Daniil M.
Ivanov
a,
Alexander S.
Novikov
a,
Galina L.
Starova
a,
Matti
Haukka
b and
Vadim Yu.
Kukushkin
*a
aInstitute of Chemistry, Saint Petersburg State University, 7/9 Universitetskaya Nab., 199034 Saint Petersburg, Russian Federation. E-mail: v.kukushkin@spbu.ru
bDepartment of Chemistry, University of Jyväskylä, P.O. Box 35, FI-40014 Jyväskylä, Finland
First published on 13th June 2016
Two previously reported 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate (PANT) chloride platinum(II) complexes [PtCl{HNC(R)NCN[C(Ph)C(Ph)]CNC(R)NH}] (R = tBu 1, Ph 2) form solvates with halomethanes 1·1¼CH2Cl2, 1·1⅖CH2Br2, and 2·CHCl3. All these species feature novel complex-solvent heterotetrameric clusters, where the structural units are linked simultaneously by two C–X⋯Cl–Pt (X = Cl, Br) halogen and two C–H⋯Cl–Pt hydrogen bonds. The geometric parameters of these weak interactions were determined using single-crystal XRD, and the natures of the XBs and HBs in the clusters were studied for the isolated model systems (1)2·(CH2Cl2)2, (1)2·(CH2Br2)2, and (2)2·(CHCl3)2 using DFT calculations and Bader's AIM analysis. The evaluated energies of the weak interactions are in the range 0.9–3.0 kcal mol−1. The XBs and HBs in the reported clusters are cooperative. In the cases of (1)2·(CH2Cl2)2 and (1)2·(CH2Br2)2, the contribution of the HBs to the stabilization of the system is dominant, whereas for (2)2·(CHCl3)2 contributions of both types of the non-covalent interactions are almost the same. Crystal packing and other forces such as, e.g. dipole–dipole interactions, also affect the formation of the clusters.
A XB is commonly treated as an electrostatic attraction between electron-rich centers and areas of electropositive potential, the so-called σ-holes, existing on the surfaces of covalently bonded halogen atoms.1–4,8–11 The electron-rich centers can be heteroatoms such as halogens or π-systems. Two types of short halogen–halogen contact are usually discussed in the literature (Fig. 1).1,3,12 Type I is believed to depend on the effects of close packing, whereas type II is due to a classic XB because a halogen atom with a 90° angle provides its lone pair for interaction and the other one provides its σ-hole. The type II interactions are more useful in crystal engineering due to the relatively strict geometrical requirements, whereas both angles around the halogen atoms in the type I interaction (which is actually not a XB, see ref. 13) can be in a wide range from 180° to 90° and less, and it hardly allows the construction of supramolecular structures.
Although the vast majority of XB studies involve metal-free organic species,1,2,14 utilization of some organometallic compounds for these purposes are also reported.15,16 The combination of unique redox, magnetic, and optical properties of metal complexes with adjustable organic moieties is very useful for the design of new materials.
XBs involving metal complexes form networks,16 where anions are XB donors and their counterions are XB acceptors. These networks were found in halogen-containing pyridinium halometallates or cyanometallates (XC5H5N)2[MX′4] (where M is a divalent metal ion, e.g., CoII, PtII, or PdII, X is a halogen except F, and X′ is a halide or cyanide ligand).16–18 Similar networks19,20 have also been found in the associations of substituted ammonium bromometallates (nPr4N)[CuBr2], (nBu4N)2[MBr4] (M = Zn, Cd, Co), and (nBu4N)2[Pt2Br6] with bromoform, tetrabromomethane, and 1,1-dibromo-1,1,2,2-tetrafluoroethane serving as XB donors. 3D-Networks formed by XBs were also observed in the associations of (nBu4N)2[PtBr4Cl2] and (nBu4N)2[Pt2Br10] with dibromine.21 Another large group of hybrid systems22,23 is represented by complexes trans-[MX2(4-X′py)2] forming intermolecular XBs between the halide ligands X− and halogen substituents X′ in the pyridine ligands. In addition, palladium NCN24 and PCP25 pincer complexes featuring halide ligands were co-crystallized with diiodine, 1,4-diiodotetrafluorobenzene, and 1,4-diiodooctafluorobutane displaying networks and chains formed by XBs.
In most reports focused on crystal engineering involving XBs, strong iodine centered XB donors were explored, which contain the large σ-holes due to electron withdrawing substituents.1,3 In contrast to a substantial number of these works, a few reports20,26–28 have shown that even simple halomethanes can be effectively used in the design of structures held by XBs. In particular, we reported26 that chloroform can act as both a XB and hydrogen bond (HB) donor forming the heterotetrameric clusters (Cl−)2·(CHCl3)2 (Fig. 2) in the solid state. The term “heterotetrameric cluster” means a symmetrical supramolecular associate formed by two pairs of different species (dimer of a dimer). This term was previously suggested for designation of neutral clusters with halomethanes containing four molecules linked by two HBs and two XBs.27,28
Fig. 2 Ball-and-stick model of the heterotetrameric cluster (Cl−)2·(CHCl3)2.26 |
In this study, we demonstrate that relevant heterotetrameric structures could be obtained using crystallization of the annulated triazapentadiene systems, viz. 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate (PANT) platinum(II) chloride complexes (Fig. 3, A), with the halomethanes CH2Cl2, CH2Br2, and CHCl3 (Fig. 3, B). The heterotetramers display the previously unreported H2ClC–Cl⋯Cl–Pt, H2BrC–Br⋯Cl–Pt, and HCl2C–Cl⋯Cl–Pt halogen and the C–H⋯Cl–Pt hydrogen bonds. These experimental data along with the results of a detailed inspection of the large amount of available literature/CCDC data open up a new family of heterotetrameric clusters held simultaneously by two C–X⋯Cl XBs and two C–H⋯Cl HBs with halomethanes. All our results are discussed in the sections that follow.
Two PANT species (R = tBu 1, Ph 2) were found to co-crystallize with halomethanes (CHCl3, CH2Cl2, and CH2Br2) forming heterotetrameric complex–halomethane clusters (Table 1). Isostructural Cl/Br exchange was detected for clusters 1 with CH2Cl2 and CH2Br2 and corresponding crystalline phases demonstrate close cell parameters and analogous packing features (for detailed information see ESI†).
R | Nos | Solvent system | Solvates |
---|---|---|---|
t Bu | 1 | CH2Cl2 | 1·1¼CH2Cl2 |
CH2Br2 | 1·1⅖CH2Br2 | ||
Ph | 2 | CHCl3 | 2·CHCl3 |
The C–X⋯Cl–Pt (X = Cl, Br) short contacts (3.447(2) Å and 3.5012(9) for Cl⋯Cl, and 3.330(2) for Cl⋯Br) that are less than the sum of Rowland's32 vdW radii (2Rw(Cl) = 3.52 Å, Rw(Cl) + Rw(Br) = 3.63 Å) were found in each cluster (Table 2). The corresponding angles around the chloride ligands are close to 90° and around solvent halogen atoms are close to 180°. These data indicate that the short contacts are due to the XB and complex molecules behave as XB acceptors of type II (Fig. 1).
Cluster | Pt–Cl⋯X–C | d(X⋯Cl), Å | ∠(C–X⋯Cl),° | ∠(X⋯Cl–Pt),° | E b | E b |
---|---|---|---|---|---|---|
a E b = −V(r)/2.38 b E b = 0.429G(r).39 c Comparison between the sum of Rowland's32 vdW radii and conventional halogen bond angle. | ||||||
(1)2·(CH2Cl2)2 | C1S–Cl1S⋯Cl1A–Pt1A | 3.447(2) | 171.8(3) | 108.41(7) | ||
3.50 | 168.4 | 109.9 | 0.9 | 1.4 | ||
3.36 | 170.8 | 108.9 | 1.6 | 1.6 | ||
(1)2·(CH2Br2)2 | C1S–Cl1S⋯Cl1A–Pt1A | 3.330(2) | 172.0(4) | 107.98(8) | ||
3.17 | 171.0 | 106.2 | 2.5 | 2.7 | ||
(2)2·(CHCl3)2 | C1S–Cl3S⋯Cl1–Pt1 | 3.5012(9) | 172.16(7) | 87.902(17) | ||
3.61 | 169.7 | 83.8 | 0.9 | 1.1 | ||
*Comparisonc | 3.52 (Cl⋯Cl) | 180 | 90 | |||
3.63 (Cl⋯Br) |
Solvates 1·1¼CH2Cl2, 1·1⅖CH2Br2 (Fig. 4), and 2·CHCl3 (Fig. 5) form independent heterotetrameric clusters comprised of two solvent molecules and two molecules of the complexes linked by two XBs and two hydrogen bonds (HBs). In 1, the geometric parameters of these heterotetramers are very similar. Structures 1·CH2Br2 and 2·CHCl3 demonstrate the first examples of the H2BrC–Br⋯Cl–Pt and the HCl2C–Cl⋯Cl–Pt XBs, and only the H2ClC–Cl⋯Cl–Pt contact was previously observed.36
Fig. 4 The halogen and hydrogen bonds in the isostructural heterotetramers from 1·1¼CH2Cl2 (a) and 1·1⅖CH2Br2 (b). Thermal ellipsoids are shown with 50% probability. |
Fig. 5 The halogen and hydrogen bonds in the heterotetramer from 2·CHCl3. Thermal ellipsoids are shown with 50% probability. |
We focused on the study of isolated heterotetrameric clusters from 1·1¼CH2Cl2, 1·1⅖CH2Br2, and 2·CHCl3 (Fig. 6, structures (1)2·(CH2Cl2)2, (1)2·(CH2Br2)2, and (2)2·(CHCl3)2, respectively) taking into account that if the crystal packing effects are significant, the structures should change substantially on going from the solid state to the gas phase during the geometry optimization procedure. Otherwise the geometries expectedly are preserved in the isolated form.37
Fig. 6 Views of the optimized heterotetrameric clusters (1)2·(CH2Cl2)2 (a), (1)2·(CH2Br2)2 (b), and (2)2·(CHCl3)2 (c). |
This commonly accepted approach helps to exclude the crystal packing effects from consideration and to investigate the short contacts only within the clusters.
The results of our theoretical calculations are summarized in Tables 2, 3 and S5.† In the case of (1)2·(CH2Cl2)2, we found an asymmetric distortion of the structure and the emergence of two new short contacts N–H⋯Cl–CH2Cl. Both HCl2C–H⋯Cl–Pt contacts are shortened (by 0.19 and 0.11 Å) one of the H2ClC–Cl⋯Cl–Pt contacts is very slightly elongated (by 0.05 Å), and another one is slightly shortened (by 0.09 Å). In the case of (1)2·(CH2Br2)2, the symmetrical structure of the cluster is preserved and both the HBr2C–H⋯Cl–Pt contacts are significantly elongated (by 0.51 Å), two new short contacts N–H⋯Br–CH2Br are formed, and the H2BrC–Br⋯Cl–Pt contacts are shortened (by 0.16 Å).
Cluster | C–H⋯Cl | d(Cl⋯H), Å | d(Cl⋯C), Å | ∠(C–H⋯Cl), ° | E b | E b |
---|---|---|---|---|---|---|
a E b = −V(r)/2.38 b E b = 0.429G(r).39 c Comparison between the sum of Rowland's32 vdW radii and the minimal hydrogen bond angle. | ||||||
(1)2·(CH2Cl2)2 | C1S–H1SA⋯Cl1A′ | 2.809 | 3.708(8) | 154.6 | ||
2.63 | 3.595 | 147.316 | 2.2 | 2.4 | ||
2.70 | 3.666 | 147.033 | 1.9 | 1.9 | ||
(1)2·(CH2Br2)2 | C1S–H1SB⋯Cl1A′ | 2.786 | 3.696(12) | 156.5 | ||
3.304 | 4.211 | 141.279 | — | — | ||
(2)2·(CHCl3)2 | C1S–H1S⋯Cl1′ | 2.795 | 3.4989(17) | 127.8 | ||
2.476 | 3.410 | 142.624 | 2.8 | 3.0 | ||
*Comparisonc | 2.86 | 3.53 | 120 |
For (2)2·(CHCl3)2, both Cl3C–H⋯Cl–Pt contacts are shortened (by 0.31 Å) and the HCl2C–Cl⋯Cl–Pt contacts are slightly elongated (by 0.11 Å) on going from the solid state to the gas phase, whereas the length of the HCl2C–Cl⋯Ph contacts remains virtually unchanged. In all three cases, the ∠(C–X⋯Cl) and ∠(X⋯Cl–Pt) angles (X = Cl, Br) are changed insignificantly and the largest deviation from the experimental values (4°) was observed in the case of the ∠(Cl⋯Cl–Pt) angle in (2)2·(CHCl3)2.
Additional information on the nature of the short contacts in (1)2·(CH2Cl2)2, (1)2·(CH2Br2)2, and (2)2·(CHCl3)2, can be obtained using the topological analysis of the electron density distribution (AIM method).40 This approach has already been successfully used by us upon studies of non-covalent interactions and properties of coordination bonds in various transition metal complexes and organic compounds.37,41–46 The low magnitude of the electron density and the positive values of the Laplacian and energy density in appropriate bond critical points (3, −1) (Table S5†) are typical for XBs47–50 and also for some HBs51 indicating that the interaction is weak.52,53 We have defined the energies of these contacts according to the procedures proposed by Espinosa et al.38 and Vener et al.39 (1–3 kcal mol−1), and one can state that these bonds may be classified as very weak mainly due to the electrostatic and dispersion interactions. The strength of the XBs decreases in the series: (1)2·(CH2Br2)2 > (1)2·(CH2Cl2)2 > (2)2·(CHCl3)2. Bond critical points (3, −1) for very long HBr2C–H⋯Cl–Pt contacts in (1)2·(CH2Br2)2 were not found.
We evaluated the vertical total energies of the heterotetrameric clusters dissociation (Ev) through the “halogen” and “hydrogen” contacts for (1)2·(CH2Cl2)2, (1)2·(CH2Br2)2, and (2)2·(CHCl3)2; corresponding values of Ev are given in Table 4. The cooperativity of the XBs and HBs was recognized for the studied heterotetramers. Thus, to quantify the relative contributions of these non-covalent interactions in the stabilization of the heterotetrameric clusters, we calculated the vertical total energies of their dissociation (Ev) through the “halogen” and “hydrogen” contacts for (1)2·(CH2Cl2)2, (1)2·(CH2Br2)2, and (2)2·(CHCl3)2, the corresponding values of Ev are given in Table 4. For (1)2·(CH2Cl2)2 the contribution of the HBs to the stabilization of the system prevail nearly twice over the contribution of XBs, for (1)2·(CH2Br2)2 – approximately by one third, and for (2)2·(CHCl3)2 contributions of both types of non-covalent interaction are almost the same. The existence of (1)2·(CH2Cl2)2 and (1)2·(CH2Br2)2 is determined mainly by HBs, whereas for (2)2·(CHCl3)2 both types of non-covalent interaction are equally essential. In the case of (2)2·(CHCl3)2, the non-covalent interactions make the major contribution to the stabilization of the cluster, whereas for (1)2·(CH2Cl2)2 and especially for (1)2·(CH2Br2)2 the role of the XBs and HBs in stabilization of these supramolecular systems is, although smaller, still quite significant.
Cluster | Dissociation | E v |
---|---|---|
(1)2·(CH2Cl2)2 | Through the XB | 12.09 |
Through the HB | 21.58 | |
(1)2·(CH2Br2)2 | Through the XB | 30.77 |
Through the HB | 38.88 | |
(2)2·(CHCl3)2 | Through the XB | 8.94 |
Through the HB | 8.26 |
Thus, the results of our theoretical calculations reveal that the crystal packing noticeably affects the geometrical features of the heterotetrameric clusters and also that the XBs and HBs in these supramolecular associates are relatively weak.
The formation of such ordered structures as the heterotetramers can be accompanied by a significant entropy decrease and stabilization of the system from the energy viewpoint. In order to prove that, we tried to carry out a geometry optimization procedure for the two model metal-free systems, viz. the “heterotetramer” and the “heterotrimer plus one outlying chloroform molecule”, (Cl−)2·(CHCl3)2 and (Cl−)2·(CHCl3) + CHCl3, respectively (M06-2X/6-311++G(d,p) level of theory). We located the minima for the heterotetramer (Cl−)2·(CHCl3)2 (Fig. 7) on the potential energy surface. However, several attempts to find an appropriate stationary point for the (Cl−)2·(CHCl3) + CHCl3 system with the outlying chloroform molecule led to the separation of this model system into two fragments Cl−·(CHCl3), which move away from each other upon the geometry optimization (Fig. 8); we finished the optimization when the distance between these fragments exceeded 13 Å. A possible rationale for this phenomenon is an electrostatic repulsion between the two chloride anions. In conjunction with the found minima for the heterotetrameric system (Cl−)2·(CHCl3)2, our results suggest that the presence of two Cl− close to each other in the crystal lattice can be provided through the formation of bridges with CHCl3. These neutral species sufficiently shield the negatively charged anions thus providing their coexistence in the close proximity.
Fig. 9 Schematic representation of the heterotetrameric clusters with R–Cl (cluster A) or Cl− (cluster B) as both the HB and XB acceptors and R′2CHCl as the XB and HB donors. |
The first type of cluster is stabilized by two C–X⋯Cl–R XBs and two C–X⋯Cl–R HBs (Fig. 9, cluster A) incorporating a neutral RCl species as the Lewis base. We also acquired data on analogous clusters where free chloride anions behave as both XB and HB acceptors (Fig. 9, cluster B). Noticeably, in each cluster the XBs and HBs alternate with each other. Other variants of bridging molecules in the clusters with two HBs and two XBs were not found.
In the case of free chloride anions as both the HB and XB acceptors, 8 type B clusters (Fig. 9) with chloroform and 3 clusters with dichloromethane were found and all of them exhibited a center of symmetry. Only one cluster in structure UPEROX was described in our previous work.26
A suitable crystal of 1·1¼CH2Cl2 was studied on an Xcalibur, Eos diffractometer. The crystal was kept at 100(2) K during data collection. Using Olex2 1.2,58 the structure was solved with the ShelXT59 structure solution program using Direct Methods and refined with the ShelXL-2014 (ref. 60) refinement package using Least Squares minimisation.
A suitable crystal of 1·1⅖CH2Br2 was studied on a SuperNova, Dual, Cu at zero, Atlas diffractometer. The crystal was kept at 100(2) K during data collection. Using Olex2,58 the structure was solved with the ShelXS60 structure solution program using Direct Methods and refined with the ShelXL60 refinement package using Least Squares minimisation. The unit cell of 1·1⅖CH2Br2 also contains disordered molecules of CH2Br2 (total potential solvent accessible void volume is 305 Å3; electron count per cell is 206 electrons) that have been treated as a diffuse contribution to the overall scattering without specific atom positions using SQUEEZE/PLATON.61
A suitable crystal of 2·CHCl3 was immersed in cryo-oil, mounted in a Nylon loop, and measured at a temperature of 100 K. The X-ray diffraction data was collected on a Bruker Smart Apex II diffractometer using Mo Kα radiation (λ = 0.71073 Å). The SAINT62 programme package was used for cell refinement and data reduction. The structure was solved using direct methods using a SHELXS-97 (ref. 60) programme. A numerical absorption correction (SADABS)63 was applied to the data. Structural refinements were carried out using SHELXL-97.60
Footnote |
† Electronic supplementary information (ESI) available: Packing features of investigated solvates, description of other weak interactions, additional information for the theoretical consideration, full information for CCDC inspection, and cartesian atomic coordinates of the calculated equilibrium structures. CCDC 1456075, 1456509 and 1470271. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ce01179a |
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