Supramolecular Assembly of Metal Complexes by (Aryl)I ⋯ d z2 [Pt II ] Halogen Bond

. The theoretical data for the half-lantern complexes [Pt(C^N)(μ-S^N)] 2 ( 1 – 3 ; С^N is cyclometalated 2-Ph-benzothiazole; S^N is 2-SH-pyridine 1 , 2-SH-benzoxazole 2 , 2-SH-tetrafluorobenzothiazole 3 ) indicate that the Pt···Pt orbital interaction leads to an increment of the nucleophilicity of the outer d z2 -orbitals to provide assembly with electrophilic species. 1 – 3 were co-crystallized with bifunctional halogen bond (XB) donors to give adducts ( 1 – 3 ) 2 ∙(1,4-diiodotetrafluorobenzene) and infinite polymeric [ 1 ·1


Introduction
Halogen bonding (XB) is an interdisciplinary area of rapidly rising interest as collaterally reflected in a substantial amount of relevant reviews and book chapters. Together with other weak interactions such as hydrogen-, [24] chalcogen- [25][26][27] or pnictogen [28] bonding, metallophilic, [29] and π-π interactions, [30] XB has been recognized as a useful tool for design of supramolecular systems and, in particular, for crystal engineering.
In the vast majority of XB studies, organic iodine species R EWG I featuring electron withdrawing group R EWG were applied as σ-hole (h) donors, while commonly used accepting centers included electronegative hetero-atoms bearing lone pair(s) (LP) such as halogens and also O, S, N, P and other atoms, electron-donating C (e.g.-CC -, or -system in alkene, alkyne, arene).Incomparably less common is the application of dz 2 -orbital donating positively charged metal centers as XB acceptors; a metal can act as XB acceptor if it contains at least one LP, which could interact with empty σ*-orbital(s) of appropriate XB donor(s).[33][34][35][36] All these XBs with the metals were observed in simple (often 1:1) adducts, while assembly or supramolecular design via R EWG X⋯dz 2 [M] XB of positively charged dz 2 [M] centers and σh-X-donating species has never been performed and this task was challenging.

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For the current work we addressed the known half-lantern complexes [37][38] (Figure 1) featuring the bridging (thio)azaheterocyclic ligands of the rigid geometry.These ligands serve as molecular staples bringing two metal centers and stimulating repulsive metal-metal interactions between dz 2 -orbitals of two Pt II centers.This repulsion, as we expected, should lead to the increased nucleophilicity of the outer orbitals.Consequently, metal centers with the increased nucleophilicity of the outer dz 2 Pt II orbitals might behave as synthons for the XB assembly involving metal centers.As σh donor we employed two symmetric iodoperfluoroarenes (Figure 2) that are rather commonly applied for XB crystal engineering (for statistics of their usage see our recent works [39][40] ).

Results and Discussion
XRD and MEP data for the XB donors and acceptors.The single-crystal X-ray diffraction (XRD) studies of parent half-lanterns 1-2 (CSD codes: RORTEZ and JACTAL, correspondingly) and 3 (this work; the Supporting Information) revealed that their structures consist of the centrosymmetric dimeric platinum complexes, where both Pt II centers exhibit a square-planar environment.The Pt-Pt distances (2.8515-2.9942Å) in each Pt2 core are less than the sum of Bondi van der Waals radii (RvdW; 3.5 Å) and this comparison favors the chemical bond between the metal centers [41][42][43][44][45][46][47][48] (Table S1, the Supporting Information).A simplified molecular orbital approach indicates that the axial interactions of the metal centers led to the dz 2 -orbitals overlap to give bonding (dσ) and antibonding (dσ*) orbitals.The antibonding character of HOMO of the dinuclear d 8 -d 8 complexes may explain why does the oxidation leads to enhanced Pt-Pt bonding on going from (Pt II )2 (2.798-2.994Å; Table S1) to (Pt III )2 (2.518-2.680Å). [49] To get a preliminary estimate of the possibility of electrostatic interaction between halflantern complexes 1-3 (Figure 3 for 2-3; Figure 5b for 1) and bifunctional XB donors 1,4-FIB

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In addition, and for comparison purposes, we also computed the MEP surface of two additional species: (i) a mononuclear model (Figure 5a) of the complex in order to analyze the effect of the Pt   (c) at the PBE0-D3/def2-TZVP level of theory; the values at the Pt and S-atoms are given in kcal/mol.The color scheme is taken from Politzer's work (Ref. [50]).
As expected, both 1,4-FIB and 1,1'-FIDB exhibit large and deep σh (+31.4 and +32.3 kcal/mol, respectively).The value at the negative belt (dark blue color) at the I atom is very small in both compounds (-1.3 kcal/mol) and that the σh is extended up to the light blue In all these structures, we observed the decrease of Pt-Pt distances as compared to the parent complexes (by 0.02-0.06Å) accompanied with the increase of the I-C bond length with respect to 1,4-FIB and 1,1'-FIDB (by 0.06-0.08Å; Table 1).These data along with the MEP data (see above) located on the σh of the I atom indicate that I•••Pt short contacts are due to 10.1002/chem.202001196

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XB in accord with the IUPAC criteria for Type II XB interactions; [51] the iodine atom from 1,4-FIB acts as a σh donor, which interacts with a dz 2 -orbital of a platinum(II) center.

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shorter than RvdW are given by dotted lines and thermal ellipsoids are shown at the 50% probability level.
The second type contact between the 1,1'-FIDB and the heterocyclic S atoms is 10.1002/chem.202001196

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DFT calculations should be further performed.
Theoretical study of XB.We computed the interaction energies of supramolecular dimeric complexes (1)2-(2)2•1,4-FIB and (1)•(1,1'-FIDB) (Figure 12) retrieved from the X-ray structures and found that these energies are moderately strong and in agreement with the obtained MEP data (see above).We studied the two types of XB in the adduct of 32•1,4-FIB (Figure 10), namely with the Pt center and with the π-system (Figure 12b,c) and the latter is weaker than the former, as expected taking into consideration the MEP surface.The supramolecular dimeric complexes were studied using the QTAIM analysis (Figures S11-13).The distribution of bond critical points (CPs) and bond paths reveals that in the three adducts, the I atom is linked to the Pt metal center and also to an H-atom of the aromatic ligand.In (3)2•1,4-FIB, the I is connected to the Pt II center and also to the F-atom of the fluorinated ligand.In (3)2•1,4-FIB, where the I points to the π-system, the interaction is characterized by a single bond CP and bond path connecting the I to one C atom of the ring.In Table 2, we summarize the values or ρ(r), electronic potential energy density [V(r)] and electronic kinetic energy densities [G(r)] at the critical points labeled in (Figures S11-S13).
The energy contributions of each interaction based on the AIM parameters (E = 0.5V(r) for 10.1002/chem.202001196

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HB [63] and E = 0.556V(r) [64] for XB] are also included.As can be inferred from inspection of the obtained data, the XB is the dominating interaction and that the HB is weak (1-2 kcal/mol).In accord with the MEP analysis, the XB contribution is larger 1 (-8.7 and -7.6 kcal/mol) than in the rest of complexes.It is noteworthy that the I•••F interaction also contributes to the binding energy in 2.1 kcal/mol, thus indicating that this interaction is attractive in its nature.In fact, the F atom of the ligand points to a region of the I-atom where the MEP value is positive.As previously commented (Figure 4) the σh at the I-atom is very extended and the negative belt is very thin and insignificant.In general, the energies predicted by the QTAIM parameters are smaller than those using the standard PBE0 binding energies probably because the QTAIM does not take into account long-range interactions that also participate in the stabilization of the supramolecular assembly.Finally, it is worthy to comment that the behavior of the energy densities (Vr and Gr) at the bond CP that interconnects the Pt atoms, denoted as CP(Pt  In an effort to shed light specifically on the I•••Pt II interaction, we performed a Natural Bond Orbital analysis focusing on the second order perturbation analysis, since it is convenient to evaluate donor-acceptor interactions.In Table 3, we collected the orbital interactions from (not pointing directly to the Pt atom).However, in this system there is also an important contribution arising from a σ(Pt-S) → σ*(C-I) electron charge donation, resulting in a concomitant stabilization energy of 3.77 kcal/mol.The orbital contribution of either HB in the rest of complexes, or the F•••I interaction in this complex are negligible, thus suggesting that electrostatic effects rather than orbital effects are responsible for those interactions. 10.1002/chem.202001196

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Donor
Acceptor Total E (2) (kcal/mol) E (PBE0) Finally, we have also examined orbital donor-acceptor interactions between the Pt atoms in both the adducts and compounds (Table 4).A very strong orbital interaction (ranging from 42 to 48 kcal/mol) is found in all adducts between the lone pair at Pt II located at the 5dz2 orbital and the empty 6dz orbital of the other Pt II atom (the one that is interacting with the iodine atom).This orbital interaction is significantly smaller in 1-3 (Table 4) that range from 6 to 18 kcal/mol.Therefore the formation of XB has a strong effect on the Pt II •••Pt II interaction.
Table 4. Orbital donor-acceptor interactions for the obtained adducts and parent complexes 1-3 at the PBE0/def2-TZVP level of theory.LP and LP* stands for lone pair, and unfilled lone pair orbital, respectively.

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( Finally, we computed the noncovalent interaction plot (NCIplot) for (3)2•1,4-FIB (Figure 13); this method is a convenient computation tool to identify which regions in a supramolecular complex interact and to know the attractive or repulsive nature of the interaction.The analysis of the plot indicates a small and green (meaning weak attractive) isosurface between the F and I atoms, thus clearly demonstrating that this interaction also contributes to the stabilization of the assembly.The plot also shows the existence of XB between the I-atom and the Pt II center and that the interaction is extended towards the S and C atoms attached to Pt II .This allows the consideration of the Pt-S and Pt-C bonds as an integrated XB acceptor sites. 10.1002/chem.202001196

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Chemistry -A European Journal This article is protected by copyright.All rights reserved.Approaches to identification of the XB in solutions.Interplays between 1-3 and the h donors were studied in solutions by 195 Pt NMR, cyclic voltammetry (CV), [65][66] and also by UV-vis. [67](i) 195 Pt NMR studies.Although NMR could be used for recognition of XB in the solid state and in solutions, this method is substantially less common than X-ray crystallography as it provides only collateral identification of XB by detection the spectral changes between bonded and unbonded forms.In solutions, conventional NMR and chemical shift titration NMR experiments [68]    (ii) CV.Complexes 1-3 undergo electrochemically reversible (2; E1/2 0.36 V) or quasireversible (Epa 0.53 V for 1, 0.07 V for 3) oxidation (vs.Fc + /Fc) corresponding to the first step (Pt II 2/Pt III 2) of the 2e --oxidation Pt II 2/Pt II 2 to Pt III 2/Pt III 2 accordingly to Ref. [41,[69][70][71][72] (Table 5,

Figure S19).
To study the effect of the added perfluoroarene on the potential, we used 1:20 molar ratios between any one of 1-3 and 1,4-FIB (or 1,1'-FIDB) to minimize competitive interactions of the half-lanterns with solvent molecules and also with the supporting electrolyte.Upon the addition of 1,4-FIB and 1,1'-FIDB to a solution of 1 in CH2Cl2, the starting curve splits into two oxidation peaks, one with a shift of 200 mV and 120 mV to the cathodic direction and the other one exhibiting 420 mV and 700 mV shift to the anodic area.We assume that these changes may be associated with the linkage of the added XB donor to one of the platinum sites resulting in CT from dz 2 Pt II -orbitals to iodine σh.This CT results in the anodic shift of one of the oxidation peaks corresponding to the generation of mixed-valent Pt II -Pt III species. [72].1002/chem.202001196

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Entry for the Table of Contents
Half-lantern dz 2 [Pt II 2] complexes, where Pt II 2 center exhibits an increased nucleophilicity of the outer orbitals (proved by DFT calculations) were assembled with symmetric XB donating diiodoperfluoroarenes to give extended supramolecular arrays formed v ia (Aryl)I•••dz 2 [Pt II ] XB that was studied by XRD and supported by extensive theoretical calculations.The CV, 195 Pt NMR, and UV-vis studies provide evidences that the XB is preserved in solutions.

Figure 1 .
Figure 1.Half-lantern complexes as XB acceptors and complex numbering.

Figure 2 .
Figure 2. Bifunctional XB donors employed for this study.

Figure 9 .
Figure 9.A fragment of the crystal structure of 22•1,4-FIB.Contacts shorter than RvdW are

Figure 10 .
Figure 10.A fragment of the crystal structure of 32•1,4-FIB.Contacts shorter than RvdW are represents an area where molecules come into contacts, and its analysis gives the possibility of an additional insight into the nature of intermolecular interactions in the crystal state.The obtained Hirshfeld surface plots (Figures S4, S5, S10) display a surface where contacts shorter than RvdW have negative values of dnorm and appear as conspicuous red spots, while contacts longer than RvdW have positive values of dnorm and are mapped in blue.The analysis for all four adducts expectedly indicates the domination of the contacts involving hydrogens).Other important contacts include I•••Pt (8%; the contribution is indicated by the contribution of contact of I with all atoms) with involvement of I•••C (12% for 12•1,4-FIB, 8% for 12•1,4-FIB and 15% for [1•1,1'-FIDB]n) contacts.For 22•1,4-FIB, we found a reduced contribution of I•••Pt (3%) and increased 10.1002/chem.202001196Accepted Manuscript Chemistry -A European Journal This article is protected by copyright.All rights reserved.contribution of I•••C (24%) contacts; a bright red spot from the F•••I (12%) contacts was also detected.

Figure 11 ).
Figure 11).The fingerprint plot and percentage contributions of each interaction to the

Figure S11 .
Figure S11.That is, the energy density values are significantly smaller in (1)-(2) compared to PtII  atomic orbitals to the antibonding C-I orbital σ*(C-I) and from the LPs of I to antibonding σ(C-H) orbital.The inspection of these data indicates that the orbital contribution is large for the LP(Pt) → σ*(C-I) in supramolecular dimeric complexes (1)2•1,4-FIB, (1)•(1,1'-FIDB), and (2)2•1,4-FIB and these conclusions are in line to the AIM, MEP, and energetic results.In fact, the orbital contribution is very similar to the binding energies, thus evidencing the importance or orbital donor-acceptor interactions.For (3)2•1,4-FIB, the LP(Pt) → σ*(C-I) contribution is smaller (3.80 kcal/mol) in line to the geometry of this complex where the C-I bond is displaced

Figure 13 .
Figure 13.NCI surfaces of (3)2•1,4-FIB.The gradient cut-off is s = 0.35 a.u., and the color could provide useful information by utilization of XB acceptors featuring NMRactive nuclei such as, for instance, 195 Pt.However, 195 Pt NMR has never been used for recognition of the I•••Pt XB and this work is the first attempt of 195 Pt NMR identification of XB involving platinum (II) centers.Half-lanterns 1-3 in CD2Cl2 exhibit resonances in the interval between approximately -3800 and -3500 ppm.The addition of the solid 1,4-FIB or 1,1'-FIDB to any one of 1-3 in a molar ratio 1:1 had only slight effect on these resonances, while further addition (chemical shift titration was up to 1:20 molar ratio; the maximum ratio was similar to the CV experiment discussed later) led to low field shifts of the 195 Pt NMR by 64 (1), 18 (2), and 1 (3) ppm (Table5and FiguresS15-S18).The addition of 1,1'-FIDB to 1 (molar ratio 1:20) resulted in 20 ppm low field shift of the 195 Pt signal.Whilst for 1 and 2 the spectral changes upon the addition of the XB donors are substantial, the spectrum of complex 3 is almost unaffected by treatment with 1,4-FIB.The NMR signal shifts are coherent with the changes of the platinum oxidation anodic peak upon addition of any one of the XB donors to solutions of 1-3 (see next subsection).
Assembly by (Aryl)I•••d z 2 [Pt II ] XB Pt orbital interaction leads to an increment of the nucleophilicity of the outer dz 2 -orbitals.Moreover, the MEP value at the Pt atom in adduct (1•1,1'-FIDB) is significantly smaller compared to 1 (-21.3kcal/mol) thus revealing that the formation of XB interaction at one Pt atom reduced the nucleophilicity of the other Pt center.
••Pt interaction upon the MEP value at the Pt center and (ii) adduct (1•1,1'-FIDB) (Figure 5c) in order to investigate the influence of XB upon the MEP of the Pt center

Table 2 .
QTAIM ρ(r), V(r) and G(r) parameters at the bond CPs labeled is Figures S11-13 in a.u. and predicted energies for each interaction using the electronic potential energy densities in kcal/mol.Chemistry -A European JournalThis article is protected by copyright.All rights reserved.*ForXRD data see the Supporting Information.

Table 5 .
The electrochemical and 195 Pt NMR data for 1-3 and the corresponding adducts.
a Measured in CH2Cl2 containing 0.1 M [ n Bu4N](BF4) at a 50 mVs -1 scan rate.The applied potentials were referenced to Fc + /Fc; at room temperature; b Measured in CD2Cl2 at room temperature; (Δ) is the difference between the initial value.
•••dz 2 [PtII] halogen bond between iodine σ-holes and lone pairs of the positively charged (Pt II )2 centers, acting as nucleophilic sites.We revealed that the halogen bond interaction between Pt II and two σ-hole-XB donors is moderately strong and dominated by orbital donor-acceptor interactions between the dz 2 -lone pair at the PtIIatom and the antibonding σ*(C-I) orbital.The 195 Pt NMR titration, UV-vis spectroscopy studies, and cyclic voltammetry data for (1-2)2•1,4-FIB indicate that the halogen bonding is preserved in CH(D)2Cl2 solutions, although excess 1,4-FIB is required.Recognized cases of metal-involving halogen bond are quite rare and only simple 1:1 adducts of halogen bond donors with metal centers, featuring an expressed Lewis basicity, were reported.At the same time, assembly or supramolecular design via R EWG X⋯dz 2 [M] halogen bonding has never been conducted and this work provides the first example of utilization of halogen⋯metal noncovalent interactions for construction of supramolecular architectures.Support of the synthetic work and compound characterizations from the Russian Foundation for Basic Research (grant 18-29-04006) is gratefully acknowledged.Electrochemical part of this work was supported by the Russian Foundation for Basic Research project 19-29-08026.E.A.K. is thankful to the Saint Petersburg State University for postdoctoral fellowship.Physicochemical studies were performed at the Center for Magnetic Resonance, Center for Xray Diffraction Studies, and Center for Chemical Analysis and Materials Research (all belonging to Saint Petersburg State University).V.Y.K. is grateful to South Ural State University (Act 211 Government of the Russian Federation, contract No 02.A03.21.0011) for putting facilities at his disposal.We are indebted to Prof. Dr. P.M. Tolstoy and Dr. D.M. Ivanov for valuable suggestions and Dr. A.V. Rozhkov for kind loan of 1,1'-FIDB and 2-mercapto-4,5,6,7-tetrafluorobenzothiazole.
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