5H) 3.69, (t, J = 4.8 Hz, 10H); 2.63, (s, 20H); 2.59, (t, J = 4.8 Hz,
10H). 13C NMR (CDCl3): δ 58.59 (5C), 56.03 (5C), 52.55 (10C).
potential measured by an Orion Ross Sure Flow 81–72BN
combination electrode connected to an Orion SA 720 pH meter.
The autoburette and pH meter were interfaced to an IBM com-
patible personal computer which controlled the addition of
titrant using a program written by Drs A. P. Arnold and P. A.
Duckworth so that successive additions of titrant caused a
decrease of ca. 4 mV in the potential reading. The electrode was
calibrated by a titration in the absence of ligand and fitting the
resulting data from this strong acid strong base titration to the
Nernst equation to find correct values for Eo and pKw. The pKa
and stability constants were determined using the program
SUPERQUAD.37 Stability constant data were gathered from
solutions to which 0.1 M metal perchlorate solution was added
so as to give a metal-to-ligand ratio in the range 0.5 : 1 to 2 : 1.
At least three titrations, with different ratios, were performed
for each metal ion.
Phec15ؒ5HBr. Hydrobromic acid (48%, 0.37 cm3, 3.25 mmol)
was added dropwise to a stirring solution of phec15 (0.28 g,
0.638 mmol) in dry ethanol (10 cm3) cooled to 0 ЊC. The
pentahydrobromide salt precipitated out as a fine cream solid
and was filtered off under nitrogen, washed with cold ethanol
(2 cm3) and dried in vacuo. Yield 279 mg, 52%. 13C NMR (d6-
DMSO): δ 56.02 (5C), 55.11 (5C), 49.00 (10C). (Found: C, 28.8;
H, 6.3; N, 8.16. C20H50Br5N5O5 requires C, 28.59; H, 6.00; N,
8.34%).
[Ba(phec15)](ClO4)2. Barium() perchlorate (0.29 g, 0.86
mmol) was dissolved in dry ethanol (5 cm3) and the solution
was added dropwise to a solution of phec15 (0.25 g, 0.57 mmol)
in dry ethanol (15 cm3) with stirring. The resultant solution was
heated to reflux for 2.5 h. On cooling, cream crystals formed
which were filtered and washed with ice cold ethanol (5 cm3).
Yield 213 mg, 48%. 13C NMR (d4-MeOH): δ 57.23 (5C), 53.29
(5C), 52.15 (10C). (Found: C, 31.2; H, 6.1; N, 8.7. C20H45-
BaCl2N5O13 requires C, 31.12; H, 5.88; N, 9.07%).
Variable temperature 13C{1H} NMR and lineshape analysis
13C{1H} NMR spectral data were recorded at 10 K intervals,
thermostatted to 0.3 K, in the temperature range 205–373 K
and at 5 K intervals around the coalescence temperature. Line-
shape analysis, leading to a determination of the rate constant,
k, characterising the rate of intramolecular exchange at each
temperature,34 was conducted using a Digital Venturis 575
computer. The temperature-dependent 13C line widths and
chemical shifts employed in the analysis were obtained by
extrapolation from low temperatures where no exchange-
induced modification occurred.
[Sr(phec15)](ClO4)2ؒ3H2O.
A solution of strontium()
perchlorate hexahydrate (220 mg, 0.77 mmol) in dry ethanol
(5 cm3) was added dropwise to a solution of phec15 (334 mg,
0.77 mmol) in dry ethanol (15 cm3) over several minutes. On
addition of the metal perchlorate the solution became cloudy
and the resultant suspension was heated to reflux for 3 h. Once
cold, the solvent was removed and the resultant cream solid
dried in vacuo. Yield 480 mg, 87%. 13C NMR (d4-MeOH): δ
56.77 (5C), 53.39 (very broad, 15C). (Found: C, 30.9; H, 6.2; N,
8.7. C20H51Cl2N5O16Sr requires C, 30.95; H, 6.62; N, 9.02%).
Ab initio modelling
Ab initio modelling was performed using Gamess-US28 at the
restricted Hartree–Fock level of theory with the in-built effect-
ive core potential-containing basis set of Stevens, Basch,
Krauss, Jasien and Cundari (the SBKJC basis set).38–40 All elec-
trons for H, C, N and O were incorporated, but only the valence
shell electrons for Ba2ϩ, Sr2ϩ and Cd2ϩ, together with their
effective core potentials. To ensure that the predicted structures
shown in Figs. 2–4 and described in Tables 3 and 4 best repre-
sent the structure having the true global energy minimum, trial
structures with pendant arms either all on the same side of the
nitrogen atom plane or on differing sides were used as starting
points for the minimisation. A range of pendant arm conform-
ations were superimposed on these structures to give a broad
selection of starting points. Irrespective of the starting point
convergence to the structure shown in Figs. 2–4 and described
in Tables 3 and 4 resulted, confirming these as the most likely
molecular structures.
[Cd(phec15)](ClO4)2. Cadmium() perchlorate hexahydrate
(895 mg, 2.1 mmol) was dissolved in dry ethanol (10 cm3) and
the solution added dropwise to a solution of phec15 (619 mg,
1.4 mmol) in dry ethanol (10 cm3). The mixture immediately
became cloudy and was refluxed overnight. After cooling half
the solvent was removed causing the complex to crystallize as
white crystals, which were filtered and washed with ice cold
ethanol (5 cm3). Yield 621 mg, 80%. 13C NMR (d6-DMSO):
δ 58.04 (1C), 56.23 (broad, 4C), 55.71 (2C), 55.32 (2C), 55.10
(2C), 53.63 (2C), 52.18 (2C), 51.52 (2C), 51.48 (1C), 50.80 (2C).
(Found: C, 32.1; H, 6.1; N, 9.1. C20H45CdCl2N5O13 requires C,
32.16; H, 6.07; N, 9.38%).
[Zn(phec15)](ClO4)2ؒH2O. Zinc() perchlorate hexahydrate
(188 mg, 0.50 mmol) was dissolved in dry ethanol (5 cm3) and
the solution was added slowly to a stirred solution of phec15
(199.5 mg, 0.46 mmol) in dry ethanol (12 cm3). A white sticky
precipitate formed and the suspension was heated at reflux for
2 h causing complete dissolution. After this time half the sol-
vent was evaporated off. On cooling the solution white crystals
of the product formed. These were filtered off, washed with
Acknowledgements
Funding by the Australian Research Council and provision
of computational resources by the South Australian
Regional Computational Chemistry Facility are gratefully
acknowledged.
cold ethanol (6 cm3) and dried in vacuo. Yield 107 mg, 33%. 13
C
NMR (d6-DMSO): δ 60.02 (1C), 56.32 (broad, 4C), 55.38 (2C),
55.11 (2C), 52.71 (2C), 51.37 (2C), 50.75 (2C), 50.18 (broad,
3C), 48.79 (2C). Found: C, 33.2; H, 6.3; N, 9.4. C20H47Cl2-
N5O14Zn requires C, 33.46; H, 6.60; N, 9.76%).
References
1 See, for example, K. P. Wainwright, Adv. Inorg. Chem., 2001, 52, 293
and references cited therein.
2 C. B. Smith, K. S. Wallwork, J. M. Weeks, M. A. Buntine,
S. F. Lincoln, M. R. Taylor and K. P. Wainwright, Inorg. Chem.,
1999, 38, 4986.
3 C. B. Smith, A. K. W. Stephens, K. S. Wallwork, S. F. Lincoln,
M. R. Taylor and K. P. Wainwright, Inorg. Chem., 2002, 41, 1093.
4 E. Kovacs, E. Archer, M. Russell and A. Sherry, Synth. Commun.,
1999, 29, 2817.
5 R. W. Hay, R. Bembi, W. T. Moodie and P. R. Norrhan, J. Chem.
Soc., Dalton Trans., 1982, 2131.
6 P. Osvath, N. F. Curtis and D. C. Weatherburn, Aust. J. Chem., 1987,
40, 811.
Potentiometric titrations
The potentiometric titrations were carried out under an inert
atmosphere of water-saturated argon in a water jacketed vessel
maintained at 25 ЊC. Data were obtained from 10 cm3 aliquots
of solution containing 0.010 M HClO4, 0.100 M NEt4ClO4, and
approximately 1.0 × 10Ϫ3 M of phec15 titrated with 0.10 M
NEt4OH. A Metrohm E665 Dosimat autoburette equipped
with a 5 cm3 burette was used to deliver the titrant and the
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J. Chem. Soc., Dalton Trans., 2002, 3571–3577