Stabilization of {Ag₂₀(S^tBu)₁₀} and {Ag₁₉(S^tBu)₁₀} Toroidal Complexes in DMSO: HPLC-ICP-AES, PL, and Structural Studies

Abstract

The presence of DMSO provides a unique ability to stabilize silver toroidal complexes in the direct reaction between AgS^tBu and AgNO₃ at 80 °C. Slow cooling results in large crystals of [NO₃@Ag_19.2(S^tBu)₁₀(DMSO)_5.2(NO₃)_8.2]·3DMSO (1), which were isolated and characterized by single crystal X-ray diffraction (SCXRD) analysis. The crystal structure contains both {Ag₂₀(S^tBu)₁₀} and {Ag₁₉(S^tBu)₁₀} clusters. The solution of these material in DMSO was studied with HPLC techniques, which demonstrated the presence of both complexes in solution. The use of [SiW₁₂O₄₀]^4– as counter anion gives crystals of a double complex salt [Ag_17.8(NO₃)_3.8(S^tBu)₁₀][SiW₁₂O₄₀]·30DMSO (2) under the same conditions. Temperature-dependent photoluminescence (PL) was studied.

1. Introduction

Reaction of (AgSR)_n polymers with Ag⁺ source in different organic solvents produces a huge pool of polynuclear silver complexes of different size and topologies [1,2,3,4]. Some small anions can occupy the central cavity of such cages playing two possible roles: (i) template for the self-assembly process or (ii) guest for the complex stabilization.

In particular, there is a class of torus-like silver complexes of {X@Ag₂₀SR₁₀} (Scheme 1) with different guest molecules (X). Here a few CO₃^2–-templated Ag₂₀ cluster thiolates exist. For example, in {[CO₃@Ag₂₀(S^tBu)₁₀(CH₃COO)₈(DMF)₂]·2H₂O}_n the Ag–CO₃ bond distances range from 2.26(2) to 2.56(2) Å. Sun et al. also found [CO₃@Ag₂₀(S^tBu)₁₀(OAc)₈(DMF)₄]·DMF·CH₃OH [5] and [SO₄@Ag₂₀(SⁱBu)₁₀(PhSO₃)₈(H₂O)₄⋅2H₂O]_n with sulfate in the cluster center [6]. With different thiolates Mak et al. reported {Ag[CO₃@Ag₂₀(SⁱPr)₁₀(CO₂CF₃)₉(CO₂HCF₃)(CH₃OH)₂]}_n and {Ag₂[CO₃@Ag₂₀(SCy)₁₀(CO₂CF₃)₁₀(CO₂HCF₃)₂(H₂O)₂]·3H₂O·3CH₃OH}_n 2D coordination networks (d(Ag-O) 2.534–2.694 Å) [7]. Zhang et al. presented a set of carbonate-centered complexes [(CO₃)@Ag₂₀(S^tBu)₁₀(NO₃)₈(DMAc)₄], [(CO₃)@Ag₂₀(S^tBu)₁₀(C₆H₅COO)₈(DMAc)₂]·2CH₃CN, [(CO₃)@Ag₂₀(S^tBu)₁₀(C₁₂H₆O₂NCH₂COO)₈]·4CH₃CN and [(CO₃)@Ag₂₀(S^tBu)₁₀(CpFeC₅H₄COO)₈(CH₃CN)₄]·CH₃CN·2H₂O (DMAc = N,N-dimethylacetamide) [8]. Typical Ag-CO₃ distances vary from 2.4 to 2.5 Å. It should be noted that in all those structures two carboxylate anions block the central cavity by coordination to the rim Ag atoms.

Several examples of Cl⁻ templated silver thiolate clusters have been reported. A family of coordination polymers including [Cl@Ag₁₄(S^tBu)₈(CF₃COO)₅(bpy)₂(DMF)]·2DMF, [Cl@Ag₁₅(S^tBu)₈(CF₃COO)_5.67(NO₃)_0.33(bpy)₂(DMF)₂]·4.3DMF·H₂O, and [Cl@Ag₁₆(S^tBu)₈(CF₃COO)₇(DMF)₄(H₂O)]·1.5DMF was reported by Bakr et al. [9]. The chloride anion can serve as a template for a larger Ag₂₀ cluster isolated as [Cl@Ag₂₀(S^tBu)₁₀(CF₃COO)₂]·(CF₃COO)₇·5CH₃OH. Here it is trapped inside the core as a supramolecular guest with very long Ag∙∙∙Cl distances of 3.4–3.5 Å [10]. In the structure of {S@Ag₁₂S₆@Ag₃₆(^tBuCC)₁₂(^tBuS)₁₂(ⁿBuPO₃)₂(ⁿBuPO₃H)₆}, the templating S^2– results from C-S bond cleavage [11]. The S@Ag₁₂ central fragment is related to I@Ag₁₂ and I@Cu₁₂ units observed in [I@Ag₁₂I₄{S₂P(CH₂CH₂Ph)₂}₆] and [PyH][I@Cu₁₂(TpMo)₄S₁₆] [12,13].

Recently we reported new large-sized silver thiolates [NO₃@Ag₂₀(S^tBu)₁₀(NO₃)₉(DMF)₆] and [NO₃@Ag₂₀(S^tBu)₁₀(NO₃)₈(NMP)₈][NO₃@Ag₁₉(S^tBu)₁₀(NO₃)₈(NMP)₆]₂(NO₃), which were isolated from DMF and NMP (N-methylpyrrolidone) solutions, correspondingly. The presence of Br⁻ in the reaction mixture can affect self-assembly process leading to [Br@Ag₁₆(S^tBu)₈(NO₃)₅(DMF)₃](NO₃)₂ host–guest complex [14]. Sometimes ligands can play a crucial role in intra-cluster and inter-cluster assembly [15]. A lot of interesting co-crystals was reported by M. Jansen [16], N. Zheng [17], and Q.-M. Wang [18].

In this research, we present our studies concerning self-assembly of AgS^tBu and Ag⁺ in DMSO. Here we present the first analytical studies of silver thiolate complexes using separation techniques. The PL data show nice correlation with the structural and analytical results.

2. Results and Discussion

2.1. Synthesis and Structure

Recently we proposed a simple way to produce {Ag₂₀(S^tBu)₁₀} complexes in DMF and NMP solutions [14]. According to the SCXRD data, crystals collected from DMSO had the same unit cell parameters as grown from DMF. The purity of all solvents is crucial for successful synthesis of the Ag clusters. The use of commercial DMF resulted in fast silver reduction even at −30 °C. In the case of DMSO only freshly distilled solvent is strictly recommended for the synthesis. Another very important point is correct temperature regime. Indeed, the use of freshly distilled DMSO gives an advantage to heat the reaction solution over 80 °C, thus significantly increasing the reaction rate. Based on these two principles we developed a very efficient way to generate Ag-S^tBu torus-like complexes, which can be isolated just after cooling the reaction solution. The use of this protocol gives an advantage to isolate complex 1 in excellent yield up to 60%. Unfortunately, the isolated crystalline material is light sensitive and progressively becomes black under irradiation. Moreover, traces of organics on the vial walls (unsatisfactory cleaned vials or organics in the lab air) immediately destroy silver thiolate complexes.

The crystal structure of 1 was studied with single crystal X-ray diffraction analysis (See Supplementary Materials, Table S1). The main structural unit is a torus like defective [NO₃@Ag_20-x(S^tBu)₁₀(DMSO)_6-x(NO₃)_10-x] complex (Figure 1). The refinement gives the x value close to 0.8. Accordingly, the bulk formula can be defined as [NO₃@Ag_19.2(S^tBu)₁₀(DMSO)_5.2(NO₃)_8.2]. Formulation Ag_19.2 means the presence of both {Ag₂₀(S^tBu)₁₀} and {Ag₁₉(S^tBu)₁₀} complexes in one crystal with the second one being a major component. Two defective positions of Ag atoms are marked in cyan (Figure 1). Four positions with closely disordered Ag atoms are marked in pink. The complex geometry is very close to an earlier reported [NO₃@Ag₂₀(S^tBu)₁₀(NO₃)₉(DMF)₆] complex [14]. All NO₃⁻ anions have practically the same geometry in both structures. Ag-O distances for the inner NO₃⁻ anions vary in 2.66–2.68 Å interval, which can be compared with 2.5–2.8 Å found in the structure with coordinated DMF. Presence of defects in Ag-atom positions can be a key to speciation in solution. The loss of cyan-marked {AgDMSO)} fragments or pink marked rim Ag atoms can generate {Ag₁₉} or {Ag₁₈} complexes in solution.

Crystals of 1 demonstrate good stability toward light exposure and vacuum drying. Grey coloration of the crystalline sample can be detected after keeping several days in air at ambient temperature. X-ray powder diffraction data show crystallinity loss after acetone washing and further vacuum drying (Figure S1).

Addition of [H₄SiW₁₂O₄₀] to the AgNO₃/AgS^tBu reaction mixture results in the formation of 2 upon cooling. It should be noted that addition of [H₃PW₁₂O₄₀] or [H₃PMo₁₂O₄₀] did not produce crystals. In the structural model of 2, silver nanoclusters and polyoxometalate (POM) anions form pseudo layers oriented in [011] crystal direction (Figure 2). The layers alternate in a ABAB∙∙∙ motif. Inside each layer, both silver clusters and POM anions fill the space according to 3⁶ plane net topology (more about topologies can be found here [19]). The structure cannot be well refined due to strong disordering of POM anions, Ag thiolate clusters, coordinated and solvated DMSO molecules and NO₃⁻ anions. X-ray powder diffraction analysis results are in a good agreement with SCXRD data (Figure S2). The complex composition was found based on analytical data. It should be noted that refinement give 17.83 Ag atom per silver thiolate nanocluster. This means presence of more defective {Ag₂₀(S^tBu)₁₀} units in the crystal structure.

2.2. Chromatography Studies

Adaptation of liquid chromatography to the study of polynuclear silver thiolates has been realized as specific modification of the silica gel with Ag⁺ ions. It should be noted, silver covalently anchored onto the thiol moiety of a mercaptopropyl modified silica gel has been tested for the separation of polycyclic aromatic hydrocarbons [20]. This approach was applied for the liquid chromatographic analysis of unsaturated fatty acid ethyl esters, triglycerols (TAGs), and long-chain alkenones [21] or mono-, di-, and triglycerols [22,23]. In fact, there is no information about analytical chemistry or separation of silver thiolate complexes in solution. From our previous data obtained from the HR-ESI-MS analysis of CH₃CN solutions of [NO₃@Ag₂₀(S^tBu)₁₀(NO₃)₉(DMF)₆], [NO₃@Ag₂₀(S^tBu)₁₀(NO₃)₈(NMP)₈][NO₃@Ag₁₉(S^tBu)₁₀(NO₃)₈(NMP)₆]₂(NO₃), and [Br@Ag₁₆(S^tBu)₈(NO₃)₅(DMF)₃](NO₃)₂ we can propose the appearance of a huge number of equilibrated species in such solutions [14]. Such equilibria, without doubt, will be very sensitive to concentration or solvent. Here we used straightforward HPLC-ICP-AES technique [24] for the analysis of Ag-S^tBu species.

Crystals of 1 were dissolved in DMSO to extract the information about real complex forms in solution. The HPLC-ICP-AES chromatogram shows two baseline-resolved peaks (t_R = 3.3 min, 5.3 min), that confirms the presence of {Ag₁₉}ⁿ⁺ (peak 1 in Figure 3) and {Ag₂₀}ⁿ⁺ (peak 2 in Figure 3) species in a ratio of 77:23, according to HPLC-ICP-AES analysis. The eluting species are detected by monitoring the silver atomic emission line at 328.0 nm following the separation by high-performance liquid chromatography. Adding an ion-pairing reagent (sodium dodecyl sulfate, SDS) to the mobile phase does not significantly affect the chromatographic behavior of the species but increases the retention time, which can be associated with an interaction of the cationic analyte with SDS. Thus, we indeed found two peaks with the ratio nearly matching found by crystal structure refinement.

The combination of structural and chromatographic data gives an assignment of each observed peak, which is the base for further solution studies. The products of the reaction between AgNO₃ (100 mg) and AgS^tBu (76 mg) in 3 mL of DMSO were monitored using combined HPLC-ICP-AES. The obtained chromatogram (Figure 4a) of a freshly prepared solution of silver clusters shows two baseline-resolved peaks (t_R = 3.3 min, 5.3 min), reflecting the presence of {Ag₁₉(S^tBu)₁₀} and {Ag₂₀(S^tBu)₁₀} species in a ratio of 77:23. The chromatogram of this solution aged for 8 h (Figure 4b) shows two peaks with percentage ratio and retention times the same as for the freshly prepared solution, but the intensity of the peaks decreased by a factor of 3.6, which can be associated with the products crystallization.

Similar behavior was observed for the products of the reaction between AgSO₃CF₃ (100 mg) and AgS^tBu (76 mg) in DMSO (3 mL). The HPLC-ICP-AES chromatogram of the freshly prepared solution (Figure 5a) also shows two resolved baseline peaks (t_R = 3.3 min, 5.3 min); however, the replacement of the AgNO₃ reagent by AgSO₃CF₃ led to a slight change in the ratio of the resulting products, which was 70:30 for {Ag₁₉(S^tBu)₁₀} and {Ag₂₀(S^tBu)₁₀}, respectively. Keeping the solution for 8 h (Figure 5b) also led to a 3.5-fold decrease in the peak intensity due to the product crystallization.

From these observations following conclusions can be drawn: (i) The essential stability of {Ag₂₀(S^tBu)₁₀} structural type in solution; (ii) the change of NO₃⁻ for SO₃CF₃⁻ does not affect the formation of the torus-like silver thiolate complexes; (iii) the ratio between the two species remains constant indicating frozen equilibrium.

The comparison between our earlier data [14] from HR-ESI-MS measured in CH₃CN solution and HPLC-ICP-AES for DMSO shows better stability of DMSO solutions. In the literature there are two different dynamic processes reported for the Ag nanoclusters. Bakr et al. observed complete thiolate-for-thiolate exchange for [Ag₄₄(SR)₃₀]^4– [25]. Wang et al. found isotopic exchange between [¹⁰⁷Ag₄₄(SR)₃₀] and [¹⁰⁹Ag₄₄(SR)₃₀] (SR = 4-mercaptobenzoic acid) nanoclusters resulting in complete exchange of all Ag atoms in the [Ag₄₄(SR)₃₀] structure [26]. In our studies we found stability of the {Ag₁₉(S^tBu)₁₀} and {Ag₂₀(S^tBu)₁₀} cluster cores, but the DMSO/NO₃ exchange can still occur and must be studied with other techniques.

To study the species evolution in the reaction solution we keep NO₃⁻-containing solution for 3 months. The changes were checked by UV-VIS and HPLC-ICP-AES techniques. We found appearance of a new peak in the UV-VIS spectrum at 350 nm indicating the presence of a new complex in solution (peak 1 in Figure 6, left). The results from hyphenated method confirm this reflecting a new peak with t_R = 2.71 min (Figure 6, right). Taking into account the tendency to reduce t_R with reducing of the Ag atoms number we can suggest the formation of {Ag₁₈} cluster during aging.

2.3. Photoluminescence

Luminescence properties of silver-based complexes are of particular interest [27,28]. In the case of silver-based nanoclusters there are metalloid and non-metalloid polynuclear complexes. Both types of objects have interesting luminescence properties with a potential for applications. Recently a silver complex with 110 ms lifetime has been reported [29]. Silver-NMP (NMP = N-methyl-2-pyrrolidone) complexes stabilized by POM anions show 30 ms lifetime [30]. The [Ag₁₇(R/S-NYA)₁₂](NO₃)₃ (R/S-NYA = N-((R/S)-1-(naphthalen-4-yl)ethyl)prop-2-yn-1-amine) crystals demonstrate a broad emission peak (centered at 745 nm) with a PLQY (photoluminescence quantum yield) of 8% and τ of 61.02 μs. The spectra of solutions containing the R/S-Ag¹⁷ cluster exhibit a slight blue shift to 715 nm with a PLQY of 1.08% and τ = 5.06 μs. When the Ag nanoclusters were embedded in polymer films, the PLQY was enhanced to 6.23%, τ increased to 46.90 μs, and the emission peak returned to approximately 745 nm. According to the calculations [31,32,33] in [Ag₁₇(R/S-NYA)₁₂](NO₃)₃ the LUMO → HOMO transitions between cluster orbitals are responsible for the NIR emission, which could be slightly affected by the ligand.

[Ag₃₁S₃(S^tBu)₁₇(CF₃COO)₇(CO₃)_0.5(CF₃COOH)_0.5(DMF)₄]·3DMF·CH₃OH demonstrates temperature-dependent orange-red emission with λ_max = 648 nm (excitation at 365 nm) at 77 K and λ_max = 631 nm at 298 K [34]. The emission can be assigned as LMCT from S 3p to Ag 5s perturbed by Ag∙∙∙Ag interactions [35,36,37]. Moreover, emission maximum and temperature are in good linear relationship, which can be described as I (intensity) = −196.654 T (temperature) + 62762.0157 (correlation coefficient = 0.991). The difference between metalloid and non-metalloid silver clusters emission can be more than 100 nm caused by the different nature of transitions.

In the case of 1, we observed luminescence with wide asymmetrical profile of the emission peak (Figure 7 and Figure S4). The luminescence maximum λ_Em = 625 nm at 77 K shifts to the λ_Em = 605 nm at 170 K and then returns to λ_Em = 625 nm at 220 K. The PL spectra can be described by at least two Gauss functions with maxima λ1 = 1.98 eV (626 nm) and λ2 = 2.23 eV (556 nm) (Figure 8 and Figure S5). The integral intensity of λ1 monotonously decreases with temperature increasing and cannot be described with the two energy levels approach. At the same time, the integral intensity of λ2 increases from 77 K to 150 K up to two times and then decreases by two orders at 220 K. Such temperature behavior can be a sign of the interrelation between these bands. Taking this into account, the luminescence can be induced by several ways: (i) emission of {Ag₁₉} and {Ag₂₀} with the possible intercluster transition; (ii) emission from the same centers of both clusters caused by LMCT from S 3p to Ag 5s [38] together with {Ag₁₉} and {Ag₂₀} intracluster CC transition (or ligand-to-metal−metal charge transfer LMMCT [39]).

The temperature dependence of the luminescence in 2 is shown in Figure 9. The PL spectra at each temperature consist of two well-resolved bands and can be described by at least two Gauss functions with maxima λ₁ = 1.73 eV (717 nm) and λ₂ = 2.03 eV (611 nm) (Figure S6). The integral intensities of both bands monotonously decrease with temperature increasing (Figure 9, right).

It is assumed that the high-energy band corresponds to the Ag clusters without splitting into two bands such as in 1. The low energy band can be ascribed either to the emission of the charge transfer excited state between the Ag cluster and POM [40] or to specific defects in the Ag cluster structure. The observation of the low-energy band in the POM-free solution (Figure 8) can indicate that the low-energy luminescence band comes from the Ag-clusters. The polyoxometalate can change the transitions probabilities, and hence, the intensities of the luminescence bands in the solid. The presence of polyoxometalate in the crystal structure of 2 results in the enhanced intensity of the low energy emission. It appears that polyoxometalate can be used for luminescence tuning in the Ag thiolate clusters.

Reaction solution containing AgNO₃ and AgS^tBu demonstrates a bright emission with λ_Em = 690 nm (Figure 10). The PL spectrum can be matched with three Gauss functions with the maxima λ₁ = 1.74 eV (713 nm), λ₂ = 1.83 eV (678 nm), and λ₃ = 2.05 eV (605 nm). The integral intensities of the bands follow the ratio 20:75:5. The bands with close maxima are observed in both 1 and 2. The values found in solution and in solids are listed in

Table 1. The comparison between PL maxima of the reaction solutions and of solid 1 and 2.

Maxima	Solution	1	2
λ1	1.74		1.73
λ2	1.83	1.98
λ3	2.05	2.23	2.03

.

So, the addition of POM resulted in solution speciation change to the appearance of the third component in a large amount. The comparison between PL data and chromatography results is a good point to find species with significantly lower concentrations. Probably this complex form has more reactivity toward chromatography column material and we did not detect its presence in solution.

3. Materials and Methods

3.1. General Information

AgS^tBu was prepared according to the standard procedure from AgNO₃ and HS^tBu in CH₃CN with an addition of Et₃N. DMSO was distilled in vacuo over NaOH. [H₄SiW₁₂O₄₀]·14H₂O was manufactured by “The Red Chemist” (Saint Petersburg, USSR), and checked with FT-IR and TGA prior to use. Other reagents were of commercial quality (Sigma Aldrich, St. Louis, MO, USA) and were used as purchased. FT-IR spectra were recorded on a Vertex 80 spectrometer. Elemental analysis was carried out on a Eurovector EA 3000 CHN analyzer (Pavia, Italy). UV-VIS spectra were recorded on a Cary 60 spectrometer (Agilent, Santa Clara, CA, USA).

3.2. Synthesis

Synthesis of [NO₃@Ag_19.2(S^tBu)₁₀(DMSO)_5.2(NO₃)_8.2]·3DMSO (1):

AgNO₃ (100 mg, 0.6 mmol) followed by AgS^tBu (76 mg, 0.4 mmol) was added into 2 mL of DMSO. The mixture was heated under vigorous stirring until full dissolution of AgS^tBu. Crystals of 1 slowly appear just after cooling of the reaction mixture. Final crop of the crystalline material was collected after 12 h and washed several times with Et₂O. Solid material was obtained after drying in vacuo for 5–7 h. Yield 60% (based on AgNO₃).

Analysis. Found C, H, N, S (%): 16.7, 3.9, 2.9, 13.2. Calcd. for 1 C, H, N, S (%): 16.2, 3.4, 3.0, 13.9.

IR (KBr, cm⁻¹, Figure S3): 2957(m), 2930(w), 2914(w), 2888(w), 2851(w), 1471(m), 1440(s), 1386(vs), 1355(vs), 1217(w), 1165(s), 1024(s), 950(m), 820(m), 705(w), 675(w), 620(w), 561(m).

Synthesis of [Ag_17.8(NO₃)_3.8(S^tBu)₁₀][SiW₁₂O₄₀]·30DMSO (2):

AgNO₃ (100 mg, 0.06 mmol) and AgS^tBu (76 mg, 0.4 mmol) were subsequently added into 2 mL of DMSO. The mixture was heated under rigorous stirring until full dissolution of AgS^tBu. After that, 20 mg of [H₄SiW₁₂O₄₀]·14H₂O was added to the reaction mixture. Crystals of 2 slowly appear just after cooling of the reaction mixture. Final crop of the crystalline material was collected after 12 h and washed several times with Et₂O. Solid material was obtained after drying in vacuo for 5–7 h. Yield 75% (based on AgNO₃).

Analysis. Found C, H, N, S (%): 14.8, 3.8, 0.7, 15.9. Calcd. for 2 C, H, N, S (%) 14.5, 3.3, 0.6, 15.5.

IR (KBr, cm⁻¹, Figure S3): the same to 1 with an addition of [H₄SiW₁₂O₄₀] fingerprints at 967(m), 920(s), 883(w), 802(s) [41] and more clearly appeared stretches at 1315(m), 1274(m), 523(w).

3.3. PL

Corrected luminescence spectra were recorded on a Fluorolog 3 spectrometer (Horiba Jobin Yvon, Edison, NJ, USA) with a cooled PC177CE-010 photon detection module equipped with R2658 photomultiplier; with continuous 450 W Xe-lamp; with two Czerny–Turner double monochromators. Temperature dependences of luminescence were studied using Optistat DN optical cryostat (Oxford Instruments, Abingdon, UK).

3.4. X-ray Diffraction on Single Crystals

Crystallographic data and refinement details are given in Table S1. The diffraction data for 1 and 2 were collected on a Bruker D8 Venture diffractometer with a CMOS PHOTON III detector and IµS 3.0 source (Mo Kα radiation, λ = 0.71073 Å) at 150 K. The φ- and ω-scan techniques were employed. Absorption correction was applied by SADABS (Bruker Apex3 software suite: Apex3, SADABS-2016/2 and SAINT, version 2018.7-2; Bruker AXS Inc.: Madison, Fitchburg, WI, USA, 2017.). Structures were solved by SHELXT [42] and refined by full-matrix least-squares treatment against |F|² in anisotropic approximation with SHELX 2014/7 [43] in ShelXle program [44].

In the case of 2, there is a set of problems that avoided full structural refinement: (i) fast decrease of the reflections intensity after d = 1 Å; (ii) full positional disordering of each Ag coordination environment; (iii) highly disordered solvent molecules of crystallization and nitrate anions; (iv) position disordering of POM anions. Such problems resulted in unstable refinement of “light” atoms. H-atoms were not located due to complicated disordering of C-atoms. SQUEEZE procedure was applied to model as the solvent mask. The full complex composition was found using analytical techniques.

CCDC 2211734 and 2211735 contain the supplementary crystallographic data for 1 and 2 correspondingly. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html (accessed on 10 October 2022), or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223-336-033; or e-mail: [email protected].

3.5. XRPD

X-ray powder diffraction patterns were measured on a Bruker D8 Advance diffractometer using LynxEye XE T discriminated CuKα radiation. Samples were layered on a flat plastic specimen holder.

3.6. HPLC-ICP-AES

Separations were performed with HPLC system Milichrom A-02 (EcoNova, Novosibirsk, Russia) equipped with a two-beam spectrophotometric detector at the wavelength range of 190−360 nm (ProntoSIL 120-5-C18AQ, 2 × 75 mm), eluents: A—water, B—acetonitrile. The gradient mode conditions: 0–1 min, 0–30% B; 1–7 min, 30–80% B; flow rate—0.2 mL min⁻¹. An ICP-AES spectrometer iCap 6500 Duo (Thermo Scientific, Waltham, MA, USA) with concentric nebulizer was applied as detector in hyphenated HPLC-ICP-AES mode. For quantitative estimations the Ag 328.0 nm spectral line was selected. All measurements were performed in three replicates. The data acquisition and processing were carried out with iTEVA (Thermo Scientific, Waltham, MA, USA) software. The ICP-AES working parameters: power supply—1150 W, nebulizer Ar flow rate—0.70 L min⁻¹, auxiliary—0.50 L min⁻¹, cooling—12 L min⁻¹. In order to eliminate plasma quenching, we diluted the liquid coming out of the column into the spray chamber with deionized water. The steady state of the plasma and the optimal values of analytical signals were finally achieved at the eluent flow rate of 0.2 mL min⁻¹, and the eluent velocity of 3 mL min⁻¹ (peristaltic pump speed—75 rpm).

4. Conclusions

This work shows formation of {Ag_20-x(S^tBu)₁₀} clusters in DMSO in the presence of either NO₃⁻ or CF₃SO₃⁻. Analytical separation methods for the control of the reactions were used for the first time in this chemistry. Crystallization from AgNO₃/AgS^tBu solutions leads to the isolation of co-crystals containing both {Ag₁₉} and {Ag₂₀} clusters. Addition of [H₄SiW₁₂O₄₀] to the reaction solution gives crystals of double complex salt with interesting PL properties. We found a significant increase in low-energy PL intensity band at 717 nm in the presence of POM. This can be explained by CT between the silver thiolate cluster and POM unit.