Ab Initio Study of Thiolate-Protected Au₁₀₂ Nanocluster

A total structural determination of the Au(102)(p-MBA)(44) nanocluster has been recently achieved via successful crystallization of the thiolated-protected gold nanocluster (Jadzinsky et al. Science 2007, 318, 430). The embedded Au(102) cluster may be viewed as a multilayered structure described as Au(54)(penta-star)@Au(38)(ten wings)@Au(10)(two pentagon caps), where the inner Au(54) "penta-star" consists of five twinned Au(20) tetrahedral subunits. To gain more insight into high stability of the Au(102)(p-MBA)(44) nanocluster, we have performed ab initio calculations to study electronic properties of a homologue Au(102)(SCH(3))(44) nanocluster, an Au(102)(SCH(3))(42) nanocluster (with two SCH(3) groups less), and an "effectively isoelectronic" Au(104)(SCH(3))(46) nanocluster with a more symmetric embedded Au(104) structure. Electronic structure calculations suggest that the Au(102)(SCH(3))(44) nanocluster possesses a reasonably large gap (approximately 0.54 eV) between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO gap), which is comparable to the measured HOMO-LUMO gap (approximately 0.65 eV) of the bare Au(58) cluster. Likewise, the Au(104)(SCH(3))(46) nanocluster has a HOMO-LUMO gap of approximately 0.51 eV, comparable to that of Au(102)(SCH(3))(44) nanocluster. In contrast, the Au(102)(SCH(3))(42) nanocluster has a zero HOMO-LUMO gap. These results confirm that high stability of the Au(102)(p-MBA)(44) nanocluster may be attributed in part to the electronic shell closing of effective 58 (= 102 - 44) valence electrons, as in the case of Au(25)(SCH(2)CH(2)Ph)(18)(-) cluster whose high stability may be attributed to the electronic shell closing of effective 8 (= 26 -18) valence electrons.