Time-Dependent Molecular Rearrangement of [Au(N⁹-adeninate)(PTA)] in Aqueous Solution and Aggregation-Induced Emission in a Hydrogel Matrix

Abstract

An in-depth study of the molecular rearrangement of the complex [Au(N 9 -adeninate)(PTA)] (1), promoted in aqueous solution, is presented. This complex, which has been previously described as forming dimers in its crystalline form, is also demonstrated as being able to assemble into an infinite Au I •••Au I chain polymer. The structural motifs are tentatively related to the dramatic modification of the photoemissive properties of 1 in water solution at long times, with the aid of UV−vis and photoluminescence measurements, PGSE-NMR, and theoretical calculations. A subtle equilibrium in favor of aurophilically governed aggregates has been envisaged as the driving force of the molecular rearrangement. Furthermore, 1 has been explored as an additive of the hydrogel of [Au(N 9 -adeninate)(PMe 3 )] (2) for a further tuning of its photophysical properties without loss of the gel texture.

Spontaneous Water-Promoted Self-Aggregation of a Hydrophilic Gold(I) Complex Due to Ligand Sphere Rearrangement

“…Complex [Au(N 9 -hypoxanthinate)(PTA)] (1) was prepared in a single step by coordinating a [Au(PTA)] + unit to the hypoxanthinate anion formed in situ by deprotonation of hypoxanthine with the acetylacetonate [(acac) − ] ligand of [Au(acac)(PTA)] (see Figure 2). A N 9 coordination mode of the [Au(PTA)] + fragment to hypoxanthinate is proposed for complex 1 by analogy with the X-ray structure of other reported gold(I) complexes of the adeninate anion [18,30,[33][34][35]. N 9 is also the most basic position of purines.…”

“…However, the time dimension of the process is seldom studied. We reported in 2021 that complex [Au(N 9 -adeninate)(PTA)], an auration product of the natural purinic nucleobase adenine (see Figure 1, center), experiences a spontaneous supramolecular rearrangement in water solution leading to broad red phosphorescence centered at 700 nm [30]. Aurophilic dimers further stabilized by C-H• • • π interactions were proposed as a source of phosphorescence, in contrast to the initial blue-fluorescent hydrogen-bonded dimers.…”

Multidisciplinary study on the hydrogelation of the digold(i) complex [{Au(9N-adeninate)}2(μ-dmpe)]: optical, rheological, and quasi-elastic neutron scattering perspectives

“…The geometry around each gold(I) center is, as depicted in Figure 1, almost linear ( 9 N-Au-P angles of 175.0(4)° and 178.0(3)°), appearing the metal coordinated to one phosphorus atom of dmpe and to the 9 N position of the adeninate ligand, as in the other reported mono-and diphosphine analogs. [15][16][17][18][19][20] Au-P bond distances of 2.238(4) and 2.241(4) Å, and Au-N of 2.030 (11) (10); Au-N: 2.040(4), 2.036(6) Å). The relative gauche disposition of the dimethylphosphino groups along the carbon-carbon bridge bond (P-C-C-P torsion of -63.45°, Figure S10) allows the appearance of a semi-supported short aurophilic interaction of 2.9921(7) Å which, in fact, is the shortest value reported to date for this type of complexes ([Au( 9 N-adeninate)(PMe3)], 15 3.2081(6) Å; [Au( 9 N-adeninate)(PTA)]•H2O, 23 3.2122(4), 3.2307(4), 3.2697(4) Å), but is slightly longer than those of the doubly-bridged cationic bis(µ-diphosphine)diauracycles 21 This interaction is responsible for the bright blue phosphorescence displayed by 2 in the solid state and, probably, in the hydrogel form (vide infra).…”