Synthesis, characterization and crystal structures of tetrairon ethanedithiolate complexes containing bridging bidentate phosphine ligands

Polyhedron 33 (2012) 166–170

Contents lists available at SciVerse ScienceDirect

Polyhedron journal homepage: www.elsevier.com/locate/poly

Synthesis, characterization and crystal structures of tetrairon ethanedithiolate complexes containing bridging bidentate phosphine ligands Xu-Feng Liu ⇑, Zhong-Qing Jiang, Zhi-Jian Jia Department of Chemical Engineering, Ningbo University of Technology, Ningbo 315016, China

a r t i c l e

i n f o

Article history: Received 29 June 2011 Accepted 15 November 2011 Available online 26 November 2011 Keywords: Tetrairon ethanedithiolate Bidentate phosphine ligand Carbonyl substitution Synthesis Crystal structure

a b s t r a c t Three tetrairon ethanedithiolate complexes [{(l-EDT)Fe2(CO)5}2L] (EDT = SCH2CH2S; L = (g5Ph2PC5H4)2Fe, 1; Ph2PCH2CH2PPh2, 2; trans-Ph2PCH = CHPPh2, 3) containing bridging bidentate phosphine ligands were prepared by carbonyl substitution reactions in the presence of the decarbonylating agent Me3NO
2H2O. The new complexes 1–3 were characterized by elemental analysis, IR and 1H (31P, 13 C) NMR spectroscopies. Furthermore, their structures were determined by single crystal X-ray diffraction analysis. The molecular structure of 1 is centrosymmetric and the two cyclopentadienyl (Cp) rings reside in a staggered conformation. The molecular structures of 2 and 3 are composed of a zigzag chain, Fe2P1C20C20AP1AFe2A, with the midpoint of the C20–C20A bond as the center of symmetry. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The diiron ethanedithiolate complex (l-EDT)Fe2(CO)6 was prepared by the reaction of Fe3(CO)12 and HSCH2CH2SH at reflux in toluene [1]. Afterwards, Seyferth’s group reported another method by the reaction of (l-LiS)2Fe2(CO)6 (generated in situ from (l-S2)Fe2(CO)6 and LiBEt3H) with BrCH2CH2Br [2]. Diiron ethanedithiolate complexes such as [Fe2{SCH2CH(CH2OH)S}(CO)6] [3], (lEDT)[Fe(CO)2PMe3]2 [4], [Fe2(S2C2H4)(CNMe)7](PF6)2 [5] and [(l-EDT){Fe(CO)2PMe3}{Fe(CO)2PPh3}] [6] were designed and synthesized because their structures were very similar to (l-PDT)Fe2(CO)6 (PDT = SCH2CH2CH2S) which acts as a model for the active site of [FeFe]-hydrogenases [7–11]. On the basis of our previous study on diiron dithiolate complexes [12–14], we recently carried out a study on the reaction of the diiron ethanedithiolate complex (l-EDT)Fe2(CO)6 with bidentate phosphine ligands and have successfully prepared three new tetrairon ethanedithiolate complexes [{(lEDT)Fe2(CO)5}2L] (L = (g5-Ph2PC5H4)2Fe, 1; Ph2PCH2CH2PPh2, 2; trans-Ph2PCH = CHPPh2, 3). Herein, we now report on the synthesis and structural characterization of tetrairon ethanedithiolate complexes containing bridging bidentate phosphine ligands. 2. Experimental 2.1. General procedures and materials All reactions were performed using standard Schlenk and vacuum-line techniques under a N2 atmosphere. Acetonitrile was ⇑ Corresponding author. Tel./fax: +86 574 87089989. E-mail address: nkxfl[email protected] (X.-F. Liu). 0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2011.11.032

distilled over CaH2 under N2. Me3NO
2H2O, Ph2PCH2CH2PPh2, trans-Ph2PCH = CHPPh2 and all the other materials were available commercially and were used as received. (l-EDT)Fe2(CO)6 [1] and (g5-Ph2PC5H4)2Fe [15] were prepared according to literature procedures. IR spectra were recorded on a Nicolet 670 FTIR spectrometer. 1 H (31P, 13C) NMR spectra were obtained on a Bruker Avance 500 MHz spectrometer. Elemental analyses were performed by a Perkin-Elmer 240C analyzer.

2.2. Synthesis of the complex [(l-EDT)Fe2(CO)5]2[(g5-Ph2PC5H4)2Fe] (1) To a solution of [(l-EDT)Fe2(CO)6] (0.186 g, 0.5 mmol) in CH3CN (20 mL) was added a solution of Me3NO
2H2O (0.056 g, 0.5 mmol) in CH3CN (10 mL). The mixture was stirred at room temperature for 15 min and then (g5-Ph2PC5H4)2Fe (0.139 g, 0.25 mmol) was added. The new mixture was stirred for 1 h to give a red solution. The solvent was reduced in vacuo and the residue was subjected to TLC separation using CH2Cl2/petroleum ether (v/v = 1:2) as the eluent. Collecting the main red band afforded 0.245 g (79%) of 1 as a red solid. Anal. Calc. for C48H36Fe5O10P2S4: C, 46.41; H, 2.92. Found: C, 46.64; H, 3.06%. IR (KBr disk, cm 1): mC„O 2044 (vs), 1975 (vs), 1950 (vs). 1H NMR (500 MHz, CDCl3, ppm): 7.35 (s, 20H, 4C6H5), 4.41, 4.21 (2s, 8H, 2C5H4), 1.81, 1.13 (2s, 8H, 4SCH2). 31P NMR (200 MHz, CDCl3, 85% H3PO4, ppm): 52.56 (s). 13C NMR (125 MHz, CDCl3, ppm): 215.70, 209.97, 209.85 (C„O), 138.77, 138.44, 132.47, 132.38, 129.93, 128.10, 128.03 (PhC), 80.10, 79.76, 74.74, 74.65, 74.07, 74.02 (CpC), 34.83 (SCH2).

167

X.-F. Liu et al. / Polyhedron 33 (2012) 166–170 Table 1 Crystal data and structure refinements details for complexes 1–3. Complex

1

2

3

Empirical formula Formula weight T (K) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g cm 3) l (mm 1) F(0 0 0) Crystal size (mm) hmin, hmax (°) Reflections collected/unique Rint hkl Range

C48H36Fe5O10P2S4 1242.20 113(2) 0.71073 monoclinic P2(1)/c 8.806(4) 19.437(7) 13.974(5) 90 94.141(8) 90 2385.5(16) 2 1.729 1.786 1256 0.20  0.14  0.12 1.80, 27.92 23 198/5691

C40H32Fe4O10P2S4 1086.24 113(2) 0.71073 monoclinic C2/c 18.140(6) 16.720(5) 15.113(5) 90 103.771(6) 90 4452(2) 4 1.621 1.591 2200 0.22  0.20  0.10 1.68, 27.88 23 044/5307

C20H15Fe2O5PS2 542.11 113(2) 0.71073 orthorhombic Pbcn 16.676(3) 14.354(2) 18.072(3) 90 90 90 4325.9(12) 8 1.665 1.638 2192 0.20  0.10  0.10 1.87, 27.88 37 948/5159

0.0606 11 6 h 6 11 25 6 k 6 25 18 6 l 6 16 99.4

0.0512 23 6 h 6 23 22 6 k 6 19 19 6 l 6 19 100.0

0.0384 17 6 h 6 21 18 6 k 6 18 23 6 l 6 22 99.8

5691/0/313

5307/0/271

5159/0/271

1.114

1.027

1.169

0.0549/0.0946 0.0704/0.1004 0.758/ 0.432

0.0384/0.0698 0.0497/0.0748 0.430/ 0.332

0.0431/0.1042 0.0458/0.1059 0.630/ 0.418

Completeness to hmax (%) Data/restraints/ parameters Goodness of fit (GOF) on F2 R1/wR2 (I > 2r(I)) R1/wR2 (all data) Largest difference in peak and hole (e Å 3)

2.3. Synthesis of the complex [{(l-EDT)Fe2(CO)5}2(Ph2PCH2CH2PPh2)] (2) The procedure was similar to that used for 1, except Ph2PCH2CH2PPh2 (0.100 g, 0.25 mmol) was used instead of (g5Ph2PC5H4)2Fe. 0.195 g (72%) of 2 was obtained as a red solid. Anal. Calc. for C40H32Fe4O10P2S4: C, 44.23; H, 2.97. Found: C, 44.02; H, 3.14%. IR (KBr disk, cm 1): mC„O 2042 (vs), 1983 (vs), 1968 (vs), 1925 (vs). 1H NMR (500 MHz, CDCl3, ppm): 7.43, 7.34 (2s, 20H, 4C6H5), 2.40 (s, 4H, 2PCH2), 1.88, 1.32 (2s, 8H, 4SCH2). 31P NMR (200 MHz, CDCl3, 85% H3PO4, ppm): 56.94 (s). 13C NMR (125 MHz, CDCl3, ppm): 215.89, 209.89, 209.85 (C„O), 136.59, 136.44, 131.79, 130.29, 128.82 (PhC), 35.14 (SCH2), 29.67 (PCH2).

Ph2PC5H4)2Fe. 0.212 g (78%) of 3 was obtained as a red solid. Anal. Calc. for C40H30Fe4O10P2S4: C, 44.31; H, 2.79. Found: C, 44.42; H, 2.98%. IR (KBr disk, cm 1): mC„O 2043 (vs), 1973 (vs), 1931 (vs). 1 H NMR (500 MHz, CDCl3, ppm): 7.56, 7.44 (2s, 20H, 4C6H5), 6.68 (t, J = 19.5 Hz, 2H, 2PCH), 1.87, 1.26 (2s, 8H, 4SCH2). 31P NMR (200 MHz, CDCl3, 85% H3PO4, ppm): 57.93 (s). 13C NMR (125 MHz, CDCl3, ppm): 214.69, 209.93, 209.83 (C„O), 141.92, 141.69 (PCH), 134.72, 134.40, 132.54, 132.50, 130.71, 128.98, 128.94 (PhC), 35.03 (SCH2). 2.5. X-ray structure determination Single crystals of 1–3 suitable for X-ray diffraction analysis were grown by slow evaporation of a CH2Cl2/hexane solution at 4 °C. A single crystal of 1, 2 or 3 was mounted on a Rigaku MM007 CCD diffractometer. Data were collected at 113 K using a graphite monochromator with Mo Ka radiation (k = 0.71073 Å) in the x–/ scanning mode. Data collection, reduction and absorption corrections were performed by the CRYSTALCLEAR program [16]. The structure was solved by direct methods using the SHELXS-97 program [17] and refined by full-matrix least-squares techniques (SHEL2 XL-97) [18] on F . Hydrogen atoms were located using the geometric method. Details of crystal data, data collections and structure refinement are summarized in Table 1. 3. Results and discussion 3.1. Synthesis and characterization Treatment of the starting material (l-EDT)Fe2(CO)6 (A) with 1 equivalent of Me3NO
2H2O in MeCN followed by addition of bidentate phosphine ligands (g5-Ph2PC5H4)2Fe, Ph2PCH2CH2PPh2, or trans-Ph2PCH = CHPPh2 afforded complexes 1–3 in 72–79% yields (Scheme 1). The new complexes 1–3 are air-stable solids, which were characterized by elemental analysis and various spectroscopic techniques. In their IR spectra there are three to four absorption bands in the range 2044–1925 cm 1, assigned to the terminal carbonyls, which are shifted towards lower frequencies relative to their parent complex A (2079, 2039, 2009, 1996 cm 1) [1]. The 1 H NMR spectra of 1–3 showed two singlets at about 1.8 and 1.2 ppm for their SCH2 groups. The 31P NMR spectra of 1–3 displayed a singlet at 52–58 ppm for their two phosphorus atoms of the bidentate phosphine ligands coordinated to one Fe atom of the diiron subsite. In addition, the 13C NMR spectra of 1–3 exhibited a singlet at about 215 ppm and a doublet at about 209 ppm for their terminal carbonyls. 3.2. X-ray crystal structures

2.4. Synthesis of the complex [{(l-EDT)Fe2(CO)5}2(Ph2PCH = CHPPh2)] (3) The procedure was similar to that used for 1, except Ph2PCH = CHPPh2 (0.099 g, 0.25 mmol) was used instead of (g5-

OC OC OC

S

S

Fe

Fe A

CO CO CO

i) Me3NO, MeCN ii) Ph2PXPPh2

The molecular structures of complexes 1–3 have been determined by single crystal X-ray diffraction analysis. The ORTEP and packing views are shown in Figs. 1–6, whilst selected bond lengths and angles are presented in Tables 2–4, respectively. As shown in

OC OC OC

S Fe

OC OC Ph 2 Fe S X P P Fe Ph2 S CO CO 1 X = (C5H4)2Fe 2 X = CH2CH2 3 X = trans-CH=CH

Scheme 1. Preparation of complexes 1–3.

CO Fe S

CO CO

168

X.-F. Liu et al. / Polyhedron 33 (2012) 166–170

Fig. 1. ORTEP view of 1 with 30% probability level ellipsoids.

Fig. 2. ORTEP view of 2 with 30% probability level ellipsoids.

Fig. 3. ORTEP view of 3 with 30% probability level ellipsoids.

Fig. 1, complex 1 contains two diiron ethanedithiolate moieties which are joined together through (g5-Ph2PC5H4)2Fe. The molecule is centrosymmetric with the Fe3 atom as an inversion center, consistent with the previously reported diiron complexes [Fe2(lSCH2OCH2S-l)(CO)5]2[(g5-Ph2PC5H4)2Fe], [Fe2(l-SCH2OCH2S-l)(C

O)5]2[(g5-Ph2PC5H4)2Ru] [19] and [(l-PDT)Fe2(CO)5]2[(g5-Ph2PC5 H4)2Fe] [12]. Each phosphorus of (g5-Ph2PC5H4)2Fe occupies an axial position of the square-pyramidal geometry of Fe2 and Fe2A, similar to the diiron dithiolate complexes containing phosphine ligands [20–23]. The Fe1–Fe2 bond length [2.5103(9) Å] is longer than that

169

X.-F. Liu et al. / Polyhedron 33 (2012) 166–170

Fig. 4. Crystal packing diagram of 1 along the a-axis.

in (l-EDT)Fe2(CO)6 [2.505(2) Å] [24] and all-carbonyl diiron dithiolate complexes such as [(l-SCH2)N(CH2CH2OH)]Fe2(CO)6 [2.501(7) Å] [25] and [(l-SCH2)NC6H4C(O)Me-p)]Fe2(CO)6 [2.4950(9) Å] [26], but it is shorter than the Fe–Fe distance in natural enzymes from Clostridium pasteurianum and Desulfovibrio desulfuricans (2.55– 2.62 Å) [27,28]. All carbons of the carbonyl ligands are 1.77–1.81 Å apart from the iron atoms, with some differences due to their equatorial and axial positions. As can be seen in Figs. 2 and 3, complexes 2 and 3 both contain two [2Fe2S] clusters which are joined together through Ph2PCH2CH2PPh2 and trans-Ph2PCH = CHPPh2, respectively. Both 2 and 3 are centrosymmetric with the midpoint of the C20–C20A bond as the symmetry center. The main framework of 2 and 3 is composed of a zigzag chain, Fe2P1C20C20AP1AFe2A, close to the structures of the complexes [{l-SCH2)CH2}Fe2(CO)5(Ph2PCH2)]2 [29] and [Fe2(CO)5(l-PDT)]2(trans-Ph2PCH = CHPPh2) [30]. The bond angle P1–C20–C20A in 3 is 125.3(3)° which means that C20–C20A is a double bond, whereas the corresponding bond angle in 2 is 111.77(19)°. In addition, the C20–C20A bond length in 2 [1.524(4) Å] is longer than the corresponding bond length in 3 [1.327(5) Å]. The Fe1–Fe2 bond length [2.4997(8) Å in 2 and 2.5026(6) Å in 3] are just shorter than parent complex A, showing that the bidentate phosphine ligands substitution has no effect on the Fe–Fe bond length.

Fig. 6. Crystal packing diagram of 3 along the a-axis.

Table 2 Selected bond lengths (Å) and angles (°) for 1. Fe(1)–S(1) Fe(1)–S(2) Fe(1)–Fe(2) Fe(2)–S(2) Fe(1)–S(1)–Fe(2) Fe(2)–S(2)–Fe(1) S(2)–Fe(1)–Fe(2) S(1)–Fe(1)–Fe(2)

2.2511(12) 2.2462(13) 2.5103(9) 2.2519(12) 67.62(3) 67.85(3) 56.19(3) 56.37(3)

Fe(2)–S(1) Fe(2)–P(1) S(1)–C(6) S(2)–C(7) S(2)–Fe(2)–Fe(1) S(1)–Fe(2)–Fe(1) C(7)–C(6)–S(1) C(6)–C(7)–S(2)

2.2604(12) 2.2374(11) 1.832(3) 1.821(3) 55.97(4) 56.02(3) 111.4(2) 112.0(2)

As shown in Figs. 4–6, intermolecular hydrogen bonds are observed in the crystal packing structures of complexes 1–3. Hydrogen bonds and van der Waals’ interactions stabilize the solid-state structures.

Fig. 5. Crystal packing diagram of 2 along the a-axis.

170

X.-F. Liu et al. / Polyhedron 33 (2012) 166–170

Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].

Table 3 Selected bond lengths (Å) and angles (°) for 2. Fe(1)–S(1) Fe(1)–S(2) Fe(1)–Fe(2) Fe(2)–S(2) C(20)–C(20A) Fe(1)–S(1)–Fe(2) Fe(2)–S(2)–Fe(1) S(2)–Fe(1)–Fe(2) S(1)–Fe(1)–Fe(2)

2.2563(9) 2.2553(9) 2.4997(8) 2.2456(8) 1.524(4) 67.40(2) 67.47(2) 56.08(2) 56.16(2)

Fe(2)–S(1) Fe(2)–P(1) S(1)–C(6) S(2)–C(7) C(6)–C(7) S(2)–Fe(2)–Fe(1) S(1)–Fe(2)–Fe(1) C(7)–C(6)–S(1) C(6)–C(7)–S(2)

2.2490(8) 2.2166(8) 1.833(2) 1.825(2) 1.520(3) 56.45(3) 56.44(2) 112.02(16) 112.18(16)

Table 4 Selected bond lengths (Å) and angles (°) for 3. Fe(1)–S(1) Fe(1)–S(2) Fe(1)–Fe(2) Fe(2)–S(2) C(20)–C(20A) Fe(1)–S(1)–Fe(2) Fe(2)–S(2)–Fe(1) S(2)–Fe(1)–Fe(2) S(1)–Fe(1)–Fe(2)

2.2531(8) 2.2480(10) 2.5026(6) 2.2437(8) 1.327(5) 67.53(2) 67.72(3) 56.06(2) 56.17(2)

Fe(2)–S(1) Fe(2)–P(1) S(1)–C(6) S(2)–C(7) C(6)–C(7) S(2)–Fe(2)–Fe(1) S(1)–Fe(2)–Fe(1) C(7)–C(6)–S(1) C(6)–C(7)–S(2)

2.2498(8) 2.2075(8) 1.832(3) 1.835(4) 1.502(5) 56.22(3) 56.30(2) 111.8(2) 112.5(2)

4. Conclusions In summary, three tetrairon ethanedithiolate complexes 1–3 were prepared by carbonyl substitution from (l-EDT)Fe2(CO)6 and bidentate phosphine ligands in high yields. The new complexes 1–3 were characterized by elemental analysis, IR and NMR spectroscopies, as well as by X-ray crystallography. Acknowledgments This work was supported by the Zhejiang Provincial Natural Science Foundation of China (Y4110663) and Ningbo Natural Science Foundation (2011A610209). Appendix A. Supplementary data CCDC 829408, 829407 and 829409 contain the supplementary crystallographic data for 1, 2 and 3. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road,

References [1] A. Winter, L. Zsolnai, G. Huttner, Z. Naturforsch. 37b (1982) 1430. [2] D. Seyferth, R.S. Henderson, L.-C. Song, Organometallics 1 (1982) 125. [3] M. Razavet, A. Le Cloirec, S.C. Davies, D.L. Hughes, C.J. Pickett, J. Chem. Soc., Dalton Trans. (2001) 3551. [4] X. Zhao, I.P. Georgakaki, M.L. Miller, R. Mejia-Rodriguez, C.Y. Chiang, M.Y. Darensbourg, Inorg. Chem. 41 (2002) 3917. [5] J.D. Lawerence, T.B. Rauchfuss, S.R. Wilson, Inorg. Chem. 41 (2002) 6193. [6] P. Li, M. Wang, C. He, X. Liu, K. Jin, L. Sun, Eur. J. Inorg. Chem. (2007) 3718. [7] C. He, M. Wang, X. Zhang, Z. Wang, C. Chen, J. Liu, B. Åkermark, L. Sun, Angew. Chem., Int. Ed. 43 (2004) 3571. [8] C.A. Boyke, T.B. Rauchfuss, S.R. Wilson, M.M. Rohmer, M. Bénard, J. Am. Chem. Soc. 126 (2004) 15151. [9] J.I. van der Vlugt, T.B. Rauchfuss, C.M. Whaley, S.R. Wilson, J. Am. Chem. Soc. 127 (2005) 16012. [10] A.K. Justice, M.J. Nilges, T.B. Rauchfuss, S.R. Wilson, L. De Gioia, G. Zampella, J. Am. Chem. Soc. 130 (2008) 5293. [11] T.-T. Zhang, M. Wang, N. Wang, P. Li, Z.-Y. Liu, L.-C. Sun, Polyhedron 28 (2009) 1138. [12] X.-F. Liu, B.-S. Yin, J. Coord. Chem. 63 (2010) 4061. [13] X.-F. Liu, X.-W. Xiao, L.-J. Shen, J. Coord. Chem. 64 (2011) 1023. [14] X.-F. Liu, B.-S. Yin, Z. Anorg. Allg. Chem. 637 (2011) 377. [15] J.J. Bishop, A. Davision, M.L. Katcher, D.W. Lichtenberg, R.E. Merril, J.C. Smart, J. Organomet. Chem. 27 (1971) 241. [16] CRYSTALCLEAR 1.3.6, Rigaku and Rigaku/MSC,. The Woodlands, TX, 2005. [17] G.M. Sheldrick, SHELXS97, A Program for Crystal Structure Solution, University of Göttingen, Germany, 1997. [18] G.M. Sheldrick, SHELXL97, A Program for Crystal Structure Refinement, University of Göttingen, Germany, 1997. [19] L.-C. Song, Z.-Y. Yang, H.-Z. Bian, Y. Liu, H.-T. Wang, X.-F. Liu, Q.-M. Hu, Organometallics 24 (2005) 6126. [20] Z. Zhao, M. Wang, W. Dong, P. Li, Z. Yu, L. Sun, J. Organomet. Chem. 694 (2009) 2309. [21] L.-C. Song, H.-T. Wang, J.-H. Ge, S.-Z. Mei, J. Gao, L.-X. Wang, B. Gai, L.-Q. Zhao, J. Yan, Y.-Z. Wang, Organometallics 27 (2008) 1409. [22] W. Gao, J. Liu, B. Åkermark, L. Sun, J. Organomet. Chem. 692 (2007) 1579. [23] B.-S. Yin, T.-B. Li, M.-S. Yang, J. Coord. Chem. 64 (2011) 2066. [24] M.C. Ortega-Alfaro, N. Hernández, I. Cerna, J.G. López-Cortés, E. Gómez, R.A. Toscano, C. Alvarez-Toledano, J. Organomet. Chem. 689 (2004) 885. [25] H.-G. Cui, M. Wang, W.-B. Dong, L.-L. Duan, P. Li, L.-C. Sun, Polyhedron 26 (2007) 904. [26] L.-C. Song, J.-H. Ge, X.-F. Liu, L.-Q. Zhao, Q.-M. Hu, J. Organomet. Chem. 691 (2006) 5701. [27] J.W. Peters, W.N. Lanzilotta, B.J. Lemon, L.C. Seefeldt, Science 282 (1998) 1853. [28] Y. Nicolet, C. Piras, P. Legrand, C.E. Hatchikian, J.C. Fontecilla-Camps, Structure 7 (1999) 13. [29] W. Gao, J. Ekström, J. Liu, C. Chen, L. Eriksson, L. Weng, B. Åkermark, L. Sun, Inorg. Chem. 46 (2007) 1981. [30] F.I. Adam, G. Hogarth, S.E. Kabir, I. Richards, C. R. Chim. 11 (2008) 890.