Biimidazole and bis(amide)bipyridine molybdenum carbonyl complexes as anions receptors

Article abstract of DOI:10.1021/ic0621650

Compounds [Mo(CO)₄(N-N)] (N-N = 4,4′-bis((4-methylphenyl) carbamoyl)-2,2′-bipyridine, bipy′, 1; or 2,2′-biimidazole, H₂biim, 2), [MoCl(η³-methallyl)(CO)₂(N-N)] (N-N = bipy′, 3; H₂biim, 4), and [Mo(η

Full text of DOI:10.1021/ic0621650

Inorg. Chem. 2007, 46, 2846−2853
Biimidazole and Bis(amide)bipyridine Molybdenum Carbonyl Complexes
as Anions Receptors
Laura Ion,† Dolores Morales,† Sonia Nieto,† Julio Pe´rez,*,† Luc´ıa Riera,† V´ıctor Riera,† Daniel Miguel,‡
Richard A. Kowenicki,¶ and Mary McPartlin#
Departamento de Qu´ımica Orga´nica e Inorga´nicasIUQOEM, Facultad de Qu´ımica, UniVersidad
de OViedo-CSIC, 33006 OViedo, Spain, Departamento de Qu´ımica Inorga´nica, Facultad de
Ciencias, UniVersidad de Valladolid, 47005 Valladolid, Spain, Chemistry Department, UniVersity
of Cambridge, CB2 1EW Cambridge, United Kingdom, and Department of Health and Human
Sciences, London Metropolitan UniVersity, N7 8DB London, United Kingdom
Received November 14, 2006
Compounds [Mo(CO)4(N
H2biim, 2), [MoCl(
3-methallyl)(CO)2(N
(N N)]BAr (Ar′ ) 3,5-bis(trifluoromethyl)phenyl; N
and their behavior toward anions was investigated in solution (IR and H NMR) and in solid state (X-ray diffraction).
−N)] (N−N
)
4,4
−
′
-bis((4-methylphenyl)carbamoyl)-2,2
N)] (N bipy , 3; H2biim, 4), and [Mo(
bipy , 5; H2biim, 6) were synthesized and characterized,
′
-bipyridine, bipy
′, 1; or 2,2′-biimidazole,
η
−N
)
′
η
3-methallyl)(CNtBu)(CO2)-
−
′
−N
)
′
4
1
Introduction
Metals can provide a positive charge that adds electrostatic
attraction to the noncovalent interactions at play.4 Among
these interactions, the relatively strong and directional
hydrogen bonds are perhaps the most useful in receptor
design. The strength of the anion‚‚‚HD interactions (HD )
hydrogen bond donor group) increases when a Lewis-acidic
metal fragment is added to the receptor structure.4,5 The metal
can also be used as an element of geometric organization;6
thus, ditopic molecules containing both hydrogen bond donor
groups and metal-binding sites can be assembled by means
of metal coordination in such a way that the several HD
groups can simultaneously interact with the target anion.7
Our group has recently applied this strategy to the design of
anion receptors based on fac-tris(pyrazole) cationic com-
plexes.8 A key requisite of these complexes is their kinetic
The incorporation of metal fragments in the structures of
supramolecular anion receptors1 can serve several purposes.
In some cases, the receptor interacts with the anion through
formation of a direct metal-anion bond.2 In other instances,
metal-decorated organic receptors act as chemosensors, the
mission of the metal fragments being to act as reporter
groups, modulating a luminescent or electrochemical signal
upon interaction of the anion with some binding group.3
* To whom correspondence should be addressed. E-mail: japm@
uniovi.es. Fax: (34) 985103446.
† Universidad de Oviedo-CSIC.
‡ Universidad de Valladolid.
¶ University of Cambridge.
# London Metropolitan University.
(1) For an overview of supramolecular anion receptor chemistry, see: (a)
Supramolecular Chemistry of Anions; Bianchi, A., Bowman-James,
K., Garc´ıa-Espan˜a, E., Eds.; Wiley-VCH: Weinheim, Germany, 1997.
(b) Schmidtchen, F. P.; Berger, M. Chem. ReV. 1997, 97, 1609. (c)
Beer, P. D.; Smith, D. K. Prog. Inorg. Chem. 1997, 46, 1. (d)
Antonisse, M. M. G.; Reinhoudt, D. N. Chem. Commun. 1998, 443.
(e) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001, 40, 486. (f)
Gale, P. A., Ed. Coord. Chem. ReV. 2003, 240, (special issue). (g)
Bowman-James, K. Acc. Chem. Res. 2005, 38, 671. (h) Anion Receptor
Chemistry; Sessler, J. L., Gale, P. A., Cho, W.-S., Eds.; RSC
Publishing: Cambridge, U.K., 2006. (i) Gale, P. A., Ed. Coord. Chem.
ReV. 2006, 250, (special issue).
(2) (a) Newcomb, M.; Horner, J. H.; Blanda, M. T.; Squattrito, P. J. J.
Am. Chem. Soc. 1989, 111, 6294. (b) Rudkevich, D. M.; Verboom,
W.; Brzozka, Z.; Palys, M. J.; Stauthamer, W. P. R. V.; van Hummel,
G. J.; Franken, S. M.; Harkema, S.; Engbersen, J. F. J.; Reinhoudt,
D. M. J. Am. Chem. Soc. 1994, 116, 4341. (c) Hawthorne, M. F.;
Zheng, Z. Acc. Chem. Res. 1997, 30, 267.
(3) For an overview of supramolecular anion sensing, see: (a) Mart´ınez-
Ma´n˜ez, R.; Sanceno´n, F. Chem. ReV. 2003, 103, 4419. (b) Anslyn, E.
V., Ed. Tetrahedron, 2004, 60, (special issue).
(4) Atwood, J. L.; Holman, K. T.; Steed, J. W. Chem. Commun. 1996,
1401.
(5) Camiolo, S.; Coles, S. J.; Gale, P. A.; Hurthouse, M. B.; Mayer, T.
A.; Paver, M. Chem. Commun. 2000, 275.
(6) Steed, J. W. Chem. Commun. 2006, 2637.
(7) (a) Bondy, C. R.; Gale, P. A.; Loeb, S. J. Chem. Commun, 2001, 729.
(b) Bondy, C. R.; Gale, P. A.; Loeb, S. J. J. Supramol. Chem. 2002,
2, 93. (c) Bondy, C. R.; Gale, P. A.; Loeb, S. J. J. Am. Chem. Soc.
2004, 126, 5030. (d) Wallace, K. J.; Daari, R.; Welcher, W. J.;
Abouderbala, L. O.; Boutelle, M. G.; Steed, J. W. J. Organomet. Chem.
2003, 666, 63.
(8) (a) Nieto, S.; Pe´rez, J.; Riera, V.; Miguel, D.; Alvarez, C. Chem.
Commun. 2005, 546. (b) Nieto, S.; Pe´rez, J.; Riera, L.; Riera, V.;
Miguel, D. Chem.sEur. J. 2006, 12, 2244.
2846 Inorganic Chemistry, Vol. 46, No. 7, 2007
10.1021/ic0621650 CCC: $37.00
© 2007 American Chemical Society
Published on Web 02/16/2007

Biimidazole and Bis(amide)bipyridine Mo Carbonyl Complexes
Scheme 1. Synthesis of Molybdenum(0) Complexes 1 and 2
substitutional inertness, without which simple substitution
of the neutral ligands by the target anion would occur.7b,d
Last, and the most pertinent to the work that we wish to
report here, metal coordination of a bis(ditopic) molecule
such as 2,2′-biimidazole (H2biim) (a) enforces the syn
conformation of H2biim, the optimal one for simultaneous
interaction of anions with both biimidazole N-H groups and
(b) precludes H2biim self-association, which would otherwise
result in a reduced solubility and compete against anion
binding. We have previously illustrated these features using
the cationic complex [RuCl(η6-p-cymene)(H2biim)]+, pre-
-
pared as its BAr′4 (Ar′ ) 3,5-bis(trifluoromethyl)phenyl)
salt in order to avoid competition of the counteranion with
the target, external anion and to enhance solubility in organic,
moderately polar solvents.9 Unlike the complexes of the
monodentate pyrazole ligands mentioned previously in this
Article, metal complexes of bidentate ligands such as H2-
biim can be expected to be, as a result of the chelate effect,
kinetically robust against dissociation for a wide range of
metal fragments. Therefore, employment of third-row metals
such as rhenium or platinum should not be necessary. For
the present study, we have chosen molybdenum carbonyl
fragments because, as it will be shown in what follows, their
complexes with the chelating, N-donor ligands are easily
accessible in two different metal oxidation states, and both
neutral and cationic complexes (we have previously devel-
Both compounds were found to be virtually insoluble in
toluene, dichloromethane, acetone, thf, and acetonitrile, a fact
that can be attributed to intermolecular hydrogen bonding
between the biimidazole or amide N-H groups and the
oxygens of carbonyl ligands. Thus, intermolecular hydrogen
bonding involving N-H groups and carbonyl ligands
has been demonstrated for the very insoluble complex
cis-[Mo(CO)4(Hdmpz)2] (Hdmpz ) 3,5-dimethylpyrazole)
by Villafan˜e et al.13-14
oped methods to prepare the latter as their BAr′4 salts)10
-
can be prepared. That presents us with the opportunity of
comparing the behavior toward anions of complexes featuring
the same metal and bidentate ditopic ligand but with different
charge and metal oxidation state. {Mo(CO)4} and {Mo(η3-
allyl)(CO)2} complexes of bidentate, N-donor heterocyclic
ligands are quite air and moisture stable. In addition, the
integrity of the complexes in the presence of external anions
can be readily ascertained by observing the strong ν(CO)
bands, occurring in a clean region of the IR spectrum. As
the bis(ditopic) bidentate ligands, we have chosen, in addition
to H2biim, an example of a 4,4′-bis(carbamoyl)-2,2′-bipyri-
dine, a type of ligand in which, as in 2,2′-biimidazole itself,
metal coordination impedes rotation around the central C-C
bond, imposing the conformation best suited for the interac-
tion with anions, and whose rhenium(I) and ruthenium(II)
complexes have been extensively studied by the group of
Beer in the context of supramolecular anion binding and
sensing.11
Compound [Mo(bipy′)(CO)4] (1) was found to be soluble
enough in DMSO-d6, and the effect of the addition of several
1
anions (as tetrabutylammonium salts) was studied by H
NMR. Significant shifts to higher frequencies were observed
for the signals corresponding to the hydrogens of the amide
N-H groups as well as for the hydrogens of the 3,3′ carbons
of the bipyridine upon addition of chloride, dihydrogenphos-
phate, and acetate, whereas for bromide, iodide, nitrate, or
hydrogensulfate, the variation was imperceptible. The per-
sistence of a cis-Mo(CO)4 IR pattern indicated the stability
(11) (a) Beer, P. D.; Dickson, C. A. P.; Fletcher, N.; Goulden, A. J.; Grieve,
A.; Hodacova, J.; Wear, T. J. Chem. Soc., Chem. Commun. 1993, 828.
(b) Beer, P. D.; Dent, S. W.; Hobbs, G. S.; Wear, T. J. Chem. Commun.
1997, 9. (c) Szemes, F.; Hesek, D.; Chen, Z.; Dent, S. W.; Drew, M.
G. B.; Goulden, A. J.; Graydon, A. R.; Grieve, A.; Mortimer, R. J.;
Wear, T.; Weightman, J. S.; Beer, P. D. Inorg. Chem. 1996, 35, 5868.
(d) Beer, P. D.; Szemes, F.; Balzani, V.; Sala`, C. M.; Drew, M. G.
B.; Dent, S. W.; Maestri, M. J. Am. Chem. Soc. 1997, 119, 11864. (e)
Cooper, J. B.; Drew, M. G. B.; Beer, P. D. Dalton Trans. 2001, 39.
(f) Uppadine, L. H.; Keene, F. R.; Beer, P. D. Dalton Trans. 2001,
218. (g) Uppadine, L. H.; Redman, J. E.; Dent, S. W.; Drew, M. G.
B.; Beer, P. D. Inorg. Chem. 2001, 40, 2860; (h) Uppadine, L. H.;
Drew, M. G. B.; Beer, P. D. Chem. Commun. 2001, 29. (i) Vickers,
M. S.; Martindale, K. S.; Beer, P. D. J. Mater. Chem. 2005, 15, 2784.
(12) Beck, W.; Goetzfried, F.; Riederer, M. Z. Anorg. Allg. Chem. 1976,
423, 97.
(13) For a precedent of the employment of the molybdenum tetracarbonyl
fragment in the construction of anion receptors, see: Kingston, J. E.;
Ashford, L.; Beer, P. D.; Drew, M. G. B. Dalton Trans. 1999, 251.
(14) Paredes, P.; Arroyo, M.; Miguel, D.; Villafan˜e, F. J. Organomet. Chem.
2003, 667, 120. For additional examples of carbonyl ligands as
hydrogen bond acceptors, see: ref 5 and (a) Braga, D.; Grepioni, F.
Acc. Chem. Res. 1997, 30, 81. (b) Haiduc, I.; Edelmann, F. T.
Supramolecular Organometallic Chemistry;Wiley-VCH: Weinheim,
Germany, 1999, p 352
Results and Discussion
Neutral molybdenum(0) cis-tetracarbonyl complexes [Mo-
(CO)4(N-N)] (N-N ) 4,4′-bis((4-methylphenyl)carbam-
oyl)-2,2′-bipyridine, bipy′, 1; or 2,2′-biimidazole, H2biim,
2, a previously known complex)12 were prepared by the
reaction of Mo(CO)6 with an equimolar amount of the
respective ligand in refluxing tetrahydrofuran (thf), as
described in the Experimental Section and shown in
Scheme 1.10
(9) Ion, L.; Morales, D.; Pe´rez, J.; Riera, L.; Riera, V.; Kowenicki, R.
A.; McPartlin, M. Chem. Commun. 2006, 91.
(10) Pe´rez, J.; Morales, D.; Nieto, S.; Riera, L.; Riera, V.; Miguel, D. Dalton
Trans. 2005, 884.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2847

Ion et al.
Table 1. Binding Constant Values for Compound 1 in DMSO-d6
anion
Cl-
Ka (M-1
)
662 ( 1
856 ( 50
397 ( 29
-
H2PO4
OAc-
Scheme 2. Synthesis of Neutral Molybdenum(II) Compounds 3 and 4
Figure 1. Molecular structure of the [MoCl(η3-methallyl)(bipy′)(CO)2]‚
[Cl-] adduct.
of 1 toward these anions, and anion exchange was found to
1
be fast. The results of H NMR titrations were used to
calculate the 1:1 binding constants (Table 1). The very low
solubility of compound [Mo(CO)4(H2biim)] (2) even in the
more polar dimethylsulfoxide precluded the NMR study of
its solution behavior toward anions.
Neutral molybdenum(II) cis-dicarbonyl complexes [MoCl-
(η3-methallyl)(bipy′)(CO)2] (3) and [MoCl(η3-methallyl)-
(CO)2(H2biim)] (4) were prepared by reaction of the respec-
tive bidentate ligand with the labile precursor [MoCl(η3-
methallyl)(CO)2(NCMe)2]10 (see Experimental Section and
Scheme 2). The IR spectra were found to feature pairs of
ν(CO) bands of similar intensity at 1942 and 1871 (3) and
1947 and 1852 (4) cm-1, values similar to those found for
previously characterized cis-dicarbonyl [MoX(η3-allyl)(CO)2-
(N-N)] complexes.15
Figure2. Molecularstructureofthe[Mo(Cl/Br)(η3-methallyl)(CO)2(H2biim)]‚
[Cl/Br-] adduct.
Table 2. Binding Constant Values for Compounds 3 and 4 in
DMSO-d6
anion
3, Ka (M-1
571 ( 0.6
)
4, Ka (M-1
)
Cl-
196 ( 7
927 ( 30
Br-
-
H2PO4
257 ( 16
342 ( 30
OAc-
Complexes 3 and 4 showed a very low solubility in organic
solvents. The extremely insoluble complex [MoCl(η3-
allyl)(CO)2(H2biim)], closely similar to 4, was previously
reported by Calhorda et al.16 The low solubility of this type
of complexes can be attributed to intermolecular hydrogen
bonding between the N-H groups and the Cl ligand, the
best hydrogen bond acceptor in these complexes. A closely
related topic, namely, the hydrogen bonds between halide
ligands and urea, has been recently studied by Steed et al.17
Due to the low solubility of 3 and 4 in most solvents, DMSO-
d6 had to be used again for the NMR studies. Fast anion
exchange was found, and the calculated binding constants
are listed in Table 2. For the bipy′ complex 3, again only
the chloride, dihydrogenphosphate, and acetate anions gave
by Beer and co-workers for metal complexes of 4,4′-bis-
(arylcarbamoyl)-2,2′-bipyridine ligands;11c the non-metal-
coordinated chloride interacts with the two amide N-H
hydrogens (N(3)‚‚‚Cl(2) ) 3.363(6) and N(4)‚‚‚Cl(2) )
3.351(7)Å;N(3)-H(3)‚‚‚Cl(2))165(6)andN(4)-H(4)‚‚‚Cl(2)
) 169(7)°), the two hydrogens at the C3 and C3′ carbons of
the bipyridine framework (C(14)‚‚‚Cl(2) ) 3.512(7) and
C(17)‚‚‚Cl(2) ) 3.497(7) Å; C(14)-H‚‚‚Cl(2) ) 173.1(1)
and C(17)-H‚‚‚Cl(2) ) 176.2(1)°), and two of the ortho-
C-H groups of the aryl substituents (C(36)‚‚‚Cl(2) )
3.554(7) and C(42)‚‚‚Cl(2) ) 3.613(8) Å; C(36)-H‚‚‚Cl(2)
) 140.6(1) and C(42)-H‚‚‚Cl(2)) 147.7(1)°).
For complex [MoCl(η3-methallyl)(CO)2(H2biim)] (4), sig-
1
rise to visible changes in the H NMR spectrum.
1
nificant H NMR downfield shifts were seen upon addition
The Bu4N salt of the 3‚[Cl-] adduct could be isolated by
crystallization, and its solid-state structure was determined
by means of single-crystal X-ray diffraction. The structure
of the 3‚[Cl-] adduct is displayed in Figure 1.
of chloride and also of bromide. The relative magnitude of
1
the binding constants for these anions, calculated from H
NMR titrations (see Table 2), was somewhat unexpected
(higher for bromide), and the determination of the solid-
state structure of the bromide adduct was sought. The
addition of the equimolar amount of tetrabutylammonium
bromide onto a saturated thf solution of 4, followed by the
slow (2 days) diffusion of hexane, afforded yellow, X-ray
quality crystals, one of which was used for the structural
determination. The results indicated a [Bu4N][MoX(η3-
methallyl)(CO)2(H2biim)]‚[Y] composition (see Figure 2),
The structure confirms the presence of the [MoCl(η3-
methallyl)(bipy′)(CO)2]‚[Cl-] supramolecular adduct, and the
hydrogen-bonding pattern is similar to those previously found
(15) tom Dieck, H.; Friedel, H. J. Organomet. Chem. 1968, 14, 375.
(16) Pinto, P.; Barranco, E.; Calhorda, M. J.; Fe´lix, V.; Drew, M. G. J.
Organomet. Chem. 2000, 601, 34.
(17) Turner, D. R.; Smith, B.; Goeta, A. E.; Evans, I. R.; Tocher, D. A.;
Howard, J. A. K.; Steed, J. W. CrystEngComm 2004, 6, 633.
2848 Inorganic Chemistry, Vol. 46, No. 7, 2007

Biimidazole and Bis(amide)bipyridine Mo Carbonyl Complexes
Scheme 3. Synthesis of Cationic Molybdenum(II) Complexes 5 and 6
Table 3. Binding Constant Values for Compounds 5 and 6 in CD3CN
anion
5, Ka (M-1
)
6, Ka (M-1
)
Cl-
Br-
I-
17169 ( 1141
7183 ( 277
217 ( 17
992 ( 15
779 ( 11
342 ( 30
25 ( 91
11452 ( 1152
10496 ( 681
315 ( 51
-
NO3
10693 ( 939
10447 ( 781
-
HSO4
OAc-
-
ReO4
436 ( 47
The IR spectroscopy provided a quick, unambiguous way
to assess if an external anion displaces the monodentate CNt-
Bu ligand. Thus, such a substitution would transform a
cationic complex into a neutral one, significantly shifting
the ν(CO) bands to lower wavenumber values (see previous
paragraphs). Moreover, the medium-intensity isocyanide
ν(CN) band would shift from 2185 to 2140 cm-1 (free CNt-
Bu) upon substitution of the isocyanide ligand.
Compounds [Mo(η3-methallyl)(CNtBu)(bipy′)(CO)2]BAr′4
(5) and [Mo(η3-methallyl)(CNtBu)(CO)2(H2biim)]BAr′4 (6)
were found to be highly soluble in dichloromethane, thf, and
acetonitrile. The fact, surprising at first sight, that these salts
are much more soluble in moderately polar organic solvents
than the neutral complexes 1-4 discussed in the preceding
sections can be attributed to the large delocalization of the
negative charge over the large BAr′4- anion, the lack of good
hydrogen bond acceptor groups on this anion, and the fact
that the extent of inter-cation hydrogen bonding (e.g.,
between N-H groups and CO ligands, as those mentioned
for the neutral tetracarbonyls) would now be opposed by
Coulombic repulsion and by anion interposition. It is
pertinent to note here that the compound [RuCl(η6-p-
cymene)(H2biim)]BAr′4,9 containing the good hydrogen bond
acceptor chloride, has been also found to be very soluble in
dichloromethane, thf, and acetonitrile.
where the chloride and bromide anions are approximately
50% disordered between the X and Y positions.
This demonstrates that the chloride ligand in 4 undergoes
substitution by external anions; at least, it partly does by
bromide over a 2 day period. Taking into account that the
IR and 1H NMR spectra of [MoX(η3-allyl)(CO)2(N-N)] (X
) Cl, Br) complexes are similar, we note that the stability
of such complexes toward external anions cannot be easily
ascertained by spectroscopic means. In such a situation, the
binding constants for 3 and 4 (Table 2) cannot be relied upon.
The fact that a halide ligand is labile in complexes of the
type [MoX(η3-allyl)(CO)2(N-N)] is not surprising; in fact,
in previous works (also, see later in this Article), we have
prepared [Mo(η3-allyl)(CO)2(N-N)L]BAr′4 (L ) neutral
monodentate ligand) compounds by reaction of the corre-
sponding [MoCl(η3-allyl)(CO)2(N-N)] precursor with L and
the NaBAr′4 salt (note that sodium salts are not strong halide-
abstracting reagents).18 A similar halide metathesis during
an attempt to crystallize a supramolecular adduct containing
a rhenium tricarbonyl bipyridine fragment was reported by
Beer et al.,11g and halide substitution occurs less readily in
rhenium tricarbonyl complexes than it does in [MoX(η3-
allyl)(CO)2(N-N)].
The behavior of compounds 5 and 6 toward several anions
1
in solution was investigated spectroscopically. IR and H
In view of the results described, we set out to replace the
chloride in complexes 3 and 4 by other ligands such that
the products are spectroscopically very different from the
neutral [MoX(η3-methallyl)(CO)2(N-N)] complexes, the
potential anation products, thus allowing for a conclusive
diagnostic of the stability of the molybdenum complexes.
The reactions of 3 or 4 with the equimolar amounts of tert-
butylisocyanide and NaBAr′4 afforded, as single products,
the new compounds [Mo(η3-methallyl)(CNtBu)(CO)2(N-N)]-
BAr′4 (N-N ) bipy′, 5; H2biim, 6), which were isolated as
crystalline solids, as detailed in the Experimental Section
(see Scheme 3). The shift to higher frequencies (compared
with those of the neutral precursors 3 and 4) in the IR
ν(CO) bands (at 1965 and 1894 cm-1 for 5 and at 1961 and
1881 cm-1 for 6) was consistent with the formation of
cationic compounds. Compounds 5 and 6 were characterized
by IR and NMR spectroscopy (see Experimental Section).19
NMR showed that 5 and 6 are stable (i.e.; they do not
undergo substitution of the monodentate CNtBu ligand) in
the presence of several anions (see the following discussion).
The addition of Bu4NX salts to solutions of 5 or 6 in CD3-
1
CN led to large downfield shifts in the H NMR signals of
the amide 5 or biimidazole 6 N-H groups, indicating strong
hydrogen bonding. The IR ν(CO) bands of 5 and 6 underwent
relatively small shifts to lower frequencies upon anion
addition (for instance, only 5 (5) or 7 cm-1 (6) for the
chloride anion, in contrast with the much larger difference
between the neutral Mo-Cl and cationic Mo-CNtBu
complexes), which is attributed to the electron density release
from the anion to the hydrogen bond acceptor groups and,
from these, through the ligand framework to the metal
centers.20
Anion exchange was found to be fast, and 1:1 binding
constants (Job plots are shown in Figure 3 (6) and in the
(18) Morales, D.; Navarro Clemente, M. E.; Pe´rez, J.; Riera, L.; Riera, V.;
Miguel, D. Organometallics 2002, 21, 4934.
(19) For previous works in Mo allylisocyanide chemistry, see: (a) King,
R. B.; Saran, M. S. Inorg. Chem. 1974, 13, 2453. (b) Deaton, J. C.;
Walton, R. A. J. Organomet. Chem. 1981, 219, 187. To the best of
our knowledge, no examples of pseudooctahedral cationic allyl
molybdenum isocyanide complexes have been previously reported.
(20) For a previous application of IR spectroscopy in the ν(CO) region to
the study of hydrogen bonding in solution, see: Peris, E.; Mata, J.
A.; Moliner, V. J. Chem. Soc,. Dalton Trans. 1999, 3893. For an
application of IR spectroscopy in the ν(CO) region to the solution
behavior of a cation receptor, see: Anson, C. E.; Creaser, C. S.;
Stephenson, G. R. J. Chem. Soc., Chem. Commun. 1994, 2175.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2849

Ion et al.
Figure 3. Job plot of receptor 6 toward chloride, hydrogensulfate, and
nitrate anions.
Figure 4. 1H NMR titration plots of receptor 5 with bromide and nitrate
anions in CD3CN.
Figure 6. (a) Molecular structure of the [Mo(η3-methallyl)(CNtBu)(H2-
biim)(CO)2]‚[Br] adduct; (b) molecular structure of the [Mo(η3-methallyl)(CNt-
Bu)(H2biim)(CO)2]‚[ReO4] adduct.
around molybdenum can be described as pseudooctahedral,
with an equatorial plane defined by the two nitrogen donor
atoms of the bipy′ or H2biim chelate and the two carbonyls
and the isocyanide and η3-methallyl ligands occupying
mutually trans positions. The Mo-CNBut distances, in the
2.1-2.2 Å range, while longer than those found for the Mo-
CO bonds (1.9-2.0 Å), are comparable with Mo-CN21 or
Mo-C(alkynyl)22 distances found in neutral complexes [Mo-
(η3-allyl)X(CO)2(N-N)] (X ) cyanide or alkynyl; N-N )
2,2-bipyridine or 1,10-phenanthroline) with similar geom-
etries. This suggests strong Mo-isocyanide bonds, in ac-
cordance with the stability of the cationic complexes even
in the presence of anions.
Figure 5. Molecular structure of the [Mo(η3-methallyl)(CNtBu)(bipy′)-
(CO)2]‚[HSO4] adduct.
1
Supporting Information (5)) were obtained from H NMR
titrations in CD3CN (see Figure 4, Table 3, and Supporting
Information), a solvent less competitive than DMSO and in
1
which significant downfield shifts in the H NMR signals
could be observed for several anions.
Attempts to obtain X-ray quality crystals from solutions
containing equimolar mixtures of either 5 or 6 and Bu4NX
salts were successful for 5 and hydrogensulfate and for 6
and bromide and perrhenate anions. The results of the
structural determinations (Figures 5 and 6) indicate the
formation of neutral supramolecular 1:1 adducts of the
composition [Mo(η3-methallyl)(CNtBu)(CO)2(N-N)]‚[X],
which crystallize separately from the salt [Bu4N][BAr′4], a
fact previously found by us.8b,9
In the 5‚HSO4 adduct, each of the amide N-H groups
forms a hydrogen bond to one of the HSO4 oxygen atoms.
One of these two oxygen atoms, O(12), is so much out of
the bipy′ plane that the formation of its hydrogen bond to
the N(40)-H group forces the p-tolylcarbamoyl moiety out
(21) Hevia, E.; Pe´rez, J.; Riera, L.; Riera, V.; Garc´ıa-Granda, S.; Garc´ıa-
Rodr´ıguez, E.; Miguel, D. Eur. J. Inorg. Chem. 2003, 1113.
(22) (a) Pe´rez, J.; Riera, L.; Riera, V.; Garc´ıa-Granda, S.; Garc´ıa-Rodr´ıguez,
E.; Miguel, D. Chem. Commun. 2002, 384. (b) Pe´rez, J.; Riera, L.;
Riera, V.; Garc´ıa-Granda, S.; Garc´ıa-Rodr´ıguez, E.; Miguel, Orga-
nometallics 2002, 21, 1622.
A common feature of the solid-state structures of the
adducts of 5 and 6 is their C2 symmetry. The geometry
2850 Inorganic Chemistry, Vol. 46, No. 7, 2007

Biimidazole and Bis(amide)bipyridine Mo Carbonyl Complexes
Table 4. Crystal Data and Refinement Details
[Mo(Cl/Br)(η3-
3‚[Bu4NCl]
methallyl)(bipy′)(CO)2]‚[Cl/Br-]
5‚[HSO4]
6‚[Br]
6‚[ReO4]
formula
Mr
C48H60Cl2MoN5O4
937.85
C
28.25H49.50BrCl1.50MoN5O2
C37H39MoN5O8S
809.73
C17H22BrMoN5O2
504.25
C17H22MoN5O6Re
674.54
720.25
cryst syst
space group
a [Å]
b [Å]
c [Å]
orthorhombic
P2(1)2(1)2(1)
14.431(17)
15.904(19)
21.68(3)
90
90
90
4975(10)
4
orthorhombic
Fdd2
37.006(5)
39.403(5)
10.1814(14)
90
90
90
14846(4)
16
monoclinic
P2(1)/c
9.179(2)
26.858(6)
16.629(4)
90
102.285(4)
90
4005.7(15)
4
orthorhombic
Ibam
29.195(6)
12.039(2)
12.783(3)
90
orthorhombic
Pnma
16.411(3)
10.172(2)
14.171(3)
90
90
90
2365.6(8)
4
R [°]
â [°]
90
90
γ [°]
V [Å3]
Z
4492.5(16)
8
Tc [K]
293(2)
1.252
1964
296(2)
1.289
1567
293(2)
1.343
1672
180(2)
1.491
2016
180(2)
1.894
1296
F
calcd [g cm-3
]
F(000)
λ(Mo KR) [Å]
0.71073
0.19 × 0.32 × 0.48
0.416
1.74 e θ e 23.24
21813
0.71073
0.13 × 0.12 × 0.12
1.567
1.51 e θ e 23.29
16736
0.71073
0.23 × 0.16 × 0.04
0.433
1.46 e θ e 23.31
18150
0.71073
0.23 × 0.14 × 0.01
2.381
3.63 e θ e 27.46
15537
0.71073
0.14 × 0.10 × 0.02
5.682
3.72 e θ e 25.06
13710
cryst size [mm]
µ[mm-1
]
scan range [°]
refl. measured
independent refl.
data/
7067
7067/0/554
4552
4552/1/356
5771
5771/0/482
2687
2687/0/150
2206
2206/1/162
restraints/
parameters
goodness-of-fit
1.076
1.033
1.025
1.105
1.142
on F2
R1/Rw2 [I > 2σ(I)]
R1/Rw2 (all data)
0.0497/ 0.1067
0.0755/ 0.1245
0.0602/ 0.1443
0.1163/ 0.1582
0.0452/ 0.0787
0.0935/ 0.0858
0.0490/ 0.0944
0.0680/ 0.1011
0.0502/ 0.0966
0.0797/ 0.1067
of the same plane (see Figure 5). While the adoption of
such a geometry allows the formation of the two simul-
taneous hydrogen bonds (N(30)‚‚‚O(11) ) 3.185(6) Å,
N(30)‚‚‚H‚‚‚O(11) ) 161.5(6)°; N(40)‚‚‚O(12) ) 3.011(5) Å,
N(40)‚‚‚H‚‚‚O(12) ) 167.4(5)°), it also involves an unfavor-
able loss of conjugation, which should partially account for
the relatively low value of the binding constant calculated
for receptor 5 and the hydrogensulfate anion. The magnitude
of the effect can be realized by comparing (see Table 3) the
large differences between the binding constants for this anion
and those for either the chloride or bromide for receptor 5
with the same differences, which are much smaller, found
for receptor 6. The geometry of the 6-hydrogensulfate
adduct could not be crystallographically demonstrated; in the
absence of such evidence, the most favorable arrangement
most likely involves the same nine-membered ring, as
described in the following for the adduct formed between 6
and the tetrahedral perrhenate anion; the high values of the
binding constants found for 6 and hydrogensulfate or nitrate
anions suggest the formation of this particularly favorable
ring structure.
The bromide anion in the 6‚[Br] adduct forms two strong
hydrogen bonds with the two biimidazole N-H groups
(N‚‚‚Br ) 3.289(4) Å, N‚‚‚H‚‚‚Br ) 164(5)°),11d in line with
the relatively high binding constant. In the 6‚[ReO4] adduct,
each of the biimidazole N-H groups forms a hydrogen
bond to one of the perrhenate oxygens (N‚‚‚O ) 2.76(1) Å,
N‚‚‚H‚‚‚O ) 165.4°), forming a nine-membered ring as the
one previously found by us for the nitrate anion and a
ruthenium biimidazole complex.9
This fact can be attributed to the more discriminating nature
of the cavity, comprising up to six hydrogen bond donor
groups (two N-H and four C-H groups, see the structure
of the [MoCl(η3-methallyl)(bipy′)(CO)2]‚[Cl-] adduct), cre-
ated by the backside of the bipy′ ligand. The fact that such
a discrimination is effected by the cationic receptor of 5 is
noteworthy since one of the drawbacks of cationic receptors
for anions is that the Coulombic attraction tends to make
them fairly unselective. On the other hand, the relatively large
values of some of the binding constants encountered for 5
and 6 and the fact that the interaction in CD3CN solution
can be detected (and measured) even for the large, charge-
delocalized anions such as iodide or perrhenate can be, at
least in part, attributed to the choice of the low interacting
-
BAr′4 counteranion.
Conclusion
The neutral complexes [Mo(CO)4(N-N)] (1, 2) and
[MoCl(η3-methallyl)(CO)2(N-N)] (3, 4) are very insoluble,
a fact attributed to intermolecular hydrogen bonding. The
stability of 3 and 4 toward external anions could not be
unambiguously demonstrated by spectroscopic means, and
at least in one case, partial chloride substitution was found.
In contrast, compounds [Mo(η3-methallyl)(CNBut)(CO)2(N-
N)]BAr′4 (5, 6) display a high solubility in moderately polar
organic solvents and are stable in solution toward external
anions, as it can be easily ascertained by IR spectroscopy.
1H NMR studies of the behavior of 5 and 6 toward several
anions indicated fast anion exchange, formation of 1:1
supramolecular adducts, and binding constants spanning a
broad range. The variation of the magnitude of the binding
constants with the nature of the anion is higher for 5, the
bis(amide)bipyridine ligand, which is able to establish up to
The most interesting difference between receptors 5 and
6 in their behavior toward anions is that binding constants
were found to span a wide range of values for the former.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2851

Ion et al.
Synthesis of [MoCl(η3-methallyl)(CO)2(H2biim)] (4). To a
solution of [MoCl(η3-methallyl)(CO)2(NCMe)2] (0.250 g, 0.770
mmol) in thf (30 mL) was added H2biim (0.103 g, 0.770 mmol).
The mixture was stirred for 3 h at room temperature. The resulting
solution was concentrated under vacuum to a volume of 5 mL,
and addition of hexane (10 mL) caused the precipitation of
compound 4 as a yellow powder, which was washed with hexane
(2 × 20 mL). Yield: 0.265 g, 92%. IR (thf, cm-): 1947, 1852
(νCO). 1H NMR (DMSO-d6): δ 12.63 (br s, 2H, NH, H2biim), 7.38
(m, 4H, H2biim), 2.87 (s, 2H, Hsyn methallyl), 1.14 (s, 2H, Hanti
η3-methallyl), 0.97 (s, 3H, CH3 η3-methallyl). 13C NMR (DMSO-
d6): δ 227.9 (CO), 139.1, 129.4, 124.0 (H2biim), 80.0 (C2
η3-methallyl), 55.8 (C1 and C3 η3-methallyl), 19.8 (CH3 η3-
methallyl). Anal. Calcd (%) for C12H13ClMoN4O2: C, 38.27; H,
3.48; N, 14.87. Found: C, 38.32; H, 3.62; N, 14.69.
six hydrogen bonds with a chloride anion, as demonstrated
by X-ray crystallography.
Experimental Section
All manipulations were carried out under a nitrogen atmosphere
using Schlenk techniques. Compound 2 was prepared as previously
reported.12 Tetrabutylammonium salts were purchased from Fluka
or Aldrich. Deuterated acetonitrile and dimethylsulfoxide (Cam-
bridge Isotope Laboratories, Inc.) were stored under nitrogen in
Young tubes and used without further purification. NMR spectra
were recorded on Bruker AC-300 and DPX-300 instruments. IR
solution spectra were obtained by a Perkin-Elmer FT 1720-X
spectrometer using 0.2 mm CaF2 cells. NMR samples were prepared
under nitrogen using Kontes manifolds purchased from Aldrich.
Oven-dried, 5 mm NMR tubes were subjected to several vacuum-
nitrogen cycles, filled with the solution of the receptor (prepared
separately in a Schlenk tube, typically in a 10-2 M concentration
in CD3CN) by means of a 1 mL syringe, and stoppered with rubber
septa. After the H1 NMR spectrum of the receptor was recorded,
the successive aliquots of the tetrabutylammonium salt (typically
4 × 10-2 M in CD3CN, separately prepared and kept in a septum-
stoppered vial during the titration) were injected through the septum
using Hamilton microsyringes (10-100 µL). The volume of each
addition was 10 µL before reaching the saturation zone (nearly
horizontal line of the titration profile), and was 20 or 40 µL
afterward. When the change in δ is small (as for ReO4-), 20 µL of
salt solution was added from the beginning. Data were treated using
the WinEQNMR program.23
Synthesis of [Mo(η3-methallyl)(CNtBu)(bipy′)(CO)2]BAr′4 (5).
To a solution of [MoCl(η3-methallyl)(CO)2(NCMe)2] (0.050 g,
0.153 mmol) in CH2Cl2 (20 mL) were added NaBAr′4 (0.136 g,
0.153 mmol) and MeCN (2 mL, excess). The mixture was stirred
at room temperature for 5 min, and then, the white solid (NaCl)
was filtered off. The solvent was evaporated to dryness, the yellow
residue was redissolved in thf (20 mL), bipy′ (0.065 g, 0.153 mmol)
was added, and the slurry was stirred at room temperature for 20
min. Then, CNtBu (0.017 mL, 0.153 mmol) was added and stirred
for another 30 min. The solution was concentrated under vacuum
to a volume of 5 mL, and addition of hexane (10 mL) caused the
precipitation of compound 5 as a black, microcrystalline solid,
which was washed with hexane (2 × 20 mL). Yield: 0.183 g, 76%.
1
IR (thf, cm-1): 1965, 1894 (νCO), 2185 (νCN). H NMR (DMSO-
Synthesis of [Mo(bipy′)(CO)4] (1). A mixture of [Mo(CO)6]
(0.150 g, 0.568 mmol) and bipy′ (0.240 g, 0.568 mmol) in thf (40
mL) was refluxed for 4 h. The solution was concentrated under
vacuum to a volume of 5 mL, and addition of diethylether (20 mL)
caused the precipitation of compound 1 as a red, microcrystalline
solid, which was washed with hexane (2 × 20 mL). Yield: 0.250
d6): δ 10.79 (br s, 2H, NH, bipy′), 9.28 (s, 2H, bipy′), 9.05 (d,
J(H,H) ) 5.2 Hz, 2H, bipy′), 8.32 (d, J(H,H) ) 5.2 Hz, 2H, bipy′),
7.85 (m, 16H, BAr′4 and AA′BB′ of bipy′), 7.62 (m, 4H, Hp BAr′4),
7.11, 7.06 (AA′BB′, 2H, bipy′), 3.65 (s, 2H, Hsyn methallyl), 2.55
(s, 6H, CH3 bipy′), 2.15 (s, 2H, Hanti η3-methallyl), 1.12 (s, 9H,
CH3 CNtBu), 1.01 (s, 3H, CH3 η3-methallyl). 13C NMR (DMSO-
d6): δ 225.2 (CO), 165.0 (CdO, bipy′), 163.8 (q, J(C,B) ) 49.9
Hz, Ci BAr′4), 156.4, 153.0, 148.1, 138.4, 132.1, 131.9, 125.3, 123.6,
123.5 (bipy′), 136.9 (Co BAr′4), 129.7 (H2biim), 131.3 (q, J(C,F)
) 31.2 Hz, Cm BAr′4), 126.8 (q, J(C,F) ) 271.9 Hz, CF3 BAr′4),
120.4 (Cp BAr′4), 94.9 (C2 η3-methallyl), 69.8 (C(CH3)3 CNtBu),
62.2 (C1 and C3 η3-methallyl), 31.8 (C(CH3)3 CNtBu), 27.9 (CH3
η3-methallyl), 23.3 (CH3 bipy′), the CNtBu signal could not be
observed. Anal. Calcd (%) for C69H50BF24MoN5O4: C, 52.59; H,
3.20; N, 4.44. Found: C, 52.69; H, 3.08; N, 4.42.
1
g, 70%. IR (thf, cm-1): 2012, 1906, 1888, 1846 (νCO). H NMR
(DMSO-d6): δ 10.79 (br s, 2H, NH, bipy′), 9.32 (s, 2H, bipy′),
9.04 (d, J(H,H) ) 5.2 Hz, 2H, bipy′), 8.11 (d, J(H,H) ) 5.2 Hz,
2H, bipy′), 7.70, 7.67, 7.24, 7.22 (AA′BB′, 8H, C6H4 of bipy′),
2.43 (s, 6H, CH3, bipy′). 13C NMR (DMSO-d6): δ 222.0 (2 × CO),
204.6 (2 × CO), 163.6 (CdO, bipy′), 155.3, 150.0, 143.4, 136.0,
133.2, 121.6, 120.5, 129.0, 118.4 (bipy′), 20.4 (CH3, bipy′). Anal.
Calcd (%) for C30H22MoN4O6: C, 57.15; H, 3.52; N, 8.84. Found:
C, 57.33; H, 3.48; N, 8.77.
Synthesis of [MoCl(η3-methallyl)(bipy′)(CO)2] (3). A mixture
of [MoCl(η3-methallyl)(CO)2(NCMe)2] (0.050 g, 0.153 mmol) and
bipy′ (0.065 g, 0.153 mmol) in thf (20 mL) was stirred at room
temperature for 30 min. The resulting dark solution was concen-
trated under vacuum to a volume of 5 mL, and addition of
diethylether (20 mL) caused the precipitation of compound 3 as a
microcrystalline solid, which was washed with hexane (2 × 20 mL).
Yield: 0.096 g, 94%. IR (thf, cm-1): 1942, 1871 (νCO). 1H NMR
(DMSO-d6): δ 10.73 (br s, 2H, NH, bipy′), 9.12 (s, 2H, bipy′),
8.97 (d, J(H,H) ) 5.2 Hz, 2H, bipy′), 8.07 (d, J(H,H) ) 5.2 Hz,
2H, bipy′), 7.67, 7.65, 7.22, 7.19 (AA′BB′, 8H, C6H4 of bipy′),
2.93 (s, 2H, Hsyn methallyl), 2.31 (s, 6H, CH3, bipy′), 1.35 (s, 2H,
Hanti η3-methallyl), 1.02 (s, 3H, CH3 η3-methallyl). 13C NMR
(DMSO-d6): δ 227.9 (CO), 163.3 (CdO, bipy′), 154.4, 153.2,
145.4, 136.7, 134.5, 125.3, 122.3, 130.1, 121.5 (bipy′), 82.3 (C2
η3-methallyl), 53.8 (C1 and C3 η3-methallyl), 21.4 (CH3, bipy′),
19.6 (CH3 η3-methallyl). Anal. Calcd (%) for C32H29ClMoN4O4:
C, 57.80; H, 4.40; N, 8.43. Found: C, 57.67; H, 4.28; N, 8.48.
Synthesis of [Mo(η3-methallyl)(CNtBu)(CO)2(H2biim)]BAr′4
(6). To a solution of 4 (0.100 g, 0.266 mmol) in CH2Cl2 (30 mL)
were added NaBAr′4 (0.236 g, 0.266 mmol) and CNtBu (0.015 mL,
0.266 mmol). The mixture was stirred at room temperature for 2
h, and then, it was filtered. The solution was concentrated under
vacuum to a volume of 5 mL, and addition of hexane (10 mL)
caused the precipitation of compound 6 as an orange powder, which
was washed with hexane (2 × 20 mL). Yield: 0.300 g, 90%. IR
1
(CH2Cl2, cm-1): 1961, 1881 (νCO), 2185 (νCN). H NMR (CD3-
CN): δ 11.15 (br s, 2H, NH, H2biim), 7.65 (m, 12H, BAr′4), 7.37
(d, J(H,H) ) 1.4 Hz, 2H, H2biim), 7.22 (d, J(H,H) ) 1.4 Hz, 2H,
H2biim), 3.45 (s, 2H, Hsyn methallyl), 1.96 (s, 2H, Hanti η3-methallyl),
1.20 (s, 9H, CH3 CNtBu), 1.08 (s, 3H, CH3 η3-methallyl). 13C NMR
(CD3CN): δ 223.8 (CO), 162.5 (q, J(C,B) ) 49.9 Hz, Ci BAr′4),
137.9 (H2biim), 134.6 (Co BAr′4), 129.7 (H2biim), 129.1 (q, J(C,F)
) 31.0 Hz, Cm BAr′4), 124.5 (q, J(C,F) ) 271.9 Hz, CF3 BAr′4),
120.7 (H2biim), 117.6 (Cp BAr′4), 89.5 (C2 η3-methallyl), 58.4 (C1
and C3 η3-methallyl), 54.3 (C(CH3)3 CNtBu), 17.4 (CH3 η3-
methallyl), the CNtBu signal could not be observed. Anal. Calcd
(23) Hynes, M. J. J. Chem. Soc., Dalton Trans. 1993, 311.
2852 Inorganic Chemistry, Vol. 46, No. 7, 2007

Biimidazole and Bis(amide)bipyridine Mo Carbonyl Complexes
(%) for C49H34BF24MoN5O2: C, 45.71; H, 2.66; N, 5.44. Found:
C, 45.64; H, 2.52; N, 5.63.
A suitable crystal was mounted directly from the mother liquor
under nitrogen at room temperature, perfluorocarbon oil being used
to protect it from the atmospheric air and moisture. Data were
collected using a Nonius KappaCCD diffractometer. The structures
were solved by direct methods, and refinement was carried out using
full-matrix least squares on F2.30 There is considerable rotational
Crystal Structure Determination. General Description for
Compounds [3]‚[NBu4Cl], [5]‚[HSO4], and [Mo(allyl)(Br/Cl)-
(CO)2(H2Biim)]‚[Br/Cl-]. A suitable crystal was attached to a glass
fiber and transferred to a Bruker AXS SMART 1000 diffractometer
with graphite monochromatized Mo KR X-radiation and a CCD
area detector. One hemisphere of the reciprocal space was collected
in each case. Raw frame data were integrated with the SAINT24
program. The structures were solved by direct methods with
SHELXTL.25 An empirical absorption correction was applied with
the program SADABS.26 In every structure, all non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were set in calculated
positions and refined as riding atoms. In the structure of [Mo(allyl)-
(Br/Cl)(CO)2(H2Biim)], it was found that the positions of Br and
Cl were disordered between the two positions (one bonded to Mo,
the other hydrogen bonded to the biimidazole ligand). The
occupancy of Br and Cl on each site was refined with the constraints
EADP and EXYZ, while keeping the total sum to unit for each
site. In the structure of [Mo(allyl)(Br/Cl)(CO)2(H2Biim)], it was
found that Br and Cl were disordered between two positions (one
bonded to Mo, the other hydrogen bonded to the biimidazole ligand.
The occupancy of Br and Cl on each site was refined with the
constraints EADP and EXYZ, while keeping the total sum to unit
for each site. Despite repeated attempts, it was not possible to find
a stable model with different Mo-Cl and Mo-Br distances.
Therefore, Cl and Br were refined at the same site, which
corresponds to the mean values of the Mo-Cl and Mo-Br
distances. Drawings and other calculations were made with
SHELXTL, PLATON,27 and PARST28 under WINGX.29 Crystal
and refinement details are collected in Table 4.
t
disorder of the Bu group, which is especially difficult to model
t
due to the central carbon atom of the Bu group lying on a mirror
plane. Local maxima within the bonding distance of C9 are included
as partial carbon atoms with site occupancies adjusted to give a
total of three carbon atoms. The methyl distances on [6]‚[ReO4]
were constrained to be equal within experimental error. For the
structure of [6]‚[Br], the hydrogen atoms on C5 were directly
located, but their thermal parameters were linked to the parent
carbon atom. The N(2)-H(2) hydrogen atom was directly located
and allowed to refine freely. All other hydrogen atoms in this
structure were modeled on idealized geometries and allowed to ride
on their parent atoms. For the structure of [6]‚[ReO4], the hydrogen
atoms on C5 were directly located, but their thermal parameters
were linked to the parent carbon atom. All other hydrogen atoms
in this structure were modeled on idealized geometries and allowed
to ride on their parent atoms. Details of the data collections and
structure solutions are given in Table 4.
Acknowledgment. We thank Ministerio de Ciencia y
Tecnolog´ıa (Grants BQU2003-08649 and CTQ2006-07036/
BQU) and European Union (ERG to L.R.) for support of
this work. L.I. thanks Ministerio de Educacio´n y Ciencia
for a FPU predoctoral fellowship. D. Morales and L.R. thank
Ministerio de Educacio´n y Ciencia for Ramo´n y Cajal
contracts. R.A.K. would like to acknowledge The States of
Guernsey and The Cambridge University Domestic and
Millenium Fund.
General Description for Compounds [6]‚[Br] and [6]‚[ReO4].
(24) SAINT+, version 6.02; SAX area detector integration program; version
6.02; Bruker AXS, Inc.: Madison, WI, 1999.
Supporting Information Available: X-ray crystallographic data
for adducts [3]‚[NBu4Cl], [5]‚[HSO4], [Mo(allyl)(Br/Cl)(CO)2(H2-
Biim)]‚[Br/Cl-], [6]‚[Br], and [6]‚[ReO4] as CIF. 1H NMR titration
profiles and Job plot of receptor 5 toward chloride, hydrogensulfate,
and nitrate anions. This material is available free of charge via the
Internet at http://pubs.acs.org.
(25) Sheldrick, G. M. SHELXTL, version 5.1; integrated system for solving,
refining, and displaying crystal structures from diffraction data; Bruker
AXS, Inc.: Madison, WI, 1998.
(26) Sheldrick, G. M. SADABS, Empirical Absorption Correction Program;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(27) (a) For PLATON, see: Spek, A. L. Acta Crystallogr., Sect A 1990,
46, C34. (b) Spek, A. L. PLATON, A Multipurpose Crystallographic
Tool; Utrecht University: Utrecht, The Netherlands, 1998.
(28) (a) Nardelli, M. Comput. Chem. 1983, 7, 95. (b) Nardelli, M. J. Appl.
Crystallogr. 1995, 28, 659.
IC0621650
(29) For WINGX 1.70.00, see: Farrugia, L. J. J. Appl. Crystallogr. 1999,
32, 837.
(30) Sheldrick, G. M. SHELX-97, Go¨ttingen: Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2853