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Crystal Structure and Magnetic Property of the Binuclear Manganese(III) Complex with /u-Acetate and Di-ji-Alkoxo Bridges

Yuzo Nishida*3, Naoko Oshinoa, and Tadashi Tokiib

a Department of Chemistry, Faculty of Science. Yamagata University, Koshirakawa Yamagata 990, Japan

b Department of Chemistry, Faculty of Science and Engineering. Saga University, Saga 840, Japan

Z. Naturforsch. 43b, 472-474 (1988); received November 9/December 17, 1987

Binuclear Manganese(III) Complex, Crystal Structure, ESR Spectra, Magnetic Property

Binuclear manganese(III) complex, [Mn :L(u-OCH3)0<-CH3COO)(OHCH : , ) ]ClO4 was pre-pared and characterized in terms of crystal structure determination, magnetic measurement, and ESR spectroscopy, where H3L represents the Schiff base derived from salicylaldehvde and 1,5-diamino-3-pentanol.

1. Introduction

Multinuclear manganese sites that are involved in the catalysis of reactions vital to biological systems are being steadily recognized and studied. Besides the photosynthetic water-oxidizing complex, which is known to utilize 4 Mn ions for the oxidation of water to molecular oxygen [1], evidence has accumulated that the Mn site of the pseudo-catalase from Lacto-bacillus planatrum is comprised of two Mn ions per protein subunit [2]. Thus there is compelling interest in the characterization of multinuclear manganese complexes in various oxidation states in order to un-ravel the more complex behaviour of the biological sites by serving as models of the structural, spectral, of functional properties. In the previous papers, Nishida et al. have studied the catalytic function of binuclear Mn(III) complexes for the decomposition of H 2 0 2 [3], and the ESR spectra of binuclear Mn(II) [4], and Mn(III) [5] complexes.

In this article we wish to report the prepa-ration, crystal structure, and magnetic proper-ties of the binuclear manganese(III) complex, [Mn2L(/*-0CH3)(//-CH3C00)(0HCH3)]C104 where H3L represents the Schiff base derived from salicyl-aldehyde and 1.5-diamino-3-pentanol.

* Reprint requests to Dr. Y. Nishida.

Verlag der Zeitschrift für Naturforschung. D-7400 Tübingen 0932 - 0776/88/0400 - 496/$ 01.00/0

2. Materials and Method

The ligand H3L was obtained by the published method [6]. The manganese(III) complex was ob-tained as green prisms from the reaction mixture (methanol solution) of Mn(CH3COO)3 • 2 H 2 0 . H3L, triethylamine, and NaC104 [7].

The crystal (0.2x0.2x0.4 mm) was mounted on a Rigaku AFC-5 four-circle automatic diffracto-meter with graphite monochromated MoKa radia-tion (A = 0.71069 A). Automatic centering and least-squares routines were carried out on 25 re-flections to obtain the cell constant. Crystal data: [Mn 2 L(0CH 3 ) (CH 3 C00)(0HCH 3 ) ]C10 4 , ortho-rhombic, space group Pca2], a = 20.006(10), b = 15.445(2), c = 8.5058(9) Ä. The 9-29 scan tech-nique was employed to record the intensities of a unique set of reflections, and 3640 of independent non-zero (FO>3CT(FO)) reflections with 26 between 2.5° and 55° were used for the crystal structure de-termination. Three check reflections were meas-ured every 100 reflections; they exhibited no sig-nificant decay during the data collection. Intensities were corrected for Lorentz and polarization effects. The data collection was performed at 294 ± 1 K. The structure was solved by direct methods (MULTAN) [8], and successive Fourier syntheses. The structure was refined by block-diagonal least-squares including anisotropic thermal parameters, giving /?(=Z|lFol - IFcl|/Z|Fo|) = 0.047, and Rw(= [Z tv(11FoI - IFCI |) :/ZW |FO|2]1 / 2) = 0.052 w h e r e w = 1. The final shifts of the parameters were less than 0.4 times their estimated standard deviations. All the calculations were performed on a Facom M-200 computer with local versions of UNICS III [9] and ORTEP [10]. The thermal ellipsoids of the ORTEP plots were drawn at the 50% probability

473 Y. Nishida etal. • Binuclear Manganese(III) Complex

level. The atomic scattering factors were taken from ref. [11]*.

3. Results and Discussion

An ORTEP drawing of the [Mn :L(OCH3)(CH3COO)(OHCH3)]+, including the atomic numbering scheme, is given in Fig. 1, and the selected bond distances and angles are summarized in Table I. Two manganese(III) ions are bridged by three groups; two alkoxo oxygen atoms and one ace-tate ion. The coordination numbers of manganese ions are six and five for Mn2 and Mn 1, respectively, and the Mn —Mn distance is 2.931(2) Ä. The temper-ature dependence of the magnetic susceptibility (81—298 K) is shown in Fig. 2. The magnetic mo-ment per manganese ion is 4.28 and 3.08 //B at 298.3 and 81.5 K, respectively. The exchange integral parameter, 7, derived from the equation based on the isotropic Heisenberg model ( > = —235^2) [12],

Table I. Selected bond lengths (Ä) and angles (°) of the co-ord ina t ion sphere in [ M n 2 L ( O C H , ) ( C H , c b O ) ( O H C H 1 ) ] f

with their es t imated s tandard deviat ions in paren theses .

Bond length (Ä ) Mn 1 —Mn2 2.931(2) Mn 1 - O l 1.826(5) Mn 1 —03 1.953(4) Mn 1 - N 1 1.992(5) Mn 1 —04 1.920(5) Mn 1 — Ol 2.159(6) Mn2—02 1.856(4) Mn2 - 0 3 1.956(4) Mn2—N2 1.999(6) Mn2 — 0 8 2.362(6) M n 2 - 0 4 1.935(5) Mn2 — 0 9 2.172(6) Bond angle (°) Mn 1 —03-Mn2 97.2(2) Mn 1 — 0 4 - Mn2 99.0(2) O 1 —Mn 1-•Nl 91.4(2) O l - Mn 1- 0 3 167.0(2) O 1 —Mn 1-0 4 93.4(2) O l - Mn 1 -0 7 100.9(2) N 1 —Mn 1 -0 3 94.4(2) N l - Mn 1 -0 4 171.7(2) N 1 —Mn 1 — 0 7 92.2(2) 0 3 - Mn 1 -0 4 79.5(2) 0 3 —Mn 1 -Ol 90.4(2) 0 4 - Mn 1 -Ol 93.5(2) 02—Mn2-•N2 91.4(2) 0 2 - Mn2- 0 3 173.3(2) 02—Mn2- 0 4 94.8(2) 0 2 - Mn2- OS 88.9(2) 02—Mn2- 0 9 95.1(2) N2- Mn2- 0 3 94.3(2) N2—Mn2- 0 4 170.2(2) N2- Mn2- OS 85.3(2) N2—Mn2- 0 9 93.5(2) 0 3 - Mn2- 0 4 79.1(2) 0 3 —Mn2- OB 88.2(2) 0 3 - Mn2- 0 9 87.9(2) 04—Mn2- OS 87.2(2) 0 4 - Mn2- 0 9 93.5(2) 08—Mn2- 0 9 175.9(2)

* Complete tables of atomic coordinates, anisotropic ther-mal parameters, bond lengths and angles, and observed and calculated structure factor amplitudes have been de-posited as the Fachinformationszentrum Energie, Phy-sik, Mathematik GmbH. D-7514 Eggenstein-Leopolds-hafen 2. The registry-Nr., CSD 52937, the names of the authors, and the reference should be given.

1 5 0 0 0

1 3 0 0 0 CO 4-> C 3

"j 11000 CTI o s:

V ^ o 9 0 0 0

7 0 0 0

5 0 0 0 100 2 0 0 300

T / K Fig. 2. Temperature dependence of magnetic susceptibility of [Mn 2 L (0CH, ) (CH,C00) (0HCH, ) ]C10 4 . • • • observed value; calculated curve based on the isotropic Heisenberg model [12] where g. J , and N a were assumed to be 1.99. —10.6 cm"1, and 0, respectively.

was estimated to be —10.6 cm - 1 . This is indicating that a weak antiferromagnetic interaction is operat-ing between the two manganese(III) ions.

The —7 value of the di-«-oxo Mn(III) —Mn(IV) complex, [Mn :02(bip)4]1+, is very large [13]. Stoufer

J l , I L

474

et al. inferred that the electrons of the atoms are aligned in an antiparallel fashion via a superexchange mechanism [13]. Since Mn = 0 (oxo oxygen atom) bonding is the strongest in [Mn202(bip)4]"1+, the dr:_v: orbital which is located along the Mn = 0 bond is vacant, and thus it is most likely that strong antifer-romagnetic interaction observed in the complex should be attributed to notable direct overlap be-tween dvv orbitals, as illustrated below. This is sup-ported by the fact that the magnetic interaction is negligible in ,w-oxo-di-«-acetato dimanganese(III) complex. [Mn20(CH3C00)2(C6H15N3)2]2+ [14] where the Mn —Mn distance (3.08 Ä) is much longer than that (2.716 Ä) of [Mn202(bip) 4]1 . In our pres-ent manganese(III) complex, it can be anticipated that no electron lies in the dr:_v: orbital because the in-plane Mn —O and Mn—N bonds are stronger than those of out-of-plane bonds. Thus, the small —7 value of the present complex can be attributed to a

Y. Nishida etal. • Binuclear Manganese(III) Complex

smaller overlap between two dvv orbitals due to a longer Mn —Mn distance (2.931 Ä).

The present dimanganese(III) complex is ESR non-detectable at 77 K (frozen solution state), whereas two other complexes. [Mn202(bip)4]^ and [Mn 2 0(CH 3 C00) 2 (QH 1 5 N 3 ) 2 ] 2 + are ESR detectable [15, 5], The ESR non-detectable nature of the pres-ent complex may be attributed to the diamagnetic ground state due to weak antiferromagnetic interac-tion, because the other two have paramagnetic ground states.

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[2] W. F. Beyer (Jr.) and I. Fridovich. Biochem. 24, 6460 (1985).

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[4] Y. Nishida. Chem. Lett. 1987, 2151. [5] Y. Nishida. submitted to J. Inorg. Biochem. [6] W. Mazurek. B. J. Kennedy. K. S. Murray. M. J.

O'Connor. J. R. Rodgers. M'. R. Snow. A. G. Wedd. and P. R. Zwack. Inorg. Chem. 24, 3258 (1985).

[7] Found: C 42.49; H 4.62; N 4.52; Mn 16.4%. Calcd for [Mn,L(0CH;)(CFL,C00)(0HCH,)]C104: C 42.19; H 4.46; N 4.28; Mn 16.78%.

[8] P. Main. M. M. Woolfson. and G. Germain. Comp-uter Programs for the Automatic Solution of Crystal Structure. Universities of York (England) and Lou-vain (Belgium) (1971).

[9] Universal Crystallographic Computer Program System (UNICS). ed. by T. Sakurai, The Crystallographic Society of Japan, Tokvo (1967).

[10] O. A. Johnson. Report No. 3794; Oak Ridge National Lab., Oak Ridge. Tennessee (1965).

[11] International Tables for X-Ray Crystallography, Vol. 4, Kynoch Press. Birmingham (1974).

[12] A. Earnshaw, Introduction to Magnetochemistry, Academic Press, London (1968).

[13] P. Plaskin, R. C. Stoufer. M. Mathew, and G. J. Palenik. J. Am. Chem. Soc. 94, 2121 (1972).

[14] K. Wieghardt. U. Bossek. D. Venture, and J. Weiss, J. Chem. Soc. Chem. Commun. 1985, 347.

[15] S. Cooper, G. C. Dismukes. M. Klein, and M. Calvin, J. Am. Chem. Soc. 100, 7248 (1978).