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[Angew Chem Int Ed - 2024 - Fukumoto - Diphosphine‐Protected IrAu12 Superatom with Open Site s   Synthesis and Programmed.pdf](https://mdr.nims.go.jp/filesets/f3a59f68-df02-4d7e-817b-e1cf5659eca6/download)

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Yuto Fukumoto, Tsubasa Omoda, Haru Hirai, Shinjiro Takano, [Koji Harano](https://orcid.org/0000-0001-6800-8023), Tatsuya Tsukuda

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[Diphosphine‐Protected IrAu<sub>12</sub> Superatom with Open Site(s): Synthesis and Programmed Stepwise Assembly](https://mdr.nims.go.jp/datasets/068744b2-278a-42db-bb2d-b2dbe00b17d2)

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Diphosphine‐Protected IrAu12 Superatom with Open Site(s): Synthesis and Programmed Stepwise AssemblyNanoclustersDiphosphine-Protected IrAu12 Superatom with Open Site(s):Synthesis and Programmed Stepwise AssemblyYuto Fukumoto+, Tsubasa Omoda+, Haru Hirai, Shinjiro Takano, Koji Harano, andTatsuya Tsukuda*Abstract: One or two phenylacetylide (PA) ligand(s)were successfully removed from the IrAu12 superatomiccore of [IrAu12(dppe)5(PA)2]+ (dppe=1,2-bis(diphenylphosphino)ethane) by reaction with con-trolled amounts of tetrafluoroboric acid. Optical andnuclear magnetic resonance spectroscopies and densityfunctional theory calculations revealed the formation ofopen Au site(s) on the IrAu12 core of [IrAu12(dppe)5-(PA)1]2+ and [IrAu12(dppe)5]3+ with the remainingstructure intact. Isocyanide was efficiently trapped at theopen electrophilic site on [IrAu12(dppe)5(PA)1]2+,whereas a dimer or trimer of the IrAu12 superatoms wasformed using diisocyanide as a linker. These resultsopen the door to designed assembly of chemicallymodified metal superatoms.IntroductionChemically modified gold superatoms (Au CMSs) are a newclass of nanosized molecules that exhibit novel and diverseproperties owing to the size-specific structures of the Aucores.[1–4] Au CMSs with crystallographically determinedstructures are promising candidates as (1) platforms for thestudy of structure–property correlations[4] and (2) buildingunits of assembled materials.[5–9] In order to assemble AuCMSs via covalent bonding, ligand exchange reactions withmultidentate ligands have been frequently used.[10–13] How-ever, design and fabrication of controlled assembled struc-tures are challenging because the number and position ofexchangeable sites of Au CMSs are difficult to control. Apromising approach to overcome this problem is to pre-install exposed sites on the Au CMSs whereby the Au CMSsare assembled into a programmed structure by multidentateligands. Furthermore, such Au CMSs with partially exposedAu sites will offer new opportunities to investigate and tunetheir catalytic properties since the accessible sites of thesubstrate can be regulated at the molecular level.[14–16] Oneof the current strategies for creating exposed sites isreduction of the surface coverage by steric repulsionbetween bulky ligands.[17–20] For example, an Au23 clusterwith naked sites catalyzed the oxidation reaction of benzylalcohol.[19] However, as it is difficult to design and predictthe number and position of exposed sites by suchapproaches, a new method is required for fabricating theexposed sites in a controlled manner.The present study aimed to achieve this goal by theselective removal of anionic ligand(s) from the predefinedCMSs. The platforms we chose for this purpose were[Au13(dppe)5(PA)2]3+, [PdAu12(dppe)5(PA)2]2+, and [IrAu12-(dppe)5(PA)2]+, where dppe and PA� H represent 1,2-bis(diphenylphosphino)ethane and phenylacetylene, respec-tively. These clusters bear two anionic PA ligands at theopposite sites of an icosahedral M@Au12 core (M=Au, Pd,Ir)[21–24] and will be referred to as AuPA23+, PdPA22+ , andIrPA2+, respectively, in terms of the dopant element, thenumber of PA ligand(s), and the total charge. Electrosprayionization mass spectrometry (ESI-MS) demonstrated thatthe PA ligands were removed stepwise only from IrPA2+ toform IrPA12+ and Ir3+ by the reaction with strong Brønstedacid. The formation of an open site in IrPA12+ wasconfirmed by nuclear magnetic resonance (NMR) spectro-scopy, density functional theory (DFT) calculations, and atrapping experiment with 1-isocyanoadamantane (IA). Bytaking advantage of the designed exposed sites on IrPA12+and Ir3+, two or three Ir@Au12 cores were linked linearly via4,4’’-p-terphenyldiisocyanide (L).[*] Y. Fukumoto,+ Prof. Dr. T. Omoda,+ Dr. H. Hirai, Prof. Dr. S. Takano,Prof. Dr. T. TsukudaDepartment of Chemistry, Graduate School of ScienceThe University of Tokyo7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JapanE-mail: tsukuda@chem.s.u-tokyo.ac.jpProf. Dr. T. Omoda+Present address: Department of Chemical Science and Engineering,School of Materials and Chemical TechnologyTokyo Institute of TechnologyO-okayama, Meguro-ku, Tokyo 152-8552, Japan.Prof. Dr. K. HaranoCenter for Basic Research on MaterialsNational Institute for Materials Science,1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.[+] These authors contributed equally to this work.© 2024 The Authors. Angewandte Chemie International Editionpublished by Wiley-VCH GmbH. This is an open access article underthe terms of the Creative Commons Attribution Non-CommercialLicense, which permits use, distribution and reproduction in anymedium, provided the original work is properly cited and is not usedfor commercial purposes.AngewandteChemieResearch Articleswww.angewandte.orgHow to cite: Angew. Chem. Int. Ed. 2024, 63, e202402025doi.org/10.1002/anie.202402025Angew. Chem. Int. Ed. 2024, 63, e202402025 (1 of 6) © 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbHhttp://orcid.org/0000-0002-2625-9817http://orcid.org/0000-0002-2778-0620http://orcid.org/0000-0001-9262-5283http://orcid.org/0000-0001-6800-8023http://orcid.org/0000-0002-0190-6379https://doi.org/10.1002/anie.202402025http://crossmark.crossref.org/dialog/?doi=10.1002%2Fanie.202402025&domain=pdf&date_stamp=2024-02-28Results and DiscussionSynthesis and Structures of MPA2 Clusters (M=Au, Pd, Ir)Cluster AuPA23+ was synthesized by the reportedmethods.[21] Clusters PdPA22+ and IrPA2+ were newlysynthesized by the ligand exchange reaction[21] of [PdAu12-(dppe)5Cl2]2+ and [IrAu12(dppe)5Cl2]+ (Refs. [22] and [24])with PA� H, respectively.[25] Figure 1 and Table S1 show thesingle-crystal X-ray diffraction (SCXRD) results of PdPA22+and IrPA2+.[26,27] The structural motifs of PdPA22+ andIrPA2+ were similar to that of AuPA23+ (Ref. [21]) andwere composed of an icosahedral M@Au12 (M=Pd or Ir)core capped by five dppe ligands and two PA ligands at thecoaxial position. Two Au� C bonds in PdPA22+ (2.04 Å and2.08 Å) and IrPA2+ (2.03 Å and 2.16 Å) were not equivalentin the crystal (Figure 1), while a single peak in the 31P{1H}NMR chart in acetone-d6 (Figures S1a and S2) indicatedthat the two Au� C bonds were equivalent in solution. Theaverage lengths of the Au� C bonds in MPA2 were 2.01,2.06, and 2.10 Å for M=Au, Pd, and Ir, respectively. Thistrend suggests that the Au� C bond becomes weaker in theorder of AuPA23+, PdPA22+, and IrPA2+ . Figure 2 summa-rizes other characterization results of IrPA2+ . The chemicalcomposition and purity were confirmed by ESI-MS (Fig-ure 2a, black). The UV/Vis absorption spectrum (Figure 2b,black) showed an onset at ~520 nm and clear peaks at ~310and ~415 nm. The photoluminescence (PL) spectrum (Fig-ure 2b, red) exhibited a band centered at ~615 nm with a PLquantum yield (QY) of 53% in Ar. The 1H NMR chart(black trace in Figure 2c, Figure S3) exhibited doublet peaksat ~7.8 ppm (peak a) due to ortho protons of the phenyl ringof PA ligands (a in Figure 2d) and a singlet peak at~8.8 ppm (peak b) due to ortho protons of two equivalentphenyl rings of dppe ligands located at the axial position (bin Figure 2d). Figure 3a shows the DFT optimized structureof [IrAu12(dmpe)5(PA)2]+ (IrPA2-m+), which was obtainedby replacing dppe of IrPA2+ with dmpe (1,2-bis(dimeth-ylphosphino)ethane).[25] The optimized structure of IrPA2-m+ reproduced the structural motif of IrPA2+ (Figure 1c).According to the Kohn–Sham (KS) orbital analysis (Fig-Figure 1. Crystal structures of (a) AuPA23+ (Ref. [21]) (b) PdPA22+ , and(c) IrPA2+ . Solvent molecules, hydrogen atoms, and counter anions areomitted for clarity. Carbon atoms in dppe ligands are depicted assticks. Color code: yellow, Au; dark blue, Ir; light blue, Pd; orange, P;gray, C.Figure 2. (a) ESI mass spectra of the acetonitrile solutions of IrPA2+ (black), a mixture of IrPA2+ and one eq. of HBF4 (red), a mixture of IrPA12+and one eq. of IA (blue). The insets compare the experimental and simulated isotope patterns. The small peak marked with an asterisk (*) wasassigned to [IrAu12(dppe)5(PA)2]2+ (oxidized species of IrPA2+). (b) Absorption (black), photoluminescence (red; λex=415 nm), and excitation(blue; λem=615 nm) spectra of IrPA2+ , IrPA12+ , and IrPA1IA12+ . (c) 1H NMR (400 MHz) charts of IrPA2+ (black), IrPA12+ (red), and IrPA1IA12+(blue). The charts of IrPA2+ and IrPA1IA12+ were measured in acetone-d6, while that of IrPA12+ was measured in acetonitrile-d3. The circles andsquares indicate the signals from dppe and PA ligands, respectively. (d) Assignment of protons in IrPA2+ , IrPA12+ , and IrPA1IA12+ . The yellowhexagon with a blue circle at the center represents the IrAu12 core.AngewandteChemieResearch ArticlesAngew. Chem. Int. Ed. 2024, 63, e202402025 (2 of 6) © 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2024, 18, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202402025 by Cochrane Japan, Wiley Online Library on [18/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licenseure S4a), the highest occupied molecular orbital (HOMO)consisted of the combination of the 1P superatomic orbitalof the Ir@Au12 core and the π orbital of the PA ligands,while the lowest unoccupied molecular orbital (LUMO)mainly consisted of the 1D superatomic orbital. Thus,IrPA2+ can be viewed as an Ir@Au12(8e) superatommodified with dppe and PA ligands.Desorption of Alkynyl Ligand by AcidCluster IrPA2+ was chosen as an initial target expecting thatthe Au� C bonds would be more easily dissociated thanthose in AuPA23+ and PdPA22+ based on the Au� C bondlength. We first studied the reaction of IrPA2+ with variousBrønsted acids (Table 1)[28–34] in acetonitrile (AN) using ESI-MS. IrPA2+ was almost completely converted to [IrAu12-(dppe)5(PA)1]2+ (IrPA12+) by adding one equivalent ofstrong acids such as HBF4 (Figure 2a, red), trifluoroaceticacid (TFA� H) (Figure S5a), and 10-camphorsulfonic acid(CSA� H) (Figure S5b). In contrast, IrPA12+ was notproduced when weaker acids such as chloroacetic acid(CH2ClCOOH) and acetic acid (CH3COOH) were added(Figures S5c and S5d). These results suggest that sufficientlystrong acids can remove a PA ligand from the Ir@Au12 coreof IrPA2+ . Given that the pKa value of PA� H in water is23.2,[35] the formation of IrPA12+ can be viewed as therelease of a weak acid (PA� H) from IrPA2+ by a strongacid (H+X� ) as follows:IrPA2þ þHþX� ! IrPA12þ þ PA� HþX� (1)The key step of eq. (1) may be weakening of the Au� Cbond via protonation of the C�C bond of the PA ligand, butfurther work is needed to elucidate the detailed mechanism.When one equivalent of HCl was mixed with IrPA2+,[IrAu12(dppe)5(PA)1Cl1]+ (IrPA1Cl1+) was generated (Fig-ure S6), indicating that low coordination ability of theconjugate base X� to gold is also necessary to leave the siteopen.The new product, IrPA12+, was characterized in moredetail. The UV/Vis absorption and PL spectra of IrPA12+are similar to those of IrPA2+ (Figure 2b), indicating thatthe removal of PA from IrPA2+ does not appreciablychange its geometric structure. This conclusion was furthersupported by the similarity of the DFT-optimized structuresof IrPA2-m+ (Figure 3a) and [IrAu12(dmpe)5(PA)1]2+(IrPA1-m2+) (Figure 3b). The exposure of a single Au atomon the Ir@Au12 surface is illustrated by a space-fillingrepresentation of IrPA1-m2+ (Figure S7a). A superatom-likeelectronic structure was retained in IrPA1-m2+ although theenergy levels and shapes of the KS orbitals were slightlydifferent from those of IrPA2-m+ (Figure S4b). In contrast,the PL QY was significantly reduced from 53 % to 25%upon the removal of one PA (Figure 2b, red). This PLquenching is ascribed to the acceleration of the nonradiativerelaxation of the photoexcited states of IrPA12+ due to poorligand packing around the Ir@Au12 core. 1H NMR spectro-scopy (red trace in Figure 2c, Figure S8) revealed that thesingle peak at ~8.8 ppm (peak b) for IrPA2+ was split intotwo (peaks b and b’) in IrPA12+ (~8.4 and ~8.7 ppm),reflecting the inequivalent environment of the phenyl groupsof dppe upon removal of one PA (b and b’ in Figure 2d).The stability of IrPA12+ in AN solution was confirmed byUV/Vis spectroscopy and ESI-MS as a function of storagetime (Figure S9). Both measurements suggested thatIrPA12+ did not decompose after storage for at least 1 weekat room temperature in the dark.The remaining PA of IrPA12+ could be removed byadding four equivalents of HBF4 to the AN solution ofIrPA2+. ESI-MS detected [IrAu12(dppe)5]3+ (Ir3+) withoutPA ligands along with the adducts with AN solvent andBF4� anion (Figure S10). The DFT-optimized structure of[IrAu12(dmpe)5]2+ (Ir-m3+) (Figure S7b) predicts that Ir3+has two open sites at opposite positions of the Ir@Au12 core.The KS orbitals of Ir-m3+ (Figure S4c) show that HOMOand HOMO-1 correspond to 1P superatomic orbitals. Theseresults demonstrate that open sites can be created in acontrolled manner on the IrAu12 superatomic core by acid-induced PA release.Then, the scope of the acid-induced PA removal wasexamined for the other clusters PdPA22+ and AuPA23+ byusing the strongest acid HBF4. The PA removal proceededpartly from PdPA22+, but not from AuPA23+ (Figure S11).Thus, the reactivity of MPA2 with acid is reduced in theorder of IrPA2+, PdPA22+, and AuPA23+, which is parallelto the order of Au� C bond length. The selective removal ofPA from IrPA2+ is probably associated with the weakerFigure 3. DFT-optimized structures of (a) IrPA2-m+ , (b) IrPA1-m2+ , and(c) IrPA1IA1-m2+ . Hydrogens are omitted for clarity. The color code isthe same as in Figure 1 except blue for N.Table 1: Reaction products with IrPA2+ and one equivalent of variousacidsAcid pKa in H2O pKa in AN ProductaHBF4 � 4.9b 1.8c IrPA12+TFA-H 0.59 or 0.32b 12.7d IrPA12+CSA-H 1.2e –f IrPA12+CH2ClCOOH 2.85g 18.8h IrPA2+CH3COOH 4.76g 22.3i IrPA2+aThe main product observed in the ESI mass spectrum. bRef. [28].cRef. [29]. dRef. [30]. eRef. [31]. fNot available. gRef. [32]. hRef. [33].iRef. [34].AngewandteChemieResearch ArticlesAngew. Chem. Int. Ed. 2024, 63, e202402025 (3 of 6) © 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2024, 18, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202402025 by Cochrane Japan, Wiley Online Library on [18/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseAu� C bond and smaller electrostatic repulsion between themonocationic IrPA2+ and H+ compared to that between thedoubly and triply charged PdPA22+ and AuPA23+ , respec-tively.Reactivity of the Open SiteDFT calculations predicted that the LUMO of IrPA1-m2+has a large lobe on the exposed site of the core (Figure S4b),implying that the open site of IrPA12+ can accommodatenucleophiles. This hypothesis was tested by a trappingexperiment. IrPA12+ was completely converted to [IrAu12-(dppe)5(PA)1(IA)1]2+ (IrPA1IA12+) upon the addition ofone equivalent of 1-isocyanoadamantane (IA) (Figure 2a,blue):(2)Further addition of IA did not proceed smoothly evenwhen two equivalents of IA were added (Figure S12). As acontrol, direct mixing of IrPA2+ with one or two equivalentsof IA was conducted. Small amounts of IrPA1IA12+ and[Au(dppe)2]+ were detected, while the majority of IrPA2+remained unreacted (Figure S13). These results indicate thatthe open site of IrPA12+ can be efficiently and selectivelyoccupied by a single IA molecule. The absorption and PLspectra of IrPA1IA12+ remained similar to those of IrPA12+,respectively (Figure 2b), indicating that the superatomicnature was retained during the coordination of IA. How-ever, the PL QY was significantly enhanced from 25 % to70 % by the incorporation of IA to IrPA12+, probably due tothe rigidification of the IrAu12 core by the completion of thedensely packed ligand layer in IrPA1IA12+. The 1H NMRchart of IrPA1IA12+ (Figure 2c, blue) exhibited similarpatterns to those of IrPA12+, indicating that the geometricstructure of the dppe ligand layer was hardly changed by theIA ligation. The DFT optimized structure of [IrAu12-(dmpe)5(PA)1(IA)1]2+ (IrPA1IA1-m2+) in Figure 3c and S7cillustrates that IA is coordinated to the open site of IrPA1-m2+ while retaining the core structure. The superatomicelectronic structure of IrPA1IA12+ was supported by KSorbitals of IrPA1IA1-m2+ (Figure S4d). Gibbs free energiescalculated for IrPA1-m2+ + IA!IrPA1IA1-m2+ and IrPA2-m+ + IA!IrPA1IA1-m2+ +PA� were � 0.5 and +5.6 eV,respectively, at T=298 K. This estimation explains why theIA could not be introduced by the ligand exchange, but bythe coordination to the open site of IrPA12+.Controlled Linkage of the IrAu12 SuperatomsEfficient coordination of isocyanide (IA) to the open site ofIrPA12+ suggests that multiple Ir3+ can be connected usingdiisocyanide, such as 4’’-p-terphenyldiisocyanide (L), as alinker. The resulting oligomers are expected to have a linearconfiguration because the open sites of Ir3+ are located atthe coaxial position of the icosahedral IrAu12 core. Further-more, the number of IrAu12 superatoms linked can becontrolled using L, Ir3+ and IrPA12+ as building unitsaccording to a strategy shown in Scheme 1. The first step isthe synthesis of the dimer and trimer of the IrAu12superatoms as shown in Scheme 1a and 1b, respectively. Thedimer is formed by addition of 0.5 eq. of L to IrPA12+ (stepi), while the trimer is formed by sequential addition of twoequivalents of L (step i) and two equivalents of IrPA12+(step ii) to Ir3+. Two IrAu12 superatoms can be added toboth ends of the dimers or trimers by acid-induced removalof two PA ligands from both sides (step iii), followed bysteps i and ii. By repeating these three steps, targetedsynthesis of multimers with any number of constituents ispossible in principle.To demonstrate the applicability of this strategy, weherein show the synthetic results of the dimer and trimer ofIrAu12 superatoms. According to Scheme 1a, 0.5 equivalentof L was added to the solution of IrPA12+. The ESI massspectrum of the purified products (Figure 4a, red) wasdominated by the peak of the target dimer (IrPA12+)2L1. Inthe 1H NMR chart (Figure 4c, red), new signals composed ofone singlet and two doublet peaks (peaks c–e) appeared inthe range of 7.95–8.10 ppm, in addition to those from dppe(peaks b and b’) and PA (peak a) of the IrPA1 moieties.These new peaks are assigned to L in (IrPA12+)2L1 due tothe similarity with the 1H NMR chart of free L (Figure S14).This assignment was further supported by the agreementbetween the ratio of integral areas for peaks a: b+b’: c–e(1.0: 11.6: 2.8) and the number of the corresponding protonsof the model structure for (IrPA12+)2L1 (4H, 40H, 12H,respectively: Figure 4d). The splitting pattern of peaks c–eindicates that the protons of L in (IrPA12+)2L1 were in threedifferent environments, which is explained by the modelstructure shown in Figure 4d.Transmission electron microscopy (TEM) measurementwas conducted to visualize the linked structure of(IrPA12+)2L1. We attempted to align (IrPA12+)2L1 along theboron nitride nanotubes (BNNTs) in the hope of observingScheme 1. Synthetic scheme of (a) even- and (b) odd-numberedoligomers of Ir@Au12 superatoms. The building blocks are shown inthe legend.AngewandteChemieResearch ArticlesAngew. Chem. Int. Ed. 2024, 63, e202402025 (4 of 6) © 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2024, 18, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202402025 by Cochrane Japan, Wiley Online Library on [18/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseTEM images from a direction perpendicular to the inter-particle bond. Figures 5 and S15 represent TEM images ofselected areas of the sample thus prepared. The blurredimages of the IrAu12 particles are due to dynamic structuralchange during the exposure time of the TEM imaging. Theaverage center-to-center distance between the IrAu12 coreswas 2.7 nm, which agrees well with the sum of the diameterof IrPA12+ (0.8 nm) and the length of L (1.9 nm). Theseresults suggest that two IrPA12+ units are successfully linkedby L.The trimer was synthesized in two steps according toScheme 1b: mixing Ir3+ and two equivalents of L, followedby capping both ends by two equivalents of IrPA12+. In theESI mass spectrum (Figure 4a, blue), the target trimer(IrPA12+)2(Ir3+)1L2 and adducts of BF4� were observed asthe main products, while a small amount of the dimers andtetramers was observed as impurities (Figure S16). In the1H NMR spectrum (Figure 4c, blue), the relative intensity ofdoublet peaks at 8.6 and 8.8 ppm from dppe (peaks b, b’,and b”) is significantly different from that of the dimer(peaks b and b’ in the red trace of Figure 4c). This behaviorwas explained by the overlap of the doublet peaks at ~8.6and ~8.8 ppm from dppe on the terminal IrAu12 cores (b andb’ in Figure 4d; 20H and 20H, respectively) and the singletpeak at 8.6 ppm from dppe on the central IrAu12 core (b” inFigure 4d; 20H). The signals from L (peak c–h, 24H) andPA (peak a; 4H) in the trimer (Figure 4c, blue) were similarto those in the dimer (Figure 4c, red). The 31P{1H} NMRspectrum (Figure S17) exhibited a singlet and two doubletpeaks, indicating that P atoms in the trimer are under threedifferent environments. One singlet is assigned to the Patoms of the dppe ligand on the central IrAu12 core (P3 inFigure 4d), and two doublets are assigned to the P atoms ofthe dppe ligands on the terminal IrAu12 cores (P1 and P2 inFigure 4d). These results indicate that the linear trimer wassuccessfully synthesized with high purity.The absorption spectrum of (IrPA12+)2(Ir3+)1L2 (Fig-ure 4b, black) was very similar to that of (IrPA12+)2L1, buttheir spectral onsets are redshifted as compared to that ofIrPA1IA12+ unit (Figure S18). This result indicates that theHOMO–LUMO gap of the IrAu12 superatom is reduced bylinkage. The PL QY decreased with an increase in thelinkage: 70, 21, and 9% for IrPA1IA12+, (IrPA12+)2L1, and(IrPA12+)2(Ir3+)1L2, respectively. These results suggest thatelectronic states and relaxation dynamics of the IrAu12superatom are affected by the neighboring IrAu12 unit(s)through linker L. The degree of perturbation might bedependent on the number and/or distance of the constituentunits and the electronic nature of linking ligands, which willbe a target of future study.ConclusionWe herein report a method for making atomically preciseopen sites on chemically modified gold superatoms withwell-defined structures. Controlled amounts of strongBrønsted acid removed one or two PA ligands from [IrAu12-(dppe)5(PA)2]+ leaving the superatomic IrAu12 core intact.A single isocyanide was selectively coordinated to theexposed site of [IrAu12(dppe)5(PA)1]2+. Furthermore, thedimer and linear trimer of IrAu12 superatoms were selec-tively synthesized by linking [IrAu12(dppe)5(PA)1]2+ and[IrAu12(dppe)5]3+ by diisocyanide. The linkage of thesuperatoms with the predesigned coordination site(s) pro-posed here is superior to the conventional ligand-exchangeapproach in terms of the controllability of the length andFigure 4. (a) ESI mass spectra of the acetonitrile solutions of (IrPA12+)2L1 (red) and (IrPA12+)2(Ir3+)1L2 (blue). The insets compare the experimentaland simulated isotope patterns. (b) Absorption (black), photoluminescence (red; λex=415 nm), and excitation (blue; λem=615 nm) spectra of(IrPA12+)2L1 and (IrPA12+)2(Ir3+)1L2. (c)1H NMR (400 MHz) charts of (IrPA12+)2L1 (red) and (IrPA12+)2(Ir3+)1L2 (blue), which were measured inacetone-d6. The circles, squares, and triangles indicate the signals from dppe, PA, and L ligands, respectively. (d) Schematic illustration of (IrPA12+)2L1 and (IrPA12+)2(Ir3+)1L2. The yellow hexagons containing a blue circle represent the IrAu12 core.Figure 5. TEM image of (IrPA12+)2L1 on BNNT.AngewandteChemieResearch ArticlesAngew. Chem. Int. Ed. 2024, 63, e202402025 (5 of 6) © 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2024, 18, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202402025 by Cochrane Japan, Wiley Online Library on [18/04/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensedirection of the assembly. This study provides the basis forfabricating the exposed sites on Au CMSs for variousapplications, such as programable assembly and selectivecatalysis.AcknowledgementsWe thank Prof. Tomohiro Shiraki (Kyushu University) forproviding us with purified BNNT for the TEM observation,and Dr. Koji Kimoto (NIMS) for his assistance with the40 kV TEM observation. This research was financiallysupported by JST, CREST (Grant No. JPMJCR20B2) andby JSPS KAKENHI Grants (Nos. JP20H00370,JP23H00284, JP23H01917, and JP23H04874).Conflict of InterestThe authors declare no conflict of interest.Data Availability StatementThe data that support the findings of this study are availablefrom the corresponding author upon reasonable request.Keywords: ligand desorption reaction · phosphine-protectedgold superatoms · programmed assembly[1] R. Jin, C. Zeng, M. Zhou, Y. Chen, Chem. Rev. 2016, 116,10346–10413.[2] I. Chakraborty, T. Pradeep, Chem. Rev. 2017, 117, 8208–8271.[3] Y. Du, H. Sheng, D. Astruc, M. Zhu, Chem. Rev. 2020, 120,526–622.[4] S. Takano, T. Tsukuda, J. Am. Chem. Soc. 2021, 143, 1683–1698.[5] P. Chakraborty, A. Nag, A. Chakraborty, T. Pradeep, Acc.Chem. Res. 2019, 52, 2–11.[6] X. Kang, M. Zhu, Coord. Chem. Rev. 2019, 394, 1–38.[7] Z. Wu, Q. Yao, S. Zang, J. Xie, ACS Materials Lett. 2019, 1,237–248.[8] A. Ebina, S. Hossain, H. Horihata, S. Ozaki, S. Kato, T.Kawawaki, Y. Negishi, Nanomaterials 2020, 10. 1105.[9] Y. Saito, C. Murata, M. Sugiuchi, Y. 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