This is the accepted version of the journal article: Sánchez Férez, Francisco; Solans Monfort, Xavier; Calvet, Teresa; [et al.]. «A Hg(i) corrugated sheet assembled by auxiliary dioxole groups and Hg· · · inter- actions». CrystEngComm, Vol. 24, Issue 24 (June 2022), p. 4351-4355. DOI 10.1039/d2ce00347c This version is available at https://ddd.uab.cat/record/280649 under the terms of the license Please do not adjust margins COMMUNICATION A Hg(I) corrugated sheet assembled by adjuvant dioxole groups and Hg···π interactions Received 11th March 20xx, Francisco Sánchez-Férez,a Xavier Solans-Monfort,a Teresa Calvet,b Mercè Font-Bardia,c and Accepted 00th January 20xx Josefina Pons*a DOI: 10.1039/x0xx00000x The formation of a new double-stranded staircase Hg(I) from 2.495 to 2.557 Å, and the coordinated atoms, has been supramolecular assembly is reported. It is arranged into 2D attributed to their electronegativity, being shortened as corrugated sheets supported by Hg(I)-Odioxole and Hg···π electronegativity increases. In presence of an O-donor interactions, and resulting from the comproportionation carboxylate linker, the Hg-Hg distance is enclosed within 2.502- reaction between Hg(II) and Hg(0) species in DMF as solvent. 2.557 Å.1 Hg(I) has a strong tendency to form linear arrays due to its soft nature and it usually adopts low coordination numbers up to four, even though it is capable to accommodate Hg as a metal has the particularity of being capable to form a coordination numbers up to seven.9 This preferred linear sort of divalent, trivalent and tetravalent polycations arranged arrangement facilitates the formation of metal···π interactions either into linear [Hg2]2+ dimeric, [Hg3]2+ trimeric, [Hg4]2+ tetrameric and [Hg]n chains or into [Hg3]4+ triangles or [Hg]n which have proven to be pivotal in defining the arrangement of layers.1 All of them present differences in the formation macromolecules.10 The electrostatic origin of metal···π conditions, connectivity, geometry and Hg-Hg distance. In interaction made it emerge as one of the strongest noncovalent particular, the formation of the [Hg2]2+ dimeric cation is driven interactions but this strength is highly dependent on the by its slightly positive E˚ value of +0.115 V which facilitates that coordinatively saturation of the metal, the nature of the π Hg2+ and Hg0 can comproportionate into Hg2+ 2 as detailed donor aromatic ring and cooperativity with other nonbonding below:2 interactions as hydrogen bonds or π···π stacking.10 In the case Hg0 +Hg2+ → Hg2+2 E˚ = +0.115 V of Hg2+, the almost fully populated d orbitals combined with the This comproportionating ability has been reported to occur in large s-d orbital energy splitting hinder the sd hybridization, polar solvents, especially in N,N-dimethylformamide (DMF)3 or albeit evidence of d orbitals implication in Hg···π interactions by strong Lewis bases inter alia O- and N-donor ligands.4,5 has been reported.11 For this reason, π to Hg donation generally Although intrinsic reduction of Hg(II) at high temperature is occurs from the molecular orbitals of the aromatic ring to the uncommon, there are previously reported examples in the unoccupied 6s orbital.12 This favors delocalized π interactions of mentioned conditions.4 DMF under high temperature can act as Hg with an offset from the centroid ring and placed a reducing agent6,7 conducting the formation of Hg0 and triggers preferentially over two (πoff(2)) or three carbon atoms (πc(3)), comproportionation. The complexation of the [Hg2]2+ dimeric and minimize those in which Hg is sitting over the center of the cation is usually stabilized by both a lower solubility compared ring (πcen(6)). These results were braced by a statistical analysis to their Hg(II) analogous and the weakening of the donor on metal···π interactions which reinforced that transition character of the ligands that minimize destabilization of the Hg- metals preferred an offset over the center of the ring in Hg bond.8 Correlation between Hg-Hg bond length, ranging delocalized π interactions.13 Thus far, there are about 28 structures containing the [Hg2]2+ specie being coordinated to O atoms.14 From them, six were constructed from carboxylate a. Departament de Química, Universitat Autònoma de Barcelona, 08193-Bellaterra, linkers inter alia two alaninate,15 one trifluoroacetate,16 one Barcelona, Spain acetate,17 one gluconate18 and one phthalate,19 all presenting b. Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain. 1D polymeric structures. Above all, only [Hg2(o-phthalate)2]n is c. Unitat de Difracció de Raig-X, Centres Científics i Tecnològics de la Universitat de arranged through an aromatic carboxylate. Examples of Barcelona (CCiTUB), Universitat de Barcelona, Solé i Sabarís, 1-3, 08028 coordinated dioxole groups to metal centers are scarce and only Barcelona, Spain † Electronic Supplementary Information (ESI) available: Experimental details, single d10 metal ions have exhibited such coordination ability. A crystal data, FTIR-ATR and 1H NMR spectra. CCDC 2155639. For ESI and reported case in the literature with Zn(II)20 and one found in our crystallographic data in .cif or other electronic format see DOI: 10.1039/x0xx00000x Please do not adjust margins Please do not adjust margins COMMUNICATION Journal Name group with Hg(II)21 have been found hitherto. In our case, contribution in the 2D fingerprint plot (S.I: Fig. S3). These chains Hg(II)···Odioxole and Hg···C interactions promoted the formation are assembled into 2D corrugated sheets through two Hg(I)- of a 2D supramolecular assembly. Therefore, the coordination Odioxole interactions (Hg1 – O7, 3.081(2) Å and Hg2 – O4, 3.132 chemistry and structural arrangement of Hg(I) with aromatic Å) complemented by double C-H···O interactions between the carboxylates has not been extensively explored, even less in Pip ligands (Fig. 3, Table S2). The importance of metal···π presence of dioxole groups. In this work, we provide an example of a Hg(I) aromatic carboxylate complex, which assembles by a) O1 Hg2 Hg(I)···Odioxole interactions, further expanded into a 3D Hg1 O5 supramolecular structure by Hg···π interactions. The formation of the [Hg2]2+ dimeric cation was observed after recrystallization of [Hg(Pip)2(4,4’-bipy)]n (1) in DMF as solvent at 105˚C for 1h.22 In these conditions the formation of Hg(0) is observed, which combined with the remaining Hg(II) in solution b) O6 comproportionate to give the [Hg2]2+ specie. The subsequent O1 Hg1 Hg2 complexation with Pip ligands results in a less soluble O5 compound that gradually nucleated and formed single crystals H11 O2 of [Hg2(Pip)2] (2). Complex 2 has been characterized by elemental analysis, FTIR- ATR and 1H NMR spectroscopies (S.I: Fig. S1 and S2), and single crystal X-ray diffraction (see details in the Supporting Information). The deprotonation and subsequent coordination Figure 1. Crystal structure representation of 2. a) dinuclear [Hg2Pip2] units displaying (µ1- of the Pip linker has been traced by the vanishing of the η1 coordination modes. b) tetranuclear [Hg2Pip4] units supported by Hg··O and C- H···O interactions (represented as dashed lines). Color codes: suva grey (Hg), υ(C=O)COOH band and the rising of bands attributable to red(O), grey (C) and white (H). υas(COO) at 1580 cm-1 and υs(COO) at 1431 cm-1. The coordination modes of the carboxylate can be inferred by a) b) calculating Δ values (Δ = υas(COO) - υs(COO)), which were found Hg1 to be 149 cm-1 falling in mid-range between bidentate bridging Hg2 πoff(η2) and bidentate chelate coordination mode.23 Therefore, this O5 O5 Hg2 data suggests the presence of both bridging and chelate Hg1 Hg2 coordination modes of the Pip units. These results agree with Hg1 πc(η3) the structural data obtained from the single crystal X-ray a diffraction method. The 1H NMR spectrum in DMSO-d6 displays the aromatic signals of Pip at 7.53, 7.35 and 6.96 ppm and the - b c CH2- at 6.08 ppm (free HPip: 7.55, 7.36, 6.99, 6.11 ppm). Compound 2 crystallizes in the Monoclinic, P21/n space group Figure 2. View of the a) 1D double-stranded staircase assembly, and b) Hg1··· πoff(η2) (S.I: Table S1) and it is composed of linear [Hg2(Pip)2] units that and Hg2···πc(η3) interactions . hold two monodentate (µ1-η1) Pip ligands (Fig. 1a), with a coordination number of 2 (Hg1-O1, 2.132(2) Å and Hg2-O5, 2.126(2) Å, that are below the sum of their covalent radii of 2.21 Å)24 displaying a Hg-Hg bond length of 2.51602(18) Å (Fig. 1a), that falls within the reported range between 2.502 and 2.557 O1 Å.1 Distances below the van der Waals sum of radii (vdWs, from b H11 O2 2.21 to 3.02 Å) have previously been included defining the secondary coordination number, and according to this criteria H8 a the coordination number of Hg1 is [2+3] (Hg1 – O2, 2.742(2) Å; c Hg1 – O6, 2.782(2) Å; and Hg1 – O5, 3.013(2) Å) and Hg2 is [2+1] Figure 3. View of the assembly of 2D corrugated sheets supported by Hg···Odioxole and C- (Hg2 – O6, 2.891(2) Å).25 The [Hg2(Pip)2] unit are joined together H···O interactions. in tetranuclear [Hg4(Pip)4] clusters by Pip ligands through the secondary coordination (2.742(2) Å and 2.891(2) Å) and interactions and their effect on the final arrangement have supported by C-H···O interactions between Pip ligands (Fig. 1b). already been demonstrated10,26 but no results were found These [Hg4(Pip)4] clusters are further expanded into a 1D regarding [Hg2]2+ cation. A search in the Cambridge Structural double-stranded staircase assembly along b axis through Hg1 – Database (CSD)14 of structures containing the [Hg2]2+ cation and O5, 3.013(2) Å (Fig. 2a). This arrangement is supported by N, O, S and P-donor atoms resulted in 129 hits. Disordered delocalized Hg1··· πoff(2) and Hg2···πc(3) interactions occurring structures were eliminated in order to include only precise within the supramolecular chains (Fig. 2b), that display crystal structure determinations. This data was sifted through highlighted regions over the aromatic rings in the Hirshfeld those with aromatic rings and was reduced to a total of 50 surface analysis and a 9.6% of Hg···C contact surface area entries with potential Hg···π interactions. One requirement is 2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins COMMUNICATION Table 1. CSD results of the selected structures exhibiting Hg(I)···π interactions Offsetb Complex CNa dHgC (Å) dHgCg (Å) dHgP (Å) Conformation Ref. (Å) 3.405(3); 3.488(3); 3.720c 3.342 1.634 This [Hg2(Pip)2] (2) 2 πoff(2) + πc(3) 3.358(3); 3.460(3); 3.647(3) 3.446d 3.318 0.9305 work 3.335; 3.419; 3.469; 3.646; 3.256e 3.213 0.5274 3.687; 3.737 [Hg2(o-phthalate)2]n (A) 2 πcen(6) + πoff(2) 19 3.801e 3.217 2.024 3.341; 3.459 (Hg2)Hg3(O3P(C6H4)PO3)2·2H2 2 3.12(2); 3.41(2); 3.45(2) 3.424f 3.137 1.372 πc(3) 27 O (B) Hg2(N(Ar)(SiMe3))2 (C) 2 3.155(3); 3.361(3); 3.458(4) 3.380g 3.143 1.243 πc(3) πoff(2) 28 Hg2(N(Ar)(SiPri3))2 (D) 2 3.413(6); 3.458(5) 3.620h 3.362 1.342 [Hg2(LoPh)]·(ClO4)2·(CH3NO2) 3 3.37(3); 3.63(3) 3.817i 3.301 1.917 πoff(2) (E) 3.478(6); 3.672(6); 3.788(8); 3.732j 3.466 1.384 [Hg2(LmPh)(DMF)2]·(ClO4)2 (F) 3 3.524(7); 3.575(8); 3.721j 3.476 1.328 πc(3) + πoff(2) 29 3.395(8); 3.540(7); 3.836k 3.300 1.956 3.28(1); 3.41(1); 3.62(1); 3.485l 3.255 1.245 [Hg2(LpPh)]·(ClO4)2 (G) 3 3.51(1); 3.66(1); 3.719l 3.497 1.266 πc(3) + πoff(2) 3.30(1); 3.58(1); 3.61(1); 3.628m 3.294 1.521 3.090(4); 3.320(4); 3.510(4); [Hg2((MesNCMe)2CH)2]·hexa 3.430n 3.077 1.516 2 3.081(4); 3.248(4); πc(3) 30 ne (H) 3.322o 3.060 1.293 3.452(4); 3.338(6); 3.570(7); 3.590(6); 3.519p 3.331 1.135 [Hg2(TIP)2](ClO4)2 (I) 3 πc(3) 31 3.428(2); 3.508(6) 3.620q 3.341 1.394 a CN = coordination number; boffset = !(dMC 2 -dMP 2 ). dHgC = distance Hg···C atom; dHgCg = distance Hg···centroid, dHgP = distance Hg···plane defined by the aromatic ring; Centroids: cC(2)-C(3)-C(4)-C(5)-C(7)-C(8); dC(10)-C(11)-C(12)-C(14)-C(15)-C(16); e C(2B)-C(3B)-C(4B)-C(5B)-C(6B)-C(7B); fC(1A)-C(2A)-C(3A)- C(4A)-C(5A)-C(6A); g C(10B)-C(15B)-C(16B)-C(17B)-C(34B)-C(37B); h C(10)-C(24)-C(33)-C(40)-C(41)-C(42); iC(1)-C(2)-C(3)-C(4)-C(5)-N(1);jC(10)-C(11)-C(12)- C(13)-C(14)-C(15); kC(1)-C(2)-C(3)-C(4)-C(5)-N(1); lC(10)-C(11)-C(12)-C(13)-C(14)-C(15); m C(44)-C(45)-C(46)-C(47)-C(48)-N(12); nC(15)-C(16)-C(17)-C(18)-C(19)- C(20); o C(44)-C(45)-C(46)-C(47)-C(48)-C(49); p N(3A)-C(4A)-C(5A)-C(6A)-C(13A); q S(1A)-C(14A)-C(15A)-C(16A)-C(17A) . (O3P(C6H4)PO3)2 = 1,4- phenylenebisphosphonic acid; N(Ar)(SiMe3) = N-(2,6-bis(Diphenylmethyl)-4-isopropylphenyl)-1,1,1-trimethylsilanaminato; N(Ar)(SiPri3) = N-(2,6- bis(Diphenylmethyl)-4-methylphenyl)-1,1,1-tri-isopropylsilanaminato; LoPh = 1,2-bis(3-(2-Pyridyl)pyrazol-1-ylmethyl)benzene-N,N',N'',N'''; LmPh = 1,3-bis(3-(2- Pyridyl)pyrazol-1-ylmethyl)benzene-N,N',N'',N'''; LpPh = 1,4-bis(3-(2-Pyridyl)pyrazol-1-ylmethyl)benzene-N,N',N'',N'''; ((MesNCMe)2CH) = 1,3-bis(2,6-di- isopropylphenyl)-N-(trimethylsilyl)-1,3-dihydro-2H-1,3,2-diazaborol-2-amino; TIP = 2-(2-thienyl)-1H-imidazo[4,5-f][1,10]phenanthroline-N7,N8. that metal acceptor has a coordinatively unsaturated orientation of the aromatic rings towards the [Hg2]2+ cation.5 Of environment that allows the bulky aromatic ring to get closer. them, only 9 hits presented delocalized π interactions with The vast majority presents crowded structures with [Hg2]2+, considering either Hg(I) to benzene plane distance (dHgP) coordination numbers of 2 with secondary interactions up to 7 below to vdWs of Hg and C atoms (3.45 Å)11 or Hg(I) to centroid [2+5]9 with solvent molecules either below or over their vdWs, distance below 4.0 Å13. For all the structures each Hg···π that hinders Hg(I)···π interactions. Besides in some examples interaction has been split into the coordination number of the the geometric preferences of the ligands hamper the proper Hg(I) atom, the distances Please do not adjust margins Please do not adjust margins COMMUNICATION between Hg and i) the nearest C atoms (dHgC); ii) the ring centroid (dHgCg); iii) the plane containing the aromatic ring (dHgP); the offset, which is defined as √(dHgCg 2 -dHgP 2 )13 and the conformation12, resulting in 14 Hg(I)···π interactions. Each interaction with the mentioned parameters has been summarized in Table 1. The general trend is that an offset of the Hg(I) center over sitting in the ring centroid axis is preferred, being πc(η3) slightly favored over πoff(2). Only [Hg2(o- phthalate)2]n (A) presents a small offset of 0.5274 Å and exhibits a πcen(6) conformation. Among them, E, G and I present Hg(I)···π···π cooperativity, which is reported to be a prevailing motif by enhancing the strength of the π···π interaction.10 The πoff(2) and πc(3) conformations are present in the remaining structures (B, C, D, F, H) with offset values from 0.9305 to 2.024 Å and between 1.243 and 1.516 Å, respectively. It can be inferred that πc(3) conformation (B, C, F, G, H and I) limits the offset range by anchoring the Hg(I) ion and preventing it to place out of the aromatic ring. The smallest offsets have been found in complexes 2 and A, both bearing structures that predispose Hg(I) atoms to sit closer to the centroid of the aromatic ring. Besides, the interaction of the dioxole O atoms to Hg1 in 2 reduce Hg···π, resulting in πoff(2) while the coordinatively unsaturated Hg1 can accommodate the πc(3) interaction. DFT (B3LYP-D2) calculations have been performed to analyse the interaction between [Hg2(Pip)2] dimers. For that, two sets of calculations were carried out: first, a full periodic calculation of Figure 4. Models constructed to analyse the interaction between dimers and the the crystal structure to determine the existing interactions associated interaction energies (without including dispersion forces in parenthesis). Yellow spots correspond to the BCPs involving Hg cations. Values in kJ mol-1 through the Bader’s Atom In Molecules (QTAIM) theory and, secondly, finite molecular calculations of all potential close interactions. The electron density and its Laplacian in the BCPs [Hg2(Pip)2] units to quantify the interaction strength between between Hg and the oxygen atoms or Hg and the aromatic ring dimers. Both sets of calculations were done with Crystal17 indicate that the interaction is mainly of electrostatic and/or package, and the basis sets were similar to those used for Van der Waals nature. The computed interaction energies describing related Hg complexes (See Supplementary between dimers range from 184.8 and 95.6 kJ mol-1. The Information). Figure 4 shows the four models constructed to strongest interaction is found for dimers interacting through determine the interaction strength between dimers, the both an out-of-plane Hg···OCOO and a Hg···p interaction while corresponding interaction energies (with and without Grimme’s the weakest interactions take place through the dioxoles. correction), and the bond critical points (BCP) involving Hg Interestingly, while the Hg···OCOO in-plane interaction is centres. Table S3 reports the main properties for the BCP marginally stronger than the out-of-plane one (in agreement involving Hg. with the shorter Hg····O distance), the Hg···p interaction, only present in the latter case, is of the same order of magnitude and The analysis performed with TOPOND located BCPs between thus, the staircase stacking is, overall stronger than the in-plane the two Hg, the Hg and the nearest O atoms (in-plane COO, out- one. of-plane -COO and dioxole fragments) as well as a BCP located in between Hg and the closest aromatic ring. The presence of Conclusions these BCP are indicative of a Hg-Hg, Hg-O and Hg···p Please do not adjust margins Please do not adjust margins Journal Name COMMUNICATION The use of DMF as solvent and the decomposition of precursor 12 H. B. Yi, H. M. Lee and K. S. Kim, J. Chem. Theory Comput., 1 to give Hg(0), has driven the formation of the [Hg2]2+ cation, 2009, 5, 1709–1717. which after coordination with Pip linker has been stabilized 13 A. Banerjee, A. Saha and B. K. Saha, Cryst. Growth Des., through precipitation by the low solubility of complex 2. Hg···π 2019, 19, 7264–7270. interactions cooperate in the formation of the double-stranded 14 C. R. Groom, I. J. Bruno, M. P. Lightfoot and S. C. Ward, staircase chains, which are connected into a 2D sheets by an Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater., uncommon Hg(I)-Odioxole interaction. Besides, literature results of Hg(I)···π interactions have been compiled and analyzed, 2016, 72, 171–179. revealing that πc(3) conformation is slightly preferred over 15 C. D. L. Saunders, N. Burford, U. Werner-Zwanziger and R. πoff(2) for the [Hg2]2+ cation. Mcdonald, 2008, 47, 3693–3699. 16 M. Sikirica and D. Grdenić, Acta Crystallogr. Sect. B, 1974, 30, 144–146. Author Contributions 17 T. J. Prior, Acta Crystallogr. Sect. E Struct. Reports Online, 2005, 61, m1523-1524. Conceptualization, J.P.; data curation, F.S.-F. and M.F.-B.; formal 18 I. G. Konkina, S. P. Ivanov and Y. I. Murinov, Russ. J. Inorg. analysis, F.S.-F. and M.F.-B.; funding acquisition, J.P.; investigation, Chem., 2019, 64, 201–206. F.S.-F.; methodology, F.S.-F.; project administration, J.P.; resources, 19 B. Lindh, 1967, 21, 2743–2752. T.C. and J.P.; software, F.S.-F.; supervision, J.P.; validation, T.C. and 20 P. V. Dau, L. R. Polanco and S. M. Cohen, Dalton Trans., J.P.; visualization, F.S.-F.; writing—original draft, F.S.-F.; writing— 2013, 42, 4013–4018. review and editing, T.C. and J.P. 21 D. Ejarque, F. Sánchez-Férez, J. A. Ayllón, T. Calvet, M. Font-Bardia and J. Pons, Cryst. Growth Des., 2020, 20, 383– Conflicts of interest 400. 22 F. Sánchez-Férez, X. Solans-Monfort, T. Calvet, M. Font- There are no conflicts to declare Bardia and J. Pons, Inorg. Chem., 2022, 61, 4965-4979. 23 G. B. Deacon and R. J. Phillips, Coord. Chem. Rev., 1980, 33, 227–250. Acknowledgements 24 J. G. Wright, M. J. Natan, F. M. Macdonnell, D. M. 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