Design, Synthesis, and X-ray Structural Characterization of New

Feb 12, 1997 - Synopsis. Four new dinucleating macrocyclic ligands were synthesized by the [2+2] condensation of dialdehydes and bis(primary amines). ...
0 downloads 7 Views 219KB Size
Download PDF
Inorg. Chem. 1997, 36, 629-636

629

Design, Synthesis, and X-ray Structural Characterization of New Dinucleating Macrocyclic Ligands and a Novel Phenolate-Bridged Dilanthanum(III) Complex Zheng Wang, Joseph Reibenspies, and Arthur E. Martell* Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255 ReceiVed June 5, 1996X

The [2+2] template condensation of 6,6′-bis(aminomethyl)-2,2′-bipyridyl with 2,6-diformyl-p-cresol in the presence of lanthanum acetate yields a homodinuclear complex of a Schiff base macrocycle (babp)2(dfc)2, 1. The crystal of [La21(OAc)4]‚4CH3CN‚3H2O is triclinic, space group P1h, with cell constants a ) 10.986(6) Å, b ) 12.231(8) Å, c ) 23.818(12) Å, R ) 86.63(5)°, β ) 85.99(5)°, γ ) 79.45(4)°, V ) 3135(3) Å3, and Z ) 2. The decacoordination geometry around each identical La3+ ion is a bicapped dodecahedron made up of two bidentate acetate anions, two phenolate oxygens, and four imine nitrogens. The 1H, 13C, and 2D-COSY NMR and UVvisible spectra of the complex are consistent with the solid state structural information obtained by IR and X-ray diffraction studies. Treatment of a solution of La21(OAc)4 in methanol with sodium cyanotrihydroborate yields the hydrogenated octaaza macrocycle R(babp)2(dfc)2, 2. The [2+2] metal-free condensation of 2,6-bis(aminomethyl)-p-cresol with 2,6-diformylpyridine yields a Schiff base macrocycle (bac)2(dfp)2, 3. Reduction of 3 with sodium borohydride yields the hydrogenated hexaaza macrocycle R(bac)2(dfp)2, 4. Under strongly acidic conditions (48% HBr), the free ligand 4 crystallizes as a hydrobromide salt 4‚H2O‚7HBr in the monoclinic system, space group C2/m, with cell constants a ) 26.737(11) Å, b ) 16.885(7) Å, c ) 10.325(4) Å, β ) 101.94(3)°, V ) 4560(3) Å3, and Z ) 4. The [2+2] nature of the macrocycles 3 and 4 is identified by 1H and 13C NMR, FAB mass spectra and by X-ray crystallography.

Introduction In recent years the design and synthesis of dinucleating macrocyclic ligands and their dinuclear complexes have been a fascinating area of research, owing to their importance in basic and applied chemistry.1,2 Particular interest has developed in dinuclear complexes as models for metalloproteins.3-5 Several polypodal dinucleating ligands have been employed to synthesize diiron complexes as models for iron-oxo proteins.6,7 However, very limited work has been reported on macrocyclic diiron complexes thus far.8,9 Our interest in macrocyclic diiron X Abstract published in AdVance ACS Abstracts, January 1, 1997. (1) (a) Izatt, R. M.; Pawlak, K.; Bradshaw, J. S. Chem. ReV. 1995, 95, 2529. (b) Mountford, H. S.; MacQueen, D. B.; Li, A.; Otvos, J. W.; Calvin, M.; Frankel, R. B.; Spreer, L. O. Inorg. Chem. 1994, 33, 1748. (c) Asato, E.; Furutachi; H.; Kawahashi, T.; Mikuriya, M. J. Chem. Soc., Dalton Trans. 1995, 3897. (2) (a) Menif, R.; Martell, A. E.; Squattrito, P. J.; Clearfield, A. Inorg. Chem. 1990, 29, 4723. (b) Chen, D.; Martell, A. E. Tetrahedron 1991, 47, 6895. (c) Nelson, S. M.; Knox, C. V.; McCann, M.; Drew, M. G. B. J. Chem. Soc., Dalton Trans. 1981, 1669. (3) (a) McKee, V. AdV. Inorg. Chem. 1993, 40, 323. (b) McKee, V.; Tandon, S. S. J. Chem. Soc., Chem. Commum. 1988, 385. (4) (a) Armstrong, W. H.; Lippard, S. J. J. Am. Chem. Soc. 1983, 105, 4837. (b) Jaynes, B. S.; Doerrer, L. H.; Liu, S.; Lippard, S. J. Inorg. Chem. 1995, 34, 5735. (5) Asato, E.; Furutachi; H.; Kawahashi, T.; Mikuriya, M. J. Chem. Soc., Dalton Trans. 1995, 3897. (6) (a) Kojima, T.; Leising, R. A.; Yan, S.; Que, L., Jr. J. Am. Chem. Soc. 1993, 115, 11328. (b) Borovik, A. S.; Hendrich, M. P.; Holman, T. R.; Mu¨nck, E.; Papaefthymiou, V.; Que, L., Jr. J. Am. Chem. Soc. 1990, 112, 6031. (c) Borovik, A. S.; Que, L., Jr.; Papaefthymiou, V.; Mu¨nck, E.; Taylar, L. F.; Anderson, O. P. J. Am. Chem. Soc. 1988, 110, 1986. (7) (a) Maeda, Y.; Kawano, K.; Oniki, T. J. Chem. Soc., Dalton Trans. 1995, 3533. (b) Campbell, V. D.; Parsons, E. J.; Pennington, W. T. Inorg. Chem. 1993, 32, 1773. (8) (a) Timken, M. D.; Marritt, W. A.; Hendrickson, D. N.; Gagne, R. A.; Sinn, E. Inorg. Chem. 1985, 24, 4202. (b) Nanda, K. K.; Dutta, S. K.; Baitalik, S.; Venkatsubramanian, K.; Nag, K. J. Chem. Soc., Dalton Trans. 1995, 1239. (9) Sessler, J. L.; Sibert, J. W.; Lynch, V.; Markert, J. T.; Wooten, C. L. Inorg. Chem. 1993, 32, 621.

S0020-1669(96)00665-9 CCC: $14.00

complexes has led us to explore reliable routes for the synthesis of dinucleating macrocyclic ligands which contain donor groups having special affinity for iron centers, such as bipyridine, pyridine, and phenol. Our approach to dinucleating macrocyclic ligands has been based on the [2+2] condensation synthesis of large tetrakis(Schiff base) macrocycles with appropriate dicarbonyl and polyamine precursors and hydrogenation of the Schiff bases. In particular, lanthanide(III) ions have been employed as effective template agents in synthesis of large macrocyclic tetrakis(Schiff base) macrocycles.10,11 Also, macrocyclic complexes of lanthanides are currently attracting much attention as radiopharmaceuticals in medical applications, as contrastenhancing agents in magnetic resonance imaging.12,13 Dinuclear lanthanide complexes have also been used to study the nature and application of lanthanide metal-metal interactions in phosphors, and they have been used as luminescence probes to determine the metal-ligand interactions and the local coordination symmetry.14,15 This paper describes the successful synthesis and characterization of a series of four new dinucleating polyaza macrocyclic (10) (a) Alexander, V. Chem. ReV. 1995, 95, 273. (b) Guerriero, P.; Vigato, P. A.; Fenton, D. E.; Hellier, P. C. Acta Chem. Scand. 1992, 46, 1025. (11) (a) Fenton, D. E.; Vigato, P. A. Chem. Soc. ReV. 1988, 17, 69. (b) Aime, S.; Botta, M.; Casellato, U.; Tamburini, S.; Vigato, P. A. Inorg. Chem. 1995, 34, 5825. (c) Smith, P. H.; Brainard, J. R.; Morris, D. E.; Jarvinen, G. D.; Ryan, R. R. J. Am. Chem. Soc. 1989, 111, 7437. (12) (a) De Cola, L.; Smailes, D. L.; Vallarino, L. M. Inorg. Chem. 1986, 25, 1729. (b) Guerriero, P.; Casellato, U.; Tamburini, S.; Vigato, P. A.; Graziani, R. Inorg. Chim. Acta 1987, 129, 127. (c) Lauffer, R. B. Chem. ReV. 1987, 87, 901. (13) (a) Moonen, C. T.; van-Zijil, P. C.; Frank, J. A.; Le-Bihan, D.; Becker, E. D. Science 1990, 250, 53. (b) Sink, R. M.; Buster, D. C.; Sherry, A. D. Inorg. Chem. 1990, 29, 3645. (c) Franklin, S. J.; Raymond, K. N. Inorg. Chem. 1994, 33, 5794. (14) (a) Kahwa, I. A.; Folkes, S.; Williams, D. J.; Ley, S. V.; O’Mahoney, C. A.; McPherson, G. L. J. Chem. Soc., Chem. Commun. 1989, 1531. (b) Matthews, K. D.; Kahwa, I. A.; Williams, D. J. Inorg. Chem. 1994, 33, 1382. (c) Harrowfield, J. M.; Ogden, M. I.; White, A. H. Aust. J. Chem. 1991, 44, 1249. (d) Ziessel, R.; Maestri, M.; Prodi, L.; Balzani, V.; Dorssedaer, A. V. Inorg. Chem. 1993, 32, 1237.

© 1997 American Chemical Society

630 Inorganic Chemistry, Vol. 36, No. 4, 1997 Chart 1

ligands containing aromatic phenol, pyridine, or bipyridine units (see formulas 1-4, Chart 1). The crystal structures of one of the new ligands, 4, and a novel phenolate-bridged dilanthanum(III) complex of 1 are reported. Experimental Section Caution! Care must be exercised in handling cyanide compounds. All operations should be performed in a well-ventilated hood. Materials. 6,6′-Bis(aminomethyl)-2,2′-bipyridyl trihydrobromide,16 2,6-diformyl-p-cresol,17 2,6-diformylpyridine,18 2,6-bis(aminomethyl)pyridine,19 and 2,6-bis(aminomethyl)-p-cresol hydrochloride20 were synthesized and purified by previously described methods. Lanthanum acetate hydrate (99.9%), sodium cyanotrihydroborate (95%), and sodium borohydride (98%) were obtained from Aldrich Chemical Co. Diethylenetriaminepentaacetic acid (DTPA) was supplied by J. T. Baker Chemical Co. Deuterated solvents CDCl3 (99.8%), D2O (99.9%), CD3OD (99.8%), and CD3CN (99.9%) were obtained from Cambridge Isotope Laboratories and used for NMR measurements without further purification. All other chemicals and solvents were of reagent grade and were used as received. Physicochemical Measurements. IR spectra were recorded as KBr pellets in the range 4000-400 cm-1 on a Mattson Galaxy Series FTIR 5000 spectrometer, and ultraviolet-visible spectra were recorded on a Perkin-Elmer 553 spectrophotometer. Melting points were determined on a Fisher-Johns apparatus. Elemental analyses were performed by Galbraith Laboratories, Inc., Knoxville, TN. All 1H, 13C, and 1H-1H 2D-COSY (homonuclear correlated spectroscopy) NMR spectra were measured with a Varian XL200 FT spectrometer. Chemical shifts are reported as δ (ppm) downfield relative to external tetramethylsilane or (15) (a) Killian, H. S.; Van Herwijnen, F. P.; Blasse, G. J. Solid State Chem. 1988, 74, 39. (b) Moret, E.; Nicolo, F.; Planchered, D.; Froidevanx, P.; Bu¨nzli, J.-C. G.; Chapuis, G. HelV. Chim. Acta 1991, 74, 65. (c) Richardson, F. S. Chem. ReV. 1982, 82, 541. (16) Wang, Z.; Reibenspies, J.; Motekaitis, R. J.; Martell, A. E. J. Chem. Soc., Dalton Trans. 1995, 1511. (17) (a) Moore, K.; Vigee, G. S. Inorg. Chim. Acta 1982, 66, 125. (b) Taniguchi, S. Bull. Chem. Soc. Jpn. 1984, 57, 2683. (18) Alcock, N. W.; Kingston, R. G.; Moore, P.; Pierpoint, C. J. Chem. Soc., Dalton Trans. 1984, 1937. (19) Chen, D.; Martell, A. E.; Sun, Y. Inorg. Chem. 1989, 28, 2647. (20) Bell, M.; Edward, A. J.; Hoskins, B. F.; Kachab, E. H.; Robson, R. J. Am. Chem. Soc. 1989, 111, 3603.

Wang et al. internal solvent. Mass spectra were obtained by fast atom bombardment (FAB+) on a VG Analytical 70s high-resolution double-focusing magnetic sector spectrometer, with nitrobenzyl alcohol or thioglycerol as the matrix solvent, at the Mass Spectrometry Applications Laboratory, Texas A&M University. Synthesis of 6,6′-Bis(aminomethyl)-2,2′-bipyridyl (babp). A solution of 6,6′-bis(aminomethyl)-2,2′-bipyridyl trihydrobromide16 (9.14 g, 20 mmol) in H2O (80 mL) was treated with 10 M NaOH to pH 12 and extracted with CH2Cl2 (3 × 100 mL). The organic phase was dried under anhydrous MgSO4 for 15 h and then evaporated under reduced pressure, yielding 4.01 g (94%) of sky blue solid product. Mp: 87-89 °C. 1H NMR (CDCl3), δ (ppm): 1.98 (br s, NH2, 4H), 4.03 (s, CH2, 4H), 7.26 (d, H5,5′, J ) 7.8 Hz, 2H), 7.77 (t, H4,4′, J ) 7.8 Hz, 2H), 8.32 (d, H3,3′, J ) 7.8 Hz, 2H); Mass spectrum (FAB+): m/z 215 ([babp + H]+). Synthesis of the Dinuclear Lanthanum Complex La21(OAc)4. A mixture of 2,6-diformyl-p-cresol (0.66 g, 4.0 mmol) and La(OAc)3‚nH2O (1.40 g, 4.0 mmol) in 300 mL of methanol was heated at 50-60 °C until all the lanthanide salt was dissolved and a clear light green solution formed. 6,6′-Bis(aminomethyl)-2,2′-bipyridyl (0.86 g, 4.0 mmol) in 350 mL of methanol was added dropwise over a 3 h period. The mixture was refluxed for 15 h and then cooled to room temperature, whereupon color of the methanolic solution changed to light yellow. A powdery white precipitate (0.42 g; a byproduct) was filtered off. The filtrate was evaporated under reduced pressure to remove all of the solvent. The desired product was obtained in the form of yellow-orange crystalline needles of [La21(OAc)4]‚10H2O. Yield: 2.26 g, 82%. Anal. Calcd for C50H66La2N8O20: C, 43.61; H, 4.83; N, 8.12. Found: C, 43.49; H, 4.75; N, 7.96. 1H NMR (CD3OD), δ (ppm): 1.36 (s, CH3CO2-, 12H), 2.27 (s, CH3, 6H), 4.84 (d, CHa-N, J ) 14.2 Hz, 4H), 6.11 (d, CHb-N, J ) 14.2 Hz, 4H), 7.30 (s, aryl in cresol, 4H), 7.59 (d, H5,5′, J ) 7.8 Hz, 4H), 8.04 (t, H4,4′, J ) 7.8 Hz, 4H), 8.21 (d, H3,3′, J ) 7.8 Hz, 4H), 8.30 (s, imine CHdN, 4H). 13C NMR (CD3OD), δ (ppm): 20.23 (Me in acetate), 23.38 (Me in cresol), 69.07 (CH2-Nd), 122.16, 124.05, 126.29, 128.19, 140.73, 141.10, 156.52, 161.72, 162.15 (aryl carbon), 167.78 (CHdN, imine), 182.75 (CO2- in acetate). Mass spectrum (FAB+) : m/z 1137 ([La21(OAc)3]+). Isolation of Crystalline [La21(OAc)4]‚4CH3CN‚3H2O (5). Recrystallization of [La21(OAc)4]‚10H2O (0.16 g, 0.12 mmol) in 20 mL of acetonitrile afforded light yellow X-ray-quality crystals. Synthesis and Isolation of Metal-Free Ligand 2. A solution of La21(OAc)4 (2.0 g, 1.5 mmol) in 200 mL of methanol was heated to 45 °C under Ar for 2 h, and then NaBH3CN (1.2 g, 20 mmol) and NaBH4 (1.5 g, 40 mmol) were added. After 2 h of vigorous stirring at 50-55 °C under Ar, the reaction solution was cooled to room temperature and evaporated to dryness. To this were added 10 mL of 6 M HCl and 100 mL of 0.5 M DTPA aqueous solution (pH was then 1-2), and the reaction mixture was stirred vigorously for 18 h. The solution was neutralized with aqueous sodium hydroxide, and the free ligand was extracted with 3 × 100 mL of CH2Cl2. The organic phase was washed twice with 2 × 80 mL of saturated NaCl solution and dried with anhydrous Na2SO4. The solution was then filtered and evaporated to give 0.98 g of the crude product as a flaky light green solid. The crude product (0.46 g) was redissolved in 25 mL of 36% HCl in methanol, and then diethyl ether was slowly diffused into the solution, yielding the metal-free macrocycle 2 hydrochloride salt as a white solid. Yield: 0.38 g, 56%. A 0.46 g sample of the crude product was redissolved in 10 mL of 48% HBr and 10 mL of ethanol; then diethyl ether was slowly diffused into the solution, giving the macrocycle 2 hydrobromide salt as a light yellow solid. Yield: 0.29 g, 43%. 1H NMR (D2O), δ (ppm): 2.06 (s, CH3, 6H), 4.12 (s, CH2, 8H), 4.47 (s, CH2, 8H), 6.98 (s, aryl in cresol, 4H), 7.42 (d, H5,5′, J ) 8.0 Hz, 4H), 7.93 (t, H4,4′, J ) 8.0 Hz, 4H), 8.24 (d, H3,3′, J ) 8.0 Hz, 4H). Mass spectrum (FAB+) : m/z 693 ([2 + H]+). Syntheses of Macrocyclic Ligands 3 and 4 by a Nontemplate Condensation Reaction. A solution of 2,6-diformylpyridine (1.06 g, 7.9 mmol) in 280 mL of methanol was added dropwise to a hot solution of 2,6-bis(aminomethyl)-p-cresol hydrochloride (1.60 g, 7.9 mmol) in 320 mL of methanol for 2 h at 55 °C with stirring. The mixture was cooled to room temperature, and a methanolic solution of KOH (0.44 g, 7.9 mmol) was added slowly. After the solution was stirred for 24 h, its volume was reduced to 200 mL by evaporation. The light yellow

Dinucleating Macrocyclic Ligands

Inorganic Chemistry, Vol. 36, No. 4, 1997 631

Table 1. Summary of Crystallographic Data formula fw space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z d(calc), g/cm3 abs coeff, mm-1 transm coeff R(F)a Rw(F2)b GOF(F2)c

5

6

C58H64N12O13La2 1415.01 triclinic, P1h 10.986(6) 12.231(8) 23.818(12) 86.63(5) 85.99(5) 79.45(4) 3135(3) 2 1.498 1.414 0.999-0.951 0.0551 0.1585 1.219

C32H47N6O3Br7 1123.11 monoclinic, C2/m 26.737(11) 16.885(7) 10.325(4) 90 101.94(3) 90 4560(3) 4 1.633 6.193 0.923-0.808 0.0980 0.1668 1.180

Scheme 1. Template Condensation of 6,6′-Bis(aminomethyl)-2,2′-bipyridyl with 2,6-Diformyl-pcresol

a R(F) ) ∑||Fo| - |Fc||/∑Fo. b Rw(F2) ) {[∑w(Fo2 - Fc2)2]/ [∑w(Fo2)2]}1/2. c GOF(F2) ) ∑w(Fo2 - Fc2)2/(ND - NP); ND ) number of data, NP ) number of parameters.

precipitate obtained was filtered off and washed with diethyl ether to give macrocycle 3 as an intermediate product. Yield: 0.94 g, 45%. 1H NMR (CD OD/DCl), δ (ppm): 2.31 (s, CH , 6H), 4.16 (s, CH , 3 3 2 8H), 5.76 (s, CH, 4H), 7.25 (s, aryl in cresol, 4H), 7.91 (d, aryl in pyridine, J ) 8.0 Hz, 4H), 8.38 (t, aryl in pyridine, J ) 8.0 Hz, 2H). A suspension of the Schiff base 3 (0.75 g, 1.4 mmol) in 80 mL of methanol was heated to 45 °C and hydrogenated with sodium borohydride (2.0 g, 50 mmol). Upon completion of the reaction, the solvent was evaporated under reduced pressure, and the product was extracted with CH2Cl2 (CH2Cl2/H2O ) 2 × 100 mL/30 mL). The organic phase was dried for 12 h with anhydrous Na2SO4 and then filtered. A green oil was obtained upon removal of the CH2Cl2 solvent under reduced pressure. About 20 mL of methanolic 36% HCl solution was added to the oily product. After 24 h at 4 °C, a white crystalline precipitate formed; this was dried to give the pure desired macrocycle 4 as the hydrochloride salt, C32H38N6O2‚CH3OH‚6HCl. Yield: 0.73 g, 66%. Overall yield: 30%. Anal. Calcd for C32Cl6H48N6O3: C, 50.23; H, 6.13; N, 10.65. Found: C, 50.58; H, 6.39; N, 10.69. 1H NMR (D2O), δ (ppm): 2.30 (s, CH3, 6H), 4.39 (s, CH2, 8H), 4.55 (s, CH2, 8H), 7.31 (s, aryl in cresol, 4H), 7.50 (d, aryl in pyridine, J ) 8.0 Hz, 4H), 7.93 (t, aryl in pyridine, J ) 8.0 Hz, 2H). 13C NMR (D2O), δ (ppm): 19.40 (CH3), 46.95 (CH2), 50.11 (CH2), 121.10, 123.34, 133.05, 134.12, 139.53, 150.39, 150.90; the last seven peaks above 120.0 ppm are assigned to aromatic carbon in pyridine and cresol groups. Mass spectrum (FAB+): m/z 539 ([4 + H]+). Isolation of Crystalline 4‚H2O‚7HBr (6). The free macrocyclic ligand 4 (0.20 g, 0.3 mmol) was recrystallized from a mixture of 10 mL of 48% HBr and 10 mL of ethanol. The solution was heated to 65 °C to reduce the volume of the filtrate by half and then allowed to evaporate at room temperature for 2 months to afford light brown crystals suitable for X-ray diffraction study. X-ray Structure Analysis. Crystal data are given in Table 1. A light yellow parallelepiped (0.32 × 0.31 × 0.14 mm) of 5 and a prismatic pale brown crystal (0.41 × 0.30 × 0.12 mm) of 6 were mounted on glass fibers with epoxy cement at room temperature. Preliminary examination and data collection were performed on a Rigaku AFC-5R X-ray diffractometer (Mo KR λ ) 0.710 73 Å radiation). Cell parameters were calculated from the least-squares fitting of the setting angles for 25 reflections. Data were collected with 4.0 e 2θ e 45° for 5 and with 4.0 e 2θ e 50° for 6. Three control reflections collected every 97 reflections showed no significant trends. Lorentz and polarization corrections were applied to 8690 reflections for 5 and 4255 reflections for 6. A semiempirical absorption correction was applied. Totals of 8226 unique reflections for 5 and 4161 for 6 were obtained. Both structures were solved by direct methods.21 Fullmatrix least-squares anisotropic refinements22 for all non-hydrogen (21) Sheldrick, G. M. SHELXS 86, Program for Crystal Structure Solution. University of Go¨ttingen, Germany, 1986. (22) Sheldrick, G. M. SHELXS 93, Program for Crystal Structure Refinement. University of Go¨ttingen, Germany, 1993.

atoms yielded R ) 0.0551, Rw(F2) ) 0.1585, and GOF ) 1.219 at convergence for 5 and R ) 0.0980, Rw(F2) ) 0.1668, and GOF ) 1.180 for 6. Hydrogen atoms were placed in idealized positions with isotropic thermal parameters fixed at 0.08 Å2. Absolute configuration of 5 was verified by Flack’s method.23 Neutral-atom scattering factors and anomalous scattering correction terms were taken from ref 24. Positional parameters for 5 and 6 are given as Supplementary Information.

Results and Discussion Syntheses. The synthetic pathways of all compounds in this study are illustrated in Schemes 1 and 2. To our knowledge, this is the first report of the preparation and the crystal structure for this type of macrocyclic ligand and of its dinuclear La(III) complex. From the kinetic point of view, condensation reactions of dialdehydes with diamines generally afford polymeric Schiff base products, which include the monomeric [1+1] diimine macrocycle,10b the [2+2] tetraimine macrocycle,2b the [3+3] (23) Flack H. D. Acta Crystallogr. 1983, A39, 876. (24) Hahn, T.; Reidel, D.; International Tables for X-ray Crystallography; Kluwer: Dordrecht, The Netherlands, 1992; Vol. C.

632 Inorganic Chemistry, Vol. 36, No. 4, 1997

Wang et al. Scheme 2. Nontemplate Condensation of 2,6-Bis(aminomethyl)-p-cresol with 2,6-Diformylpyridyl

Figure 1. ORTEP drawing of [La21(OAc)4]‚4CH3CN‚3H2O. Ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity.

Figure 2. Perspective view of the extended double dodecahedral decacoordination geometry around the two La3+ ions.

hexaimine macrocycle,25a the [4+4] octaimine macrocycle,25b and other polymeric Schiff bases, depending upon reaction conditions and template conditions which involve the presence of metal ions acting as template in the cyclization reaction. In this work, condensation of equimolar amounts of 2,6-diformylp-cresol and 6,6′-bis(aminomethyl)-2,2′-bipyridyl in the presence of La(OAc)3‚nH2O as a template agent leads to a tetraimine Schiff base macrocyclization forming the dinuclear lanthanum complex La21(OAc)4 in high yield. This [2+2] condensation is clearly favored by the use of lanthanide or lead ions26 as the template core. The large ionic radius of the metal plays an important role in directing the reaction to preferentially form and stabilize the large [2+2] rather than [1+1] macrocycle. This is known as the thermodynamic template effect.10a,11a Selbin and co-workers27 synthesized the first series of dilanthanide macrocyclic complexes in the condensation of 2,6diformyl-p-cresol and triethylenetetramine by using lanthanum nitrate as the template agent. The solubilities of Selbin’s complexes are low in most solvents except DMSO. On the contrary, our complex, La21(OAc)4, is very soluble in CH3OH (25) (a) Aspinall, H. C.; Black, J.; Dodd, I.; Harding, M. M.; Winkly, S. J.; J. Chem. Soc., Dalton Trans. 1993, 709. (b) McKee, V. J.; Shepard, W. B. J. Chem. Soc., Chem. Commun. 1985, 158. (26) Wang, Z.; Martell, A. E. Unpublished results. (27) Kahwa, I. A.; Selbin, J.; Hsieh, T. C.-Y.; Laine, R. A. Inorg. Chim. Acta 1986, 118, 179.

and appreciably soluble in CHCl3, CH3CN, and H2O. Crystalline [La21(OAc)4]‚4CH3CN‚3H2O was formed by recrystallization of [La21(OAc)4]‚10H2O in CH3CN. In previous work only two macrocycles containing different aliphatic units have thus far successfully yielded single crystals.14a,b The new complex 5 containing aromatic bipyridines in the macrocycle and the metal-free ligand 6 containing aromatic pyridines in the macrocycle provide significant additions to crystal structure information on this class of compounds. Hydrogenation of the complex La21(OAc)4 with NaBH4 and NaBH3CN in methanol gave the metal-free macrocycle 2, which was isolated with the use of DTPA to remove the lanthanum ion in aqueous solution. The successful isolation of the saturated macrocycle is rather interesting when one considers a related macrocycle recently reported by Kahwa and co-workers.14b Their macrocyclic dinuclear lanthanide complexes, prepared by Schiff base condensation of 2,6-diformyl-p-cresol and 1,8-diamino3,6-dioxaoctane, are also readily reduced to the saturated form. However the reduced product is unstable toward atmospheric oxidation, finally giving a partially oxidized diamine-diimine macrocycle. In our work, macrocycle 2 is stable in air for a long period of time under both acidic and alkaline conditions. No oxidation of CH2-NH to CHdN was seen with evidence obtained from both 1H NMR and FAB mass spectroscopy. A different synthetic strategy was used to prepare the 24membered macrocycles containing pyridine units instead of bipyridine units, in that a nontemplate condensation was

Dinucleating Macrocyclic Ligands

Inorganic Chemistry, Vol. 36, No. 4, 1997 633

Table 2. Selected Interatomic Distances (Å) and Bond Angles (deg) for 5a La(1)‚‚‚La(2) La(1)-O(1) La(1)-O(7) La(1)-O(10) La(1)-N(4) La(1)-N(3) La(2)-O(1) La(2)-O(5) La(2)-O(6) La(2)-N(8) La(2)-N(7) O(1)-La(1)-O(2) La(1)-O(1)-La(2) O(2)-La(1)-O(7) O(2)-La(1)-O(9) O(1)-La(1)-O(10) O(7)-La(1)-O(10) O(1)-La(1)-N(1) O(7)-La(1)-N(1) O(10)-La(1)-N(1) O(2)-La(1)-N(4) O(9)-La(1)-N(4) N(1)-La(1)-N(4) O(2)-La(1)-O(8) O(9)-La(1)-O(8) N(1)-La(1)-O(8) O(1)-La(1)-N(3) O(7)-La(1)-N(3) O(10)-La(1)-N(3) N(4)-La(1)-N(3) O(1)-La(1)-N(2) O(7)-La(1)-N(2) O(10)-La(1)-N(2) N(4)-La(1)-N(2) N(3)-La(1)-N(2) O(2)-La(1)-La(2) O(9)-La(1)-La(2) N(1)-La(1)-La(2) O(8)-La(1)-La(2) a

4.135(12) 2.508(7) 2.585(8) 2.641(8) 2.650(9) 2.707(9) 2.511(7) 2.605(8) 2.639(8) 2.648(9) 2.682(9) 69.4(2) 111.0(3) 70.4(3) 142.1(2) 70.2(3) 165.8(3) 68.7(3) 66.4(3) 111.6(3) 68.0(3) 108.9(3) 177.8(3) 77.3(2) 139.5(3) 106.4(3) 145.5(3) 117.1(3) 76.6(3) 60.7(3) 126.1(3) 78.4(3) 113.4(3) 117.6(3) 60.1(3) 34.8(2) 111.3(2) 90.9(2) 109.1(2)

La(1)-O(2) La(1)-O(9) La(1)-N(1) La(1)-O(8) La(1)-N(2) La(2)-O(2) La(2)-O(3) La(2)-N(5) La(2)-O(4) La(2)-N(6) O(1)-La(2)-O(2) La(2)-O(2)-La(1) O(1)-La(1)-O(9) O(7)-La(1)-O(9) O(2)-La(1)-O(10) O(9)-La(1)-O(10) O(2)-La(1)-N(1) O(9)-La(1)-N(1) O(1)-La(1)-N(4) O(7)-La(1)-N(4) O(10)-La(1)-N(4) O(1)-La(1)-O(8) O(7)-La(1)-O(8) O(10)-La(1)-O(8) N(4)-La(1)-O(8) O(2)-La(1)-N(3) O(9)-La(1)-N(3) N(1)-La(1)-N(3) O(8)-La(1)-N(3) O(2)-La(1)-N(2) O(9)-La(1)-N(2) N(1)-La(1)-N(2) O(8)-La(1)-N(2) O(1)-La(1)-La(2) O(7)-La(1)-La(2) O(10)-La(1)-La(2) N(4)-La(1)-La(2) N(3)-La(1)-La(2)

Distances N(1)-C(8) 2.523(7) N(2)-C(10) 2.598(8) N(3)-C(19) 2.646(9) N(4)-C(21) 2.681(8) N(5)-C(29) 2.733(9) N(6)-C(31) 2.517(8) N(7)-C(40) 2.608(8) N(8)-C(42) 2.646(10) N(9)-C(51) 2.663(8) N(11)-C(55) 2.695(9) Angles 69.4(2) N(2)-La(1)-La(2) 110.3(3) O(1)-La(2)-O(5) 78.8(2) O(1)-La(2)-O(3) 135.2(3) O(5)-La(2)-O(3) 99.1(3) O(2)-La(2)-O(6) 49.4(3) O(3)-La(2)-O(6) 113.8(3) O(2)-La(2)-N(5) 70.7(3) O(3)-La(2)-N(5) 113.4(3) O(1)-La(2)-N(8) 113.6(3) O(5)-La(2)-N(8) 69.0(3) O(6)-La(2)-N(8) 139.4(2) O(1)-La(2)-O(4) 49.3(3) O(5)-La(2)-O(4) 139.6(3) O(6)-La(2)-O(4) 72.5(3) N(8)-La(2)-O(4) 126.4(3) O(2)-La(2)-N(7) 72.5(3) O(3)-La(2)-N(7) 117.3(3) N(5)-La(2)-N(7) 74.0(3) O(4)-La(2)-N(7) 147.1(3) O(2)-La(2)-N(6) 69.6(3) O(3)-La(2)-N(6) 60.2(3) N(5)-La(2)-N(6) 74.3(3) O(4)-La(2)-N(6) 34.6(2) O(1)-La(2)-La(1) 81.9(2) O(5)-La(2)-La(1) 84.1(2) O(6)-La(2)-La(1) 91.2(2) N(8)-La(2)-La(1) 150.1(2) N(7)-La(2)-La(1)

1.28(2) 1.34(2) 1.34(2) 1.25(2) 1.26(2) 1.347(14) 1.344(14) 1.25(2) 1.15(2) 1.15(2)

149.8(2) 143.1(2) 79.6(2) 135.9(2) 71.4(3) 135.0(3) 68.3(3) 109.2(3) 68.7(3) 109.4(3) 68.7(3) 70.5(2) 136.1(3) 170.9(3) 110.6(3) 147.3(2) 67.4(3) 118.6(3) 111.0(3) 127.7(3) 70.0(3) 61.3(3) 73.6(3) 34.5(2) 112.1(2) 86.2(2) 91.2(2) 150.3(2)

N(1)-C(9) N(2)-C(14) N(3)-C(15) N(4)-C(20) N(5)-C(30) N(6)-C(35) N(7)-C(36) N(8)-C(41) N(10)-C(53) N(12)-C(57)

O(1)-La(1)-O(7) O(2)-La(2)-O(5) O(2)-La(2)-O(3) O(1)-La(2)-O(6) O(5)-La(2)-O(6) O(1)-La(2)-N(5) O(5)-La(2)-N(5) O(6)-La(2)-N(5) O(2)-La(2)-N(8) O(3)-La(2)-N(8) N(5)-La(2)-N(8) O(2)-La(2)-O(4) O(3)-La(2)-O(4) N(5)-La(2)-O(4) O(1)-La(2)-N(7) O(5)-La(2)-N(7) O(6)-La(2)-N(7) N(8)-La(2)-N(7) O(1)-La(2)-N(6) O(5)-La(2)-N(6) O(6)-La(2)-N(6) N(8)-La(2)-N(6) N(7)-La(2)-N(6) O(2)-La(2)-La(1) O(3)-La(2)-La(1) N(5)-La(2)-La(1) O(4)-La(2)-La(1) N(6)-La(2)-La(1)

1.46(2) 1.35(2) 1.35(2) 1.46(2) 1.47(2) 1.350(14) 1.374(14) 1.452(14) 1.14(2) 1.15(2)

96.7(3) 78.9(2) 143.8(2) 101.3(2) 49.3(3) 112.5(3) 70.2(3) 111.6(3) 113.0(3) 70.1(3) 178.6(3) 101.4(3) 49.0(3) 69.4(3) 125.5(2) 74.7(3) 76.8(3) 60.0(3) 143.0(3) 72.3(3) 115.0(3) 117.3(3) 60.8(3) 34.9(2) 112.1(2) 90.2(2) 84.7(2) 148.6(2)

Numbers in parentheses are estimated standard deviations in the last significant digit.

employed to prepare macrocycle 3. The metal-free condensation between 2,6-bis(aminomethyl)-p-cresol and 2,6-diformylpyridine in methanol leads to the formation of the [2+2] tetrakis(Schiff base) macrocycle 3. Hydrogenation of 3 produced the saturated macrocycle 4, which was extracted with an organic solvent from aqueous solution under alkaline conditions. The free ligand 4 was converted to both the hydrochloride and hydrobromide salts. Crystalline 4‚H2O‚7HBr suitable for X-ray structure determination was obtained under very acidic conditions (48% HBr with EtOH). Spectral and Crystal Structure Data. Solution characterization of La21(OAc)4, 2, 3, and 4 was accomplished by 1H, 13C, and 1H-1H 2D-COSY NMR and ultraviolet-visible spectral measurements. Characterizations of solid La21(OAc)4, 2, and 4 were carried out by elemental analysis, by IR and FAB mass spectra, and, in the cases of 5 and 6, by X-ray crystallography (see Table 1). The composition of La21(OAc)4, indicated by elemental analysis and FAB mass spectra, is further supported by the strong IR absorption peak at 1635-1643 cm-1, typical of the CdN stretching mode in related compounds11. A strong peak found at 1548-1552 cm-1 is characteristic of the phenolic C-O stretching mode acquiring partial double-bond character through conjugation with the imine system in chelate rings.25 Electronic absorption of 5 occurs at 371 nm, which is associated with the presence of the CdN chromophore according to the previous work by Selbin and co-workers.27 The crystal structure of [La21(OAc)4]‚4CH3CN‚3H2O reveals entrapment of a pair of La3+ cations in the twin 18-membered

coordination compartments of the 30-membered macrocycle 1 (see Figure 1). Both lanthanum atoms lie within the macrocycle and are bridged by the two phenolate oxygen anions. Each lanthanum atom is decacoordinate, being bound by two phenolate oxygens, two bipyridyl nitrogens, two Schiff base nitrogens, and two bidentate acetate anions. The coordination polyhedron can be described as an extended double dodecahedron of approximate noncrystallographic D2 symmetry (see Figure 2). The 2-fold axis passes through the center of, and is perpendicular to, the La2O2 plane formed by the La3+ cations and their bridging phenolic oxygen atoms. The vertical C2 axis is accompanied by two C2 axes perpendicular to it, one passing through the two La3+ cations and the other passing through two phenolic oxygen atoms. The La2O2 ring is planar (mean deviation from plane 0.01 Å). The La(1)-La(2) distance is 4.135 Å , which is comparable to that found in other complexes containing the Ln2O2 core.14a,b The four acetonitrile and three water molecules are not involved in coordination to either lanthanum atom. In the macrocycle, Schiff base CHdN bonds are essentially coplanar with the adjacent phenolic aromatic rings (mean deviation from plane 0.11 Å). The aromatic rings are inclined by 47.6° relative to the La2O2 mean plane. On the other hand, the bipyridine rings are slightly twisted (mean deviation from plane 0.12 Å) and inclined by 69.6° relative to the La2O2 mean plane. The angle between the two bipyridine planes is 40.8°. The single C-N bonds adjacent to the bipyridine moieties are rotated out of these planes to adapt to a suitable coordination geometry. The La-O coordination distances (see Table 2) are in the range 2.51-2.68 Å, the shortest

634 Inorganic Chemistry, Vol. 36, No. 4, 1997

Wang et al. Table 3. Interatomic Distances [Å] and Bond Angles [deg] for 6a O(1)-C(11) N(1)-C(3) N(1)-C(3)i N(2)-C(5) N(2)-C(4) N(3)-C(14) N(3)-C(13) N(4)-C(15) N(4)-C(15)i C(1)-C(2)i C(1)-C(2) C(2)-C(3) C(3)-C(4)

Figure 3. Relevant region of the 200 M Hz 1H-1H 2D-COSY NMR spectrum of [La21(OAc)4]‚10H2O in CDCl3.

C(3)-N(1)-C(3)i C(5)-N(2)-C(4) C(14)-N(3)-C(13) C(15)-N(4)-C(15)i C(2)i-C(1)-C(2) C(1)-C(2)-C(3) N(1)-C(3)-C(2) N(1)-C(3)-C(4) C(2)-C(3)-C(4) C(3)-C(4)-N(2) N(2)-C(5)-C(6) C(7)-C(6)-C(11) C(7)-C(6)-C(5) C(11)-C(6)-C(5) C(8)-C(7)-C(6) C(7)-C(8)-C(9)

Distances 1.394(14) C(5)-C(6) 1.35(2) C(6)-C(7) 1.35(2) C(6)-C(11) 1.49(2) C(7)-C(8) 1.51(2) C(8)-C(9) 1.479(14) C(8)-C(12) 1.50(2) C(9)-C(10) 1.369(14) C(10)-C(11) 1.369(14) C(10)-C(13) 1.35(2) C(14)-C(15) 1.35(2) C(15)-C(16) 1.39(2) C(16)-C(17) 1.45(2) C(17)-C(16)i Angles 122(2) C(7)-C(8)-C(12) 115.7(11) C(9)-C(8)-C(12) 116.0(10) C(8)-C(9)-C(10) 123(2) C(11)-C(10)-C(9) 122(2) C(11)-C(10)-C(13) 118.6(14) C(9)-C(10)-C(13) 119.1(13) C(10)-C(11)-O(1) 117.3(12) C(10)-C(11)-C(6) 123.5(13) O(1)-C(11)-C(6) 114.0(11) N(3)-C(13)-C(10) 112.2(11) N(3)-C(14)-C(15) 122.6(12) N(4)-C(15)-C(16) 120.1(11) N(4)-C(15)-C(14) 117.3(12) C(16)-C(15)-C(14) 118.0(13) C(17)-C(16)-C(15) 120.7(12) C(16)-C(17)-C(16)i

1.57(2) 1.37(2) 1.40(2) 1.34(2) 1.38(2) 1.50(2) 1.39(2) 1.38(2) 1.51(2) 1.50(2) 1.42(2) 1.36(2) 1.36(2) 118.3(13) 120.9(13) 122.7(12) 116.7(13) 124.6(13) 118.6(13) 122.5(12) 119.2(13) 118.3(12) 111.9(11) 113.8(10) 118.5(13) 117.5(12) 123.8(13) 119(2) 123(2)

a Numbers in parentheses are estimated standard deviations in the last significant digits. Symmetry transformation used to generate equivalent atoms: (i) x,-y + 1, z.

Figure 4. ORTEP drawing of 4‚H2O‚7HBr. Ellipsoids are drawn at the 50% probability level.

contacts being to the phenolate oxygens and the longest ones being to the acetate oxygens. The La-N coordination distances are in the range 2.64-2.73 Å; the imine nitrogen atoms of the Schiff bases coordinate closer to the metal ions than do the nitrogen atoms in the bipyridine units. The C-N single-bond distances are around 1.46 Å, the Schiff base CHdN doublebond distances are around 1.26 Å, and the C-N bonds in the aromatic bipyridine rings are in the range 1.34-1.38 Å. The 1H and 13C NMR spectra of La21(OAc)4 are consistent with the crystal structure. In particular, several spectral assignments for the complex are based on 1H-1H 2D-COSY with the attached proton test (APT). For example, two protons in the CH2 group adjacent to the imine nitrogen are not equivalent and show a set of two doublets at δ 4.84, 6.11 ppm in CD3OD and δ 4.56, 6.19 ppm in CDCl3, respectively. The chemical shift differences of 1.27 ppm in CD3OD and 1.63 ppm in CDCl3 seem too large for the two protons to be on the same carbon atom. However, 1H-1H 2D-COSY NMR spectrum in CDCl3 (see Figure 3) shows several correlative couplings which include these two protons (Ha, Hb). This result gives clear structural information: first, the nonequivalence of two protons (Ha, Hb) in a CH2 group implies that the macrocyclic ring is made rigid by complexation with the dilanthanum center; second, the steric factors and the magnetic anisotropy effect of the presence of

two unsaturated π-electron systems in the vicinity of two protons (Ha, Hb) are considered to account for the large chemical shift difference. Thus, 2D-COSY NMR provides structural information about hydrogen atoms, which cannot be obtained from X-ray diffraction studies. The metal-free ligand 2 has been obtained from La21(OAc)4 as both the hydrochloride and hydrobromide, but so far attempts to grow single crystals of 2 have been unsuccessful. However, routine NMR and FAB mass spectra analyses indicate complete hydrogenation to give the desired macrocycle 2. After hydrogenation, the nonequivalence of two protons (Ha, Hb) of the CH2 group in the complex La21(OAc)4 disappears, and the two singlets at 4.10 and 4.47 ppm in the metal-free ligand indicate the tetraamine nature of macrocycle 2. The 24-membered macrocycles 3 and 4 have been synthesized by a nontemplate reaction. The heptahydrobromide salt (6) of the hydrogenated macrocycle 4 crystallized as monoclinic with the symmetry of space group C2/m. The X-ray crystallographic analysis of 6 shows all six nitrogens of the macrocycle are protonated and a hydronium ion is also present. A summary of crystallographic data is given in Table 1. Bond lengths and angles of 6 are given in Table 3. The macrocycle molecule of 6 adopts the Cs symmetry shown in Figure 4. A mirror plane passes through the two nitrogens of the pyridyl groups on the two sides of the macrocyle, the two bromide anions (Br(1), Br(3)), and the hydronium ion. The macrocycle is associated directly with six bromide anions, which are situated close to the six protonated nitrogens (with positive charge) on the periphery of the macrocycle. The distances between the six bromide anions (Br(1), Br(2), Br(2A), Br(3), Br(4), and Br(4A) of Figure 4) and the six adjacent protonated nitrogens are 3.42(1), 3.21(1), 3.21(1), 3.36(1), 3.23(1), and 3.23(1) Å, respectively. It is clearly demonstrated that the four bromide anions (Br(2), Br(2A), Br(4), and Br(4A)) proximal to the four amino nitrogens (N(3), N(3A), N(2), and N(2A)) are more strongly held than the two bromide anions (Br(1), and Br(3))

Dinucleating Macrocyclic Ligands Scheme 3. FAB-Induced Decompositon Pattern of 2

near the two pyridyl nitrogens (N(1), and N(4)). The other bromide anion (Br(5) of Figure 4) is situated 4.07(1) Å away from the periphery of the macrocycle, apparently as a counteranion outside the cavity. The structure therefore could be described as [4‚(HBr)6‚H3O+]Br-. In the macrocycle, the C-N bond distances are in the range 1.35-1.51 Å, the shorter ones for the aromatic C-N bonds and the longer ones for the C-N single bonds. The crystal structure data provide clear evidence of the [2+2] nature of macrocycle 4. The structure of macrocycle 3 from the initial condensation step has been characterized by its 1H NMR spectrum and further confirmed by the hydrogenation of the Schiff base to form 4. All assignments of the 1H NMR spectra of 3 and 4 on the basis of the integrated signal intensity are consistent with the crystal structure. The peaks with the largest chemical shift change (1.21 ppm) between the two spectra of 3 and 4 indicate the complete hydrogenation of the Schiff base -CdN- bonds of compound 3 to give 4. The 13C NMR spectrum of 4 shows characteristic peaks at δ 19.40 (CH3), 46.95 (CH2), and 50.11 ppm (CH2) and also indicates the formation of the desired [2+2] tetraamine macrocycle. Recently, FAB mass spectrometry has been employed for the structural characterization of macrocyclic Schiff bases.28 Several FAB-induced decomposition patterns were proposed for the variety of macrocyclic structures and side chains. However, no systematic research has been reported for hydrogenated Schiff base macrocycles. In this work, we undertook FAB mass spectrometric studies of macrocycles 2 and 4, both as the hydrochloride salts. The mechanism of decomposition and (28) Guerriero, P.; Tamburini, S.; Vigato, P. A.; Seraglia, R.; Traldi, P. Org. Mass Spectrom. 1992, 27, 231.

Inorganic Chemistry, Vol. 36, No. 4, 1997 635 Scheme 4. FAB-Induced Decomposition Pattern of 4

fragmentation patterns for both macrocycles are shown in Schemes 3 and 4, respectively. The protonated molecule of macrocycle 2, [M + H]+, gives rise to the peak at m/z 693. Scheme 3 shows a preferential primary decomposition, which leads to twin peaks [M/2 + H]+ and [M/2]•+ at m/z 347 and 346, respectively. The symmetrical cleavage of the C-N bonds adjacent to the two phenols of the macrocycle with H rearrangement allows the loss of a fragment, C12H14N4, leading to the formation of the [C30H31N4O2]+ ion at m/z 479. The peak at m/z 213 is responsible for the [C12H14N4 - H]+ ion fragment. The further cleavage of the C-N bond adjacent to the phenol gives the ionic species [C9H10O + H]+ at m/z 135. The protonated molecule of macrocycle 4, [M + H]+, gives rise to the peak at m/z 539. Scheme 4 also shows the first primary decomposition, giving the characteristic twin peaks [M/2 + H]+ and [M/2]•+ at m/z 270 and 269, respectively. The second pathway involves breaking the macrocycle with H rearrangement, by the loss of a fragment, C7H11N3, leading to [C25H28N3O2]+ at m/z 402. The peak at m/z 136 corresponds to the [C7H11N3 - H]+ fragment. The further cleavage of the C-N bond adjacent to the phenol gives the ionic species [C9H10O + H]+ at m/z 135, which is identical to the final species formed from macrocycle 2. It is interesting to note that macrocycles 2 and 4 show two similar FAB-induced fragmentation pathways. The primary decomposition gives twin peaks for [M/2 + H]+ and [M/2]•+ ions, which also occurs in the Schiff base macrocycle decomposition pattern known as the SS1 mechanism.28 The next symmetrical cleavage seems to prefer the release of a diamine fragment with H rearrangement, breaking the macrocycle and leading to a large fragment peak (m/z 479 for 2, m/z 402 for 4). The diamine fragment forms a corresponding peak as the [diamine - H]+ fragment. Further cleavage gives the same ionic species [C9H10O + H]+ at m/z 135 for both 2 and 4, which

636 Inorganic Chemistry, Vol. 36, No. 4, 1997 reflects the structural similarity of phenol groups in both 2 and 4. Hence, the formulation of a general fragmentation pattern for the saturated polyaza phenolic macrocycles is proposed, based on the FAB mass spectral studies of 2 and 4. Conclusions Both template condensation and metal-free condensations with different dialdehydes and diamines for the preparation of new dinucleating macrocyclic ligands containing pyridine or bipyridine subunits have been investigated. The results indicate that the formation of these interesting compounds is dependent on choosing appropriate starting materials and controlling reaction conditions, such as solvent, temperature, concentration, and basicity. IR and FAB mass spectra and X-ray diffractions provided evidence for the formation and [2+2] nature of the macrocycles. Characterization of solutions of these macrocycles by 1H, 13C, and 2D-COSY NMR and UV-vis spectra is consistent with the structures obtained for the crystalline compounds. Herein we have reported the synthetic procedures and the spectroscopic characteristics for a novel dinuclear lanthanum complex and a series of new dinucleating macrocyclic ligands 1-4, as well as the X-ray crystal structures of one of the new ligands, 4, and a phenolate-bridged dilanthanum (III) complex

Wang et al. of 1. Further studies of their dinuclear iron complexes are now in progress. Acknowledgment. This research was supported by the Robert A. Welch Foundation through Grant A-259. The crystallographic computing system in the Crystal and Molecular Structure Laboratory of the Department of Chemistry, Texas A & M University, was purchased with funds provided by the National Science Foundation (Grant CHE-8513273). We thank Dr. Ishenkumba A. Kahwa, University of the West Indies, Mona, Jamaica, for providing 2,6-diformyl-p-cresol. We thank Dr. Abraham Clearfield, Texas A&M University, for use of the AFC5R X-ray diffractometer and also thank Dr. Lloyd W. Sumner for his assistance with the mass spectral analyses. Supporting Information Available: Tables of crystal data, atomic coordinates and equivalent isotropic displacement parameters, interatomic distances and bond angles, anisotropic displacement parameters, and H atom coordinates and isotropic displacement parameters for 5 and 6 and figures showing the molecular structures, atom numbering schemes, and packing diagrams for 5 and 6, 1H NMR spectra for La21(OAc)4, 2, 3, and 4, and 13C NMR spectra for La21(OAc)4 and 4 (20 pages). Ordering information is given on any current masthead page. IC960665V