the isolation and structural characterization of nanometer-sized molecular species
from the binary material, builds upon previous reports detailing the gas-phase
structures of metal-chalcogenide clusters similarly prepared via laser ablation
techniques [38]. The layered structure in 9 (Figure 13.7) can also be described as
consisting of A–B–A (Se 10 aSe 15 aSe 10 ) packed layers of selenium, with the copper
centers distributed between them and the surface PEt 3 ligands stabilizing the
Cu 70 Se 35 core. This same arrangement of [Cu 70 Se 35 (PR 3 ) 21 ] has been reported
to form from solution techniques, from the reaction of CuOAc and Se(SiMe 3 ) 2
with P
t BuMe 2 [39]. Indeed, the dominance of this structural type is demonstrated
with the structures of [Cu 70 Se 35 (PR 3 ) x ] (x ¼ 21–24) [31, 40], [Cu 72 Se 36 (PPh 3 ) 20 ]
[41] and [Cu 73 Se 35 (SePh) 3 (P
i Pr 3 ) 21 ] [36]. Thus the Cu 70 Se 35 frame is quite tolerant
to variation of the number and types of phosphine ligands. Similarly, the incorporation of 1–3 additional Cu centers occurs with little overall structural change,
these additions occurring at the corners of the 1.6 Â 1.6 Â 0.9 nm
3 Cu 70 Se 35 trigonal prismatic core. The molecule to solid transition for these megaclusters has also
been demonstrated where thermolysis of [Cu 70 Se 35 (PEt 2 Ph) 24 ] results in a cleavage
of the phosphine ligand shell, and the formation of bulk a-Cu 2 Se. Evidence has
been provided for the intermediate formation of 10 nm particles en route to the
solid via this method [42].
13.3.1.2 Spherical Cu 2 E
Of particular note is that in the series of copper selenide nanoclusters, there appears to be a definite ‘‘transition point’’ where the Cu 2x Se x clusters no longer exhibit the characteristic layered arrangement present in the clusters Cu 70 Se 35 !
Cu 146 Se 73 . For the copper selenide clusters synthesized to date, where the number
of Cu atoms is less than 60, an arrangement of the CuSe core best described as
being spherical in nature is typically observed, with experimental evidence for the
preferential formation of certain Cu 2x Se x structural motifs [31]. For example, the
cluster [Cu 44 Se 22 (PEt 2 Ph) 18 ] 10 (Figure 13.8) is known, where a non-bonded Se 22
polyhedral arrangement is observed in which the 44 Cu(I) centers are interspersed
[43]. The requirement of 18 surface phosphine ligands in 10 can be contrasted
with the structure of [Cu 44 Se 22 (P
n Bu
t Bu 2 ) 12 ] in which a similar Cu 44 Se 22 core
is observed, but with twelve larger surface PR 3 ligands. A notable effect of the
lower phosphine coverage however is the reduced number (12) of copper centers
‘‘pulled’’ out towards the cluster surface versus that in complex 10, as is commonly
observed with these phosphine ligated clusters. A partial listing of ‘‘spherical’’
copper selenide and copper selenide selenolate clusters isolated from Se(SiMe 3 ) 2 /
RSeSiMe 3 reagents is given in Table 13.1 [31, 36, 39–41, 43–47].
The number of copper sulfide clusters reported from the reaction of CuX and
S(SiMe 3 ) 2 is smaller than for the heavier congener selenium, with [Cu 12 S 6 (PR 3 ) 8 ]
[48, 49], [Cu 20 S 10 (PRR
0 2 ) 8 ] (R ¼ R
0 ¼ Ph; R ¼
n Bu, R
0 ¼
t Bu) [48, 49], [Cu 24 S 12 Á
(P
i Pr 2 Me) 12 ], [Cu 28 S 14 (P
t Bu 2 Me) 12 ] 11 and [Cu 50 S 25 (P
t Bu 2 Me) 16 ] 12 [39] having
been reported to date. None of these molecular species displays a clear structural
relationship to the binary solid Cu 2 S. This is perhaps due to the fact that the
‘‘transition point’’ for these clusters has yet to be reached (vide supra). Coordina13 Large Semiconductor Molecules
426
from the binary material, builds upon previous reports detailing the gas-phase
structures of metal-chalcogenide clusters similarly prepared via laser ablation
techniques [38]. The layered structure in 9 (Figure 13.7) can also be described as
consisting of A–B–A (Se 10 aSe 15 aSe 10 ) packed layers of selenium, with the copper
centers distributed between them and the surface PEt 3 ligands stabilizing the
Cu 70 Se 35 core. This same arrangement of [Cu 70 Se 35 (PR 3 ) 21 ] has been reported
to form from solution techniques, from the reaction of CuOAc and Se(SiMe 3 ) 2
with P
t BuMe 2 [39]. Indeed, the dominance of this structural type is demonstrated
with the structures of [Cu 70 Se 35 (PR 3 ) x ] (x ¼ 21–24) [31, 40], [Cu 72 Se 36 (PPh 3 ) 20 ]
[41] and [Cu 73 Se 35 (SePh) 3 (P
i Pr 3 ) 21 ] [36]. Thus the Cu 70 Se 35 frame is quite tolerant
to variation of the number and types of phosphine ligands. Similarly, the incorporation of 1–3 additional Cu centers occurs with little overall structural change,
these additions occurring at the corners of the 1.6 Â 1.6 Â 0.9 nm
3 Cu 70 Se 35 trigonal prismatic core. The molecule to solid transition for these megaclusters has also
been demonstrated where thermolysis of [Cu 70 Se 35 (PEt 2 Ph) 24 ] results in a cleavage
of the phosphine ligand shell, and the formation of bulk a-Cu 2 Se. Evidence has
been provided for the intermediate formation of 10 nm particles en route to the
solid via this method [42].
13.3.1.2 Spherical Cu 2 E
Of particular note is that in the series of copper selenide nanoclusters, there appears to be a definite ‘‘transition point’’ where the Cu 2x Se x clusters no longer exhibit the characteristic layered arrangement present in the clusters Cu 70 Se 35 !
Cu 146 Se 73 . For the copper selenide clusters synthesized to date, where the number
of Cu atoms is less than 60, an arrangement of the CuSe core best described as
being spherical in nature is typically observed, with experimental evidence for the
preferential formation of certain Cu 2x Se x structural motifs [31]. For example, the
cluster [Cu 44 Se 22 (PEt 2 Ph) 18 ] 10 (Figure 13.8) is known, where a non-bonded Se 22
polyhedral arrangement is observed in which the 44 Cu(I) centers are interspersed
[43]. The requirement of 18 surface phosphine ligands in 10 can be contrasted
with the structure of [Cu 44 Se 22 (P
n Bu
t Bu 2 ) 12 ] in which a similar Cu 44 Se 22 core
is observed, but with twelve larger surface PR 3 ligands. A notable effect of the
lower phosphine coverage however is the reduced number (12) of copper centers
‘‘pulled’’ out towards the cluster surface versus that in complex 10, as is commonly
observed with these phosphine ligated clusters. A partial listing of ‘‘spherical’’
copper selenide and copper selenide selenolate clusters isolated from Se(SiMe 3 ) 2 /
RSeSiMe 3 reagents is given in Table 13.1 [31, 36, 39–41, 43–47].
The number of copper sulfide clusters reported from the reaction of CuX and
S(SiMe 3 ) 2 is smaller than for the heavier congener selenium, with [Cu 12 S 6 (PR 3 ) 8 ]
[48, 49], [Cu 20 S 10 (PRR
0 2 ) 8 ] (R ¼ R
0 ¼ Ph; R ¼
n Bu, R
0 ¼
t Bu) [48, 49], [Cu 24 S 12 Á
(P
i Pr 2 Me) 12 ], [Cu 28 S 14 (P
t Bu 2 Me) 12 ] 11 and [Cu 50 S 25 (P
t Bu 2 Me) 16 ] 12 [39] having
been reported to date. None of these molecular species displays a clear structural
relationship to the binary solid Cu 2 S. This is perhaps due to the fact that the
‘‘transition point’’ for these clusters has yet to be reached (vide supra). Coordina13 Large Semiconductor Molecules
426