Molecular, 1D, and 2D systems built from phenylcyanamido ligands. Syntheses, crystal structures, and characterization of their magnetic properties

Article abstract of DOI:10.1021/ic025931l

Several Mn^II compounds with phenylcyanamido ligands have been synthesized and characterized by means of single-crystal X-ray structural determination. The reported compounds show a wide variety of nuclearity from mononuclear and dinuclear systems to 1D chains and 2D networks in which X-phenylcyanamide (X-pcyd) anions act as the bridging ligand. Mononuclear compound [Mn(H₂O)₂(4-bzpy)₂(3-Cl-pcyd)₂] (1) crystallizes in the monoclinic system, P21/a space group, dinuclear compounds (μ_1,33-Cl-pcyd)₂[Mn(2,2′-bpy) (3-Cl-pcyd)(MeOH)]₂ (2) and (μ1,3-3-Cl-pcyd)₂[Mn(2,2′-bpy)(3-Cl-pcyd) (EtOH)]₂ (3) crystallize in the triclinic system, P1 space group, 1D chain {(μ1,3-4-Cl-pcyd)₂[Mn(2,2′-bpy)]}_n (4) crystallizes in the monoclinic system, 12/a space group, and 2D network [Mn(μ-4,4′-bpy)(μ_1,3-3-F-pcyd)₂] _n (5) crystallizes in the monoclinic system, C2 space group. Susceptibility measurements on compounds 2-4 reveal moderate antiferromagnetic coupling in all cases. MO calculations have been made to elucidate the main factors that control the superexchange pathway for this kind of ligand. Comparison of their magnetic behavior with that of related ligands such as azido and dicyanamido is reported.

Full text of DOI:10.1021/ic025931l

Inorg. Chem. 2003, 42, 541−551
Molecular, 1D, and 2D Systems Built from Phenylcyanamido Ligands.
Syntheses, Crystal Structures, and Characterization of Their Magnetic
Properties
,†
Albert Escuer,* Nu´ria Sanz,† Ramon Vicente,† and Franz A. Mautner‡
Departament de Qu´ımica Inorga`nica, UniVersitat de Barcelona, c/ Mart´ı Franque´s 1-11,
08028 Barcelona, Spain, and Institut fu¨r Physikalische und Theoretische Chemie, Technische
UniVersita¨t Graz, A-8010 Graz, Austria
Received August 6, 2002
II
Several Mn compounds with phenylcyanamido ligands have been synthesized and characterized by means of
single-crystal X-ray structural determination. The reported compounds show a wide variety of nuclearity from
mononuclear and dinuclear systems to 1D chains and 2D networks in which X-phenylcyanamide (X-pcyd) anions
act as the bridging ligand. Mononuclear compound [Mn(H O)2(4-bzpy)2(3-Cl-pcyd)2] (1) crystallizes in the monoclinic
2
system, P21/a space group, dinuclear compounds (µ1,3-3-Cl-pcyd)2[Mn(2,2′-bpy)(3-Cl-pcyd)(MeOH)]2 (2) and (µ1,3-
3-Cl-pcyd)2[Mn(2,2′-bpy)(3-Cl-pcyd)(EtOH)]2 (3) crystallize in the triclinic system, P1h space group, 1D chain {(µ1,3-
4-Cl-pcyd)2[Mn(2,2′-bpy)]}n (4) crystallizes in the monoclinic system, I2/a space group, and 2D network [Mn(µ-
4,4′-bpy)(µ1,3-3-F-pcyd)2]n (5) crystallizes in the monoclinic system, C2 space group. Susceptibility measurements
on compounds 2−4 reveal moderate antiferromagnetic coupling in all cases. MO calculations have been made to
elucidate the main factors that control the superexchange pathway for this kind of ligand. Comparison of their
magnetic behavior with that of related ligands such as azido and dicyanamido is reported.
Introduction
two main coordination modes. One of these modes uses the
two terminal N-atoms (µ1,3 mode), but a µ1,1 mode also occurs
in which only one N-atom coordinates two metallic ions.1
Other exotic modes involving coordination to three4 or even
four5 metallic ions have been reported. From the magnetic
point of view, azido ligand is able to transmit strong
ferromagnetic (F) or antiferromagnetic (AF) interactions,
depending on the coordination mode,1 whereas dca deriva-
tives are always weakly coupled.6
Work on polynuclear systems derived from azide1 or
dicyanamide2 (dca) anions acting as bridging ligands is a
fast-growing research field due to the large variety of
topologies, dimensionalities, and magnetic properties that can
be obtained. Dicyanamide may act as a bidentate ligand by
coordination to two different metallic centers by means of
the terminal nitrile N-atoms (µ1,5 mode) or as a tridentate
ligand giving a variety of rutile-like 3D [M(dca)2] compounds
by means of the additional coordination of the central amide
N-atom3 (µ1,3,5 mode). Azido ligand also frequently shows
In contrast, much less is known about the phenylcyana-
mido (pcyd) ligands, despite the formal similarities with the
azido or dca ligands, Chart 1. The triatomic -NCN group
is electronically similar to the azido ligand, and similar
coordination modes may be reasonably expected. On the
other hand, the nitrile group approaches the coordination
properties of the dca ligand (mainly for M-N-C and M-N
bond parameters).
* Author to whom correspondence should be addressed. E-mail:
albert.escuer@qi.ub.es.
† Universitat de Barcelona.
‡ Technische Universita¨t Graz.
(1) Ribas, J.; Escuer, A.; Monfort, M.; Vicente, R.; Corte´s, R.; Lezama,
L.; Rojo, T. Coord. Chem. ReV. 1999, 193-195, 1027.
(2) Van der Werff, P. M.; Batten, S. R.; Jensen, P.; Moubaraki, B.; Murray,
K. S. Inorg. Chem. 2001, 40, 1718. Raebiger, J. W.; Manson, J. L.;
Sommer, R. D.; Geiser, U.; Rheingold, A. L.; Miller, J. S. Inorg. Chem.
2001, 40, 2578. Vangdal, B.; Carranza, J.; Lloret, F.; Julve, M.; Sletten,
J. J. Chem. Soc., Dalton Trans. 2002, 566 and references therein.
(3) Manson, J. L.; Kmety, C. R.; Epstein, A. J.; Miller, J. S. Inorg. Chem.
1999, 38, 2552. Batten, S. R.; Harris, A. R.; Jensen, P.; Murray, K.
S.; Ziebell, A. J. Chem. Soc., Dalton Trans. 2000, 3829. Kutasi, A.
M.; Batten, S. R.; Moubaraki, B.; Murray, K. S. J. Chem. Soc., Dalton
Trans. 2002, 819 and references therein.
(4) Goher, M. A. S.; Cano, J.; Journaux, Y.; Abu-Youssef, M. A. M.;
Mautner, F. A.; Escuer, A.; Vicente, R. Chem.sEur. J. 2000, 6, 778.
(5) Papaefstathiou, G. S.; Perlepes, S. P.; Escuer, A.; Vicente, R.; Font-
Bardia, M.; Solans, X. Angew. Chem. 2001, 113, 908; Angew. Chem.,
Int. Ed. 2001, 40, 884.
(6) Escuer, A.; Sanz, N.; Mautner, F. A.; Vicente, R. Inorg. Chem. 2000,
39, 1668.
10.1021/ic025931l CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/24/2002
Inorganic Chemistry, Vol. 42, No. 2, 2003 541

Escuer et al.
Chart 1
materials possessing useful electronic and/or magnetic
properties”.7
With the aim of exploring the magnetic and synthetic
possibilities of this kind of ligand, we prepared several
neutral [Mn(L2)(X-pcyd)2] derivatives in which the L2 ligands
are pyridinic ligands and the X-pcyd ligands are chloro- or
fluoro-substituted phenylcyanamides. Successful syntheses
and structural characterization have been carried out for
several representative complexes, with formulas [Mn(H2O)2-
(4-bzpy)2(3-Cl-pcyd)2] (1), (µ1,3-3-Cl-pcyd)2[Mn(2,2′-bpy)-
(3-Cl-pcyd)(MeOH)]2 (2), (µ1,3-3-Cl-pcyd)2[Mn(2,2′-bpy)(3-
Cl-pcyd)(EtOH)]2 (3), {(µ1,3-4-Cl-pcyd)2[Mn(2,2′-bpy)]}n (4),
and [Mn(µ-4,4′-bpy)(µ1,3-3-F-pcyd)2]n (5), in which 4-bzpy
is 4-benzoylpyridine, 2,2′-bpy and 4,4′-bpy correspond to
2,2′- and 4,4′-bipyridyl, and 3-Cl-pcyd, 4-Cl-pcyd, and 3-F-
pcyd are the 3-chloro-, 4-chloro-, and 3-fluorophenylcyana-
mido ligands. These compounds were obtained by reaction
in alcoholic medium of manganese salts and deprotonated
phenylcyanamide in the presence of the corresponding
pyridinic or bipyridinic ligands. The X-ray crystal structure
determination reveals a wide variety of topologies and
supramolecular arrangements: compound 1 is a mononuclear
complex, but a net of hydrogen bonds gives a highly
symmetric 2D network, compounds 2 and 3 are dinuclear
complexes bridged by double phenylcyanamido ligands,
giving supramolecular 1D systems by means of hydrogen
bonds, compound 4 is a chain of manganese atoms linked
by double phenylcyanamido bridges, and finally, compound
5 is a 2D system formed by the crossing of phenylcyanamido
and 4,4′-bpy chains. Magnetic measurements for compounds
2-5 reveal a moderate AF coupling which lies in an
intermediate position between the typical magnitudes of the
couplings induced by µ1,3-azido and µ1,5-dicyanamido bridges.
MO calculations on the free pcyd- anions and the main
distortions in the bridging region point out the effect of the
halo substituent in the para position, the chair distortion of
the Mn-(NCN)2-Mn unit, or the effect of the torsion of the
phenyl rings on the superexchange interaction. The super-
exchange pathway has also been compared with those of
related azido and dicyanamido ligands.
This intermediate position between the azido and dca
ligands also appears in regard to the MO involved in the
superexchange interaction for each ligand. Azide ion has two
efficient nonbonding orthogonal π orbitals, whereas dca
ligand has one π and one σ orbital, a much less efficient
superexchange pathway due to the low contribution of nitrile
N-atoms and the shape of the MOs.1,6 Like dca, phenylcy-
anamide ion also exhibits π and σ orbitals of adequate
energy, but as occurs in the azido bridge, phenylcyanamide
is much more efficient in transmitting the magnetic interac-
tions due to the higher electronic density in the coordinating
N-atoms.
In a recent review about the phenylcyanamido ligands,7
the poorly developed coordination chemistry of these ligands
was pointed out by R. J. Crutchley, who indicated that their
“coordination chemistry is expected to be as potentially rich
as that of the pseudohalides azide or thiocyanate”. This
implies that, to date, complexes for most of the transition
metals have not been reported. The most developed pcyd
coordination chemistry is related to ruthenium cation, for
which a large family of pcyd derivatives has been studied.
But only structural information about several mononuclear
ruthenium compounds,7,8 three (µ-pcyd)2AgI, -CuI, and -CuII
dinuclear complexes,9 and some mononuclear CuII, NiII, PdII,
and MnII compounds has been published,10 together with
nonstructurally characterized families of monomeric deriva-
tives.7 Another unexplored property of pcyd- anions is their
behavior as superexchange mediators. To date, only the
intriguing behavior of the closely related 1,4-phenyldicy-
anamido ligand has been studied from the magnetic point
of view in dinuclear copper or ruthenium compounds.7,11
These compounds show strong coupling between RuIII centers
separated by more than 13 Å, but magnetic properties for
the µ1,3 and µ1,1 coordination modes of the pcyd- bridges
have never been studied. In this sense, R. J. Crutchley
indicates that “The ability of the dicyd2- bridging ligands
to mediate metal-metal coupling suggests that phenylcy-
anamide derivatives may find their way into molecular
In the present paper we give the first structural data for
polynuclear phenylcyanamide derivatives with MnII, the first
examples of 1D or 2D systems derived from these ligands,
and the first experimental variable-temperature susceptibility
data and study as superexchange mediators for their µ1,3
coordination mode.
(7) Crutchley, R. J. Coord. Chem. Rew. 2001, 219-221, 125-155.
(8) Sondaz, E.; Gourdon, A.; Launay, J. P.; Bonvoisin, J. Inorg. Chim.
Acta 2001, 316, 79.
(9) Brader, M. L.; Ainscough, E. W.; Baker, E. N.; Brodie, A. M. J. Chem.
Soc., Dalton Trans. 1990, 2785. Ainscough, E. W.; Baker, E. N.;
Brader, M. L.; Brodie, A. M.; Ingham, S. L.; Waters, J. M.; Hanna,
J. V.; Healy, P. C. J. Chem. Soc., Dalton Trans. 1991, 1243.
Ainscough, E. W.; Brodie, A. M.; Cresswell, R. J.; Turnbull, J. C.;
Waters, J. M. Croat. Chim. Acta 1999, 72, 377.
(10) Crutchley, R. J.; Hynes, R.; Gabe, E. Inorg. Chem. 1990, 29, 4921.
Letcher, R. J.; Zhang, W.; Bensimon, C.; Crutchley, R. J. Inorg. Chim.
Acta 1993, 210, 183. Zhang, W.; Bensimon, C.; Crutchley, R. J. Inorg.
Chem. 1993, 32, 580. Shen, X.; Shan, J.; Sun, H. B.; Kang, B. S. J.
Chin. Chem. Soc. 1999, 46, 179.
Experimental Section
Physical Methods. Magnetic susceptibility measurements were
carried out on polycrystalline samples with a DSM8 pendulum
susceptometer working in the range 4-300 K under magnetic fields
of approximately 1 T. Diamagnetic corrections were estimated from
the Pascal tables. The infrared spectra (4000-400 cm-1) were
recorded from KBr pellets on a Nicolet 520 FTIR spectrophotom-
eter. EPR spectra were recorded with a Bruker ES200 spectrometer
at X-band frequency. Thermogravimetric measurements were
carried out in a Mettler TG 50 instrument at a heating rate of 10
(11) Aquino, M. A. S.; Lee, F. L.; Gabe, E. J.; Bensimon, C.; Greedan, J.
E.; Crutchley, R. J. J. Am. Chem. Soc. 1992, 114, 5130. Cheruiyot, L.
L.; Thompson, L. K.; Greedan, J. E.; Liu, G.; Crutchley, R. J. Can. J.
Chem. 1995, 73, 573.
°C‚min-1
.
542 Inorganic Chemistry, Vol. 42, No. 2, 2003

Systems Built from Phenylcyanamido Ligands
Table 1. Crystal Data and Structure Refinement for 1-5
1
2
3
4
5
empirical formula
MW
space group
a, Å
b, Å
c, Å
C38H30Cl2MnN6O4
760.52
P21/a
7.630(3)
12.559(5)
18.886(7)
90
93.00(3)
90
1807(1)
2
C50H40Cl4Mn2N12O2
1092.62
P1h
C52H44Cl4Mn2N12O2
1120.67
P1h
C24H16Cl2MnN6
514.27
I2/a
8.620(4)
10.482(3)
24.860(9)
90
99.45(4)
90
2215(1)
4
C24H16F2MnN6
481.37
C2
17.276(9)
11.599(6)
10.646(6)
90
103.35(3)
90
2075(2)
4
9.683(3)
10.826(4)
11.926(3)
88.71(2)
77.04(3)
83.16(3)
1209.7(7)
1
10.684(4)
11.980(5)
12.003(5)
117.64(3)
95.76(3)
104.24(3)
1277(1)
1
R, deg
â, deg
γ, deg
V, Å3
Z
T, °C
27
186
186
25
185
λ(Mo KR), Å
0.71069
1.398
0.562
0.0473
0.1196
0.71069
1.410
0.798
0.0499
0.1425
0.71069
1.457
0.758
0.0439
0.1177
0.71069
1.542
0.863
0.0426
0.1256
0.71069
1.540
0.680
0.0473
0.1295
F
calcd, g‚cm-3
µ(Mo KR), mm-1
R1a
ωR2b
a R1(Fo) ) ∑Fo Fc/∑Fo. b wR2(Fo)2 ) {∑[w((Fo)2 - (Fc)2)2]/∑[w(Fo)4]}1/2
.
-
Crystal Structure Determination and Refinement of the
Structures. Crystal data and details of the structure determinations
are presented in Table 1. Data were collected on a modified STOE
four-circle diffractometer with graphite-monochromated Mo KR
radiation (λ ) 0.71069 Å) and the ω-scan technique. The data of
1 and 4 were collected at room temperature and those of 2, 3, and
5 at -185(2) °C and processed in the usual way (corrections for
Lp but not for absorption). The structures were solved by direct
methods using the SHELXS-86 computer program12 and refined
by full-matrix least-squares methods on F2, using the SHELXL-93
program13 incorporated in the SHELXTL/PC V 5.03 program
library14 and the graphics program PLUTON.15 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms bonded to
donor atoms were located from difference Fourier maps; the
remaining ones were located on calculated positions by use of the
HFIX utility of the SHELXL-93 program. Racemic twin refinement
was applied in the case of 5. Selected bond parameters are given
in Tables 2-6 for compounds 1-5, respectively.
to evaporate, giving a yellow crystalline compound suitable for
X-ray measurements in a few days. Yield: 42%. Anal. Calcd for
MnC38H30Cl2N6O4 (760.52): C, 60.0; H, 4.0; N, 11.1. Found: C,
59.9; H, 4.1; N, 11.2.
The method for compounds 2-4 was the same as that indicated
for compound 1, using 1 mmol of 2,2′-bpy instead of 2 mmol of
4-benzoylpyridine and using ethanol instead of methanol for
compound 3. The yields of the corresponding yellow products were
18%, 23%, and 51%, respectively. Anal. Calcd for 2, Mn2C50H40-
Cl4N12O2 (1092.62): C, 55.0; H, 3.7; N, 15.4. Found: C, 54.5; H,
3.6; N, 15.3. Anal. Calcd for 3, Mn2C52H44Cl4N12O2 (1120.67): C,
55.7; H, 3.9; N, 15.0. Found: C, 55.5; H, 3.8; N, 15.3. Anal. Calcd
for 4, MnC24H16Cl2N6 (514.27): C, 56.0; H, 3.1; N, 16.3. Found:
C, 55.8; H, 3.2; N, 16.5.
Yellow crystals of compound 5 were obtained by a similar
procedure using 4,4′-bpy instead of 2,2′-bpy. Yield: 20%. Anal.
Calcd for Mn2C24H16F2N6 (481.37): C, 59.9; H, 3.4; N, 17.5.
Found: C, 59.6; H, 3.4; N, 17.5.
Crystallographic data (excluding structure factors) for structures
1-5 have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC-185830 (1),
-185831 (2), -185832 (3), -160794 (4), and 167320 (5). Copies of
the data can be obtained free of charge on application to CCDC,
12 Union Rd., Cambridge CB2 1EZ, U.K. (fax, (+44) 1223-336-
033; e-mail, deposit@ccdc.cam.ac.uk).
Synthesis. Neutral 3-fluoro-, 3-chloro-, and 4-chlorophenylcy-
anamide (X-pcyd-H), in all cases, were prepared by desulfurization
of the corresponding X-phenylthiourea with lead acetate, following
the general synthetic procedure described for the halo derivatives
of phenylcyanamide.16
Compound 1 was prepared by reaction of a solution of
manganese nitrate hexahydrate (1 mmol) and 4-benzoylpyridine (2
mmol) in 20 mL of methanol with a solution of 3-Cl-pcyd-H (2
mmol) in 5 mL of NaOH (0.2 M) to deprotonate the ligand. After
the reagents were mixed, the resulting clear solution was allowed
For compounds 1-3, thermogravimetric analysis performed
between 30 and 500 °C with a heating rate of 10 °C‚min-1 shows
well-defined losses of weight at moderate temperatures due to the
coordinated solvents. For 1, a 4.5% loss was observed at 130 °C
(theoretical H2O loss is 4.7%), followed by decomposition of the
compound at temperatures higher than 150-160 °C. Compound 2
shows a loss of 5.6% due to the coordinated methanol molecules
(theoretical MeOH loss is 5.85%) centered at 80 °C. After this first
step the resulting compound is stable up to 300 °C. Compound 3
shows a loss of 8.3% due to the coordinated ethanol molecules
(theoretical EtOH loss is 8.21%) centered at 85 °C. Decomposition
of the resulting compound takes place at temperatures greater than
290 °C. Compounds 2 and 3 may lose coordinated solvent at room
temperature when finely powdered samples are stored for several
days. To avoid errors in the magnetic measurements, the corre-
sponding samples were freshly extracted from the mother solutions,
dried, and powdered just prior to the measurements being per-
formed.
(12) Sheldrick, G. M. SHELXS-86, Program for the Solution of Crystal
Structure; University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(13) Sheldrick, G. M. SHELXL-93, Program for the Refinement of Crystal
Structure; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(14) SHELXTL 5.03 (PC-Version), Program Library for the Solution and
Molecular Graphics; Siemens Analytical Instruments Division: Madi-
son, WI, 1995.
(15) Spek, A. L. PLUTON-92; University of Utrecht: Utrecht, The
Netherlands, 1992.
(16) Hollebone, B. R.; Nyholm, R. S. J. Chem. Soc A 1971, 332.
Results and Discussion
Infrared Spectra. Neutral pcyd-H shows a characteristic
IR ν(NCN) stretching absorption in a low-wavenumber range
(2225-2249 cm-1), which shifts down to ca. 2120 cm-1 for
deprotonated pcyd-, suggesting a lower contribution of the
resonance form containing the nitrile fragment. Nitrile-N-
Inorganic Chemistry, Vol. 42, No. 2, 2003 543

Escuer et al.
Figure 1. Labeled plot of 1 and the 2D supramolecular arrangement of compound 1 by means of H-bonds. Phenyl groups of the 4-Bzpy and 3-Cl-pcyd
ligands have been omitted for clarity.
coordinated pcyd- ligands exhibit intermediate positions
(always lower than 2200 cm-1), with a dependence on the
nature of the metallic center and the number of halo groups.7
For the ligands used in this work, the ν(NCN) appears at
2239 cm-1 for 3-Cl-pcyd-H, 2238 cm-1 for 4-Cl-pcyd-H,
and 2235 cm-1 for 3-F-pcyd-H. Coordination to MnII atoms
shifts the signals down to 2154 cm-1 for 3-F-pcyd in
compound 5 and 2133 cm-1 for 3-Cl-pcyd in compound 4
(only one kind of µ1,3-pcyd ligand). For 3-Cl-pcyd, the signal
appears at 2160 cm-1 for 1 (only nitrile-N-coordinated pcyd
ligands) and at 2155-2132 cm-1 for 2 and 2159-2133 cm-1
for 3 (containing the two µ1,3-pcyd and nitrile-N-coordinated
pcyd coordination modes). These latter data indicate a
criterion to differentiate the nitrile N coordination (2160-
2155 cm-1 range) of the µ1,3 bridging mode, for which lower
wavenumbers are found (2132-2133 cm-1). Structurally
characterized µ1,3 copper dimers agree reasonably with this
assignation: (µ1,3-pcyd)2[Cu(2,2′-bpy)(pcyd)2]2 also exhibits
two similar absorptions at 2175 and 2103 cm-1, whereas the
CuI compound (µ1,3-4-Me-pcyd)2[Cu(PPh3)2]2 with only µ1,3-
4-Me-pcyd ligands shows a single absorption at 2167-74
cm-1.9 The wavenumber sequence for the ν(NCN) stretching
absorption seems then to be pcyd-H > µ1,3-pcyd > nitrile N
coordination or anionic pcyd-. These limited data referred
to MnII derivatives suggest the above order, but further
experimental data are required to obtain a general assignation.
Description of the Structure of [Mn(H2O)2(4-bzpy)2(3-
Cl-pcyd)2] (1). This compound consists of centrosymmetric
monomeric units in which the three different kinds of ligands
adopt a trans arrangement around the central MnII ion, Figure
1. Bond distances are 2.145(2) Å between the MnII ion and
the oxygen of the water molecules, a similar value of 2.154-
(3) Å to the terminal N(2) of the cyanamido group, and a
larger distance of 2.389(2) Å to the pyridinic N(1) atom of
the 4-bzpy ligand, giving an elongated octahedron. Bond
angles around the Mn atom are close to 90° in all cases.
Monodentate phenylcyanamido ligand shows a linear coor-
dination to the manganese atom with a Mn(1)-N(2)-C(13)
bond angle of 179.0(3)°.
The linear -NCN unit is asymmetric with bond distances
of N(3)-C(13) ) 1.290(4) Å and C(13)-N(2) ) 1.156(3)
Å. The cyanamido unit is practically coplanar with the 3-Cl-
phenyl group and shows a C(14)-N(3)-C(13) bond angle
of 116.1(2)°. The most interesting feature of this structure
lies in the moderately strong hydrogen bonds formed between
the water molecules and N(3) nitrogen atoms from phenyl-
cyanamido ligands of neighboring monomeric complexes,
with N(3′)‚‚‚O(1) distances of 2.856(4) and 2.843(4) Å and
bond angles of 168(3)° for N(3′)-H(6)-O(1) and 167(2)°
for N(3′′)-H(7)-O(1). Each monomeric unit participates in
four H-bonds, giving a supramolecular arrangement consist-
ing of two-dimensional H-bonded layers, Figure 1. Selected
bond parameters are given in Table 2.
Description of the Structure of (µ1,3-3-Cl-pcyd)2[Mn-
(2,2′-bpy)(3-Cl-pcyd)(MeOH)]2 (2). The structure consists
of centrosymmetric dinuclear Mn units linked by double end-
to-end 3-chlorophenylcyanamido bridges, Figure 2. The six
coordination sites around the Mn atoms are occupied by one
2,2′-bpy ligand, one terminal nitrile atom of one 3-Cl-pcyd
ligand, two bridging cyanamido ligands, and one solvent
molecule (methanol). The linked 2,2′-bpy and the variety of
ligands distort the coordination polyhedron of the Mn atom:
bond angles range between 71.3(1)° for N(1)-Mn(1)-N(2)
and 101.7(1)° for N(3a)-Mn(1)-N(5). The different natures
of the N-atoms of the phenylcyanamido ligand also induce
different bond parameters in the bridging region: Mn(1)-
544 Inorganic Chemistry, Vol. 42, No. 2, 2003

Systems Built from Phenylcyanamido Ligands
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2
Mn(1)-O(1)
Mn(1)-N(1)
Mn(1)-N(2)
Mn(1)-N(4)
Mn(1)-N(5)
Mn(1)-N(3a)
N(3)-C(11)
N(4)-C(11)
2.216(2) N(5)-C(18)
2.319(3) N(6)-C(18)
2.270(3) O(1)-H(26)
2.291(2) Cl(1)-C(14)
2.142(3) Cl(2)-C(21)
2.176(2)
1.170(4)
1.287(4)
0.87(3)
1.737(3)
1.742(4)
1.173(4)
1.292(4)
O(1)-Mn(1)-N(1)
O(1)-Mn(1)-N(2)
O(1)-Mn(1)-N(4)
O(1)-Mn(1)-N(5)
O(1)-Mn(1)-N(3a)
N(1)-Mn(1)-N(2)
N(1)-Mn(1)-N(4)
N(1)-Mn(1)-N(5)
N(1)-Mn(1)-N(3a)
N(2)-Mn(1)-N(4)
N(2)-Mn(1)-N(5)
89.11(9)
88.20(8)
174.30(9)
88.12(9)
89.13(9)
Mn(1)-N(4)-C(11)
110.7(2)
Mn(1a)-N(3)-C(11) 140.3(2)
Mn(1)-N(5)-C(18)
C(11)-N(4)-C(12)
C(18)-N(6)-C(19)
172.3(2)
117.0(2)
118.5(3)
176.1(3)
175.5(3)
71.27(10) N(3)-C(11)-N(4)
85.57(9)
164.8(1)
93.2(1)
92.0(1)
93.7(1)
N(5)-C(18)-N(6)
N(2)-Mn(1)-N(3a) 164.26(9)
N(3a)-Mn(1)-N(4) 89.1(1)
N(3a)-Mn(1)-N(5) 101.7(1)
N(4)-Mn(1)-N(5) 97.54(9)
the main plane. The torsion angle between the plane
determined by the two -NCN- groups and the N(4)-Mn-
(1)-N(3a) plane is 36.5°. The 3-Cl-pcyd ligand is practically
planar with a minor torsion, C(13)-C(12)-N(4)-N(3), of
6.5°. The phenylcyanamido ligand is placed out of the main
(NCN)2 plane, which forms an acute angle of 28.6(2)° with
the N(4)-C(12) bond direction. The shortest Mn‚‚‚Mn
intradimer distance is 5.292(1) Å.
The dinuclear units generate a supramolecular one-
dimensional H-bonded system by means of the -OH group
of the coordinated methanol molecules and the N(6b) atoms
of the terminal 3-Cl-pcyd ligands. Between each dinuclear
unit appear two of these H-bonds, giving a structurally
alternating 1D system, Figure 2. The N(6b)-O(1) distance
is 2.699(4) Å, and the bond angle O(1)-H(26)-N(6b) takes
a value of 167(4)°. Selected bond parameters are given in
Table 3.
Description of the Structure of (µ1,3-3-Cl-pcyd)2[Mn-
(2,2′-bpy)(3-Cl-pcyd)(EtOH)]2 (3). The structure of this
compound is similar to that of 2 by substitution of the
coordinated methanol by one ethanol molecule, Figure 3.
Bond parameters are very similar to those indicated for
compound 2 in the (2° range of difference. Phenylcyana-
mido ligands are also out of the main (NCN)2 plane, which
determines an acute angle of 23.9(1)° with the N(2)-C(2)
bond direction.
As occurs for the above compound, dinuclear units are
linked between them by double H-bonds between the N(4)
atom of the terminal 3-Cl-pcyd ligand and the H-atom of
the coordinated ethanol group, giving a one-dimensional
supramolecular arrangement. The O(1)-N(4b) distance is
2.722(1) Å, and the O(1)-H(1)-N(4b) angle is 172(3)°.
Selected bond parameters are given in Table 4.
Figure 2. Labeled plot of 2 and the 1D supramolecular arrangement of
compound 2 by means of H-bonds. Compound 3 shows an identical H-bond
pattern.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1
Mn(1)-O(1)
Mn(1)-N(1)
Mn(1)-N(2)
N(2)-C(13)
N(3)-C(13)
N(3)-C(14)
2.145(2) Cl(1)-C(16)
2.389(2) O(2)-C(6)
2.155(3) O(1)-H(6)
1.155(4) O(1)-H(7)
1.290(4)
1.747(4)
1.194(5)
0.82(3)
0.82(3)
1.410(4)
O(1)-Mn(1)-N(1)
O(1)-Mn(1)-N(2)
88.98(9)
89.8(1)
O(1)-Mn(1)-O(1a) 180.00
Mn(1)-N(2)-C(13)
179.0(3)
178.0(3)
116.1(2)
N(2)-C(13)-N(3)
C(13)-N(3)-C(14)
H(6)-O(1)-H(7)
O(1)-Mn(1)-N(1a)
O(1)-Mn(1)-N(2a)
N(1)-Mn(1)-N(2)
91.02(9)
90.2(1)
93.12(9)
112(3)
N(1)-Mn(1)-N(1a) 180.00
N(1)-Mn(1)-N(2a)
86.88(9)
N(2)-Mn(1)-N(2a) 180.00
N(4) takes a value of 2.291(2) Å, whereas Mn(1)-N(3a) is
only 2.176(2) Å. Mn-N-C bond angles are also different,
Mn(1)-N(4)-C(11) being 110.7(2)° in contrast with Mn-
(1)-N(3a)-C(11a), which takes a greater value of 140.3-
(2)°. As occurs in 1, the monodentate phenylcyanamido
ligands coordinate to the manganese atom in a quasi linear
arrangement, with a Mn(1)-N(5)-C(18) bond angle of
172.3(2)°. The C-N-C angles between the cyanamido and
the phenyl groups are similar for the terminal and bridging
ligands: 118.5(3)° and 117.0(2)°, respectively. The Mn-
(NCN)2-Mn subunit shows a chair distortion similar to those
often found in similar systems with double azido bridges.1
This means that the two -NCN- groups are in the same
plane with the manganese atoms placed 0.946(1) Å out of
Description of the Structure of {(µ1,3-4-Cl-pcyd)2[Mn-
(2,2′-bpy)]}n (4). The structure consists of a one-dimensional
Mn system where the coordination environment around the
Mn atoms includes one 2,2′-bpy ligand and four N-atoms
of bridging 4-Cl-pcyd ligands.
Inorganic Chemistry, Vol. 42, No. 2, 2003 545

Escuer et al.
Figure 4. ORTEP plot of 4 with thermal ellipsoids at the 40% probability
level.
Figure 3. ORTEP plot of 3 with thermal ellipsoids at the 50% probability
level.
Table 5. Selected Bond Lengths (Å) and Angles (deg) for 4
Mn(1)-N(2)
Mn(1)-N(3)
Mn(1)-N(1b)
2.253(2) N(1)-C(1)
2.284(3) N(2)-C(1)
2.223(3) Cl(1)-C(5)
1.168(4)
1.292(4)
1.746(3)
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 3
Mn(1)-O(1)
Mn(1)-N(2)
Mn(1)-N(3)
Mn(1)-N(5)
Mn(1)-N(6)
Mn(1)-N(1a)
N(1)-C(1)
2.209(2) N(4)-C(9)
2.291(3) N(4)-C(8)
2.146(3) O(1)-H(1)
2.302(3) Cl(1)-C(4)
2.297(2) Cl(2)-C(11)
2.197(2)
1.401(3)
1.290(4)
0.83(4)
1.743(3)
1.739(3)
N(2)-Mn(1)-N(3)
N(2)-Mn(1)-N(2a)
N(2)-Mn(1)-N(3a)
N(2)-Mn(1)-N(1b)
N(2)-Mn(1)-N(1c)
N(3)-Mn(1)-N(3a)
N(3)-Mn(1)-N(1b)
N(3)-Mn(1)-N(1c)
97.22(9)
94.94(9)
166.61(9)
88.2(1)
Mn(1b)-N(1)-C(1) 140.4(2)
Mn(1)-N(2)-C(1)
C(1)-N(2)-C(2)
N(1)-C1-N(2)
111.4(2)
116.6(2)
176.2(3)
90.8(1)
1.174(4)
1.167(3)
71.32(9)
84.0(1)
97.2(1)
N(3)-C(8)
O(1)-Mn(1)-N(2)
O(1)-Mn(1)-N(3)
O(1)-Mn(1)-N(5)
O(1)-Mn(1)-N(6)
O(1)-Mn(1)-N(1a)
N(2)-Mn(1)-N(3)
N(2)-Mn(1)-N(5)
N(2)-Mn(1)-N(6)
N(1a)-Mn(1)-N(2)
N(3)-Mn(1)-N(5)
N(3)-Mn(1)-N(6)
172.14(9)
Mn(1)-N(2)-C(1)
111.9(2)
90.08(9)
86.44(9)
85.42(9)
90.03(9)
97.78(9)
85.95(9)
94.06(9)
88.62(9)
163.43(9)
91.94(9)
Mn(1a)-N(1)-C(1) 142.8(2)
N(1b)-Mn(1)-N(1c) 178.47(9)
N(1c)-Mn(1)-N(3a) 84.0(1)
Mn(1)-N(3)-C(8)
C(1)-N(2)-C(2)
C(8)-N(4)-C(9)
N(1)-C(1)-N(2)
N(3)-C(8)-N(4)
168.1(2)
118.1(2)
118.2(2)
175.0(3)
176.5(3)
interchain Mn‚‚‚Mn distance is 8.520(1) Å. The structures
of compounds 2 and 3 closely approach that of compound
4, by elimination of the solvent molecules. Selected bond
parameters are given in Table 5.
Description of the Structure of [Mn(µ-4,4′-bpy)(µ1,3-
3-F-pcyd)2]n (5). Substitution of the 2,2′-bpy by 4,4′-bpy
determines a trans octahedral arrangement around the Mn
atoms, Figure 5. The coordination sites around the manganese
atom are occupied by two N-atoms of two bridging 4,4′-
bpy ligands and by four bridging 3-F-pcyd ligands. Between
the manganese atoms double cyanamido bridges determine
a trans-3-F-pcyd-Mn chain. The structure may then be
described as a two-dimensional system with 4,4′-bpy-Mn
chains crossed by Mn-3-F-pcyd chains, Figure 5.
The bond parameters in the bridging region again show a
clear difference between nitrile and amide N-atoms of the
ligand: the bond lengths for Mn(1)-N(2) and Mn(2)-N(4)
are 2.361(5) and 2.314(4) Å, whereas those for Mn(1)-N(3)
and Mn(2)-N(1) are 2.179(4) and 2.189(5) Å, respectively.
Bond angles related to the nitrile N-atom, Mn(1)-N(3)-
C(8), 145.5(5)°, and Mn(2)-N(1)-C(1), 144.1(5)°, are larger
than the angles related to the amide N-atom, Mn(1)-N(2)-
C(1), 112.0(4)°, and Mn(2)-N(4)-C(8), 113.4(3)°. As
N(1a)-Mn(1)-N(3) 101.46(9)
N(5)-Mn(1)-N(6)
N(1a)-Mn(1)-N(5)
N(1a)-Mn(1)-N(6) 165.86(9)
71.65(9)
94.74(9)
Double cyanamido bridges link the Mn atoms, giving a
cis chain, Figure 4. The bond parameters in the bridging
region show, in this case, similar bond lengths for Mn(1)-
N(2), 2.253(2) Å, and Mn(1)-N(1b), 2.223(3) Å. However,
as also occurs for the above compounds 2 and 3, the bond
angle Mn(1)-N(2)-C(1), 111.4(2)°, is clearly smaller than
Mn(1)-N(1b)-C(1b), 140.4(2)°. The Mn-(NCN)2-Mn
subunit shows a chair distortion with the Mn atoms 0.964-
(1) Å out of the (NCN)2 main plane and a dihedral angle of
36.8° between the N(1b)-Mn(1)-N(2) plane and the mean
(NCN)2 plane. In this case the deviation of the phenyl groups,
given by the acute angle between the bond direction N(2)-
C(2) and the (NCN)2 plane is only 15.1(2)°. Mn‚‚‚Mn
intrachain distances are 5.328(1) Å, whereas the minimum
546 Inorganic Chemistry, Vol. 42, No. 2, 2003

Systems Built from Phenylcyanamido Ligands
Figure 5. ORTEP plot of the basic unit of 5 with thermal ellipsoids at the 50% probability level and view of the 2D arrangement of 5 by means of the
3-fluorophenylcyanamido and 4,4′-bpy bridges.
occurs for the above compounds, Mn-(NCN)2-Mn subunits
show a clear chair distortion with the Mn atoms placed
0.730-0.750(1) Å out of the cyanamido plane. A dihedral
angle of 27.7-27.0° is found between the (NCN)2 plane and
the N(2)-Mn(1)-N(3) or N(1)-Mn(2)-N(4) plane. Bridg-
ing phenylcyanamido ligands are far from planarity, showing
torsion angles N(3)-N(4)-C(9)-C(10) of 40.5(4)° and
N(1)-N(2)-C(2)-C(3) of 15.0(3)°.
reference (NCN)2 plane. The Mn‚‚‚Mn distance in the
cyanamido unit is 5.435(1) Å, that through the 4,4′-bpy
bridge is 11.599(1) Å, and the minimum interplane Mn‚‚‚
Mn distance is 10.404(1) Å. Selected bond parameters are
given in Table 6.
Magnetic Measurements and Coupling Constant Cal-
culation. Magnetic measurements were performed for com-
pounds 1-5 in the 300-4 °C temperature range on freshly
powdered crystalline samples (see the Experimental Section).
Compound 1 shows a practically constant øMT value over
the whole temperature range, indicating that the H-bond
In this case strong deviation of the 3-fluorophenyl groups
is evidenced by the 45.9(4)° or 46.2(4)° acute angle between
the bond direction N(4)-C(9) or N(2)-C(2) and the
Inorganic Chemistry, Vol. 42, No. 2, 2003 547

Escuer et al.
Figure 6. Susceptibility plots for compounds 2 and 3 (left) and for compounds 4 and 5 (right; 4, filled squares; 5, open circles).
Table 6. Selected Bond Lengths (Å) and Angles (deg) for 5
sion for an isotropic S ) 5/2 chain system17 derived by Fisher
from the Hamiltonian H ) ∑-JSiSi+1; the best fit parameters
were J ) -2.6(1) cm-1, g ) 2.02(1) and J ) -1.4(1) cm-1,
g ) 2.03(1) for 4 and 5, respectively.
Mn(1)-N(2)
Mn(1)-N(3)
Mn(1)-N(5)
Mn(1)-N(6b)
N(1)-C(1)
2.361(5) Mn(2)-N(1)
2.179(4) Mn(2)-N(4)
2.279(8) Mn(2)-N(7)
2.248(8) Mn(2)-N(8a)
1.165(7) N(3)-C(8)
1.292(7) N(4)-C(8)
1.351(8) F(2)-C(11)
2.189(5)
2.314(4)
2.283(9)
2.262(8)
1.148(7)
1.302(7)
1.333(8)
The EPR spectra for compound 1 show an isotropic broad
band with a peak-to-peak increment (∆pp) of 527 G at room
temperature, centered at g ) 2.11. Compounds 2 and 3 show
similar features; between room temperature and 77 K the
two compounds show one isotropic band centered at g )
2.01 with a ∆pp of 254-270 G. At 4 K the spectra exhibit
the main signal centered at g ) 2.02-2.03 and a second
weaker half-field band isotropically deplaced at g ) 5.15
and 4.26, respectively. For compound 3, two shoulders split
symmetrically 760 G with respect to the central value of g
) 2.00 appear clearly defined, reflecting weak anisotropy
at very low temperature. The spectra of compounds 4 and 5
correspond nicely to that expected for 1D systems with
moderate antiferromagnetic coupling and weak dipolar
interactions (Mn‚‚‚Mn distances around 5.5 Å).18 Between
room temperature and 77 K the isotropic signals centered at
g ) 2.01 show ∆pp values of 74 and 85 G, respectively. We
note that, for analogous MnII, doubly bridged chains with
an end-to-end azido ligand with similar Mn‚‚‚Mn intrachain
distances have J values that typically lie around -10 cm-1,
the peak-to-peak line width being only 35 G due to the
greater superexchange narrowing.19 For weaker coupling, like
that found in doubly dca bridged MnII chains, the peak-to-
peak line width is much greater, reaching values around
100-120 G.6 On cooling to 4 K, the isotropic bands show
dipolar broadening with ∆pp values of 275 and 328 G,
respectively.
N(2)-C(1)
F(1)-C(4)
N(2)-Mn(1)-N(3)
N(2)-Mn(1)-N(5)
N(2)-Mn(1)-N(6b)
N(2)-Mn(1)-N(2d)
N(2)-Mn(1)-N(3d)
N(3)-Mn(1)-N(5)
N(3)-Mn(1)-N(6b)
N(3)-Mn(1)-N(2d)
N(3)-Mn(1)-N(3d)
N(5)-Mn(1)-N(6b)
N(5)-Mn(1)-N(2d)
N(5)-Mn(1)-N(3d)
N(2d)-Mn(1)-N(6b)
N(2d)-Mn(1)-N(3d)
N(3d)-Mn(1)-N(6b)
Mn(1)-N(2)-C(1)
Mn(1)-N(3)-C(8)
C(1)-N(2)-C(2)
87.8(1)
94.2(1)
85.8(1)
171.5(2)
92.6(1)
86.9(2)
93.1(2)
92.6(1)
173.9(2)
180.00
N(1)-Mn(2)-N(4)
89.2(2)
87.3(2)
92.7(2)
174.6(2)
91.1(2)
92.7(1)
87.3(1)
91.1(2)
174.5(2)
180.00
87.3(2)
92.7(1)
89.2(2)
87.3(1)
92.7(2)
113.4(3)
144.1(5)
117.0(5)
172.5(6)
N(1)-Mn(2)-N(7)
N(1)-Mn(2)-N(8a)
N(1)-Mn(2)-N(1e)
N(1)-Mn(2)-N(4e)
N(4)-Mn(2)-N(7)
N(4)-Mn(2)-N(8a)
N(4)-Mn(2)-N(1e)
N(4)-Mn(2)-N(4e)
N(7)-Mn(2)-N(8a)
N(7)-Mn(2)-N(1e)
N(7)-Mn(2)-N(4e)
N(4e)-Mn(2)-N(1e)
N(4e)-Mn(2)-N(8a)
N(1e)-Mn(2)-N(8a)
Mn(2)-N(4)-C(8)
Mn(2)-N(1)-C(1)
C(8)-N(4)-C(9)
94.2(1)
86.9(2)
85.8(1)
87.8(1)
93.1(2)
112.0(4)
145.5(5)
117.8(5)
176.2(6)
N(1)-C(1)-N(2)
N(3)-C(8)-N(4)
network is not relevant at the magnetic level. For compounds
2-5 with their µ1,3-pcyd bridging groups, the overall
interaction is moderately antiferromagnetic in all cases. The
susceptibility plots for compounds 2 and 3 are practically
identical, as may be expected from the similar bond
parameters, Figure 6.
The susceptibility plots increase gradually on cooling and
reach a maximum at 8 K for compound 2 and at 10 K for 3.
Best fit parameters obtained using the analytical expression
derived from the isotropic Hamiltonian H ) -JS1S2 were J
) -2.3(1) cm-1, g ) 2.01(1) and J ) -2.3(2) cm-1, g )
2.01(1), respectively.
The magnetic susceptibility for compounds 4 and 5 also
increases on cooling, reaching a broad maximum at 20 and
7 K, respectively, Figure 6. Coupling through the 4,4′-bpy
bridges is negligible, so 2D compound 5 should be assumed
as magnetically 1D through the cyanamido bridges. The
experimental data were analyzed with the analytical expres-
Superexchange Mechanism. Pcyd-bridged systems show
evident similarities with the previously studied azido and
dca, but the phenyl ring attached to the amide N-atom
introduces an important number of variables which are not
(17) Fisher, M. E. Am. J. Phys. 1964, 32, 343.
(18) Bencini, A.; Gatteschi, D. EPR of Exchange Coupled Systems;
Springer-Verlag: Berlin, Heidelberg, 1990; Chapter 10 and references
therein.
(19) Abu-Youssef, M. A. M.; Escuer, A.; Gatteschi, D.; Goher, M. A. S.;
Mautner, F. M.; Vicente, R. Inorg. Chem. 1999, 38, 5716.
548 Inorganic Chemistry, Vol. 42, No. 2, 2003

Systems Built from Phenylcyanamido Ligands
pcyd- , 4-Cl-pcyd-. The following MO corresponds to a
σ 2a′ MO for pcyd- and 4-Cl-pcyd- or a π 3a′′ MO for
3-F- and 3-Cl-pcyd-. As can be seen in Figure 8, the 2a′
MO has two well-directed lobes in the metal-ligand bond
direction, whereas 3a′′ is practically a ring MO.
But this latter MO will not be relevant in the superex-
change pathway due to the poor electronic density in the
NCN region. It is relevant that despite this change in the
HOMO order, the first σ 2a′ MO has practically the same
energy for the four ligands. The ability of the following 4a′
MO as the superexchange pathway is strongly dependent on
the C-N-M bond angle. In the compounds reported in this
work, for which the bond angle between the manganese atom
and the nitrile end of the bridge lies around 140-150°, the
overlap should be negligible because the M-N bond
direction corresponds to the nodal plane placed on the N
atom, and then the 4a′ MO should be poorly useful in the
superexchange interaction. The two lower 5a′ and 6a′′ MOs,
useful for shape and density in the NCN group, should give
a lower contribution to the superexchange pathways due to
their lower energy. From these data, we can conclude, in
good agreement with partial previous calculations, that the
relevant MOs involved in the superexchange pathways
should be 1a′′ and 2a′.7,11 Each of these MOs is able to
participate in two well-differentiated pathways: the 1a′′ MO
should be able to transmit some AF coupling by overlapping
with atomic orbitals with a z component (xz, yz) of the
metallic ions (π pathway), whereas 2a′ MO can overlap with
the eg atomic orbitals of the paramagnetic centers (mainly
Figure 7. Scheme of the models used in the MO calculations. Other
parameters assumed: F-C and Cl-C bond distances of 1.350 and 1.750
Å; remainder of the coordination sites around the Mn atoms as NH3 ligands
with a Mn-N bond distance of 2.100 Å.
Table 7. ∆ Values for the Gaps between the Symmetric and
Antisymmetric Combinations of the Pairs of Atomic Orbitals of the
Metallic Centers with the Corresponding MOs of the Bridge and ∑∆2
for Dinuclear Units Modeled As Shown in Figure 7b (Pcyd, 3-F-pcyd,
3-Cl-pcyd, and 4-Cl-pcyd), Figure 7c (Pcyd, Chair 30°), and Figure 7d
(Pcyd, Rotated 25°)a
2
2
2
∆(x - y , dz )
∆(xz, yz)
∑∆2
pcyd
3-F-pcyd
3-Cl-pcyd
4-Cl-pcyd
pcyd, chair 30°
pcyd, Ph rotation 30°
0.295, 0.455
0.295, 0.454
0.295, 0.454
0.295, 0.454
0.095, 0.183
0.113, 0.263
0.302, 0.319
0.307, 0.325
0.282, 0.291
0.542, 0.527
0.313, 0.281
0.291, 0.335
0.487
0.493
0.458
0.864
0.220
0.281
2
2
d
x -y ), using the well-directed lobes in the Mn-N bond
direction (σ pathway).
The next step was to perform MO calculations on a dimeric
unit with a double X-pcyd bridge, modeled as shown in
Figure 7b. In this case, the Mn-(NCN)2-Mn unit and the
position of the phenyl rings were assumed as rigorously
coplanar. Analysis of the results was made following the
Hay-Thibeault-Hoffmann formalism,21 in which the anti-
ferromagnetic component of the coupling constant J is related
with the ∑∆i2 parameter, where each ∆i is the gap between
the symmetric and antisymmetric combinations derived from
each atomic orbital of the paramagnetic centers. In this case,
for a d5 ion such as MnII, ∑∆2 is the sum of five individual
contributions. The result of the calculations is summarized
in Table 7. As may be expected, the contribution to the
superexchange mechanism due to the combinations of dxy
atomic orbitals is negligible, and the interactions are propa-
gated by the two π and σ routes indicated above, one based
a The contribution of the dxy orbitals (always lower than ∆ ) 0.02 eV)
has not been included.
present in the other ligands. Some of these factors are related
to the distortions on the Mn-(NCN)2-Mn unit (bond lengths
and angles), derived from the asymmetric coordination of
the nitrile and amide N-atoms or from the relative position
of the phenyl rings and their halo groups. As an approach to
the properties of the phenylcyanamido ligands as superex-
change mediators, we have performed MO calculations with
the CACAO program20 for several ligands and complex
distortions to evaluate the main factors that influence the
superexchange mechanism. The calculations have been done
on the models schematized in Figure 7 and using the
indicated bond parameters. Hu¨ckel parameters were the
standard of the program.
2
2
2
in the dx -y or dz atomic orbitals and the 2a′ MO of the
bridge, and the other based in the π interaction of the 1a′′
MO and the dxz or dyz atomic orbitals. From the data in Table
7, the contributions to the antiferromagnetic component of
J should clearly be similar for the phenylcyanamido and
3-(chloro or fluoro)phenylcyanamido ligands. However,
greater antiferromagnetic contribution to the antiferromag-
netic component may be expected for the 4-Cl-pcyd bridging
As a starting point, we calculated the MO diagram for
the X-pcyd anions using the bond parameters indicated in
Figure 7a, under Cs symmetry. The filled HOMOs are three
π MOs and three σ MOs, Figure 8. The frontier MO is in
all cases the same π 1a′′ MO, with adequate electronic
density in the NCN fragment overlapping with the adequate
atomic orbitals of the metallic ions. The energy of this orbital
increases following the sequence pcyd- < 3-F-pcyd- < 3-Cl-
(20) Mealli, C.; Proserpio, D. M. CACAO program (Computed Aided
(21) Hay, P. J.; Thibeault, J. C.; Hoffmann, R. J. Am. Chem. Soc. 1975,
97, 4884.
Composition of Atomic Orbitals). J. Chem. Educ. 1990, 67, 399.
Inorganic Chemistry, Vol. 42, No. 2, 2003 549

Escuer et al.
Figure 8. Left: energy levels for the set of three π (solid lines) and three σ (dotted lines) HOMOs of the X-pcyd ligands. Right: the six MOs potentially
useful for the superexchange interaction (the main plane of the ligand placed in the xy plane).
ligand. This effect is directly related to the higher energy of
the 1a′′ HOMO orbital of 4-Cl-pcyd, which increases the
relative energy of the corresponding antibonding MOs in the
dimeric unit, increasing the efficiency of the π pathway.
These results show that the positions of the halo groups can
modify the coupling, whereas the electronegativity of the
substituent seems less relevant.
The following calculations were devoted to the main
distortions in the bridging region such as the planarity of
the Mn-(NCN)2-Mn unit and the relative positions of the
phenyl rings. The first calculations were done on the
dinuclear model shown in Figure 7c, where a chair distortion
of 30° was introduced, maintaining the phenyl rings coplanar
with the (NCN)2 plane. As is reflected in Table 7, there is a
drastic decrease of ∑∆2 and then of the AF contribution,
due mainly to the loss of overlap in the σ pathway. This
result is very similar to that reported for the azido ligand,
for which chair distortion in related doubly bridged azido
systems is one of the most important factors that contribute
to potential reduction of the AF coupling.1
Finally, the effect of the position of the phenyl rings was
studied. One possible distortion is the loss of planarity by
rotation along the amide N‚‚‚ring C bond direction. Calcula-
tions were performed on the model schematized in Figure
7b, varying the dihedral angle between the X-phenyl ring
and the main Mn-(NCN)2-Mn plane, within the reasonable
limits of (30° (similar to the maximum deviation experi-
mentally observed). In these limits, the results of the
calculations shown as the loss of planarity of the ligand do
not modify the magnitude of the coupling. In contrast, a
significant decrease in the ∑∆2 parameter is observed when
the phenyl rings are placed 25° out of the Mn-(NCN)2-Mn
plane by rotation on the N-C-N axis as schematized in
Figure 7d. From structural data, this kind of distortion is
weak for 2 and 3 but important for 4 and 5. As shown in
Table 7, the torsion of the phenylcyanamido ligand out of
the bridging plane reduces the contribution of the σ pathway.
The reason may be easily envisaged as the loss of overlap
due to the decreasing coplanarity between the eg atomic
orbitals and the 2a′ MO, which rotates out of the xy plane.
In conclusion, we may predict the following general rules
for the µ1,3 coordination mode of pcyd- ligands.
(a) Pcyd- ligands are able to transmit moderate AF
coupling between two paramagnetic centers using two clearly
differentiated and equally important σ and π pathways for a
d5 system. Obviously, each pathway will be more or less
relevant as a function of the electronic configuration of the
paramagnetic center. Hence, the π pathway will be the only
important one for a d3 cation; the σ pathway will be the only
important one for a d8 or d9 cation.
(b) Maximum AF coupling will be obtained for a planar
arrangement of the atoms involved in the bridging region
and phenyl groups. A decrease of the AF coupling will be
obtained for chair distortion of the Mn-(NCN)2-Mn bridging
region.
(c) Greater AF coupling should be expected for 4-X-pcyd-
ligands in comparison with pcyd- or 3-X-pcyd- bridging
ligands.
(d) A decrease of the AF coupling will be obtained for
systems in which the phenyl groups are out of the bridging
plane by rotation along the NCN axis.
In our case, the above rules may be applied to compounds
4 and 5 for which the calculated J values show a drastic
variation of 50% (-2.6 cm-1 for 4 and -1.4 cm-1 for 5).
The two compounds show similar bond environments in the
bridging region and then similar a and b conditions. In
contrast, following rule c, compound 4 (ligand 4-Cl-pcyd-)
should be more AF than 5 (ligand 3-F-pcyd-). Also following
rule d, compound 4 should be more AF coupled than 5 due
to the larger NCN rotation of the phenyl rings (15.1° out of
plane for 4 and around 46° out of plane for 5). Experimen-
tally, greater coupling corresponds to compound 4 in good
agreement with the expected addition of both factors.
Absolute comparison of the J values between compounds 4
550 Inorganic Chemistry, Vol. 42, No. 2, 2003

Systems Built from Phenylcyanamido Ligands
and 5 and 2 and 3 should be assumed with caution due to
the different nuclearities of the systems, but for similar chair
distortions and m-F or -Cl substitution, greater AF coupling
was found for 2 and 3 in comparison with 5, attributable to
the lower out of plane rotation of the phenyl groups along
the NCN axis.
yz).1 For the X-pcyd- ligands, the interaction through the σ
(xy) pathway is reduced and is comparable with that through
the π (xz, yz) pathway. However, for the µ1,5-dicyanamido
ligand, both interactions are very weak and only the π (xz,
yz) interaction is relevant.6
Acknowledgment. A.E., R.V., and N.S. thank the Min-
isterio de Ciencia y Tecnolog´ıa (Spain), Project BQU2000/
0791, for financial support of this research. F.A.M. thanks
Prof. Belaj and Prof. Kratky (Technische Universita¨t Graz)
for the use of experimental equipment and OENB (Project
7967) for financial support.
A final comparison can be made for the azido, phenylcy-
anamido, and dicyanamido systems linked to MnII centers.
From theoretical and experimental data, we can conclude
that the efficiency of transmitting the superexchange interac-
-
-
tions goes in the N3 > X-pcyd- . N(CN)2 order with
typical values of the J parameter in 1D systems around -7/-
15 cm-1 (azido), -1/-3 cm-1 (X-pcyd-), and weaker than
-0.5 cm-1 for dicyanamide. For the azido ligand the main
superexchange pathway corresponds to the π interaction in
the bridging xy plane with a comparatively lower contribution
of the π overlap with the orbitals with a z component (xz,
Supporting Information Available: Listings of the final values
of refined atomic parameters with esd’s and bond lengths and angles
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC025931L
Inorganic Chemistry, Vol. 42, No. 2, 2003 551