Khodayar
Gholivand
*a,
Kaveh
Farshadfar
a,
S. Mark
Roe
b,
Mahdieh
Hosseini
a and
Akram
Gholami
a
aDepartment of Chemistry, Faculty of Science, Tarbiat Modares University, Tehran, Iran. E-mail: gholi_kh@modares.ac.ir
bDepartment of Chemistry, School of Life Sciences, University of Sussex, Brighton, BN1 9QJ, UK
First published on 10th August 2016
Herein, we reported the synthesis of copper(I) thiocyanate complexes with ortho-pyridinyl carbohydrazones containing a thiophene (L1) or a furyl ring (L2) as a mixture of two different crystals for each compound, linkage isomers of C1N, [Cu(NCS)(L1)PPh3] and C1S, [Cu(SCN)(L1)PPh3], for L1, whereas monomeric and polymeric structures C2N, [Cu(NCS)(L2)PPh3], and C2P, [–(NCS)Cu(L2)–]n, for L2. Crystallographic information and theoretical calculations, mainly noncovalent interaction reduced density gradient (NCI-RDG) analyses, were pursued to generate a profound understanding of the structure-directing interactions in these complexes. The supramolecular assemblies are first driven by cooperative π⋯π interactions and hydrogen bonds followed by CH⋯π, S⋯S and S⋯π linkages. In the case of the linkage isomers, intermolecular interactions may have a significant role in the formation of the less stable S-bound isomer C1S.
The triatomic pseudohalide, thiocyanate anion (SCN−), is an excellent versatile ambidentate ligand with two donor atoms, S or N.23 It can coordinate to metal ions both in terminal and bridging coordination modes and potentially provide fascinating examples of linkage isomerism.24–26 When SCN− acts as a terminal ligand, it affords potential interaction sites to generate non-covalent intermolecular interactions and, accordingly, can direct the crystal packing. Controlling the self-assemblies in the solid state on the basis of molecular structures and through the use of weak interactions is a long-standing goal of supramolecular chemistry.27
Very recently in our previous work, cuprous halide complexes of ortho-, meta- and para-pyridinyl carbohydrazones were introduced.28 The influence of ligand structure and halide variations on the molecular structures and supramolecular arrays of the complexes were studied both experimentally and theoretically. In the following, we employed cuprous pseudohalide, CuSCN, for the synthesis of complexes with two ortho-pyridinyl carbohydrazones. Copper(I) thiocyanate compounds are very interesting in solar cell applications as a p-type semiconductor.29–31
In this contribution, we report the structural characteristics of complexes from the reaction of CuSCN with PPh3 and ortho-pyridinyl carbohydrazones containing a thiophene (L1) or a furyl ring (L2); see Scheme 1. The former resulted in two linkage isomers: C1N [Cu(NCS)(L1)PPh3] and C1S [Cu(SCN)(L1)PPh3], while the later afforded monomeric and polymeric complexes of C2N [Cu(NCS)(L2)PPh3] and C2P [–(NCS)Cu(L2)–]n. We have also used a recently introduced alternative interpretive technique, the non-covalent interaction (NCI) approach, to manifest the diverse NCIs at the crystal packing structures. This method is based on the analysis of the electron density and enables us to identify and visualize the interactions.32 Various non-covalent interactions, including hydrogen bonding,33 S⋯S, S⋯π,34 π⋯π35 and CH⋯π36 interactions, have been investigated in this work.
A solution of the ligand in CHCl3 was added dropwise to a mixture of copper(I) thiocyanate and PPh3 while stirring in CH3CN and then the mixture was filtered off. After slow diffusion of diethyl ether in the filtered solutions, two different crystals were obtained for each compound including the light orange needle crystals (C1N) and clear light red irregular crystals (C1S) for L1 and orange needle crystals (C2N) and dark orange hexagonal crystals (C2P) for L2. A mixture of the isomeric crystals C1N and C1S is shown in Fig. 1.
Various ratios of acetonitrile and chloroform solvents were assessed in the crystallization of C1. Upon using more chloroform, the percentage of C1N was dominant, whereas a higher amount of acetonitrile in the reaction pot increased the percentage of C1S. For C2, the formation of crystals depended on the concentration of the reaction mixture. At a high concentration, the polymeric compound precipitated fast and we only obtained crystals of C2N, but slower diffusion of diethyl ether in the more dilute solution afforded crystals of both C2P (as the dominant product) and C2N suitable for X-ray diffraction.
ORTEP diagrams of the molecular structures are shown in Fig. 2. The crystallographic data of the complexes are listed in Table 1. Selected bond distances and angles are summarized in Table 2.
Compound | C1N | C1S | C2N | C2P |
---|---|---|---|---|
Formula | C30H24CuN4OPS2 | C30H24CuN4OPS2 | C30H24CuN4O2PS | C12H9CuN4O2S |
Fw | 615.16 | 615.16 | 599.10 | 336.83 |
λ/Å | 1.54184 | 0.71073 | 1.54184 | 1.54184 |
T/K | 173 | 173 | 173 | 173 |
Crystal system | Triclinic | Triclinic | Triclinic | Monoclinic |
Space group | P | P | P | P21/c |
a/Å | 9.8334(5) | 10.7768(9) | 9.8386(7) | 15.7005(7) |
b/Å | 10.2673(6) | 11.0362(8) | 10.1356(6) | 8.0099(4) |
c/Å | 15.0986(9) | 12.2584(5) | 14.9963(10) | 10.3633(5) |
α/° | 87.742(5) | 85.195(5) | 90.004(5) | 90 |
β/° | 89.510(4) | 78.024(5) | 90.051(6) | 94.374(4) |
γ/° | 66.545(5) | 80.116(6) | 113.105(7) | 90 |
V/Å3 | 1397.31(15) | 1403.30(17) | 1375.48(17) | 1299.49(11) |
D calc/Mg m−3 | 1.462 | 1.456 | 1.447 | 1.722 |
Z | 2 | 2 | 2 | 4 |
μ/mm−1 | 3.292 | 1.015 | 2.666 | 3.948 |
F(000) | 632 | 632 | 616 | 680 |
2θ/° | 142.128 | 59 | 143 | 142 |
R(int) | 0.025 | 0.030 | 0.030 | 0.041 |
GOOF | 1.022 | 1.11 | 1.04 | 1.03 |
R 1 (I > 2σ(I)) | 0.0295 | 0.0444 | 0.0373 | 0.0356 |
wR2 (I > 2σ(I)) | 0.0778 | 0.1072 | 0.1078 | 0.0955 |
C1N | |||
Cu1–P1 | 2.1880(6) Å | Cu1–N2 | 2.1367(16) Å |
Cu1–N1 | 1.979(18) Å | Cu1–N3 | 2.1501(16) Å |
P1–Cu1–N1 | 119.83(5)° | N1–Cu1–N2 | 99.81(7) |
P1–Cu1–N2 | 121.68(5)° | N1–Cu1–N3 | 101.96(7) |
P1–Cu1–N3 | 126.46(4)° | N2–Cu1–N3 | 77.56(6) |
C1S | |||
Cu1–S1 | 2.2936(9) Å | Cu1–N2 | 2.050(2) Å |
Cu1–P1 | 2.1990(7) Å | Cu1–N3 | 2.181(2) Å |
S1–Cu1–P1 | 117.60(3)° | P1–Cu1–N2 | 117.49(6)° |
S1–Cu1–N2 | 107.38(6)° | P1–Cu1–N2 | 103.74(6)° |
S1–Cu1–N3 | 127.28(6)° | N2–Cu1–N3 | 77.65(8)° |
C2N | |||
Cu1–P1 | 2.1893(6) Å | Cu1–N2 | 2.1547(19) Å |
Cu1–N1 | 2.1411(19) Å | Cu1–N4 | 1.983(2) Å |
P1–Cu1–N1 | 121.44(6)° | N1–Cu1–N2 | 77.23(7)° |
P1–Cu1–N2 | 126.25(5)° | N1–Cu1–N4 | 98.52(8)° |
P1–Cu1–N4 | 121.53(7)° | N2–Cu1–N4 | 101.32(8)° |
C2P | |||
Cu1–N1 | 2.105(2) Å | Cu1–N4 | 1.906(2) Å |
Cu1–N2 | 2.131(2) Å | Cu1–S1 | 2.2971(8) Å |
N1–Cu1–N2 | 77.74(9)° | N2–Cu1–N4 | 130.03(9)° |
N1–Cu1–N4 | 109.43(9)° | N2–Cu1–S1 | 103.43(7)° |
N1–Cu1–S1 | 111.59(7)° | N4–Cu1–S1 | 117.54(7)° |
In the structure of C1N, each molecular unit of the complex is joined to the neighbouring unit by means of three 2-fold interactions including classical and non-classical hydrogen bonds N4–H4⋯S1 and C7–H7⋯S1, respectively (Table 3), and πpy–πthiophene interactions (Table 4).
Structure | D–H⋯A | d D–H | d H⋯A | d D⋯A | ∠ D–H⋯A | Symm. codes |
---|---|---|---|---|---|---|
C1N | N4–H4⋯S1 | 0.880 | 2.6800 | 3.5042(18) | 157.00 | 1 − x, 1 − y, 1 − z |
C7–H7⋯S1 | 0.950 | 2.8700 | 3.6680(2) | 143.00 | 1 − x, 1 − y, 1 − z | |
C3–H3⋯S1 | 0.930 | 2.8754 | 3.7910(2) | 162.00 | −x, 2 − y, 1 − z | |
C21–H21⋯S2 | 0.930 | 3.0230 | 3.5480(2) | 116.00 | 1 − x, 1 − y, 2 − z | |
C1S | C10–H10⋯N1 | 0.950 | 2.5580 | 3.4540(4) | 157.30 | 1 − x, 1 − y, 1 − z |
C7–H7⋯N1 | 0.950 | 2.7990 | 3.5690(5) | 138.80 | 1 − x, 1 − y, 1 − z | |
N4–H4⋯N1 | 0.880 | 2.2330 | 3.0760(3) | 163.16 | 1 − x, 1 − y, 1 − z | |
C2N | N3–H3⋯S1 | 0.879 | 2.6810 | 3.4930(2) | 153.90 | 1 − x, 1 − y, 1 − z |
C6–H6⋯S1 | 0.949 | 2.8469 | 3.6410(3) | 141.80 | 1 − x, 1 − y, 1 − z | |
C10–H10⋯N4 | 0.950 | 2.7230 | 3.5320(3) | 143.60 | 1 + x, 1 + y, z | |
C2–H2⋯S1 | 0.950 | 2.8812 | 3.8020(2) | 163.60 | 2 − x, 2 − y, 1 − z | |
C15–H15⋯S1 | 0.950 | 2.9839 | 3.8270(3) | 148.60 | x, −1 + y, z | |
C2P | C9–H9⋯O2 | 0.950 | 2.4970 | 3.3940(4) | 157.40 | x, 1/2 − y, −1/2 + z |
N3–H3⋯O1 | 0.880 | 2.3140 | 3.1000(3) | 148.70 | x, 1/2 − y, −1/2 + z | |
C2–H2⋯N4 | 0.950 | 2.6850 | 3.5830(4) | 157.90 | 2 − x, 1/2 + y, 1/2 − z | |
C11–H11⋯N4 | 0.950 | 2.5310 | 3.3480(4) | 144.10 | 1 − x, −1/2 + y, 1/2 − z | |
C11–H11⋯O1 | 0.950 | 2.6870 | 3.1830(4) | 113.10 | 1 − x, −1/2 + y,1/2 − z |
Structure | Interaction | C–C (Å) | P–P° | P–CC° | CH⋯CgI | C⋯Cg (Å) | C–H–Cg (°) | Symm. code |
---|---|---|---|---|---|---|---|---|
Cg stands for the centre of gravity of the mentioned ring: for C1N: Cg2: S2, C9–C12; Cg3: N2, C2–C6; Cg4: C13–C18; Cg6: C25–C30; for C1S: Cg7: C25–C30; for C2N: Cg2: O2, C8–C11; Cg4: C13–C18; Cg6: C25–C30; for C2P: Cg2: O2, C8–C11; Cg3: N1, C1–C5. | ||||||||
C1N | πpy–πthiophene | 3.749 | 7.52 | 19.63 | — | — | — | 1 − x, 1 − y, 1 − z |
27.14 | ||||||||
πpy–πpy | 3.486 | 0.0 | 7.88 | — | — | — | −x, 1 − y, 1 − z | |
CH⋯πPPh3 | — | — | — | C4–H4A⋯Cg6 | 3.725 | 165.63 | −x, 1 − y, 1 − z | |
CH⋯πPPh3 | — | — | — | C5–H5⋯Cg4 | 2.689 | 145.87 | −x, 1 − y, 1 − z | |
CH⋯πpy | — | — | — | C11–H11⋯Cg3 | 3.737 | 134.12 | 1 + x, −1 + y, z | |
CH⋯πthiophene | — | — | — | C14–H14⋯Cg2 | 3.134 | 145.84 | −1 + x, 1 + y, z | |
CH⋯πthiophene | — | — | — | C2–H2⋯Cg2 | 3.592 | 134.97 | −1 + x, 1 + y, z | |
C1S | Amide⋯πpy | 3.403 | — | — | — | — | — | 1 − x, 1 − y, 1 − z |
CH⋯πPPh3 | — | — | — | C11–H11⋯Cg7 | 2.749 | 141.19 | 1 + x, y, z | |
CH⋯πPPh3 | — | — | — | C17–H17⋯Cg7 | 3.275 | 132.77 | 1 − x, −y, 2 − z | |
C2N | πpy–πfuryl | 3.719 | 11.74 | 17.28 | — | — | — | 1 − x, 1 − y, 1 − z |
28.73 | ||||||||
πpy–πpy | 3.461 | 0.0 | 5.15 | — | — | — | 2 − x, 1 − y, 1 − z | |
CH⋯πfuryl | — | — | — | C1–H1⋯Cg2 | 3.602 | 135.83 | 1 + x, 1 + y, z | |
CH⋯πPPh3 | — | — | — | C4–H4⋯Cg6 | 2.721 | 145.84 | 2 − x, 1 − y, 1 − z | |
CH⋯πPPh3 | — | — | — | C3–H3A⋯Cg4 | 3.761 | 166.03 | 2 − x, 1 − y, z | |
C2P | S⋯πpy | 3.882 | — | 19.60 | — | — | — | x, y, 1 + z |
πpy–πpy | 3.801 | 0.0 | 28.19 | — | — | — | 2 − x, 1 − y, −z | |
πfuryl–πfuryl | 3.583 | 0.0 | 17.13 | — | — | — | 1 − x, −y, −z |
The dimers are further connected to each other through πpy–πpy and C5–H5⋯πPPh3 interactions along the a-direction (Fig. 3a) to afford chains which are laterally linked together via various intermolecular interactions to generate a 3D network. The interactions which link the chains along the b-axis include (i) S1⋯S1, (ii) C3H3⋯S1, (iii) C11–H11⋯πpy, (iv) C2–H2⋯πthiophene and (v) C14–H14⋯πthiophene linkages (Fig. 3b). In addition, C21H21⋯S2 H-bonds plus weak C27–H27⋯πPPh3 interactions (C⋯Cg: 4.090 Å) connect them along the c-direction (Fig. 3c). The distance of the S⋯S interaction was found to be about 3.456 Å which is 4% shorter than the sum of the van der Waals radii of two sulfur atoms. A summary of the parameters for the other interactions mentioned above are presented in Tables 3 and 4.
The crystal structure of C1S contains hydrogen bonded dimers generated by three pairwise interactions, N4–H4⋯N1, C7–H7⋯N1 and C10–H10⋯N1 (Table 3 and Fig. 4a). It is worth noting that the coordination of sulfur to the Cu(I) atom and consequently the orientation of the N1 atom direct the formation of hydrogen bonds and lead to supernumerary slippage of molecules on each other. The offset of pyridine and thiophene rings prevents the formation of a πpy–πthiophene interaction, unlike in the structure C1N. Thus, instead of a πpy–πthiophene interaction, a CO⋯π interaction is established between the discrete molecules in the dimers. In addition, S⋯S interactions connect the dimers to form [001] chains. The distance between two sulfur atoms is equal to 3.594 Å. These chains are held together by C11–C11⋯πPPh3 and C17–H17⋯πthiophene linkages (Table 4) along the a- and b-directions, respectively, which complete a 3D network (Fig. 4b–d).
Although the coordination structure of C2P is different from the others, π–π interactions still have an important contribution in the crystal packing. Herein, πfuryl–πfuryl interactions establish two-fold sheets of the neighbouring chains which are also fortified by bifurcated hydrogen bonds. The other side of the chains in the sheets is involved in πpy–πpy stacking and H-bonding interactions, leading to the connection of the (011) layers along the a-direction to complete the overall supramolecular association (Fig. 6b). In other words, each coordination chain is associated with four other chains in a 3D arrangement, from one side through πfuryl–πfuryl, C11–H11⋯N4 and C11–H11⋯O1 linkages and from the other side by πpy–πpy stacking and C2–H2⋯N4 interactions (Fig. 6c). In addition, these chains are laterally linked through interesting S⋯πpy interactions in the b-direction (Fig. 6d).
As the sign of λ2 describes the essence of the interaction, 2D plots comprising sign(λ2) × ρ versus RDG s would indicate a non-covalent interaction near-zero area in the horizontal axis.38–44 Close contacts between atoms change the behaviour of the reduced gradient signal more compared to the contacts among the atoms present in the tails, leading to troughs in the 2D NCI plots. These troughs, specially the ρ value at the troughs, are the basis of the NCI approach. The 2D NCI plots are then applied as inputs to construct 3D NCI plots, including isosurfaces of the reduced gradient of the density enabling the spatial visualization of the close contacts.
We applied this method to unravel the nature of supramolecular interactions in the title complexes. NCI analysis has been performed on the structure of complexes including the diverse noncovalent interactions. The considered structures were cut out directly from the CIF data. Since dimerization is the prominent feature of the crystal packing in the monomeric complexes (C1N, C1S and C2N), the main NCIs are related to the interactions involved in the formation of dimers. The 2D and 3D NCI plots of dimers are shown in Fig. 7. Accordingly, we have done calculation once on the dimers including only the carbohydrazone ligands (Cu+ and SCN− ions and PPh3 moieties have been eliminated) and again for the whole dimeric units of complexes. Some of the other interesting intermolecular interactions in the crystal structures have also been investigated by the NCI method. The presence of noncovalent interactions is characterized by spikes at negative to near-zero sign of λ2, whereas the peaks at positive sign indicate the repulsive steric contacts due to the ring formation.45 The spikes at the zero area (sign(λ2)ρ between ±0.015 a.u.) show vdW interactions. Notable points of the NCI calculations have been illustrated in the following:
Fig. 7 Left: The NCI RDG s vs. sign(λ2)ρ plots for dimers of ligands and complexes. Right: Coloured RDG-based NCI isosurfaces for the dimers of complexes. |
(i) As shown in Fig. 7, for the ligand dimers, the spikes that appeared at 0.024 a.u. belong to the pyridine ring closure. These spikes shift to lower values (less repulsion) in the whole dimeric units of complexes. It can be explained by the effect of metal ion in the charge redistribution as well as the electrostatic interaction between atoms within the rings.
(ii) In the case of C1N, the thiophene ring closure spike (sign(λ2)ρ) is located between 0.042 and 0.044 a.u. while in the 2D plot and the 3D isosurface of C2N, the furyl ring has a much lesser repulsion of ring closure than the thiophene alternative. It may be caused by the greater charge perturbation due to the presence of an oxygen atom which leads to more electrostatic interactions. Consistent with this, natural bond orbital (NBO) analysis also reveals the stabilizing energy of 54 kcal mol−1 for the electronic delocalization “lone pair (O) → π* (C–C) orbital” which is more than that for the corresponding charge transfer energy in the thiophene ring (LP(S) → π*(C–C): 48 kcal mol−1).
(iii) C1N and C1S compounds are linkage isomers, in a way that SCN− is coordinated from N or S atoms, respectively. Optimization of the isomers, in the gas phase and also acetonitrile and chloroform solutions, indicates that the stability of C1S is approximately 3–4 kcal mol−1 less than that of C1S; however, it has been also formed in the solid state. The formation of C1S can be attributed to stronger intermolecular attractions particularly those involved in dimerization which compensate for the lesser stability of the discrete units of C1S. RDG isosurfaces show stronger interactions in the C1S dimer rather than in C1N. Counterpoise calculations at the M06-2X/6-311G* level indicate that the binding energy of two complexes in a dimer, ΔEdimer, for C1S is 2.8 kcal mol−1 more than for C1N as well.
(iv) It was thought to be of interest to further investigate the sulfur interactions to figure out their nature in the solid state structures. The sulfur atom, due to its large van der Waals radius and high polarizability, is able to establish several interactions with its local environment.46 Morgan and co-workers first proposed the hypothesis that a strong interaction exists between aromatic rings and divalent sulfur atoms.47 The importance of the S⋯π aromatic interaction is revealed in the high degree of its conservation across members in protein folding and stabilization.34,48
Fig. 8 represents the 3D plots of S⋯S and S⋯π interactions in the solid state structures. The compact and small, flat, pill-shaped isosurfaces, concentrated on the NCI critical points indicate that these interactions are significantly attractive and contribute to the crystal packing stability.45
Pyridine, thiophene and furyl rings, the polarized aromatic systems, have an important role in governing the supramolecular assembly of the complexes by establishing π–π interactions. However, the coordination of sulfur to the Cu(I) atom in C1S leads to supernumerary slippage of the neighbouring molecules which prevents the formation of πpy–πthiophene connections. CH–π interactions between PPh3 moieties contribute to further stabilization of the self-association in the monomeric complexes (C1N, C1S and C2N).
A prominent feature of the crystal packing in the monomeric complexes is the formation of the dimeric motifs via hydrogen bonding and π–π stacking interactions. Formation of the less stable S-bound isomer C1S can be attributed to stronger intermolecular attractions particularly those involved in dimerization which compensate for the lesser stability of the discrete units of C1S compared to C1N.
Another interesting feature of the solid state structures is the presence of the lesser known S⋯S and S⋯π interactions. NCI-RDG analysis clearly indicates the significant contribution of these interactions in maintaining favourable packing interactions in the complex.
A solution of ligand (0.20 mmol) in CHCl3 (4 mL) was added dropwise to a stirred solution of a mixture of copper(I) thiocyanate (0.20 mmol) and triphenylphosphine (0.20 mmol) in CH3CN (2 ml). The colour of the reaction mixture turned from orange to red. The reaction mixture was filtered; slow diffusion of diethyl ether in the filtered solution afforded suitable single crystals (total yields for the mixture of C1N and C1S: 81%, and for that of C2N and C2P: 76%). The complexes were obtained in good yields. Physical and spectroscopic data of the compounds are presented below:
Natural bond orbital (NBO) analysis58 was performed on the crystal structure of the complexes using the NBO 3.1 module in Gaussian 09 at the B3LYP/6-311+G** level of theory. The binding energy of two complexes in a dimer, ΔEdimer, for C1N, C1S and C2N were calculated at the M062X/6-311G* level based on the energy difference between the dimer and its units. The interaction energies have been corrected for the basis set superposition error (BSSE) using the counterpoise (CP) procedure.59
Footnote |
† Electronic supplementary information (ESI) available: IR and NMR spectra of all compounds and crystallographic files in CIF format for structural determination of complexes. CCDC 1401344, 1401345, 1469718 and 1469717. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ce01339b |
This journal is © The Royal Society of Chemistry 2016 |