Struct Chem (2008) 19:735–740 DOI 10.1007/s11224-008-9346-3
ORIGINAL RESEARCH
Tetranuclear manganese (III) salicylaldoxime ensemble Avinash S. Kumbhar Æ Mahesh P. Mulay Æ Subhash B. Padhye Æ Sudam S. Tavale Æ Vedavati G. Puranik
Received: 1 January 2008 / Accepted: 16 June 2008 / Published online: 3 September 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Crystal structure of {[Mn(salicylaldoximeH) (salicylaldoxime)]4} 3CHCl3 1 formed by the interaction of MnCl2 4H2O and salicylaldoxime in a 1:1 ratio is described. The compound crystallizes in the orthorhombic space group Pbca (No 61) with the lattice parameters; ˚, a = 27.769 (3), b = 22.672 (2), c = 21.650 (2) A 3 ˚ V = 13630 (2) A , Z = 8, R1 = 0.0776, wR2 = 0.2356, S = 1.164. The cluster with four Mn (III) centers formed by four terminal and four bridging salicylaldoxime ligands results in a central rotating wheel-like core with the Mn–Mn ˚ and with the separation varying from 3.531 to 3.576 A ˚ . Four intramolecdiagonal distances being 4.156–4.165 A ular H-bonds between a terminal oxime (NOH) group and the adjacent phenolate oxygen atom of another ligand stabilize the structure of the cluster. Spectral, magnetic, and cyclic voltammetry studies corroborate a stable Mn (III) tetramer. Keywords Salicylaldoxime Manganese cluster Crystal structure
The article was accepted and intended for the Special issue but was left out due to a production error. A. S. Kumbhar (&) M. P. Mulay S. B. Padhye (&) Department of Chemistry, University of Pune, Pune 411007, India e-mail:
[email protected] S. B. Padhye e-mail:
[email protected] S. S. Tavale V. G. Puranik Centre for Materials Characterization, National Chemical Laboratory, Pune 411008, India
Introduction Polynuclear transition metal complexes are of current interest to both biologists and bioinorganic chemists investigating the structure and function of polynuclear metal centers in proteins [1, 2] and to physicists and physical inorganic chemists for new materials [3, 4] displaying interesting electronic properties. Manganese has been the metal of choice for both biological modeling purposes (for example the tetranuclear Mn site responsible for photosynthetic water oxidation in green plants and cyanobacteria) and the fact that manganese aggregates formed have interesting magnetic properties. The elucidation of the crystal structures of oxygen-evolving photosystem II from ˚ resolution by Thermosynechococcus elongatus at 3.8 A Zouni et al. [5] and Thermosynechococcus vulcanus at ˚ resolution by Kamiya and Shen [6], respectively, 3.7 A indicated that a tetranuclear manganese center is at the heart of the water splitting reaction, triggered efforts toward the synthesis of structural and functional analogues of the oxygen-evolving complex. The three general classes of tetranuclear manganese complexes with variable oxidation states which are synthesized are (i) the [Mn4(l3-O)2] core using the carboxylate aggregate developed by Christou and Hendrickson [7–9] (ii) the [Mn4(L)2(O)2(CH3COO)2] core where L = the schiff base ligands 2,6-bis(salicylideneaminomethyl)-4-methylphenol or 1,5-bis-(salicylideneamino)-3pentanol or 2,6-bis(N-(4-imidazolylethyl)iminomethyl]-4methylphenol reported by Mikuriya et al. [10–13] and (iii) the inorganic analogues of M2+(12-crown-4) such as Mn(II)[Mn(III)-salicylhydroximate]4 described by Pecoraro et al. [14, 15] In all the above cases the Mn4(III) aggregate is formed with the participation of ancillary bridging ligands such as acetato-, benzoato-, etc. Herein we report the X-ray structure of a neutral tetranuclear Mn(III) cluster containing
123
736
deprotonated oximino bridges and protonated oximino groups of salicylaldoxime, an ancient ligand, coordination features of which were reviewed by Chaudhuri [16]. However there are numerous studies where bridging groups such as oxo-, chloroacetato-, triphenylacetato-, propionato-, benzoato-, and benzilato- ligands cooperate with a ligand viz. salicylaldoxime, to build high-nuclearity clusters. In the present work we report a tetranuclear Mn (III)-salicylaldoxime cluster without any bridging co-ligands. It is interesting to note that the X-ray structures of the divalent nickel [17], copper [18, 19], zinc [20], palladium [21], and platinum [21] complexes of salicylaldoxime and substituted salicylaldoxime ligand reveal a mononuclear bis bidentate ligation.
Experimental Materials All reagent grade chemicals were used without purification unless otherwise specified. Salicylaldehyde, hydroxylamine hydrochloride, MnCl2 4H2O were received from S.D.Fine Chemicals (India). Solvents methanol and chloroform were distilled prior to use. Salicylaldoxime was prepared by literature methods [22]. Synthesis of 1 Reaction of MnCl2 4H2O (0.10 mmol) with salicylaldoxime (0.10 mmol) after reflux for 1 h yielded a dark brown compound from which crystals suitable for X-ray diffraction were grown by the liquid diffusion method using a chloroform: hexane solvent pair. Needle shaped brown crystals of 1 deposited, which were washed with ether and dried in vacuum over P2O5. Yield * 25%. Anal. Calcd (found) C56H44O16N8Mn4 3CHCl3: C, 42.48(42.61); H, 2.81(2.85); N, 6.67(6.73). X-ray structural studies Single crystals of the complex 1 were grown by the liquid diffusion method using chloroform: hexane solvent pair. A brown colored needle of approximate size 0.52 9 0.47 9 0.28 mm3, was used for data collection on an Enraf Nonius CAD-4 single crystal X-ray diffractometer with graphite monochromated MoKa radiation using a fine focus tube at 50 kV and 30 mA. h range = 1.46–23.41°, completeness to h of 23.41° is 99.6%. C56H44O16N8Mn4 3(CHCl3), M = 1662.86. Crystals belong to the orthorhombic space group Pbca, a = 27.769 ˚ , b = 22.672(2) A ˚ , c = 21.650(2) A ˚ , V = 13630(2) (3) A 3 -3 ˚ A , Z = 8, Dc = 1.621 mg m , l (MoKa) = 1.148 mm-1, T = 293(2) K, 9991 unique reflections [I [ 2r(I)], R value
123
Struct Chem (2008) 19:735–740 Table 1 Crystal data and structure refinement for C56 H44 O16 N8 Mn4 3(CHCl3) Empirical formula
C56H44O16N8Mn4 3(CHCl3)
Formula weight
1662.86
Temperature
293(2) K ˚ 0.70930 A
Wavelength Crystal system, space group Unit cell dimensions
Orthorhombic, Pbca ˚ a = 27.769(3) A ˚ b = 22.672(2) A
Volume
˚ c = 21.650(2) A ˚3 13630(2) A
Z, Calculated density
8, 1.621 Mg/m3
Absorption coefficient F(000)
1.148 mm-1 6704
Crystal size
0.52 9 0.47 9 0.28 mm
Theta range for data collection 1.46–23.41° Limiting indices
0 B h B 30, 0 B k B 25, 0 B l B 24
Reflections collected/unique
9991/9991 [R(int) = 0.0000]
Completeness to theta = 23.41
99.6%
Max. and min. transmission Refinement method
0.7430 and 0.5839 Full-matrix least-squares on F2
Data/restraints/parameters
9991/0/869
Goodness-of-fit on F
2
1.164
Final R indices [I [ 2r(I)]
R1 = 0.0777, wR2 = 0.2347
R indices (all data)
R1 = 0.1432, wR2 = 0.3038
Largest diff. peak and hole
0.905 and -0.842 eA3
0.0776, wR2 = 0.2356. All the data were corrected for Lorentzian, polarization, and absorption effects. NRCVAX was used for structure solution and SHELX-97 (ShelxTL) [23] for structure refinement for full matrix least squares refinement on F2. Hydrogen atoms were included in the refinement as per the riding model. Data collection and refinement parameters are listed in Table 1. Crystallographic data for the structural analysis have been deposited with Cambridge Crystallographic Data Centre, CCDC– 104041 for compound 1. Copies of this information may be obtained free of charge from The Director, CCDC, 12, Union Road, Cambridge CB2 1EZ, UK [FAX +44(1223) 336-033 or email:
[email protected].
Results and discussion The interaction of MnCl2 4H2O with salicylaldoxime in a 1:1 ratio resulted in a brown solid from which crystals were obtained by diffusion of chloroform: hexane solution. Single crystal X-ray analysis revealed the structure of the compound 1 to be a cluster containing four Mn(III) centers along with three molecules of chloroform as
Struct Chem (2008) 19:735–740
737
Fig. 1 ORTEP diagram of 1. Ellipsoids are drawn at 30% probability
solvent of crystallization. The cluster with four Mn(III) centers is formed by four terminal and four bridging salicylaldoxime ligands. Each Mn(III) is coordinated by a terminal bidentate salicylaldoxime (NO) donor ligand and other four (1N and 3O) atoms originating from three of the four bridging salicylaldoxime ligands. The bridged ligand further joins two other Mn(III) centers through its oximate oxygen while the oximate nitrogen links this Mn–O–Mn moiety to another Mn(III) center resulting in a tetranuclear cubane-like ensemble (Fig. 1) The selected bond distances and angles are shown in Table 2 and the coordination sphere of each Mn center is shown in Fig. 2. In the central manganese tetramer core with a rotating wheel-like motif (Fig. 3), the Mn–Mn separation varies from 3.531 to ˚ with the diagonal distance being 4.156–4.165 A ˚. 3.576 A These distances are different than those reported for the photosystem II manganese cluster and also all the manganese are in +3 oxidation state unlike that in PSII. For all the four Mn(III) centers, Mn–O distance (derived from ˚ ) than bridged salicylaldoxime) is greater (average 2.247 A the other three (one from the other bidentate
salicylaldoxime and two from the bridging salicylaldoxime ˚ ). Four intramolecular H-bonds ligand) (average 1.914 A between a terminal oxime (NOH) group and the adjacent phenolate oxygen atom of another ligand stabilize the structure of the cluster (Fig. 4). Apart from these H-bonds, the C–HCl and C–HO short contacts stabilize the crystal structure (Table 3) as shown in the packing of the molecules down ‘b’ axis (Fig. 5). The present structure is similar to the [{Fe(salH) (HsalH)}4] [24] but different from the other tetranuclear complexes as it lacks other ancillary bridging ligands such as oxo-, acetato-, etc. It is interesting to note that the X-ray structures of the divalent metals such as nickel, copper, zinc, platinum, and palladium with the same salicylaldoxime or substituted salicylaldoxime ligands result in bis bidentate square planar or distorted trigonal bipyramidal with H2O as the fifth ligand while the trivalent metal ions manganese and iron result in tetranuclear clusters. The effective magnetic moment of the complex decreases from 10.45 B.M at 238.5 K to 7.39 B.M at 5 K indicating weakly coupled antiferromagnetic centers
123
738
Struct Chem (2008) 19:735–740
˚ ] and angles [8] for C56H44O16 Table 2 Selected bond lengths [A N8Mn4 3(CHCl3) cluster Mn(1)–O(15)
1.876(6)
Mn(1)–O(5)
1.930(6)
Mn(1)–O(25)
1.965(6)
Mn(1)–N(23)
2.011(7)
Mn(1)–O(35)
2.230(6)
Mn(1)–N(13)
2.251(7)
Mn(2)–O(34)
1.868(6)
Mn(2)–O(45)
1.890(6)
Mn(2)–O(35)
1.954(6)
Mn(2)–N(26)
2.040(7)
Mn(2)–O(55) Mn(2)–N(53)
2.236(6) 2.260(8)
Mn(3)–O(64)
1.882(6)
Mn(3)–O(65)
1.906(6)
Mn(3)–O(24)
1.955(6)
Mn(3)–N(56)
2.052(7)
Mn(3)–O(25)
2.223(6)
Mn(3)–N(73)
2.251(7)
Mn(4)–O(44)
1.869(6)
Mn(4)–O(75)
1.922(6)
Mn(4)–O(55)
1.954(6)
Mn(4)–N(36)
2.068(7)
Mn(4)–N(83)
2.209(8)
Mn(4)–O(24)
2.300(6)
O(15)–Mn(1)–O(5)
91.8(3)
O(15)–Mn(1)–O(25)
173.5(3)
O(5)–Mn(1)–O(25) O(15)–Mn(1)–N(23)
93.1(3) 87.6(3)
O(5)–Mn(1)–N(23)
176.0(3)
O(25)–Mn(1)–N(23)
87.8(3)
O(15)–Mn(1)–O(35)
90.8(2)
O(5)–Mn(1)–O(35)
95.6(2)
O(25)–Mn(1)–O(35)
84.5(2)
N(23)–Mn(1)–O(35)
88.4(2)
O(15)–Mn(1)–N(13)
93.2(3)
O(5)–Mn(1)–N(13)
83.8(3)
O(25)–Mn(1)–N(13)
91.5(3)
N(23)–Mn(1)–N(13)
92.3(3)
O(35)–Mn(1)–N(13)
175.9(3)
O(34)–Mn(2)–O(45)
93.7(3)
O(34)–Mn(2)–O(35)
174.6(3)
O(45)–Mn(2)–O(35) O(34)–Mn(2)–N(26)
90.7(3) 87.9(3)
O(45)–Mn(2)–N(26)
175.2(3)
O(35)–Mn(2)–N(26)
88.0(3)
O(34)–Mn(2)–O(55)
93.6(3)
O(45)–Mn(2)–O(55)
97.3(2)
O(35)–Mn(2)–O(55)
82.6(2)
N(26)–Mn(2)–O(55)
87.1(3)
123
Table 2 continued O(34)–Mn(2)–N(53)
91.0(3)
O(45)–Mn(2)–N(53)
85.7(3)
O(35)–Mn(2)–N(53)
92.6(3)
N(26)–Mn(2)–N(53)
89.7(3)
O(55)–Mn(2)–N(53)
174.3(2)
O(64)–Mn(3)–O(65)
93.2(3)
O(64)–Mn(3)–O(24)
174.4(3)
O(65)–Mn(3)–O(24)
92.4(3)
O(64)–Mn(3)–N(56)
87.3(3)
O(65)–Mn(3)–N(56) O(24)–Mn(3)–N(56)
177.1(3) 87.2(3)
O(64)–Mn(3)–O(25)
95.1(3)
O(65)–Mn(3)–O(25)
94.9(3)
O(24)–Mn(3)–O(25)
84.5(2)
N(56)–Mn(3)–O(25)
88.0(2)
O(64)–Mn(3)–N(73)
90.6(3)
O(65)–Mn(3)–N(73)
84.6(3)
O(24)–Mn(3)–N(73)
89.9(3)
N(56)–Mn(3)–N(73)
92.5(3)
O(25)–Mn(3)–N(73)
174.3(3)
O(44)–Mn(4)–O(75)
93.1(3)
O(44)–Mn(4)–O(55)
174.4(3)
O(75)–Mn(4)–O(55)
91.9(3)
O(44)–Mn(4)–N(36)
89.0(3)
O(75)–Mn(4)–N(36)
176.7(3)
O(55)–Mn(4)–N(36) O(44)–Mn(4)–N(83)
86.1(3) 90.9(3)
O(75)–Mn(4)–N(83)
86.2(3)
O(55)–Mn(4)–N(83)
91.8(3)
N(36)–Mn(4)–N(83)
91.1(3)
O(44)–Mn(4)–O(24)
93.8(2)
O(75)–Mn(4)–O(24)
96.0(2)
O(55)–Mn(4)–O(24)
83.3(2)
N(36)–Mn(4)–O(24)
86.4(2)
N(83)–Mn(4)–O(24)
174.7(3)
C(6)–O(5)–Mn(1)
121.2(6)
(J = -12 cm-1). The fact that it is EPR silent and the cyclic voltammogram profile is featureless in the range +1.0 V to -2.0 V corroborates a stable Mn (III) cluster.
Conclusions The X-ray structure of a tetranuclear ensemble resulting from the reaction of Manganese chloride and salicylaldoxime with terminal and bridging salycylaldoxime is reported. Though the structural, spectroscopic, and electrochemical characteristics are different from those found in PS-II this structure is interesting from the coordination chemistry point of view.
Struct Chem (2008) 19:735–740
739
Fig. 2 The tetranuclear Mn(III) cluster showing the coordination sphere of each metal center
Fig. 3 The central rotating wheel-like core of 1
Fig. 4 The overall structure of the cluster showing H-bonds
123
740
Struct Chem (2008) 19:735–740
Fig. 5 Packing of the molecules down ‘b’ axis
Table 3 Analysis of potential hydrogen bonds Donor–Hacceptor
HA
DA
D–HA
O(14)–H(14)O(65)
1.96
2.741(11)
158
O(54)–H(54)O(5)
1.95
2.719(9)
156
O(74)–H(74)O(75)
2.07
2.742(9)
140
O(84)–H(84)O(45)
1.88
2.675(10)
164
C(47)–H(47)O(84)
2.51
3.204(12)
131
C(77)–H(77)O(74)
2.59
3.300(11)
133
C(80)–H(80)Cl(94)i
2.75
3.371(15)
125
C(96)–H(96)O(64)ii
2.56
3.37(2)
141
Intramolecular
Intermolecular
Equivalent position code i = 1/2 - x, 1/2 + y, z ii = 1 - x, -1/2 + y, 3/2 - z Acknowledgments Financial support from Council of Scientific and Industrial Research (CSIR), New Delhi, is gratefully acknowledged.
References 1. 2. 3. 4.
Fieg AL, Lippard SJ (1994) Chem Rev 94:759 Pecoraro VL (1992) Manganese redox enzymes. VCH, New York Kahn O (1993) Molecular magnetism. VCH, New York Gatteschi D (1994) Adv Mater 6:635
123
5. Zouni A, Witt HJ, Kern J, Fromme P, Krauz N, Saenger W, Orth P (2001) Nature 409:739 6. Kamiya N, Shen J-R (2003) Proc Natl Acad Sci USA 100:98 7. Bouwman E, Bolcar MA, Libby E, Huffman JC, Folting K, Christou G (1992) Inorg Chem 31:5185 8. Libby E, McCusker JK, Schmitt EA, Folting K, Hendrickson DN, Christou G (1991) Inorg Chem 30:3486 9. Wemple MW, Tsai H-L, Folting K, Hendrickson DN (1993) Inorg Chem 32:2025 10. Mikuriya M, Yamato Y, Tokii T (1992) Bull Chem Soc Jpn 65:2624 11. Mikuriya M, Nakadera K, Kotera T, Tokii T, Mori W (1995) Bull Chem Soc Jpn 68:3077 12. Mikuriya M, Yamato Y, Tokii T (1991) Chem Lett 1429 13. Mikuriya M, Hashimoto Y, Kawamori K (1995) Chem Lett 1095 14. Pecoraro VL, Stemmler AJ, Gibney BR, Bodwin JJ, Wang H, Kampf JW, Barwinski A (1997) Prog Inorg Chem 45:83, and references therein 15. Lah MS, Pecoraro VL (1989) J Am Chem Soc 111:7258 16. Chaudhuri P (1999) Proc Indian Acad Sci (Chem Sci) 111:397 17. Merritt LM, Guare C, Lessor AE (1956) Acta Crystallogr 9:253 18. Orioli PL, Lingafelter EC (1964) Acta Crystallogr 17:1113 19. Jarski MA, Lingafelter EC (1964) Acta Crystallogr 17:1109 20. Potocnak I, Heineman FW, Rausch M, Steinborn D (1997) Acta Crystallogr C53:54 21. Cox EG, Pinkard FW, Wardlaw W, Webster KC (1935) J Chem Soc 459 22. Aggarwal RC, Singh NK, Singh RP (1984) Synth React Inorg Met-Org Chem 14:637 23. Sheldrick GM (1997) SHELX-97 program for crystal structure solution and refinement. University of Gottingen, Germany 24. Thorpe JM, Beddoes RL, Collison D, Garner CD, Helliwell M, Holmes JM, Tasker PA (1999) Angew Chem Int Ed 38:1119
