Syntheses, structures, and characterization of two new Zn(ii)/Cd(ii) complexes with phenanthroline derivative

2.1 Structural analysis

The crystal structure of 1 belongs to a monoclinic with space group C2/c, made up of a Cd(ii) ion, two L ligands, a Cl⁻ ion, and a half-free SO₄ ²⁻ anion. A distorted tetragonal dipyramid [CdN₄Cl₂] environment is presented by the four N atoms (N(1)–Cd(1) = 2.443(4), N(2)–Cd(1) = 2.321(4), N(5)–Cd(1) = 2.344(4), and N(6)–Cd(1) = 2.340(3) Å; Table 1) from two distinct L ligands chelating to the Cd(ii) ion and the Cl⁻ ion (Cl(3)–Cd(1) = 2.5981(13) Å), as seen in Figure 1. It is interesting to note that a binuclear [Cd₂L₄Cl₂] molecular structure is formed by Cl⁻ ions bridging with the neighboring asymmetric units with Cd···Cd distance of 3.983 Å.

Figure 1

View of the coordination environment of the Cd(ii) atom of 1 (symmetry codes: ⁱ−x + 3/2, −y + 1/2, −z + 1).

What is more remarkable is that C(17)–H(17)⋯π ¹ stacks (2.74 Å; π ¹: ring centroids of imidazole (N(7)/C(30)–C(31)/N(8)/C(32), symmetry operation: 1 − x, −y, 1 − z; Table 2) and C(34)–Cl(2)⋯π ² stacks (3.154(3) Å; π ²: ring centroids of benzimidazole (N(7)/C(23)–C(31)/N(8)/C(32), symmetry operation: 2 − x, −y, 1 − z; Table 2) are formed between H(17) with the imidazole ring of the L ligand and Cl(2) atoms with the benzimidazole ring of the L ligand, respectively. These C–H⋯π and C–Cl⋯π interactions further convert the binuclear [Cd₂L₄Cl₂] structure into a 2D supramolecular structure (Figure 2). Moreover, N–H⋯O and N–H⋯S hydrogen bonds (N(4)–H(4)⋯S(1)^vii, N(4)–H(4)⋯O(2)^vii, N(8)–N(8)⋯S(1), and N(8)–H(8 A)⋯O(1)ⁱⁱ; Table 3) interaction exists in the adjacent 2D supramolecular layers, as shown in Figure 3, and these hydrogen bonds eventually make 2D supramolecular layers to develop into a 3D stereo structure.

Figure 2

View of the 2D layer structure of 1 constructed by the C–H⋯π and C–Cl⋯π interactions.

Figure 3

View of the 3D supramolecular structure of 1.

As depicted in Figure 4, 2 crystallizes in the P2/c space group. The asymmetric unit of 2 contains two Zn(ii) ions, two L ligands, a deprotonated sip³⁻ anion, one OH⁻ anion, and the free of a water molecule. The coordination patterns of the two Zn(ii) ions are interestingly identical. Each Zn(ii) ion is mainly five-coordinated by two nitrogen atoms from one L ligand, one oxygen atom from coordinated OH⁻ anion, and two oxygen atoms from the carboxylic acid group of one sip³⁻ anion and the sulfonic acid group of another sip³⁻ anion, they form a twisted [ZnN₂O₃] square-pyramid geometry. The overall coordination geometry of [ZnN₂O₃] bears resemblance to that in {[Zn(bim)(bdc)]·0.8DMF·0.4EtOH·0.1H₂O} _n (bim = bis(imidazol-1-yl)methane, bdc²⁻ = terephthalate) [27]. The lengths of Zn–N bonds cover 2.087(5)–2.149(6) Å, the Zn–O bonds fall within the range of 1.961(4)–2.227(5) Å (Table 1), which are alike those reported for analogous Zn(ii) complexes [28]. The OH⁻ anion further connects adjacent Zn(ii) ions to generate the binuclear [Zn₂L₂(OH)] structural unit. The sip³⁻ anion joins neighboring binuclear [Zn₂L₂(OH)] structural units with μ ₄ -η ¹ :η ¹ :η ⁰ :η ¹ :η ⁰ :η ⁰ :η ¹ manner to gain a 1D double-chain structure along the a-axis (Figure 5).

Figure 4

View of the coordination environment of the Zn(ii) atom of 2 (symmetry codes: ⁱ −x, −y + 2, −z + 1; ⁱⁱ −x + 1, −y + 2, −z + 1).

Figure 5

View of the 1D layer structure of 2 constructed by sip³⁻ anion.

Notably, there exits two π–π interactions in 2. The L ligands provide with π–π stacking interactions between the approximately parallel L ligands (Cg4⋯Cg4^vi, ca. 2.9(3)° and Cg7⋯Cg7^v, ca. 0.4(3)°) of neighboring double-chain structures (Cg4⋯Cg4^vi, centroid-to-centroid distance of 3.577(4) Å, and Cg7⋯Cg7^v, centroid-to-centroid distance of 3.612(3) Å; Table 4), which make the double-chain structure grow into a 2D supramolecular structure (Figure 6). Additionally, N–H⋯O, N–H⋯F, and O–H⋯N hydrogen bonds (N(4)–H(4)⋯O(5)^iv, N(4)–H(4)⋯F(1), and O(2W)–H(2A)⋯N(3); Table 3) further stabilize the 2D supramolecular structure.

Figure 6

View of the 2D supramolecular structure of 2.

2.2 Hirshfeld surface (HS) analysis

HS analysis is carried out using Crystal Explorer 17.5 [29], in an effort to analyze intermolecular interactions in the crystal structure of 1. We obtain the three important graphs: d_norm and curvedness, as well as the associated two-dimensional fingerprint plots. Visualization of the d_norm diagram is performed using a red–white–blue color scheme. In Figure 7, the bright-red spots on the HSs indicate hydrogen bond interactions, which represent distances smaller than the sum of van der Waals radii. White dots represent distance close to the sum of van der Waals radii, and the blue dots clearly state distances greater than the sum of van der Waals radii. Significant π–π stacking interactions are visible on the shape-index surface, symbolized by red-yellow and blue-green triangles (and back-to-back diamonds) (Figure 8). The planarity of the 1H-imidazo[4,5-f][1,10]phenanthroline sections is depicted by the curvedness where great majority of the surface is flat (Figure 9).

Figure 7

HS evaluated over d_norm for 1.

Figure 8

HS evaluated over shape-index for 1.

Figure 9

HS evaluated over curvedness for 1.

The two-dimensional fingerprint plots of different types of interactions are presented in Figure 10, where C⋯H/H⋯C(23.7%), H⋯H(17.4%), and Cl⋯H/H⋯Cl(11.5%) contacts make the largest contributions to the HS. Additionally, O⋯H/H⋯O(10.4%), F⋯H/H⋯F(9.5%), N⋯H/H⋯N(8.6%), and C⋯C(8.1%) interactions also contribute to the HS. Furthermore, there are other weak C⋯Cl/Cl⋯C(4.7%) and C⋯N/N⋯ C(1.7%) intermolecular contacts that make a minor contribution.

Figure 10

Two-dimensional fingerprint plots analysis for 1.

Preparation of [Cd₂(L)₄(Cl)₂]·(SO₄) (1)

CdSO₄ (0.4 mmol, 0.083 g), gallic acid (H₄gal) (0.4 mmol, 0.068 g), NaCl (0.4 mmol, 0.023 g), and L (0.22 mmol, 0.077 g) were mixed in deionized water, and the pH value of the mixture was adjusted to 2.17 with triethylamine. The mixture was continuously stirred at room temperature for 10 min to obtain a mixed solution. Then the solution was shifted to a 15 mL Teflon-lined reactor and heated at 443 K for 4 days. When cooled to room temperature, crystals of 1 were obtained in 32% yield based on Cd. Anal. Calcd for C₇₆H₄₀Cd₂Cl₆F₄N₁₆O₄S, %: C, 51.09%; H, 2.26%; N, 12.54%. Found: C, 50.68%; H, 2.24%; N, 12.42%.

Preparation of {[Zn₂(L)₂(Sip)(OH)]·H₂O} _n (2)

ZnSO₄·7H₂O (0.4 mmol, 0.115 g), 5-sulfoisophthalic acid monosodium salt (NaH₂Sip) (0.4 mmol, 0.108 g), and L (0.12 mmol, 0.042 g) were dissolved in deionized water, which was then adjusted to a pH value of 7.08 by the addition of triethylamine. The mixture was stirred at room temperature for 10 min. Then the mixture was sealed in a 15 mL Teflon-lined reactor and heated at 433 K for 4 days before being completely cooled. Crystals of 2 were obtained in 37% yield based on Zn. Anal. Calcd for C₄₆H₂₆Cl₂F₂N₈O₉SZn₂, %: C 49.93%; H, 2.37%; N, 10.13%. Found: C, 49.54%; H, 2.34%; N, 10.03%.

X-ray crystallography

Single-crystal X-ray diffraction analyses of 1 and 2 were obtained using an ω–ϕ scan method on a Bruker-AXS Smart CCD diffractometer equipped with graphite-monochromatized Mo-Kα radiation (λ = 0.71073 Å) at 298 (2) K. The structures were solved primarily by direct methods using SIR2014 [30] and refined with the SHELXL2018/3 program [31] by full-matrix least-squares method based on F ² . The non-hydrogen atoms of 1 and 2 were refined anisotropically. All non-hydrogen atoms were anisotropically refined, and hydrogen atoms were placed in the calculation position and refined into riding atoms. Crystal data and selected bond distances and angles are gathered in Table 1, while structure refinements 1 and 2 are listed in Table 5. Full details of the X-ray structure determination of complexes 1 and 2 have been deposited with the Cambridge Crystallographic Data Center, the CCDC 2354484 and 2354485 represent 1 and 2.