Thermoluminescent Antimony-Supported Copper-Iodo Cuboids: Approaching NIR Emission via High Crystallographic Symmetry

Abstract

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, i Pr, t Bu, Ph); triphenyl, i Pr2Ph, 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 [(Sb i Pr3)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 t Bu-substituted cuboid [(Sb t Bu3)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 Sb t Bu3 ligand should red-shift emission beyond that of the Sb i Pr3-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 [∼2.45 → 2.35 Å] and (ii) highly delocalized (and therefore low-energy) A 1 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.

Stabilization of the Elusive Antimony(I) Cation and Its Coordination Complexes with Transition Metals

“…TheS b1ÀCu1 bond length is 2.4579(8) ,s horter than in the case of Sb III -Cu I complexes (2.571(2) )i ndicating strong s-donation of Sb I . [38] TheCu I •••Cu I separation is 2.8741 (13) which is close to the sum of van der Waals radii of Cu I centers. [39] Complex 7 crystallizes in triclinic P1S ohncke (chiral) space group as obtained from the X-ray diffraction data (Table S1).…”

Synthesis and Magnetic Properties of Antimony-Ligated Co(II) Complexes: Stibines versus Phosphines

“…22,23 Similarly, we determined that only alkylated or partially alkylated ligands provided access to thermoluminescent copper(I) cuboids, one of which exhibited NIR luminescence. 22,23 In this work, the isolation of these elusive, paramagnetic cobalt stibine complexes allow for the first time an experimental (and corresponding theoretical) investigation of the electronic effects of heavy 5p donor ligation to a paramagnetic metal ion. The possible effects (synergistic, additive, or competing) of translational SOC and ligand field (donor strength) in a 3d−5p coordination system are quantitatively evaluated.…”

“…In the last few years, we have utilized alkylated antimony ligands and developed metalation conditions that allow for the isolation of Sb–M­(3d) complexes of copper­(I), nickel­(II), and iron­(II). , For example, while commercially available SbPh 3 does not bind nickel­(II), a variety of trialkyl or mixed alkyl/aryl SbR 3 ligands supported square planar or five-coordinate nickel­(II) motifs, some of which were uniquely effective in enabling nickel metal deposition compared with their phosphine analogues. , Similarly, we determined that only alkylated or partially alkylated ligands provided access to thermoluminescent copper­(I) cuboids, one of which exhibited NIR luminescence. , In this work, the isolation of these elusive, paramagnetic cobalt stibine complexes allow for the first time an experimental (and corresponding theoretical) investigation of the electronic effects of heavy 5p donor ligation to a paramagnetic metal ion. The possible effects (synergistic, additive, or competing) of translational SOC and ligand field (donor strength) in a 3d–5p coordination system are quantitatively evaluated.…”

“…20 In the last few years, we have utilized alkylated antimony ligands and developed metalation conditions that allow for the isolation of Sb−M(3d) complexes of copper(I), nickel(II), and iron(II). 22,23 For example, while commercially available SbPh 3 does not bind nickel(II), a variety of trialkyl or mixed alkyl/ aryl SbR 3 ligands supported square planar or five-coordinate nickel(II) motifs, some of which were uniquely effective in enabling nickel metal deposition compared with their phosphine analogues. 22,23 Similarly, we determined that only alkylated or partially alkylated ligands provided access to thermoluminescent copper(I) cuboids, one of which exhibited NIR luminescence.…”

“…22,23 For example, while commercially available SbPh 3 does not bind nickel(II), a variety of trialkyl or mixed alkyl/ aryl SbR 3 ligands supported square planar or five-coordinate nickel(II) motifs, some of which were uniquely effective in enabling nickel metal deposition compared with their phosphine analogues. 22,23 Similarly, we determined that only alkylated or partially alkylated ligands provided access to thermoluminescent copper(I) cuboids, one of which exhibited NIR luminescence. 22,23 In this work, the isolation of these elusive, paramagnetic cobalt stibine complexes allow for the first time an experimental (and corresponding theoretical) investigation of the electronic effects of heavy 5p donor ligation to a paramagnetic metal ion.…”