RESUMEN
We report the syntheses, structures, and luminescence properties of a series of copper-iodo cuboids supported by L-type antimony ligands. The cuboids are of general formula [(SbR3)4Cu4(I)4] (1-4, 8), where SbR3 is a series of homoleptic and heteroleptic stibines containing both phenyl and a variety of alkyl substituents (R = Cy, iPr, tBu, Ph); triphenyl, iPr2Ph, and Me2Ph stibines resulted in the formation of dimers of type [(SbR3)4(Cu)2(I)2] (5-7). While similar luminescent copper-halide cubes have been studied, the corresponding "heavy-atom" congeners have not been studied, and ligation of such heavy-atom moieties is often associated with long-lived triplet states and low-energy absorption and emission profiles. Overall, two obligate parameters are found to imbue NIR emission: (i) short Cu-Cu bonds and (ii) high crystallographic symmetry; both of these properties are found only in [(SbiPr3)4Cu4(I)4] (1, in I23; λem = 711 nm). The correlation between NIR emission and high crystallographic symmetry (which intrinsically includes high molecular symmetry)-versus only molecular symmetry-is confirmed by the counterexample of the molecularly symmetric tBu-substituted cuboid [(SbtBu3)4Cu4(I)4] (3, λem = 588 nm, in R-3), which crystallizes in the lower symmetry trigonal space group. Despite the indication that the stronger donor strength of the SbtBu3 ligand should red-shift emission beyond that of the SbiPr3-supported cuboid, the emission of 3 is limited to the visible region. To further demonstrate the connection between structural parameters and emission intensity, X-ray structures for 1 and 3 were collected between 100 and 300 K. Lastly, DFT calculations for 1 on its singlet (S0) and excited triplet state (T1) demonstrate two key factors necessary for low-energy NIR emission: (i) a significant contraction of the interconnected Cu4 intermetallic contacts [â¼2.45 â 2.35 Å] and (ii) highly delocalized (and therefore low-energy) A1 symmetry HOMO/LUMO orbitals from which the emission occurs. Thus, any molecular or crystallographic distortion of the Cu4 core precludes the formation of highly symmetric (and low-energy) HOMO/LUMO orbitals in T1, thereby inhibiting low-energy NIR emission.
RESUMEN
Reactions of the homoleptic and heteroleptic antimony ligands Sb iPr3, Sb iPr2Ph, SbMe2Ph, and SbMePh2 with NiI2 generate rare NiII stibine complexes in either square planar or trigonal bipyramidal (TBP) geometries, depending on the steric size of the ligands. Tolman electronic parameters were calculated (DFT) for each antimony ligand to provide a tabulated resource for the relative strengths of simple antimony ligands. The electronic absorbance spectra of the square planar complexes exhibit characteristic bands [λmax ≈ 560 nm (17â¯900 cm-1), ε ≈ 4330 M-1 cm-1] at lower energies compared to the reported phosphine complexes, indicating the weak donor strength of the stibine ligands and resultant low-energy ligand field dâ d transitions. The square planar complex Ni(I)2(Sb iPr3)2 reacts with CO to form the TBP complex Ni(I)2(Sb iPr3)2(CO). Lastly, the complexes were investigated for nickel metal deposition on Si|Cu(100 nm) substrates. The complexes with the strongest donating ligand, Sb iPr3, deposited the purest layer of NiCu alloy according to the balanced reaction Ni(I)2(SbIII iPr3)2 â Ni0 + SbV( iPr3)I2; the iodinated SbV byproduct was unambiguously detected in the supernatant by 1H NMR and mass spectrometry. Complexes with weaker ligands (poor I2 acceptors/scavengers) resulted undesired deposition of iodine and CuI on the surface. This work thus serves as a guide for the design and synthesis of 3 d metal complexes with neutral, heavy main-group donors that are useful for metal deposition applications.