Mono-, di- and tri-nuclear Ni(II) complexes of N-, O-donor ligands: structural diversity and reactivity

Mono-, di- and tri-nuclear Ni(II) complexes of N-, O-donor ligands: structural diversity and reactivity

Inorganic Chemistry Communications 5 (2002) 924–928 www.elsevier.com/locate/inoche Mono-, di- and tri-nuclear Ni(II) complexes of N-, O-donor ligands...

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Inorganic Chemistry Communications 5 (2002) 924–928 www.elsevier.com/locate/inoche

Mono-, di- and tri-nuclear Ni(II) complexes of N-, O-donor ligands: structural diversity and reactivity Mishtu Dey a, Chebrolu P. Rao a

a,*

, Pauli K. Saarenketo b, Kari Rissanen

b

Bioinorganic Laboratory, Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400 076, India b Department of Chemistry, University of Jyvaskyla, Jyvaskyla, Fin 40351, Finland Received 7 May 2002; accepted 24 August 2002

Abstract A series of mono-, di- and tri-nuclear Ni(II) complexes of N, O-donating molecules possessing AH2 CANHA and AHC@NA moieties have been synthesized and characterized and the structures have been determined by single crystal X-ray diffraction. All these exhibited interesting molecular packing in their crystal lattices. Di-nuclear complexes were found to be cleaved in pyridine to result in mononuclear ones with additional coordinations being provided by pyridine. Di-nuclear complexes were found to form urea adducts as demonstrated based on absorption and vibrational studies. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Mono-, di- and tri-nuclear Ni(II) complexes; Urea adduct; Pyridine bound mononuclear Ni(II) complex; N-, O-donor molecules

1. Introduction Structure and reactivity studies of transition-metal complexes of N, O-donor ligands containing AH2 CA NHA and AHC@NA moieties have been considered to be important in the bioinorganic chemistry owing to the biomimetic nature of such complexes in the context of metalloenzymes [1,2]. In pursuit of understanding the coordination chemistry and biomimetic aspects of such molecules, we report herein the complexes of Ni(II) since nickel is an essential element of life by being present in a number of enzymes [3]. Thus the present study of Ni(II) with diverse structural cores emerge.

2. Results and discussion Complexes of Ni(II), 1–10 were synthesized from the reactions of 1:1 or 1:2 nickel acetate to ligand ratios in methanol using molecules possessing one Ph–OH, and

*

Corresponding author. Tel.: +91-22-576-7162; fax: +91-22-5723480. E-mail address: [email protected] (C.P. Rao).

one, two or three alkoxy-OH, in addition to a AHC@ NA (H2 L1, H2 L2, H3 L3 or H4 L4) or AH2 CANHA (H2 L5) moiety as shown in Scheme 1. The reactions carried out in 1:2 ratio resulted in a mononuclear complex of the type [NiðHx1 LyÞ2 ] fx ¼ 2–4; y ¼ 1–4g as found in 1–4 [4–7]. However, the corresponding 1:1 reactions resulted in a di-nuclear complex of the type ½ðNiðHx1 LyÞ ðCH3 COOÞðH2 OÞ2 as found in 5–8 [8–11] using H2 L1–H4 L4 respectively, and a tri-nuclear one, 9, with H2 L5 [12]. FT IR spectra are characteristic of the binding of the imine nitrogen in 1–8 and the absence of this moiety in 9. The electronic absorption spectra of the complexes [4– 11] exhibit distinct bands, one in the range 600–620 nm and a second one at 970 nm assigned to spin allowed 3 3 d–d transition 3 T2g A2g and 3 T1g A2g respectively of high spin octahedral Ni(II) [13,14]. In some of the complexes, a weak band near 750 nm was also observed that could be assigned to a spin forbidden tran3 sition band 1 Eg A2g . This observation is in agreement with that reported in the literature for dinuclear nickel complexes [15]. In addition to this, an intense band observed in the region 348–370 nm is attributable to the p–p transition associated with the azomethine linkages [16,17].

1387-7003/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 2 ) 0 0 6 0 2 - 0

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Scheme 1. Ni(II) complexes of AOHA rich molecules. Ô*Õ refers to the structure determined by single crystal XRD. Hx Ly represents H2 L1 (R1 ¼ R2 ¼ H), H2 L2 (R1 ¼ R2 ¼ CH3 ), H3 L3 (R1 ¼ CH3 , R2 ¼ CH2 OH), H4 L4 (R1 ¼ R2 ¼ CH2 OH). 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 respectively are ½NiðHL1Þ2 , ½NiðHL2Þ2 , ½NiðH2 L3Þ2 , ½NiðH2 L4Þ2  ½NiðHL1ÞðCH3 COOÞðH2 OÞ2 , ½NiðHL2ÞðCH3 COOÞðH2 OÞ2 , ½NiðH2 L3ÞðCH3 COOÞðH2 OÞ2 , ½NiðH3 L4ÞðCH3 COOÞðH2 OÞ2 , ½Ni3 ðHL5Þ2 ðCH3 COOÞ4 ðCH3 OHÞ2 , ½NiðH2 L3ÞðpyÞ3 ðCH3 COOÞ. Reaction conditions: (i) Ni:L/1:1, where Ni@NiðCH3 COOÞ2 4H2 O; (ii) Ni:L/1:2; (iii) NaBH4 , 0 °C, CH3 OH, (iv) pyridine (py).

Molecular ion peaks observed in FAB mass spectra of the complexes, are consistent with the corresponding molecular weights [4–12]. The intensity ratios of isotopic peak patterns observed in the spectra match well with the theoretically calculated ones. Single crystal X-ray structures of mono- (1, 3), di- (5, 6) and tri- (9) nuclear complexes were determined [18]. In all these three types of complexes, each Ni(II) center is in a distorted octahedral environment. In 1 and 3, both the ligands act as tridentate by binding through phenolic AOH (Ophe ), imine nitrogen (Nimi ) and alcoholic AOH (Oalk ) groups as shown in Fig. 1(a). Tridentate coordination by these ligands was also observed in case of the oxo metal ion complexes of cis-VOþ 2 [19], and cis-MoO2þ [20] and the complexes of non-oxo2 Zn(II) [21]. Complexes 5 and 6 exhibit the presence of di-nuclear nickel units leading to a centrosymmetric structure. Each Ni(II) is bound to phenoxo, an imine nitrogen, an alkoxo, an acetate moiety and a water molecule. The phenoxo moiety that is bound to the metal center is also involved in bridging the two nickel centers to result in a di-bridged Ni2 O2 rhomb, giving rise to octahedral coordination at each nickel centre. This feature is in contrast with our previous study of the oxo 2þ species of cis-VOþ 2 [19b] and trans-UO2 [22], wherein the di-nuclear complexes involve bridging of the alkoxo

moiety instead of the phenoxo group as seen in the dinuclear nickel complexes (Fig. 1(b)). Conversion of AHC@NA moiety in H2 L2 by NaBH4 results in the formation of AH2 ACANHA (as in H2 L5). This introduces further flexibility in the ligand, giving rise to a tri-nuclear complex 9, instead of a di-nuclear one, 6. As a result, in 9, the central Ni(II) sits on a center of symmetry thereby leading to two coordinatively different types of nickel centers. The terminal ones are bound to Ophe (bridging), Oalk , Nami , a methanol OH, bridging monodentate acetate and another bridging bidentate acetate as shown in Fig. 1(c). Thus, of the four bridging acetates, two are bidentate and the remaining two are monodentate. On the other hand, the central Ni(II) is bound to two bridging phenoxo groups and four bridging acetate moieties. Thus the complex possesses three Ni centers bound by only two main ligands wherein the two adjacent Ni(II) centers are triply bridged. The reactivity of the di-nuclear complexes in pyridine has been studied. In pyridine the Ni2 O2 rhomb present in 7, breaks down to a mononuclear complex, 10 [18]. Crystal structure of 10 demonstrates that Ni(II) is bound to one ligand in tridentate fashion and remaining three coordination sites are occupied by three pyridine molecules as shown in Fig. 2, to result in a meridional

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Fig. 1. Molecular structures showing 50% probability thermal ellipsoids using ORTEP for complexes: (a) 1; (b) 6 and (c) 9. Structures of 3 and 5 are similar to that of 1 and 6, respectively except for the difference in the ligand. Solvent molecules are not shown for clarity.

Fig. 2. Molecular structure of 10 showing 50% probability thermal ellipsoids using ORTEP. Solvent molecules are not shown for clarity.

octahedral complex. The main ligand being monoanionic, an acetate moiety was found as counter anion. The metric parameters of the coordination spheres in all the complexes were consistent with distorted octahedral geometry about each nickel center. The CAN  observed in the Schiff base bond length of 1.278–1.303 A complexes, 1–8, differ substantially upon going to the , confirming the Mannich base complex 9, 1.490 A

change occurred in the bond order in these two types of complexes. The NiAOphe , NiANimi and NiAOalk were , 1.981–2.048 found to be in the range of 1.985–2.068 A  and 2.079–2.183 A  respectively and are in well A agreement with those observed in the literature [15]. The , in di- and observed Ni Ni distance, 3.082–3.103 A tri-nuclear complexes, is indicative of the absence of any bond between the two nickel centers. The packing of the molecules in the unit cell results in connecting these through OAH O type of interactions leading to the formation of interesting three-dimensional structures. Though the structure of 1 was reported by Chumakov et al. [23], there are some crystallographic differences between theirÕs and the present one. The changes reflected not only in terms of the crystal system and the space group but also in terms of solvent of crystallization. In the present study, the methanol of crystallization manifests the lattice of 1 in the formation of channels filled with MeOH as shown in Fig. 3. In 5, the molecules are stacked in columns. In 6, four adjacent molecules provide a core for the channel into which the metal-bound acetates of a pair of the diagonal ones are placed. On the other hand, in 10, the molecules are stacked in segregated columns.

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Fig. 3. Packing diagram of 1 exhibiting corrugated sheet pattern with methanol filled channels.

Fig. 4. Absorption spectra of 6 and the corresponding urea adduct measured in CH2 Cl2 . a ¼ precursor complex; b ¼ urea adduct.

Adducts were prepared from the reaction of the dinuclear complexes, 5–7 with excess urea either in CH2 Cl2 or in C2 H5 OH. When the isolated product of urea adducts were measured in CH2 Cl2 , the shoulder found at 504 nm in the precursor spectrum of the dinuclear complexes disappeared and the band observed around 604 nm was broadened and shifted to 645–655 nm indicating the adduct formation. A representative spectrum of 6 and the corresponding urea adduct is shown in Fig. 4. These results are consistent with those reported in the literature [15a]. The bands observed near 3340–3460 cm1 , due to mðNAHÞ and 1670 cm1 arising from mðC@OÞ in the FT IR spectra are suggestive of the binding of urea through its oxygen [15]. Thus the reaction of N, O-donor ligands resulted in the formation of mono-, di- and tri-nuclear complexes having metal to ligand ratios of 1:2, 1:1 and 3:2 respectively. Only the di- and tri-nuclear complexes of Ni(II) were found to exhibit phenoxo oxygen bridging.

However, these ligands do not exhibit phenoxo bridge [19,22] in case of the di-nuclear complexes of cis-VO2þ 2 and trans-UO2þ 2 and tetranuclear complexes of Cu(II) [24]. In 9, acetates bridge both in mono- as well as in bidentate fashion and the central Ni(II) is coordinatively different from the terminal ones. Conversion of imine moiety to amine brings a concomitant change in the nuclearity of the complex, by going from a di-nuclear to a tri-nuclear one. All these complexes exhibited interesting crystal structures as a manifestation of OAH O interactions and some of these led to channels filled with MeOH or metal ion bound acetate moieties. While pyridine breaks the di-nuclear complex, urea forms adduct with these. Further studies in this direction are currently underway in our laboratory. Thus, these molecules are expected to have potential in mimicking bioinorganic systems.

Acknowledgements CPR acknowledges the financial support from CSIR and DST, New Delhi. MD gratefully acknowledges the SRF fellowship from CSIR. Thanks are due to RSIC, CDRI Lucknow for FAB mass spectral measurements.

References [1] (a) C.R. Cornman, G.J. Colpas, J.D. Hoeschele, J. Kampf, V.L. Pecoraro, J. Am. Chem. Soc. 114 (1992) 9925; (b) C.J. Carrano, C.M. Nunn, R. Quan, J.A. Bonadies, V.L. Pecoraro, Inorg. Chem. 29 (1990) 944; (c) X. Li, M.S. Lah, V.L. Pecoraro, Inorg. Chem. 27 (1998) 4567. [2] (a) D.C. Crans, H. Chen, O.P. Anderson, M.M. Miller, J. Am. Chem. Soc. 115 (1993) 6769; (b) D.C. Crans, P.M. Ehde, P.K. Shin, L. Pettersson, J. Am. Chem. Soc. 113 (1993) 3728.

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[3] (a) H.L. Mobley, R.P. Hausinger, Microbiol. Rev. 53 (1989) 85; (b) E. Jabri, M.B. Karr, R.P. Hausinger, P.A. Karplus, Science 268 (1995) 998. [4] Analytical Data for 1 2CH3 OH: Yield: 61%; 216–220 °C; FT IR (cm1 ): 1645 ðmC@N Þ; Anal. Calcd for C20 H28 N2 O6 Ni: C, 53.25; H, 6.26; N, 6.21%. Found: C, 52.79; H, 6.38; N, 5.86%; FAB-MS m/z 482 (½1 3CH3 OHþ , 10%), 387 (½NiðHL1Þ2 þ , 5%); UV–Vis, kmax / nm, (e=Lmol1 cm1 ), (DMF): 224 (9710), 364 (1950), 670 (3.9) and 721 (2.7). [5] Analytical Data for 2 CH3 OH: Yield: 58%; 128 °C (decomposes); FT IR (cm1 ): 1636 ðmC@N Þ; Anal. Calcd for C23 H32 N2 O5 Ni: C, 58.13; H, 6.79; N, 5.90%; Found: C, 58.22; H, 6.37; N, 5.42%. FAB-MS m/z 479 (½2þ , 10%); UV–Vis, kmax /nm, ðe=Lmol1 cm1 Þ, (DMF): 348 (3367), 409 (1146), 499 (136), 592 (6) and 971 (5). [6] Analytical Data for 3 2CH3 OH: Yield: 80%; 228–230 °C; FT IR (cm1 ): 3135 ðmOH Þ, 1631 ðmC@N Þ; Anal. Calcd for C24 H36 N2 O8 Ni: C, 53.46; H, 6.73; N, 5.20%. Found: C, 53.39; H, 6.28; N, 5.41%; FAB-MS m/z 475 (½3þ , 100%), 266 (½NiðH2 L3Þþ , 75%); UV–Vis, kmax /nm, (e=Lmol1 cm1 ), (DMF): 375 (12730) and 590 (3). [7] Analytical Data for 4 H2 O: Yield: 59%; 230 °C (decomposes); FT IR (cm1 ): 3311 ðmOH Þ, 1629 ðmC@N Þ, Anal. Calcd for C22 H30 N2 O9 Ni: C, 50.32; H, 5.76; N, 5.33%. Found: C, 50.80; H, 5.79; N, 5.28%. FAB-MS m/z 511 (½4þ , 70%), 283 (½NiðH3 L4Þþ , 80%); UV–Vis, kmax /nm, (e=Lmol1 cm1 ), (DMF): 267 (11878), 374 (12192), 585 (15) and 926 (14). [8] Analytical Data for 5: Yield: 48%; mp 188–190 °C; FT IR (cm1 Þ: 3295 ðmOH Þ, 1654 ðmC@N Þ, 1538, 1415 ðmOAC Þ; Anal. Calcd for C22 H30 N2 O10 Ni2 : C, 44.05; H, 5.04; N, 4.67%. Found: C, 44.33; H, 5.18; N, 4.01%; FAB-MS m/z 593 (½5þ , 10%), 443 (½Ni2 ðL1Þ2 þ , 38%); UV–Vis, kmax /nm, (e=Lmol1 cm1 ), (DMF): 271 (11581), 368 (10507), 624 (2) and 983 (4); (CH3 OH): 268 (14050), 365 (13150), 626 (7) and 646 (6). [9] Analytical Data for 6 2C2 H5 OH: Yield: 33%; 156–158 °C; FT IR ðcm1 Þ: 3266 ðmOH Þ, 1642 ðmC@N Þ, 1555, 1405 ðmOAC Þ; Anal. Calcd for C30 H50 N2 O12 Ni2 : C, 48.17; H, 6.74; N, 3.75%. Found: C, 48.16; H, 6.34; N, 4.25%; FAB-MS m/z 750 (½6:2C2 H5 OHþ , 48%), 499 (½Ni2 ðHL2Þ2 þ , 100%), 250 (½NiðHL2Þþ , 42%); UV–Vis, kmax / nm, (e=Lmol1 cm1 ), (DMF): 380 (3784), 412 (2378), 450 (775), 492 (308), 513 (85), 603 (15) and 968 (5); (CH3 OH): 225 (85700), 236 (88300), 363 (21000), and 614 (8); (CH2 Cl2 ): 253 (76600), 349 (15200), 415 (6800), 451 (1680), 504 (540) and 603 (15). [10] Analytical Data for 7 2CH3 OH: Yield: 27%; 175 °C (decomposes); FT IR ðcm1 Þ: 3252 ðmOH Þ, 1636 ðmC¼N Þ, 1548, 1407 ðmOAC Þ; Anal. Calcd for C28 H46 N2 O14 Ni2 : C, 44.72; H, 6.17; N, 3.73%. Found: C, 44.56; H, 6.48; N, 4.19%. FAB-MS m/z 750 (½72CH3 OHþ , 5%); UV–Vis, kmax /nm, ðe=Lmol1 cm1 Þ, (DMF): 269 (13071), 370 (11821), 505 (104), 594 (21), 747 (2) and 923 (11); (CH3 OH): 227(72500), 236(73400), 266(22800), 365(17100), and 604 (3); ðCH2 Cl2 Þ: 253 (77600), 323 (11550), 348 (12980), 415 (5050), 451 (1680), 504 (540) and 503 (15). [11] Analytical Data for 8 CH3 OH: Yield: 40%; 244–246 °C; FT IR ðcm1 Þ: 3308 ðmOH Þ, 1628 ðmC@N Þ, 1541, 1446 ðmOAC Þ; Anal. Calcd for C27 H42 N2 O15 Ni2 : C, 43.12; H, 5.63; N, 3.73%. Found: C, 43.49; H, 5.96; N, 4.05%; FAB-MS m/z 565 (½Ni2 ðH3 L4Þ2 þ , 10%), 509 (½NiðH3 L4Þ2 þ , 60%), 282 (½NiðH3 L4Þþ , 65%); UV–Vis, kmax / nm, (e=Lmol1 cm1 ), (DMF): 270 (21017), 375 (22203), 592 (9) and 937 (13).

[12] Analytical Data for 9 2H2 O: Yield: 30%; 175 °C (decomposes); FT IR (cm1 Þ: 3139 ðmOH Þ, 1538, 1419 ðmOAC Þ; Anal. Calcd for C32 H56 N2 O16 Ni3 : C, 42.66; H, 6.27; N, 3.11%. Found: C, 42.44; H, 6.43; N, 2.90%; FAB-MS m/z 904 (½9 2H2 Oþ , 5%), 563 (½Ni2 ðHL5Þ2 þ , 10%); UV–Vis, kmax /nm, (e=Lmol1 cm1 ), (DMF): 401 (56), 682 (16) and 732 (14). [13] L. Sacconi, Coord. Chem. Rev. 1 (1966) 192. [14] S. Yamada, Coord. Chem. Rev. 1 (1966) 415. [15] (a) T. Koga, H. Furutachi, T. Nakamura, N. Fukita, M. Ohba, K. Takahashi, H. Okawa, Inorg. Chem. 37 (1998) 989; (b) S. Uozumi, H. Furutachi, M. Ohba, H. Okawa, D.E. Fenton, K. Shindo, S. Murata, D.J. Kitko, Inorg. Chem. 37 (1998) 6281. [16] T.N. Sorrell, W.E. Allen, P.S. White, Inorg. Chem. 34 (1995) 952. [17] B. Bosnich, J. Am. Chem. Soc. 90 (1968) 627. [18] X-ray data for 1 2CH3 OH: Empirical Formula: C20 H28 N2 O6 Ni; ): Crystal system: Orthorhombic, P21 nb; Unit cell Dimension (A 3 : 2071.8(3); Z: 4; Dc =g cm3 9.969(1), 9.976(1), 20.832(1); V/A 1.446; Unique reflections: 2207; Final R [I > 2rðIÞ]: 0.0246 and Rw 0.0656; 3 2CH3 OH: Empirical Formula: C24 H36 N2 O8 Ni; Crystal ): 12.385(1), system: Monoclinic, P21 =n; Unit cell Dimension (A 3 : 3066.0(5); Z: 4; 10.090(1), 24.736(2); b/deg: 97.31(1); V/A Dc =g cm3 1.168; Unique reflections: 4919; Final R [I > 2rðIÞ]: 0.1507 and Rw 0.3672; 5: Empirical Formula: C22 H30 N2 O10 Ni2 ; ): Crystal system: Monoclinic, P21 =n; Unit cell Dimension (A 3 : 2476.0(3); Z: 9.439(1), 17.623(1), 14.944(1); b/deg: 95.10(1); V/A 4; Dc =g cm3 1.609; Unique reflections: 5659; Final R [I > 2rðIÞ]: 0.0306 and Rw 0.0754; 6 2CH3 CH2 OH: Empirical Formula: C30 H50 N2 Ni2 O12 ; Crystal system: Monoclinic, P21 =c; Unit cell ): 9.461(2); 14.024(1), 13.378(1); b/deg: 105.78(1); V/ Dimension (A 3  A : 1708.1(4); Z: 2; Dc =g cm3 1.455; Unique reflections: 3096; Final R [I > 2rðIÞ]: 0.0376 and Rw 0.1036; 9 2H2 O: Empirical Formula: C32 H56 N2 Ni3 O16 ; Crystal system: Triclinic, P-1; Unit ): 9.5908(4), 10.2403(4); 12.0277(4); a/deg: cell Dimension (A 3 : 973.60(6); 96.862(2); b/deg: 106.635(2); c/deg: 116.156(2); V/A 3 Z: 1; Dc =g cm 1.537; Unique reflections: 3415; Final R [I > 2rðIÞ]: 0.0283 and Rw 0.0667; 10 CH3 COO: Empirical Formula: C28 H32 N4 NiO5 ; Crystal system: Monoclinic, P21 =c; ): 10.218(2), 29.212(5), 10.380(1); b/deg: Unit cell Dimension (A 3 : 2709.1(8); Z: 4; Dc =g cm3 1.381; Unique 119.03(1); V/A reflections: 3766; Final R [I > 2rðIÞ]: 0.0533 and Rw 0.1039. [19] (a) G. Asgedom, A. Sreedhara, J. Kivikoski, J. Volkonen, E. Kolehmainen, C.P. Rao, Inorg. Chem. 35 (1996) 5674; (b) C.P. Rao, A. Sreedhara, P.V. Rao, B.M. Verghese, K. Rissanen, E. Kolehmainen, N.K. Lokanath, M.A. Sridhar, J.S. Prasad, J. Chem. Soc. Dalton Trans. (1998) 2383. [20] C.P. Rao, A. Sreedhara, P.V. Rao, N.K. Lokanath, M.A. Sridhar, J.S. Prasad, K. Rissanen, Polyhedron 18 (1999) 289. [21] M. Dey, C.P. Rao, P.K. Saarenketo, K. Rissanen, Eur. J. Inorg. Chem. (2002) 2207. [22] P.V. Rao, C.P. Rao, A. Sreedhara, E.K. Wegelius, K. Rissanen, E. Kolehmainen, J. Chem. Soc. Dalton Trans. (2000) 1213. [23] Yu.M. Chumakov, V.N. Biyushkin, T.I. Malinovskii, V.I. Tsapkov, M.S. Popov, N.M. Samus, Koord. Khim. 17 (1991) 1398. [24] M. Dey, C.P. Rao, P.K. Saarenketo, K. Rissanen, Inorg. Chem. Commun. 5 (2002) 380.