Structure and spin-spin interactions in a linear trinuclear Ni(II) complex

Article abstract of DOI:10.1515/znb-1996-0507

[Ni₃(C₂H₃O₂)₂(C ₃H₈NO)₂L₂] [(L=N,N'-1,3-propyl-disalicylaldimine), (C₂H₃O₂)=acetate, (C₃H₈NO)=hydroxymethyl-dimethylamine] has been synthesized and ils crystal structure determined, [C₄₄H₅₄N₆O₁₀Ni₃], triclinic, space group P1?, a = 9.560(1), b = 10.681(1), c = 12.200(1) ?, α = 112.17(1), β = 101.25(1), γ = 90.32(1)°, V = 1127.3 ?³ Z = 1. The molecule is linearly trinuclear with octahedral coordination of each nickel ion. The Ni-Ni distance is 3.048(1) ?. Each nickel(II) atom is in an octahedral coordination. Magnetic susceptibility measurements in the range 4.2 < T < 280 K have revealed antiferromagnetic coupling between adjacent Ni atoms (J₁ = -2.2 cm^-1) and between the terminal Ni atoms (J₂ = -1.7 cm^-1).

Full text of DOI:10.1515/znb-1996-0507

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Structure and Spin-Spin Interactions in a Linear Trinuclear Ni(II) Complex
Ayhan Elmalia, Yalcin Elerman3, Ingrid Svoboda*3, Hartmut Fuessb*, Klaus Griesar0,
Wolfgang Haasec
a Department of Engineering Physics, Faculty of Sciences,
University of Ankara, 06100 Besevler-Ankara, Turkey
b Strukturforschung, Fachbereich Materialwissenschaft, Technische Hochschule Darmstadt,
Petersenstrasse 20, D-64287 Darmstadt, Germany
c Institut für Physikalische Chemie, Technische Hochschule Darmstadt,
Petersenstrasse 20, D-64287 Darmstadt, Germany
Z. Naturforsch. 51 b, 665-670 (1996); received October 20, 1994
X-Ray, Linear Trinuclear Nickel Complex, Magnetic Properties, Antiferromagnetic Coupling
[Ni3(C2H302)2(C3H8N0)2L2] 1(L=N,N'-1,3-propyl-disalicylaldimine), (C2H30 2)=acetate,
(C3H><NO)=hydroxymethyl-dimethylamine] has been synthesized and its crystal structure de-
termined, [C44H54N6OioNi3], triclinic, space group Pi, a = 9.560(1), b = 10.681(1), c =
12.200(1) A ,a = 112.17(1), ß = 101.25(1), 7 = 90.32(1)°, V= 1127.3 A \Z = l.The molecule
is linearly trinuclear with octahedral coordination of each nickel ion. The Ni-Ni distance is
3.048( 1) A. Each nickel(II) atom is in an octahedral coordination. Magnetic susceptibility mea-
surements in the range 4.2 < T < 280 K have revealed antiferromagnetic coupling between
adjacent Ni atoms (J\ = -2.2 cm-1) and between the terminal Ni atoms (/2 =-1.7 cm-1).
The present work provides the results of the X-ray
structure analysis and of temperature-dependent
susceptibility measurements of
[Ni3(C2H302)2(C3H8N0 )2L2] (L = N,N'-l,3-pro-
pyl-disalicylaldimine).
Introduction
Only very few linear trinuclear complexes with
face sharing octahedra are known [1-3]. The title
compound provides an interesting example of a lin-
ear trinuclear compound in which the crystal lattice
is built up of magnetically isolated, octahedrally
coordinated nickel ions, with two unpaired eg spins
per atom. Theoretical considerations suggest that
the magnetic properties of such an arrangement of
unpaired spins might exhibit at least two features.
1) Two different, nonzero exchange integrals for
a linear trinuclear molecule, one between adjacent
metal atoms and the other between the terminal
atoms. 2) The exchange integral between the ad-
jacent Ni atoms may be positive (ferromagnetic).
The linear trimeric molecule [Ni3(acac)ö](acac =
acetylacetonate) has been characterised both struc-
turally and magnetically [4 - 7]. It was reported
that the spins on adjacent Ni atoms interact ferro-
magnetically (26 cm-1 ) and that the spins of the
two terminal Ni atoms interact antiferromagneti-
cally (-7 cm-1 ).
Experimental
Preparation
The ligand (N,N’-l,3-propyl-disalicylaldimine) has
been prepared by the reaction between 0.002 mol salicy-
laldehyde and 0.001 mol 1,3 - diaminopropane in ethanol
solution.
Scheme 1. N,N'-l,3-Propyl-disalicylaldimine.
For the preparation of the complex two solutions of
0.5 g dimethylammoniumchloride in 5 ml pure water and
0.2 g NaOH in 2 ml pure water were added to a so-
lution of 5 mmol N,N'-l,3-propyl-disalicylaldimine in
50 ml methanol. This reaction yields hydroxymethyl-
dimethylamine(N,N-dimethylaminocarbinol).
* Reprint requests to Prof. Dr. H. Fuess.
0939-5075/96/0500-0665 $ 06.00
© 1996 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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A. Eimali et cd. ■Structure and Spin-Spin Interactions in a Linear Trinuclear Ni(II) Complex
6 6 6
Tab. II. Final positional and equivalent isotropic ther-
mal parameters (A:) with estimated standard deviation in
parentheses.
Hydroxymethyl-dimethylamine(N,N-dimethylinocar-
binol) is unstable and hydroxymethyl-dimethylamine will
be stable when it is coordinated to ametal atom. Then aso-
lution of 5 mmol NHCH^COOh^FLO in 30 ml methanol
was added to the former solution. The mixture was re-
fluxed for 5 h. Light green crystals were formed during
the reflux operation and were washed twice with ethanol.
Atom xJa
y/b
z/c
Ueq
1.1688(1)
1.1521(4)
1.2406(6) 0.030(1)
Ni( 1)
0(1)
C(l)
1.2080(1) 0.9034( 1)
0.029(1)
0.031(1)
1.0808(4)
1.1998(6)
1.1635(5)
1.1993(7)
Analysis for C^H^NftOioNh
0.041(1)
0.045(1)
1.2483(6)
1.1140(7) 1.3071(6)
1.1472(7) 1.4317(7) 1.3412(6)
C(2)
C(3)
Calcd C 52.58 H 5.62 N 8.36%,
Found C 52.51 H 5.55 N 8.30%.
C(4)
1.2707(7) 1.4547(7) 1.4320(6) 0.050(1)
1.3571(7) 1.3526(7) 0.045(1)
C(5)
1.4251(6)
1.3244(7) 1.2228(6) 1.3333(6) 0.032(1)
1.4189(7) 1.1220(6) 1.3397(6) 0.034(1)
C(6)
C(7)
0.9936(6)
0.9087(7)
0.7891(7)
0.6797(7)
0.7203(5)
0.034(1)
N(l)
C(8)
C(9)
C(10)
N(2)
C (ll)
1.3985(6)
1.5097(6)
1.4570(8)
1.3625(7)
1.2215(6)
1.1138(7)
1.2817(5)
1.3018(6) 0.043(1)
1.3229(6) 0.052(1)
1.2148(6) 0.043(1)
0.1794(5) 0.030(1)
0.6381(7) 1.1556(6) 0.038(1)
0.9654(7) 0.6567(6) 1.1159(6) 0.033(1)
C(12)
0.5673(6)
0.5745(7)
0.6731(7) 1.0403(6) 0.043(1)
0.7616(7) 1.0309(6) 0.039(1)
0.038(1)
0.045(1)
C( 13) 0.8624(7)
C( 14) 0.7171(7)
C(15) 0.6723(7)
C(16) 0.7704(7)
1.1201(6)
1.0853(6)
0.032(1)
0.033(1)
1.3351(4) 0.043(1)
0.7579(6) 1.0715(6)
0.8449(4) 1.0639(4)
1.1270(5) 0.9714(5)
0.9186(7)
1.0118(5)
C( 17)
0(2)
0(3)
C( 18)
Scheme 2. The investigated linearly trinuclear nickel com-
plex.
1.0415(7) 1.3453(6) 0.040(1)
1.0236(7)
1.0112(6)
C( 19) 1.1250(7)
0.045(1)
0.061(1)
1.1376(6) 1.4495(5)
1.1804(7) 1.5551(6)
N(3)
1.4542(7) 0.081(1)
1.0267(4) 0.040(1)
0.9316(6) 0.040(1)
0.8872(7) 1.2170(7)
C(20)
0(4)
0.8420(5)
0.8657(7)
0.8310(7)
0.0000
1.3080(5)
Table I. Crystal structure data.
C(21) 1.2694(7)
C(22) 1.3680(8)
Ni(2) 0.0000
0.074(1)
0.028(1)
0.8463(7)
0.0000
prism, 0.15x0.05x0.08 mm
C44H54N60,()Ni3
1005.06
Crystal size
Empirical formula
Formula weight(gmol_ 1)
Crystal system
0.9026(4) 0.040(1)
0.9166(5)
0(5)
1.1550(5)
triclinic
Cell constants ( A;° )
a= 9.560(1)
Susceptibility' measurements
b = 10.681(1)
c = 12.200(1)
a = 112.17(1)
ß = 101.25(1)
7 = 90.32(1)
Pi (No. 2)
1
1127.3
1.48
12.78
Magnetic susceptibility measurements were performed
on a Faraday-type magnetometer consisting of a CAHN
D-200 microbalance, a Leybold Heraeus VNK 300 he-
lium flux cryostat and a Bruker BE 25 magnet connected
with a Bruker B-Mn 200/60 power supply in the temper-
ature range 4.2-280 K. The applied field was ss 1.2 T.
Experimental susceptibility data were corrected for the
underlying diamagnetism and the temperature indepen-
dent paramagnetism (NQ= 300xl0~6cnr/mol per Ni(II))
[8]. Magnetic moments were obtained from the relation
p eff = 2.828(\T)1/2.
Space group
Formula units/ unit cell
Volume of unit cell (A')
Calculated density(g-cm-3)
Linear absorption
coefficient (cm
)
Number of reflections
collected
Number of symmetry
independent reflections
Reflections with F > 4cr(F)
R
6320
5101
X-ray structure determination
2215
0.0698
0.0487
X-ray data collection was carried out on a CAD-4
diffractometer using a single crystal with dimensions
Rw
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A. Elmali et al. • Structure and Spin-Spin Interactions in a Linear Trinuclear Ni(II) Complex
667
Table III. Selected bond lengths (A) and bond angles (°).
Distances
sions were determined by least-squares refinement on the
setting angles of 25 reflections (4.52° < 6 < 26.06°) care-
fully centered on the diffractometer. The standard reflec-
tions (304, 212 and 112) were measured every 7200s and
the orientation of the crystal was checked after every 600
reflections. These measurements (298 K) did not indicate
any variation in the experimental conditions, but a de-
crease of 0.6% in the intensity of the standard reflections
indicated a decay of the crystal. Data reduction and cor-
rections for absorption and decomposition were achieved
using the Enraf-Nonius Structure Determination Pack-
age^]. The structure was solved with SHELXS-86 [10]
and refined (on F) with SHELX-76 [11]. The positions of
H atoms were calculated (C-H distance 1.08 A), but not
refined. The final positional parameters are presented in
Table II. List of atomic parameters as well as structure
factor tables have been deposited [12].
Ni(l) - Ni(2)
Ni(l) - 0(1)
Ni(l) - 0(2)
Ni(l) - 0(3)
Ni(l) - 0(4)
N i(l)-N (l)
Ni( 1) - N(2)
Ni(2) - 0( 1)
Ni(2) - 0(2)
Ni(2) - 0(5)
3.048(1)
2.019(4)
1.998(4)
2.180(4)
2.035(4)
2.034(5)
2.012(5)
2.068(4)
2.075(4)
2.074(4)
Angles
172.9(2)
96.4(2)
96.8(2)
78.8(2)
87.6(2)
89.3(2)
0 (1)
89.6(2) 0(4) - Ni(l) - 0(3)
N(l) - Ni(l) -
N(2) - Ni( 1) -
0 (1) 171.7(2) Ni(l) - 0(1) - Ni(2)
Ni( 1) - 0(2) - Ni(2)
N(2) - Ni( 1) - N( 1)
0(2) - Ni(l) - 0 (1)
97.9(2)
81.7(2) 0(2) - Ni(2) - 0( 1)
170.9(2) 0(5) - Ni(2) - 0( 1)
90.6(2) 0(5) - Ni(2) - 0(2)
0(2) - Ni(l) -
0(2) - Ni(l) -
0(3) - Ni(l) -
N(l)
N(2)
0 (1)
Results and Discussion
89.4(2)
84.2(2)
87.8(2)
92.8(2)
93.1(2)
89.3(2)
90.5(2)
94.1(2)
X-ray structure
0(3) - Ni(l) - N(l)
0(3) - Ni( 1) -
0(3) - Ni(l) -
N(2)
0 (2)
Selected bond lengths and angles are summa-
rized in Table III. The Ni(2) atom is situated on
an inversion center, forming a linearly trinuclear
nickel complex. The N i-N i distance is 3.048(1) A
with octahedral coordination of each nickel ion(see
Fig. 2). Hydroxymethyl-dimethylamine moiety is
bonded to the terminal Ni atom. The terminal Ni( 1)
atom and Ni(2) at the middle are connected via two
oxygen atoms and one acetate bridge. The terminal
Ni atoms are coordinated by four O atoms and two
N atoms, whereas the Ni(2) atom at the middle is
only coordinated by O atoms.
0(4) - Ni(l) - 0 (1)
0(4) - Ni( 1) - N(l)
0(4) - Ni(l) -
N(2)
0(4) - Ni(l) - 0 (2)
The nickel-oxygen bond lengths show significant
differences between those bonds in which the oxy-
gen is connected to only one nickel atom or shared
between two nickel atoms. The difference in bond
lengths must be in part due to the change of the
atomic radius of oxygen following rehybridization.
Fig. 1. View of the molecule (Numbering of the atoms
corresponds to Table II).
0.15 x 0.05 x 0.08 mm with graphite monochromatized
MoKq radiation (A = 0.71069 A). Experimental condi-
tions are summarized in Table I. Precise unit cell dimen-
Fig. 2. The coordination of the nickel atoms.
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668
A. Elmali et al. • Structure and Spin-Spin Interactions in a Linear Trinuclear Ni(II) Complex
behaviour is not markedly influenced by the value
of either the zero-field splitting parameter D or the
inter-dimer interactions [13]. For a linear arrange-
ment such as displayed in Scheme 3, two different
exchange interactions are to be considered. Thus,
the Hamiltonian may be written as:
H = - 2 J i[ 5 i5 2 + S2S3] - 2 J2[5 ,5 3]
(2)
Ji
j-i
N i------- N i-------- Ni
Fig. 3. Molar susceptibility and effective magnetic mo-
ment per nickel vs. temperature curves.
J2
Scheme 3. Definition of the parameters Ji and J2 as
the exchange integrals between nearest neighbours
(Ji)and next nearest neighbours (J2).
Also, significant differences in the nickel - nitrogen
bond lengths are observed. It follows from the selec-
tion of bond angles in Table III. that the octahedral
coordination of the three nickel centers is distorted.
All of the O - Ni - O, N - Ni - O and N - Ni - N
angles deviate more or less from 90° and the “ax-
ial” arrangement N(2) - N i(l) - 0(1), for example,
is only 171.7(2)°, instead of 180°.
With S\ = S2 = S3 = \, the susceptibility can be
expressed by equation (3).
A correction for a small amount of paramagnetic
impurities (molar fraction xp\ 5 = 1 ) which obeys
a Curie-law was also taken into account.
x
-.1
x e)x T' •
M agnetic data
xMo„„= ^ m S(5+1)withS=,
(3)
Magnetic susceptibility data for a solid powdered
sample of the Ni-complex were collected in the tem-
perature range 4.2 - 280 K. The data are displayed
in Fig. 3 as molar susceptibilities and effective mag-
netic moments versus temperature.
yrj
^
A + B + C + D + E + F
X
=
k T
9 G + H + I + J + K + L + M
using
The effective magnetic moment per Ni atom de-
creases gradually from 3.18 ^ b at 277 K down to
1.67 /iß at 4.2 K, clearly indicating the presence
of an antiferromagnetic exchange interaction. How-
ever, this interaction is not very pronounced since
no characteristic maximum in the \(T ) curve was
observed. Accordingly, the molar susceptibility at
room temperature is within the Curie law limit. To
explain the magnetic behaviour of the present com-
pound, the structure can be reduced to a central
Ni^-core. The spin Hamiltonian for this trinuclear
compound can be derived assuming that interac-
tion in each pair can be described in terms of the
Heisenberg-Hamiltonian (1).
A = 42 exp(2(2.i’ + y))\ B = 15 exp(2(y —x ));
C = 15 exp(2(.r - y )); D = 3 exp(2(y — 3x));
E = 3 exp(-20r + y))\ F = 3 exp(—4z/);
G = 7 exp(2(2.r + y))\
1 = 5 exp(2(£ - y))\
H = 5 exp(2(y —a?));
J = 3 exp(2(y - 3x));
K
= 3 exp (-2(x + y))\ L = 3 exp(—4y);
M = exp(—2(2x + y));
x = -J\/kT;
y = Ji/kT .
The best-fitparameters which were obtained by
using a standard least-squares program were g =
2.2; J 1 = -2.2 cm-1 ; J 2 = -1.7 cm-1 and xP =
H
=
-U ijSiSj
(1) 1.5%.
It is very instructive to compare the nature of the
exchange coupling constants J\ and / 2 and the struc-
tural properties of the Ni-trimer with those reported
for [Ni3(acac)6] [4 - 7] which exhibits a trimeric
In the case of antiferromagnetically coupled
polynuclear Ni(II) complexes, the intra-dimer ex-
change terms Jx] are dominant in the spin-
Hamiltonian. Consequently, the overall magnetic
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