Introduction

Nature is capable of spontaneous association of multiple protein subunits into giant functional superstructures via precise biological self-organization protocols. One accessible and fascinating natural example is a virus capsid, which is the outer shell of a virus, comprising many non-covalently linked protein subunits that self-assemble into an icosahedral shell. The icosahedral design by natural systems has myriad advantages, including aesthetic appeal, high stability, and storage capacity, as well as minimal information coding requirements1. Inspired by this elegant biology, researchers have recently pursued self-organization through supramolecular interactions, such as metal-coordination bonds, to spontaneously fabricate multiple smaller subunits into larger artificial nanoconstruct, to mimic viral geometries2,3,4. In this regard, a few cases of icosahedral coordinative capsules have been successfully achieved5,6,7,8,9. By contrast, buckling well-defined H-bonded icosahedra is much more challenging, let alone gaining insights into assembled mechanism, in part due to the difficulty in manipulating relatively weak H-bonds compared with strong coordination covalent bonds. However, rational design protocols regarding icosahedral H-bonded assemblages are significant in that protein-protein interactions described above are mainly formed from many weak noncovalent interactions including hydrogen bonds.

Supramolecular ensembles are latterly possible with atom-precise coinage-metal (Cu/Ag/Au) clusters as attractive building blocks. These ultrasmall coinage-metal clusters represent a new category of crystalline materials, which typically consist of a metal core passivated by a ligand shell. That the library of protective ligands is extensive and affords diverse noncovalent contacts, which directs cluster-cluster assembly to create various well-defined superstructures10,11,12, including helical aggregates13,14,15,16 and hierarchical assemblies17,18,19,20. Nevertheless, without strong coordinate bonding linkages21,22,23,24, assembled cluster-based supramolecular systems are relatively fragile and easily collapsed architectures to polycrystallinity, particularly at high temperatures or after the removal of guest solvents, which has hampered the more extensive study of their potential applications. Additionally, programmed assembly of cluster tectons into sophisticated 3D superstructures and/or periodic zeolitic-like crystalline supramolecular networks, topologically similar to metal-organic frameworks (MOFs)25,26,27,28,29,30 but conferring a significant advantage of solution-processability, poses a formidable challenge. The main reason comes from the complexity of intercluster interactions, and/or the lack of suitable cluster modules and structure-directing forces.

Based on the above considerations, in this work, we report the discovery of cluster-based H-bonded pseudo icosahedral capsules Cu60 spontaneously formed through the assembly of cationic copper clusters and anions (PF6−), by means of 48 charge-assisted CH···F hydrogen bonds. The key geometric fragments of the icosahedron could be detected by cold-spray ionization mass spectrometry (CSI-MS), which provides insight into the underlying rules of multicomponent H-bonded assembly. Moreover, each intrinsic hollow icosahedral capsule is connected to six adjacent equivalent ones by edge-sharing to generate a robust three-periodic zeolitic-like supramolecular architecture with extrinsic helical channels, conferring thermal durability, and resistance to acids and bases. The resulting assembled 3D superstructure, referred to as cluster-based supramolecular frameworks (CSFs), gives a case of controlling assemblies of stable zeolitic-like cluster-based supramolecular solids without utilizing strong covalent and coordinate bonding linkage, and is an emerging link between coinage-metal clusters and hydrogen-bonded organic frameworks (HOFs).

Results

Synthesis and structural characterization of cluster-based tectons

Actively seeking accessible construction strategies to create 3D stable crystalline CSFs, our attention was initially captivated by robust HOFs materials, such as well-known HOF-1 that relies on the H-bonded assembly of purely organic tectons with tetrahedral geometry to form 3D crystalline networks31,32. Taking inspiration from structural characteristic feature of HOF-1 (Supplementary Fig. 1), we envisioned that harnessing tetrahedrally symmetric clusters as modular building blocks may facilitate building robust CSFs with distinctive topologies and architectures. To this end, we synthesized a tetrahedral copper cluster [Cu5L4((p-F-Ph)3P)4]PF6 (1) (where 2-mercapto-1-phenylimidazole = HL, and (p-F-Ph)3P = tris(4-fluorophenyl) phosphine) through reducing the copper salts with NaBH4 in the presence of HL and (p-F-Ph)3P under ambient conditions. The cluster structure of 1 was firstly elucidated by NMR spectroscopy, of which 1H NMR exhibits a set of shifted ligand signals (Supplementary Fig. 2), verifying the protection of the cluster surface by the mixed ligands. The precise mass and composition of 1 were further confirmed by electrospray ionization mass spectrometry (ESI-MS) in positive mode (Supplementary Fig. 3 and Supplementary Table 1). The parent cluster ion was found at the most dominant peak, m/z 2283.0142, which could be identified with isotopic envelopes corresponding to [Cu5L4((p-F-Ph)3P)4]+ (calc. m/z = 2283.0307). Density functional theory (DFT) optimized structure of [Cu5L4((p-F-Ph)3P)4]+, characterized as an energy minimum, was found to be of S4 symmetry (Supplementary Fig. 4), which agrees quite well with the X-ray structure (vide infra). TD-DFT calculated results match well with the experimental UV/Vis absorption spectrum of 1 measured in dichloromethane (CH2Cl2), which showed two major UV absorption bands at 358 and 368 nm and a tail up to about 400 nm (Supplementary Fig. 5), indicating the cluster retains intact in solution.

Colorless crystals of 1 suitable for X-ray crystallography were obtained by slow vapor diffusion of n-hexane into a concentrated CH2Cl2 solution of the corresponding cluster (PF6− salt) at ambient temperature. Microscopic image of single crystals, exhibit rhombic dodecahedra shape with twelve well-defined diamond facets (Fig. 1a). Single-crystal X-ray diffraction (SCXRD) analysis revealed that 1 crystallizes in the higher-symmetry cubic crystal system with the non-centrosymmetric space group \(P {\bar{4}}\) 3n (No. 218, Supplementary Table 2). Its overall composition contains a cationic cluster [Cu5L4((p-F-Ph)3P)4]+, as well as one PF6− counterion and interstitial CH2Cl2 molecules. As portrayed in Fig. 1b, the structural anatomy of [Cu5L4((p-F-Ph)3P)4]+ can be viewed as a Cu5 kernel wrapped by four peripheral (p-F-Ph)3P and four deprotonated L− ligands. The metal core adopts a centered tetrahedral geometry. The Cu-Cu bond length in the metal skeleton from the central Cu atom to the vertexes of the Cu4 tetrahedron is equal (2.655(1) Å), suggestive of the presence of significant intramolecular cuprophilic interactions. It is worthy of note that such a centered tetrahedral Cu5 skeleton is quite unusual, as a Cambridge Structural Database (CSD) search33 yielded previously reported some discrete Cu5 clusters featuring a planar conformation or a bipyramidal geometry (Fig. 1c)34,35. The center Cu atom is tetrahedrally bonded to all four L− molecules via four Cu-S bonds, while each terminal Cu atom in the Cu4 tetrahedron is tetrahedrally completed by two μ3-S atoms and one N atom from three different L− molecules plus one P atom from one (p-F-Ph)3P. Thus, the entire cationic cluster lies in a special position with S4 symmetry.

Fig. 1: Crystalline Cluster-based H-Bonded Icosahedral Capsule.
figure 1

a Dodecahedral rhombohedral crystal habit of 1, as observed by polarization microscope. b Crystal structure of [Cu5L4((p-F-Ph)3P)4]+. Color code: gray, C blue, N orange, P green, F yellow, S turquoise, Cu. c Previously reported Cu5 cores with a planar conformation or a bipyramidal geometry. d Arrangement of twelve copper clusters at the vertexes of the pseudo icosahedron. e Schematic representation of the pseudo icosahedron and its expansion surface. f Electrostatic potential (ESP) diagram of [Cu5L4((p-F-Ph)3P)4]+. g Charge-assisted C–H···F H-bonding patterns between PF6− and [Cu5L4((p-F-Ph)3P)4]+.

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Crystalline cluster-based H-bonded icosahedral assembly

Inspection of the rhombic dodecahedral crystal habit in the case of 1 is unexpected among crystalline forms of coinage metallic clusters, which is evocative of an example of icosahedral viruses crystallized into cubic crystals in a similar dodecahedral shape36. This inspire us to conjecture that extraordinary arrangement and packing of cluster tectons might exist. To our delight, the most attractive structural feature of 1 is that twelve molecular copper clusters per unit cell self-assemble into an enclosed approximately icosahedral capsule denoted as Cu60 (Fig. 1d) with an approximate diameter of 3.0 nm. The surface of the pseudo icosahedron contains two types of triangular faces (Fig. 1e): 8 equilateral triangles and 12 isosceles triangles, each equilateral triangle with side lengths of 16 Å (the centroid-centroid distances of two adjacent clusters) and each isosceles triangle with side and base lengths of 16 and 13 Å, respectively. It is worth noting that this is the only possible combinatorial outcome for the pseudo icosahedron buckled from these equilateral triangles and isosceles triangles, based on the ChatGPT prediction37. The internal hollow icosahedral capsule Cu60 could accommodate a sphere with a diameter of about 25 Å, corresponding to a sphere volume of ~8177 Å3. Our observation of the supramolecular icosahedral assembly that involves solid-state aggregation of individual clusters is intriguing. It was previously reported that atomically precise metal nanoclusters functionalized with capsid-targeting ligands which were used to label specific components of the surface of enteroviruses created icosahedral arrangement of clusters38,39. But once the absence of capsid-targeting ligands and without linking to the viral surfaces, cluster-based icosahedra are difficult to achieve. More importantly, the atomically accurate cluster-based icosahedral capsule will provide much more detailed information for further identifying the possible assembled origin of the icosahedron as the largest of the Platonic solids.

Figure 1f shows the electrostatic potential (ESP) mapped onto the electron isodensity surface of [Cu5L4((p-F-Ph)3P)4]+. It is calculated that the surface ESP is highly positive and may be strongly inclined to interact with negatively charged species (i.e., counter anions) to make supramolecular assemblages. As a result, PF6− counterions lie at the center of equilateral triangles of the icosahedron, wherein half fluoride atoms of each PF6− anion interact with three neighboring [Cu5L4((p-F-Ph)3P)4]+ clusters to form a supramolecular trimer (Fig. 1g). Each copper cluster located at the vertice of icosahedron could be visualized as two parts, a Cu(p-F-Ph)3P and a Cu3L4((p-F-Ph)3P)3 moiety, which points inside and outside the surface of icosahedral capsule, respectively. As illustrated in Fig. 1g, a closer inspection of the intermolecular contact patterns reveals each F atom of the PF6− participates in two H-bonds with two fluorobenzenes from two neighboring Cu(p-F-Ph)3P moieties by means of C–H···F charge-assisted hydrogen bonds (dH···F = 2.56–2.61 Å and θC-H···F = 127.3°–130.5°). These small H–F separations match well with previous studies of other fluorobenzenes in crystals40. In total, the icosahedral capsule is held together by way of 48 CH···F hydrogen bonds. Such cluster-based icosahedral H-bonded capsule Cu60 is reminiscent of copies of identical protein clusters assembled into icosahedral viral capsids. As mentioned at the outset, some discrete supramolecular coordinative icosahedral entities have been identified, such as molybdenum oxide cluster Mo1325 and metal-organic capsule Fe126,7. However, bonding energy for hydrogen bonds (25–40 kJ mol−1)41,42 is generally much smaller than those of coordinate covalent bonds (90–350 kJ mol−1)42, making well-defined H-bonded icosahedrons more challenging to assembly than their coordination counterparts. It is especially interesting to note the icosahedral Cu60 shows distinct trigonal types, which are different from those observed in the face-directed coordinative icosahedra. The trigonal panels of the former which are constructed from anions hydrogen-bonded to cationic clusters produce interesting C3-symmetric facial chirality (Fig. 1g), while the trigonal faces of the latter are generated from planar tritopic linkers coordination-bonded to metal acceptors (Supplementary Fig. 6)6,7. Additionally, from the view of capsule size, the diameter of the supramolecular H-bonding capsule Cu60 is 3.0 nm, making it comparable to that of the nanosized icosahedral Mo132 (2.9 nm).

CSI-MS characterization

To explore the disassembly behavior of the icosahedral nanoconstruct in solution, we carried out CSI-MS characterization, as a variant of ESI-MS operating at low temperature. The CSI-MS was measured by dissolving crystals of 1 in CH2Cl2, in which the ion source temperature is 0 °C. Positive-mode CSI-MS affords three sequentially charged ion species (2+ to 4+), centered at m/z 3497.526, 3903.006 and 4711.996, that we attributed to cluster-based H-bonded oligomers, including trimeric {[Cu5L4((p-F-Ph)3P)4]3·PF6}2+, pentameric {[Cu5L4((p-F-Ph)3P)4]5·(PF6)2}3+, and octameric {[Cu5L4((p-F-Ph)3P)4]8·(PF6)4}4+, respectively. The m/z values along with isotopic distribution patterns of each charge state closely match the simulated ones (Fig. 2), verifying the assignment. These H-bonded oligomers showcase the increasing cluster aggregations concomitant with the associated increase in anions PF6− present which bring discrete copper clusters together into the oligomers. The optimized H-bonded oligomeric structures (Supplementary Fig. 7) are quite similar to those observed in the crystallographic data. These H-bonded species are considered as key geometric fragments of the icosahedral units, which is primarily important to understand the mechanism of formation of the icosahedral capsules from this reaction system. Especially, the detection of the most dominant peak of the trimeric {[Cu5L4((p-F-Ph)3P)4]3·PF6}2+, is significant, which represents the basic trigonal unit of the icosahedron. CSI-MS results indicate that the charge-assisted CH···F contacts play a pivotal role in the assembly of copper clusters coupling with anions into identifiable H-bonded oligomers in solution, prior to crystallization.

Fig. 2: High-resolution CSI-MS characterization.
figure 2

Positive-mode CSI-MS of crystal 1 dissolved in CH2Cl2. Insets: selected cationic cluster-based H-bonded oligomers (2+, 3+, 4+, from left to right) with experimental (in blue) and simulated (in red) isotopic distributions.

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3D robust zeolitic-like CSFs

Fascinatingly, each pseudo icosahedral capsule―considered to be a supramolecular secondary building unit―connects with six other icosahedral ones through sharing bases of isosceles triangles of the pseudo icosahedron, thereby yielding an extended three-periodic zeolitic-like CSF (Fig. 3a), which sets it apart from HOFs and MOFs. Of note, topologically, if each discrete cluster is regarded as a 10-connected node, the whole architecture of the CSF is an unimodal 10-connected framework with the Schläfli symbol (315.423.55). When viewed in projection down the a axis, the intricate 3D CSF is seen to contain two types of 1D infinite channels (α and β). As illustrated in Fig. 3b, the α-type channel has a cross-section of 3.7 Å × 7.2 Å to which the phosphine moieties of clusters are exposed, and guest CH2Cl2 solvents are inside the channel. The β-type channel is formed with phenylimidazole arms of clusters and its channel cross-section is 7.0 Å × 7.0 Å. Surprisingly, in tunnel β, the clusters are arranged to form 1D spirals, with four clusters adopting different rotations per spiral of unit cell length. The spirals in turn are intertwined to give the two strands of an infinite double helix with the same right-handedness (Fig. 3c). The helical features of the double helix are defined by a pitch length of 5.2 nm and width of 3.6 nm. The entwined strands are stabilized by charge-assisted CH···F H-bonding interactions between the cationic clusters and anions. The tunnels alongside these double helices are filled with disordered CH2Cl2. The existence of guest molecules CH2Cl2 was also supported by 1H NMR (Supplementary Fig. 2). It is significant to observe that identical supramolecular double helices are produced along a, b, and c-axes, respectively, therefore producing unusual mutually perpendicular double helices in three dimensions (Fig. 3d). It is worth of noting that it is only recently that 1D double-helical self-assembly has been observed in the realm of coinage metallic clusters aggregates13,14,15,16. Hence, the superstructure of 1 contains another structural feature of double-stranded helicates which extend in three perpendicular directions, forming 3D orthogonal double-helical patterns, which is advocative of the assembly of double-stranded DNA into various nanostructures in different dimensions43,44,45.

Fig. 3: 3D zeolitic-like CSF before and after removal of solvates from channels.
figure 3

a 0D pseudo-icosahedron capsule and edge-sharing pseudo-icosahedron stacking for the formation of a 3D framework. b 3D robust zeolitic-like CSFs in 1 revealing two types of infinite channels (α and β), and 1 transformed by heat into 1-d with open channels (α′ and β′). c Double helix with each helix distinguished by red- or blue copper clusters. Inset: overlay of crystal structures of [Cu5L4((p-F-Ph)3P)4]+ in 1 and 1-d. d Schematic 3D orthogonal double-helical patterns.

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Despite the lack of strong metal-coordination bonds, it is the CSF, achieved by charge-assisted hydrogen bonds, that might exhibit improved stability because of the additional electrostatic attraction between the components46,47. To confirm the idea, we accessed the chemical durability of crystals of 1 in aqueous solutions with a broad pH range (pH 1–14). After solid 1 was soaked in the solutions above-mentioned for three days, there was no obvious difference in morphology and color (Supplementary Fig. 8). Crystals of 1 still retained their single crystallinity, enabling the SCXRD and their unit cell parameters are almost identical to that of as-synthesized 1. Moreover, the powder XRD (PXRD) patterns of the sample after prolonged treatment in acidic and basic conditions agree well with the simulated, suggesting that the integrity of the framework is preserved toward both acids and bases (Fig. 4a).

Fig. 4: The chemical and thermal stabilities of 1.
figure 4

a PXRD of 1 after the immersion in aqueous solution with a broad pH range (1–14) for 3 days. b TGA of crystals 1 and 1-d. c Variable-temperature PXRD of 1.

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Thermogravimetric analysis (TGA) profile (Fig. 4b) of freshly prepared crystals 1 showed the first continuous weight loss stepping from room temperature to ~170 °C corresponds to the loss of CH2Cl2 molecules. The superstructure of 1 began to decompose at a temperature higher than ~215 °C. To thoroughly understand the thermal robustness of the CSF of 1, we measured variable-temperature PXRD, which revealed that no phase transition or architecture collapse at elevated temperature range 30–200 °C (Fig. 4c). The PXRD results reflect an uncharacteristic robustness of the cluster-based H-bonded assembly even after removal of the occluded solvent molecules from channels, where many other noncovalent coinage-metal cluster-based frameworks would fail.

By slowly heating crystals of 1 to 170 °C under inert atmospheres or in vacuo, to our delight, 1 could be fully desolvated to obtain CH2Cl2-free crystals 1-d. The complete removal of guest CH2Cl2 was also confirmed by 1H NMR spectroscopy (Supplementary Fig. 2), where the chemical shift at 5.25 ppm corresponding to CH2Cl2 disappears completely after activation. The desolvated crystals 1-d exhibited high thermal stability with negligible weight loss occurred until ~215 °C (Fig. 4b). No significant loss of crystallinity was observed when the CH2Cl2 molecules were removed gently. The resultant crystals 1-d were successfully examined by X-ray crystallographic analysis, explicitly confirming the single-crystal-to-single-crystal transformation. 1-d retained the same \(P {\bar{4}}\) 3n space group (Supplementary Table 2) as 1, with shortened lattice parameters from 26.1645 Å for (1) to 25.8013 Å (1-d). The mechanical contraction of the network, with ~2% reduction of the initial unit cell volume, occurs without damaging the crystal upon the full removal of occluded CH2Cl2. The atomic resolution of SCXRD allows us to discern subtle variations in the CSF before and after heating. As displayed in Fig. 3b, the portal of open channel α′ in 1-d kept almost unchanged as observed in the original channel α in 1. Closer examination of channel β′ along the a-direction (Fig. 3c), however, revealed structural subtleties, wherein the chelating arrangement of the imidazole plane restricts its rotation, but a clear rotation of the phenyl group attached to the imidazole moiety partially blocks the portal of the open channel β′, resulting in the shrinkage of the resulted window size (4 Å × 4 Å). CO2 adsorption-desorption measurement for 1-d at 273 K showed a fully reversible type-I Langmuir profile (Supplementary Fig. 9), verifying the supramolecular architectural stability and permanent microporous characteristic of 1-d. Notably, the framework of 1-d can revert to its original architecture of 1 when simply recrystallized from CH2Cl2, featuring the structural dynamism and regeneration ability of the CSF.

Effect of ligand on the CSF

In general, the cluster-cluster interactions can be tailored via modification of the protective shield of ligands. For 1, due to the inductive effect associated with the fluorine atom at the para-position of benzene, the positively polarized surfaces of the fluorinated aromatics are prone to interact with electron-rich anions. We reasoned that substitution of the para-F atom with H atom may be expected to disrupt CH···F hydrogen bonds, further markedly affecting the structure and stability of the resulting CSFs. To verify this, we tried to synthesize another analog [Cu5L4(PPh3)4]PF6 (2), by replacing P(C6H4F)3 with triphenylphosphine (PPh3), under identical synthesis conditions. X-ray diffraction analysis at 173 K for a single crystal of 2 established that it occurs in the centrosymmetric tetragonal space group P4/ncc (No. 130, Supplementary Table 3) with the composition of [Cu5L4(PPh3)4]PF6·CH2Cl2, proved by ESI-MS (Supplementary Fig. 10 and Supplementary Table 4). As anticipated, the cationic cluster [Cu5L4(PPh3)4]+ is isostructural with [Cu5L4((p-F-Ph)3P)4]+. In comparison with 1, however, SCXRD revealed that 2 exhibits distinctly different cluster-based assembly behavior, whereby [Cu5L4(PPh3)4]+ clusters spontaneously organize into another 3D CSF. The topology of 2 can be described as a compressed pcu (primitive cubic) net with nodes defined as [Cu5L4(PPh3)4]+ clusters. The basic repeating unit of the 3D CSF contains a double cubane-like cage fused by two same compressed cubic supramolecular cages (Supplementary Fig. 11), of which each is formed by eight clusters through weak tecton-tecton contacts (i.e., weak CH···π and H···H interactions) (Supplementary Fig. 12). Interestingly, self-assembled hexafluorophosphate-dichloromethane anionic clusters of [PF6·(CH2Cl2)4]− are docked in the confined cavities of the double cubane-like cage, respectively. Structural characterization reveals that PF6− anion in the [PF6·(CH2Cl2)4]− only uses one fluoride atom as quadruple H-bond acceptors to bond with four CH2Cl2 molecules as single H-bond donor, thereby resulting in four weak nonconventional C–H···F hydrogen bonds (dH···F = 2.58 Å and θC-H···F = 144°). Strikingly, [PF6·(CH2Cl2)4]− has a C4 symmetry with a 4-fold axis passing through F-P-F of PF6−, thus producing two equivalent enantiomers, R-[PF6·(CH2Cl2)4]− and S-[PF6·(CH2Cl2)4]− (Supplementary Fig. 13). Notably, this is the structural evidence on chiral PF6−-CH2Cl2 solvated anionic clusters imprisoned in the supramolecular cage.

The calculated independent gradient model based on Hirshfeld partition (IGMH) analysis on the supramolecular species {[Cu5L4((p-F-Ph)3P)4]+·PF6−} indicates the apparent strong CH···F interactions in the green section occur between C–H groups of the fluorobenzene rings and F atoms from PF6− anion (Fig. 5a), which is crucial for the enhanced stability of the rigid supramolecular framework in 148,49,50. In contrast, 2 does not form the stable target {[Cu5L4(PPh3)4]+·PF6−} due to calculated negligible weak CH···F interactions between PF6− and phenyl rings (Fig. 5a). On the contrary, the PF6− in 2 has a high tendency to be solvated by CH2Cl2 molecules, leading to the formation of solvated anions as discussed above. With the above considerations in mind, we surmised that the absence of strong charge-assisted CH···F H-bonding interactions in 2 will make the CSF more labile. As anticipated, the crystals 2 are extremely fragile, quickly cracked, and lost its crystallinity after being taken out of the mother liquor.

Fig. 5: IGMH analysis and solid-state luminescence.
figure 5

a Noncovalent interactions analysis of {[Cu5L4((p-F-Ph)3P)4]+·PF6−} and {[Cu5L4(PPh3)4]+·PF6−}. Color code: gray, C blue, N yellow, S pink, P green, F turquoise, Cu. b Solid-state UV/vis diffuse-reflectance spectroscopy and temperature-dependent emission spectra from 80 to 290 K of 1. c Time-resolved emission decay at 510 nm of 1 (80 K). Inset shows the afterglow imaging of crystalline 1 observed at different time intervals before and after switching off the light excitation (365 nm) at 80 K.

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Solid-state optical and luminescence properties

Solid-state UV/Vis diffuse-reflectance spectroscopy of the crystalline sample of 1 displayed that it is transparent in the visible region of 400–800 nm (Fig. 5b). Subsequently, we investigated the steady-state photoluminescence (PL) spectra of 1 at room temperature, which presented a weak green emission band at around 547 nm upon excitation at 365 nm, with a substantial Stokes shift (~182 nm). Additionally, the temperature-dependent PL measurements were conducted from 300 to 80 K (Fig. 5b). The PL emission intensity is enhanced as the temperature changes from 300 to 80 K. A significant blue shift was observed from 547 to 510 nm with the temperature decrement. The increased emission intensity upon cooling is a typical phosphorescence characteristic owing to the effective reduction of nonradiative pathways at low temperature, whereas the 40-nm hypsochromic-shifted emission may be caused by the restriction of the rotation of the phenyl group attached to the imidazole moiety at low temperature. Remarkably, the time-resolved PL decay curve gave relatively long lifetimes of 13–16 ms at 80–170 K (Supplementary Table 5), and the green afterglow was visible to the naked eyes over 0.8 s after switching off the UV lamp (Fig. 5c). Both long emission lifetime (millisecond) and large Stokes shift in 1 suggest the green emission mechanism is phosphorescence-type, primarily emanating from a process involved ligand-to-metal charge transfer (LMCT) or ligand-to-metal-metal charge transfer (LMMCT)51,52,53. Of note, the millisecond-long emission with obvious afterglow in crystalline 1 surpasses other thiolate-protected luminescent copper clusters with microsecond lifetimes53,54,55,56, which are difficult to observe by the naked eyes after removing the light source.

Discussion

In summary, the results presented here demonstrate that the icosahedral H-bonded nanocapsules can be assembled from individual clusters featuring with tetrahedral metal cores and anions. These capsules further propagate through edge-sharing into a 3D zeolitic-like CSF, offering the distinct advantages of being both excellently chemically and thermally stable. This intrinsic stability can be ascribed to the multiple charge-assisted CH···F hydrogen bonds. This wholly cluster-based H-bonding framework expands the scope of complicated cluster-based supramolecular architectures and bridges the gap between coinage-metal clusters and HOFs. We expect that this finding can inspire future exploration of the uncovering zeolitic-like CSFs, which may in turn find applications in, for example, gas storage, separation processes, and catalysis.

Methods

Synthetic procedure for 1

3.0 mL CH2Cl2/CH3OH (v:v = 2:1) solution containing copper(II) trifluoroacetate hydrate (43.4 mg, 0.15 mmol) and tetrabutylammonium hexafluorophosphate (11.6 mg, 0.03 mmol) was stirred for 10 min, and then (p-F-Ph)3P (63.2 mg, 0.2 mmol) and 2-mercapto-1-phenylimidazole (35.0 mg, 0.2 mmol) were added under vigorous stirring. After stirring for another 15 min, a freshly prepared solution of NaBH4 (20.0 mg dissolved in 1.0 mL water) was added dropwise to the mixture under vigorous stirring. The reaction continued for 6 h at room temperature and aged at 4 °C for 12 h. Next, the aqueous phase was removed and the obtained organic phase was washed with water for several times. Finally, the resulted solution was centrifuged for 3 min at 10000 rpm min−1, and the red-brown solution was filtered. Dodecahedral rhombohedral colorless crystals of 1 were obtained via slow diffusion of n-hexane into the cluster solution after three days (20% yield based on Cu). Elemental analysis (%) calcd for C109H78S4P4F12N8Cl2Cu5: C 55.27, H 3.32, N 4.73; Found: C 54.84, H 3.15, N 4.42. High-resolution ESI-MS: m/z = 2283.0307 ([Cu5(C9H8N2S)4(P(C6H4F)3)4]+).

Synthetic procedure for 2

2 was synthesized by a similar procedure of 1, except PPh3 (52.6 mg, 0.2 mmol) instead of (p-F-Ph)3P. Block colorless crystals were obtained after four days (14% yield based on Cu). Elemental analysis (%) calcd for C108H88S4P5F6N8Cu5: C 58.62, H 4.01, N 5.06; Found: C 58.93, H 3.95, N 4.75. High-resolution ESI-MS: m/z = 2067.173 ([Cu5(C9H8N2S)4(P(C6H5)3)4]+).