Syntheses, Crystal Structures and Properties of Mn(II) and Co(II) Coordination Complexes Based on 1, 10-Phenanthroline Derivative

1. INTRODUCTION

Recently, the design and synthesis of new coordination complexes are currently attracting considerable attention due to their potential applications as functional materials^[1-4]. It is well known that novel complexes can be specially designed under hydrothermal conditions by the selection of metal ions with preferred coordination geometries, in consideration of the structures of organic ligands and the effects of reaction conditions^[5-7]. Therefore, great quantities of coordination complexes with fascinating topological structures and properties have been synthesized and reported so far^[8-11]. As we know, covalent bonds and noncovalent intermolecular forces can be used to construct various supramolecular architectures^[12]. Recent study indicates that 1, 10-phenanthro-line derivatives have been widely used to construct supramolecular architectures not only because of their excellent coordinating ability, but also of their large conjugated system and good accepter-donor system to form π-π interactions and hydrogen bonding interactions. Based on those factors, a number of coordination complexes have been prepared from zero-dimensional molecules or one-dimensional chains, generating extended two-dimensional layers or three-dimensional network supramolecular structures through π-π interactions and hydrogen bonding interactions^{[13, 14]}. So, we selected 1, 10-phenanthroline derivative, 2-(2-fluoro-6-fluorophenyl)-1H-imidazo[4, 5-f][1, 10]phenanthroline (L), as a N-donor chelating ligand and two carboxylate ligands as organic linkers, yielding two coordination complexes, namely [Mn(L)₂(DNSA)] (1) and [Co(L)(1, 4-bdc)]_n (2).

2. EXPERIMENTAL

2.1 Generals

The commercially available reagents were used without further purification. Elemental analysis was measured on a Perkin-Elmer 240 CHN elemental analyzer. The powder X-ray diffractions (PXRD) were measured on a Rigaku Dmax 2000 X-ray diffractometer with graphite-monochromatized CuKα radiation. The emission spectra were measured on a Renishaw inVia Raman Microscope. Thermal stability experiment was performed on a TG SDT2960 thermal analyzer under a nitrogen atmosphere.

2.2 Synthesis of [Mn(L)₂(DNSA)] (1)

A mixture of H₂DNSA (0.30 mmol), MnSO₄ (0.30 mmol) and L (0.25 mmol) was dissolved in 12 mL water. When the pH value of the mixture was adjusted to ca. 7.5 with KOH, the solution was put into a 25-mL Teflon-lined Parr and heated in an autoclave at 150 ℃ for 4 days, obtaining yellow crystals of 1 in 31% yield based on L. Anal. Calcd. for C₄₅H₂₂Cl₂F₂MnN₁₀O₇ (%): C, 55.23; H, 2.27; N, 14.31. Found (%): C, 55.09; H, 2.23; N, 14.19.

2.3 Synthesis of [Co(L)(1, 4-bdc)]_n (2)

The pH value of a mixture of 1, 4-H₂bdc (0.30 mmol), Co(NO₃)₂∙6H₂O (0.10 mmol) and L (0.05 mmol) in 10 mL water distilled water was adjusted to 5.7 with KOH. The resultant solution was heated at 185 ℃ in a 25-mL Teflon-lined stainless-steel autoclave for 4 days, resulting in brown crystals of 2 with the yield of 42% based on L. Anal. Calcd. for C₂₇H₁₄ClCoFN₄O₄ (%): C, 56.71; H, 2.47; N, 9.80. Found (%): C, 56.43; H, 2.41; N, 9.72.

2.4 X-ray structure determination

A crystal of 1 suitable for X-ray diffraction was chosen and mounted on a Bruker P4 diffractometer equipped with graphite-monochromatized MoKα (λ = 0.71073 Å) radiation by using an ω scan method at 293(2) K. And a crystal of 2 was selected for data collection performed on a Rigaku RAXIS-RAPID CCD detector diffractometer equipped with graphite-monochromatic MoKα radiation (λ = 0.71073 Å) with an ω-φ scan mode at 293(2) K. The crystal structures were solved by direct methods with SIR2014 (Burla et al., 2014)^[15] and refined with SHELXL2018/3 (Sheldrick, 2015)^[16] by full-matrix least-squares techniques on F². The non-hydrogen atoms of the complex were refined with anisotropic temperature parameters. All H atoms were positioned geometrically (C–H = 0.93 Å) and refined as riding with U_iso(H) = 1.2U_eq(carrier).

3. RESULTS AND DISCUSSION

3.1 Description of the crystal structure

Selected bond lengths and bond angles of 1 and 2 are given in Table 1, and hydrogen bond lengths and bond angles of 1 in Table 2. The asymmetric unit of 1 consists of one Mn(II) atom, two L ligands and one DNSA anion (Fig. 1). Each Mn(II) atom is six-coordinated by two oxygen atoms (O(1) and O(2)) from one DNSA anion, and four nitrogen atoms (N(1), N(2), N(5) and N(6) are from two L ligands in a distorted octahedral coordination sphere. The atoms N(1), N(2), N(5) and O(1) constitute the basal plane of the octahedron, while N(6) and O(2) are located at the axial positions. The Mn–O bond lengths range from 2.100(2) to 2.118(2) Å, and the Mn–N distances vary from 2.256(2) to 2.303(2) Å. The carboxylate group of DNSA anion shows a η¹: η⁰ monodentate mode, whereas each DNSA anion chelates one Mn(II) atom in a bidentate mode. The adjacent [Mn(L)₂(DNSA)] molecules form a bimolecular structure through N–H∙∙∙O (N(3)–H(3A)∙∙∙O(2)ⁱⁱ, N(3)–H(3A)∙∙∙O(3)ⁱⁱ, symmetric code: ⁱⁱ x–1, y, z–1, as shown in Table 2) hydrogen-bonding interactions (Fig. 2). Furthermore, the bimolecular structures are linked into a two-dimensional supramolecular layer structure by N–H∙∙∙N (N(7)–H(7A)∙∙∙N(4)^v, symmetric code: ^v x–1/2, –y+1/2, z+1/2, as illustrated in Table 2) hydrogen-bonding interactions between the adjacent bimolecular structures (Fig. 2).

Table 1

Table 1.  Selected Bond Lengths (Å) and Bond Angles (°) for 1 and 2

DownLoad: CSV

1
Bond	Dist.		Bond	Dist.		Bond	Dist.
Mn(1)–N(1)	2.273(2)		Mn(1)–N(5)	2.278(2)		Mn(1)–O(1)	2.100(2)
Mn(1)–N(2)	2.303(2)		Mn(1)–N(6)	2.256(2)		Mn(1)–O(2)	2.118(2)
Angle	(°)		Angle	(°)		Angle	(°)
O(1)–Mn(1)–O(2)	81.91(7)		N(6)–Mn(1)–N(1)	107.66(8)		O(1)–Mn(1)–N(2)	90.03(8)
O(1)–Mn(1)–N(6)	90.68(7)		O(1)–Mn(1)–N(5)	107.28(8)		O(2)–Mn(1)–N(2)	108.05(8)
O(2)–Mn(1)–N(6)	157.26(8)		O(2)–Mn(1)–N(5)	88.80(8)		N(6)–Mn(1)–N(2)	93.35(8)
O(1)–Mn(1)–N(1)	154.86(8)		N(6)–Mn(1)–N(5)	72.85(8)		N(1)–Mn(1)–N(2)	72.28(7)
O(2)–Mn(1)–N(1)	86.70(8)		N(1)–Mn(1)–N(5)	94.75(8)		N(5)–Mn(1)–N(2)	157.61(8)
2
Bond	Dist.		Bond	Dist.		Bond	Dist.
N(1)–Co(1)	2.134(2)		N(2)–Co(1)	2.147(2)		O(1)–Co(1)	2.362(2)
O(2)–Co(1)	2.1231(18)		O(3)–Co(1)	2.0481(18)		O(4)–Co(1)iii	2.0304(18)
Angle	(°)		Angle	(°)		Angle	(°)
O(4)iii–Co(1)–O(3)	89.82(8)		O(4)iii–Co(1)–O(2)	96.64(7)		O(3)–Co(1)–O(2)	101.94(7)
O(4)iii–Co(1)–N(1)	121.30(8)		O(3)–Co(1)–N(1)	101.66(8)		O(2)–Co(1)–N(1)	134.87(7)
O(4)iii–Co(1)–N(2)	86.11(8)		O(3)–Co(1)–N(2)	173.73(8)		O(2)–Co(1)–N(2)	83.29(8)
N(1)–Co(1)–N(2)	76.52(8)		O(4)iii–Co(1)–O(1)	154.25(7)		O(3)–Co(1)–O(1)	91.90(7)
O(2)–Co(1)–O(1)	57.89(7)		N(1)–Co(1)–O(1)	83.45(7)		N(2)–Co(1)–O(1)	93.84(8)
Symmetry transformation used to generate the equivalent atoms: 2 (i)–x+ 1, y, –z+ 1/2; (ii)–x, –y+ 1, –z+ 1; (iii)–x, y, –z+ 1/2

Table 2

Table 2.  Hydrogen Bond Lengths (Å) and Bond Angles (°) for 1

DownLoad: CSV

Crystal	D–H∙∙∙A	d(D–H)	d(H∙∙∙A)	d(D∙∙∙A)	∠DHA
1	N(3)–H(3A)∙∙∙O(2)iiN(3)–H(3A)∙∙∙O(3)iiN(7)–H(7A)∙∙∙N(4)v	0.860.860.86	2.621.872.23	3.219(3)2.731(3)3.054(3)	127175160
Symmetry transformation: 1 (i) x– 1/2, –y+ 1/2, z– 1/2; (ii)–x+ 1, –y, –z+ 1; (iii)–x+ 1/2, y– 1/2, –z+ 3/2; (iv)–x+ 1/2, y+ 1/2, –z+ 1/2; (v) x– 1/2, –y+ 1/2, z+ 1/2

Figure 1

Figure 1.  View of the molecular structure of 1

DownLoad: Full-Size Img PowerPoint

Figure 2

Figure 2.  View of the layer structure of 1 formed by hydrogen-bonding interactions (N–H···O and N–H···N)

DownLoad: Full-Size Img PowerPoint

As can be observed in Fig. 3, there are one Co(II) atom, one L ligand, and two halves of 1, 4-bdc anions in the asymmetric unit of 2. The 1, 4-bdc anion resides on an inversion center. Each Co(II) atom is six-coordinated by two nitrogen atoms from one L ligand (Co(1)–N(1) = 2.134(2), Co(1)–N(2) = 2.147(2) Å), and four carboxylate oxygen atoms from three different 1, 4-bdc anions (Co(1)–O(1) = 2.362(2), Co(1)–O(2) = 2.1231(18) Å, Co(1)–O(3) = 2.0481(18), Co(1)–O(4)ⁱⁱⁱ = 2.0304(18) Å, symmetric code: ⁱⁱⁱ –x, y, –z+1/2). In particular, the two 1, 4-bdc anions show different coordination modes (Fig. 3). For convenience, the 1, 4-bdc anions containing the oxygen atoms labeled O(1) and O(3) are designated 1, 4-bdc1 and 1, 4-bdc2, respectively. Each carboxylate group of 1, 4-bdc2 bridges two Co(II) atoms in a bis-bridging mode, whereas each carboxylate group of 1, 4-bdc1 anion chelates one Co(II) atom in a bis-chelating mode to yield a dimer. The distance between the Co(II) atoms in the dimer is about 10.879 Å. Most interestingly, the binuclear units are bridged by the backbones of 1, 4-bdc2 ligands to form a chain structure (Fig. 4) and are further connected by the 1, 4-bdc2 ligands in bis-chelating modes to give rise to a layer structure (Fig. 4). The L ligands are attached to both sides of the layer structures, which allow the formation of π-π stacking between the two pyridine rings of the L ligands with the centroid-to-centroid distance of 3.764(2) Å and face-to-face distance of 3.387(1) Å, and the dihedral angle between the two planes is ca. 0.0(1)^o (Two pyridine rings are composed of N(1)/C(1)~C(5) and N(1)^iv/C(1)^iv~C(5)^iv, respectively; symmetry code: ^iv –x + 1/2, –y + 1/2, –z + 1) (Fig. 6). These π-π stacking interactions linked the adjacent layers into a 3D supramolecular architecture (Fig. 4).

Figure 3

Figure 3.  Coordination environment of 2 (Symmetric codes: (i) –x + 1, y, –z + 1/2; (ii) –x, –y + 1, –z + 1; (iii) –x, y, –z + 1/2)

DownLoad: Full-Size Img PowerPoint

Figure 4

Figure 4.  Three-dimensional supramolecular architecture of the title complex constructed by π-π interactions

DownLoad: Full-Size Img PowerPoint

3.2 PXRD patterns and UV-vis absorption spectrum

The powder X-ray diffraction (PXRD) patterns for complexes 1 and 2 were recorded at room temperature to confirm their phase purity (Fig. 5). The experimental PXRD patterns of 1 and 2 well correspond to the simulated ones of 1 and 2, respectively, indicating the synthesized bulk materials and the measured single crystals are the same. The UV-vis absorption spectra of 1 were registered from the crystalline state at r. t. (Fig. 6). The energy bands of 1 from 200 to 560 nm can be assigned as metal-to-ligand charge-transfer (MLCT) transitions^[17]. The above analysis is consistent with the crystal structure determination.

Figure 5

Figure 5.  Experimental and simulated PXRD patterns of 1 and 2

DownLoad: Full-Size Img PowerPoint

Figure 6

Figure 6.  UV-vis absorption spectrum of 1

DownLoad: Full-Size Img PowerPoint

3.3 Luminescent properties

The luminescent properties of the free organic ligands and complex 1 have been studied in the solid state at room temperature (Fig. 7). The main emission peaks of H₂DNSA and L are located at about 548 (λ_ex = 325 nm) and 404 nm (λ_ex = 325 nm), respectively, which may be attributed to π* → n or π* → π transition^[18]. Complex 1 shows an emission band at 545 nm (λ_ex = 325 nm). This emission is similar to that of H₂DNSA (λ_em = 545 nm). Therefore, the emission of 1 should originate from the H₂DNSA ligand.

Figure 7

Figure 7.  Solid state emission spectra of 1, 2, 3-H₂DNSA, L and 1 at room temperature

DownLoad: Full-Size Img PowerPoint

3.4 Thermogravimetric analysis

The stabilities of 1 and 2 were evaluated by thermo-gravimetric analysis (TGA). As depicted in Fig. 8, the TGA curve of 1 shows two main steps of weight loss. The first step of 21.4% from 202 to 310 ℃ corresponds to the release of the organic group C₇H₂N₂O₆ of DNSA anions (calcd. 21.5%), and the second step of 71.2% in the range of 317~572 ℃ to the elimination of L ligands (calcd.: 71.3%). The anhydrous complex 2 begins to decompose at 227 ℃ and ends above 632 ℃. The weight loss is attributed to both L ligands and the organic group C₈H₄O₃ of 1, 4-bdc anions (obsd. 86.8%, calcd. 86.9%). However, it is difficult to determine this weight loss accurately as these processes are overlapped with the weight loss due to the dissociation of organic fractions.

Figure 8

Figure 8.  TGA curves of complexes 1 and 2

DownLoad: Full-Size Img PowerPoint

4. CONCLUSION

Two new coordination complexes, [Mn(L)₂(DNSA)] (1) and [Co(L)(1, 4-bdc)]_n (2), have been successfully synthesized by the reaction of two transition metal ions, different aromatic carboxylic ligands and 2-(2-fluoro-6-fluorophenyl)-1H-imidazo[4, 5-f][1, 10]phenanthroline (L) with different architectures under hydrothermal conditions. The difference of the structures indicates that carboxylic ligands and metal cations play important roles in the formation of complexes. 1 shows weak emission in the solid state at room temperature. The thermal behaviors of 1 and 2 have been studied. We believe that more metal complexes containing L ligand with interesting structures and physical properties will be synthesized in the future.

References

1. [1]

   Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O'Keeffe, M.; Yaghi, O. M. Modular chemistry:   secondary building units as a basis for the design of highly porous and robust metal-organic carboxylate frameworks. Acc. Chem. Res. 2001, 34, 319–330.  doi: 10.1021/ar000034b
   

2. [2]

   Yoshii, Y.; Sakai, K.; Hoshino, N.; Takeda, T.; Noro, S.; Nakamura, T.; Akutagawa, T. Crystal-to-crystal structural transformation of hydrogen-bonding molecular crystals of (imidazolium)(3-hydroxy-2-quinoxalinecarboxylate) through H₂O adsorption-desorption. CrystEngComm. 2015, 17, 5962–5969.  doi: 10.1039/C4CE02519A
   

3. [3]

   Kong, Z. G.; Guo, S. N.; Zhao, X. Y.; An, X. An unusual 2D → 3D polythreading framework based on (4)-c sql networks with arms: synthesis, structure and luminescence. Mendeleev Commun. 2016, 26, 52−53.  doi: 10.1016/j.mencom.2016.01.020
   

4. [4]

   Zheng, B. S.; Luo, X.; Wang, Z. X.; Zhang, S. W.; Yun, R. R.; Huang, L.; Zeng, W. J.; Liu, W. L. An unprecedented water stable acylamide-functionalized metal-organic framework for highly efficient CH₄/CO₂ gas storage/separation and acid-base cooperative catalytic activity. Inorg. Chem. Front. 2018, 5, 2355–2363.  doi: 10.1039/C8QI00662H
   

5. [5]

   Sebastian, H.; Andreas, S.; Shobhna, K.; Roland, W.; Roland, A. F. Zinc-1, 4-benzenedicarboxylate-bipyridineframeworks-linker functionalization impacts network topology during solvothermal synthesis. J. Mater. Chem. 2012, 22, 909–918.  doi: 10.1039/C1JM14791A
   

6. [6]

   Han, X.; Xu, Y. X.; Yang, J.; Xu, X.; Li, C. P.; Ma, J. F. Metal-assembled, resorcin[4]arene-based molecular trimer for efficient removal of toxic dichromate pollutants and knoevenagel condensation Reaction. ACS Appl. Mater. Inter. 2019, 11, 15591–15597.  doi: 10.1021/acsami.9b02068
   

7. [7]

   Rubio-Martinez, M.; Avci-Camur, C.; Thornton, A. W.; Imaz, I.; Maspoch, D.; Hill, M. R. New synthetic routes towards MOF production at scale. Chem. Soc. Rev. 2017, 46, 3453–3480.  doi: 10.1039/C7CS00109F
   

8. [8]

   Martin, B. D.; Suzanne, M. N.; Stuart, R. B. Variable length ligands: a new class of bridging ligands for supramolecular chemistry and crystal engineering. Chem. Commun. 2009, 37, 5579–5581.
   

9. [9]

   Wang, X. Y.; Li, G. T.; Wang, H.; Song, Y.; Liu, D. X; Xu, Z. L. Crystal structure, thermal behavior and luminescence of a new copper coordination polymer constructed with 4-(carboxymethoxy)-benzoic acid. Chin. J. Struct. Chem. 2019, 38, 629–634.
   

10. [10]

    Mala, N.; Pramendra, K. S. Chemistry and applications of organotin(IV) complexes of Schiff bases. Dalton Trans. 2011, 40, 7077–7121.  doi: 10.1039/c0dt01426e
    

11. [11]

    Lin, Z. J.; Lü, J.; Hong, M. C.; Cao, R. Metal-organic frameworks based on flexible ligands (FL-MOFs): structures and applications. Chem. Soc. Rev. 2014, 43, 5867–5895.  doi: 10.1039/C3CS60483G
    

12. [12]

    Ferey, G. Microporous solids: from organically templated inorganic skeletons to hybrid frameworks∙∙∙ecumenism in chemistry. Chem. Mater. 2001, 13, 3084–3098.  doi: 10.1021/cm011070n
    

13. [13]

    Wang, X. Y.; He, Y.; Zhao, L. N.; Kong, Z. G. An unusual 2D → 3D polythreading framework based on a long 1, 10-phenanthroline derivative ligand. Inorg. Chem. Commun. 2011, 14, 1186–1189.  doi: 10.1016/j.inoche.2011.04.024
    

14. [14]

    Kong, Z. G.; Han, Q.; Zhang, L.; Liu, D. X.; Hu, B.; Wang, X. Y. A new Cd(II) coordination polymer constructed by 1, 10-phenanthroline derivative: syntheses, structure, physical properties and theoretical calculation. Chin. J. Struct. Chem. 2019, 38, 2141–2147.
    

15. [15]

    Burla, M. C.; Caliandro, R.; Carrozzini, B.; Cascarano, G. L.; Cuocci, C.; Giacovazzo, C.; Mallamo, M.; Mazzone, A.; Polidori, G. Crystal structure determination and refinement via SIR2014. J. Appl. Cryst. 2015, 48, 306–309.  doi: 10.1107/S1600576715001132
    

16. [16]

    Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Cryst. 2015, C71, 3–8.
    

17. [17]

    Chen, X. M.; Liu, G. F. Double-stranded helices and molecular zippers assembled from single-stranded coordination polymers directed by supramolecular interactions. Chem. Eur. J. 2002, 8, 4811–4817.  doi: 10.1002/1521-3765(20021018)8:20<4811::AID-CHEM4811>3.0.CO;2-R
    

18. [18]

    Zhang, S. H.; Feng, C. Microwave-assisted synthesis, crystal structure and fluorescence of novel coordination complexes with Schiff base ligands. J. Mol. Struct. 2010, 997, 62–66.