Synthesis and luminescence modulation of pyrazine-based gold(iii) pincer complexes

A second nitrogen for modulation: cyclometallated gold(iii) complexes based on pyrazine provide a new family of photoluminescent compounds which allow facile modulation of the emission wavelengths without the need for modifying the basic ligand framework.


Synthesis of (C^N pz^C )AuCl (2)
(C^N pz^C H)HgCl·2HOAc F (1) (0.79 g, 1.14 mmol) and K[AuCl 4 ] (0.43 g, 1.14 mmol) were stirred in a mixture MeCN/water: 1/1 (30 mL) at reflux for 72 h. After the mixture had cooled to room temperature, the crude product, a pale orange precipitate, was filtered off and washed with water (2 × 20 mL) and MeCN (20 mL) of and dried under vacuum. For further purification this orange powder was dissolved in DMSO (50 mL) and stirred at 120 C for 2 h. The solution was cooled to room temperature and water (100 mL) was added, causing the precipitation of a yellow product. The mixture was filtered through celite. The residue was washed with water, followed by acetone and then dichloromethane. A yellow solution was obtained. The solvents were evaporated. The yellow residue was dissolved in CH 2 Cl 2 (200 mL) and washed with water (3 × 50 mL). The organic phase was dried with Na 2 SO 4 and the solvent evaporated. The product was washed with cold hexane to afford pure 2 as a yellow powder ( S6 Figure S3. 1 H NMR spectrum of 2. Figure S4. 13 C NMR spectrum of 2.

Synthesis of (C^N pz^C )AuCCPh (5a)
(C^N pz^C )AuCl 2 (0.060 g, 0.10 mmol) and AgCCPh (0.033 g, 0.16 mmol) were charged into a vial and protected from the light. Dichloromethane (10 mL) was added. The mixture was sonicated for 1 h and stirred vigorously for 24 h before being filtered through celite.

Synthesis of [(N-HC^N pz^C )AuCl]BF 4 (6)
(C^N pz^C )AuCl 2 (0.050 g, 0.087 mmol) was stirred at room temperature under N 2 atmosphere in distilled diethyl ether (5 mL). To this was added HBF 4 ·Et 2 O (0.012 mL, 0.087 mmol), leading to an immediate colour change from yellow to orange. The mixture was stirred for 30 min at room temperature. After evaporation of the solvent the red solid residue was suspended in dichloromethane. The addition of hexane led to the precipitation of a red product which was filtrated, washed with hexane (3 × 5 mL) and dried to afford the pure product as a red powder (

S2. X-ray crystallography
Crystals of each sample were mounted in MiTeGen MicroMesh systems and fixed in the cold nitrogen stream on a diffractometer. Diffraction intensities were recorded al low temperature on an Oxford Diffraction Xcalibur-3/Sapphire3-CCD diffractometer, equipped with Mo-Kα radiation and graphite monochromator or Rigaku HG Saturn724+ (2×2 bin mode). Data were processed using the CrystAlisPro-CCD and -RED software or CrystalClear-SM Expert 3.1 b27, been the absorption correction done at this stage. S2 The structures of all samples were determined by the direct methods routines with SHELXS or SHELXT programs and refined by full-matrix least-squares methods on F 2 in SHELXL. S3 Nonhydrogen atoms were generally refined with anisotropic thermal parameters. Hydrogen atoms were included in idealised positions. No missed symmetry was reported by PLATON. S4 Refinement results are included in Table S1. Computer programs used in this analysis were run through WinGX. S5 Scattering factors for neutral atoms were taken from reference S6.

Crystallographic details for (C^N pz^C )AuCl (2):
Orange block (0.1×0.1×0.3 mm) grown by slow evaporation of a saturated solution of the crude in a mixture DMSO:acetone (1:9) at room temperature. The asymmetric unit is formed by one half molecule of 2. A positional disorder was found in one of the t Bu groups and this was modelled with 0.6 and 0.4 occupancy. Some peaks higher than 1 e.Å -3 were found in the vicinity of the Au center without any chemical meaning.
(C^N pz^C )Audmpz (4): Yellow needles (0.21×0.03×0.01 mm) grown by slow evaporation of a concentrated solution in dichloromethane. Several peaks higher than 1 e.Å -3 were found in the vicinity of the Au center without any chemical meaning.
(C^N pz^C )AuC≡CPh (5a): Yellow needles (0.2×0.05×0.05 mm) grown by slow evaporation of a solution of the complex in a mixture CH 2 Cl 2 :i-PrOH (9:1) at room temperature. Several peaks higher than 1 e.Å -3 were found in the vicinity of the Au center without any chemical meaning.

S4. Theoretical Calculations
The structure of the ground (S 0 ) and lowest triplet (T 1 ) states for all of the complexes were optimised at DFT(PBE0) S8 level using the ORCA quantum chemistry program. S9 During the optimisation a def2-SVP basis set S10 was used for all of the atoms. The excited state energies were computed using linear response time-dependent density functional theory (LR-TDDFT) S11 within the Tamm-Damcoff Approximation. S12 These were simulated using the optimally tuned S13 range-separated functional (LC-BLYP). S14 In range-separated functionals the amount of exact exchange is weighted according to the inter electron distance, r 12 : The optimal value of μ was obtained using the ΔSCF method. S13 Here we minimised the energy difference between energy of the HOMO (ε HOMO ) and first ionisation potential (IP) of the neutral system and the energy difference between energy of the HOMO of the anionic system, (ε HOMO+1 ) and the electron affinity (EA) of the neutral system. These conditions are expressed as: 0 = |ε ( ) + ( )| and 1 = |ε ( + 1) + ( )| Therefore our overall goal is to minimise the relationship: Optimisation of the range-separated parameter, μ, using the above expression was performed within the approximation of the LC-BLYP exchange-correlation functional. The effect of the solvent was included using the PCM approach and the parameters of dichloromethane. This was only included during the calculation of the excited states and not during the tuning of μ. This is consistent with the conclusions of refs S15 who reported that μ tuning within a continuum solvent model can result in unrealistic values due to a significant underestimation of vertical ionisation potential. For all of the complexes studied herein, he optimum value of μ, was found to be a consistent value of μ=0.18±0.01 bohr -1 similar to a study of iridium photosensitisers.       Figure S30. The frontier orbitals of complex 2.