A straightforward synthesis of diverse nickel dithiolene complexes appended with hydrogen-bond donor/acceptor groups

Article abstract of DOI:10.1021/ic050174n

Nickel dithiolene complexes symmetrically appended with hydrogen-bond donor/acceptor functionalities such as imide, amide, or cyano/amide groups have been synthesized by a straightforward method of wide applicability starting from one single precursor. Single-crystal X-ray structures reveal the occurrence of one type of ribbon common to all compounds that is based on a recurrent self-complementary intermolecular hydrogen-bonded ring motif linking the symmetrically substituted complexes.

Full text of DOI:10.1021/ic050174n

Inorg. Chem. 2005, 44, 3380−3382
A Straightforward Synthesis of Diverse Nickel Dithiolene Complexes
Appended with Hydrogen-Bond Donor/Acceptor Groups
Ste´phane A. Baudron, Narcis Avarvari,* and Patrick Batail*
Chimie, Inge´nierie Mole´culaire et Mate´riaux d’Angers (CIMMA), UMR 6200 CNRS-UniVersite´
d’Angers, Baˆtiment K, 2 bouleVard LaVoisier, 49045 Angers, France
Received February 1, 2005
Nickel dithiolene complexes symmetrically appended with hydrogen-
bond donor/acceptor functionalities such as imide, amide, or cyano/
amide groups have been synthesized by a straightforward method
of wide applicability starting from one single precursor. Single-
crystal X-ray structures reveal the occurrence of one type of ribbon
common to all compounds that is based on a recurrent self-
complementary intermolecular hydrogen-bonded ring motif linking
the symmetrically substituted complexes.
themselves.8 Herein, we report on the straightforward
synthesissstarting from one single precursorsof a series of
nickel dithiolene complexes symmetrically functionalized by
hydrogen-bond donor/acceptor groups, including imides,
orthodiamides, and dual complexes, ortho-functionalized by
a cyano group and a primary amide group. This reaction is
important, as it also provides the network designer with a
set of unprecedented models whose patterns of self-assembly
in the solid state is analyzed.
Neiland’s 4,5-diamido-2-oxo-1,3-dithiole,9 1, was selected
as the starting material for the preparation of amide-
functionalized nickel dithiolene complexes. Paralleling the
work of the Riga group for the preparation of the complex
bearing a uracil-type dithiolate ligand, this dithiocarbonate
is reacted with 4 equiv of sodium methanolate in methanol.
Subsequent metathesis with nickel nitrate and an ammonium
or phosphonium halide salt unexpectedly affords [Ni(midt)2]2-
(22-), a complex of the ligand maleimide dithiolate (midt).
It is of interest to note the dual effect of sodium methanolate,
which acts both as a nucleophile for opening the dithio-
carbonate ring and as a base, abstracting protons and inducing
a synchronous, intramolecular reaction between the two
ortho-amide functionalities to produce an imide upon ring
closure and subsequent elimination of ammonia (Scheme 1).
Note also that the reaction occurs when only 2 equiv of
sodium methanolate are used. This complex can be further
oxidized with iodine to produce [Ni(midt)2]- (2-). Analysis
of the crystal structure of these complexes reveals one-
dimensional chains generated out of self-complementary
intermolecular hydrogen-bond motifs (Figure 1 and Table
1), a feature common to both dianionic (Bu4N)2Ni(midt)2
and (Ph4P)2Ni(midt)2 salts, as well as to the monoanionic,
paramagnetic complex (Ph4P)Ni(midt)2. In the case of both
dianionic complexes, the cations form isolated chains (Sup-
porting Information), whereas in (PPh4)Ni(midt)2, two chains
run parallel to each other, albeit with a slight offset (Figure
An enormous amount of work has been devoted to metallic
and superconducting salts based on nickel dithiolene com-
plexes1,2 and, recently, to the advent of single-component
molecular metals.3 Nevertheless, hydrogen-bonding inter-
actionssand their redox-activated intermolecular patternss
which are the focus of much current attention in the field of
molecular materials,4 have not been used per se to direct
the solid-state structures of metal dithiolene complexes and
manipulate the electronic structure of a class of conducting
and magnetic materials where the double-band concept2,3,5
has yet to reach its full potential. This is because metal
dithiolene complexes appended with hydrogen-bond donor/
acceptor functionalities are not available. Typically then,
crystal engineering issues6 featuring an important class of
functional redox complexes have thus far focused solely on
interactions between ammonium or pyridinum cations and
paramagnetic nickel dithiolene anionic complexes such as
[Ni(mnt)2]-7 or on the organization of the countercations by
* To whom correspondence should be addressed. E-mail:
patrick.batail@univ-angers.fr (P.B.), narcis.avarvari@univ-angers.fr (N.A.).
(1) (a) Robertson, N.; Cronin, L. Coord. Chem. ReV. 2002, 227, 93-127.
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3380 Inorganic Chemistry, Vol. 44, No. 10, 2005
10.1021/ic050174n CCC: $30.25
© 2005 American Chemical Society
Published on Web 04/15/2005

COMMUNICATION
Scheme 1. Synthesis of [Ni(midt)2]2-/1- a
Scheme 2. Synthesis of (PPh4)[Ni(madt)2] and (PPh4)[Ni(mant)2]a
a (i) NaSMe, Ni(NO3)2‚6H2O; (ii) MeOH reflux.
1
a (i) NaOMe, Ni(NO3)2‚6H2O; (ii) /2I2
Figure 1. Discrete set of two parallel chains as observed in (PPh4)Ni-
(midt)2. Selected bond lengths (Å) and angles (deg): Ni1-S1 2.174(1),
Ni1-S2 2.172(1), Ni1-S3 2.170(1), Ni1-S4 2.176(1); S1-Ni1-S2 93.62-
(4), S3-Ni1-S4 93.66(4), S1-Ni1-S3 86.15(4), S2-Ni1-S4 86.62(4).
Table 1. Hydrogen-Bond Distances and Angles Averaged over the
Two, Essentially Symmetrical Dimer Motifs
compound
N‚‚‚O (Å)
H‚‚‚O (Å)
R
N-H‚‚‚O (deg)
Figure 2. Slab of complexes in (PPh4)Ni(madt)2, with an emphasis on
the formation of ribbons through the R2 (8) motif (thick dotted bonds). The
thin dotted lines represent N-H‚‚‚O bonds within stacks. Selected bond
lengths (Å) and angles (deg): Ni-S1 2.150(1), Ni-S2 2.149(1), Ni-S3
2.145(1), Ni-S4 2.150(1); S1-Ni-S2 91.60(5), S3-Ni-S4 91.49(5), S1-
Ni-S3 88.15(5), S2-Ni-S4 88.83(5).
(Bu4N)2Ni(midt)2
(PPh4)2Ni(midt)2.CH3CN
(PPh4)Ni(midt)2
(PPh4)Ni(madt)2
(PPh4)Ni(mant)2
2.914
2.863
2.925
2.938
2.878
2.925
2.055
2.03
2.08
2.08
2.02
2.07
174.5
163.5
168
170.5
175
2
(Bu4N)2Ni(mant)2
173
+0.72 V/SCE, corresponding to the formation of
[Ni(midt)2]0. The latter electrochemical event observed at
such “normal” concentrations (>1 mM) indicates a rather
modest stability of the neutral complex, as typically observed
in nickel dithiolene complexes bearing attracting groups, such
as CN in [Ni(mnt)2]n-.12 Note that [Ni(midt)2]- is a para-
magnetic analogue of pyrometillimide (bis-imide of benzene-
1,2,4,5-tetracarboxylic acid) and that its deprotonated form
is a potential ligand for bimetallic complexes.13
1),10 giving rise to two intermolecular interactions amounting
to âI ) 0.17 and âII ) 0.19 eV, as determined by extended
Hu¨ckel calculations. This suggests an alternated spin chain
magnetic behavior in agreement with the observed temper-
ature evolution of the magnetic susceptibility (Supporting
Information).
It is of interest to note that only the dimer motif is present
here, in contrast to the preference for a catemer chain
established by a recent CSD analysis of hydrogen-bond
networks involving imide functionalities.11 Cyclic volt-
ammetry experiments for (PPh4)Ni(midt)2 in MeCN reveal
a reversible wave at -0.14 V/SCE, corresponding to the
couple [Ni(midt)2]2-/1-, and an ill-defined oxidation at
To form the nickel dithiolene tetraamide complex, one
therefore has to avoid proton abstraction from the amide,
the primary event toward ring closure and formation of the
imide. Thus, a nonbasic nucleophile has to be used to
generate the dithiolate. Hence, and as expected, sodium
methanethiolate, NaSMe, successfully promotes the quantita-
tive formation of diamido-dithiolate, as demonstrated by
reacting the dithiocarbonate 1 with 2 equiv of NaSMe and
subsequent cation exchange, which affords the complex
[Ni(madt)2]- (3-, madt ) maleamide dithiolate) (Scheme
2).
The crystal structure of 3- (Figure 2) shows,10 somewhat
surprisingly, an “open” type of conformation of the maleo-
diamide framework; that is, there is no intramolecular
hydrogen bond, in contrast of the structure of EDT-TTF-
(CONH2)2 (EDT ) ethylenedithio).14 To our knowledge, only
one such open form of primary 1,2-diamides has been
observed so far in the case of a dihydro barrelene tetra-
(10) Crystal data for (PPh4)Ni(midt)2 (2-) (C32H22N2O4PS4Ni): triclinic,
space group P1h, a ) 10.9413(17) Å, b ) 11.9501(17) Å, c ) 13.0235-
(16) Å, R ) 77.422(16)°, â ) 76.190(17)°, γ ) 74.858(17)°,
V ) 1574.1(4) Å3, T ) 293(2) K, Z ) 2, 15845 reflns measured,
5657 unique reflns (Rint ) 0.061) were used in the refinement by full-
matrix least-squares methods on F2, R ) 0.0396, Rw ) 0.0783 (all
data). Crystal data for (PPh4)Ni(madt)2 (3-) (C32H24N4O5PS4Ni):
triclinic, space group P1h, a ) 10.3180(14) Å, b ) 13.0706(19) Å,
c ) 15.399(2) Å, R ) 114.341(15)°, â ) 94.651(16)°, γ ) 101.106-
(17)°, V ) 1826.5(4) Å3, T ) 293(2) K, Z ) 2, 18612 reflns measured,
6595 unique reflns (Rint ) 0.0635) were used in the refinement by
full-matrix least-squares methods on F2, R ) 0.0549, Rw ) 0.1938
(all data). Note the presence of a highly disordered solvent molecule,
isotropically refined as O5. Crystal data for (PPh4)Ni(mant)2 (4-)
(C32H24N4O2PS4Ni): triclinic, space group P1h, a ) 10.1114(16),
b ) 13.1679(17), c ) 14.002(2) Å, R ) 72.019(16), â ) 70.639(17),
γ ) 77.020(17)°, V ) 1657.3(4) Å3, T ) 293(2) K, Z ) 2, 16291
reflns measured, 5918 unique reflns (Rint ) 0.1411) were used in the
refinement by full-matrix least-squares methods on F2, R ) 0.0515,
Rw ) 0.1162 (all data). Crystallographic data for the structure reported
in this paper and in the Supporting Information have been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC 257976-257981. Copies of the data can be
obtained free of charge upon application to CCDC, 12 Union Road,
Cambridge, CB21EZ, U.K. (Fax: (+44) 1223-336-033. E-mail:
deposit@ccdc.cam.ac.uk.)
(12) Geiger, W. E.; Barrie`re, F.; LeSuer, R.; Trupia, S. Inorg. Chem. 2001,
40, 2472-2473.
(13) (a) Adams, H.; Bailey, N. A.; Briggs, T. N.; McCleverty, J. A.;
Colquhoun, H. M. J. Chem. Soc., Dalton Trans. 1986, 813.
(b) Colquhoun, H. M.; Fairman, R.; Tootell, P.; Williams, D. J. J.
Chem. Soc., Dalton Trans. 1999, 2651.
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(14) Baudron, S. A.; Avarvari, N.; Batail, P.; Coulon, C.; Cle´rac, R.;
Canadell, E.; Auban-Senzier, P. J. Am. Chem. Soc. 2003, 125, 11583.
100.
Inorganic Chemistry, Vol. 44, No. 10, 2005 3381

COMMUNICATION
amide.15 In 3-, ribbons of complexes symmetrically linked
by self-complementary intermolecular ring motifs (Figure 2
and Table 1), also encountered in the crystalline structure
of 2, run along b and stack upon each other along a,
connected by self-complementary, transverse, and larger ring
motifs based on longer N-H‚‚‚O distances.
Although, upon dithiolate generation, the same workup
conditions as for the preparation of 22- were used, the
monoanionic complex is obtained directly this time. Very
likely, this behavior finds its origin in the lower 2-/1-
oxidation potential for the [Ni(madt)2]2- complex. Indeed,
cyclic voltammetry experiments for (PPh4)Ni(madt)2 in
MeCN show a reversible wave at -0.28 V/SCE, correspond-
ing to the couple [Ni(madt)2]2-/1-, and an irreversible
oxidation wave at +0.5 V/SCE, corresponding to the
formation of [Ni(madt)2]0. The lower stability of 32- species,
when compared with 22-, could be the consequence of the
nonplanarity of the diamide groups, as observed in the X-ray
structure of (PPh4)Ni(madt)2 (vide supra), strongly hampering
conjugation with the dithiole ring and hence diminishing their
electron-withdrawing effects. Thus, the synthesis of such
highly functionalized nickel dithiolene complexes demon-
strates that the use of alkylthiolates as nonbasic nucleophiles
in the ring opening of dithiolones constitutes a straightfor-
ward method for the generation of dithiolates in smooth
conditions, one that could be generalized to other such
functional dithiolones, sensitive to “classical” basic reagents
generally used in this kind of chemistry.
We further report here our discovery that reflux of complex
3- in methanol affords the bis-dehydrated complex (PPh4)-
[Ni(mant)] 4-, where mant ) maleamido-nitrilo-dithiolate
(Scheme 2). This reaction was all the more unexpected in
that water elimination from 1,2-diamides typically requires
such drastic conditions as reflux in acetic anhydride for the
preparation of ortho-cyanobenzamide from phthalamide.16
Here, the reaction occurs smoothly, probably because the
electron-rich character of the present diamide favors a
protonation of a carbonyl oxygen followed by water elimina-
tion. Note that, in addition to its inherent hydrogen-bond
donor/acceptor character, complex 4- also contains two trans
cyano groups, capable of engaging in coordination with other
metallic centers. (PPh4)[Ni(mant)2] crystallized in the triclinic
system, space group P1h, with two independent half-
complexes located on inversion centers and one independent
cation in a general position.10 Here, again, the recurrent,
robust self-complementary ring motif (Table 1) links the
symmetrically functionalized complexes into ribbons running
along b and connected along a by self-complementary, larger
ring motifs based on very short (2.235 Å for H‚‚‚O)
Figure 3. Fragment of the slab of complexes in (PPh4)Ni(mant)2,
emphasizing the two self-complementary ring motifs. Selected bond lengths
(Å) and angles (deg): Ni1-S1 2.139(2), Ni1-S2 2.146(2), Ni2-S3 2.140-
(2), Ni2-S4 2.147(2); S1-Ni1-S2 92.08(7), S3-Ni2-S4 92.01(7).
N-H‚‚‚O bonds (Figure 3). The cyano groups protrude out
of the dithiolene slab and are engaged in weaker hydrogen
bonds with phenyl protons of the cations.
Cyclic voltammetry experiments for (PPh4)[Ni(mant)2] in
MeCN reveal a reversible wave at -0.1 V/SCE correspond-
ing to the couple [Ni(mant)2]2-/1-, and an irreversible
oxidation wave at +0.67 V/SCE, corresponding to the
formation of [Ni(mant)2]0. Thus, electrocrystallization of
(n-Bu4N)2[Ni(mant)2] (42-) is performed through the reduc-
tion of (n-Bu4N)[Ni(mant)2] (4-) (Supporting Information).
Note that the same self-complementary ring motifs link the
dianionic forms 42- into discrete 1D ribbons isolated from
each other by the cations.
In summary, we have reported the synthesis of a series of
three nickel dithiolene complexes appended with hydrogen-
bond donor/acceptor functionalities. One very attractive
feature of complexes [Ni(midt)2]2-/1- and [Ni(mant)2]2-/1-
,
distinctive from any other metal dithiolene complexes, is that
they contain outer NH and CN groups, respectively, for
coordination reactions to additional metal complexes to
prepare extended networks by a building block approach.
All of the complexes described herein show extended
networks based on self-complementary, hydrogen-bonded
ring motifs that direct their supramolecular organization in
the solid state. Of particular note is the introduction, disclosed
here, of NaSMe as a new nonbasic dithiocarbonate ring-
opening reagent. Use of this reagent in other areas such as
highly functionalized tetrathiafulvalenes can be envisioned
with great prospect. The extension of the chemistry of these
three new dithiolene ligands to other metal centers is also
under way.
Acknowledgment. Financial support from the CNRS
(Ph.D. fellowship to S.A.B.) is gratefully acknowledged.
Supporting Information Available: Experimental details for
syntheses and X-ray structures in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org.
(15) Beerli, R.; Rebek, J., Jr. Tetrahedron Lett. 1995, 36, 1813.
(16) Murthy, A. R. K.; Wong, O. T.; Reynolds, D. J.; Iris, I. H. Pharm.
Res. 1987, 4, 21.
IC050174N
3382 Inorganic Chemistry, Vol. 44, No. 10, 2005