CH OH NCH 2 4NdCl 3 + 12NaNH 2 + 4H 3 L + Na 2 CO 3 1 + 12NaCl + 12NH 3 H 3 L = thf 25 °C 2 2 + 4thf dme CHOH O(01′) Na(1′) O(1′) O(12a′) O(22a′) N(101a′) N(201′) Nd(1′) Nd(1a′) N(101′) N(201a′) O(02′) O(12a) O(2) O(02) Na(1) O(01) O(12) N(101) N(201) N(101a) O(1) Nd(1) O(22) O(10a) O(22a) O(20a) O(20) Nd(1a) O(10) O(12′) O(22′) N(201a) O C O O Nd Nd Nd Nd Na Na I A tetranuclear neodymium cage which tightly binds sodium carbonate molecules Glen B. Deacon,* a Tiecheng Feng, a David C. R. Hockless, b Peter C. Junk, a Brian W. Skelton b and Allan H. White b a Chemistry Department, Monash University, Clayton, Victoria 3168, Australia b Department of Chemistry, University of Western Australia, Nedlands, WA 6907, Australia The complexes [Na 2 Nd 4 L 4 (CO 3 )LA 4 ] [H 3 L = (o- HOC 6 H 4 CHNNCH 2 ) 2 CHOH, LA = tetrahydrofuran or LA 2 = 1,2-dimethoxyethane] have novel cage structures in which Nd 4 O 12 N 8 bowl-shaped frameworks of Nd 4 L 4 molecules entrap solvated Na 2 CO 3 molecules within the cavity of the bowl. Lanthanoid alkoxide cage complexes are of great interest, 1 but aryloxide analogues are much less common. Some rare examples are based on the 4-methylphenoxide ion and include [Na 3 La 2 (m 4 -OAr) 3 (m-OAr) 6 (thf) 5 ], (thf = tetrahydrofuran, Ar = 4-MeC 6 H 4 ). 2 Cage complexes have the capacity to act as hosts for a variety of guest species, 3 and there is a current focus on incorporation of anionic species, e.g. environmentally important contaminants such as phosphate. 4 The Schiff-base ligand (o-HOC 6 H 4 CHNNCH 2 ) 2 CHOH (H 3 L), which is known to give bimetallics for d-block metals, 5 has the potential, on deprotonation to L 32 , to form mixed aryloxo–alkoxo cages with lanthanoid metals. We now report the synthesis and structure of a tetranuclear neodymium cage based on this ligand. This host tightly encapsulates solvated sodium carbonate within the cavity of the cluster, and a novel binding mode of CO 3 22 is observed. Reaction of anhydrous NdCl 3 , H 3 L, sodium amide and sodium carbonate in thf at room temperature (Scheme 1) resulted in triple deprotonation of the ligand and gave a blue solution from which was isolated air- and moisture-sensitive pink [Na 2 Nd 4 L 4 (CO 3 )(thf) 4 ] 1, in good yield.† Recrystallisation of 1 from 1,2-dimethoxyethane (dme) yielded the air- and moisture-sensitive pink complex [Na 2 Nd 4 L 4 (CO 3 )(dme) 2 ]·1.5 dme, 2·1.5 dme.† A synthesis in the absence of sodium carbonate gave a product with analytical composition NdL(thf) 2 which could not be crystallized in a form suitable for X-ray studies nor were the solubility properties suitable for characterization in solution. The molecular structures of both 1 and 2 (Fig. 1), established by X-ray crystallography,‡ feature a tetranuclear, bowl-shaped, cage [Nd 4 L 4 ] with quasi-twofold symmetry. Within the cavity of the cage resides a multiply anchored, solvated sodium carbonate molecule, Na 2 CO 3 LA 4 (LA = thf or LA 2 = dme). One carbonate oxygen bridges two sodium atoms, whilst each of the others bridges one sodium and two neodymium atoms. The carbonate coordination appears unique in combining m 6 - bridging with chelation to two of the bridged atoms (I). This contrasts the known simple m 6 -bridging 6 for the unique CO 3 22 in the centre of [(VO) 6 (m 6 -CO 3 )(m-CO 3 ) 3 (OH) 9 ] 52 , and the recently observed m 9 -bridging in a lithium siloxane complex. 7 Each sodium is five-coordinate, being bound not only by the chelating carbonate and thf or dme, but also by a bridging aryloxide oxygen of the cage (see below). Thus, sodium carbonate is securely bonded to the cage. The Nd 4 L 4 cage contains square-antiprismatic eight-coordi- nate neodymium atoms with Nd(1) and Nd(1a) of 2 different from Nd(1A) and Nd(1aA) (Fig. 1). The former are coordinated by two imide nitrogens, one h 1 - and two m-aryloxide (NdONd and NdONa) oxygens, one m 3 - and one m-alkoxide oxygen, and a m 3 - carbonate oxygen (ONd 2 Na). By contrast, the latter pair are Scheme 1 Fig. 1 Molecular projection of [Na 2 Nd 4 L 4 (CO 3 )(dme) 2 ] 2 normal to the quasi-twofold axis; hydrogen atoms have been omitted for clarity. Selected bond distances (Å): Nd–(h 1 -OAr), Nd(1)–O(22) 2.24(3), Nd(1a)–O(22a) 2.32(3), Nd(1A)–O(22aA) 2.35(2), Nd(1aA)–O(22A) 2.22(2); M–(m-OAr), Nd(1)–O(12) 2.26(1), Nd(1)–O(12aA) 2.57(2), Nd(1a)–O(12a) 2.34(1), Nd(1a)–O(12A) 2.61(2), Nd(1A)–O(12A) 2.42(2), Nd(1aA)–O(12aA) 2.39(2), Na(1)–O(12) 2.34(3), Na(1A)–O(12a) 2.25(3); M–(m-OCH), Nd(1)–O(10) 2.40(1), Nd(1a)–O(10a) 2.34(2), Nd(1A)–O(10) 2.36(2), Nd(1aA)–O(10a) 2.43(2); M–(m 3 -OCH), Nd(1)–O(20) 2.54(2), Nd(1a)–O(20a) 2.57(1), Nd(1A)–O(20) 2.47(1), Nd(1A)–O(20a) 2.46(2), Nd(1aA)–O(20) 2.49(2), Nd(1aA)–O(20a) 2.48(1); Na–(m-OCO 2 ), Na(1)–O(2) 2.37(2), Na(1A)–O(2) 2.35(2); M–(m 3 -OCO 2 ), Nd(1)–O(1) 2.51(2), Nd(1a)–O(1A) 2.48(2), Nd(1A)–O(1A) 2.56(1), Nd(1aA)–O(1) 2.51(1), Na(1)–O(1) 2.56(1), Na(1A)– O(1A) 2.50(1); Nd–N, 2.51(2)–2.63(2); Na–O(dme), 2.48(2)–2.60(2). Se- lected bond angles (°) O(1)–C(1)–O(1A) 123(1), O(1)–C(1)–O(2) 117(2), O(1A)–C(1)–O(2) 120(2). Chem. Commun., 1997 341 Published on 01 January 1997. 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