Syntheses and structures’ influence on the nonlinear optical properties of o-ferrocenylbenzoate compounds

Inorganica Chimica Acta 362 (2009) 599–604

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Syntheses and structures’ influence on the nonlinear optical properties of o-ferrocenylbenzoate compounds Linke Li, Xiaohui Li, Hongwei Hou *, Yaoting Fan Department of Chemistry, Zhengzhou University, Henan 450052, PR China

a r t i c l e

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Article history: Received 28 January 2008 Received in revised form 2 April 2008 Accepted 8 April 2008 Available online 4 June 2008 Keywords: o-Ferrocenylbenzoate Crystal structure Influence Nonlinear optical properties Electrochemistry

a b s t r a c t Two complexes containing o-ferrocenylbenzoate [o-OOCH4C6Fc, Fc = (g5-C5H5)Fe(g5-C5H4)] components: {[Pb(g2-o-OOCH4C6Fc)2(phen)](NO3)} (phen = phenanthroline) (1) and {[Zn(g2-o-OOCH4C6Fc)2(bpe)](CH3OH)}n (bpe = 1,2-bis(4-pyridyl) ethene) (2) have been synthesized and structurally characterized by single crystal X-ray diffraction. 1 gives a discrete mononuclear framework, 2 features an infinite 1-D chain structure constructed by the bpe linking two adjacent zinc (II) ions. The third-order nonlinear optical (NLO) properties of complexes 1, 2 and the reactant o-NaOOCH4C6Fc were determined by Z-scan techniques in DMF solution. The results show that the structures of complexes have great impact on NLO properties. Complex 1 and o-NaOOCH4C6Fc display self-defocusing behaviors, while complex 2 exhibits strong self-focusing effect. The solution-state differential pulse voltammograms of complexes 1, 2 and o-NaOOCH4C6Fc were investigated as well. The results reveal that the half-wave potential of the ferrocenyl moieties is strongly influenced by the Pb(II) or Zn(II) ions in complexes 1 and 2. Ó 2008 Published by Elsevier B.V.

1. Introduction The coordination chemistry involving ferrocene has attracted great interest since it has been discovered by Kealy and Pauson 50 years ago. A lot of ferrocene derivatives have been used as multifunctional organic ligands to construct metal–organic complexes [1]. These metal-organic complexes not only possess versatile topological structures, but also have fascinating potential applications in electrochemical sensors, molecular magnetic and nonlinear optical (NLO) materials, etc. [2–5]. Up to now, a variety of ferrocenecontaining complexes have been normally constructed by elaborate selection of the metal ions and multidentate ferrocenyl bridging ligands [6], many of which exhibit intriguing structures and properties. For example, Chen reported a novel ferrocenylcarboxylate complex [Mn3(FcCO2)6(CH3OH)4]n with swastika-like shaped skeleton and interesting magnetic properties [7], our group synthesized Ferrocenylphosphonate cluster [Cd4(fmpa)4(phen)4]7CH3OH with cages feature and NLO behavior [8]. However, the rational synthesis of these attractive coordination complexes is still having a significant meaning because of their increasing role in the rapidly growing area of materials, especially the third-order NLO materials [9]. Design and synthesis of new third-order nonlinear optical (NLO) materials represent an active research field in modern chemistry, physics and materials science owing to their great potential applications [10]. Within this field, metal–organic complexes have at* Corresponding author. Tel./fax: +86 371 67761744. E-mail address: [email protected] (H. Hou). 0020-1693/$ - see front matter Ó 2008 Published by Elsevier B.V. doi:10.1016/j.ica.2008.04.010

tracted considerable attention in recent years, since the metal center can impart important structural and electronic properties to organic ligands, which results in the enhancement of third-order nonlinearity [11,12]. To gain coordination complexes with better third-order NLO effects, people have done a lot of work to study the third-order NLO properties of metal–organic complexes, and found that central metal ions make a large influence [13]. However, we think that the complex structures also have an effect on NLO properties, and this aspect is rarely investigated. In order to further explore the influence of complex structures on NLO properties, we utilized o-ferrocenylbenzoate as the main reactant to design metal–organic complexes with different structures. Herein, we select phen and bpe as ancillary ligands, as anticipated, the mononuclear complex 1 and 1-D chain polymer 2 were obtained, due to consideration that the chelating effect of phen usually results in metal carboxylates with a lower dimensionality, and bpe can be acted as a bridge which leads to the infinite extended coordination complexes. Determination of the third-order NLO properties of 1, 2 and the reactant o-NaOOCH4C6Fc shows that the structures of coordination complexes have significant effect on the NLO properties. In addition, their electrochemical properties were also investigated. 2. Experimental 2.1. General information and materials All the chemicals were of reagent grade quality obtained from commercial sources and used without further purification.

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Elemental analyses (C, H, and N) were carried out on a CarloErba1106 elemental analyzer. IR data were recorded on a BRUKER TENSOR 27 spectrophotometer with KBr pellets in the 400– 4000 cm1 region. o-Ferrocenylbenzoic acid and its sodium salt were prepared according to the literature method [14]. 2.2. Synthesis of {[Pb(g2-o-OOCH4C6Fc)(phen)](NO3)} (1) A methanol solution of phen (19.6 mg, 0.1 mmol) and o-NaOOCH4C6Fc (32.8 mg, 0.1 mmol) was added dropwise to a 3 mL aqueous solution of Pb(NO3)2 (33.2 mg, 0.1 mmol). Red single crystals were obtained after the reaction mixture was put in the dark for one week. Yield: 72%. Anal. Calc. for C29H21FeN3O5Pb: C, 46.08; H, 2.83; N, 5.62. Found: C, 46.12, H, 2.78; N, 5.57%. IR (cm1, KBr): 3433 (s), 3080 (m), 1513 (s), 1385 (s), 1309 (s), 1103 (m), 857 (m), 762 (m), 727 (m), 454 (m). 2.3. Synthesis of {[Zn(g2-o- OOCH4C6Fc)2(bpe)](CH3OH)}n (2) A methanol solution of o-NaOOCH4C6Fc (32.8 mg, 0.1 mmol, 4 mL) was added into the 3 mL methanol solution of Zn(OAc)22H2O (11.8 mg, 0.05 mmol), then 5 mL methanol solution of bpe (9.1 mg, 0.05 mmol) was added dropwise to the above mixture. The resultant solution was allowed to stand at room temperature in the dark. Red single crystals suitable for X-ray diffraction were obtained one week later. Yield: 69%. Anal. Calc. for C24H22FeNO3Zn0.5: C, 62.50; H, 4.75; N, 2.98. Found: C, 62.48; H, 4.77; N, 3.04%. IR (cm1, KBr): 3421 (m), 3099 (m), 1612 (s), 1503 (m), 1380 (s), 1106 (m), 1071 (m), 1027 (m), 830 (s), 762 (m), 553 (m), 480 (m). 2.4. X-ray crystallographic analyses A single crystal suitable for X-ray diffraction is mounted on a glass fiber. All diffraction data were collected on a Rigaku RAXISIV CCD diffractometer with graphite monochromated Mo Ka radiation (k = 0.71073 Å). The data were collected at a room temperature and corrected for Lorenz-polarization effects. The structures were solved by direct methods, expanded with Fourier techniques and refined by the full-matrix least-squares method on F2 with SHELXL-97 crystallographic software package [15]. All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were located in a different map phased on the non-hydrogen atoms and included as isotropic contributors in the final least-squares cycles. All the crystal data and structure refinement details for the two compounds are given in Table 1. Table 2 lists the data of relevant bond distances and angles. 2.5. Nonlinear optical measurements A DMF solution of complexes 1, 2 and o-NaOOCH4C6Fc was placed in a 1 mm quartz cuvette for NLO measurements, respectively. The NLO properties were measured as described in the literature [16]. 2.6. Electrochemical determines Differential pulse voltammetry studies were recorded with a CHI650 electrochemical analyzer utilizing the three-electrode configuration of a Pt working electrode, a Pt auxiliary electrode, and a commercially available saturated calomel electrode as the reference electrode with a pure N2 gas inlet and outlet. The measurements were performed in a DMF solution containing tetrabutyl ammonium perchlorate (n-Bu4NClO4) (0.1 mol dm3) as supporting electrolyte, which has a 50 ms pulse width and a 20 ms sample

Table 1 Crystal data and structure parameters of complexes 1 and 2 complexes

1

2

Formula Fw Crystal system Crystal size (mm) Space group A (Å) B (Å) C (Å) a (°) b (°) c (°) V (Å3) Dc (Mg m3) z l (mm1) Reflns collected/unique

C29H21FeN3O5Pb 754.53 Orthorhombic 0.20  0.20  0.18 Pna2(1) 9.4836(19) 12.265(3) 21.941(4) 90 90 90 2552.2(9) 1.964 4 7.203 8683 / 5190 R(int) = 0.0592 5190/1/349 0.0450 0.0823 1.050 0.962 and 1.261

C48H44ZnFe2N2O6 921.92 Monoclinic 0.20  0.18  0.16 C2/c 30.901(6) 8.2835(17) 17.348(4) 90 93.48(3) 90 4432.4(16) 1.382 8 1.232 5004 / 3646 R(int) = 0.0772 3646/0/273 0.0635 0.1274 1.034 0.469 and 0.450

Data/restraints/parameters R1a Rwb GOF on F2 Dqmin and Dqmax(e Å3) a b

P P R1 ¼ jjF j  jF c jj= jF 0 j: P 0 P Rw ¼ ½ wðF 20  F 2c Þ2 = wðF 20 Þ2 1=2 :

Table 2 Selected bond lengths (Å) and angles (°) for complexes 1 and 2 Complex 1 Pb(1)-O(1) Pb(1)-N(2) O(1)-Pb(1)-N(1) O(1)-Pb(1)-N(2) N(1)-Pb(1)-N(2)

2.444(7) 2.577(8) 81.1(3) 76.8(2) 64.0(3)

Pb(1)-N(1) Pb(1)-O(2) O(1)-Pb(1)-O(2) N(1)-Pb(1)-O(2) O(2)-Pb(1)-N(2)

2.550(9) 2.573(8) 52.4(2) 83.1(2) 123.3(3)

Complex 2a Zn1-N1#1 Zn1-O1#1 Zn1-O1 N1#1-Zn1-N1 N1#1-Zn1-O1 N1#1-Zn1-O2#1 O1-Zn1-O2#1 O1#1-Zn1-O2 N1-Zn1-O1#1 O1#1-Zn1-O1 O2#1-Zn1-O2

2.083(5) 2.179(5) 2.179(5) 95.7(3) 149.0(2) 115.0(2) 93.9(2) 93.9(2) 149.0(2) 91.6(3) 141.5(3)

Zn1-N1 Zn1-O2#1 Zn1-O2 N1#1-Zn1-O1#1 N1-Zn1-O1 N1-Zn1-O2#1 N1#1-Zn1-O2 O1-Zn1-O2 O1#1-Zn1-O2#1 N1-Zn1-O2

2.083(5) 2.246(6) 2.246(6) 94.5(2) 94.5(2) 91.1(2) 91.1(2) 58.1(2) 58.1(2) 115.0(2)

a Symmetry transformations used to generate equivalent atoms in complex 2: #1 x, y, z + 1/2 #2 x, y + 3, z.

width. The potential was scanned from +0.2 to +0.9 V at a scan rate of 100 mV s1. 3. Results and discussion 3.1. Description of crystal structures 3.1.1. Crystal structure of {[Pb(g2-o-OOCH4C6Fc)2(phen)](NO3)} (1) Crystallographic analysis reveals that complex 1 crystallizes in the space group Pna21 and exhibits a discrete mononuclear structure as shown in Fig. 1. Central Pb(II) ion is four-coordinated in a distorted tetrahedral environment with two oxygen atoms from chelate g2-o-FcC6H4COO unit and two nitrogen atoms from phen ligand. The uncoordinated NO3  acts as the counterion to balance the charge. The Pb–O distances vary from 2.444(7) to 2.573(8) Å, and the two Pb–N bond lengths are 2.557(8) and 2.550(9) Å, respectively, both of which are comparable to those in [Pb(g1l2-OOCCH = CHFc)2(phen)]n [17] and [Pb(endc)2(phen)]n [18] (endc = endonorbornene-cis-5,6-dicarboxylate). The bond angles

L. Li et al. / Inorganica Chimica Acta 362 (2009) 599–604

Fig. 1. The structure of complex 1. The hydrogen atoms are omitted for clarity.

around Pb(II) ion range from 52.4(2)° to 123.3 (3)°. The oFcC6H4COO unit and organic ligand phen are distributed unevenly around the metal center with an identifiable void, which may be due to the effect of stereo-chemically active lone pair of electrons on a lead atom. Furthermore, the discrete molecules of {[Pb(g2-oOOCH4C6Fc)2(phen)](NO3)} are connected by the weak interactions between Pb atoms and O atoms of the uncoordinated NO3  (the Pb  O distance is 2.761–3.213 Å) leading to a one-dimensional chain as shown in Fig. 2. 3.1.2. Crystal structure of {[Zn(g2-o-OOCH4C6Fc)2(bpe)](CH3OH)}n (2) The structure of complex 2 is depicted in Fig. 3, from which we can see that each o-FcC6H4COO is bidentate coordinated and or-

601

ganic ligand bpe link the central Zn(II) ions to form a 1-D zigzag chain. In the structure unit, the central Zn(II) ion is six-coordinated in a distorted octahedron environment with four oxygen atoms from two chelate g2-o-FcC6H4COO units and two nitrogen atoms from two bridging bpe ligands. The bond lengths of Zn1–O1 and Zn1–O2 are 2.179(5) and 2.246(6) Å, respectively. The Zn1–N bond distance of 2.083(2) Å is slightly shorter than that in the reported polymer [Zn(FcCOO)(g2-FcCOO)(bbp)]n [19] (the Zn1–N bond distance is 2.108(2) Å), and the angle O1–Zn1–N1 is 95.7(3)°. The dihedral angle between the two py rings which connecting Zn(II) ion is 59.3°. All bpe units connect all Zn(II) ions to form an infinite   Zn  bpe  Zn  bpe   chain, and the neighboring Zn  Zn distance is 13.485 Å, which is longer than that of complex [Zn(FcCOO)(g2-FcCOO)(bbp)]n [20] (Zn  Zn distance is 12.180 Å). Viewed along the c-axis, {[Zn(g2-o-OOCH4C6Fc)2(bpe)](CH3OH)}n chains pack each other by intermolecular interactions (Fig. 4). The uncoordinated methanol molecules and chains are connected by C–H  O hydrogen bonds. The structure of 2 is similar to that of polymer [Zn(FcCOO)(g2FcCOO)(bbp)]n, in which central Zn(II) ions are five-coordinated in a distorted trigonal bipyramidic arrangement. All Zn atoms are connected by bbp units leading to an infinite 1-D zigzag chain. Complex 2 and [Zn(FcCOO)(g2-FcCOO)(bbp)]n belong to a family of coordination polymers with ferrocene units in the side chain. 3.2. Nonlinear optical properties The third-order NLO properties of complexes 1, 2 and o-NaOOCH4C6Fc were investigated with a 532 nm laser pulse of 8 ns duration in a DMF solution. The NLO refractive data were assessed by dividing the normalized Z-scan data obtained under closedaperture configuration by the normalized Z-scan data obtained under the open aperture configuration. The experimental results were depicted in Fig. 5. We found that the NLO properties of 1 and oNaOOCH4C6Fc are very similar, but quite different from that of 2. Complex 1 and o-NaOOCH4C6Fc have negative sign for the refractive nonlinearity, which give rise to weak self-defocusing behaviors, while complex 2 has a positive sign for the nonlinear refraction and exhibits strong self-focusing behavior. An effective

Fig. 2. View of the infinite 1-D chain structure of complex 1, generated through weak interactions.

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Fig. 3. The one-dimensional zigzag chain structure of complex 2.

properties, because their crystal structures are distinct. Complex 2 possesses a large p-conjugation system formed by metal ions which can enhance the delocalization of p-electron cloud over the whole chain and then increase the NLO properties [21]. Thus, complex 2 shows larger c value and exhibits very strong self-focusing behavior. But as for complex 1, it cannot form an extensive pconjugated system due to the existence of only one metal Pb(II) ion in the structure, which results in its optical nonlinearity is similar to the reactant o-NaOOCH4C6Fc. Similar results can be seen in reported complexes [Zn(4-PFA)2(NO3)2](H2O) and [Cd2(OAc)4(4BPFA)2] [22]. From the above discussion, we can see that the structures of complexes have a large effect on the NLO properties. Therefore, the NLO properties of coordination complexes can be altered through structural manipulation. We believe that our exploration may provide a useful guide to the design of metal-organic complexes with good third-order NLO materials. Fig. 4. The solid-state structure of complex 2.

3.3. Electrochemical properties third-order NLO refractive index n2 can be calculated to be 7.53  1018 m2 W1 for o-NaOOCH4C6Fc, 3.23  1018 m2 W1 for 1, 1.13  1018 m2 W1 for 2. NLO In accordance with the n2 values, the effective third-order cn2 n susceptibility v(3) values can be calculated by jvð3Þ j ¼ 800 p2 . Where c is the speed of light in a vacuum and n0 is the linear refractive index of the sample. The v(3) values of o-NaOOCH4C6Fc and complexes 1 and 2 are calculated to be 1.84  1011 esu, 7.89  1012 esu and 2.76  1011 esu, respectively. Their v(3) values are larger than those observed in other ferrocenyl complexes, such as {[Pb(l2-g2-OOCC6H4Fc)2](CH3OH)2}n, (6.19  1013 esu), [Zn(OOCC6H4Fc)2(bpe)]n, (5.9  1013 esu) [20] and [Pb(g1-l2-OOCCH=CHFc)2(phen)]n (1.05  1012 esu) [17]. The corresponding modulus of the hyperpolarizability |c| is obtained from |c| = v(3)/NF4, where N is the number density of the compound in the solution (in cm3), F4 = 3 is the local field correction factor. The |c| values of ligand, 1 and 2 are 5.01  1030 esu, 4.95  1030 esu and 1.74  1029 esu, respectively. It is worthy to note that the two metal complexes have the same o-OOCH4C6Fc ligand, but they show different NLO

The solution-state differential pulse voltammograms of complexes 1, 2 and o-NaOOCH4C6Fc show single peaks with a halfwave potential at 0.504 V for 1, 0.512 V for 2, and 0.480 V for o-NaOOCH4C6Fc (versus SCE) (Fig. 6). Obviously, the half-wave potential of complexes 1 and 2 shifted to higher potentials compared with that of the free o-NaOOCH4C6Fc (0.480 V). It is apparent that the central metal ions in these complexes have a large influence on the half-wave potential of the ferrocenyl moieties, they can lead the FeII/FeIII oxidation potential of ferrocene-containing complexes to shift to higher potential in comparison with the reactant o-NaOOCH4C6Fc, and this is consistent with our previous results [17,20]. The reason is that the electron-withdrawing nature of the coordinated metal centers will make the ferrocene unit harder to oxidize [23,24]. In addition, it should be pointed out that the half-wave potential of 2 is slightly higher than 1. This shift also can be attributed to the effect of the complexes’ structures. There is a large conjugated p-electron system in complex 2, which can more effectively disperse electron density among the ferrocene, so Fe(II) center of 2 is harder oxidized to Fe(III) center than 1.

L. Li et al. / Inorganica Chimica Acta 362 (2009) 599–604

a

603

0.68

Normalized Transimittance

0.66 0.64 0.62 0.60 0.58 0.56 0.54 0.52 0.50 0.48 -120

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-80

-60

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0

Z position (mm)

b

Fig. 6. Differential pulse voltammograms of 1 (a), 2 (b), and o-NaOOCH4C6Fc (c) (1.0  103 M) in DMF containing n-Bu4NClO4 (0.1 M) at a scan rate of 20 mV s1 (vs. SCE).

0.65

Normalized Transittance

0.64

from The Cambridge Crystallographic Data Center via www.ccdc. cam.ac.uk/data_request cif.

0.63 0.62

Acknowledgement 0.61

The authors thank the National Natural Science Foundation of China (No. 20671082), NCET and Ph.D. Programs Foundation of Ministry of Education of China for financial support.

0.60 0.59

References 0.58 -120

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0

40

60

Z position (mm)

c Normalized Transmittance

1.10

1.05

1.00

0.95

0.90

0.85 -60

-40

-20

0

20

Z position (mm) Fig. 5. NLO refractive properties: (a) The self-defocusing effect of o-NaOOCH4C6Fc in 2.03  103 mol dm3 DMF solution at 532 nm. (b) The self-defocusing effect of 1 in 8.83  104 mol dm3 DMF solution at 532 nm. (c) The self-focusing effect of 2 in 8.83  104 mol dm3 DMF solution at 532 nm.

4. Supplementary material CCDC 675113 and 675114 contain the supplementary crystallographic data for 1 and 2. These data can be obtained free of charge

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