Elsevier

Polyhedron

Volume 20, Issues 9–10, 30 April 2001, Pages 915-922
Polyhedron

An approach to heterometallic alkoxide-β-diketonate complexes with a M4O4 cubane-like core and new prospects of their application in preparation of solid catalysts. X-ray single crystal study of (Co,Ni)4(acac)43-OMe)4(MeOH)4, Co2Ni2(acac)43-OMe)4(OAc)2 and Mg4(acac)43-OMe)4(MeOH)4

https://doi.org/10.1016/S0277-5387(01)00754-9Get rights and content

Abstract

The interaction of the individual M4(acac)43-OMe)4(MeOH)4 complexes, M=Co, Ni in toluene/methanol media provided crystals of (Co,Ni)4(acac)43-OMe)4(MeOH)4 (I) — the product of co-crystallization of isomorphous products. The oxidation of a MeOH solution of I in air in the presence of NaOAc and aminoalcohols as catalysts gave Co2Ni2(acac)43-OMe)4(OAc)2 (II), an individual heterometallic derivative. The interaction of Mg(OCH(CH3)CH2NMe2)2 with Cu(acac)2 in toluene/methanol media produced Mg4(acac)43-OMe)4(MeOH)4 (III) as the only isolatable product. The starting Co and Ni homometallic complexes as well as the heterometallic CoNi complex II were used to prepare the zeolite-supported oxide catalysts which exhibited extremely high activity towards methanol oxidation.

Introduction

Heteroleptic alkoxide complexes of late 3d transition metals (Co, Ni and Cu), containing mainly β-diketonate groups as heteroligands, attracted attention during the last few decades due to their unusual magnetic properties (ferromagnetism in (Ni(acac)(OMe)(MeOH)]4 [1], [2] and diamagnetism in [Cu4{OC(OMe)(2-C5H4N)2}4(OMe)2]2+ [3]) and also due to their high solubility and volatility in comparison with homoleptic alkoxides, which made them attractive as precursors for oxide materials. For example, [Cu(β-diket)(OMe)(MeOH)]4 [4] were reported as precursors for HTSC materials via the sol–gel technique. The analogous complexes of alkaline earth metals (Ca–Ba) have also been extensively investigated as precursors of HTSC materials via both sol–gel and MOCVD routes [5]. There is very little reported so far about the heterometallic derivatives following this structure motive: only the determination of the unit cell parameters and the study of magnetic properties in the 103–297 K temperature interval were reported for Co2Ni2(acac)4(OMe)4(MeOH)4 [6]. We present here the results of the application of different synthetic approaches to their preparation and the structural and magnetic characterization of the products obtained.

As an example of the practical applications of polynuclear complexes, they were used to prepare zeolite-supported oxide catalysts. The employment of polynuclear metal complexes as precursors was shown to afford extraordinary active catalysts, supposedly, because of the ultra-high, next to molecular, dispersion of an active component [7].

Section snippets

Experimental

All the manipulations, except for the preparation of Mg(ORN)2, RN=CH(CH3)CH2NMe2 were carried out in ambient atmosphere. The solvents, toluene and methanol, were purchased from Merck (pure for analysis quality) and used without further purification. [M(acac)(OMe)(MeOH)]4, M=Ni, Co were prepared from the hydrated acetates by treatment with sodium acetylacetonate in MeOH according to Halcrow et al. [2]. IR spectra of nujol mulls were registered with a Perkin–Elmer IR-1700 spectrometer. UV spectra

Synthetic approaches

Developing the approach to heterometallic alkoxide–acetylacetonate complexes of late transition metals, we planned originally to apply the idea that has earlier permitted us to isolate individual nickel–copper aminoalkoxide–carboxylate derivatives. The latter has been achieved via the interaction of an aminoalkoxide (dimethylaminoisopropoxide) of a metal cation, being a harder acid according to Pearson, with an acetylacetonate of a softer acid. To get better solubility we applied the 2:1 and

Supplementary material

Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 152565–152567 for compounds (IIII), respectively. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1 EZ, UK (fax: +44-1223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).

Acknowledgements

The authors would like to express their gratitude to Dr M. Ruf for the assistance in the solution of the structure of II and to Dr A.I. Yanovsky for the assistance in the solution of the structure of III. O.N.K., E.E.K., I.F.M. and B.V.R. thank the Russian Foundation for Basic Research (Grant No. 99-03-32648) for financial support of their work.

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