Sodium sulfide, Na 2 S, has proven to be an effective reagent for the synthesis of
nickel-sulfide clusters, when reacted with phosphine-solubilized Ni(II) salts. The
nanocluster [Ni 15 S 15 (PPh 3 ) 6 ] 4 (Figure 13.4) can be described as a columnar arrangement of triangular {Ni 3 S 3 } stacked units [24]. These units are parallel and
staggered with respect to each other, with the sulfide centers acting as both intraand inter-triangle m 3=4 -S bridging ligands, and the oblong cluster is capped at
both ends with three PPh 3 groups. The isostructural [Ni 15 Se 15 (PPh 3 ) 6 ] 5 can be
prepared from nickel chloride and Se(SiMe 3 ) 2 under room temperature conditions
[25]. The reaction between the nickel(II) source and the silylated selenium reagent
invariably results in a distribution of products formed, however these provide
mechanistic insight into the manner in which the columnar cluster forms. These
products include triangular [Ni 3 Se 2 X 2 (PR 3 ) 4 ] (X ¼ Cl, SeSiMe 3 ), which can be
viewed as the building blocks leading to the higher nuclearity complex 5 [26]. Recent theoretical work suggests that continued condensation of such Ni 3 units to
yield clusters [Ni 3n Se 3n (PR 3 ) 6 ] (n ¼ 6–9) should be accessible [27], consistent with
the previous experimental observations [26].
The synthesis and structural characterization of the spherical nanocluster
[Ni 34 Se 22 (PPh 3 ) 10 ] 6 (Figure 13.5) illustrates clearly that nanometer-sized pieces of
the binary material can be accessed [28]. Cluster 6 is formed from the reaction
of NiCl 2 (PPh 3 ) 2 and Se(SiMe 3 ) 2 . The structure of the NiSe core in 6 is quite
unique with respect to other Ni/E clusters, with virtual five-fold symmetry and
layers of 5, 10, 10, and 5 nickel atoms. A Ni 4 unit resides at the center of the
molecule. The selenium atoms all act as m 4 -capping ligands, save for the two m 5 -Se
that cap the top and bottom Ni 5 pentagons. A similar spherical arrangement of
Fig. 13.4. The condensed, columnar framework observed in
[Ni 15 E 15 (PPh 3 ) 6 ] (4, E ¼ S; 5, E ¼ Se) illustrating the buildup
from Ni 3 E 3 units [24, 25].
13 Large Semiconductor Molecules
422
nickel-sulfide clusters, when reacted with phosphine-solubilized Ni(II) salts. The
nanocluster [Ni 15 S 15 (PPh 3 ) 6 ] 4 (Figure 13.4) can be described as a columnar arrangement of triangular {Ni 3 S 3 } stacked units [24]. These units are parallel and
staggered with respect to each other, with the sulfide centers acting as both intraand inter-triangle m 3=4 -S bridging ligands, and the oblong cluster is capped at
both ends with three PPh 3 groups. The isostructural [Ni 15 Se 15 (PPh 3 ) 6 ] 5 can be
prepared from nickel chloride and Se(SiMe 3 ) 2 under room temperature conditions
[25]. The reaction between the nickel(II) source and the silylated selenium reagent
invariably results in a distribution of products formed, however these provide
mechanistic insight into the manner in which the columnar cluster forms. These
products include triangular [Ni 3 Se 2 X 2 (PR 3 ) 4 ] (X ¼ Cl, SeSiMe 3 ), which can be
viewed as the building blocks leading to the higher nuclearity complex 5 [26]. Recent theoretical work suggests that continued condensation of such Ni 3 units to
yield clusters [Ni 3n Se 3n (PR 3 ) 6 ] (n ¼ 6–9) should be accessible [27], consistent with
the previous experimental observations [26].
The synthesis and structural characterization of the spherical nanocluster
[Ni 34 Se 22 (PPh 3 ) 10 ] 6 (Figure 13.5) illustrates clearly that nanometer-sized pieces of
the binary material can be accessed [28]. Cluster 6 is formed from the reaction
of NiCl 2 (PPh 3 ) 2 and Se(SiMe 3 ) 2 . The structure of the NiSe core in 6 is quite
unique with respect to other Ni/E clusters, with virtual five-fold symmetry and
layers of 5, 10, 10, and 5 nickel atoms. A Ni 4 unit resides at the center of the
molecule. The selenium atoms all act as m 4 -capping ligands, save for the two m 5 -Se
that cap the top and bottom Ni 5 pentagons. A similar spherical arrangement of
Fig. 13.4. The condensed, columnar framework observed in
[Ni 15 E 15 (PPh 3 ) 6 ] (4, E ¼ S; 5, E ¼ Se) illustrating the buildup
from Ni 3 E 3 units [24, 25].
13 Large Semiconductor Molecules
422