- Email: [email protected]
Crystal structures, electronic absorption and reflectance spectral behaviors, and electrochemical properties of five-coordinated chlorocopper(II) complexes with 5,6-disubstituted-1,10-phenanthroline
Polyhedron 21 (2002) 2143 /2147 www.elsevier.com/locate/poly
Crystal structures, electronic absorption and reflectance spectral behaviors, and electrochemical properties of five-coordinated chlorocopper(II) complexes with 5,6-disubstituted-1,10-phenanthroline Yasunori Yamada *, Hideyuki Sakurai, Yoshitaro Miyashita, Kiyoshi Fujisawa, Ken-ichi Okamoto * Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan Received 8 April 2002; accepted 7 June 2002
Abstract The five-coordinated geometries around the Cu(II) centers in [CuCl(dmphen)2]PF6 (1; dmphen /5,6-di-methyl-1,10-phenanthroline) and [CuCl(phendione)2]PF6 ×/H2O (2; phendione /1,10-phenanthroline-5,6-dione) are distorted square-pyramidal in contrast to the distorted trigonal-bipyramidal [CuCl(phen)2]PF6 (phen /1,10-phenanthroline), reflecting introductions of substituents into the 5- and 6-positions on phen. It has been found that these geometries in 1 and 2 are considerably dependent on the interactions between the p-electronic systems of the phen frameworks. The diffuse reflectance spectra significantly reflect geometrical differences of 1 and 2 from [CuCl(phen)2]PF6. The electronic absorption spectra suggest that the geometries of 1 and 2 in solution are similar to those in the crystalline state, while the geometry of [CuCl(phen)2]PF6 seems to be changed from distorted trigonal-bipyramid to square-pyramid. The electrochemical experiments indicate that the redox properties of these complexes are appreciably influenced by the electronic characters of the substituents on the phen frameworks. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Five-coordinated chlorocopper(II) complexes; 1,10-Phenanthroline and its 5,6-disubstituted derivatives; X-ray structures; Electronic absorption and diffuse reflectance spectra; Cyclic voltammetry
1. Introduction The five-coordinated copper(II) complexes comprised of both molecules of 1,10-phenanthroline (phen) or the related ligands and one monodentate co-ligands have been attracting great interest for their diverse stereoand physicochemical properties [1 /14]. It is well known that these copper(II) complexes take either trigonalbipyramidal or square-pyramidal geometry, depending on the ligands, co-ligands, and counterions [1 /13]. In addition, various structure-sensitive spectral and redox behaviors are recognized for such copper complexes [10,14]. Therefore, the evaluations for correlations of stereochemistry with spectroscopy and electrochemistry
* Corresponding authors. Tel./fax: /81-298-53-4323 E-mail address: [email protected] (K.-i. Okamoto).
are of fundamental importance for these copper(II) complexes. Recently, it has been found from these standpoints that introductions of the substituents into the phen frameworks, even at stereo-inactive 5- and 6positions, result in considerable changes on the structural and electronic characteristics of the parent phen complex. This implies that electronic effects by the diimine ligands cannot be ignored for stereochemistry, spectroscopy, and electrochemistry of these complexes. One of the present used ligands, 1,10-phenanthroline5,6-dione (phendione) [15], has a fairly distinct electronic character from phen due to the two carbonyl groups, and is expected to influence the properties of the complex significantly. On the other hand, another used ligand, 5,6-dimethyl-1,10-phenanthroline (dmphen), possesses an iso -p-electronic system with phen, and is considered to give some information on effects by the sdonations of the methyl groups. In order to know about
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 1 5 7 - 9
2144
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
the contributions by the 5,6-disubstitutions in the phen frameworks in more detail, we have determined the crystal structures of [CuCl(dmphen)2]PF6 (1) and [CuCl(phendione)2]PF6 ×/H2O (2) under the regulated condition with the same monodentate co-ligand and counteranion. The crystal structures of 1, 2 and [CuCl(phen)2]PF6, in which the structure of [CuCl(phen)2]PF6 was already determined [10], are discussed in relation to their absorption and reflectance spectral, and electrochemical behaviors.
2. Experimental 2.1. Materials CuCl2 ×/2H2O, 1,10-phenanthroline monohydrate and NH4PF6 were purchased from Wako Pure Chemical Ind. Co., Ltd. 5,6-Dimethyl-1,10-phenanthroline was obtained from Aldrich Chemical Co., Inc. The other chemicals were purchased from Wako Pure Chemical Ind. Co., Ltd., Aldrich Chemical Co., Inc., or Tokyo Chemical Co., Ltd. All of the chemicals were of reagent grade and were used without further purification. 1,10Phenathroline-5,6-dione was synthesized as described in the literature [15]. [CuCl(phen)2]PF6, which was used for the comparative studies on spectroscopic and electrochemical properties of the present complexes, was prepared by a modified method from the literature [10]. 2.2. Preparations of the complexes 2.2.1. Synthesis of [CuCl(dmphen)2]PF6 (1) This complex was prepared by a similar method to that for [CuCl(phen)2]PF6 [10]. To a solution containing dmphen (0.052 g, 0.25 mmol) in 20 ml EtOH was added a solution of CuCl2 ×/2H2O (0.021 g, 0.13 mmol) in 10 ml EtOH, and the mixture was stirred at room temperature (r.t.) for 20 h. After removing any undissolved materials by filtration, a solution containing NH4PF6 (0.41 g, 2.5 mmol) in 10 ml EtOH was added to the filtrate. The whole was stirred for 1 day and the resulting green fine crystals were collected by filtration. The crystals were recrystallized from CH3CN and a well-formed crystal was used for the X-ray structural analysis. Yield: 0.072 g (88%). Anal. Found: C, 50.92; H, 3.66; N, 8.48%. Calc. for C28H24N4F6PClCu (1): C, 50.73; H, 3.69; N, 8.41%. UV /Vis: nmax (103 cm1) (o , mol 1 dm3 cm 1) (MeCN): 10.27 (141), 13.72 (190), 29.41 (1775), 36.10 (49 500), 44.05 (48 600). Diffuse reflectance spectrum: nmax (103 cm 1): 10.22, 13.35, 28.74, 31.85, 35.09. EPR: g½½ /2.02, g /2.11 (solid, 140 K); 2.12 (MeCN solution, 140 K). Cyclic voltammetry (MeCN): E 8?//0.39 V.
2.2.2. Synthesis of [CuCl(phendione)2]PF6 (2) This complex was prepared by a similar method to that for [CuCl(dmphen)2]PF6 (1). To a solution containing phendione (0.10 g, 0.50 mmol) in 20 ml EtOH was added a solution of CuCl2 ×/2H2O (0.043 g, 0.25 mmol) in 10 ml EtOH, and the mixture was stirred at r.t. for 20 h. After removing any undissolved materials by filtration, a solution containing NH4PF6 (0.82 g, 5.0 mmol) in 10 ml EtOH was added to the filtrate. The whole was stirred for 1 day and the resulting green fine crystals were collected by filtration. Recrystallization was accomplished by slow diffusion of ether into a solution of the compound in CH3CN. A well-formed crystal was used for the X-ray structural analysis. Yield: 0.16 g (92%). Anal . Found: C, 41.16; H, 2.30; N, 8.00%. Calc. for C24H14N4O5F6PClCu (2): C, 41.78; H, 2.31; N, 7.97%. UV/Vis: nmax (103 cm 1) (o , mol 1 dm3 cm 1) (MeCN): 10.24 (112), 13.76 (179), 28.65 (2440), 33.22 (15 200), 39.68 (52 000). Diffuse reflectance spectrum: nmax (103 cm1): 10.12, 13.89, 27.40, 31.55, 38.02. EPR: 2.10 (solid, 140 K); 2.11 (MeCN solution, 140 K). Cyclic voltammetry (MeCN): E 8?//0.79, /0.14 V. 2.3. Measurements Electronic absorption and diffuse reflectance spectra were recorded with JASCO Ubest V-560 and V-570 spectrophotometers, respectively. EPR spectra were measured with a Bruker EMX-T ESR spectrometer. Electrochemical measurements were made with a CV50W apparatus (Bioanalytical Systems, Inc.; BSI) using a platinum disk as working electrode. The Ag/AgCl/ MeCN electrode (BSI) and a platinum wire were used as reference and auxiliary electrodes, respectively. These experiments were conducted at r.t. in a 0.1 mol dm 3 MeCN solution of Bu4N as a supporting electrolyte, and at concentrations of the complexes or ligand with 1.0 mmol dm 3. Elemental analyses (C, H, N) were performed by the Analysis Center of the University of Tsukuba. 2.4. X-ray structure determination Intensity data for 1 and 2 were collected on the Rigaku RASA-7S four-circle diffractometer with graphite-monochromatized Mo Ka radiation (l/0.71069 ˚ ). The structures were solved by the direct method A using SIR92 and refined by the full-matrix least-squares method using a TEXSAN program package [16]. All calculations were performed on an Indigo II computer. Crystal data for 1/C28H24N4F6PClCu, F.W./660.49, triclinic, space group P/1¯ (#2), a/11.497(3), b / ˚ , a /100.23(2)8, b/ 14.526(4), c /8.750(2) A ˚ 3, Z /2, 112.20(2)8, g/88.35(2)8, V /1330.2(5) A 3 1 Dcalc /1.649 g cm , m/1.051 mm , crystal size 0.23 /0.33 /0.58 mm, trans. factors 0.88 /1.00, 6385
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
reflections measured (2umax /55.08), 4302 observed reflections [I /2.00s(I )] used in the refinement, R / 0.053, Rw /0.071 and GOF /1.81 for 370 parameters. Crystal data for 2/C24H14N4O5F6PClCu, F.W./ 682.36, monoclinic, space group P 21/c (#14), a / ˚ , b / 13.167(7), b /14.225(8), c /15.171(3) A 3 ˚ 114.06(3)8, V /2594(2) A , Z /4, Dcalc /1.747 g cm 3, m/1.095 mm 1, crystal size 0.15 /0.15 /0.20 mm, trans. factors 0.96 /1.00, 6200 reflections measured (2umax /55.08), 1913 observed reflections [I /2.00s(I)] used in the refinement, R /0.056, Rw /0.065 and GOF /1.41 for 442 parameters.
3. Results and discussion 3.1. Crystal structures The X-ray structural analyses revealed that each of 1 and 2 consists of a discrete monovalent complex cation and one PF6 anion, and that 2 additionally involves one H2O molecule. As shown in Fig. 1, both of the complex cations in 1 and 2 possess five-coordinated environments with CuClN4 chromophores similar to that in [CuCl(phen)2]PF6 [10]. Namely, each of the Cu atoms in 1 and 2 is coordinated by four N atoms from two phen frameworks and one Cl atom. As shown in ˚) Table 1, however, the Cu /Cl distances in 1 (2.257(1) A ˚ and 2 (2.250(2) A), which are almost identical with each other, are significantly shorter than that in ˚ ). Furthermore, the values [CuCl(phen)2]PF6 (2.294(2) A of differences between the longest and shortest Cu /N ˚ for 1 and 0.190(7) bond distances, DCu /N /0.188(3) A
2145
Table 1 ˚ ) and angles (8) of 1, 2 and, [CuCl(phen)2]PSelected bond distances (A F6 a 1
2
[CuCl(phen)2]PF6
Cu Cl Cu N1 Cu N2 Co N3 Co N4
2.257(1) 2.016(3) 2.073(3) 1.998(3) 2.186(3)
2.250(3) 2.011(6) 2.052(7) 1.997(6) 2.187(6)
2.294(2) 2.001(4) 2.076(4) 2.003(4) 2.157(4)
Cl Cu N(1) Cl Cu N(2) Cl Cu N(3) Cl Cu N(4) N(1) Cu N(2) N(1) Cu N(3) N(1) Cu N(4) N(2) Cu N(3) N(2) Cu N(4) N(3) Cu N(4)
95.72(8) 150.13(8) 92.86(8) 107.40(8) 80.3(1) 170.8(1) 95.4(1) 93.9(1) 102.4(1) 78.9(1)
95.6(2) 154.0(2) 90.7(2) 106.2(2) 79.8(3) 173.7(3) 100.1(2) 94.1(3) 99.9(2) 79.0(2)
93.4(1) 131.6(1) 91.0(1) 114.4(1) 81.0(2) 175.2(2) 96.3(2) 97.5(2) 114.1(2) 80.1(2)
a
Ref. [10].
˚ for 2, are considerably different from that for A ˚ ) [17]. These suggest that [CuCl(phen)2]PF6 (0.156(4) A the geometries around Cu(II) centers in 1 and 2 are fairly distinct from that in [CuCl(phen)2]PF6. The largest angle around the Cu(II) center (b : N3 /Cu / N1 /170.8(1)8 for 1, 173.7(3)8 for 2) is considerably different from the second-largest one (a : N2 /Cu /Cl/ 150.13(8)8 for 1, 154.0(2)8 for 2). This implies that the geometries around Cu(II) centers in 1 and 2 are of distorted square-pyramidal or trigonal-bipyramidal one. Since the angular structural index parameter, t /(b/ a )/60, is evaluated by the two largest angles (a B/b ) in the five-coordinated geometry [18], the value of t /0.34
Fig. 1. Perspective views of the complex cations in 1 (a) and 2 (b) with the atomic labeling schemes (ellipsoids at 50% probabilities).
2146
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
for 1 or 0.33 for 2 seems to indicate a distorted squarepyramid. This is in marked contrast to the unsubstituted phen complex, [CuCl(phen)2]PF6, with a distorted trigonal-bipyramidal geometry (t /0.73) [10]. In both crystals of 1 and 2, no PF6 anions are close enough to interact with the Cu(II) centers in the complex cations, as in the case of [CuCl(phen)2]PF6 [10]. As shown in Fig. 2(a), however, one dmphen framework in the complex cation in 1 is in close proximity to that in the other complex cation accompanied by the formation of a dimeric unit. Namely, the interplane distance and angle between the neighboring ˚ and 0.000(1)8, two dmphen frameworks are 3.356(7) A respectively, indicating the interaction between the two p-electronic systems of dmphen frameworks. Although slight differences due to the O atoms on the 5- and 6positions of phen are recognized for the interactions between the p-electronic systems in 2, the formation of a dimeric unit based on the interaction between the adjacent two phendione frameworks (interplane dis˚ , interplane angle: 0.000(3)8) occurs as tance: 3.36(1) A in the case of 1 (Fig. 2(b)). However, the morphology of interactions between the p-frameworks in 1 and 2 is obviously distinguishable from that in [CuCl(phen)2]PF6, in which each of the two phen frameworks interacts with one phen framework in the adjacent complex cation to form a polymeric chain [10]. Considering these facts, it can be concluded that the five-coordinated geometries of these complexes are appreciably governed by the interactions between the p-frameworks. Since the interactions of p-frameworks are significantly dependent on the steric and electronic natures of the substituents,
the five-coordinated geometries of the present complexes seem to be brought by the introductions of the substituents into the phen frameworks. 3.2. Electronic absorption and diffuse reflectance spectral behaviors The reflectance spectrum of [CuCl(phen)2]PF6 exhibits single peak due to the dxz :/dyz 0/dz2 transition at 12.10 /103 cm1 accompanied by a shoulder due to the 2 dxy 0/dz2 transition at 10.50 /103 cm1 [19], as reported by Hathaway et al. [10]. In the UV region, the complex shows additional four bands at 27.47, 30.40, 33.22, and 35.84 /103 cm 1. Among these bands, the corresponding band to the 27.47 /103 cm 1 one is also observed for [CuCl(bpy)2]Cl (bpy / 2,2?-bipyridine) with a different kind of p character [18]. Therefore, the 27.47 /103 cm 1 band of [CuCl(phen)2]PF6 can be assigned as a Cl-to-Cu CT transition [20,21]. The remaining bands in the UV region seem to be mainly due to the p /p* transitions localized on the phen frameworks. While similar spectral patterns in the UV region are also recognized for 1 and 2, both complexes exhibit well-resolved two peaks due to the d/d transitions (10.22 and 13.35 /103 cm 1 for 1, 10.12 and 13.89 /103 cm 1 for 2) in contrast to [CuCl(phen)2]PF6. These spectral features seem to reflect differences from [CuCl(phen)2]PF6 in the geometries around Cu(II) centers and the resulting one-electron ground-state configurations of 1 and 2 [10]. In MeCN, the absorption spectra of 1 and 2 exhibit similar spectral patterns to the reflectance spectra, indicating almost the same geometries around the Cu(II) centers as in the crystalline state. On the other hand, the d-d bands for [CuCl(phen)2]PF6 are observed as the well-resolved two components, which are appeared at similar energies to those for 1 and 2. This implies that the geometry around the Cu(II) center of [CuCl(phen)2]PF6 in solution is distinct from that in the crystalline state and is considered to be rather similar to those of 1 and 2 with a distorted squarepyramid. This is supported by the results of the EPR spectral measurements for the present complexes. Namely, for instance, the anisotropic spectral pattern for the polycrystalline sample of [CuCl(phen)2]PF6 is slightly different from that in frozen MeCN solution, but seems to be rather similar to that for the polycrystalline sample of 1 with a distorted square-pyramidal geometry [19]. It is suggested therefore that the geometries around the Cu(II) centers of these complexes in the crystalline state are significantly governed by the lattice forces. 3.3. Electrochemical properties
Fig. 2. Dimeric structures in the crystalline state of 1 (a) and 2 (b).
The cyclic voltammogram at platinum disk electrode for [CuCl(phen)2]PF6 displays only one reversible
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
Cu(II)/Cu(I) redox couple with E 8?//0.37 V [19]. While 1 also shows the redox couple in a similar potential region, the value of E 8? (/0.39 V) is of slightly negative compared with that for [CuCl(phen)2]PF6. It is known that the redox potential for Cu(II)/Cu(I) process is shifted to more negative as the electron-donating ability of the substituents on the phen framework becomes higher [14]. Accordingly, it can be regarded that a slight difference in the Cu(II)/Cu(I) redox couple between [CuCl(phen)2]PF6 and 1 is due to the electrondonating methyl groups on 5- and 6-positions at phen framework. Contrary to the cases of these complexes, 2 shows two reversible redox couples with E 8?//0.79 and /0.14 V in the negative potential region. Among these redox couples, the one with E 8?//0.79 V is also observed for the free phendione ligand [22], and can be assigned as the redox process in the phendione. Although the couple with E8? //0.14 V of 2 can be regarded as the Cu(II)/Cu(I) redox process, the potential is located on rather positive region than [CuCl(phen)2]PF6 and 1. This seems to reflect the characteristic electronic nature of 2 due to the electron-withdrawing substituents on 5- and 6-positions at phen framework. It can be concluded, therefore, that the electrochemical properties of these complexes are significantly influenced by the electronic characters of the substituents on the phen frameworks.
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 181117 and 181118 for 1 and 2, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: /441223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgements This work was partially supported by a Grant-in-Aid for Scientific Research No. 13555257 from the Ministry of Education, Science, Sports, and Culture.
2147
References [1] H. Nakai, Y. Deguchi, Bull. Chem. Soc. Jpn. 48 (1975) 2557. [2] O.P. Anderson, Inorg. Chem. 14 (1975) 730. [3] H. Nakai, Y. Noda, Bull. Chem. Soc. Jpn. 51 (1978) 1386. [4] D. Boys, C. Escobar, S. Martı´nez-Carrera, Acta Crystallogr., Sect. B 37 (1981) 351. [5] S. Tyagi, B. Hathaway, S. Kremer, H. Stratemeier, D. Reinen, J. Chem. Soc., Dalton Trans. (1984) 2087. [6] C.J. Simmons, N.W. Alcock, K. Seff, W. Fitzgerald, B.J. Hathaway, Acta Crystallogr., Sect. B 41 (1985) 42. [7] W.D. Harrison, D.M. Kennedy, M. Power, R. Sheahan, B.J. Hathaway, J. Chem. Soc., Dalton Trans. (1981) 1556. [8] O. Carugo, C.B. Castellani, J. Chem. Soc., Dalton Trans. (1990) 2895. [9] P. Nagle, E. O’Sullivan, B.J. Hathaway, E. Muller, J. Chem. Soc., Dalton Trans. (1990) 3399. [10] G. Murphy, P. Nagle, B. Murphy, B. Hathaway, J. Chem. Soc., Dalton Trans. (1997) 2645 and references therein. [11] D. Tran, B.W. Skelton, A.H. White, L.E. Laverman, P.C. Ford, Inorg. Chem. 37 (1998) 2505. [12] M. Brophy, G. Murphy, C. O’Sullivan, B. Hathaway, B. Murphy, Polyhedron 18 (1999) 611. [13] S.M. Morehouse, H. Suliman, J. Haff, D. Nguyen, Inorg. Chim. Acta 297 (2000) 411. [14] P.M. Bush, J.P. Whitehead, C.C. Pink, E.C. Gramm, J.L. Eglin, S.P. Watton, L.E. Pence, Inorg. Chem. 40 (2001) 1871 (and references therein). [15] M. Yamada, Y. Tanaka, Y. Yoshimoto, Bull. Chem. Soc. Jpn. 65 (1992) 1006. [16] ‘TEXSAN. Molecular Structure Corporation. Single Crystal Structure Analysis Software. Version 1.9,’ MSC, 3200 Research Forest Drive, The Woodlands, TX77381, USA, 1998. [17] The DCu/N value means a difference between the longest and shortest Cu/N bond distances. [18] A.W. Addison, T.N. Rao, J. Reedijk, J. Rijn, G.C. Verschoor, J. Chem. Soc., Dalton Trans. (1984) 1349. [19] Spectral and electrochemical data of [CuCl(phen)2]PF6 are as follows: UV /Vis: nmax (103 cm 1) (o , mol 1 dm3 cm 1) (MeCN): 10.35 (127), 13.66 (183), 37.04 (57 500), 44.44 (62 900). Diffuse reflectance spectrum: nmax (103 cm 1): 10.50, 12.10, 27.47, 30.40, 33.22, 35.84. EPR: g½½ /2.01, g /2.17 (solid, 140 K); g½½ / 2.01, g /2.14 (MeCN solution, 140 K). Cyclic voltammetry (MeCN): E 8?//0.37 V. [20] F.S. Stephens, P.A. Tucker, J. Chem. Soc., Dalton Trans. (1973) 2293. [21] A. Altomare, M.C. Burla, M. Camalli, M. Cascarano, C. Giacovazzo, A. Guagliardi, G. Polidori, J. Appl. Crystallogr. 27 (1994) 435. [22] Cyclic voltammetry (MeCN) for the free 1,10-phenanthroline-5,6dione: E 8?//0.79 V.
Crystal structures, electronic absorption and reflectance spectral behaviors, and electrochemical properties of five-coordinated chlorocopper(II) complexes with 5,6-disubstituted-1,10-phenanthroline Yasunori Yamada *, Hideyuki Sakurai, Yoshitaro Miyashita, Kiyoshi Fujisawa, Ken-ichi Okamoto * Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan Received 8 April 2002; accepted 7 June 2002
Abstract The five-coordinated geometries around the Cu(II) centers in [CuCl(dmphen)2]PF6 (1; dmphen /5,6-di-methyl-1,10-phenanthroline) and [CuCl(phendione)2]PF6 ×/H2O (2; phendione /1,10-phenanthroline-5,6-dione) are distorted square-pyramidal in contrast to the distorted trigonal-bipyramidal [CuCl(phen)2]PF6 (phen /1,10-phenanthroline), reflecting introductions of substituents into the 5- and 6-positions on phen. It has been found that these geometries in 1 and 2 are considerably dependent on the interactions between the p-electronic systems of the phen frameworks. The diffuse reflectance spectra significantly reflect geometrical differences of 1 and 2 from [CuCl(phen)2]PF6. The electronic absorption spectra suggest that the geometries of 1 and 2 in solution are similar to those in the crystalline state, while the geometry of [CuCl(phen)2]PF6 seems to be changed from distorted trigonal-bipyramid to square-pyramid. The electrochemical experiments indicate that the redox properties of these complexes are appreciably influenced by the electronic characters of the substituents on the phen frameworks. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Five-coordinated chlorocopper(II) complexes; 1,10-Phenanthroline and its 5,6-disubstituted derivatives; X-ray structures; Electronic absorption and diffuse reflectance spectra; Cyclic voltammetry
1. Introduction The five-coordinated copper(II) complexes comprised of both molecules of 1,10-phenanthroline (phen) or the related ligands and one monodentate co-ligands have been attracting great interest for their diverse stereoand physicochemical properties [1 /14]. It is well known that these copper(II) complexes take either trigonalbipyramidal or square-pyramidal geometry, depending on the ligands, co-ligands, and counterions [1 /13]. In addition, various structure-sensitive spectral and redox behaviors are recognized for such copper complexes [10,14]. Therefore, the evaluations for correlations of stereochemistry with spectroscopy and electrochemistry
* Corresponding authors. Tel./fax: /81-298-53-4323 E-mail address: [email protected] (K.-i. Okamoto).
are of fundamental importance for these copper(II) complexes. Recently, it has been found from these standpoints that introductions of the substituents into the phen frameworks, even at stereo-inactive 5- and 6positions, result in considerable changes on the structural and electronic characteristics of the parent phen complex. This implies that electronic effects by the diimine ligands cannot be ignored for stereochemistry, spectroscopy, and electrochemistry of these complexes. One of the present used ligands, 1,10-phenanthroline5,6-dione (phendione) [15], has a fairly distinct electronic character from phen due to the two carbonyl groups, and is expected to influence the properties of the complex significantly. On the other hand, another used ligand, 5,6-dimethyl-1,10-phenanthroline (dmphen), possesses an iso -p-electronic system with phen, and is considered to give some information on effects by the sdonations of the methyl groups. In order to know about
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 1 5 7 - 9
2144
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
the contributions by the 5,6-disubstitutions in the phen frameworks in more detail, we have determined the crystal structures of [CuCl(dmphen)2]PF6 (1) and [CuCl(phendione)2]PF6 ×/H2O (2) under the regulated condition with the same monodentate co-ligand and counteranion. The crystal structures of 1, 2 and [CuCl(phen)2]PF6, in which the structure of [CuCl(phen)2]PF6 was already determined [10], are discussed in relation to their absorption and reflectance spectral, and electrochemical behaviors.
2. Experimental 2.1. Materials CuCl2 ×/2H2O, 1,10-phenanthroline monohydrate and NH4PF6 were purchased from Wako Pure Chemical Ind. Co., Ltd. 5,6-Dimethyl-1,10-phenanthroline was obtained from Aldrich Chemical Co., Inc. The other chemicals were purchased from Wako Pure Chemical Ind. Co., Ltd., Aldrich Chemical Co., Inc., or Tokyo Chemical Co., Ltd. All of the chemicals were of reagent grade and were used without further purification. 1,10Phenathroline-5,6-dione was synthesized as described in the literature [15]. [CuCl(phen)2]PF6, which was used for the comparative studies on spectroscopic and electrochemical properties of the present complexes, was prepared by a modified method from the literature [10]. 2.2. Preparations of the complexes 2.2.1. Synthesis of [CuCl(dmphen)2]PF6 (1) This complex was prepared by a similar method to that for [CuCl(phen)2]PF6 [10]. To a solution containing dmphen (0.052 g, 0.25 mmol) in 20 ml EtOH was added a solution of CuCl2 ×/2H2O (0.021 g, 0.13 mmol) in 10 ml EtOH, and the mixture was stirred at room temperature (r.t.) for 20 h. After removing any undissolved materials by filtration, a solution containing NH4PF6 (0.41 g, 2.5 mmol) in 10 ml EtOH was added to the filtrate. The whole was stirred for 1 day and the resulting green fine crystals were collected by filtration. The crystals were recrystallized from CH3CN and a well-formed crystal was used for the X-ray structural analysis. Yield: 0.072 g (88%). Anal. Found: C, 50.92; H, 3.66; N, 8.48%. Calc. for C28H24N4F6PClCu (1): C, 50.73; H, 3.69; N, 8.41%. UV /Vis: nmax (103 cm1) (o , mol 1 dm3 cm 1) (MeCN): 10.27 (141), 13.72 (190), 29.41 (1775), 36.10 (49 500), 44.05 (48 600). Diffuse reflectance spectrum: nmax (103 cm 1): 10.22, 13.35, 28.74, 31.85, 35.09. EPR: g½½ /2.02, g /2.11 (solid, 140 K); 2.12 (MeCN solution, 140 K). Cyclic voltammetry (MeCN): E 8?//0.39 V.
2.2.2. Synthesis of [CuCl(phendione)2]PF6 (2) This complex was prepared by a similar method to that for [CuCl(dmphen)2]PF6 (1). To a solution containing phendione (0.10 g, 0.50 mmol) in 20 ml EtOH was added a solution of CuCl2 ×/2H2O (0.043 g, 0.25 mmol) in 10 ml EtOH, and the mixture was stirred at r.t. for 20 h. After removing any undissolved materials by filtration, a solution containing NH4PF6 (0.82 g, 5.0 mmol) in 10 ml EtOH was added to the filtrate. The whole was stirred for 1 day and the resulting green fine crystals were collected by filtration. Recrystallization was accomplished by slow diffusion of ether into a solution of the compound in CH3CN. A well-formed crystal was used for the X-ray structural analysis. Yield: 0.16 g (92%). Anal . Found: C, 41.16; H, 2.30; N, 8.00%. Calc. for C24H14N4O5F6PClCu (2): C, 41.78; H, 2.31; N, 7.97%. UV/Vis: nmax (103 cm 1) (o , mol 1 dm3 cm 1) (MeCN): 10.24 (112), 13.76 (179), 28.65 (2440), 33.22 (15 200), 39.68 (52 000). Diffuse reflectance spectrum: nmax (103 cm1): 10.12, 13.89, 27.40, 31.55, 38.02. EPR: 2.10 (solid, 140 K); 2.11 (MeCN solution, 140 K). Cyclic voltammetry (MeCN): E 8?//0.79, /0.14 V. 2.3. Measurements Electronic absorption and diffuse reflectance spectra were recorded with JASCO Ubest V-560 and V-570 spectrophotometers, respectively. EPR spectra were measured with a Bruker EMX-T ESR spectrometer. Electrochemical measurements were made with a CV50W apparatus (Bioanalytical Systems, Inc.; BSI) using a platinum disk as working electrode. The Ag/AgCl/ MeCN electrode (BSI) and a platinum wire were used as reference and auxiliary electrodes, respectively. These experiments were conducted at r.t. in a 0.1 mol dm 3 MeCN solution of Bu4N as a supporting electrolyte, and at concentrations of the complexes or ligand with 1.0 mmol dm 3. Elemental analyses (C, H, N) were performed by the Analysis Center of the University of Tsukuba. 2.4. X-ray structure determination Intensity data for 1 and 2 were collected on the Rigaku RASA-7S four-circle diffractometer with graphite-monochromatized Mo Ka radiation (l/0.71069 ˚ ). The structures were solved by the direct method A using SIR92 and refined by the full-matrix least-squares method using a TEXSAN program package [16]. All calculations were performed on an Indigo II computer. Crystal data for 1/C28H24N4F6PClCu, F.W./660.49, triclinic, space group P/1¯ (#2), a/11.497(3), b / ˚ , a /100.23(2)8, b/ 14.526(4), c /8.750(2) A ˚ 3, Z /2, 112.20(2)8, g/88.35(2)8, V /1330.2(5) A 3 1 Dcalc /1.649 g cm , m/1.051 mm , crystal size 0.23 /0.33 /0.58 mm, trans. factors 0.88 /1.00, 6385
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
reflections measured (2umax /55.08), 4302 observed reflections [I /2.00s(I )] used in the refinement, R / 0.053, Rw /0.071 and GOF /1.81 for 370 parameters. Crystal data for 2/C24H14N4O5F6PClCu, F.W./ 682.36, monoclinic, space group P 21/c (#14), a / ˚ , b / 13.167(7), b /14.225(8), c /15.171(3) A 3 ˚ 114.06(3)8, V /2594(2) A , Z /4, Dcalc /1.747 g cm 3, m/1.095 mm 1, crystal size 0.15 /0.15 /0.20 mm, trans. factors 0.96 /1.00, 6200 reflections measured (2umax /55.08), 1913 observed reflections [I /2.00s(I)] used in the refinement, R /0.056, Rw /0.065 and GOF /1.41 for 442 parameters.
3. Results and discussion 3.1. Crystal structures The X-ray structural analyses revealed that each of 1 and 2 consists of a discrete monovalent complex cation and one PF6 anion, and that 2 additionally involves one H2O molecule. As shown in Fig. 1, both of the complex cations in 1 and 2 possess five-coordinated environments with CuClN4 chromophores similar to that in [CuCl(phen)2]PF6 [10]. Namely, each of the Cu atoms in 1 and 2 is coordinated by four N atoms from two phen frameworks and one Cl atom. As shown in ˚) Table 1, however, the Cu /Cl distances in 1 (2.257(1) A ˚ and 2 (2.250(2) A), which are almost identical with each other, are significantly shorter than that in ˚ ). Furthermore, the values [CuCl(phen)2]PF6 (2.294(2) A of differences between the longest and shortest Cu /N ˚ for 1 and 0.190(7) bond distances, DCu /N /0.188(3) A
2145
Table 1 ˚ ) and angles (8) of 1, 2 and, [CuCl(phen)2]PSelected bond distances (A F6 a 1
2
[CuCl(phen)2]PF6
Cu Cl Cu N1 Cu N2 Co N3 Co N4
2.257(1) 2.016(3) 2.073(3) 1.998(3) 2.186(3)
2.250(3) 2.011(6) 2.052(7) 1.997(6) 2.187(6)
2.294(2) 2.001(4) 2.076(4) 2.003(4) 2.157(4)
Cl Cu N(1) Cl Cu N(2) Cl Cu N(3) Cl Cu N(4) N(1) Cu N(2) N(1) Cu N(3) N(1) Cu N(4) N(2) Cu N(3) N(2) Cu N(4) N(3) Cu N(4)
95.72(8) 150.13(8) 92.86(8) 107.40(8) 80.3(1) 170.8(1) 95.4(1) 93.9(1) 102.4(1) 78.9(1)
95.6(2) 154.0(2) 90.7(2) 106.2(2) 79.8(3) 173.7(3) 100.1(2) 94.1(3) 99.9(2) 79.0(2)
93.4(1) 131.6(1) 91.0(1) 114.4(1) 81.0(2) 175.2(2) 96.3(2) 97.5(2) 114.1(2) 80.1(2)
a
Ref. [10].
˚ for 2, are considerably different from that for A ˚ ) [17]. These suggest that [CuCl(phen)2]PF6 (0.156(4) A the geometries around Cu(II) centers in 1 and 2 are fairly distinct from that in [CuCl(phen)2]PF6. The largest angle around the Cu(II) center (b : N3 /Cu / N1 /170.8(1)8 for 1, 173.7(3)8 for 2) is considerably different from the second-largest one (a : N2 /Cu /Cl/ 150.13(8)8 for 1, 154.0(2)8 for 2). This implies that the geometries around Cu(II) centers in 1 and 2 are of distorted square-pyramidal or trigonal-bipyramidal one. Since the angular structural index parameter, t /(b/ a )/60, is evaluated by the two largest angles (a B/b ) in the five-coordinated geometry [18], the value of t /0.34
Fig. 1. Perspective views of the complex cations in 1 (a) and 2 (b) with the atomic labeling schemes (ellipsoids at 50% probabilities).
2146
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
for 1 or 0.33 for 2 seems to indicate a distorted squarepyramid. This is in marked contrast to the unsubstituted phen complex, [CuCl(phen)2]PF6, with a distorted trigonal-bipyramidal geometry (t /0.73) [10]. In both crystals of 1 and 2, no PF6 anions are close enough to interact with the Cu(II) centers in the complex cations, as in the case of [CuCl(phen)2]PF6 [10]. As shown in Fig. 2(a), however, one dmphen framework in the complex cation in 1 is in close proximity to that in the other complex cation accompanied by the formation of a dimeric unit. Namely, the interplane distance and angle between the neighboring ˚ and 0.000(1)8, two dmphen frameworks are 3.356(7) A respectively, indicating the interaction between the two p-electronic systems of dmphen frameworks. Although slight differences due to the O atoms on the 5- and 6positions of phen are recognized for the interactions between the p-electronic systems in 2, the formation of a dimeric unit based on the interaction between the adjacent two phendione frameworks (interplane dis˚ , interplane angle: 0.000(3)8) occurs as tance: 3.36(1) A in the case of 1 (Fig. 2(b)). However, the morphology of interactions between the p-frameworks in 1 and 2 is obviously distinguishable from that in [CuCl(phen)2]PF6, in which each of the two phen frameworks interacts with one phen framework in the adjacent complex cation to form a polymeric chain [10]. Considering these facts, it can be concluded that the five-coordinated geometries of these complexes are appreciably governed by the interactions between the p-frameworks. Since the interactions of p-frameworks are significantly dependent on the steric and electronic natures of the substituents,
the five-coordinated geometries of the present complexes seem to be brought by the introductions of the substituents into the phen frameworks. 3.2. Electronic absorption and diffuse reflectance spectral behaviors The reflectance spectrum of [CuCl(phen)2]PF6 exhibits single peak due to the dxz :/dyz 0/dz2 transition at 12.10 /103 cm1 accompanied by a shoulder due to the 2 dxy 0/dz2 transition at 10.50 /103 cm1 [19], as reported by Hathaway et al. [10]. In the UV region, the complex shows additional four bands at 27.47, 30.40, 33.22, and 35.84 /103 cm 1. Among these bands, the corresponding band to the 27.47 /103 cm 1 one is also observed for [CuCl(bpy)2]Cl (bpy / 2,2?-bipyridine) with a different kind of p character [18]. Therefore, the 27.47 /103 cm 1 band of [CuCl(phen)2]PF6 can be assigned as a Cl-to-Cu CT transition [20,21]. The remaining bands in the UV region seem to be mainly due to the p /p* transitions localized on the phen frameworks. While similar spectral patterns in the UV region are also recognized for 1 and 2, both complexes exhibit well-resolved two peaks due to the d/d transitions (10.22 and 13.35 /103 cm 1 for 1, 10.12 and 13.89 /103 cm 1 for 2) in contrast to [CuCl(phen)2]PF6. These spectral features seem to reflect differences from [CuCl(phen)2]PF6 in the geometries around Cu(II) centers and the resulting one-electron ground-state configurations of 1 and 2 [10]. In MeCN, the absorption spectra of 1 and 2 exhibit similar spectral patterns to the reflectance spectra, indicating almost the same geometries around the Cu(II) centers as in the crystalline state. On the other hand, the d-d bands for [CuCl(phen)2]PF6 are observed as the well-resolved two components, which are appeared at similar energies to those for 1 and 2. This implies that the geometry around the Cu(II) center of [CuCl(phen)2]PF6 in solution is distinct from that in the crystalline state and is considered to be rather similar to those of 1 and 2 with a distorted squarepyramid. This is supported by the results of the EPR spectral measurements for the present complexes. Namely, for instance, the anisotropic spectral pattern for the polycrystalline sample of [CuCl(phen)2]PF6 is slightly different from that in frozen MeCN solution, but seems to be rather similar to that for the polycrystalline sample of 1 with a distorted square-pyramidal geometry [19]. It is suggested therefore that the geometries around the Cu(II) centers of these complexes in the crystalline state are significantly governed by the lattice forces. 3.3. Electrochemical properties
Fig. 2. Dimeric structures in the crystalline state of 1 (a) and 2 (b).
The cyclic voltammogram at platinum disk electrode for [CuCl(phen)2]PF6 displays only one reversible
Y. Yamada et al. / Polyhedron 21 (2002) 2143 /2147
Cu(II)/Cu(I) redox couple with E 8?//0.37 V [19]. While 1 also shows the redox couple in a similar potential region, the value of E 8? (/0.39 V) is of slightly negative compared with that for [CuCl(phen)2]PF6. It is known that the redox potential for Cu(II)/Cu(I) process is shifted to more negative as the electron-donating ability of the substituents on the phen framework becomes higher [14]. Accordingly, it can be regarded that a slight difference in the Cu(II)/Cu(I) redox couple between [CuCl(phen)2]PF6 and 1 is due to the electrondonating methyl groups on 5- and 6-positions at phen framework. Contrary to the cases of these complexes, 2 shows two reversible redox couples with E 8?//0.79 and /0.14 V in the negative potential region. Among these redox couples, the one with E 8?//0.79 V is also observed for the free phendione ligand [22], and can be assigned as the redox process in the phendione. Although the couple with E8? //0.14 V of 2 can be regarded as the Cu(II)/Cu(I) redox process, the potential is located on rather positive region than [CuCl(phen)2]PF6 and 1. This seems to reflect the characteristic electronic nature of 2 due to the electron-withdrawing substituents on 5- and 6-positions at phen framework. It can be concluded, therefore, that the electrochemical properties of these complexes are significantly influenced by the electronic characters of the substituents on the phen frameworks.
4. Supplementary material Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 181117 and 181118 for 1 and 2, respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: /441223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgements This work was partially supported by a Grant-in-Aid for Scientific Research No. 13555257 from the Ministry of Education, Science, Sports, and Culture.
2147
References [1] H. Nakai, Y. Deguchi, Bull. Chem. Soc. Jpn. 48 (1975) 2557. [2] O.P. Anderson, Inorg. Chem. 14 (1975) 730. [3] H. Nakai, Y. Noda, Bull. Chem. Soc. Jpn. 51 (1978) 1386. [4] D. Boys, C. Escobar, S. Martı´nez-Carrera, Acta Crystallogr., Sect. B 37 (1981) 351. [5] S. Tyagi, B. Hathaway, S. Kremer, H. Stratemeier, D. Reinen, J. Chem. Soc., Dalton Trans. (1984) 2087. [6] C.J. Simmons, N.W. Alcock, K. Seff, W. Fitzgerald, B.J. Hathaway, Acta Crystallogr., Sect. B 41 (1985) 42. [7] W.D. Harrison, D.M. Kennedy, M. Power, R. Sheahan, B.J. Hathaway, J. Chem. Soc., Dalton Trans. (1981) 1556. [8] O. Carugo, C.B. Castellani, J. Chem. Soc., Dalton Trans. (1990) 2895. [9] P. Nagle, E. O’Sullivan, B.J. Hathaway, E. Muller, J. Chem. Soc., Dalton Trans. (1990) 3399. [10] G. Murphy, P. Nagle, B. Murphy, B. Hathaway, J. Chem. Soc., Dalton Trans. (1997) 2645 and references therein. [11] D. Tran, B.W. Skelton, A.H. White, L.E. Laverman, P.C. Ford, Inorg. Chem. 37 (1998) 2505. [12] M. Brophy, G. Murphy, C. O’Sullivan, B. Hathaway, B. Murphy, Polyhedron 18 (1999) 611. [13] S.M. Morehouse, H. Suliman, J. Haff, D. Nguyen, Inorg. Chim. Acta 297 (2000) 411. [14] P.M. Bush, J.P. Whitehead, C.C. Pink, E.C. Gramm, J.L. Eglin, S.P. Watton, L.E. Pence, Inorg. Chem. 40 (2001) 1871 (and references therein). [15] M. Yamada, Y. Tanaka, Y. Yoshimoto, Bull. Chem. Soc. Jpn. 65 (1992) 1006. [16] ‘TEXSAN. Molecular Structure Corporation. Single Crystal Structure Analysis Software. Version 1.9,’ MSC, 3200 Research Forest Drive, The Woodlands, TX77381, USA, 1998. [17] The DCu/N value means a difference between the longest and shortest Cu/N bond distances. [18] A.W. Addison, T.N. Rao, J. Reedijk, J. Rijn, G.C. Verschoor, J. Chem. Soc., Dalton Trans. (1984) 1349. [19] Spectral and electrochemical data of [CuCl(phen)2]PF6 are as follows: UV /Vis: nmax (103 cm 1) (o , mol 1 dm3 cm 1) (MeCN): 10.35 (127), 13.66 (183), 37.04 (57 500), 44.44 (62 900). Diffuse reflectance spectrum: nmax (103 cm 1): 10.50, 12.10, 27.47, 30.40, 33.22, 35.84. EPR: g½½ /2.01, g /2.17 (solid, 140 K); g½½ / 2.01, g /2.14 (MeCN solution, 140 K). Cyclic voltammetry (MeCN): E 8?//0.37 V. [20] F.S. Stephens, P.A. Tucker, J. Chem. Soc., Dalton Trans. (1973) 2293. [21] A. Altomare, M.C. Burla, M. Camalli, M. Cascarano, C. Giacovazzo, A. Guagliardi, G. Polidori, J. Appl. Crystallogr. 27 (1994) 435. [22] Cyclic voltammetry (MeCN) for the free 1,10-phenanthroline-5,6dione: E 8?//0.79 V.