] 0 rather than the ion pair [Cl@Ag 18 (S-4CBM) 16 (PPh 3 ) 8 ] - [PPh 4 ] + ; and (4) singlet-coupled singly occupied orbitals are involved in the optical absorption of the Cl - -templated Ag NC.