Inorg. Chem. 1986, 25, 384-389
384
Contribution from the Research School of Chemistry, The Australian National university, Canberra 2601,Australia, Department of Physical and Inorganic Chemistry, The University of Western Australia, Nedlands 6009,Australia, Division of Applied Organic Chemistry, Commonwealth Scientific and Industrial Research Organization, Melbourne 3001, Australia, and Department of Physical and Inorganic Chemistry, University of Adelaide, Adelaide 5001, Australia
Macrobicyclic Chromium(111) Hexaamine Complexes Peter Combs,'.* Inge 1. Creaser,' Lawrence R. G a h a ~ ~ ,Jack ' . ~ MacB. Harr~wfield,~ Geoffrey A. Lawrance,'~~ Lisandra L. Martin,' Albert W. H. Mau,6 Alan M. Sargeson,*' Wolfgang H. F. Sasse,6 and Michael R. Snow' Received December 28, 1984
The syntheses and characterization of the macrobicyclic hexaamine chromium(II1) complexes of diamsar (1,s-diamino3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane) and sar (3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane) ligands (1-3) are reported. The complexes were isolated as stable, paramagnetic, and monomeric salts. [Cr(diamsar)]CI3.H20 crystallized in the space group P2,/c, ( Z = 4, a = 9.474 (2) A, b = 13.331 ( 3 ) A, c = 18.221 (5) A, p = 92.756 (0)O) with the octahedral cation in the CJel conformation and an average Cr-N distance of 2.070 (3) A. The complexes are high-spin d3 with room-temperature magnetic moments near the spin-only value of 3.87 pB. The aqueous electrochemistry exhibits a quasi-reversible Cr(III/II) couple below -1 V for each complex and a further irreversible Cr(II/O) reduction near -1.6 V; the chromium(I1) complexes are not stable in the coulometric time scales (minutes). The Cr(II1) electronic spectra show the expected spin-allowed absorption bands of 4T2, 4A2gand 4T,, 4A2, origin as well as weak spin-forbidden bands of 2E,,2Tl, 4A, origin in the visible region. The first of these (4T2, transition) is split by -400 cm-I and is relatively high in intensity, and the splitting is probably due to the lowered emit rather strongly at 77 K (@pH" = 0.02), but give no detectable emission above symmetry ( D 3 ) .Cr(sar))+ and Cr(diam~ar)~' 273 K. Photodecomposition of Cr(diamsar)" is 104-fold smaller than that of the Cr(en),)+ ion, and possible reasons for this are discussed.
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Introduction Encapsulation of the inert d6 metal ions Co(III), Rh(III), Ir(III), and Pt(IV) as nearly octahedral complexes in saturated hexacoordinate amine macrobicycles has been achieved recently,*-I1 by template synthesis about the M(en)3"+precursor (en = 1,2-ethanediamine) with formaldehyde and ammonia o r nitromethane in basic solution.'* A m i n e Cr(II1)-N bond lengths (average 2.09 A) are longer than Co(II1)-N bond lengths (average 1.97 A) but are similar to Pt(1V)-N bond lengths (average 2.08 A) . I 3 Therefore, encapsulation of Cr(II1) in a macrobicyclic amine ligand, already achieved for Co(II1) and Pt(IV), should be chemically feasible. However our attempts at encapsulation of the inert d3 Cr(en)33+precursor were not successful d u e to the rapid dissociation of intermediate imine species formed during the r e a ~ t i 0 n . l Nevertheless, ~ recently, Endicott et al.I5 claimed to have synthesized C r ( ~ e p ) ~by + such a route. This paper now explores the synthesis of Cr(II1) macrobicyclic complexes via the free ligands (1-3) and the Cr(I1) oxidation state. Structural, electrochemical, spectroscopic, photochemical, photophysical, and magnetic properties a r e also reported. Experimental Section Detailed syntheses and characterization of the metal-free ligands will be published elsewhere.16 Australian National University. Present address: Institute de Chimie Minerale et Analytique, Universite de Lausanne, 1005 Lausanne, Switzerland. Present address: Chemistry Department, University of Queensland, St. Lucia QLC 4067, Australia. Univerity of Western Australia. Present address: Chemistry Department, The University of Newcastle, NSW 2308, Australia. CSIRO.
University of Adelaide. Creaser, I. I.; Geue, R. J.; Harrowfield, J . MacB.; Herlt, A. J.; Sargwn, A. M.; Snow, M. R.; Springborg, J. J . Am. Chem. SOC.1977,99,3 181. Hambley, T. W.; Geue, R. J.; Harrowfield, J. MacB.; Sargeson, A. M.; Snow, M. R. J . Am. Chem. SOC.1984,106, 5478. Harrowfield, J. MacB.; Herlt, A. J.; Lay, P. A.; Sargeson, A. M.; Bond, A. M.; Mulac, W. A,; Sullivan, J. C. J . Am. Chem. SOC.1983,105, 5503. Boucher, H. A.; Lawrance, G. A.; Lay, P. A.; Sargeson, A. M.; Bond, A. M.; Sangster, D. F.; Sullivan, J. C. J . Am. Chem. SOC.1983,205, 4652. Sargeson, A. M. Chem. Br. 1979,15, 23. "Molecular Structure by Diffraction Methods"; The Chemical Society: London, 1973-1978; Spec. Period. Rep., Vol. 1-6. Creaser, I. I.; Harrowfield, J. MacB., unpublished observations. Ramasami, T.; Endicott, J. F.; Brubaker, G . R. J . Phys. Chem. 1983, 87. 5057 and references therein.
Y
Y
I ( Y = HI 2 ( Y = NHp) 3 (Y = NHs') ( 1,8-Diamino-3,6,10,13,16,19hexaazabicyclo[6.6.6]eicosane)chromium(II1) Chloride Monohydrate. Diamsar ligand16 (3.0 g) was dissolved in dry dimethyl sulfoxide (25 mL) and the solution warmed on a steam bath. Zinc powder (0.1 g) and anhydrous chromic chloride (1.51 g) were added, and the solution was gently warmed for 5 min. The resulting green-yellow solution was added to a large volume of water and filtered. The filtrate was sorbed on a column of Dowex 50W-X2 (H' form) resin, and washed with water and 1 M HCI. Elution with 3 M HCI gave a major yellow band, which was collected and evaporated to dryness by using a rotary evaporator. The yellow solid was redissolved in a large volume of water and rechromatographed on SP Sephadex C-25 (Na' form) cation-exchange resin. After being washed with water and 0.1 M NaCl solution, the column was eluted with 0.3 M NaCl solution and the major yellow band collected. This eluate was sorbed on a column of Dowex 50W-X2 (H' form) resin, washed with 0.5 M HCI, and eluted with 3 M HCI solution. The yellow solid obtained upon evaporation of the solvent was crystallized from aqueous propan-2-01 solution, following the addition of 2 equiv of lithium hydroxide, as yellow needles (2.5 9). Anal. Calcd for C,4H36C13CrN,0: C , 34.25; H, 7.39; N, 22.83; Cr, 10.59; CI, 21.67. Found: C, 34.7; H , 7.3; N, 23.2; Cr, 10.3; CI, 21.6. (3,6,10,13,19-Hexaazabicyclo[6.6.6]eicosane)cbromium(III) Trifluoromethanesulfonate. Sar ligandI6 (3.0 g) was dissolved in dry dimethyl sulfoxide (25 mL) and the solution warmed on a steam bath. Zinc powder (0.1 g) and anhydrous chromic chloride (1.73 g) were added, and the solution was gently heated for 2 min. The mixture was chromatographed and the yellow solid isolated from aqueous HCI as described for the diamsar analogue except for the additions of LiOH.
(16) Bottomley, G. A.; Creaser, I. I.; Gahan, L. R.; Harrowfield, J. MacB.; Lawrance, G. A.; Martin, L. L.; Sargeson, A. M.; See, A. J., to be submitted for publication.
0020-1669/86/1325-0384$01.50/0 0 1986 American Chemical Society
Inorganic Chemistry, Vol. 25, No. 3, 1986 385
Macrobicyclic Cr(II1) Hexaamine Complexes The yellow chloride salt was recrystallized as the trifluoromethanesulfonate salt from water upon addition of excess Na CF3S03and cooling (2.0 g). Anal. Calcd for C17H32CrF9N609S3: C, 26.05; H, 4.12; N , 10.73; Cr, 6.63; S, 12.27. Found: C, 26.3; H, 4.4; N, 10.7; Cr, 6.6; S, 12.3. Photochemical experiments were carried out by using an ILC Cermax xenon illuminator (1 50 W) with 450-nm light dispersed by a Bausch and Lomb monochromator cf= 3.6). The total number of photons absorbed was measured by ferrioxalate actinometry. The disappearance of chromium(II1) complexes was monitored by HPLC on a Zorbax ODS column (Du Pont; 25 X 0.46 cm). The eluent was an aqueous solution of T H F (lo%), acetic acid ( l a ) , sodium heptasulfonate monohydrate (0.88%), and methanesulfonic acid (0.02%), adjusted to RH 3.1 with tetramethylammonium hydroxide. Phosphorescence lifetime measurements were carried out with a nitrogen laser pumped dye laser (Molectron DL11). Signals were detected by an EM1 9816B photomultiplier through a Spex double-mate monochromator, and were displayed with a Tektronix 7834 osci1loscope.l' The complexes were dissolved in appropriate solvents (- lo4 M) and deaerated with high-purity N2. The temperature of the Dewar containing the sample was monitored with a thermocouple. The complexes were deuterated at the N centers in neutral D20, and the level of deuteration was checked by IR spectroscopy and FAB mass spectrometry. Electrochemical studies were performed by using a conventional three-electrode configuration with iR compensation and a PAR Model 170 electrochemical system. For rapid-scan cyclic voltammograms a Tektronix (2-70 oscilloscope camera connected to a Tektronix 503 1 storage oscilloscopeand the PAR Model 170 system were used. Working electrodes were a dropping mercury electrode (DME), a hanging mercury drop electrode (HMDE) and stationary Pt or Au electrodes. The reference electrode was a saturated calomel or a silver/silver chloride electrode and was separated from the working and auxiliary electrodes in an electrode bridge with a fine-porosity frit. The auxiliary electrode was a platinum coil. Solutions were degassed with solvent-saturated argon through a standard purge tube. Double glass distilled water or dried analytical grade organic solvents were employed. Sodium perchlorate (0.1 M), sodium trifluoromethanesulfonate (0.1 M), or tetramethylammonium trifluoromethanesulfonate (0.1 M) were used as electrolytes. Complex concentrations close to millimolar were used throughout. Coulometric analyses were performed with a PAR Model 337A coulometry cell system using either a stirred mercury pool or platinum basket working electrode and an Amel Model 551 potentiostat and Model 731 digital integrator. Room-temperature magnetic moments were determined by both the standard Gouy method and the Faraday method. Details of the instrumental methods and a full temperature-dependent study of the magnetism will be published elsewhere." Visible absorption spectra were recorded with a Cary 17 spectrophotometer. Visible absorption spectra of electrochemially reduced solutions in water were determined by circulating the solution from the coulometry cell through a flow cell in a Hewlett-Packard 8450A spectrophotometer. Infrared spectra (KBr disks) were recorded with a Perkin-Elmer 457 spectrometer. Crystal Structure Analysis. A crystal needle of [Cr(diamsar)]CI3.H2O of dimensions 0.09 X 0.09 X 0.30 mm3 was mounted on a glass fiber and coated with cyanoacrylate glue. Lattice parameters at 25 OC were determined by a least-squares fit to the setting angles of 25 independent reflections, measured and refined by scans performed on an Enraf-Nonius CAD-4 four-circle diffractometer employing graphite-monochromated Mo K a radiation. Crystal data: CI4H&I3CrN80, fw 490.85, monoclinic space group P2p2, a = 9.474 (2) A, b = 13.331 (3) A, c = 18.221 (5) A, fi = 92.756 (O)', D, = 1.418 g V = 2290.93 A3,Z = 4, p(Mo Ka) = 8.57 m-l, X(Mo Ka) = 0.7107 A, F(000) = 940 e. Intensity data were collected in the range 1.5 < 0 < 24.5 by using an w n / 3 0 scan, where n (=6) was optimized by profile analysis of a typical reflection. The w scan angles and horizontal counter apertures employed were (0.9 0.35 tan 0)' and (2.40 0.5 tan 0) mm respectively. Three standard reflections, monitored after every hour of data collection, indicated that by completion of the data collection no decomposition had occurred. Data reduction and application of Lorentz and polarization corrections were performed by using the program SUSCAD.I9 Absorption corrections were applied
+
+
(17) Johansen, 0.;Mau, A. W.-H.; Sam, W. H. F. Chem. Phys. Lett. 1983, 94, 107. (18) Martin, L. L.;Murray, K. S.; Sargeson, A. M., to be submitted for publication. (19) SUSCAD and ABSORD data reduction programs for the CAD-4 diffractometer, University of Sydney, 1976; SHELX program for crystal structure determination, Sheldrick, G. M., 1976.
Table I. Positional Parameters for [Cr(diamsar)]C13-H20,Excluding Hydrogen Atomso
atom
X
25097 (5) 2353 (1) 9256 (1) 4212 (1) 2931 (5) -1841 (3) 6853 (3) 840 (2) 2199 (2) 1127 (3) 2792 (2) 4065 (2) 4058 (3) -419 (3) -220 (4) -512 (3) 688 (3) 5438 (3) 5429 (3) 5368 (3) 4293 (3) 3015 (3) 4400 (3) 606 (3) 2028 (3) 1928 (3) 3376 (4)
Y 26242 (3) 4321 (1) 4727 (1) 3932 (1) -2041 (5) 3854 (1) 1346 (2) 2922 (2) 4001 (2) 1964 (2) 1374 (2) 3377 (2) 2115 (2) 3495 (2) 2522 (3) 3287 (3) 4297 (2) 1740 (2) 1784 (2) 2794 (2) 1037 (2) 4775 (2) 4315 (2) 2017 (2) 1572 (3) 1716 (3) 1329 (2)
2
12940 (2) -595 (1) 3687 (1) 3252 (1) 998 (3) 1863 (2) 754 (2) 550 (1) 1792 (1) 1994 (1) 645 (1) 754 (1) 2056 (1) 1682 (2) 2124 (2) 854 (2) 1895 (2) 914 (2) 1754 (2) 569 (2) 574 (2) 1386 (2) 1179 (2) 74 (2) -14 (2) 2690 (2) 2506 (2)
'All coordinates are X104 except those for Cr (XIOs). with the program ABSORB.19 Maximum and minimum transmission factors were estimated to be 0.94 and 0.84, respectively. Of the 3182 reflections collected, 704 with Z > 2.5u(I) were considered unobserved and not used in the calculations. The structure was solved and refined by application of the heavy-atom technique. Successive difference syntheses located all non-hydrogen atoms of the structure, including one water molecule. In the refinement by full-matrix least-squares techniques, the hydrogen atoms were either fixed at their found positions (water and N H 2 sites) or allowed to ride in fixed orientation to their connections ( N H and CH2 sites; d = 0.95 A). A weighting scheme was applied and refined, converging at w = 0.97/(u2(FO) 0.O074(F,J2). Refinement converged with R = 0.0313 and R, = 0.0350 at which state the largest peak in the final difference map was
