MixedCopper±LanthanideMetallomesogens KoenBinnemans,* [a] Katleen Lodewyckx, [a] Bertrand Donnio, [b] andDanielGuillon [b] Abstract: This paper describes the first examples of heteropolynuclear metal- lomesogens that contain both a transi- tion metal ion and a trivalent lanthanide ion. Adducts were formed between a mesomorphic [Cu(salen)] complex (salen  2,2'-N,N'-bis(salicylidene)ethyl- enediamine) with six terminal tetrade- cyloxy chains and a lanthanide nitrate (Ln  La, Gd). Different stoichiome- tries were found, depending on the lanthanide ion: a trinuclear copper± lanthanum±copper complex [La- (NO 3 ) 3 {Cu(salen)} 2 ] and a binuclear cop- per-gadolinium complex [Gd(NO 3 ) 3 Cu- (salen)]. The compounds exhibit a hex- agonal columnar mesophase (Col H ) over a wide temperature-range with rather low melting temperatures. Although the clearing point could be observed for the parent [Cu(salen)] complex, the mixed f ± d complexes decomposed in the high- temperature part of the mesomorphic domain before clearing. On the basis of X-ray diffraction measurements and molecular modelling, a structural model for the mesophase of the metal com- plexes is proposed. Keywords: copper ¥ lanthanides ¥ liquid crystals ¥ metallomesogens ¥ supramolecular chemistry Introduction During recent years, considerable research effort has been invested in the design of new metal-containing liquid crystals (metallomesogens) with the aim of combining the unique properties of anisotropic fluids (anisotropy of physical properties and fast orientational response to external fields) with the specific properties of metals (magnetic, electronic). [1] Furthermore, metals offer multiple structural possibilities for novel molecular architectures, which in turn may lead to new types of molecular organisations or mesophases. For example, mesomorphism has been achieved in nonconventional metal complexes, with octahedral, [2] square-antiprismatic, [3] trigo- nal-bipyramidal [4] and tetrahedral [5] coordination geometry. Recently, the synthesis of mesomorphic metallacrowns, [6] butterfly compounds, [7] metallodendrimers [8] and polynuclear systems [9] opened up the field for the construction of original structures able to contain a large number of metallic centres. Liquid crystals incorporating paramagnetic metal ions are of particular interest in the sense that they can be switched by weak external magnetic fields and can find new applications in the display and communication technologies. Examples of such paramagnetic metal ions include Cu II , [10] oxovanadi- um, [11] and the trivalent lanthanide ions. [12] Although several mixed f ± d complexes have been syn- thesised and their magnetic behaviour studied in detail, [13] there is still no report on heteropolynuclear metallomesogens that contain both a transition metal ion and a lanthanide (rare-earth) ion. Such mixed f±d metallomesogens could represent an intriguing new class of materials, since they combine specific magnetic interactions of f ± d coordination compounds (such as magnetic exchange interactions) with the properties of liquid crystals. Furthermore, from a materials processing point of view, such f±d metallomesogens could be advantageous because of the strong tendency of the lantha- nide-based metallomesogens to form a glassy state on cooling rather than to crystallise, and thus giving the possibility to freeze-in the mesomorphic order, whereas common non- mesomorphic f ± d coordination complexes are obtained as crystalline powders. In this paper, we report on the structural design and on the thermal behaviour of two novel mixed f ± d metallomesogens, based on binuclear or trinuclear copper±lanthanide com- plexes. ResultsandDiscussion To obtain these mixed f±d metallomesogens, our approach consisted of modifying the structures of previously described non-mesomorphic f±d complexes in such a way that a sufficient structural anisotropy was obtained to favour the formation of mesophases. This can be achieved by extending [a] Dr. K. Binnemans, K. Lodewyckx Katholieke Universiteit Leuven, Department of Chemistry Celestijnenlaan 200F, 3001 Leuven (Belgium) Fax: ( 32)16-32-79-92 E-mail: koen.binnemans@chem.kuleuven.ac.be [b] Dr. B. Donnio, Dr. D. Guillon Institut de Physique et Chimie des Mate ¬riaux de Strasbourg Groupe des Mate ¬riaux Organiques 23 rue du Loess, 67037 Strasbourg Cedex (France) E-mail: bertrand.donnio@ipcms.u-strasbg.fr Supporting information for this article is available on the WWW under http://wiley-vch.de/home/chemistry/ or from the author: Experimental details of the synthesis of the salen ligand L and additional X-ray diffraction data. FULL PAPER Chem. Eur. J. 2002, 8, No. 5 ¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 0947-6539/02/0805-1101 $ 17.50+.50/0 1101