Nonbridging and monodentate carboxylate coordination of calcium(2+) through the use of intramolecular hydrogen bonding in a new sterically hindered carboxylate ligand

Article abstract of DOI:10.1002/ejic.200400441

The sterically hindered carboxylate ligand 2,6-bis(2,2- dimethylpropionylamino)benzoic acid (HL) has been prepared. The two intramolecular hydrogen bonds in HL are exploited to restrict the corresponding carboxylate anion (L^-) to non-bridging coordination and to preorganise its sterically bulky substituents proximal to the first and second coordination sphere of the bound metal ion. The crystal structures of the ligand anion as the ammonium salt [NH₄][L] and the distorted octahedral calcium complex CaL₂(H₂O)₂, in which L ^- binds to the calcium(2+) ion in a monodentate, nonbridging mode, are described. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400441

FULL PAPER
Nonbridging and Monodentate Carboxylate Coordination of Calcium(2؉)
Through the Use of Intramolecular Hydrogen Bonding in a New Sterically
Hindered Carboxylate Ligand
Jonathan D. Crane,*[a] David J. Moreton,[b] and Eleanor Rogerson[a]
Keywords: Calcium / Hydrogen bonds / Carboxylate ligands / Sterically hindered ligands
The sterically hindered carboxylate ligand 2,6-bis(2,2-di-
ligand anion as the ammonium salt [NH4][L] and the dis-
methylpropionylamino)benzoic acid (HL) has been prepared. torted octahedral calcium complex CaL2(H2O)2, in which L−
The two intramolecular hydrogen bonds in HL are exploited
to restrict the corresponding carboxylate anion (L−) to non-
bridging coordination and to preorganise its sterically bulky
substituents proximal to the first and second coordination
sphere of the bound metal ion. The crystal structures of the
binds to the calcium(2+) ion in a monodentate, nonbridging
mode, are described.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
examples of such calcium(2ϩ) coordination for small mol-
ecules in the Cambridge Crystallographic Database,[5] these
are all apparently serendipitous, arising unpredictably from
the use of polydentate ligands and/or fortuitous packing ar-
rangements.[6]
Sterically hindered ligands are commonly used to control
the coordination environment of metal ions, and hence their
properties, through favouring lower coordination numbers
and/or by preventing the unwanted formation of polynu-
clear species that often arise through ligand bridging.[1] This
approach is particularly challenging for carboxylate ligands,
nevertheless over recent years the application of this strat-
egy has proven to be effective for the synthesis of some low
molecular weight model compounds for transition metal
ion sites in proteins, in which the role of the protein in pro-
viding a preorganised arrangement of carboxylate ligands
at a metal ion binding site has been to some extent repro-
duced by the use of steric hindrance.[2] With sterically hin-
dered carboxylate ligands the challenge is not primarily to
limit coordination numbers, but rather to inhibit the strong
natural tendency of the carboxylate group to bridge be-
tween two or more metal ions which results in the undesired
formation of polymeric or highly polynuclear species. This
is particularly problematic for the coordination chemistry
We wished to design a sterically hindered carboxylate li-
gand that specifically excludes the possibility of laterally
bridging coordination to calcium(2ϩ) or other metal ions.
The sterically hindered 2,6-dialkyl- or 2,6-diarylbenzoic
acid derivatives currently used for transition metal studies
were not considered appropriate as the carboxylate group
is free to rotate out of the plane of the aromatic ring and
thus bridging is still allowed to occur.[2] The chosen design
strategy was to use two intramolecular hydrogen bonds
from adjacent amide groups to constrain the carboxylate
group to be coplanar with the aromatic ring and therefore
prevent lateral bridging to metal ions, whilst preorganising
two sterically bulky groups proximal to the first and second
coordination spheres of any bound metal ion. We herein
report the synthesis of the tert-butyl-substituted ligand HL,
the structure of its anion (as the ammonium salt) and its
complexation with calcium(2ϩ). Moreover, the straightfor-
ward synthesis of HL should allow the facile preparation
of derivatives with a wide variety of R substituents, thus
˚
of calcium(2ϩ) which has an ionic radius of 0.99 A, sub-
stantially larger than divalent transition metal ions [e.g.,
high-spin iron(2ϩ), 0.78 A], and as a consequence the triply
bridging motif I and related structures are commonplace
for simple carboxylate ligands.[3] In contrast, monodentate,
nonbridging carboxylates are common ligands for
calcium(2ϩ) in proteins,[4] and although there are several
˚
[a]
Department of Chemistry, University of Hull
Cottingham Road, Kingston-upon-Hull, HU6 7RX,UK
E-mail: j.d.crane@hull.ac.uk
[b]
Lubrizol International Laboratories
Belper, Derby, DE56 1QN, UK
Eur. J. Inorg. Chem. 2004, 4237Ϫ4241
DOI: 10.1002/ejic.200400441
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4237

J. D. Crane, D. J. Moreton, E. Rogerson
FULL PAPER
providing the opportunity for further control over the first
The structure of the carboxylate anion L؊ is revealed by
and second coordination spheres of any metal ion and the single-crystal X-ray structure determination of the am-
greater scope for the design of metallobiosite model com- monium salt 3 (Figure 1). As expected, there are intramol-
plexes where restriction of the carboxylate coordination ecular hydrogen bonds between the two amide NϪH groups
mode is required.
and the carboxylate oxygen atoms. The X-ray diffraction
data were of sufficient quality for the amide NϪH hydrogen
atoms to be located in the difference Fourier map and freely
˚
refined; the NϪH bond lengths of 0.90(3) A indicate that
there is no significant lengthening of the NϪH bonds com-
˚
pared with the expected value of 0.85Ϫ0.90 A, as deter-
mined by X-ray diffraction.[5] In addition, the N(1)···O(1)
˚
and N(2)···O(2) distances of 2.564(3) and 2.571(3) A are
relatively long, and the N(1)ϪH(1)···O(1) and
N(2)ϪH(2)···O(2) angles of 142(2) and 147(3)° are signifi-
cantly more acute than the usual range of 160Ϫ180° for
strong hydrogen bonds. Furthermore, the carboxylate and
two amide groups are slightly twisted out of the plane of
the central aromatic ring with torsional angles between the
respective pairs of least-squares planes of 21.3(1), 10.6(1)
and 18.7(1)°. All these structural parameters suggest that
these hydrogen bonds are weaker than in the near-planar
2,6-dihydroxybenzoate anion (Table 1),[13] and indicate that
HL should be a weaker acid than 2,6-dihydroxybenzoic
acid. However, the most important effect of these hydrogen
bonds is that they successfully preorganise the planar, trans-
primary-amide groups and therefore position the bulky tert-
butyl groups to restrict coordination to the carboxylate
group. In the lattice of 3 the packing of the carboxylate
anions leaves cavities that are each occupied by a pair of
ammonium counterions, with an inter-ammonium cation
Results and Discussion
The carboxylic acid HL was readily prepared in 41%
yield by the oxidation of the aromatic methyl group of di-
amide 1[7] with potassium permanganate in aqueous pyri-
dine at reflux (Scheme 1).[12] The two intramolecular hydro-
gen bonds in HL would be expected to stabilise the corre-
sponding carboxylate anion, but less so than for 2,6-di-
hydroxybenzoic acid (vide supra).[13] In nonprotogenic
solvents (e.g., chloroform) the carboxylic acid HL was
found readily to eliminate water over several hours to form
1
the benzoxazine 2. H and 13C NMR spectroscopy showed
that in chloroform an equilibrium (1:2) mixture of HL/2
(and water) was formed after approximately 24 h. Pure 2
could be obtained in quantitative yield by the deliberate
dehydration of a toluene solution of HL with excess acetic
anhydride. Under mildly basic conditions in the presence
of water both HL and 2 were found to rapidly reform the
carboxylate anion L؊.
˚
(N···N) distance of 3.675(3) A, which, although short, is
typical for ammonium carboxylate structures.[14] This elec-
trostatically unfavourable arrangement is compensated for
by the formation of hydrogen bonds to all four of the am-
monium NϪH bonds, thus the two ammonium ions are
imprisoned in a cage of eight appropriately positioned hy-
drogen bond acceptor oxygen atoms (Figure 2, Table 2).
Figure 1. ORTEP[18] view of the molecular structure of 3 with ther-
mal ellipsoids shown at 40%; hydrogen bonds are denoted by
˚
dashed lines; selected bond lengths [A]: C(8)ϪN(1) 1.344(3),
C(8)ϪO(3) 1.228(3), C(10)ϪN(2) 1.342(3), C(10)ϪO(4) 1.222(3)
Scheme 1
4238
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 4237Ϫ4241

Nonbridging and Monodentate Carboxylate Coordination of Calcium(2ϩ)
Table 1. Structural parameters related to the intramolecular hydrogen bonding of the carboxylate group in 3 and 4
FULL PAPER
Ϫ
[a]
Compound
{ArCO2
}
3
4
Hydrogen-bonding geometry
(X ϭ O)
0.81(2), 0.83(2)
1.78(2), 1.77(2)
2.511(2), 2.542(2)
(X ϭ N)
0.90(3), 0.90(4)
1.79(3), 1.77(4)
2.564(3), 2.571(3)
(X ϭ N)
˚
X(1)ϪH(1), X(2)ϪH(2) [A]
0.88(3), 0.90(3)
1.93(3), 1.88(3)
2.683(2), 2.622(2)
142(2), 138(2)
0.88(3)
1.82(3)
2.671(2)
˚
˚
H(1)···O(1), H(2)···O(2) [A]
X(1)···O(1), X(2)···O(2) [A]
X(1)ϪH(1)···O(1), X(2)ϪH(2)···O(2) [°]
149(2), 153(2)
142(3), 147(3)
˚
O(5)ϪH(3) [A]
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
˚
H(3)···O(2) [A]
˚
O(5)···O(2) [A]
O(5)ϪH(3)···O(2) [°]
162(3)
Carboxylate group geometry
˚
C(1)ϪO(1), C(2)ϪO(2) [A]
1.283(2), 1.260(2)
1.481(2)
1.4(1)
1.235(3), 1.248(3)
1.519(3)
21.3(1)
1.270(2), 1.255(2)
1.519(2)
33.6(1)
˚
C(1)ϪC(2) [A]
Ϫ
ArϪCO2 torsional angle [°]
[a]
2,6-Dihydroxybenzoate anion, ref.[13]
˚
only slightly longer than the value of 2.337 A found for the
comparable, unhindered octahedral complex Ca(acac)2-
(H2O)2.[15] The CaϪO(1) distance is the longest in the
˚
calcium coordination sphere in 4, 2.3830(11) A, presumably
due to the steric congestion of the carboxylate group, and
the carboxylate is clearly monodentate with a very long
˚
Ca(1)···O(2) distance of 3.7205(12) A. It is particularly
noteworthy that this coordination mode is preferred over a
more symmetrical bidentate coordination, or the formation
of simple second coordination sphere [Ca(H2O)n]2ϩ hydro-
gen-bonded salts of the ligand anion. One possible reason
for the stability of 4 is that the long CaϪO(1) bond is sup-
ported by a strong hydrogen bond between the adjacent
water ligand and the nonbound carboxylate oxygen atom
Figure 2. ORTEP[18] view of the ammonium cation hydrogen-bond-
ing environment in 3 with thermal ellipsoids shown at 40%; hydro-
gen bonds are denoted by dashed lines; the majority of the ligand
structures have been omitted for clarity; symmetry transformations:
a: 2 Ϫ x, 1 Ϫ y, z; b: 3/2 Ϫ x, 1/2 ϩ y, z; c: x, 1/2 ϩ y, 1/2 ϩ z
Table 2. Hydrogen-bonding geometry of the ammonium cation in 3
DϪH···A[a]
DϪH
H···A
D···A
ЄDϪH···A
N(3)ϪH(3)···O(1)
N(3)ϪH(4)···O(3b)
N(3)ϪH(5)···O(2a)
N(3)ϪH(6)···O(4c)
0.90(3)
0.99(3)
1.00(3)
0.95(3)
1.83(3)
1.79(3)
1.77(3)
1.85(3)
2.713(3)
2.750(3)
2.749(3)
2.776(3)
166(3)
160(2)
168(3)
166(3)
[a]
Symmetry transformations: a: 2 Ϫ x, 1 Ϫ y, z; b: 3/2 Ϫ x, 1/2 ϩ
y, z; c: x, 1/2 ϩ y, 1/2 ϩ z.
The structure of 4 (Figure 3) shows that the carboxylate
ligand is bound to the calcium ion in the desired monodent-
ate and nonbridging manner, and that the calcium ion is
restricted to six coordination and a distorted octahedral ge-
ometry. Indeed, the ‘‘average’’ coordination environment
for calcium(2ϩ) in proteins is octahedral, and moreover
with a mixture of carboxylate, peptide carbonyl and water
Figure 3. ORTEP[18] view of the structure of 4 with thermal ellip-
soids shown at 50%; hydrogen bonds are denoted by dashed lines;
for clarity only one ligand is shown in its entirety; selected bond
˚
lengths [A] and angles [°]: Ca(1)ϪO(1) 2.3830(11), Ca(1)ϪO(5)
2.3378(11), Ca(1)ϪO(3b) 2.3560(11), C(8)ϪN(1) 1.349(2),
C(8)ϪO(3) 1.241(2), C(10)ϪN(2) 1.362(2), C(10)ϪO(4) 1.232(2);
O(1)ϪCa(1)ϪO(5)
80.45(4),
O(1)ϪCa(1)ϪO(1a)
93.16(6),
O(1)ϪCa(1)ϪO(3b) 164.67(4), O(3b)ϪCa(1)ϪO(3c) 90.37(6),
O(3b)ϪCa(1)ϪO(5) 84.29(4), O(5)ϪCa(1)ϪO(5b) 177.44(7); sym-
metry transformations: a: 3 Ϫ x, y, 3/2 Ϫ z; b: 1/2 ϩ x, 1/2 ϩ y, z;
ligands,[4] coincidently very similar to the specific structure
˚
described here. The average CaϪO bond length is 2.359 A, c: 5/2 Ϫ x, 1/2 ϩ y, 3/2 Ϫ z
Eur. J. Inorg. Chem. 2004, 4237Ϫ4241
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4239

J. D. Crane, D. J. Moreton, E. Rogerson
FULL PAPER
pure sample could not be obtained by recrystallisation due to the
facile conversion of HL to N-(2-tert-butyl-4-oxo-4H-benzo-
[d][1,3]oxazin-5-yl)-2,2-dimethylpropionamide (2). 1H NMR
(400 MHz, CDCl3): δ ϭ 1.32 (s, 18 H, CH3), 7.20 (br. s, 1 H,
O(2) (Table 1); thus the carboxylate group is effectively act-
ing as a bidentate ligand to a CaϪOH2 group. Indeed, sev-
eral similar structural motifs have been described over re-
cent years in the transition metal chemistry of sterically hin-
dered carboxylate ligands,[2] and in calcium(2ϩ) coordi-
nation chemistry.[16] The coordination sphere of the calcium
ion is completed by one amide carbonyl group from each
CO2H), 7.49 (t, J ϭ 8.3 Hz, 1 H, Ha), 8.26 (d, J ϭ 8.3 Hz, 2 H,
Hb), 10.44 (s, 2 H, NH) ppm. 13C NMR (100.6 MHz, CDCl3): δ ϭ
27.6, 40.3, 106.8, 117.1, 134.3, 140.9, 169.6, 177.5 ppm. IR (KBr):
ν˜ ϭ 3407 (m), 2970 (m), 2874 (w), 1694 (s), 1636 (m), 1610 (m),
1582 (s), 1514 (s), 1464 (s), 1368 (m), 1294 (m), 1222 (s), 1163 (m),
1125 (w), 812 (m), 785 (m), 752 (m), 701 (w), 420 cmϪ1 (w). MS
3
3
of two equivalent neighbouring molecules, and the
˚
Ca(1)ϪO(3a) bond length of 2.3560(11)
A
and
Ca(1)ϪO(3a)ϪC(8a) angle of 169.98(11)° are typical of a (EI): m/z (%) ϭ 320 (14) [Mϩ], 302 (26) [Mϩ Ϫ H2O].
predominantly electrostatic interaction with the metal ion.
This interaction also results in a slight perturbation of the
N-(2-tert-Butyl-4-oxo-4H-benzo[d][1,3]oxazin-5-yl)-2,2-dimethyl-
propionamide (2): In nonaqueous solutions (e.g., chloroform) HL
was found to eliminate water over a period of a few hours to give
an equilibrium mixture of HL, the benzoxazine 2 and water. The
deliberate dehydration of HL with excess acetic anhydride in tolu-
ene gave a near quantitative yield of pure 2. A sample for analysis
was recrystallised from petroleum ether (boiling range 60Ϫ80 °C)
as colourless needles. C17H22N2O3 (302.37): calcd. C 67.53, H 7.33,
N 9.26; found C 67.49, H 7.46, N 9.25. 1H NMR (400 MHz,
amide group with a longer C(8)ϭO(3) distance of 1.241(2)
˚
˚
A and shorter C(8)ϪN(1) distance of 1.349(2) A compared
˚
to 1.232(2) and 1.362(2) A, respectively for the other, non-
coordinated amide group. Similar to as described above for
3, the carboxylate and two amide groups in 4 are twisted
out of the plane of the central aromatic ring. The torsional
angles between the respective pairs of least-squares planes
of 33.6(1), 25.0(1) and 10.1(1)° show that the ligand in 4
has larger distortions from planarity than in 3, particularly
with regard to the carboxylate group. For 3 and 4 these
variations in torsional angles probably primarily arise from
different packing effects and bonding requirements of the
ammonium and calcium(2ϩ) ions, respectively.
3
CDCl3): δ ϭ 1.37 (s, 9 H, CH3), 1.40 (s, 9 H, CH3), 7.26 (d, J ϭ
8.2 Hz, 1 H, Hb), 7.75 (t, 3J ϭ 8.2 Hz, 1 H, Ha), 8.79 (d, 3J ϭ
8.2 Hz, 1 H, Hc), 11.39 (s, 1 H, NH) ppm. 13C NMR (100.6 MHz,
CDCl3): δ ϭ 27.5, 27.6, 37.8, 40.6, 103.9, 118.2, 120.8, 137.9, 141.6,
147.1, 162.5, 167.2, 178.5 ppm. IR (KBr): ν˜ ϭ 3298 (w), 2968 (m),
1716 (m), 1698 (s), 1645 (m), 1610 (m), 1580 (s), 1542 (m), 1475
(m), 1291 (m), 1182 (m), 1157 (s), 1049 (m), 914 (w), 817 (s), 715
(m), 690 (m), 556 cmϪ1 (w). MS (EI): m/z (%) ϭ 302 (31) [Mϩ],
245 (100) [Mϩ Ϫ C4H9].
In conclusion, the sterically hindered ligand HL designed
for nonbridging coordination to metal ions has been suc-
cessfully prepared and its desired mode of coordination
Ammonium 2,6-Bis(2,2-dimethylpropionylamino)benzoate, [NH4]L
structurally characterised for a mononuclear calcium(2ϩ) (3): Carboxylic acid HL (0.96 g, 3 mmol) and potassium hydroxide
(0.16 g, 2.9 mmol) were dissolved in methanol/water (1:1, 40 mL).
Concentrated aqueous ammonia (20 mL) was added, the solution
filtered and allowed to concentrate slowly. Large, colourless, X-ray
quality crystals of 3 were obtained after 2Ϫ3 d. Yield: 0.56 g (55%).
C17H27N3O4 (337.42): calcd. C 60.51, H 8.07, N 12.45; found C
60.35, H 8.32, N 12.32. 1H NMR (400 MHz, [D6]DMSO): δ ϭ 1.20
(s, 18 H, CH3), 7.14 (t, 3J ϭ 8.2 Hz, 1 H, Ha), 7.24 (br. s, 4 H,
NH4ϩ), 8.21 (d, 3J ϭ 8.2 Hz, 2 H, Hb), 14.04 (br. s, 2 H, NH) ppm.
13C NMR (100.6 MHz, [D6]DMSO): δ ϭ 27.5, 111.5, 113.1, 129.1,
141.6, 171.3, 176.3 (the tBu peak at ca. 40 ppm is masked by the
solvent peak). IR (KBr): ν˜ ϭ 3080 (m), 2970 (m), 2155 (w), 1943
(w), 1654 (m), 1611 (m), 1580 (s), 1473 (s), 1433 (s), 1362 (s), 1252
(m), 916 (w), 839 (m), 785 (m), 709 (w), 548 (w), 421 cmϪ1 (w).
complex. The coordination chemistry of HL and related li-
gands with transition metal and lanthanide ions is currently
under investigation.[17]
Experimental Section
General: N-[3-(2,2-Dimethylpropionylamino)-2-methylphenyl]-2,2-
dimethylpropionamide (1) was prepared from 2,6-diaminotoluene
and trimethylacetyl chloride by a literature method.[7] Elemental
analyses were obtained with a Fisons EA1108 CHNS analyser. IR
spectra were recorded as KBr disks with a PerkinϪElmer Paragon-
100 FT-IR spectrophotometer. NMR spectra were recorded using
a Jeol JNM-LA400 spectrometer at room temperature (20 °C) and
are reported relative to tetramethylsilane. Mass spectra were re-
corded with a Finnigan 1200 (EI) mass spectrometer.
Calcium Bis[2,6-bis(2,2-dimethylpropionylamino)benzoate] Dihy-
drate, CaL2(H2O)2 (4): Carboxylic acid HL (0.96 g, 3 mmol) and
potassium hydroxide (0.16 g, 2.9 mmol) were dissolved in water
(45 mL). A solution of calcium acetate monohydrate (0.24 g,
1.5 mmol) in water (5 mL) was added and the resulting solution
was filtered. Large, colourless, X-ray quality crystals of 4 were ob-
tained after 3Ϫ4 d. Yield: 0.68 g (63%). C34H50CaN4O10 (714.87):
2,6-Bis(2,2-dimethylpropionylamino)benzoic Acid (HL): Potassium
permanganate (4.75 g, 30 mmol) and diamide 1 (4.35 g, 15 mmol)
in pyridine/water (1:1, 150 mL) was heated at reflux with constant
stirring for 2 h, or until the purple colour of the permanganate had
disappeared. The reaction mixture was allowed to cool to room
temperature, water (250 mL) added, then the solution filtered to
remove the dark brown precipitate of hydrated manganese dioxide.
The pale yellow filtrate was concentrated to near dryness under
reduced pressure and water (150 mL) added. The insoluble residue
of unchanged 1 was filtered off, concentrated hydrochloric acid
(20 mL) added to the filtrate and the precipitate of HL extracted
into dichloromethane (3 ϫ 40 mL). The dichloromethane extracts
were combined, dried (MgSO4), filtered, and the solvents evapo-
rated to dryness under reduced pressure. Yield: 2.55 g (53%). The
product was sufficiently pure for subsequent use, but an analytically
1
calcd. C 57.13, H 7.05, N 7.84; found C 56.97, H 7.01, N 7.66. H
NMR (400 MHz, [D6]DMSO): δ ϭ 1.21 (s, 18 H, CH3), 3.35 (br.
3
3
s, 2 H, H2O), 7.16 (t, J ϭ 8.3 Hz, 1 H, Ha), 8.22 (d, J ϭ 8.3 Hz,
1 H, Hb), 13.85 (br. s, 2 H, NH) ppm. 13C NMR (100.6 MHz,
[D6]DMSO): δ ϭ 27.5, 111.0, 113.2, 129.4, 141.7, 172.2, 176.3 (the
tBu peak at ca. 40 ppm is masked by the solvent peak). IR (KBr):
ν˜ ϭ 3398 (m), 3133 (m), 2967 (m), 1652 (m), 1626 (m), 1591 (m),
1480 (s), 1441 (m), 1360 (s), 1306 (m), 1252 (m), 1172 (m), 991 (w),
917 (w), 831 (m), 783 (m), 747 (m), 640 (w), 549 (w), 416 cmϪ1 (w).
Crystal Structure Determinations: Data were collected at 150(2) K
˚
employing a wavelength of 0.71073 A (Mo-Kα) with a Stoe IPDS
4240
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 4237Ϫ4241

Nonbridging and Monodentate Carboxylate Coordination of Calcium(2ϩ)
Table 3. Crystal data and structure refinement for 3 and 4
FULL PAPER
Compound
3
4
Empirical formula
C17H27N3O4
337.42
C34H50CaN4O10
714.86
Mr [g molϪ1
]
Crystal system
Space group
orthorhombic
Aba2
20.6625(17)
11.3308(10)
17.0301(12)
3987.1(6)
8, 1.124
0.080
orthorhombic
C2221
12.6255(6)
13.7423(8)
21.4274(11)
3717.7(3)
4, 1.277
0.228
1528
˚
a [A]
˚
b [A]
˚
c [A]
3
˚
V [A ]
Z, Dcalcd. [g cmϪ3
]
]
µ(Mo-Kα) [mmϪ1
F(000)
1456
Crystal dimensions [mm]
θmin/θmax [°]
0.40 ϫ 0.35 ϫ 0.20
1.97/29.74
Ϫ28/24, Ϫ15/15, Ϫ23/21
14100/2928
1, 242
Ϫ
0.0842
0.924
0.60 ϫ 0.50 ϫ 0.40
2.90/34.85
Ϫ20/20, Ϫ21/21, Ϫ33/34
28175/8040
0, 241
0.8410/0.9402
0.0500
1.116
h, k, l ranges
Collected/unique reflections
Restraints, parameters
Tmin/Tmax
Rint
Goodness-of-fit on F2
R indices [I Ͼ 2σ(I)]
R indices (all data)
Flack parameter
R1 ϭ 0.0480, wR2 ϭ 0.1137
R1 ϭ 0.0617, wR2 ϭ 0.1214
Ϫ
R1 ϭ 0.0555, wR2 ϭ 0.1469
R1 ϭ 0.0586, wR2 ϭ 0.1516
0.00(3)
Ϫ3
˚
Largest difference peak/hole [e·A
]
0.232/Ϫ0.220
0.602/Ϫ0.552
[3d]
Acta 1988, 152, 9Ϫ16.
A. Karipides, C. Miller, J. Am.
II image plate diffractometer. Space groups were determined by an
examination of the systematic absences in the data, and their cor-
rect identification was confirmed by the successful solution and
refinement of the structures. Solutions were provided by direct
methods using SHELXS-97 and refined by full-matrix least squares
on F2 using SHELXL-97.[8] Numerical absorption corrections were
applied to 4 using X-RED/X-SHAPE.[9] All non-hydrogen atoms
were refined anisotropically. All hydrogen atoms were placed in cal-
culated positions with Uiso set at 1.2 times the Ueq of the parent
atom, and methyl groups were allowed to rotate about their XϪC
bonds; the positions of all NϪH and OϪH groups were freely re-
fined. The analysis of the structures was carried out with PLA-
TON[10] and WinGX.[11] Details are given in Table 3. Supplemen-
tary data for 3 and 4 are available free of charge from the Cam-
bridge Crystallographic Data Centre (CCDC), 12 Union Road,
Cambridge, CB2 1EZ, UK [Fax: ϩ 44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk], quoting the deposition numbers CCDC-
239602 and -239601, respectively.
Chem. Soc. 1984, 106, 1494Ϫ1495.
E. Pidcock, G. R. Moore, J. Biol. Inorg. Chem. 2001, 6,
[4]
[5]
[6]
[7]
479Ϫ489.
D. A. Fletcher, R. F. McMeeking, D. Parkin, J. Chem. Inf.
Comput. Sci. 1996, 36, 746Ϫ749.
A. Kaufman Katz, J. P. Glusker, S. A. Beebe, C. W. Bock, J.
Am. Chem. Soc. 1996, 118, 5752Ϫ5763.
B. D. Andrews, I. D. Rae, Aust. J. Chem. 1971, 24, 413Ϫ422.
[8] [8a]
G. M. Sheldrick, SHELXS-97 Program for the Solution of
[8b]
Crystal Structures; Universität Göttingen, 1997.
Sheldrick, SHELXL-97 Program for the Refinement of Crystal
Structures; Universität Göttingen, 1997.
Stoe & Cie, X-RED and X-SHAPE, Stoe & Cie GmbH, Darm-
stadt, 2001.
A. L. Spek, PLATON A Multipurpose Crystallographic Tool,
Utrecht University, 2000.
G. M.
[9]
[10]
[11]
[12]
[13]
L. J. Farrugia, J. Appl. Crystallogr. 1999, 32, 837Ϫ838.
M. V. Sargent, J. Chem. Soc., Perkin Trans. 1 1982, 1095Ϫ1098.
F. Cariati, L. Erre, G. Micera, A. Panzanelli, G. Ciani, A. Si-
roni, Inorg. Chim. Acta 1983, 80, 57Ϫ65.
[14] [14a]
H. Hosomi, Y. Ito, S. Ohba, Acta Crystallogr., Sect. C
Acknowledgments
We acknowledge Lubrizol and the University of Hull for support.
1998, 54, 142Ϫ145. [14b] H. A. Barnes, J. C. Barnes, Acta Crys-
[14c]
tallogr., Sect. C 1996, 52, 731Ϫ736.
H. Herbertsson, B.
[14d]
Hedman, Acta Crystallogr., Sect. B 1982, 38, 320Ϫ322.
E. J. Gabe, J. P. Glusker, J. A. Minkin, A. L. Patterson, Acta
Crystallogr. 1967, 22, 366Ϫ375.
[1] [1a]
B. Twamley, S. T. Haubrich, P. P. Power, Adv. Organomet.
[15]
Chem. 1999, 44, 1Ϫ65. [1b] C. C. Cummins, Prog. Inorg. Chem.
1998, 47, 685Ϫ836.
J. J. Sahbari, M. M. Olmstead, Acta Crystallogr., Sect. C 1983,
39, 208Ϫ211.
[2] [2a]
[16] [16a]
J. R. Hagadorn, T. I. Zahn, L. Que, Jr., W. B. Tolman, J.
L. R. Nassimbeni, H. Su, J. Chem. Soc., Dalton Trans.
[2b]
Chem. Soc., Dalton Trans. 2003, 1790Ϫ1794.
Lippard, Inorg. Chem. 2002, 41, 2704Ϫ2719.
Hung, B. Spingler, S. J. Lippard, Inorg. Chem. 2002, 41,
521Ϫ531.
D. Lee, S. J.
D. Lee, P. L.
2000, 349Ϫ352. [16b] A. M. Bahl, S. Krishnaswamy, N. G. Mas-
sand, D. J. Burkey, T. P. Hanusa, Inorg. Chem. 1997, 36,
[2c]
5413Ϫ5415. [16c] M. B. Inoue, P. Oram, M. Inoue, Q. Fernando,
[2d]
[16d]
D. Lee, S. J. Lippard, Inorg. Chim. Acta 2002,
D. Lee, L. Sorace, A. Caneschi, S. J. Lippard,
Inorg. Chim. Acta 1996, 246, 401Ϫ412.
Wang, Inorg. Chem. 1994, 33, 5113Ϫ5121.
J. D. Crane, D. J. Moreton, E. Rogerson, unpublished results.
L. J. Farrugia, J. Appl. Crystallogr. 1997, 30, 565.
Received May 26, 2004
S. R. Breeze, S.
[2e]
341, 1Ϫ11.
[17]
[18]
Inorg. Chem. 2001, 40, 6774Ϫ6781.
[3] [3a]
R. Murugavel, V. V. Karambelkar, G. Anantharaman, M.
G. Walawalkar, Inorg. Chem. 2000, 39, 1381Ϫ1390. [3b] A. Kari-
pides, C. White, K. Peiffer, Acta Crystallogr., Sect. C 1992, 48,
1015Ϫ1018. [3c] R. Helems, L. B. Cole, E. M. Holt, Inorg. Chim.
Early View Article
Published Online September 7, 2004
Eur. J. Inorg. Chem. 2004, 4237Ϫ4241
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4241