Crystal Structures, Luminescent Properties and Hirshfeld Surface Analyses of Zn(II) and Cd(II) Compounds Based on 1-(2-Carboxyl-phenyl)-3-(pyridin-2-yl)pyrazole①

ZHANGLi-YngLULi-PingZHUMio-Li,bFENGSi-Si,bGAOXio-Li

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Crystal Structures, Luminescent Properties and Hirshfeld Surface Analyses of Zn(II) and Cd(II) Compounds Based on 1-(2-Carboxyl-phenyl)-3-(pyridin-2-yl)pyrazole①

ZHANG Li-YangaLU Li-Pinga②ZHU Miao-Lia, b②FENG Si-Sia, bGAO Xiao-Lic

a(Institute of Molecular Science, Key Laboratory of Chemical Biology and Molecular Engineering of the Education Ministry, Shanxi University, Taiyuan, Shanxi 030006, China)b(Key Laboratory of Materials for Energy Conversion and Storage of Shanxi Province, Institute of Molecular Science, Shanxi University, Taiyuan, Shanxi 030006, China)c(Department of Chemistry, Taiyuan Normal University, Jinzhong, Shanxi 030619, China)

Hcppp,zinc(II) and cadmium(II) compounds, Hirshfeld surface, luminescent properties;

1 INTRODUCTION

The rational design and construction of coor- dination compounds have received considerable attention over the past ten years because of their intriguing molecular topologies and wide range of potential applicationsin luminescence, nonlinear optics, gas storage, magnetism and so on[1, 2]. The architecturaldiversities found in coordination com- pounds result from not only covalent metal-ligand bonds, but also weak non-covalent interactions, such as hydrogen and halogen bonding,-anion,-cation and-stacking interactions[3].However, the syn- thesis in a truly rational manner continues to be a challenging task, on account of factors that influence the structures, such as the nature of ligand and metal, solvents, reaction temperature, the ratio of metal to ligand,H, counter ions,[4-6].

Ligand Hcppp contains one carboxylate and two nitrogen heterocyclic groups to construct coor- dination frameworks with versatile structures[7]. At the same time, unprecedented attention has been paid to10metal coordination compounds because of their outstanding luminescent properties[8-11]. In this text, we report two10metal compounds[Zn2(Hcppp)2(cppp)2(H2O)2]·6H2O·2NO3(1) and [Cd(Hcppp)2Cl2]·3H2O (2) containingdifferent counter ions.The as-synthesized samples were characterized by X-ray single-crystal and powder diffractions, thermal gravimetric analysis and infra- red spectra.Theirweak non-covalent interactions and luminescent properties were also studied.

2 EXPERIMENTAL

2. 1 Materials and measurements

2. 2 Synthesis

2. 2. 1 Synthesis of[Zn2(Hcppp)2(cppp)2(H2O)2]· 2NO3·6H2O(1)

A 5 mL aqueous solution of Hcppp (26.50 mg, 0.10 mmol) and a 5 mL aqueous solution of Zn(NO3)2·4H2O (36.49 mg, 0.10 mmol) were added dropwise in a 50 mL of flask with constant stirring, and then 0.20 mol/L KOH (0.50 mL) was added. The mixture solution was stirred for 8 h at RT. The resulting solution was filtered and the filtrate was kept for slow evaporation at room temperature. After a few days,colorless crystals were obtained with ayield of45% (based on Zn). Elemental analysis:Calcd. for C60H58Zn2N14O22(MW 1457.96): C,49.43; H,4.01; N,13.45%. Found: C,49.48; H,4.06; N,13.47%. IR (cm-1): 3427 (), 3284 (), 1670 (), 1602 (), 1572 (), 1531 (), 1506 (),1433 (), 1367 (), 1157(), 1098 (), 972 (), 949(), 799 (), 760 (), 505 (),474(), 405 ().

2. 2. 2 Synthesis of[Cd(Hcppp)2Cl2]·3H2O (2)

The synthesis of 2 followed the same procedures as1, and only the metal salt was changed asCdCl2·2.5H2O (22.80 mg, 0.10mmol). Yield: 60% (based on Cd). Elemental analysis:Calcd. for C30H30CdN6O7Cl2(MW 770.06): C, 46.80; H, 3.93; N, 10.92%. Found: C, 46.83; H, 3.95; N, 10.95%. IR (cm-1): 3483(), 3172(), 1664(), 1528(), 1434(), 1370(), 1157(), 1122(), 1097(), 974(), 949(), 774(), 762(), 616(),474(), 406().

2. 3 Crystal structure determination

Table 1. Selected Bond Lengths (?) and Bond Angles (°), and the Distances of p-pWeak Interactions (?) for Compounds 1 and 2

Symmetry code for compound (1): (i) ?+1, ?, ?. Symmetry code for compound (2):(i)?+1, ?+2, ?+1.Cg(5) is the centre of N(1), C(1)～C(5) and Cg(6) is the centre of N(4), C(16)～C(20) and Cg(7) is the centre of C(9)～C(14) and Cg(8) is the centre of C(24)～C(29) for compound 1

Table 2. Hydrogen Bond Lengths (?) and Bond Angles (°), and the Distances of C-H-pWeak Interactions (?) for Compounds 1 and 2

Symmetry codes: (ii) ?+1,?1/2, ?+1/2; (iii), ?+1/2,+1/2; (iv)?1,,; (v) ?, ?+1, ?; (vi)+1,,;(vii) 2?, ?, ?;(viii) 2?, ?1/2+, 1/2?for 1. (i) ?+1, ?+2, ?+1; (ii)?1,?1,; (iii) ?+1, ?+1; (iv) 1?, 1?, ?for compound 2.Cg(7)is the centre of C(9)～C(14)and Cg(8) is thecentre of C(24)～C(29) for compound 1. Cg(4) is the centre of N(1), C(1)～C(5) for compound 2

2. 4 Hirshfeld surface calculations

Hirshfeld surfaces and related graphical tools have been shown to enhance exploration of the nature of the interactions between molecules in crystals. Since the local nature of the surface is dictated by the electron density and position of neighboring atoms inside and outside the surface, it reflects in considerable detail the immediate envi- ronment of a molecule in a crystal, and summarizes all intermolecular interactions in a remarkable graphical fashion. The Hirshfeld surface partitions crystal space into smooth non-overlapping volumes associated with each molecule, and is defined implicitly where the ratio of promolecule to pro- crystal electron densities equals 0.5. Three-dimen- sional (3) Hirshfeld surface maps are generated withdusing a red-white-blue color scheme, indicating shorter contacts, the van der Waals (vdW) contacts, and longer contacts, respectively, and two-dimensional (2) fingerprint plots are generated usingdandd,dfor the distance from the Hirshfeld surface to the nearest atom outside the surface,dfor the distance from the Hirshfeld surface to the nearest atom inside the surface, anddis defined in terms ofdanddand the vdW radii of atoms.

3 RESULTS AND DISCUSSION

3. 1 Crystal structure

3. 1. 1 Crystal structure of compound 1

X-ray diffraction analysis reveals that compound 1crystallizes in the monoclinicsystem, space group21/. The whole molecule is a binuclear structure through the operation of the symmetric center. The asymmetric consists of a crystallographically inde- pendent Zn(II) cation, one completely deprotonated cppp-anion, one Hcppp ligand, one coordinated water, one NO3–counter ion and three lattice water molecules.

As shown in Fig. 1a, The Zn(II) atomis octahe- drally coordinated with ZnN4O2geometrybyfour N atoms ((N(1), N(2), N(4) & N(5))from two Hcppp ligandswith the Zn–N bond distances ranging from 2.1316(15) to 2.2179(14) ? (Table 1), and two oxygen atoms (O(3) & O(5)) from one cppp–ligandand a coordinated water moleculewiththe Zn–O coordination distances changing from 2.0692(14) to 2.1498(14) ?, which are comparable to those reported for other Zn(II) compounds[17]. The different Zn–N and Zn–O bond distancesindicate the coordinated geometry is a slightly distorted octahedron.

As shown in Fig. 1a, the cppp-displays2-N,N′:O and the Hcppp shows1-N,N′ coordination modes,then two carboxylic O atoms from two cppp–ligands link adjacent Zn(II) ions in a bridge-mode to form a binuclear [Zn2(Hcppp)2(cppp)2(H2O)2] unit.

The crystal packing in 1 is stabilized by a com- bination of intermolecular O–H···O hydrogen bonds, C-H···and···stacking interactions (Table 2, Fig. 1b). The crystal structure gives rise to an infi- nite subloop chain consisting of 12-membered rings (5 5(12) ring with O(7)–H···O(1)iv, O(5)–H···O(4) and O(5)–H···O(8), O(8)–H···O(7), O(2)–H···O(4) hydrogen bonds). The O(8) atom also acts as a hydrogen-bond donor to the O(6)iiatom. Meanwhile, the O(7) atom of lattice water takes part in one intermolecular hydrogen bond,O(7)-H···O(9)iii, thusa one-dimensional hydrogen bonded polymer with a linear chain along theaxisis formed.Then, 1chains are further expanded into 2D networks through hydrogen bonds involving O(2)–H···O(4)vi.A 3supramolecular networks is further built through hydrogen bonds involving O(6)-H···O(10)vand weak intermolecular C-H···and···interactions (Symmetry codes: (ii) ?+1,?1/2, ?+1/2; (iii), ?+1/2,+1/2; (iv)?1,,; (v) ?, ?+1, ?; (vi)+1,,).

Fig. 1. (a)ORTEP view with 30% probability level ofthe coordination unit of 1 (H atoms are omitted for clarity). Symmetry code: i ?+1, ?+2, ?+1. (b) Perspective view of the 2network with the5 5(12) ring in 1

3. 1. 2 Crystal structure of compound 2

As depicted in Fig. 2a, the Cd(II)cation is six- coordinated by four N atoms in-N,N-chelating fashion from two Hcppp ligands and two chlorine ions. The coordination geometry of the Cd(II)cation can be described asa slightly distorted octahedral CdN4Cl2geometry, in which four atoms (Cl(1), N(1), N(4) & N(2)) occupy the basal plane, and two atoms (Cl(2) & N(5)) sit on the axial positions (Fig. 2a). The Cd–N coordination distances range from 2.365(2) to 2.474(2) ? and the Cd–Cl bond distances range from 2.528(1) to 2.532(1) ? (Table 1), which are comparable to those reported in other Cd(II) compounds[18-20].

Fig. 2. (a) ORTEP view with 30% probability level of 2.(b) Perspective view of the 2network with the(1)4 4(10) pattern in the A, B, C and D independent molecules

As shown in Fig. 2b, molecules are held in the crystal through a compound pattern of O–H···O and O–H···Clhydrogen bonds. In particular, the inde- pendent molecules A and B are hydrogen bonded through one(1)4 4(10) pattern, two carboxylic O donors and two carboxylic O acceptors (O(5)– H···O(2)iand O(3)–H···O(2)i, symmetry code: (i) ?+1, ?+2, ?+1). The independent molecules A and C are hydrogen bonded involving one O(6) atom of the lattice water acting as a hydrogen-bond donor to Cl(2) atom,O(6)–H···Cl(2)ii(symmetry code: (ii)?1,?1,). Besides, the independent molecules A and D are hydrogen bonded through O(6)– H···Cl(1)iii(symmetry code: (iii) ?+1, ?+1, ?). In addition, there are also weak C-H···interactions(Table 2).As a result, a 3supramolecular network is finally built along different directions by intermolecular interactions.

3. 2 Hirshfeld surface analysis

The Hirshfeld surfaces and 2fingerprint plots[21]of compounds 1 & 2 are illustrated in Figs. 3～6. Besides O–H···O (1) hydrogen bonds, there are also C–H···(2) and···(3) weak interactions in compound 1, as shown in Fig. 3[21]. There are also C–H···(2) weak interactions besides O–H···O (1) and O–H···Cl (4) hydrogen bonds in compound 2 (Fig. 5). Using the CrystalExplorer17[22]software, the percentages of contacts contributed to the total Hirshfeld surface area of molecules are shown in Figs. 4 and 6 for compounds 1 and 2, respectively. The proportions of O–H···O, C–H···and···interactions are 24.1%, 25.1% and 3.0% of the total Hirshfeld surfaces for 1. However, the proportions of O–H···O, C–H···and O–H···Cl interactions are 18.6%, 22.3%, and 14.0% of the total Hirshfeld surfaces for 2, that is to say, the O–H···Cl hydrogen bonds in 2 instead of the···interactions of 1 may be attributing to the influence of the coordination of chlorine atoms.

Fig. 3. Hirshfeld surfaces of compound 1mapped withnormproperty, the molecules in tube/licorice representation within the transparent surface maps. O–H···O (1), C–H···(2) and···(3)

Fig. 4. Fingerprint plots of compound 1: O–H···O (1), C–H···(2) and···(3) contacts, listing the percentages of contacts contributed to the total Hirshfeld surface area of molecules

Fig. 5. Hirshfeld surfaces of compound 2mapped withnormproperty, the molecules in tube/licorice representation within the transparent surface maps, O–H···O (1)and C–H···(2), O–H···Cl (4)

Fig. 6. Fingerprint plots of compound 2: O–H···O (1)and C–H···(2), O–H···Cl (4) contacts, listing the percentages of contacts contributed to the total Hirshfeld surface area of molecules

3. 3 PXRD and TG analyses

The as-synthesized samples of 1 and 2 are charac- terized by powder X-ray diffraction (PXRD). As shown in Fig. 7a and Fig. 7b, the PXRD patterns are almost consistent with the simulated spectrum, demonstrating the high phase purity of the com- pounds.

Fig. 7. Powder X-ray diffraction patterns of compounds 1(a) and 2(b)

TGA curve of 1 exhibits two main weight loss steps (Fig. 8a). The first weight loss of 7.24% from 25 to 110 ℃ corresponded to the release of six lattice water molecules (calcd. 7.18%). The second weight loss of 2.63% from 110 to 180 ℃was attributable to the removal of two coordinated water molecules (calcd. 2.47%). From 310 ℃, the com- pound began to lose weight rapidly. On further heating, the framework gradually decomposed.The TGA curve (Fig 8b) indicated that compound 2 lost its three coordinated water molecules (7.16%) from room temperature upon heating, which is consistent with the calculated value (7.03%). After the loss of guest water molecules, the framework began to decompose above 315 ℃, which could be attributed to the decomposition of the ligand.

Fig. 8. TGA curves for compounds 1(a) and 2(b)

Fig. 9. Solid-state luminescence spectra of 1, 2 and Hcpppat room temperature

3. 4 Luminescent property

4 CONCLUSION

Two compounds based on (1-(2-carboxyl-phen- yl)-3-(pyridin-2-yl)pyrazole have been constructed successfully.The ligand Hcppp exhibits different coordination modes to connect Zn(II) or Cd(II) centre to form discrete binuclear (1) or mononuclear (2) structure. Hirshfeld surface analyses indicate effective roles of O–H···O, C–H···,···and O–H···Cl contacts in crystal packings of 1 and 2. Both compounds emit the luminescence which may be assigned to the intra-ligand transitions (-*) luminescence emission when coordinated with the metal atoms. However, the existence of NO3–or Cl–ions decreases the luminescence intensity.

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9 June 2017;

8 October 2017 (CCDC 1539574 for 1 and 1539575 for 2)

① This project was supported by the National Natural Science Foundation of China (Nos. 21571118 and 21671124) andthe Natural Science Foundation of Shanxi Province (2015021031). A portion of this work was performed on the Scientific Instrument Center of Shanxi University of China

Lu Li-Ping, professor, majoring in Biology and Molecular Engineering. E-mail: luliping@sxu.edu.cn Zhu Miao-Li, professor, majoring in coordination chemistry. E-mail: miaoli@sxu.edu.cn

10.14102/j.cnki.0254-5861.2011-1752