Ligand Substitution in Cubic Clusters: Surprising Isolation of the Cocrystallization Products of Cu8(μ8-Se)[S2P(OEt)2]6 and Cu6[S2P(OEt)2]6

The cluster {Cu8(μ8-Se)[S2P(OEt)2]6}0.54{Cu6[S2P(OEt)2]6}0.46 (2) was prepared in 78% yield from the reaction of
Cu8(Se)[Se2P(OPr)2]6 (1) and NH4S2P(OEt)2 in toluene. The central selenide ion in 2 was characterized by 77Se
NMR at δ −976 ppm. The simulated solid-state 31P NMR spectrum shows two components with an intensity ratio
close to 55:45. The peak centered at 100.7 ppm is assigned to the 31P nuclei in the hexanuclear copper cluster,
and that at 101.1 ppm is due to the octanuclear copper cluster. The single-crystal X-ray diffraction analysis confirms
the cocrystallization structures of Cu8(Se)[S2P(OEt)2]6 (54%) and Cu6[S2P(OEt)2]6 (46%) (2:  trigonal, space group
R3̄, a = 21.0139(13) Å, c = 11.404(3) Å, γ = 120°, Z = 3). While the octanuclear copper cluster possesses a
3-fold crystallographic axis which pass through the Cu(2), Se, and Cu(2A) atoms, the six copper atoms having the
S6 point group symmetry in Cu6[S2P(OEt)2]6 form a compressed octahedron. The Cu8(μ8-Se) cubic core in Cu8(μ8-Se)[S2P(OEt)2]6 is larger in size than the metal core in Cu8(μ8-Se)[Se2P(OPr)2]6 (1) although the bite distance
of the Se-containing bridging ligand is larger than that of the S ligand. To understand the nature of the structure
contraction of the metal core and metal−μ8-Se interaction, molecular orbital calculations have been carried out at
the B3LYP level of density functional theory. MO calculations suggest that Cu−μ8-Se interactions are not very
strong and a half bond can be formally assigned to each Cu−μ8-Se bond. Moderate Cu···Cu repulsion exists, and
it is the bridging ligands that are responsible for the observed Cu···Cu contacts. Hence, the S-ligating copper
clusters have greater Cu···Cu separations because each Cu carries more positive charge in the presence of the
more electronegative S-containing ligands.

该簇合物 {Cu8(μ8-Se)[S2P(OEt)2]6}0.54{Cu6[S2P(OEt)2]6}0.46 (2) 以78%的收率通过Cu8(Se)[Se2P(OPr)2]6 (1) 与NH4S2P(OEt)2在甲苯中的反应制备而成。化合物2中的中心硒化物离子经77Se核磁共振波谱（δ −976 ppm）表征。模拟的固态31P核磁共振波谱显示出两个成分，其强度比接近55:45。位于100.7 ppm处的峰被归因于六核铜簇中的31P核，而位于101.1 ppm处的峰则归因于八核铜簇。单晶X射线衍射分析证实了Cu8(Se)[S2P(OEt)2]6 (54%) 和Cu6[S2P(OEt)2]6 (46%) (2: 三角晶系，空间群R3̄，a = 21.0139(13) Å，c = 11.404(3) Å，γ = 120°，Z = 3)的共结晶结构。尽管含有硒的桥连配体的咬合距离大于硫配体，但Cu8(μ8-Se)立方核在Cu8(μ8-Se)[S2P(OEt)2]6中的尺寸大于Cu8(μ8-Se)[Se2P(OPr)2]6 (1)中的金属核。为了理解金属核结构收缩的性质以及金属-μ8-Se相互作用的本质，已在密度泛函理论B3LYP水平上进行了分子轨道计算。分子轨道计算表明Cu-μ8-Se相互作用并不强烈，每个Cu-μ8-Se键可以正式分配一个半键。存在适度的Cu···Cu排斥，并且是桥连配体导致了观察到的Cu···Cu接触。因此，由S配位的铜簇具有更大的Cu···Cu间距，因为在含有更具电负性的S含配体的情况下，每个Cu都携带更多的正电荷。