Two new zinc ( II ) coordination complexes constructed by phenanthroline derivate: Synthesis and structure

: Two new Zn ( II ) coordination complexes [ Zn ( L ) ( dna )( H 2 O )] ( 1 ) and [ Zn ( L )( glu )] 2 · H 2 O ( 2 ) ( L = 2 -( 4 - ﬂ uoro - phenyl )- 1 H - imidazo [ 4,5 - f ][ 1,10 ] phenanthroline, H 2 dna = 3,5 - dinitrosalicylic acid, H 2 glu = glutaric acid ) have been hydrothermally synthesized and characterized by single crystal X - ray di ﬀ raction, elemental analysis, ﬂ uorescence spectrum, and infrared spectroscopy. For complex 1 , the dna 2 − anion adopts μ 1 - η 1 : η 1 chelating bidentate mode to coordinate with one Zn ( II ) atom and π – π stacking inter - actions are formed between the L ligands. For complex 2 , glu 2 − anions connect Zn ( II ) atoms to form a wavy two - dimensional layer, and the L ligands are attached on two sides of the two - dimensional layer.


Introduction
As an emerging class of unique and interesting organoinorganic hybrid crystalline materials, coordination complexes built of metal ions/clusters (Song et al., 2021;Yang et al., 2010) and bridging organic ligands have got a lot of attention in the past several decades (Chen, 2016;Wei et al., 2008). It is an infinite extension driven by self-assembly into one-dimension (Wang et al., 2017), two-dimension (Zhu et al., 2008), or three-dimension (Aghabozorg et al., 2011;Mirzaeib et al., 2014). In the process, many different factors can affect the architecture of the coordination complexes (Chen et al., 2021a;Zhang et al., 2020). Among these factors, the selection of excellent carboxylate ligands (Wang et al., 2014 and nitrogencontaining ancillary ligands (Bhargao et al., 2020;Li et al., 2022) make a number of significant contributions to obtain desired structures and properties (Bazargana et al., 2019;Chen et al., 2021b). Carboxylic acid ligands could be divided into two types, namely rigid aromatic ligands or heterocyclic acids (Zhang et al., 2015) and flexible aliphatic ligands (Wang et al., 2009). The flexible aliphatic ligands due to their aliphatic chain can provide multiple possibilities for the construction of frameworks . For example, glutaric acid (H 2 glu) as a flexible ligand can exhibit diverse coordination modes and topologies by means of its two carboxylate groups. Dutta et al. (2019) reported [Zn(glu)(4-nvp)] (4-nvp = 4-(1-naphthylvinyl)pyridine) with glutaric acids, and the results interestingly showed that two Zn(II) centers are equivalently bridged by four μ 2 , η 2 -carboxylate groups from four different glutaric acids. In addition, compared with flexible aliphatic ligands, rigid aromatic ligands are usually used to control and stable the framework. For example, 3,5-dinitrosalicylic acid as an asymmetric bridging ligand can form a six-membered ring through the coordination of the carboxylate groups and hydroxyl groups with metal ions, which can increase the stabilization of the solid networks. Tian et al. (2020) synthesized a new coordination polymer, [{Bu 2 Sn(3,5-(NO 2 ) 2 -2-OC 6 H 2 COO)} 2 (4,4′-bpy)] n and 3,5-dinitrosalicylate as doubly charged anion ligand to coordinate to tin atoms. In addition to the ligands, the choice of metal ions is also very important. Compared with rare earth metals, transition metals are cheaper and easier to obtain; therefore, it can replace expensive rare earth metals to build coordination polymers. Not only that, but it is of great significance in the field of photoluminescence. Zinc metal ions have a variety of coordination modes, which can increase the structural stability of zinc coordination polymer after binding with organic ligands Wang et al., 2020). Taking the advantage of above interesting properties, we have synthesized and characterized two zinc(II) coordination complexes with glutaric acid and 3,5-dinitrosalicylic acid.
As can be observed in Figure 6, the asymmetric unit of 2 contains two Zn(II) atoms, two chelating L ligands, two glu 2− anions, and one free water molecule. Each Zn(II) atom bonds to three carboxylate oxygen atoms from three different glu 2− anions and two nitrogen atoms from one chelating L ligand in a distorted tetragonal pyramid geometry. As seen in Figure 7, two Zn(II) centers are connected by carboxylate groups from one glu 2− anion with μ 2 -η 1 :η 1 coordination manners, generating a binuclear Zn 2 unit with a Zn⋯Zn distance of 10.628 Å. Further linkage of these Zn 2 units by the other μ 4 -glu 2− anions forms a wavy two-dimensional layer with equatorial plane symmetry along the c-axis.
As illustrated in Figure 8, the conjugated L ligands are attached on two sides of the layer. As shown in Figure 9 Table 2) further consolidates the three-dimensional supramolecular structure.

IR spectroscopy
The IR spectroscopy curve of 2 was shown in the region of 4,000-400 cm −1 (Figure 11). The broad band at 3,428 cm −1 may be assigned to the vibrations of water molecules of 2.
The two peaks at 1,608 and 1,312 cm −1 correspond to the asymmetric and symmetric vibrations of carboxylate groups of the glu 2− anions. Peaks at 1,405 and 1,074 cm −1 were observed, which is characteristic of the C-N and C]N stretching vibrations of L ligand stretching frequency of the L ligand.

Luminescent properties
The luminescent properties of the free organic ligands and 2 have been studied in the solid state at room temperature ( Figure 12). The free L ligand and H 2 glu show emission bands centered at 557 nm (λ ex = 325 nm) and 536 nm (λ ex = 325 nm), respectively, which can be attributed to the π*-n or π*-π transition. The emission peak of Zn(II)-containing 2 occurs at 575 nm (λ ex = 325 nm). Compared with the free L ligand, the emission peak of 2 is red-shifted by 18 nm. Due to the configuration of d 10 , Zn(II) ions are difficult to oxidize or reduce (Yam and Wong, 2011). Therefore, the emission of 2 is neither metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) (Guo et al., 2009). The emission of 2 could be owing to the intraligand transitions.

Conclusions
In summary, two new Zn(II) coordination complexes were obtained and their structures were characterized. In 1, the L ligands furnish π-π stacking interactions between the L ligands of adjacent bimolecular structures, generating a one-dimensional supramolecular chain. The adjacent 1D chains were extended 3D supramolecular structures through the hydrogen bonds. In 2, the adjacent Zn 2 units are linked together via the other glu 2− anions to yield a wavy two-dimensional layer. Moreover, the 2D layers are further packed into a 3D supramolecular framework through hydrogen bond interactions.

Experimental
All chemicals for syntheses were used as received from commercial sources (Shanghai Hengfei Biological Technology Co., Ltd and Henan Pusai Chemical Products Co., Ltd, China). Elemental analysis (C, H, N) was carried out using a Perkin-Elmer 240 CHN elemental analyzer (Perkin-Elmer, North

Preparation of [Zn(L)(dna)(H 2 O)] (1)
Zn(SO 4 )·7H 2 O (0.15 mmol, 0.043 g), L (0.15 mmol, 0.047 g), 3,5-dinitrosalicylic acid (0.3 mmol, 0.068 g), and anhydrous ethanol (1.5 mL) were mixed and dissolved in deionized water (10 mL). NaOH (0.6 mmol, 0.024 g) was added, and then, the reaction mixture was sealed in a 20 mL stainless steel vessel and heated at 453 K for 96 h. Yellow block crystals of 1 were obtained with a yield of 0.052 g (ca. 56%, based on the L    X-ray crystallography X-ray diffraction data of 1 and 2 were collected at 296(2)K on a Rigaku RAXIS-RAPID diffractometer, with graphitemonochromatized Mo-Kα radiation (λ = 0.71073 Å) using the ω scan technique. The structures were resolved using SIR2014 (Burla et al., 2015) and refined using the SHELXL2018/3 program (Sheldrick, 2015). The models were refined on F 2 by a full-matrix least-squares technique. Non-hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms of the organic ligands were placed in ideal positions and refined as riding atoms. Detailed information about the crystal data for 1 and 2 was summarized in Table 3. Detailed information about the selected bond lengths and bond angles were given in Table 4. Full details of the X-ray structure determination of coordination complexes 1 and 2 have been deposited with the Cambridge Crystallographic Data Center, and the CCDC 2182024 and 2209851 represent 1 and 2. Author contributions: Jingdong Feng: writingoriginal draft, methodology, experimental work; Beihao Su: writingoriginal draft, writingreview and editing; Xinxin Yi: experimental work; Zhiguo Kong: writingreview and editing, visualization, software; Limin Chang: data curation, validation.

Conflict of interest:
The authors declare no competing financial interest with any financial organization regarding the material discussed in the manuscript.