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J. Titisˇ et al. / Polyhedron 26 (2007) 1523–1530
3
3
gy ¼ ge ꢀ 2k½4j2y =Dyð Ag ! B2gÞꢂ
ð9Þ
[4,5]furo[3,2-c]pyridine (abbr. bzfupy) have been conducted
in accordance with published recipes [6–9].
vTIP ¼ NAl0l2Bð2=3Þ½4j2x=Dxð Ag ! B3gÞ
3
3
Nickel(II) acetate was synthesized by adding potassium
acetate to a nickel(II) chloride ethanol solution. Elemental
analysis (C, H, N) was performed on an elemental analyzer
Eager 300 (Carlo Erba). The nickel content was determined
chelatometrically using murexide as indicator.
The two complexes [Ni(bzfupy)2(ac)2(H2O)2] (5) and
[Ni(Me2fupy)2(H2O)4](ac)2 (6) were prepared from nickel
acetate. Into the solution of nickel acetate a stoichiometric
amount of ligand was added and stirred for half hour.
After 2 days the solid complexes were collected. Single crys-
tals were grown from the ethanol solution. The complex
[Ni(Me2iz)4(H2O)2]Cl2 Æ 3H2O (7) was prepared by reacting
nickel(II) chloride with a four-fold excess of 1,2-dimethy-
limidazole in warm ethanol over a 4 h reflux. The single
crystals of (7) were obtained by slow evaporation at room
temperature. Syntheses of compounds 8 and 9 are
described elsewhere [11,12].
3
3
þ 4j2y =Dyð Ag ! B2gÞ þ 4jz2=Dzð Ag ! B1gÞꢂ ð10Þ
3
3
These spin-Hamiltonian parameters are frequently
understood as internal characteristics of the complex under
study (molecular constants) and fixed by fitting the experi-
mental data (magnetic susceptibility, magnetization, heat
capacity, INS, ESR, MCD and FAR-IR spectra). However,
all of them originate in the electronic structure of the com-
plex and they can be reconstructed with the help of the more
principal electronic-structure parameters [2]: the Racah
parameters B and C (electron repulsion), the crystal-field
strengths Dq, Ds, . . . (or more exactly the crystal-field poles
for each ligand F2(L) and F4(L)), the spin–orbit coupling
constant n, and the orbital reduction factors j (which could
be anisotropic, jz, jx). With a tetragonal compression (neg-
ative structural tetragonality), the ground state is the C5-
multiplet, and D is negative. On tetragonal elongation
(positive structural tetragonality) the ground state is C4-
multiplet, and D is positive. Such a general forecast, how-
ever, is tuned by the orbital reduction factors jz and jx.
Three publications preceded the present communication
[3–5] where the axial zero-field parameter D (subtracted
from the susceptibility and magnetization data sets) has
been correlated with the structural anisotropy parameter
Dstr that characterizes the degree of the tetragonality. The
complexes involved in such a correlation were either homo-
leptic (imidazole and its derivative, {NiN6}-chromophore),
N-donor only of the [Ni(base)4(NCS)2] type (possessing the
fNiN4N02g-chromophore), or heteroleptic complexes of the
type [Ni(base)2(carboxylate)2(H2O)2] having the fNiN2-
Anal. Calc. for (5) C26H24N2NiO8: C, 56.66; H, 4.39; N,
5.08. Found: C, 56.09; H, 4.52; N, 5.04%. Calc. for (6)
C22H32N2NiO10: C, 48.65; H, 5.94; N, 5.16. Found: C,
48.30; H, 6.17; N, 5.47%. Calc. for (7) C20H42Cl2N8NiO5:
C, 39.76; H, 7.01; N, 18.55. Found: C, 40.0; H, 7.05; N, 18.5%.
2.2. Physical measurements
Single-crystal X-ray diffraction experiments for all com-
plexes have been performed using an Xcalibur CCD appa-
ratus (Oxford Diffraction). Data reduction and empirical
absorption correction were performed by SHELXS-97.
Electronic spectra were measured using the DRIFT
method on a Magna FTIR 750 spectrometer (Nicolet) in
the region 5000–11000 cmꢀ1 and in Nujol mull on a Spe-
O2O0 g-chromophore. We prepared and structurally charac-
2
cord 200 (Analytical Jena) in the range 50000–10000 cmꢀ1
.
terized some more members of the above series with the
{NiO4N2}, and {NiN4O2} chromophores, respectively
(three complexes). Five complexes were subjected to magne-
tochemical studies and involved in the above mentioned
correlation.
Magnetic susceptibility and magnetization measure-
ments were done using a SQUID magnetometer (Quantum
Design) between 2 and 300 K at B = 0.1 T. The magnetiza-
tion data until B = 5.5 T were taken at T = 2.0 and 4.6 K,
respectively. Raw susceptibility data were corrected for
underlying diamagnetism using a set of Pascal constants
[10]. The effective magnetic moment has been calculated
as usual: leff/lB = 798(v0T)1/2 when SI units are employed.
Because the present paper is, in fact, a continuation of
our previous work on heteroleptic Ni(II) complexes [5],
we have kept numbering of the previously characterized
complexes as follows: [Ni(Meiz)2(HCOO)2(H2O)2] (1),
[Ni(Me2iz)2(HCOO)2(H2O)2] (2), [Ni(iqu)2(CH3COO)2-
(H2O)2] (3), [Ni(fupy)2(CH3COO)2(H2O)2] (4). The new
complexes under study are: [Ni(bzfupy)2(ac)2(H2O)2] (5),
[Ni(Me2fupy)2(H2O)4](ac)2 (6), [Ni(Me2iz)4(H2O)2]Cl2 Æ
3H2O (7), [Ni(pz)4(ac)2] (8) and [Ni(LNN)2(H2O)2] (9).
3. Results and discussion
3.1. Molecular and crystal structure
Crystal data for compounds 5 through to 7 are collected
in Table 1. The molecular structure is viewed in Fig. 1.
The structure of complex 5 consist of [Ni(bzfupy)2(ac)2-
(H2O)2] monomeric units in which the central Ni(II) atom
has a distorted octahedral configuration. The coordination
around the Ni(II) atom is defined by two aqua ligands (w),
two acetate ligands (a) and two neutral benzo[4,5]furo-
2. Experimental
2.1. Synthesis
The starting materials (1,2-dimethylimidazole, NiCl2 Æ
6H2O and CH3COOK) were purchased from commercial
sources and were used as received. The syntheses of 2,3-
dimethylfuro[3,2-c]pyridine (abbr. Me2fupy) and benzo-
˚
[3,2-c]pyridine (b). The Ni–O(a) distances are 2.060(2) A,
˚
the Ni–O(w) distances are 2.073(2) A and the Ni–N(b) dis-