Reactions of Platinum Carbonyl Chini Clusters with Ag (NHC) Cl

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Reactions of Platinum Carbonyl Chini Clusters with Ag(NHC)Cl Complexes: Formation of Acid−Base Lewis Adducts and Heteroleptic Clusters Marco Bortoluzzi,† Cristiana Cesari,‡ Iacopo Ciabatti,‡ Cristina Femoni,‡ Maria Carmela Iapalucci,‡ and Stefano Zacchini*,‡ †

Dipartimento di Scienze Molecolari e Nanosistemi, Ca’ Foscari University of Venice, Via Torino 155, 30175 Mestre, Venice, Italy Dipartimento di Chimica Industriale “Toso Montanari″, University of Bologna, Viale Risorgimento 4, I-40136 Bologna Italy

‡

S Supporting Information *

ABSTRACT: The reactions of anionic platinum carbonyl Chini clusters [Pt3n(CO)6n]2− [n = 2 (1), 3 (2), 4 (3)] with Ag(IPr)Cl [IPr = C3N2H2(C6H3iPr2)2] afford the neutral acid−base Lewis adducts [Pt9(CO)18(AgIPr)2] (4) and [Pt6(CO)12(AgIPr)2] (5). These are thermally transformed into the homometallic heteroleptic neutral cluster [Pt3(CO)4(IPr)2] (6). Alternatively, 6 can be obtained from the reactions of 1−3 with an excess of the free IPr carbene ligand. The formation of 6 is sometimes accompanied by trace amounts of [Pt4(CO)4(IPr)3] (7). The reaction of 6 with free IPr affords the closely related [Pt 3 (CO) 3 (IPr) 3 ] (8) heteroleptic cluster by substitution of the unique terminal CO ligand with a third IPr ligand. The reactions of 1−3 with Ag(IMes)Cl [IMes = C3N2H2(C6H2Me3)2] proceed differently from those involving Ag(IPr)Cl. Indeed, the only product isolated after workup is the bimetallic tetranuclear cluster [Pt3(CO)3(IMes)3(AgCl)] (9). 9 slowly reacts under a CO atmosphere, resulting in the pentanuclear [Pt5(CO)7(IMes)3] (10) complex. All of the new clusters 4−10 have been spectroscopically characterized and their molecular structures determined by Xray crystallography. 4 and 5 retain the original trigonal-prismatic structures of the parent anionic Chini clusters, which are capped by two [Ag(IPr)]+ moieties. Conversely, 6−9 are based on a Pt3 triangular core decorated by CO and N-heterocyclic carbene ligands as well as Pt(CO) (in the case of 7) and AgCl (9) moieties. 10 displays an edge-bridged tetrahedral geometry. Venanzi.24−26 Recently, the ability of the heteropleptic monomeric Chini-type [Pt3(CNR)3(μ-CO)3]2− [R = 2,6-(2,6(i-Pr)2C6H3)2C6H3] anion to add [Au(PCy3)]+ fragments has been demonstrated, affording the mono- and bicapped clusters [Pt 3 (CNR) 3 (μ-CO) 3 (AuPPh 3 )] − and [Pt 3 (CNR) 3 (μCO)3(AuPPh3)2].6 N-Heterocyclic carbenes (NHCs) are nowadays widely employed as ligands in inorganic, organometallic, and coordination chemistry and catalysis.27−32 Recently, their use for the stabilization of NPs and ultrasmall NPs has been investigated.33−36 In contrast, examples of molecular clusters containing NHC ligands are more scarce, and systematic studies have mainly been focused on ruthenium and osmium clusters.37−40 The inclusion of NHC ligands in the coordination sphere of carbonyl clusters of other transition metals and the use of higher nuclearity clusters and heterometallic clusters are some exciting aspects of this chemistry that have started to be investigated in the very recent years.37,40−42 A general approach for the synthesis of heterometallic CO/NHC clusters might be

1. INTRODUCTION Anionic platinum Chini clusters of the type [Pt3n(CO)6n]2− (n = 1−8) have represented a milestone in the chemistry of molecular clusters and metal carbonyls.1 They are composed of a stack of triangular Pt3 units and can interconvert by simple redox reactions,2 up to the formation of continuous chains and conductive wires.3−7 Chini clusters can be used as catalysts in themselves, or as precursors of heterogeneous catalysts, metal nanoparticles (NPs), and nanowires.8−13 Their thermal decomposition under milder conditions affords globular platinum nanoclusters,14−17 whereas their redox condensation with metal carbonyls and salts can lead to bimetallic clusters.18,19 We have recently reported the possibility to functionalize Chini clusters via CO substitution with miscellaneous phosphine ligands, affording heteroleptic analogues of Chini carbonyls.20,21 Theoretical models predict that anionic Chini clusters should behave as Lewis bases via their external triangular faces.22 Nonetheless, the only acid−base Lewis adduct of anionic Chini clusters reported to date is [Pt9(CO)18(μ3-CdCl2)2]2−.23 Conversely, the Lewis base donor ability of the neutral Pt3L3(μ-CO)3 and Pt3L4(μ-CO)3 clusters (L = phosphine) were discovered and exploited by Imhof and © XXXX American Chemical Society

Received: March 13, 2017

A

DOI: 10.1021/acs.inorgchem.7b00665 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry represented by the reaction of preformed metal carbonyl clusters with M(NHC)X complexes (M = Cu, Ag, Au; X = Cl, Ph), as was recently described in a few papers.43−46 Herein we report on the reactions of [Pt3n(CO)6n]2− clusters [n = 2 (1), 3 (2), 4 (3)] with Ag(NHC)Cl [NHC = C3N2H2(C6H3iPr2)2 (IPr), C3N2H2(C6H2Me3)2 (IMes)] complexes as well as free NHC ligands. These afford new bimetallic platinum−silver and homometallic platinum carbonyl clusters containing NHC ligands.

2. RESULTS AND DISCUSSION 2.1. Synthesis, Spectroscopic, and Structural Characterization of [Pt9(CO)18(AgIPr)2] (4) and [Pt6(CO)12(AgIPr)2] (5). [Pt9(CO)18]2− (2) reacts with a slight excess of Ag(IPr)Cl, affording the neutral adduct 4 as the major product (Scheme 1). With a further increase in the amount of Scheme 1. Synthesis of 4 and 5 Figure 1. (a) Molecular structure of 4 and (b) its space-filling model (color legend: Pt, purple; Ag, yellow; N, blue; O, red; C, gray; H, white).

Ag(IPr)Cl, 5 is formed in a mixture with 4. The two clusters can be separated because of the greater solubility of 5 in toluene, whereas 4 is then extracted in CH2Cl2. Moreover, pure 5 can be more conveniently obtained from the direct reaction of [Pt6(CO)12]2− (1) with an excess of Ag(IPr)Cl. In contrast, the reaction of [Pt12(CO)24]2− (3) with Ag(IPr)Cl does not afford the purported [Pt12(CO)24(AgIPr)2]. Conversely, a mixture of 4 and 5 is formed, whose composition depends on the amount of silver carbene complex employed (Scheme 1). The addition of Ag(IPr)Cl as well as free IPr to a solution of 4 results in the formation of 5. It is worth noting that 1 and 2 do not react with stoichiometric amounts of Ag(IPr)Cl and formation of the adducts 4 and 5 always requires an excess of Ag(IPr)Cl. Both bimetallic platinum−silver adducts have been spectroscopically characterized by means of IR and 1H and 13C NMR spectroscopies and their molecular structures determined via single-crystal X-ray diffractometry as their 4·C5H12· 0.5toluene, 4·2CH2Cl2, and 5·2CH2Cl2 solvated solids. 4 and 5 consist of neutral Lewis acid−base adducts between the parent trigonal-prismatic 2 and 1 anions, respectively, and two μ3-[AgIPr]+ groups (Figures 1 and 2). The [Pt9(CO)18]2− and [Pt6(CO)12]2− moieties retain the original structures of 2 and 1, consisting of three and two stacked Pt3(CO)3(μ-CO)3 units, respectively. The intratriangle Pt−Pt bonds (see Table 1) are considerably shorter than the interlayer Pt−Pt contacts, as found in the parent clusters and the closely related [Pt9(CO)18(μ3-CdCl2)2]2−.23 The two external triangular faces of the distorted trigonal-prismatic [Pt3n(CO)6n]2− (n = 2, 3) moiety are capped by two Ag atoms, with Pt−Ag distances comprised of a very narrow range (see Table 1). 4 and 5 represent the first examples of adducts between anionic Chini clusters and [AgL]+ moieties and the second acid−base Lewis adducts involving anionic Chini clusters.23 Conversely, several derivatives of the neutral Pt3L3(μ-CO)3 and Pt3L4(μ-CO)3 clusters (L = phosphine) with Lewis acids are

Figure 2. (a) Molecular structure of 5 and (b) its space-filling model (color legend: Pt, purple; Ag, yellow; N, blue; O, red; C, gray; H, white).

known.24−26,47−49 A few examples of such adducts containing silver have been also reported, including [{Pt3(PiPr3)3(μCO) 3 } 2 Ag] + , 50 [Pt 3 (PPh 3 ) 4 (μ-CO) 3 (AgPPh 3 )] + , 51 and [Pt3(PCy3)2(dppp)(μ-CO)3(AgO3SCF3)] [dppp = 1,3-bis(diphenylphosphino)propane].52 The Ag(IPr) complexes 4 and 5 are also related to the mono- and bicapped Au(PCy3) Chini-type clusters [Pt3(CNR)3(μ-CO)3(AuPPh3)]− and [Pt 3 (CNR) 3 (μ-CO) 3 (AuPPh 3 ) 2 ] [R = 2,6-(2,6-(iPr)2C6H3)2C6H3],6 except that 4 and 5 are in oligomeric and homoleptic forms, whereas the isocyanide derivatives are monomeric and heteroleptic. The IR spectra of 4 (2059 and 1869 cm−1) and 5 (2040 and 1857 cm−1) display ν(CO) bands for the terminal and bridging carbonyls at higher wavenumbers compared to the parent 2 (2030 and 1840 cm−1) and 1 (1995 and 1795 cm−1) in accordance with the formation of neutral adducts of the parent B


Article

Inorganic Chemistry Table 1. Main Bond Distances (Å) of 4 and 5 Pt−Pt (intratriangle) Pt−Pt (intertriangle) Pt−Ag Ag−C a

4a

4b

5c

2.6590(7)−2.6716(7) average 2.667(2) 2.9631(7)−3.0191(7) average 2.9965(17) 2.8071(10)−2.8962(11) average 2.853(3) 2.096(12) and 2.124(13)

2.6513(12)−2.6688(12) average 2.656(4) 2.9930(12)−3.0328(12) average 3.005(3) 2.8260(19)−2.863(2) average 2.844(5) 2.07(2) and 2.14(2)

2.652(3)−2.672(3) average 2.66(2) 2.938(2)−3.014(2) average 2.977(10) 2.795(4)−2.888(4) average 2.84(3) 2.050(19)−2.142(18) average 2.09(8)

As found in 4·C5H12·0.5toluene. bAs found in 4·2CH2Cl2. cHeight-independent molecules are present in the unit cell.

required or how 4 is transformed into 5 upon the further addition of Ag(IPr)Cl. Therefore, more complicated mechanistic pathways cannot be excluded. 2.2. Synthesis, Spectroscopic, and Structural Characterization of [Pt3(CO)4(IPr)2] (6), [Pt4(CO)4(IPr)3] (7), and [Pt3(CO)3(IPr)3] (8). 4 and 5 are stable in solution under N2, CO, and H2 atmospheres at room temperature. Conversely, after refluxing in CH2Cl2 under a N2 atmosphere, they are converted into the homometallic heteroleptic neutral cluster 6 (Scheme 3). Alternatively, 6 can be obtained by reacting 1 or 2 with an excess of the free IPr carbene ligand.

anionic Chini clusters. The two IPr ligands of both 4 and 5 show a unique set of resonances in the 1H and 13C NMR spectra, in accordance with their solid-state structures. The carbene C atoms resonate at very similar chemical shifts and display a direct coupling to Ag [δC 184.2, 1JC−Ag = 270 (109Ag) and 234 (107Ag) Hz for 4; δC 191.2, 1JC−Ag = 272 (109Ag) and 230 (107Ag) Hz for 5]. In the CO region, the 13C NMR spectrum of 5 (enriched with 13CO) displays two sets of resonances in a 1:1 ratio due to the six μ-CO (δC 213.6, 1JC−Pt = 658 Hz) and six t-CO (δC 197.9, 1JC−Pt = 2242 Hz, 2JC−Pt = 186 Hz), which are bonded to two equivalent Pt3 triangles (Scheme 2). Conversely, 4 displays four resonances in the CO region of

Scheme 3. Synthesis of 6−8

Scheme 2. Schematic Representation of 4 and 5

Formation of 6 from 4 and 5 may be viewed as an oxidative transmetalation, where the IPr carbene ligand is transferred from silver to platinum with concomitant oxidation of platinum (formally from −2/9 in 4 and −2/6 in 5 to 0 in 6) and reduction of silver(I) to silver(0). Indeed, a silver mirror was observed at the end of the reaction. Part of the platinum is also lost as platinum metal. This should be contrasted with other transmetalation reactions involving Ag(NHC)Cl, in which the NHC is transferred from silver(I) to a metal ion or atom, without a concomitant redox reaction.27−32,43−46 In this respect, 4 and 5 are intermediates in the oxidative transmetalation process, which occurs after thermal treatment. 6 consists of a Pt3 triangle bonded to three μ-CO, one terminal CO, and two IPr ligands (Figure 3 and Table 2). Its structure is closely related to previously reported Pt3L3(μ-CO)3 clusters53,54 as well as [Pd3(CO)3(IMes)3]42 and Pt2Ru(CO)6(IMes)2.40c The IR spectrum of 6 recorded in a CH2Cl2 solution displays ν(CO) bands attributable to t-CO (2013 cm−1) and μ-CO (1823 and 1792 cm−1) ligands. The NMR data in solution are in keeping with the solid-state structure of 6, displaying two equivalent IPr ligands, one terminal CO, and two types of μ-CO in the ratio 1:2. In

the 13 C NMR spectrum, attributable to the two external Pt3(μCO)3(CO)3 triangles (Pta in Scheme 2; δC 208.7, 6 μ-CO, 1 JC−Pt = 675 Hz; δC 194.9, 6 t-CO, 1JC−Pt = 2284 Hz, 2JC−Pt = 192 Hz) and the internal one (Ptb in Scheme 2; δC 208.8, 3 μCO, 1JC−Pt = 662 Hz; δC 194.3, 3 t-CO, 1JC−Pt = 2148 Hz, 2JC−Pt = 218 Hz). The coupling patterns are comparable to those observed for the parent clusters 1 and 2. The formation of 4 and 5 may be formally viewed as the addition of two electrophilic [Ag(IPr)]+ cationic fragments to the external triangular faces of the homoleptic and homometallic Chini clusters 1 and 2. Nonetheless, this hypothesis does not explain why an excess of Ag(IPr)Cl is C


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Inorganic Chemistry

cluster possessing 54 cluster valence electrons.57 7 may be viewed also as an adduct between the Pt3(μ-CO)3(IPr)3 cluster (8; see below) and a Pt(CO) fragment. The reaction of 6 with free IPr affords the closely related 8 heteroleptic cluster by substitution of the unique terminal CO ligand with a third IPr ligand. The formation of 8 is likely to proceed through an associative mechanism with the formation of a [Pt3(CO)4(IPr)3] intermediate followed by CO elimination. Indeed, both related [Pt 3 (CO) 3 (PR 3 ) 3 ] and [Pt 3 (CO) 3 (PR 3 ) 4 ] derivatives were previously described.24−26,47−49,53,54 The molecular structure of 8 (Figure 5 and Table 2) is reminiscent of those previously reported for the phosphine derivatives [Pt3(CO)3(PR3)3] and the palladium analogue [Pd3(CO)3(IMes)3].42,53,54 8 displays a unique ν(CO) band at 1763 cm−1 in toluene attributable to the three equivalent μ-CO ligands, indicating that the structure shown in the solid state is retained in solution. Similarly, both 1H and 13C NMR spectra display a single set of resonances for the three equivalent IPr ligands. 2.3. Synthesis, Spectroscopic, and Structural Characterization of [Pt 3 (CO) 3 (IMes) 3 (AgCl)] (9) and [Pt5(CO)7(IMes)3] (10). The reactions of 1−3 with Ag(IMes)Cl proceed differently from those involving Ag(IPr)Cl. Indeed, the only product isolated after workup is the bimetallic tetranuclear cluster 9 (Scheme 5). Thus, in this case, there is no evidence for the formation of acid−base Lewis adducts between the anionic Chini clusters and the [Ag(IMes)]+ fragments. It might be that, even if formed, such adducts are not stable in the presence of IMes instead of IPr and, thus, they rapidly decompose, leading to 9. It is worth noting that 9 resembles 8 apart from the presence of a AgCl additional fragment, which probably arises from the transmetalation reaction involving Ag(IMes)Cl. Surprisingly, 1−3 do not react with free IMes, even if employed in large excess. It must be remarked that, as in the case of the reactions of 1 and 2 with Ag(IPr)Cl (section 2.1), also those involving Ag(IMes)Cl require an excess of the silver carbene reagent, whereas no reaction was observed by employing stoichiometric amounts of it. The molecular structure of 9 (Figure 6 and Table 3) was determined by single-crystal X-ray diffractometry as both its 9· 1.5CH2Cl2 and 9·0.5toluene solvates. It consists of a tetrahedral Pt3Ag metal core and can be described as an adduct between the triangular Pt3(μ-CO)3(IMes)3 cluster and a AgCl moiety (Scheme 6). Therefore, it is closely related to the species 7 and 8 described in the previous section. The IR spectrum of 9 shows a single ν(CO) band at 1784 cm−1 in toluene attributable to the three equivalent μ-CO ligands. The three IMes ligands display a single set of


particular, the carbene C atom resonates at δC 198.8 (1JC−Pt = 1754 Hz and 2 J C−Pt = 145 Hz). The unique μ-CO symmetrically bridging the Ptb−Ptb edge (Scheme 4) resonates at δC 258.9 and displays an identical coupling (1JC−Pt= 740 Hz) to the equivalent Ptb atoms. Conversely, the two equivalent μCO ligands bridging the Pta−Ptb edges resonate at δC 248.3 and display two different coupling constants to Ptb (1JC−Pt = 914 Hz) and Pta (1JC−Pt = 484 Hz). This indicates asymmetric coordination of μ-CO to the two Pt atoms, as previously found in analogous polynuclear platinum carbonyl compounds55,56 and in agreement with the solid-state structure of 6. Thus, the larger 1JPt−C values correspond to shorter Ptb−C(O) bonds [2.017(11)−2.033(4) A] and the smaller ones to longer Pta− C(O) bonds [2.116(11)−2.150(11) A]. The unique t-CO ligand displays a resonance at δC 206.8 with the expected coupling pattern (1JC−Pt = 1966 Hz and 2JC−Pt = 132 Hz). As shown in Scheme 3, the formation of 6 is sometimes accompanied by trace amounts of 7. Only a few crystals of 7 as its 7·C5H12 solvate have been obtained, which allowed its structural and IR spectroscopic characterization. 7 displays ν(CO) bands as a solid in a Nujol mull at 1935, 1852, and 1786 cm−1. The crystals dissolved in CH2Cl2 show ν(CO) bands at 1934, 1853, and 1788 cm−1, in accordance with the solid-state structure that shows one terminal and three edge-bridging CO ligands (Figure 4 and Table 2). The cluster displays a tetrahedral structure as expected for a tetranuclear platinum Table 2. Main Bond Distances (Å) of 6−8 Pta−Ptb Ptb−Ptb Ptb−Ccarbene Pta−COterminal Pta−CObridging Ptb−CObridging (ab)a Ptb−CObridging (bb)b

a

6

7

8

2.6597(11) and 2.6700(11) 2.6620(14) 2.033(10) and 2.036(10) 1.871(10) 2.116(11) and 2.150(11) 2.017(11) and 2.032(11) 2.039(12) and 2.055(10)

2.7369(8), 2.7338(8), and 2.7485(8) 2.6845(8), 2.6864(8), and 2.6919(8) 1.971(17), 1.987(15), and 2.010(14) 1.719(16)

2.6417(7), 2.6447(7), and 2.6491(7) 2.016(12), 2.022(13), and 2.038(12)

1.983(16)−2.051(16) average 2.01(4)

2.040(12)−2.105(13) average 2.07(3)

CO bridging the Pta−Ptb edge. bCO bridging the Ptb−Ptb edge. D


Article

Inorganic Chemistry Scheme 4. Schematic Representations of 6−8



111 Hz) as well as a small residual coupling to silver (2JC−Ag = 10 Hz). The mechanism leading to the formation of 9 starting from clusters 1 and 2 and Ag(IMes)Cl is not clear. The first step might be the formation of the purported [Pt9(CO)18(AgIMes)2] and [Pt6(CO)12(AgIMes)2] adducts closely related to 4 and 5. The following step should involve the cluster oxidation and ligand transmetalation, with formation of a platinum(0)-containing “Pt3(μ-CO)3” fragment that is saturated by three IMes ligands. In turn, the resulting (and not observed) [Pt3(CO)3(IMes)3] heteroleptic cluster acts as a Lewis base adding the AgCl Lewis acid. This last reaction is reminiscent of analogous reactions previously observed in the case of the neutral Pt3L3(μ-CO)3 and Pt3L4(μ-CO)3 clusters (L = phosphine).24−26,47−52 9 slowly reacts under a CO atmosphere, resulting in the pentanuclear 10 complex. 10 displays an edge-bridged tetrahedral structure (Figure 7) coordinated to three IMes, two terminal, and five μ-CO ligands. 10 is isostructural and isoelectronic with CO/phosphine clusters of the type [Pt5(CO)6L4] (L = monodentate phosphine) previously described in the literature.58,59 2.4. Density Functional Theory (DFT) Calculations. DFT ωB97X calculations have been carried out on the experimental geometries of platinum−silver compounds 4, 5, and 9, replacing the N-bonded substituents of the NHC ligands with methyl groups for ease of calculation (the substitution is highlighted in the numbering of the compounds below). As reported in Figure S1, these clusters are characterized by quite high highest occupied molecular orbital (HOMO)−lowest


Scheme 5. Synthesis of 9 and 10

resonances in the 1H and 13C NMR spectra, indicating their equivalence in solution. The carbene C atoms resonate δC 196.4 and display the usual coupling pattern for a terminal ligand bonded to a Pt3 triangle (1JC−Pt = 1024 Hz and 2JC−Pt = E


Article

Inorganic Chemistry Table 3. Main Bond Distances (Å) of 9 and 10 (See Scheme 6 for Labeling) Ptb−Ptb Pta−Ptb Pta−Ptc Pta−Ptd Ptb−Ptc Ptb−Ptd Ptb−Pte Ptc−Ptd Ptc−Pte Ptb−Ag Pt−Ccarbene Pt−COterminal Pt−CObridging a

9a

9b

2.6422(3)−2.6588(2) average 2.6504(5)

2.6524(4)−2.6634(4) average 2.6566(10)

10

2.7996(17) 2.8765(19) 2.6720(17) 2.7602(19) 2.7685(19) 2.6777(18) 2.9274(17) 2.6767(18) 2.7945(4)−2.8261(4) average 2.8134(7) 2.009(5)−2.013(5) average 2.011(9)

2.7863(7)−2.8086(6) average 2.7992(15) 2.006(8)−2.022(8) average 2.01(2)

2.063(5)−2.079(5) average 2.071(12)

2.046(8)−2.079(8) average 2.06(3)

2.00(3)−2.02(3) average 2.01(5) 1.82(3) and 1.87(3) 1.90(4)−2.47(4) average 2.06(13)

As found in 9·1.5CH2Cl2. bAs found in 9·0.5toluene. Two independent molecules are present in the unit cell.

Scheme 6. Schematic Representations of 9 and 10

close to the bonding π orbitals of the NHC rings. HOMO−61 and HOMO−60 (ε = −14.07 and −13.81 eV, respectively) are at the basis of the strongest interactions in 4Me, and HOMO− 46 and HOMO−45 play the same role in 5Me (ε = −13.91 and −13.70 eV, respectively). These MOs are depicted in Figure 8, and the overlap among d-type functions localized on the metal centers is evident. Hirshfeld population analysis attributes about 0.405 au of positive charge to each [Ag(NHC)] fragment of 4Me, highlighting the Lewis acidic behavior toward the anionic platinum carbonyl core. Very similar results have been obtained from the charge distribution of 5Me. The tendency of silver-based fragments to attract electron density from platinum cores is confirmed by the charge distribution computed for the Pt3Ag cluster 9Me, with −0.402 au being the value calculated for the [AgCl] fragment. A negative Hirshfeld partial charge was also obtained for the [Pt(CO)] fragment of the comparable Pt4 tetrahedral complex 7Me, but the absolute value is lower (−0.250 au). Delocalization of the electron density from the [Pt3(CO)3(NHC)3] cluster to [AgCl] in 9Me and, to a lesser extent, to [Pt(CO)] in 7Me causes a meaningful lowering of the frontier orbital energy, as is observable from a comparison of the MOs of 7Me, 8Me, and 9Me in Figure S1. The HOMOs of these three species are, however, comparable and mainly account for Pt−μ-CO overlaps. The occupied MOs of 9Me most involved in the Pt−Ag bonds are


unoccupied molecular orbital (LUMO) energy gaps, from 5.92 to 7.28 eV, values comparable to those obtained for the other new compounds described in this paper. The high-energy occupied molecular orbitals (MOs) of the heterometallic clusters 4Me and 5Me scarcely participate in the formation of Ag−Pt bonds. The most important Pt−Ag σ overlaps involve orbitals with quite low energy, about 8 eV below the HOMO, F


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Inorganic Chemistry

Figure 8. Selected MOs of 4Me and 5Me involved in Pt−Ag bonds (color legend: Pt, purple; Ag, yellow; N, blue; O, red; C, gray; H, white). Surface isovalue = 0.03 au.

HOMO−8 (ε = −8.48 eV) and HOMO−14 (ε = −9.75 eV), depicted in Figure 9. Probably because of the formal neutral

platinum−silver and homometallic platinum carbonyl clusters containing NHC ligands. The outcome of these reactions strongly depends of the nature of the NHC ligand employed. Thus, in the case of IPr, the Lewis acid−base bimetallic adducts 4 and 5 have been obtained. These retain the trigonal-prismatic structure and stereochemistry of the CO ligands of the parent Chini clusters, which are capped by two [Ag(IPr)]+ moieties. Conversely, by employment of IMes, the bimetallic tetranuclear cluster 9 is formed, which implies partial degradation and rearrangement of the original Chini clusters. The reactivity of 4, 5, and 9 has been investigated, allowing isolation of the new species 6−8 and 10. 4 and 5 represent rare cases of Lewis acid−base adducts involving intact Chini clusters, with [Pt9(CO)18(μ3-CdCl2)2]2− being the only example reported in the literature prior to this work.23 This may be explained on the basis of the fact that anionic Chini clusters usually prefer other reactions, such as redox and substitution reactions, as well as redox and thermal condensation reactions.1−23 It is likely that the very bulky IPr ligand is able to stabilize these acid−base adducts, which rearrange only after thermal treatment. This is not the case of the less sterically demanding IMes, which directly affords lowernuclearity clusters, through a rearrangement/degradation process. The mechanism leading to formation of the heteroleptic neutral complexes 6−9 starting from the anionic Chini clusters 1 and 2, as well as their platinum−silver adducts 4 and 5, is not clear. It might be described as an oxidative transmetalation because it should involve cluster oxidation and ligand transmetalation. Indeed, platinum displays a formal negative oxidation state in 1−5, whereas its oxidation state is zero in 6− 9. The oxidation process is accompanied by transmetalation because the NHC ligand is transferred from silver to platinum. Overall, the reactions described herein allow the preparation of heteroleptic CO/NHC platinum and platinum−silver clusters with nuclearities ranging from 3 to 11 metal atoms. These reactions add to the rich chemistry displayed by Chini clusters and confirm their versatility as starting materials for the preparation of new molecular nanoclusters, bimetallic and functionalized platinum-based clusters, nanoparticles, and nanowires.1−23

Figure 9. Selected MOs of 9Me involved in Pt−Ag bonds (color legend: Pt, purple; Ag, yellow; N, blue; Cl, green; O, red; C, gray; H, white). Surface isovalue = 0.03 au.

charge of the [AgCl] fragment, these two orbitals lie much closer to the frontier with respect to those describing the Pt− Ag bonds in the Ag(NHC) platinum derivatives, being respectively about 1.11 and 2.34 eV below the HOMO. The electron densities on the Pt−Pt−Ag planes of 4Me, 5Me, and 9Me are compared in Figure 10. The properties at the Pt− Ag bond critical points are very similar, with an electron density of around 0.04 au and electron localization function values between 0.17 and 0.18. Also, the relative position of the bond critical points with respect to the attractors is almost constant. All of these data suggest comparable Pt−Ag bonds in the three heterometallic clusters reported here.

3. CONCLUSIONS The reactions of anionic platinum Chini clusters 1−3 with Ag(NHC)Cl (NHC = IPr, IMes) afforded new bimetallic G


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Inorganic Chemistry

Figure 10. Electron density on the Pt−Pt−Ag planes of 4Me, 5Me, and 9Me with gradient lines. Pt−Ag bond critical points are highlighted in blue. m-CHAr), 7.31 (d, 4JH−Ag = 2 Hz, 4H, CHimid), 2.59 (sept, 3JHH = 8 Hz, 8H, CH(CH3)2), 1.27 (d, 3JHH = 8 Hz, 24H, CH(CH3)2), 1.18 (d, 3 JHH = 8 Hz, 24H, CH(CH3)2). 13C{1H} NMR (CD2Cl2, 298 K): δ 208.8 (3 μ-CO, 1JC−Pt = 662 Hz), 208.7 (6 μ-CO, 1JC−Pt = 675 Hz), 194.9 (6 t-CO, 1JC−Pt= 2284 Hz, 2JC−Pt = 192 Hz), 194.3 (3 t-CO, 1 JC−Pt = 2148 Hz, 2JC−Pt = 218 Hz), 184.2 (C−Ag, 1JC−Ag = 270 and 234 Hz), 145.7, 134.6, 130.5, 124.2 (CAr), 123.9 (CHimid, 3JC−Ag = 7 Hz), 28.6 (CH(CH3)2), 24.4, 23.7 (CH(CH3)2). 4.3. Synthesis of 5·2CH2Cl2. A solution of Ag(IPr)Cl (1.82 g, 3.42 mmol) in acetone (10 mL) was added to a solution of [NEt4]2[Pt6(CO)12] (0.85 g, 0.48 mmol) in acetone (20 mL) over a period of 1 h. The resulting mixture was stirred at room temperature for 1 h and then the solvent removed in vacuo. The residue was extracted with toluene (20 mL). After filtration, the toluene was removed under vacuum and the residue dissolved in CH2Cl2 (15 mL). Crystals of 5·2CH2Cl2 suitable for X-ray analyses were obtained by layering n-pentane (30 mL) on the CH2Cl2 solution (yield 0.65 g, 51% based on platinum). Elem anal. Calcd for C68H76Ag2Cl4N4O12Pt6 (2669.37): C, 30.60; H, 2.87; N, 2.10; Ag, 8.08; Pt, 43.85. Found: C, 30.42; H, 3.11; N, 1.87; Ag, 7.89; Pt, 43.96. IR (Nujol, 293 K): ν(CO) 2041, 1850 cm−1. IR (toluene, 293 K): ν(CO) 2040, 1857 cm−1. 1H NMR (CD2Cl2, 298 K): δ 7.48 (t, 3JH−H = 8 Hz, 4H, p-CHAr), 7.15 (d, 3JH−H = 8 Hz, 8H, m-CHAr), 7.06 (d, 4JH−Ag = 1 Hz, 4H, CHimid), 2.25 (sept, 3JHH = 8 Hz, 8H, CH(CH3)2), 1.05 (d, 3JHH = 8 Hz, 24H, CH(CH3)2), 0.79 (d, 3 JHH = 8 Hz, 24H, CH(CH3)2). 13C{1H} NMR (CD2Cl2, 298 K): δ 213.6 (μ-CO, 1JC−Pt = 658 Hz), 197.9 (t-CO, 1JC−Pt = 2242 Hz, 2JC−Pt = 186 Hz), 191.2 (C−Ag, 1JC−Ag = 272 and 230 Hz), 145.2, 138.7, 130.7, 124.3 (CAr), 124.7 (CHimid), 28.5 (CH(CH3)2), 24.3, 23.7 (CH(CH3)2).

4. EXPERIMENTAL SECTION 4.1. General Procedures. All reactions and sample manipulations were carried out using standard Schlenk techniques under a N2 atmosphere and in dried solvents. All of the reagents were commercial products (Aldrich) of the highest purity available and were used as received, except [NEt4]2[Pt6(CO)12], [NEt4]2[Pt9(CO)18],1 Ag(IPr)Cl, and Ag(IMes)Cl,60 which have been prepared according to the literature. Analyses of platinum and silver were performed by atomic absorption on a Pye-Unicam instrument. Analyses of carbon, hydrogen, and nitrogen were obtained with a Thermo Quest Flash EA 1112NC instrument. IR spectra were recorded on a PerkinElmer Spectrum One interferometer in CaF2 cells. 1H and 13C NMR measurements were performed on a Varian Mercury Plus 400 MHz instrument. The proton and carbon chemical shifts were referenced to the nondeuterated aliquot of the solvent. Structure drawings have been performed with SCHAKAL99.61 4.2. Synthesis of 4·2CH2Cl2. A solution of Ag(IPr)Cl (1.82 g, 3.42 mmol) in acetone (10 mL) was added to a solution of [NEt4]2[Pt9(CO)18] (1.16 g, 0.46 mmol) in acetone (20 mL) over a period of 1 h. The resulting mixture was stirred at room temperature for 1 h and then the solvent removed in vacuo. The residue was washed with toluene (20 mL), dried under vacuum, and extracted with CH2Cl2 (20 mL). Crystals of 4·2CH2Cl2 suitable for X-ray analyses were obtained by layering n-pentane (40 mL) on the CH2Cl2 solution (yield 0.71 g, 45% based on platinum). Similarly, crystals of 4·C5H12· 0.5toluene were obtained from toluene/n-pentane. Elem anal. Calcd for C74H76Ag2Cl4N4O18Pt9 (3422.74): C, 25.97; H, 2.24; N, 1.64; Ag, 6.30; Pt, 51.30. Found: C, 26.11; H, 2.08; N, 1.47; Ag, 6.56; Pt, 51.11. IR (Nujol, 293 K): ν(CO) 2048, 1866 cm−1. IR (CH2Cl2, 293 K): ν(CO) 2059, 1869 cm−1. 1H NMR (CD2Cl2, 298 K): δ 7.54 (t, 3JH−H = 8 Hz, 4H, p-CHAr), 7.35 (d, 3JH−H = 8 Hz, 8H, H


Article

Inorganic Chemistry 4.4. Synthesis of 6·3CH2Cl2. A. ) From 4·2CH2Cl2. A solution of 4·2CH2Cl2(0.68 g, 0.20 mmol) in CH2Cl2 (15 mL) was refluxed for 12 h under a N2 atmosphere. Then, the solvent was removed in vacuo and the residue extracted with toluene (20 mL). After filtration, the toluene was removed under vacuum and the residue dissolved in CH2Cl2 (15 mL). Crystals of 6·3CH2Cl2 suitable for X-ray analyses were obtained by layering n-pentane (30 mL) on the CH2Cl2 solution (yield 0.25 g, 24% based on platinum and 73% based on IPr). B. ) From [NEt4]2[Pt9(CO)18] and IPr. A solution of IPr (0.88 g, 2.26 mmol) in acetone (10 mL) was added to a solution of [NEt4]2[Pt9(CO)18] (0.58 g, 0.23 mmol) in acetone (20 mL) over a period of 1 h. The resulting mixture was stirred at room temperature for 1 h and then the solvent removed in vacuo. The residue was extracted with toluene (20 mL). After filtration, the toluene was removed under vacuum and the residue dissolved in CH2Cl2 (15 mL). Crystals of 6·3CH2Cl2 suitable for X-ray analyses were obtained by layering n-pentane (30 mL) on the CH2Cl2 solution (yield 0.66 g, 55% based on platinum). Elem anal. Calcd for C61H78Cl6N4O4Pt3 (1729.24): C, 42.37; H, 4.55; N, 3.24; Pt, 33.84. Found: C, 42.62; H, 4.22; N, 3.05; Pt, 34.08. IR (Nujol, 293 K): ν(CO) 2031, 1867, 1820, 1782 cm−1. IR (CH2Cl2, 293 K): ν(CO) 2013, 1823, 1792 cm−1. IR (toluene, 293 K): ν(CO) 2018, 1820, 1786 cm−1. 1H NMR (CD3COCD3, 298 K): δ 7.62 (s (pseudotriplet), 4JH−Pt = 13 Hz, 4H, CHimid), 7.29 (t, 3JH−H = 7.6 Hz, 4H, p-CHAr), 7.12 (d, 3JH−H = 7.6 Hz, 8H, m-CHAr), 3.06 (sept, 3JHH = 6.8 Hz, 8H, CH(CH3)2), 1.09 (d, 3JHH = 6.8 Hz, 24H, CH(CH3)2), 0.90 (d, 3JHH = 6.8 Hz, 24H, CH(CH3)2). 13C{1H} NMR (CD3COCD3, 298 K): δ 258.9 (1 μ-CO, 1JC−Pt = 740 Hz), 248.3 (2 μ-CO, 1JC−Pt = 914 and 484 Hz), 206.8 (1 t-CO, 1JC−Pt = 1966 Hz, 2 JC−Pt = 132 Hz), 198.8 (C−Pt, 1JC−Pt = 1754 Hz, 2JC−Pt = 145 Hz), 146.9, 137.0, 130.4, 124.8 (CAr), 125.8 (CHimid, 3JC−Pt = 55 Hz), 29.2 (CH(CH3)2), 26.4, 23.8 (CH(CH3)2). A few crystals of 7·C5H12 have sometimes been obtained during crystallization of 6·3CH2Cl2. IR (Nujol, 293 K): ν(CO) 1935, 1852, 1786 cm−1. IR (CH2Cl2, 293 K): ν(CO) 1934, 1853, 1788 cm−1. 4.5. Synthesis of 8·toluene. A solution of IPr (0.47 g, 1.20 mmol) in toluene (12 mL) was added to a solution of 6·3CH2Cl2 (0.52 g, 0.30 mmol) in toluene (20 mL) over a period of 3 h. The resulting mixture was stirred at room temperature for 1 h and then the solvent removed in vacuo. The residue was extracted with toluene (15 mL). Crystals of 8·toluene suitable for X-ray analyses were obtained by layering n-pentane (30 mL) on the toluene solution (yield 0.34 g, 58% based on platinum). Elem anal. Calcd for C91H116N6O3Pt3 (1927.16): C, 56.71; H, 6.07; N, 4.36; Pt, 30.37. Found: C, 56.28; H, 5.86; N, 4.55; Pt, 30.07. IR (Nujol, 293 K): ν(CO) 1763 cm−1. IR (toluene, 293 K): ν(CO) 1763 cm−1. 1H NMR (CD2Cl2, 298 K): δ 7.75 (br, 6H, CHimid), 7.14 (t, 3 JH−H = 7.4 Hz, 6H, p-CHAr), 6.94 (d, 3JH−H = 7.4 Hz, 12H, m-CHAr), 3.00 (sept, 3JHH = 6.6 Hz, 12H, CH(CH3)2), 1.13 (d, 3JHH = 6.6 Hz, 36H, CH(CH3)2), 0.95 (d, 3JHH = 6.6 Hz, 36H, CH(CH3)2). 13C{1H} NMR (CD3COCD3, 298 K): δ 146.2, 137.0, 130.0, 123.6 (CAr), 125.4 (CHimid), 27.9 (CH(CH3)2), 25.3, 23.2 (CH(CH3)2). 4.6. Synthesis of 9·1.5CH2Cl2. A solution of Ag(IMes)Cl (1.88 g, 4.20 mmol) in acetone (10 mL) was added to a solution of [NEt4]2[Pt9(CO)18] (0.85 g, 0.34 mmol) in acetone (20 mL) over a period of 1 h. The resulting mixture was stirred at room temperature for 1 h and then the solvent removed in vacuo. The residue was extracted with toluene (20 mL). After filtration, the toluene was removed under vacuum and the residue dissolved in CH2Cl2 (15 mL). Crystals of 9·1.5CH2Cl2 suitable for X-ray analyses were obtained by layering n-pentane (30 mL) on the CH2Cl2 solution (yield 0.79 g, 41% based on platinum). Similarly, crystals of 9·0.5toluene were obtained from toluene/n-pentane. Elem anal. Calcd for C67.5H75AgCl4N6O3Pt3 (1853.27): C, 43.75; H, 4.08; N, 4.53; Ag, 5.82; Pt, 31.58. Found: C, 43.98; H, 3.85; N, 4.74; Ag, 5.54; Pt, 31.89. IR (Nujol, 293 K): ν(CO) 1785 cm−1. IR (toluene, 293 K): ν(CO) 1784 cm−1. 1H NMR (CD2Cl2, 298 K): δ 7.07 (s, 6H, CHimid), 6.71 (s, 12H, CHAr), 2.27 (s, 18H, Me), 1.84 (s, 36H, Me). 13 C{1H} NMR (CD3COCD3, 298 K): δ 255.8 (μ-CO, 1JC−Pt = 610 Hz), 196.4 (C−Pt, 1JC−Pt = 1024 Hz, 2JC−Pt = 111 Hz, 2JC−Ag = 10 Hz),

137.7, 135.9, 135.4, 129.4 (CAr), 122.4 (CHimid, 3JC−Pt = 57 Hz), 21.4, 18.2 (CH3). 4.7. Synthesis of 10·toluene. A solution of 9·1.5CH2Cl2 (0.53 g, 0.29 mmol) in toluene (15 mL) was stirred under a CO atmosphere for 2 days. A few crystals of 10·toluene suitable for X-ray analyses were obtained by layering n-pentane (25 mL) on the toluene solution under a CO atmosphere (yield 0.087 g, 23% based on platinum). Elem anal. Calcd for C77H80N6O7Pt5 (2176.92): C, 42.48; H, 3.70; N, 3.86; Pt, 44.81. Found: C, 42.21; H, 3.38; N, 4.05; Pt, 45.07. IR (Nujol, 293 K): ν(CO) 1994, 1893, 1806, 1762 cm−1. IR (CH2Cl2, 293 K): ν(CO) 2004, 1819, 1786, 1750 cm−1. 1H NMR (CD2Cl2, 298 K): δ 7.16, 6.76, 6.72 (s, 12H, CHAr), 7.08, 7.04, 6.78 (s, 6H, CHimid), 2.35, 2.32, 2.22, 2.21, 2.12, 2.08 (s, 54H, Me). 4.8. X-ray Crystallographic Study. Crystal data and collection details for 4·2CH2Cl2, 4·C5H12·0.5toluene, 5·2CH2Cl2, 6·3CH2Cl2, 7· C5H12, 8·toluene, 9·1.5CH2Cl2, 9·0.5toluene, and 10·toluene are reported in Table S.1. The diffraction experiments were carried out on a Bruker APEX II diffractometer equipped with a CCD detector using Mo Kα radiation. Data were corrected for Lorentz polarization and absorption effects (empirical absorption correction SADABS).62 Structures were solved by direct methods and refined by full-matrix least squares based on all data using F2.63 H atoms were fixed at calculated positions and refined by a riding model. All non-H atoms were refined with anisotropic displacement parameters, unless otherwise stated. Among the nine crystal structures reported herein, three structures present alerts of levels A and B, and four structures present alerts of level B. Almost all of the alerts of levels A and B are due to high values for the residual electron density. These maxima are located close to the Pt atoms, in positions that are not realistic for any atom, and they are series termination errors that are common with heavy atoms such as Pt, especially in the case of high-nuclearity clusters. 4·2CH2Cl2. The asymmetric unit of the unit cell contains one cluster molecule and one CH2Cl2 (located on general positions) and the halves of two CH2Cl2 molecules disordered over two symmetry-related (by inversion centers) positions. The disordered molecules have been refined isotropically. All of the C atoms have been restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.02) and isotropic behavior (ISOR line in SHELXL, s.u. 0.02). The CH2Cl2 molecules have been restrained to have similar geometries (SAME line in SHELXL, s.u. 0.02). 4·C5H12·0.5toluene. The asymmetric unit of the unit cell contains one cluster molecule and one C5H12 (located on general positions) and half of a toluene molecule equally disordered over two symmetryrelated (by an inversion center) positions. The C5H12 molecule is disordered and has been split into two positions and refined with one occupancy parameter. All disordered molecules have been refined isotropically. Some C and O atoms of the cluster have been restrained to isotropic behavior (ISOR line in SHELXL, s.u. 0.01). The atoms of the toluene molecule have been constrained to fit a regular hexagon (AFIX 66 line in SHELXL) and restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.02). The C−C distances of the C5H12 molecule have been restrained to 1.53 Å (DFIX line in SHELXL, s.u. 0.02). 5·2CH2Cl2. The asymmetric unit of the unit cell contains eight cluster molecules and 16 CH2Cl2 molecules (all located on general positions). Because of the large size of the unit cell and the large number of independent atoms, it has not been possible to locate the C atom of one of the 16 CH2Cl2 molecules but only its two Cl atoms. For the same reason, several restraints have been employed. The CH2Cl2 molecules have been refined isotropically. All the C, O, and N atoms have been restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.01) and isotropic behavior (ISOR line in SHELXL, s.u. 0.01). The aromatic C6 rings have been constrained to fit regular hexagons (AFIX 66 line in SHELXL) and the C3N2−IPr rings to fit regular pentagons (AFIX 56 line in SHELXL). Restraints to bond distances were applied as follows (s.u. 0.02): 1.18 Å for C−O in carbonyl ligands; 1.51 Å for C(sp2)−C(sp3) and 1.53 Å for C(sp3)− C(sp3) in IPr ligands; 1.75 Å for C−Cl in CH2Cl2. I


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Inorganic Chemistry 6·3CH2Cl2. The asymmetric unit of the unit cell contains one cluster and three CH2Cl2 molecules (all located on general positions). One CH2Cl2 molecule is disordered and has been split into two positions and refined with one occupancy parameter. The C−Cl distances of the disordered CH2Cl2 have been restrained to 1.75 Å (s.u. 0.02). All of the atoms of the disordered CH2Cl2 have been restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.01) and isotropiclike behavior (ISOR lien in SHELXL, s.u. 0.01). 7·C5H12. The asymmetric unit of the unit cell contains one cluster and one C5H12 molecule (all located on general positions). The crystals are racemically twinned with the refined Flack parameter 0.552(11). The C5H12 molecule is disordered and has been split into two positions and refined isotropically with one occupancy parameter. The C−C distances of the disordered C5H12 have been restrained to 1.53 Å (s.u. 0.02). All of the atoms of the disordered C5H12 have been restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.01) and similar geometries (SAME line in SHELXL, s.u. 0.02). All of the atoms of the IPr ligands have been restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.02). Several C atoms of the cluster have been restrained to have isotropic-like behavior (ISOR line in SHELXL, s.u. 0.01). 8·toluene. The asymmetric unit of the unit cell contains one cluster and one toluene molecule (all located on general positions). The crystals are racemically twinned with the refined Flack parameter 0.467(11). The toluene molecule is disordered and has been split into two positions and refined with one occupancy parameter. Some C and O atoms of the cluster have been restrained to isotropic behavior (ISOR line in SHELXL, s.u. 0.003). The disordered toluene rings have been constrained to fit regular hexagons (AFIX 66 line in SHELXL), and their C atoms have been restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.01). 9·1.5CH2Cl2. The asymmetric unit of the unit cell contains one cluster molecule and one CH2Cl2 (located on general positions) and half of a CH2Cl2 molecule disordered over two symmetry-related (by an inversion center) positions. The atoms of the CH2Cl2 molecules have been restrained to have similar U parameters (SIMU line in SHELXL, s.u. 0.02). Restraints to bond distances were applied as follows (s.u. 0.02): 1.75 Å for C−Cl in CH2Cl2. 9·0.5toluene. The asymmetric unit of the unit cell contains one cluster molecule (located on a general position) and half of a toluene molecule disordered over four positions, two by two related by an inversion center. The atoms of the toluene molecule have been restrained to isotropic behavior (ISOR line in SHELXL, s.u. 0.02) and to have similar U parameters (SIMU line in SHELXL, s.u. 0.02), and constrained to fit regular hexagons (AFIX 66 line in SHELXL). 10·toluene. The asymmetric unit of the unit cell contains one cluster molecule and one toluene (located on general positions). Similar U restraints have been applied to all of the C atoms (SIMU line in SHELXL, s.u. 0.01). Some C, N, and O atoms have been restrained to isotropic behavior (ISOR line in SHELXL, s.u. 0.01). 4.9. Computational Details. The electronic structures of the compounds were optimized using the range-separated ωB97X DFT functional64 in combination with Ahlrichs’ split-valence polarized basis set and effective core potentials on silver and platinum.65 The “restricted” formalism was applied in all cases. Partial charges were obtained from the Hirshfeld population analysis.66 The software used was Gaussian 09.67 Properties at bond critical points were obtained using the software Multiwf n, version 3.38.68

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Accession Codes

CCDC 1527357,1527358, and 1535502−1535508 and contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/ data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +39 051 2093711. Web: https://www.unibo.it/sitoweb/stefano.zacchini/en. ORCID

Cristina Femoni: 0000-0003-4317-6543 Stefano Zacchini: 0000-0003-0739-0518 Notes

The authors declare no competing financial interest.

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REFERENCES

(1) (a) Longoni, G.; Chini, P. Synthesis and chemical characterization of platinum carbonyl dianions [Pt3(CO)6]n2− (n = ∼ 10, 6, 5, 4, 3, 2, 1). A new series of inorganic oligomers. J. Am. Chem. Soc. 1976, 98, 7225. (b) Calabrese, J. C.; Dahl, L. F.; Chini, P.; Longoni, G.; Martinengo, S. Synthesis and structural characterization of platinum carbonyl dianions, [Pt3(CO)3(μ-CO)3]n2− (n = 1, 3, 4, 5). A new series of inorganic oligomers. J. Am. Chem. Soc. 1974, 96, 2614. (2) (a) Ciabatti, I.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S. Platinum Carbonyl Clusters Chemistry: Four Decades of Challenging Nanoscience. J. Cluster Sci. 2014, 25, 115. (b) Gao, F.; Li, C.; Heaton, B. T.; Zacchini, S.; Zarra, S.; Longoni, G.; Garland, M. The inter-conversions of platinum carbonyl dianionic clusters, [Pt3(CO)6]n2− (n = 2−5), in THF and acetonitrile. A combined in situ FTIR spectroscopic and BTEM study leading to the characterization of the new [H4‑xPt15(CO)19]x− (x = 2−4) clusters. Dalton Trans. 2011, 40, 5002. (3) (a) Femoni, C.; Kaswalder, F.; Iapalucci, M. C.; Longoni, G.; Mehlstäubl, M.; Zacchini, S. High-yield one-step synthesis in water of [Pt3n(CO)6n]2− (n > 6) and [Pt38(CO)44]2−. Chem. Commun. 2005, 5769. (b) Femoni, C.; Kaswalder, F.; Iapalucci, M. C.; Longoni, G.; Mehlstäubl, M.; Zacchini, S.; Ceriotti, A. Synthesis and Crystal Structure of [NBu4]2[Pt 24(CO)48 ]: An Infinite 1D Stack of {Pt3(CO)6} Units Morphologically Resembling a CO-Insulated Platinum Cable. Angew. Chem., Int. Ed. 2006, 45, 2060. (4) (a) Femoni, C.; Kaswalder, F.; Iapalucci, M. C.; Longoni, G.; Zacchini, S. Infinite Molecular {[Pt3n(CO)6n]2−}∞ Conductor Wires by Self-Assembly of [Pt3n(CO)6n]2− (n = 5−8) Cluster Dianions Formally Resembling CO-Sheathed Three-Platinum Cables. Eur. J. Inorg. Chem. 2007, 2007, 1483. (b) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Lovato, T.; Stagni, S.; Zacchini, S. Self-Assembly of [Pt3n(CO)6n]2− (n = 4−8) Carbonyl Clusters: from Molecules to Conducting Molecular Metal Wires. Inorg. Chem. 2010, 49, 5992. (5) (a) Greco, P.; Cavallini, M.; Stoliar, P.; Quiroga, S. D.; Dutta, S.; Zacchini, S.; Iapalucci, M. C.; Morandi, V.; Milita, S.; Merli, P. G.; Biscarini, F. Conductive Sub-micrometric Wires of Platinum-Carbonyl Clusters Fabricated by Soft-Lithography. J. Am. Chem. Soc. 2008, 130, 1177. (b) Serban, D. A.; Greco, P.; Melinte, S.; Vlad, A.; Dutu, C. A.; Zacchini, S.; Iapalucci, M. C.; Biscarini, F.; Cavallini, M. Towards AllOrganic Field-Effect Transistors by Additive Soft Lithography. Small 2009, 5, 1117. (6) Barnett, B. R.; Rheingold, A. L.; Figueroa, J. S. Monomeric ChiniType Triplatinum Clusters Featuring Dianionic and Radical-Anionic π*-Systems. Angew. Chem., Int. Ed. 2016, 55, 9253. (7) Zacchini, S. Using Metal Carbonyl Clusters To Develop a Molecular Approach towards Metal Nanoparticles. Eur. J. Inorg. Chem. 2011, 2011, 4125.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00665. Computed MO energies (eV) for 4Me−10Me and crystal data and experimental details for 4·2CH2Cl2, 4·C5H12· 0.5toluene, 5·2CH2Cl2, 6·3CH2Cl2, 7·C5H12, 8·toluene, 9·1.5CH2Cl2, 9·0.5toluene, and 10·toluene (PDF) J


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