Structure–property relationship of a complex photoluminescent arylacetylide-gold(I) compound. I: a pressure-induced phase transformation caught in the act

A pressure-induced triclinic-to-monoclinic phase transition has been caught ‘in the act’ in the course of a wider series of high-pressure synchrotron diffraction experiments conducted on a moderately photoluminescent gold(I) compound. Our experiments illustrate how conducting a fast series of experiments, enabled by modern equipment at synchrotrons, can lead to an inaccurate estimation of the actual pressure of a phase transformation.


S1.1 Crystals placement in the DAC-s
In the first high-pressure data collection series (I), four crystal specimens of pyrEt were placed in a membrane DAC of BX90-type (cullet diameter 600µm, gasket hole 300µm, gasket thickness 100µm, 2θ OA 32 • ) with gaseous He as a PTM.The objectives were: to gain more data coverage by collecting diffraction data from two specimens at each pressure point, and to compensate for radiation damage (Figure S1.1 left).The first objective was not achieved, as specimens turned out to be all in similar orientations, with the same main face on a cullet.These specimens yielded a total of 29 useful datasets pressure range from 0.25 GPa to 2.0 GPa (crystals 2 and 3) and then up to 9.03 GP (the remaining two specimens) Two datasets, at pressure of 0.61 (crystal 2) and 0.65 GPa (crystal 3) accordingly, are commented in more detail.In the second series, a single crystal specimen (crystal 4) was placed in a membrane DAC of the same design alongside single crystals of three other substances (Figure S1.1 middle).It yielded a total of 16 useful datasets in pressure range from 0.25 GPa to 5.98 GPa, two of which were collected 20 minutes apart at the same pressure of 0.82 GPa.
In order to increase the reciprocal space coverage for the new crystal phase and facilitate unrestrained structure refinement, a total of 5 larger pieces cut out of a single crystal 5 of pyrEt were placed in a single DAC of a Merill-Basset design in various orientations (cullet diameter 750µm, gasket hole 400µm, gasket thickness 200µm, 2θ OA 40 • ) with ParatoneN oil as PTM -the only liquid PTM available on site just then which would not dissolve our sample.As its composition is the closest to the recognized Fluorinert or Vaseline oils, it is safe to assume that ParatoneN can still provide quasi-hydrostatic conditions at 1.1 GPa, although it would be highly unsuitable for structural studies in a wider pressure range.(Klotz, Chervin, Munsch & Le Marchand 2009, Tateiwa & Haga 2009) Useful diffraction datasets were collected from the three largest pieces (Figure S1.1 right).the RT phase displays twice shorter a unit cell constant than at 100K (Figure S2.1).The crystal structures of pyrEt aP and pyrEt mP determined in experimental series II from crystal 4 were necessarily refined with substantial number of restraints and constraints.This was due to: a) low completeness of diffraction data, resulting directly from placing plate-like crystals in a bulky DAC on one of their own faces and b) the lowered data quality due to experiment being conducted at the point of phase transformation.The general reasonableness of the obtained models was confirmed by comparing the structures of II-aP and II-mP with the structures determined at 300K at 1 atm or at 1.10 GPa in the course of unrestrained refinements.Figure S2.3 illustrates the structural overlays of the main structural motifs of the II-aP against the 300K and accordingly II-mP at 1.10 GPa.In both instances the RMS deviation as calculated by Mercury (

S2.4 CCDC deposition numbers
Structures determined for the purpose of this paper were deposited as individual entries within Cambridge Structural Database (Groom, Bruno, Lightfoot & Ward 2016).Exact deposition number for each structure have been presented in Table S2.1.

Figure S1. 1 :
Figure S1.1:Crystal specimens placed in a DAC in high-pressure experimental series.Specimens discussed in details in this work are numbered in white.Three pieces of Crystal 5 in the multi-crystal experiment marked tentatively as a, b and c.Radiation damage marks visible as darker spots on the surfaces of crystals in series I.

Figure S2. 1 :
Figure S2.1:Crystal structure of pyrEt determined at 1 atm and 300K (C atoms blue) in relation to the formerly described structure at 100K (C atoms dark-grey).View along [001] in triclinic cell setting.H atom positions omitted for clarity, as well as -Et 3 groups, here schematically represented as F or G, depending on the conformation.The alternative position of atom Au4 with associated phosphines represented in light-grey.

Figure
Figure S2.2:(a) The main building block of the crystal structure of pyrEt mP at 1.10 GPa: an infinite chain of Au• • • Au atoms along [010] direction.Atomic displacement parameters presented for atoms from asymmetric unit only at 50 % probability.H atom positions omitted for clarity.

Figure S2. 3 :
Figure S2.3:Comparison of the main structural motifs in (a) the pyrEt aP phase, comparing the II-aP structure (dark blue) against structure determined at 300K at 1 atm (cyan) and (b) the pyrEt mP phase comparing the II-aP structure (orange) against structure determined at 293K at 1.10 GPa (light orange).

Table S1 .
1: Unit cell constants obtained in variable-pressure experiments series I and II.Data suitable for structure refinements.TableS1.2:Unit cell constants obtained in variable-pressure experiments series I.
Aurophilic interactions Au• • • Au within the rod are quite short, while the 'external' Au• • • Au distance is significantly longer, over 4.4 Å.This general arrangement is retained at room temperature, with one important difference.Instead of two adjacent, distinct and perfectly ordered Au• • • Au chains there is only one chain, with a disorder in the position of Au4 and the connected -PEt 3 ligands.As a consequence, Table S1.3:Unit cell constants obtained in variable-pressure experiments series II.
TableS2.1: CCDC deposition numbers of crystal structures determined for the purpose of this work, sorted by crystal phase and exerted pressure.