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Synthesis and structure of a Zwitterionic Nd complex containing aminophenoxide ligands
Journal of Molecular Structure 478 (1999) 139–143
Synthesis and structure of a Zwitterionic Nd complex containing aminophenoxide ligands Pingrong Wei, David A. Atwood* Department of Chemistry, The University of Kentucky, Lexington, KY 40506-0055, USA Received 26 May 1998; accepted 8 October 1998
Abstract In the course of attempting to prepare molecular precursors to lanthanide-aluminum oxide materials the unique Zwitterionic complex, Nd(H2L)3(CF3SO3)3 (1), was discovered (L [2,4-( tBu)2-6-(CH2N iPr)PhO]). In the crystal structure of (1) the threetriflate groups and the three oxygens of the aminophenoxide ligand (H2L) coordinate the Nd atom. To maintain charge balance the three ligands are protonated at the amine nitrogens. This explains the fact that the ligand is monodentate and does not displace one (or more) of the triflate groups to form a chelated cation. Both hydrogens of the ammonium groups are hydrogenbonded to oxygens of the triflates. 䉷 1999 Elsevier Science B.V. All rights reserved. Keywords: Aminophenoxide; Chelate; Neodymium; Triflate
1. Introduction The lanthanide elements have far-ranging applications in materials science [1]. They are used in the fabrication of superconducting ma materials [2], magnetic materials [3], and more recently, in the catalytic converters of automobiles [4]. They also have important uses as magnetic resonance imaging contrast agents [5], and as Lewis acid catalysts [6]. The ability of these elements to adopt coordination numbers from six to twelve provides a rich and variable structural chemistry. Elucidation of the structures these elements adopt is important if applications are to be targeted in a rational, systematic manner. While a great deal of information is now known about these elements surprises still occur. One such surprise, Nd(H2L)3(CF3SO3)3 (1), will be reported here. It
* Corresponding author.
contains Zwitterionic aminophenoxide ligands and monodentate triflate groups.
2. Experimental General: All manipulations were conducted using Schlenk techniques in conjunction to an inert atmosphere glove box. All solvents were rigorously dried prior to use. NMR data were obtained on JEOL-GSX400 and -270 instruments at 270.17 ( 1H) and are reported relative to SiMe4 and (in ppm). Elemental analyses were obtained on a Perkin–Elmer 2400 Analyzer and were consistent with the given formulation for (1). The complex L2AlLi(thf)2 (L [2,4( tBu)2-6-(CH2N iPr)PhO]) was prepared according to the literature [7]. Preparation of Nd(H2L)3(CF3SO3)3 (1): To a solution of L2AlLi(thf)2 (0.65 g, 0.89 mmol) in thf (20 ml) was added a solution of Nd(CF3SO3)3 (0.53 g,
0022-2860/99/$ - see front matter 䉷 1999 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(98)00655-3
140
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
Table 1 Data collection and processing parameters for compound (1) Compounds Formula Formula weight Colour, habit Crystal size (mm 3) Crystal system Space group ˚) a (A ˚) c (A a (⬚) g (⬚) ˚ 3) V (A Z F(000) D(calcd) (g cm ⫺3) m(mm ⫺1) Collection range; 2u max Unique data measured Observed data, n No. of variables, p R1 wR2 S (goodness of fit)
1 C19H31NO4F3SNd0.33 474.59 pale blue prism 0.50 × 0.25 × 0.20 Trigonal R -3 18.372(1) 83.359(4) 90 120 24369(2) 36 8892 1.164 0.784 ^ h, ^ k, ^ l; 45⬚ 1869 1834 [F ⱖ 4s (F)] 253 0.053 0.136 1.27
0.89 mmol) in thf (20 ml). The resulting mixture was stirred for 6 h at room temperature. After filtration and concentration, pale blue crystals were grown at ⫺30⬚C (0.45 g, 37%). Mp 186⬚C (dec); 1H NMR (270 MHz, d 6-DMSO): d 1.04 (d, 6H, CHCH3), 1.21 (s, 9H, CCH3), 1.33 (s, 9H, CCH3), 2.74 (m, 1H, NCH), 3.83 (s, 2H, PhCH2), 6.87 (d, 1H, PhH), 7.05 (d, 1H, PhH).
3. Structure determination X-ray Data for 1 was collected on a Siemens SMART-CCD unit with Moka radiation. The position of the Nd atom was determined with a Patterson function. Subsequently, the structure was refined using the Siemens software package SHELXTL 4.0. All of the non-hydrogen atoms were refined anisotropically with the exception of three of the ligand tBu groups. These were disordered and modeled by dividing the occupancy for each atom across two atom positions. This provided a symmetric model consisting of six atoms having half-occupancy each. Except for the disordered carbons and the ammonium hydrogen, hydrogens were put into calculated
positions. The ammonium hydrogens were originally found from the difference Fourier maps and then put into positions fixed to the attached nitrogen. Absorption corrections were not employed. Further details of the structure analysis are given in Table 1. Positional parameters and selected bond lengths and angles are presented in Tables 2 and 3, respectively.
4. Results and discussion As part of a program to prepare molecular precursors to mixed-metal oxide solid-state materials the combination of various aluminates with Nd(OTf)3 was examined. The goal was to prepare mixed-metal derivatives supported by a range of bidentate aminophenoxide ligands (Scheme 1a). Unfortunately, these reactions have led, up to the present, to ill-defined products. In only one instance was a well-characterized product obtained (Scheme 1b). This product (compound 1) is apparently the result of addition of adventitious water to the reaction mixture. It should be noted, however, that it is often difficult to prevent water from adding to a reaction containing lanthanide reagents even under inert conditions. For example, this can be observed in the formation of Ln5(OiPr)13(m5-O) in aged samples of Ln(OiPr)3 (Ln Yb [8], La, Y) [9]. Compound (1) is soluble in thf and dmso. A 1H NMR spectrum of (1) in the latter solvent demonstrates that the solution structure contains equivalent environments for the three ligands. Based upon the fact that the nitrogens are protonated, it is likely that the triflate groups remain coordinated in solution and that the ligands remain monodentate. The equivalence of the three ligands and three triflate groups are evident in the crystal structure of (1). In the structure there is a three-fold axis of symmetry passing through the Nd atom. It is coordinated by six oxygen atoms in a trigonally distorted octahedral arrangement, three from the ligand and three from the triflates. It is interesting to note that the ligands are grouped so that all three of each occupies one triangular face. By comparison, the structure of [La(OTf)3(thf)(tetraethyleneglycol)], contains OTf groups that are evenly distributed about the central metal [6]. The unusual ligand arrangement in (1) can be attributed to intramolecular hydrogen bonding
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
141
Table 2 ˚ 2 × 10 3) for compound (1) a Atomic coordinates ( × 10 4 for atoms), equivalent isotropic thermal parameters (A Atom
x
y
z
Ueq
Nd(H2L)3(CF3SO3)3 (1) Nd(1) O(1) O(2) O(3) O(4) N(1) S(1) F(1) F(2) F(3) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(10 0 ) C(11) C(11 0 ) C(12) C(12 0 ) C(13) C(14) C(15) C(16) C(17) C(18) C(19)
3333 2658(3) 3872(3) 2912(4) 4403(4) 3003(5) 3728(2) 3202(6) 4508(7) 3625(5) 2361(6) 1746(6) 1357(6) 692(7) 898(7) 2027(7) 1505(6) 1823(7) 1535(7) 1956(16) 1087(22) 1836(14) 2256(19) 557(16) 755(20) 2403(7) 2672(5) 3329(5) 2506(6) 2248(9) 2986(8) 3759(11)
6667 5383(4) 7766(4) 8294(4) 9240(4) 4212(5) 8422(2) 7595(6) 8462(5) 8897(5) 4628(7) 4342(6) 4858(6) 4404(7) 4997(7) 5700(7) 3562(7) 3052(6) 2202(7) 1725(16) 1498(22) 2410(14) 2059(19) 1622(16) 1858(20) 3330(7) 4102(6) 4391(6) 3319(6) 3321(8) 2868(7) 8338(9)
145(1) 250(1) ⫺ 74(1) ⫺ 103(1) ⫺ 102(1) ⫺ 23(1) ⫺ 134(1) ⫺ 401(1) ⫺ 395(1) ⫺ 418(1) 321(1) 445(1) 505(1) 638(1) 365(1) 570(1) 512(1) 468(1) 553(1) 479(3) 401(4) 737(3) 588(4) 536(3) 644(4) 346(1) 270(1) 146(1) ⫺ 81(1) ⫺ 255(2) ⫺ 66(2) ⫺ 348(2)
40(1) 50(2) 56(2) 83(2) 78(2) 60(2) 55(1) 139(3) 133(3) 136(3) 45(2) 44(2) 53(3) 91(4) 82(3) 82(3) 55(3) 56(3) 85(4) 97(8) 150(11) 85(7) 128(10) 92(8) 125(10) 60(3) 43(2) 50(3) 71(3) 117(5) 104(4) 89(4)
a
The atoms C(10),C(11) and C(12) in compound (1) have half site occupancy.
Table 3 ˚ ) and angles (⬚) for compound (1) a Selected bond distances (A Nd(H2L)3(CF3SO3)3 (1) Nd(1)– O(1) Nd(1)– O(2) N(1)– O(3a) N(1)– O(4b) O(1a)– Nd(1)– O(1) O(1)– Nd(1)– O(2b) O(1)– Nd(1)– O(2) O(2b)– Nd(1)– O(2) O(1)– Nd(1)– O(2a)
2.224(6) 2.526(6) 2.907 3.113 105.4(2) 86.8(2) 157.0(2) 73.7(2) 89.4(2)
Symmetry code for (1): (a), ⫺ x ⫹ y, ⫺ x ⫹ 1, z; (b), ⫺ y ⫹ 1, x ⫺ y ⫹ 1, z. a
between the ammonium hydrogens and oxygens of the triflates (Figs. 1 and 2). Specifically, the contacts are ˚ ) and O3…H1B (2.04 A ˚ ). between O4…H1A (2.35 A There are six of these contacts in the molecule forming a network around the ‘‘top’’ of the molecule. While the distances are not accurate (the hydrogens are fixed) it is clear from the orientation of the groups involved that such bonding exists. The most closely related complexes to (1) are those containing tripodal amine phenol ligands such as tren (tris(2-aminoethyl)amine). In their most simple form the structures of these complexes contain a sevencoordinate metal with the oxygens and nitrogens of one ligand coordinated to the metal [10,11]. The
142
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
Scheme 1. General syntheses related to the formation of (1).
Nd–O distances in (1) (Table 3) are similar to those ˚ ) [10]. These observed in (Saltren)Nd ( t 2.2 A tripodal ligands can adopt other geometries depending on the synthetic conditions [11,12]. This includes a ‘‘capped’’ derivative ((L)Ln(NO3)3) in which only the oxygens of the ligand are coordinated to the metal. The ligand and nitrates occupy opposite sides of a distorted octahedron. There is intramolecular hydrogen bonding within the ligand (NH…O) of these derivatives although this interaction does not dictate the observed geometry. By comparison, it appears that the hydrogen-bonding interaction in (1) does causes the observed geometry. Fig. 1. Molecular structure of (1) with hydrogen atoms omitted for clarity.
Acknowledgements This work was supported by the donors of the Petroleum Research Fund (Grant 31901-AC3), administered by the American Chemical Society. The receipt of an NSF-CAREER award (CHE 9625376) is also gratefully acknowledged.
References
Fig. 2. Molecular structure of (1) emphasizing the hydrogenbonding interactions.
[1] L.G. Hubert-Pfalzgraf, New. J. Chem. 19 (1995) 727. [2] R.J. Cava, Scientific American, (1990) 42. [3] J.-P. Sutter, M.L. Kahn, S. Golhen, L. Ouahab, O. Kahn, Chem. Eur. J. 4 (1998) 571 (and references therein). [4] C.K. Narula, Mat. Res. Soc. Symp. Proc. 271 (1992) 181; C.K. Narula, W.H. Weber, J.Y. Ying, L.F. Allard, J. Mater. Chem. 7 (1997) 1821. [5] R.B. Lauffer, Chem. Rev. 87 (1987) 901; K. Micskei, L. Helm, E. Brucher, A.E. Merbach, Inorg. Chem. 32 (1993) 3844; K. Kumar, M.F. Tweedle, Pure Appl. Chem. 65 (1993) 515; C.F.G. Geraldes, A.M. Urbano, M.C. Alpoin, A.D. Sherry, K.T. Kuan, R. Rajagopalan, F. Maton, R.M. Muller, Magn.
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
[6]
[7] [8] [9]
Res. Imaging (1995) 401; S. Aime, A. Barge, F. Benetollo, G. Bombieri, M. Botta, F. Uggeri, Inorg. Chem. 36 (1997) 4287. H.C. Aspinall, J.L.M. Dwyer, N. Greeves, E.G. McIver, J.C. Wooley, Organometallics 17 (1998) 1884 (and references therein). M.S. Hill, D.A. Atwood, Main Group Chem. 1998, in press. P. Wei, D.A. Atwood, Angew, manuscript in preparation. P.S. Coan, L.G. Hubert-Pfalzgraf, K.G. Caulton, Inorg. Chem. 31 (1992) 1262.
143
[10] M. Kanesato, T. Yokoyama, O. Itabashi, T.M. Suzuki, M. Shiro, Bull. Chem. Soc. Jpn. 69 (1996) 1297. [11] L.-W. Yang, S. Liu, E. Wong, S.J. Rettig, C. Orvig, Inorg. Chem. 34 (1995) 2164. [12] S. Liu, L. Gelmini, S.J. Rettig, R.C. Thompson, C. Orvig, J. Am. Chem. Soc. 114 (1992) 6081; S. Liu, L.-W. Yang, S.J. Rettig, C. Orvig, Inorg. Chem. 32 (1993) 2773.
Synthesis and structure of a Zwitterionic Nd complex containing aminophenoxide ligands Pingrong Wei, David A. Atwood* Department of Chemistry, The University of Kentucky, Lexington, KY 40506-0055, USA Received 26 May 1998; accepted 8 October 1998
Abstract In the course of attempting to prepare molecular precursors to lanthanide-aluminum oxide materials the unique Zwitterionic complex, Nd(H2L)3(CF3SO3)3 (1), was discovered (L [2,4-( tBu)2-6-(CH2N iPr)PhO]). In the crystal structure of (1) the threetriflate groups and the three oxygens of the aminophenoxide ligand (H2L) coordinate the Nd atom. To maintain charge balance the three ligands are protonated at the amine nitrogens. This explains the fact that the ligand is monodentate and does not displace one (or more) of the triflate groups to form a chelated cation. Both hydrogens of the ammonium groups are hydrogenbonded to oxygens of the triflates. 䉷 1999 Elsevier Science B.V. All rights reserved. Keywords: Aminophenoxide; Chelate; Neodymium; Triflate
1. Introduction The lanthanide elements have far-ranging applications in materials science [1]. They are used in the fabrication of superconducting ma materials [2], magnetic materials [3], and more recently, in the catalytic converters of automobiles [4]. They also have important uses as magnetic resonance imaging contrast agents [5], and as Lewis acid catalysts [6]. The ability of these elements to adopt coordination numbers from six to twelve provides a rich and variable structural chemistry. Elucidation of the structures these elements adopt is important if applications are to be targeted in a rational, systematic manner. While a great deal of information is now known about these elements surprises still occur. One such surprise, Nd(H2L)3(CF3SO3)3 (1), will be reported here. It
* Corresponding author.
contains Zwitterionic aminophenoxide ligands and monodentate triflate groups.
2. Experimental General: All manipulations were conducted using Schlenk techniques in conjunction to an inert atmosphere glove box. All solvents were rigorously dried prior to use. NMR data were obtained on JEOL-GSX400 and -270 instruments at 270.17 ( 1H) and are reported relative to SiMe4 and (in ppm). Elemental analyses were obtained on a Perkin–Elmer 2400 Analyzer and were consistent with the given formulation for (1). The complex L2AlLi(thf)2 (L [2,4( tBu)2-6-(CH2N iPr)PhO]) was prepared according to the literature [7]. Preparation of Nd(H2L)3(CF3SO3)3 (1): To a solution of L2AlLi(thf)2 (0.65 g, 0.89 mmol) in thf (20 ml) was added a solution of Nd(CF3SO3)3 (0.53 g,
0022-2860/99/$ - see front matter 䉷 1999 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(98)00655-3
140
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
Table 1 Data collection and processing parameters for compound (1) Compounds Formula Formula weight Colour, habit Crystal size (mm 3) Crystal system Space group ˚) a (A ˚) c (A a (⬚) g (⬚) ˚ 3) V (A Z F(000) D(calcd) (g cm ⫺3) m(mm ⫺1) Collection range; 2u max Unique data measured Observed data, n No. of variables, p R1 wR2 S (goodness of fit)
1 C19H31NO4F3SNd0.33 474.59 pale blue prism 0.50 × 0.25 × 0.20 Trigonal R -3 18.372(1) 83.359(4) 90 120 24369(2) 36 8892 1.164 0.784 ^ h, ^ k, ^ l; 45⬚ 1869 1834 [F ⱖ 4s (F)] 253 0.053 0.136 1.27
0.89 mmol) in thf (20 ml). The resulting mixture was stirred for 6 h at room temperature. After filtration and concentration, pale blue crystals were grown at ⫺30⬚C (0.45 g, 37%). Mp 186⬚C (dec); 1H NMR (270 MHz, d 6-DMSO): d 1.04 (d, 6H, CHCH3), 1.21 (s, 9H, CCH3), 1.33 (s, 9H, CCH3), 2.74 (m, 1H, NCH), 3.83 (s, 2H, PhCH2), 6.87 (d, 1H, PhH), 7.05 (d, 1H, PhH).
3. Structure determination X-ray Data for 1 was collected on a Siemens SMART-CCD unit with Moka radiation. The position of the Nd atom was determined with a Patterson function. Subsequently, the structure was refined using the Siemens software package SHELXTL 4.0. All of the non-hydrogen atoms were refined anisotropically with the exception of three of the ligand tBu groups. These were disordered and modeled by dividing the occupancy for each atom across two atom positions. This provided a symmetric model consisting of six atoms having half-occupancy each. Except for the disordered carbons and the ammonium hydrogen, hydrogens were put into calculated
positions. The ammonium hydrogens were originally found from the difference Fourier maps and then put into positions fixed to the attached nitrogen. Absorption corrections were not employed. Further details of the structure analysis are given in Table 1. Positional parameters and selected bond lengths and angles are presented in Tables 2 and 3, respectively.
4. Results and discussion As part of a program to prepare molecular precursors to mixed-metal oxide solid-state materials the combination of various aluminates with Nd(OTf)3 was examined. The goal was to prepare mixed-metal derivatives supported by a range of bidentate aminophenoxide ligands (Scheme 1a). Unfortunately, these reactions have led, up to the present, to ill-defined products. In only one instance was a well-characterized product obtained (Scheme 1b). This product (compound 1) is apparently the result of addition of adventitious water to the reaction mixture. It should be noted, however, that it is often difficult to prevent water from adding to a reaction containing lanthanide reagents even under inert conditions. For example, this can be observed in the formation of Ln5(OiPr)13(m5-O) in aged samples of Ln(OiPr)3 (Ln Yb [8], La, Y) [9]. Compound (1) is soluble in thf and dmso. A 1H NMR spectrum of (1) in the latter solvent demonstrates that the solution structure contains equivalent environments for the three ligands. Based upon the fact that the nitrogens are protonated, it is likely that the triflate groups remain coordinated in solution and that the ligands remain monodentate. The equivalence of the three ligands and three triflate groups are evident in the crystal structure of (1). In the structure there is a three-fold axis of symmetry passing through the Nd atom. It is coordinated by six oxygen atoms in a trigonally distorted octahedral arrangement, three from the ligand and three from the triflates. It is interesting to note that the ligands are grouped so that all three of each occupies one triangular face. By comparison, the structure of [La(OTf)3(thf)(tetraethyleneglycol)], contains OTf groups that are evenly distributed about the central metal [6]. The unusual ligand arrangement in (1) can be attributed to intramolecular hydrogen bonding
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
141
Table 2 ˚ 2 × 10 3) for compound (1) a Atomic coordinates ( × 10 4 for atoms), equivalent isotropic thermal parameters (A Atom
x
y
z
Ueq
Nd(H2L)3(CF3SO3)3 (1) Nd(1) O(1) O(2) O(3) O(4) N(1) S(1) F(1) F(2) F(3) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(10 0 ) C(11) C(11 0 ) C(12) C(12 0 ) C(13) C(14) C(15) C(16) C(17) C(18) C(19)
3333 2658(3) 3872(3) 2912(4) 4403(4) 3003(5) 3728(2) 3202(6) 4508(7) 3625(5) 2361(6) 1746(6) 1357(6) 692(7) 898(7) 2027(7) 1505(6) 1823(7) 1535(7) 1956(16) 1087(22) 1836(14) 2256(19) 557(16) 755(20) 2403(7) 2672(5) 3329(5) 2506(6) 2248(9) 2986(8) 3759(11)
6667 5383(4) 7766(4) 8294(4) 9240(4) 4212(5) 8422(2) 7595(6) 8462(5) 8897(5) 4628(7) 4342(6) 4858(6) 4404(7) 4997(7) 5700(7) 3562(7) 3052(6) 2202(7) 1725(16) 1498(22) 2410(14) 2059(19) 1622(16) 1858(20) 3330(7) 4102(6) 4391(6) 3319(6) 3321(8) 2868(7) 8338(9)
145(1) 250(1) ⫺ 74(1) ⫺ 103(1) ⫺ 102(1) ⫺ 23(1) ⫺ 134(1) ⫺ 401(1) ⫺ 395(1) ⫺ 418(1) 321(1) 445(1) 505(1) 638(1) 365(1) 570(1) 512(1) 468(1) 553(1) 479(3) 401(4) 737(3) 588(4) 536(3) 644(4) 346(1) 270(1) 146(1) ⫺ 81(1) ⫺ 255(2) ⫺ 66(2) ⫺ 348(2)
40(1) 50(2) 56(2) 83(2) 78(2) 60(2) 55(1) 139(3) 133(3) 136(3) 45(2) 44(2) 53(3) 91(4) 82(3) 82(3) 55(3) 56(3) 85(4) 97(8) 150(11) 85(7) 128(10) 92(8) 125(10) 60(3) 43(2) 50(3) 71(3) 117(5) 104(4) 89(4)
a
The atoms C(10),C(11) and C(12) in compound (1) have half site occupancy.
Table 3 ˚ ) and angles (⬚) for compound (1) a Selected bond distances (A Nd(H2L)3(CF3SO3)3 (1) Nd(1)– O(1) Nd(1)– O(2) N(1)– O(3a) N(1)– O(4b) O(1a)– Nd(1)– O(1) O(1)– Nd(1)– O(2b) O(1)– Nd(1)– O(2) O(2b)– Nd(1)– O(2) O(1)– Nd(1)– O(2a)
2.224(6) 2.526(6) 2.907 3.113 105.4(2) 86.8(2) 157.0(2) 73.7(2) 89.4(2)
Symmetry code for (1): (a), ⫺ x ⫹ y, ⫺ x ⫹ 1, z; (b), ⫺ y ⫹ 1, x ⫺ y ⫹ 1, z. a
between the ammonium hydrogens and oxygens of the triflates (Figs. 1 and 2). Specifically, the contacts are ˚ ) and O3…H1B (2.04 A ˚ ). between O4…H1A (2.35 A There are six of these contacts in the molecule forming a network around the ‘‘top’’ of the molecule. While the distances are not accurate (the hydrogens are fixed) it is clear from the orientation of the groups involved that such bonding exists. The most closely related complexes to (1) are those containing tripodal amine phenol ligands such as tren (tris(2-aminoethyl)amine). In their most simple form the structures of these complexes contain a sevencoordinate metal with the oxygens and nitrogens of one ligand coordinated to the metal [10,11]. The
142
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
Scheme 1. General syntheses related to the formation of (1).
Nd–O distances in (1) (Table 3) are similar to those ˚ ) [10]. These observed in (Saltren)Nd ( t 2.2 A tripodal ligands can adopt other geometries depending on the synthetic conditions [11,12]. This includes a ‘‘capped’’ derivative ((L)Ln(NO3)3) in which only the oxygens of the ligand are coordinated to the metal. The ligand and nitrates occupy opposite sides of a distorted octahedron. There is intramolecular hydrogen bonding within the ligand (NH…O) of these derivatives although this interaction does not dictate the observed geometry. By comparison, it appears that the hydrogen-bonding interaction in (1) does causes the observed geometry. Fig. 1. Molecular structure of (1) with hydrogen atoms omitted for clarity.
Acknowledgements This work was supported by the donors of the Petroleum Research Fund (Grant 31901-AC3), administered by the American Chemical Society. The receipt of an NSF-CAREER award (CHE 9625376) is also gratefully acknowledged.
References
Fig. 2. Molecular structure of (1) emphasizing the hydrogenbonding interactions.
[1] L.G. Hubert-Pfalzgraf, New. J. Chem. 19 (1995) 727. [2] R.J. Cava, Scientific American, (1990) 42. [3] J.-P. Sutter, M.L. Kahn, S. Golhen, L. Ouahab, O. Kahn, Chem. Eur. J. 4 (1998) 571 (and references therein). [4] C.K. Narula, Mat. Res. Soc. Symp. Proc. 271 (1992) 181; C.K. Narula, W.H. Weber, J.Y. Ying, L.F. Allard, J. Mater. Chem. 7 (1997) 1821. [5] R.B. Lauffer, Chem. Rev. 87 (1987) 901; K. Micskei, L. Helm, E. Brucher, A.E. Merbach, Inorg. Chem. 32 (1993) 3844; K. Kumar, M.F. Tweedle, Pure Appl. Chem. 65 (1993) 515; C.F.G. Geraldes, A.M. Urbano, M.C. Alpoin, A.D. Sherry, K.T. Kuan, R. Rajagopalan, F. Maton, R.M. Muller, Magn.
P. Wei, D.A. Atwood / Journal of Molecular Structure 478 (1999) 139–143
[6]
[7] [8] [9]
Res. Imaging (1995) 401; S. Aime, A. Barge, F. Benetollo, G. Bombieri, M. Botta, F. Uggeri, Inorg. Chem. 36 (1997) 4287. H.C. Aspinall, J.L.M. Dwyer, N. Greeves, E.G. McIver, J.C. Wooley, Organometallics 17 (1998) 1884 (and references therein). M.S. Hill, D.A. Atwood, Main Group Chem. 1998, in press. P. Wei, D.A. Atwood, Angew, manuscript in preparation. P.S. Coan, L.G. Hubert-Pfalzgraf, K.G. Caulton, Inorg. Chem. 31 (1992) 1262.
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