Study of the Nature of Closed-Shell HgIIÂ·Â·Â·MI (M = Cu, Ag, Au

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Study of the Nature of Closed-Shell HgII···MI (M = Cu, Ag, Au) Interactions José M. López-de-Luzuriaga,* Miguel Monge, M. Elena Olmos, and David Pascual Departamento de Química, Centro de Investigación en Síntesis Química (CISQ), Complejo Científico-Tecnológico, Universidad de La Rioja, 26004 Logroño, La Rioja, Spain S Supporting Information *

ABSTRACT: Heteronuclear complexes [HgM(o-C6H4PPh2)2]X (M = Au, X = ClO4 (1); M = Ag, X = BF4 (2); M = Ag, X = CF3CO2 (3); M = Cu, X = Br (4)) were prepared by the treatment of [Hg(o-C6H4PPh2)2] with one equivalent of the corresponding coinage metal salt. Their crystal structures, determined by X-ray diffraction methods, display HgII··· MI (M = Au, Ag, Cu) contacts. Ab initio calculations show similar interaction energies (ca. 40 kJ·mol−1) and similar origin (dispersive forces) for these Hg···Au, Hg···Ag, and Hg···Cu interactions.

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such as AgI, BiIII, TlI, or CuI, among others.17−23 Thus, for instance, with the, in principle, more favorable coinage congeners, the energy of AuI···AgI and AuI···CuI contacts has been theoretically estimated to be 22 and 17 kJ·mol−1, respectively. Besides, both of them have in common a high electronic correlation contribution probably induced by the relativistic effects present in gold.24 In addition, the importance of the dispersive-type forces is evident in the intermetallic acid−base interactions that take place between gold(I) and thallium(I) or bismuth(III), which are, in both cases, around 20% of the total interaction.22,25 A recent study in our laboratory of a surprising metallophilic interaction is the one that takes place between AuI and HgII fragments, in which the interaction energy is the highest one described until now between two neutral units (−73 kJ·mol−1). The theoretical study of this AuI···HgII interaction revealed, as expected, a very important contribution of the relativistic effects, reaching 21% of the total energy of the interaction.5 This result may induce us to think that, as in the case of gold, the number of compounds with Hg···M contacts would be numerous due to the high relativistic contribution to the metal−metal interaction. Nevertheless, the number of examples described in the literature is very limited, especially with 11group elements. Thus, there are a few examples of complexes displaying interactions between mercury and gold(I) or gold(III), such as, for instance, [HgAuCl2(μ-2-C6H4PPh2)2],26 [HgAu(CH2P(S)Ph2)2][PF6],27 {[Au(μ-C3,N3-bzim)]3}2[Hg(o-C6F4)]3,28 [Hg(C6F5)2{Au(C6F5)(PMe3)}2],5,29 [Hg{Au(C 6 F 5 )(μ-2-C 6 H 4 PPh 2 )} 2 ], and [Hg{Au(C 6 F 5 )Cl 2 (μ-2-

INTRODUCTION Nowadays, relativistic effects have shown an enormous importance to understand the chemical and physical properties of the heaviest 6s transition and post-transition metallic elements. From them, the element whose physical and chemical properties are more influenced by these effects is gold.1−3 Probably, the most important structural consequence of the relativistic effects in gold is the high tendency to form closedshell interactions between gold(I) centers. This type of interactions were first described by Schmidbaur in 1988,4 and subsequently, theoretical studies quantified the strength of these interactions up to −57 kJ·mol−1, a surprisingly strong value, from which a non-negligible 26% is due to relativistic effects.5 These strong interactions made possible a high number of structural motifs,2,6 and in addition, parallel to this, the complexes often displayed interesting optical properties.7−9 In the case of other heavy atoms, although the contraction of the radius due to the relativistic effects is not so important as in gold, these effects also play an important role in their properties.10−14 Also, more recent studies on the relativity of the lead−acid or mercury batteries attribute a non-negligible 80% or 30%, respectively, of the electromotoric forces to the relativistic effects.15,16 On the other hand, a logical next step in these studies was the study of the relativity in heteronuclear systems in which different metals maintain noncovalent interactions between them and in which at least one of them is a heavy 6s element, preferably gold. The synthesis of these complexes has been possible, making use of different synthetic strategies (acid− base, transmetalation, etc.). In such a way, a good number of heterometallic gold(I) compounds were described in which gold maintains an interaction with different closed shell ions © XXXX American Chemical Society

Received: April 21, 2015

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DOI: 10.1021/acs.organomet.5b00334 Organometallics XXXX, XXX, XXX−XXX

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Organometallics C6H4PPh2)}2],30 [6-(Ph2P)-5-Ace]2Hg·AuCl, and {[6-(Ph2P)5-Ace]2Hg·Au}[O3SCF3] ([6-(Ph2P)-5-Ace] = 6-diphenylphosphinoacenaphth-5-yl);31 or a very few examples of the interaction between mercury and silver or copper, as the hexanuclear complex [Ag2Hg(mes)2(SO3CF3)2]2 (mes = mesityl)32 or [6-(Ph2P)-5-Ace]2Hg·AgCl and [6-(Ph2P)-5Ace]2Hg·Ag(O3SCF3),31 which are the only examples that present short Ag(I)···Hg(II) interactions, or [Hg{Fe[Si(OMe)3](CO)3(μ-dppm)}2Cu]PF6 (dppm = PPh2CH2PPh2)33 and [Cu{Hg(Ph−CHN−CH2−CH2−NCH-Ph)}2}],34 which are the only two examples reported with Hg(II)··· Cu(I) contacts. Interestingly, a recent study by Hupf et al.31 also reports about the low number of complexes bearing Hg(II)···M (M = Hg(II), Au(I), and Ag(I)) interactions. A very recent review highlights the increasing number of examples displaying Hg(II)···Hg(II) interactions.35 In the work of Hupf et al.31 the authors characterize several complexes displaying such interactions by the use of a rigid phosphinomercurial as ligand for d10 closed-shell metals. The analysis of the electron density of these complexes obtained through single-point energy calculations of the X-ray structures at the DFT level of theory points to the observation of the existence of weak interactions. This study shows that the electron density values at the M···M bond critical points decrease for increasing M···M distances, regardless of the metals involved in the interaction. It is worth mentioning that, for a precise description of the metallophilicity, the use of unbridged model systems is compulsory in order to avoid a metal−metal approximation imposed by the ligand architecture. This is especially important when very rigid ligands are used as bridging ligands between closed-shell metal centers. At this point and, taking into account the previous studies, we envisaged the need for an indepth study of the nature of the Hg(II)···M(I) (M = Cu, Ag, Au) interactions on fully optimized unbridged model systems, in which the metal−metal interactions are not imposed by the ligand architecture. For this analysis, we have employed noncorrelated (HF) and correlated (MP2) levels of theory, which permit us to account for the dispersive contributions to these closed-shell interactions. In addition, there is no report of a full comparative theoretical study of the nature of the HgII··· AuI, HgII···AgI, and HgII···CuI metallophilic interactions. With these precedents, in this paper we describe the synthesis of a series of new heteronuclear compounds containing Hg···M (M = Cu, Ag, Au) interactions and the theoretical study of the nature of these d10−d10 contacts. This study of the interaction between mercury and elements with similar electronic d10 configuration allows us to analyze the influence of the increasing nuclear charge on the origin and strength of the metallophilic interactions.

Scheme 1. Synthesis of Complexes 1−4

complex, and the coordination of the gold center to the phosphine ligands in solution due to the deshielding of the original position that appears at −1.8 ppm in the starting mercury derivative. Finally, its IR spectrum in Nujol mulls shows absorptions arising from the perchlorate anion at 1080 and 623 cm−1, indicating its ionic nature. This fact is confirmed by the measurement of its molar conductivity in dichloromethane solution, finding that complex 1 is a uniunivalent electrolyte. On the other hand, the reaction between the same mercury precursor, [Hg(o-C6H4PPh2)2] and silver salts such as AgBF4 or Ag(tfa) (tfa = CF3COO−) in a 1:1 molar ratio in dichloromethane gives rise to the Ag−Hg heterometallic complexes [AgHg(o-C6H4PPh2)2][BF4] (2) or [AgHg(o-C6H4PPh2)2](μCF3CO2) (3) (see Scheme 1). The 31P{1H} NMR spectrum of 2 in CDCl3 at room temperature shows a broad signal at 13.6 ppm that is resolved in two doublets centered at δ = 13.8 ppm (1J (107,109Ag−31P) = 467, 538 Hz) at 253 K. In the case of [AgHg(o-C6H4PPh2)2](μ-CF3CO2) (3), its 31P{1H} NMR spectrum shows a well-defined couple of doublets even at room temperature centered at δ = 13.8 ppm (1J (107,109Ag−31P) = 443, 512 Hz). In both cases the chemical shifts found are in agreement with the coordination of the phosphorus centers to the silver atoms. Furthermore, the ratio obtained from the 109 Ag−31P and 107Ag−31P coupling constants (1.152 (2) and 1.156 (3)) is close to the gyromagnetic ratio (1.149) of the two silver isotopes. For 2 and 3, their 19F NMR spectra show the signals corresponding to their anions at δ = −151.9 (s) (BF4−) and −74.9 ppm (s) (CF3CO2−), respectively. Furthermore, the IR spectra of these Ag−Hg complexes show, among others, absorptions at 1097 (2) and 1654, 1373, and 1204 (3), due to the presence of these anionic groups in the complexes. Interestingly, the molar conductivity measurements of complexes 2 and 3 in dichloromethane solutions give values of 62.6 (2) and 0.1 Ω−1·cm2·mol−1 (3), indicating that the tetrafluoroborate ion is dissociated in solution, while the

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RESULTS AND DISCUSSION Synthesis and Characterization. Treatment of [Hg(oC6H4PPh2)2] with one equivalent of [Au(tht)2]ClO4 (tht = tetrahydrothiophene) in CH2Cl2 leads to the substitution of the labile tht ligand by the phosphine units of the mercury starting material, giving rise to the heterometallic complex [AuHg(oC6H4PPh2)2]ClO4 (1) (see Scheme 1). The high-resolution electrospray mass spectra of 1 show the peak corresponding to the anion [ClO4]− at m/z = 98.94, and the peak due to the cation [AuHg(o-C6H4PPh2)2]+ at m/z = 921.10. In addition, the 31P{1H} NMR spectrum of 1 in CDCl3 shows a signal at δ = 38.6 (s) ppm. This result reveals the chemical and magnetic equivalence of the two phosphorus atoms present in this B


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Organometallics trifluoroacetate anion of 3 remains bonded to the metal center. Finally, as in the case of complex 1, the high-resolution electrospray mass spectra show the signals corresponding to the anions at m/z = 86.99 (2, BF4−) and 122.99 (3, CF3COO−), and the peak corresponding to the cation [AgHg(oC6H4PPh2)2]+ at m/z = 831.04 (2) and 831.03 (3). To obtain the Cu−Hg heterometallic complex, we have followed a similar procedure to that described previously. Thus, the reaction of [Hg(o-C6H4PPh2)2] with one equivalent of CuBr in dichloromethane as solvent gives rise to the complex [CuHg(o-C6H4PPh2)2Br] (4) as a white solid. Its analytical and spectroscopic data agree with the proposed stoichiometry. For instance, its 31P{1H} NMR spectrum shows a singlet centered at δ = −2.6 ppm, showing a slightly different chemical shift with respect to the mercury precursor. In addition, in the MS-ESI spectrum, besides the peak due to the bromide anion (m/z = 80.91), the signal that corresponds to the cation [CuHg(oC6H4PPh2)2]+ also appears at m/z = 787.07. Finally, the molar conductivity of [CuHg(o-C6H4PPh2)2Br] (4) in CH2Cl2 solution indicates that, as in the case of complexes [AuHg(oC6H4PPh2)2I]33 and 3, the anion, instead of dissociating in solution, is bonded to a metal center. X-ray Structural Determination. By slow diffusion of nhexane into solutions of the new compounds in 1,2-dichloroethane (1), tetrahydrofuran (2 and 3), or toluene (4), single crystals suitable for X-ray diffraction studies were obtained and their crystal structures determined. The four complexes crystallize with a higher or a lower amount of solvent, 1· 2C2H4Cl2, 2·2THF, 3·THF, or 4·0.5C7H8, which in the case of [AgHg(o-C6H4PPh2)2][BF4] (2) and [AgHg(o-C6H4PPh2)2(μCF3CO2)] (3) appears coordinated to the silver atom. In the case of [CuHg(o-C6H4PPh2)2Br] (4), the asymmetric unit contains two independent molecules of the dinuclear complex and one molecule of toluene. Tables 1−4 contain selected bond

Table 3. Selected Bond Lengths (Å) and angles (deg) for 3· THF Hg−Ag Hg−C(1) Hg−C(11) Ag−P(1) Ag−P(2) Ag−O(1) Ag−O(3) Hg−O(2) C(1)−Hg−C(11) C(1)−Hg−Ag C(11)−Hg−Ag

2.9194(7) 2.078(14) 2.103(15) 2.309(3) 2.309(3) 3.023(16) 3.142(16)

C(1)−Hg−C(11) C(1)−Hg−Au C(11)−Hg−Au Au−Hg−O(3) P(2)−Au−P(1) P(2)−Au−Hg P(1)−Au−Hg

177.2(5) 90.6(4) 91.7(4) 174.86(35) 170.08(12) 85.40(9) 84.68(8)

Symmetry transformations used to generate equivalent atoms: #1x-1, +y, +z.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2· 2THF Hg−Ag Hg−C(1) Hg−C(11) Ag−P(1) Ag−P(2) Ag−O(1) Ag−O(2) C(11)−Hg−C(1) C(11)−Hg−Ag C(1)−Hg−Ag Ag−Hg−F(3)

3.0544(2) 2.089(3) 2.085(3) 2.4191(7) 2.4304(7) 2.411(2) 2.669(2) 175.38(11) 90.63(8) 93.30(8) 170.68(5)

O(1)−Ag−P(1) O(1)−Ag−P(2) P(1)−Ag−P(2) O(1)−Ag−Hg P(1)−Ag−Hg P(2)−Ag−Hg O(2)−Ag−O(1) O(2)−Ag−P(1) O(2)−Ag−P(2) O(2)−Ag−Hg O(2)−Ag−O(1)

O(1)−Ag−P(1) O(1)−Ag−P(2) P(1)−Ag−P(2) O(1)−Ag−Hg P(1)−Ag−Hg P(2)−Ag−Hg O(3)−Ag−O(1) O(3)−Ag−P(1) O(3)−Ag−P(2) O(3)−Ag−Hg

103.99(14) 113.98(14) 140.35(6) 104.33(12) 80.15(4) 79.83(4) 79.12(16) 109.55(13) 89.07(12) 168.85(12)

lengths and angles, Table S1 contains the experimental details of the data collection and refinement, and Figures 1−4 show the molecular structures of 1·2C2H4Cl2, 2·2THF, 3·THF, or 4· 0.5C7H8. The four crystal structures contain a similar skeleton consisting of an eight-member metallacycle formed by both metals and two PC2 fragments of the bridging ligands in a headto-head disposition with Hg−C and M−P bonds and with the metal atoms at interacting distances. This eight-member ring appears in a twisted conformation in 1·2C2H4Cl2 and 2·2THF, while it adopts an envelope type conformation in 3·THF and 4· 0.5C7H8. The Hg−C bond distances, which vary from 2.078(14) Å in 1·2C2H4Cl2 to 2.117(6) Å in 3·THF, as well as the C−Hg−C angles (from 173.98(22)° in 3·THF to 178.24(13)° in 4·0.5C7H8), compare well with those found in the crystal structures of other complexes containing the fragment [Hg(o-C6H4PPh2)2], in which the Hg−C bond lengths range from 2.084(5) Å in [Pd{η2-(2-Ph2PC6H4)2Hg}{η1-(2-Ph2PC6H4)(2-Ph2P(O)C6H4)Hg}]34 to 2.12(1) Å in [HgBr2{(2-Ph2PC6H4)2Hg}],34 and display a linear environment for the mercury atoms. As commented above, the four crystal structures display intramolecular Hg···M interactions aided by the (2diphenylphosphino)phenyl ligands. In the case of 1· 2C2H4Cl2, the AuI−HgII distance of 2.9194(7) Å is one of the shortest described until date, being longer only than that of 2.866(2) Å recently described for [6-(Ph2P)-5-Ace]2Hg· AuCl.31 The rest of the AuI−HgII lengths reported range from 2.934(1) to 3.361(1) Å in complexes containing bridging ligands between the metal atoms26−28,30,31,33,36−39 and from 3.1860(2) to 3.4983(3) Å in the case of unsupported intermetallic contacts.5,6 The Au−P bond lengths of 2.309(3) Å are very similar to those described for other Au(I)/Hg(II) complexes containing bridging C,P-donor ligands in a head-to-head disposition, such as [6-(Ph2P)-5-Ace]2Hg·AuCl (2.313(3) and 2.327(3) Å),31 [{6-(Ph2P)-5-Ace}2Hg·Au]+ (2.319(2) and 2.322(3) Å),31 or [AuHg(o-C6H4PPh2)2I] (2.3298(11) and 2.3323(11) Å).33 Regarding the environment of gold in 1·2C2H4Cl2, it can be described as linear if the intermetallic contact is not considered (P−Au−P angle of 170.08(12)°) or as T-shaped if it is taken into account (see Table 1). As shown in Figure 1, the perchlorate anion in 1·2C2H4Cl2 weakly interacts with the mercury center, showing a Hg−O distance of 3.023(16) Å. If the intermetallic interaction is considered, a distorted square planar coordination environment for the mercury center (see Table 1), with the metal atom only 0.064 Å above the plane described by Au, C(1), C(11), and O(3), is observed.

Table 1. Selected Bond Lengths (Å) and Angles (deg) for 1· 2C2H4Cl2 Hg−Au Hg−C(1) Hg−C(11) Au−P(1) Au−P(2) Hg−O(3) Au−O(4)#1

3.0347(5) 2.096(6) 2.117(6) 2.4235(17) 2.4326(17) 2.368(5) 2.736(5) 2.999(5) 173.98(22) 91.43(16) 94.20(17)

103.18(7) 99.06(7) 154.18(2) 164.85(6) 78.459(17) 76.670(18) 95.06(8) 100.50(6) 90.35(6) 99.46(5) 95.06(8)

C


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Organometallics Table 4. Selected Bond Lengths (Å) and Angles (deg) for 4·0.5C7H8 Hg(1)−Cu(1) Hg(2)−Cu(2) Hg(1)−C(1) Hg(1)−C(11) Hg(2)−C(71) Hg(2)−C(61) Cu(1)−Br(1) Cu(2)−Br(2) Cu(1)−P(1) Cu(1)−P(2) Cu(2)−P(3) Cu(2)−P(4) C(1)−Hg(1)−C(11) C(1)−Hg(1)−Cu(1) C(11)−Hg(1)−Cu(1)

2.8656(5) 2.8619(5) 2.095(3) 2.100(3) 2.096(3) 2.098(3) 2.3751(6) 2.3903(5) 2.2459(10) 2.2584(9) 2.2682(9) 2.2499(9) 178.24(13) 90.66(10) 90.25(10)

C(71)−Hg(2)−C(61) C(71)−Hg(2)−Cu(2) C(61)−Hg(2)−Cu(2) P(1)−Cu(1)−P(2) P(1)−Cu(1)−Br(1) P(2)−Cu(1)−Br(1) P(1)−Cu(1)−Hg(1) P(2)−Cu(1)−Hg(1) Br(1)−Cu(1)−Hg(1) P(4)−Cu(2)−P(3) P(4)−Cu(2)−Br(2) P(3)−Cu(2)−Br(2) P(4)−Cu(2)−Hg(2) P(3)−Cu(2)−Hg(2) Br(2)−Cu(2)−Hg(2)

177.94(13) 90.31(10) 90.36(10) 133.95(4) 116.57(3) 109.33(3) 85.87(3) 83.26(3) 99.345(19) 132.15(4) 117.61(3) 109.42(3) 87.07(3) 81.27(3) 93.973(17)

Figure 1. ORTEP-style diagram of the molecular structure of complex 1·2C2H4Cl2 (30% probability). Hydrogen atoms have been omitted for clarity.

Additionally, the counterparts are also held together by two weak C−H···O hydrogen bonds (see Table S2). Finally, Au···O weak intermolecular interactions of 3.142(16) Å, and additional C−H···O hydrogen bonds, give rise to polymeric chains that run parallel to the crystallographic a axis. As occurs in 1·2C2H4Cl2, in the crystal structures of the Hg/ Ag derivatives 2·2THF and 3·THF, the mercury center maintains weak interactions with the anion, which in the latter is also coordinated to the silver atom, thus bridging both metals and forming a bicycle. Furthermore, the tetrahydrofuran molecules appear connected to silver through their oxygen atoms (see Figures 2 and 3). The Hg−Ag distances in these two complexes, 3.0544(2) (2·2THF) and 3.0347(5) Å (3· THF), are longer than in the doubly bridged derivatives [{6(Ph2P)-5-Ace}2Hg·AgCl] (3.011(2) Å) and [{6-(Ph2P)-5Ace}2Hg·Ag(O3SCF3)] (2.919(3) Å),31 which display a lower coordination number than 2·2THF and 3·THF. In contrast, the Hg−Ag distance in [{6-(Ph2P)-5-Ace}2Hg·Ag(NCMe)2]+ (3.051(2) Å),31 which displays the same coordination number as that of 2·2THF and 3·THF, is identical to that found in the former. Finally, the mesytyl-bridging complex [HgAg2(mes)2(SO3CF3)2] displays longer intermetallic distances, ranging from 3.1012(11) to 3.3863(12) Å.32 The Ag−P bond lengths (Tables 2 and 3), of 2.4191(7) and 2.4304(7) Å in 2·2THF, and of 2.4235(17) and 2.4326(17) Å in 3·THF, are of the same order, and they all compare well with those of 2.421(2) and 2.435(2) Å observed in [{6-(Ph2P)-5Ace}2Hg·Ag(O3SCF3)],31 while [{6-(Ph2P)-5-Ace}2Hg·AgCl]

Figure 2. ORTEP-style diagram of the molecular structure of complex 2·2THF (30% probability). Hydrogen atoms have been omitted for clarity.

Figure 3. ORTEP-style diagram of the molecular structure of complex 3·THF (30% probability). Hydrogen atoms have been omitted for clarity.

and [{6-(Ph2P)-5-Ace}2Hg·Ag(NCMe)2]+ display longer Ag−P distances (2.446(2) Å in the former, and 2.489(4) and 2.503(3) D


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Organometallics Å in the latter).31 In contrast, the Ag−O distances to the solvent molecules are dissimilar, showing values of 2.411(2) and 2.669(2) Å in 2·2THF and of 2.736(5) Å in 3·THF, although in all the cases they are shorter than the sum of van der Waals radii of silver and oxygen (3.24 Å).40 The stronger Ag−O interaction is that corresponding to the trifluoroacetate, with a Ag−O bond distance of 2.368(5) Å, a not uncommon value in silver derivatives containing bridging trifluoroacetate ions. In complex 3·THF, this anion unusually bridges asymmetrically silver and mercury, with a Hg−O distance of 2.999(5) Å, which indicates a nonbonding interaction of CF3CO2− with mercury (sum of van der Waals radii of mercury and oxygen 3.07 Å).40 This Hg−O distance is, in fact, longer than the Hg−O distances to trifluoroacetate described until date, which display an average distance of 2.353 Å (from 102 values found in 37 entries in the CCDC). Regarding the coordination environment of silver in 2·2THF and 3·THF, if the nonbonding interactions are considered, both complexes display pentacoordinated silver atoms. A careful analysis of the angles around Ag(I) and the geometric parameter τ41 reveals that the environment of silver in 2· 2THF is better described as square-pyramidal (τ = 0.18) with O2 in the apical position and O1, P1, P2, and Hg at the base of the pyramid, while in the case of 3·THF the geometry is intermediate between square-pyramidal, with O1 in the vertex of the pyramid, and trigonal-bipyramidal, with O3−Ag−Hg as the principal axis (τ = 0.475). The connection between the counterparts in 2·2THF occurs via a Hg···F contact of 3.017(2) Å, and a couple of weak C− H···F hydrogen bonds (see Figure 2). Considering nonbonding interactions in 2·2THF, the environment of the mercury center can be described as distorted square planar (see Table 2), with the metal atom 0.139 Å above the plane described by Ag, C(1), C(11), and F(3). Finally, a series of C−H···F (2·2THF) or C− H···O (3·THF) hydrogen bonds give rise to a 3D-array or to a dimer, respectively. The main difference between the X-ray structure of 4·0.5C7H8 and the other three described above is that in this last case the anion (bromide), instead of keeping a contact with mercury, is bonded to the copper center, as shown in Figure 4. Thus, the Hg(II) atom is linearly coordinated to two carbons (C−Hg−C angles of 178.24(13) and

177.94(13)°) if the metal−metal interaction is not taken into account. The Hg−Cu distances in 4·0.5C7H8 are 2.8656(5) and 2.8619(5) Å (two independent molecules), which are intermediate between the Hg−Cu separations found in the two unique compounds previously reported with Hg···Cu contacts. Thus, [Hg{Fe[Si(OMe)3](CO)3(μ-dppm)}2Cu]PF6 displays a Hg−Cu distance of only 2.689(2) Å,42 while in [{Hg(C6H4−CHN−CH2−CH2−NCH-C6H4)}2Cu]ClO4 the intermetallic Hg−Cu distances are 2.921(7) and 2.919(7) Å,43 close to the sum of van der Waals radii of mercury and copper (2.95 Å),40 although in this last case there is a larger number of atoms between the metal centers. The Cu−P bond lengths in 4·0.5C7H8, ranging from 2.2459(10) and 2.2682(9) Å, are, in general, slightly longer than the Cu−P average distance of 2.249 Å found for threecoordinated copper complexes containing the fragment [Cu{PPh2(C6H4-X)}2Br] but shorter than the average distance of 2.296 Å in four-coordinated compounds with the same fragment. Again, the Cu−Br bond lengths in 4·0.5C7H8 (2.3751(6) and 2.3903(5) Å) are intermediate between those corresponding to three- (average Cu−Br distance of 2.341 Å) and four-coordinated compounds (average Cu−Br distance of 2.496 Å) containing the fragment [Cu{PPh2(C6H4-X)}2Br], although they are closer to that of three-coordinated complexes. This result is in accordance with the presence of an intramolecular contact (not covalent bond) between the metal atoms. However, the geometry at copper(I) is better described as tetrahedral, clearly distorted by the rigidity of the metallacycle, with broad P−Cu−P angles. Finally, both independent molecules are connected in a dimer through four weak C−H···Br hydrogen bonds (see Supporting Information). Theoretical Studies. In order to explain the nature of the Hg(II)···M(I) M = (Au, Ag, Cu) interactions, we have carried out theoretical calculations at the HF and MP2 levels of theory on different model systems. To account for the metallophilic interaction strengths, we have built up three unbridged model systems [Hg(C6H5)2]···[Au(PMe3)2]+ (1a), [Hg(C6H5)2]··· [Ag(PMe3)2]+ (2a), and [Hg(C6H5)2]···[Cu(PMe3)2]+ (4a) (Figure 5; “a” refers to quasirelativistic pseudopotentials) The presence of unsupported interactions in these models permits analysis of the interaction energy, making use of the counterpoise correction to the basis-set superposition error (BSSE). If we compare the experimental structures with these model systems, we have broken a P−C bond of the bidentate C,P-donor ligand and we have changed the phenyl groups in the phosphorus atoms by hydrogen atoms in order to save computational costs. Models 1a, 2a, and 4a were built up through the disposition of the fully MP2-optimized mononuclear fragments in a perpendicular arrangement in order to avoid any other type of weak interactions and exclusively study the metallophilic interaction. The D2h point symmetry was assumed for the mercury fragment, while the D3h symmetry was used for the heterometallic [M(PH3)2]+ cation. We have evaluated the interaction energy at different intermetallic distances for models 1a, 2a, and 4a at the HF and MP2 levels of theory (see Figure 5). The MP2 curves display a minimum at 3.16 (1a), 3.11 (2a), and 3.05 Å (4a), respectively. These distances are longer than the ones determined experimentally (2.92 (Au···Hg), 3.03 (Ag···Hg), and 2.87 Å (Cu···Hg)), probably due to the substitution of the bridging o-C6H4PPh2 ligand by monodentate PH3 and C6H5 groups, even though the MP2 level of theory exaggerates the

Figure 4. ORTEP-style diagram of the molecular structure of complex 4·0.5C7H8 (30% probability). Hydrogen atoms have been omitted for clarity. E


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Organometallics

Figure 5. Theoretical model systems [Hg(C6H5)2]···[Au(PMe3)2]+ (1), [Hg(C6H5)2]···[Ag(PMe3)2]+ (2), and [Hg(C6H5)2]···[Cu(PMe3)2]+ (4) (top) and Hg···M (M = Au, Ag, or Cu) interaction curves at the HF and MP2 levels of theory, using quasirelativistic (QR) pseudopotentials (red curves) and nonrelativistic (NR) pseudopotentials (blue curves) (bottom).

Table 5. Interaction Energies and Equilibrium Distances for Models 1a−b, 2a−b, and 4a−b at the HF and MP2 Levels of Theory interaction energy (kJ·mol−1)/equilibrium distance (Å) Model Model Model Model Model Model a

1a 1b 2a 2b 4a 4b

MP2

HFa

ΔE interaction from QR to NR ECPs (kJ·mol−1)

−42.11/3.16 −35.36/3.31 −42.74/3.11 −35.69/3.22 −38.90/3.05 −31.57/3.18

Repulsive Repulsive Repulsive Repulsive Repulsive Repulsive

6.75 7.05 7.33

The repulsive behavior at the HF level is measured at the MP2 equilibrium distance.

fragments in the corresponding models arises from dispersive forces (van der Waals interactions). These interactions are of similar nature but weaker than the one described previously by us for the model [Hg(C6F5)2]··· [Au(C6F5)(PH3)], which mainly differs with the models studied in this work in the perhalophenyl groups bonded to Hg(II) and Au(I) centers, and led to a stabilization energy for the Au(I)···Hg(II) interaction of −73.3 kJ/mol.5 Also, if we compare the AuI···HgII, AgI···HgII, and CuI···HgII heterometallic interactions with the corresponding AuI···HgII and AuIII···HgII contacts studied previously in our research group in models

metallophilic attraction. The interaction energies related to these three metallophilic interactions at the MP2 level are −42.11 (Au···Hg), −42.74 (Ag···Hg), and −38.9 kJ·mol−1 (Cu···Hg). At the MP2 equilibrium distances, the HF curves are repulsive for the three models (see Table 5). If we assume that a possible electrostatic component of the interaction energy is obtained at the HF level and that the dispersion-type component of the interaction is obtained when correlation effects are included at the MP2 level, we can state that the interaction between Au(I), Ag(I), or Cu(I) with Hg(II) F


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Organometallics

than 0.05 in both cases (see Table 6). In contrast, in the case of models 1a and 1b, an important change in the charge over the

[Hg(C6H5)2]···[Au(C6F5)(PMe3)] (−38.9 kJ/mol) and [Hg(C6H5)2]···[Au(C6F5)Cl2(PMe3)] (−46.8 kJ/mol),30 respectively, we observe similar interaction strengths regardless of the oxidation state of the gold center or the ligands bonded to this metal ion. The main difference of the latter with the models studied in this paper is the perhalophenyl group bonded to Au(I) instead of a phosphine ligand or the AuIII fragment with two Cl and one C6F5 groups. In view of these results, we can state that, in the Hg···M (M = Au, Ag, Cu) interactions, the heterometal interacting with mercury, the ligands coordinated to them or, even, the formal oxidation state of the gold centers is not essential in the stabilization energy of these metallophilic interactions. However, the ligands linked to the mercury center (C6H5 or C6F5) provoke an important variation in the strength of the Hg(II)···Au(I) interaction, from −38.9 to −73.3 kJ/mol. On the other hand, as we have commented above, the relativistic effects for mercury are among the strongest ones, and these would affect the Au···Hg, Ag···Hg, and Cu···Hg interaction energies and distances. We have analyzed the absence of relativistic effects in models 1b, 2b, and 4b at the HF and MP2 levels of theory (see Figure 5; “b” refers to nonrelativistic pseudopotentials). These models are similar to models 1a, 2a, and 4a, respectively, but using nonrelativistic pseudopotentials and the corresponding basis set for the metals. Thus, the MP2 curves for 1b, 2b, and 4b show an attractive minimum at 3.31, 3.22, and 3.18 Å, respectively. These values, as expected, are slightly larger (+0.15 (Au···Hg), +0.11 (Ag···Hg), and +0.13 Å (Cu···Hg)) than the ones obtained for their respective relativistic models 1a, 2a, and 4a. The stabilization energy for these three models is −35.36 (1b), −35.69 (2b), and −31.57 kJ/mol (4b) (see Table 5). We have also carried out the analysis of the NBO charges (MP2 density) for model systems 1a−b, 2a−b, and 4a−b and for the corresponding monometallic fragments in each case. The [Hg(C6H5)2] fragment displays a similar charge on the Hg(II) center for the free [Hg(C6H5)2] fragment (+0.945) and for models 1a (+0.931), 2a (+0.934), and 4a (+0.929), indicating that the charge of the Hg(II) center is affected in a similar way when Hg(II) is not interacting with another heterometal and when it interacts with any element of group 11: CuI, AgI, or AuI. The same trend applies for the Cipso atoms bonded to Hg(II) in all cases. In the same way, when the same models are studied using nonrelativistic pseudopotentials (models [Hg(C6H5)2], 1b, 2b, and 4b), the results obtained for the charge at the mercury centers are, again, very similar: +1.069 ([Hg(C6H5)2]), +1.058 (1b), +1.066 (2b), and +1.061 (4b), indicating that, as in the case of the quasirelativistic (QR) models, all of them display a similar charge on this element. In contrast, if we analyze the Au(I), Ag(I), or Cu(I) centers, the results of the NBO charges are different, both in the free fragments and in the corresponding models interacting with the [Hg(C6H5)2] unit. Thus, while the charges on silver (+0.306) and copper (+0.302) are very similar in models 2a and 4a, in the case of model 1a, the formally Au(I) center displays a charge of +0.072, very close to a Au0 oxidation state. Similarly, the free [M(PH3)2]+ fragments display a parallel tendency, with +0.114, +0.384, and +0.290 being the corresponding NBO charges for the metal centers (Au, Ag, and Cu, respectively). When we compare the NBO charge of these metals when the relativity is not considered in models 1b, 2b, and 4b with the results obtained with models 1a, 2a and 4a, in which relativity is taken into account, it is possible to observe that the charges at the Ag and Cu centers do not suffer an important variation, less

Table 6. NBO Charges for the Free Fragments and for Models 1a, 2a, 4a and 1b, 2b, 4b at the MP2 Level Using QR and NR ECPs for the Metals NBO charges Model Model Model Model Model Model

1a 1b 2a 2b 4a 4b

Hg

Cipso

M

P

+0.931 +1.058 +0.935 +1.066 +0.929 +1.061

−0.485 −0.534 −0.488 −0.534 −0.489 −0.535

+0.072 +0.282 +0.306 +0.355 +0.302 +0.315

+0.236 +0.121 +0.120 +0.089 +0.134 +0.120

gold center from +0.282 (1b) to +0.072 (1a) is computed (see Figure 6). We have also checked that when relativistic effects

Figure 6. NBO charges at Au, Hg, and P atoms on model systems 1a and 1b.

are not considered for gold, it behaves like relativistic silver, as observed in their corresponding NBO charges and electronic configurations. Furthermore, the same trend is observed for the free fragments. This result reveals that, as expected, the relativistic effects have a higher influence in gold than in the other elements of the same group, such as silver and copper, in which the charge over the metals remains almost constant whether the relativity is considered or it is not. It is also worth mentioning that when relativistic effects are considered, the P atoms bonded to Au(I) display more positive charges than in the nonrelativistic case or with Ag(I) or Cu(I). The P atoms show a better donating ability to the relativistic Au(I). If we take into account the similar Hg(II)···M MP2 stabilization energies calculated above, we can conclude that the absence of relativistic effects seems to affect in the same way the metallophilic interaction strength (ca. 7 kJ/mol decrease) but to result in a larger increase in the NBO charge of Au(I) in the corresponding [Au(PH3)2]+ fragment (see Table 6). This last G


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Organometallics

C36H28AuClHgO4P2: C 42.41, H 2.77; found: C 42.40, H 2.76. MS (ES+): m/z 921.10 [AuHg(o-C6H4PPh2)2]+; (ES-): 98.94 [ClO4]−. ΛM (dichloromethane) = 52.6 Ω−1·cm2·mol−1. Synthesis of [AgHg(o-C 6H 4 PPh2 )2 ][BF4 ] (2) and [AgHg(oC6H4PPh2)2](m-CF3CO2) (3). To a solution of [Hg(2-C6H4PPh2)2] (0.164 g, 0.227 mmol) in 30 mL of dichloromethane was added AgBF4 (0.044 g, 0.227 mmol) (2) or Ag(CF3COO) (0.050 g, 0.227 mmol) (3). The reaction mixtures were stirred for 1 h, and the solutions were concentrated to ca. 2 mL. Further addition of n-hexane gave rise to the precipitation of complexes 2 and 3, respectively, as white solids. Data for 2: Yield: 90%; 1H NMR (300 MHz, CDCl3): δ = 7.19− 7.56 ppm (m, 28 H, aromatic Hs); 13C{1H} NMR (75.8 MHz, CDCl3): δ = 129.4 (m), 130.7 (s), 131.2 (s), 134.0 (m) due to the PPh2 carbons and low-intensity peaks at δ 128.6 (s), 130.0 (m), 135.0 (s), 138.6 (m), 140.0 (m), 177.8 (m) due to the C6H4 carbons; 31 1 P{ H} NMR (121.5 MHz, CDCl3): δ = 13.8 ppm (2d, 1J (107Ag−31P) = 467 Hz, 1J (109Ag−31P) = 538 Hz, 2 P); 19F NMR (283 MHz, CDCl3): δ = −151.9 ppm (s, 4F); FT-IR (Nujol mull): ν (BF 4 ) = 1097 cm −1 ; elemental analysis calcd. (%) for C36H28AgBF4HgP2: C 47.11, H 3.07; found: C 47.11, H 3.05. MS (ES+): m/z 831.04 [AgHg(o-C6H4PPh2)2]+; (ES-): 86.99 [BF4]−. ΛM (dichloromethane) = 62.6 Ω−1·cm2·mol−1. Data for 3: Yield: 90%; 1H NMR (300 MHz, CDCl3): δ = 7.20− 7.67 ppm (m, 28 H, aromatic Hs); 13C{1H} NMR (75.8 MHz, CDCl3): δ = 129.1 (m), 130.1 (s), 130.6 (s), 134.0 (m) due to the PPh2 carbons and low-intensity peaks at δ 128.2 (s), 131.4 (m), 135.0 (s), 138.4 (m), 141.2 (m), 177.9 (m) due to the C6H4 carbons; 31 1 P{ H} NMR (121.5 MHz, CDCl3): δ = 13.8 ppm (2d, 1J 107 ( Ag−31P) = 443 Hz, 1J (109Ag−31P) = 512 Hz, 2 P); 19F NMR (283 MHz, CDCl3): δ = −74.9 ppm (s, 3F); FT-IR (Nujol mull): ν (CF3COO) = 1654, 1373, and 1204 cm−1; elemental analysis calcd. (%) for C38H28AgF3HgO2P2: C 48.35, H 2.99; found: C 48.30, H 2.99. MS (ES+): m/z 831.03 [AgHg(o-C6H4PPh2)2]+; (ES-): 112.99 [CF3CO2]−. ΛM (dichloromethane) = 0.1 Ω−1·cm2·mol−1. Synthesis of [CuHg(o-C6H4PPh2)2Br] (4). To a dichloromethane solution (30 mL) of [Hg(2-C6H4PPh2)2] (0.164 g, 0.227 mmol) was added CuBr (0.033 g, 0.227 mmol). The reaction mixture was stirred for 60 min at room temperature. Evaporation of the solvent under vacuum and addition of n-hexane gave rise to complex 4 as a white solid. Yield: 82%. 1H NMR (300 MHz, CDCl3): δ = 7.14−7.46 ppm (m, 28 H, aromatic Hs); 13C{1H} NMR (75.8 MHz, CDCl3): δ = 128.6 (m), 129.8 (s), 132.3 (s), 133.7 (m) due to the PPh2 carbons and low-intensity peaks at δ 128.0 (s), 132.2 (m), 134.5 (s), 137.7 (m), 139.9 (m), 178.2 (m) due to the C6H4 carbons; 31P{1H} NMR (121.5 MHz, CDCl3): δ = −2.6 ppm (s, 2 P); elemental analysis calcd. (%) for C36H28AuBrHgP2: C 44.89, H 3.25; found: C 44.89, H 3.23. MS (ES+): m/z 787.07 [CuHg(o-C6H4PPh2)2]+; (ES-): 80.91 [Br]−. ΛM (dichloromethane) = 5.1 Ω−1·cm2·mol−1. Crystallography. Crystals were mounted in inert oil on glass fibers and transferred to the cold gas stream of a Nonius Kappa CCD diffractometer equipped with an Oxford Instruments low-temperature attachment. Data were collected using monochromated MoKa radiation (λ= 0.71073 Å). Scan type: ω and Φ. Absorption corrections: semiempirical (based on multiple scans). The structures were solved by Patterson and refined on F2 using the program SHELXL-97.46 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included using a riding model. Disorder of one of the THF molecules of 2·2THF was modeled with occupancies refined to 0.5 for each position. In 4·0.5C7H8 one of the phenyl rings is also disordered over two different positions with occupancies refined to 0.6 and 0.4. Further details of the data collection and refinement are given in Table S1. Selected bond lengths and angles are collected in Tables 1−4; the crystal structures of 1·2C2H4Cl2, 2·2THF, 3·THF and 4·0.5C7H8 appear in Figures 1-4. CCDC-1055853−1055856 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving. html (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223−336−033; or email: [email protected]).

characteristic is slightly more pronounced when the Au(I) center is maintaining an interaction with Hg(II). This result is similar to the one reported by us recently,30 in which the theoretical analysis of the Hg(II)···Au(I) d10−d10 and Hg(II)··· Au(III) d10−d8 interactions displayed a very similar interaction energy of ca. 40 kJ/mol and a clear reduction of the Au(III) NBO charge, while keeping the Hg(II) fragment unaffected, as in the present case. We also carried out natural population analysis (NPA) to compare the different electronic configurations (EC) that the metals display in these metallophilic interactions. Thus, as for the NBO analysis, the electronic configuration of mercury is the same in models 1a, 2a, and 4a, and it is close to a d10s1 configuration, taking into account the coordination of two phenyl ligands to the formally Hg(II) center (see Supporting Information Table S3). In the case of the heterometals, the orbitals 5d, 4d, and 3d for gold, silver, and copper, respectively, present the same occupancy, which is close to a filled d10 orbital. Nevertheless, while the s orbitals in the case of Cu and Ag show an occupancy of 0.61 and 0.58, respectively, in the case of model 1a, the gold 6s orbital is almost filled (0.91), very close to a real d10s1 configuration, taking into account the coordination of the phosphine ligands.

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CONCLUSIONS

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EXPERIMENTAL SECTION

The use of [Hg(o-C6H4PPh2)2] as precursor has allowed the synthesis of new heterometallic Hg−M (Au, Ag, Cu) complexes. Their X-ray structures display similar dispositions that make possible a theoretical comparison of these metallophilic interactions. The theoretical study quantifies a strength of ca. 40 kJ·mol−1 for the Hg···Au, Hg···Ag and Hg···Cu interactions. In all cases, the origin is the same, i.e. dispersive forces, which are reinforced by relativistic effects. In the Au(I)··· Hg(II) case, the interaction takes place between two almost d10s1 ions.

General Procedures. All reactions were carried out under dry and deoxygenated argon atmosphere using Schlenk techniques. Solvents used in the spectroscopic studies were degassed prior to use. [Au(tht)2]ClO4 and [Hg(2-C6H4PPh2)2] were prepared according to literature methods.44,45 Caution! Due to the toxicity of mercury compounds, extra care was taken to avoid contact with solid, solution, and airborne mercury products. Instrumentation. IR spectra in the 4000−200 cm−1 range were recorded on Nicolet Nexus FT-IR using Nujol mulls between polyethylene sheets. Carbon and hydrogen analyses were carried out with a PerkinElmer 240C microanalyzer. 31P{1H}, 13C{1H}, 1H, and 19 F NMR spectra were recorded on a Bruker ARX 300 spectrometer in CDCl3 solutions. Chemical shifts are quoted relative to H3PO4 85% (31P external), SiMe4 (1H and 13C, external), and CFCl3 (19F, external). Molar conductivity measurements were carried out with a digital Jenway 4010 instrument. Synthesis of [AuHg(o-C6H4PPh2)2]ClO4 (1). To a solution of [Hg(2C6H4PPh2)2] (0.164 g, 0.227 mmol) in CH2Cl2 (30 mL) was added one equivalent of [Au(tht)2]ClO4 (0.029 g, 0.227 mmol), and the mixture was stirred for 60 min at RT. Evaporation of the solvent under vacuum and addition of n-hexane gave rise to complex 1 as a white solid. Yield: 87%; 1H NMR (300 MHz, CDCl3): δ = 7.23−7.65 ppm (m, 28 H, aromatic Hs); 13C{1H} NMR (75.8 MHz, CDCl3): δ = 129.9 (m), 132.3 (s), 132.5 (s), 134.1 (m) due to the PPh2 carbons and low-intensity peaks at δ 128.0 (s), 129.0 (m), 135.6 (s), 137.2 (m), 140.2 (m), 176.9 (m) due to the C6H4 carbons; 31P{1H} NMR (121.5 MHz, CDCl3): δ = 38.6 ppm (s, 2 P); FT-IR (Nujol mull): ν (ClO4) = 1080 and 623 cm−1; elemental analysis calcd. (%) for H


Article

Organometallics Computational Details. All calculations were performed using the Gaussian 09 suite of programs47 using Hartree−Fock (HF) and MP248,49 levels of theory. The interaction energy between metal fragments at Hartree−Fock (HF) and MP2 levels of theory was obtained according to equation:

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(AB) ΔE = EAB − EA(AB) − EB(AB) = V (R )

A counterpoise correction for the basis-set superposition error (BSSE)50 on ΔE was thereby performed. We fitted the calculated points using a four-parameter equation, which had been previously used51 to derive the Herschbach-Laurie relation:

ΔE = V (R ) = A e−BR − CR−n Basis Sets. The 19-valence electron (VE) quasirelativistic (QR) pseudopotential (PP) was employed for gold, silver, and copper52 together with two f-type polarization functions.24 Similarly, the 20valence valence electron (VE) quasirelativistic (QR) pseudopotential (PP) of Andrae52 was employed for mercury together with two f-type polarization functions.53 The atoms P, and C were treated by Stuttgart pseudopotentials,54 including only the valence electrons for each atom. For these atoms double-ζ basis sets of ref 54 were used, augmented by d-type polarization functions.55 For the H atom, a double-ζ, plus a ptype polarization function was used.56

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ASSOCIATED CONTENT

* Supporting Information S

Tables of details of data collection and structure refinement, hydrogen bonds, NPA electronic configurations, and Cartesian coordinates; NMR spectra; and X-ray crystallographic data in CIF format for 1·2C2H4Cl2, 2·2THF, 3·THF, and 4·0.5C7H8 (CCDC 1055853−1055856). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00334.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The DGI (MEC)/FEDER (project number CTQ 2013-48635C2-2-P) is acknowledged for financial support. D.P. also acknowledges the C.A.R. for a FPI grant. We gratefully thank CESGA for computer support.

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REFERENCES

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