Thermochemistry of aniline-derivative adducts of nickel(II) acetylacetonate

Article abstract of DOI:10.1016/S0040-6031(99)00084-2

The compounds [Ni(acac)₂(L)₂] (where acac is acetylacetonate and L is aniline (an), 2,6-dimethylaniline (dimean), o- or m-chloroaniline (o- or m-clan)) were synthesized and characterized by melting points, elemental analysis, TG-DTG, and DSC curves and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, Ni(II) acetylacetonate and ligands in a 1 : 3 (v/v) mixture of aqueous HCl 1.2 M and methanol, were measured and by using thermochemical cycles the following thermochemical parameters for the adducts have been determined: The standard enthalpies for the Lewis acid/base reaction (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean standard enthalpies of the nickel-nitrogen bonds have been estimated.

Full text of DOI:10.1016/S0040-6031(99)00084-2

Thermochimica Acta 333 (1999) 5±11
Thermochemistry of aniline-derivative adducts of nickel(II) acetylacetonate
P.O. Dunstan*
Â
Instituto de Quõmica, Universidade Estadual de Campinas, C.P. 6154, CEP 13083-970, Campinas, SaÄo Paulo, Brazil
Received 19 January 1999; received in revised form 2 April 1999; accepted 2 April 1999
Abstract
The compounds [Ni(acac)2(L)2] (where acac is acetylacetonate and L is aniline (an), 2,6-dimethylaniline (dimean), o- or m-
chloroaniline (o- or m-clan)) were synthesized and characterized by melting points, elemental analysis, TG±DTG, and DSC
curves and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, Ni(II) acetylacetonate and ligands in a
1 : 3 (v/v) mixture of aqueous HCl 1.2 M and methanol, were measured and by using thermochemical cycles the following
thermochemical parameters for the adducts have been determined: The standard enthalpies for the Lewis acid/base reaction
(ÁrHꢀ), the standard enthalpies of formation (ÁfHꢀ), the standard enthalpies of decomposition (ÁDHꢀ), the lattice standard
enthalpies (ÁMHꢀ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (ÁrHꢀ(g)). The mean
standard enthalpies of the nickel±nitrogen bonds have been estimated. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Ni±N bonds; Nickel(II) acetylacetonate adducts; Thermochemical parameters; Thermochemistry
1. Introduction
aromatic ring and on the nitrogen atom. This paper
describes the interaction of Ni(II) acetylacetonate
with o- and m-chloroaniline and 2,6-dimethylaniline.
Calorimetric measurements were made to determine
the mean strength of the Ni±N bonds and study the
effect of introducing a chlorine atom or two methyl
groups into the phenyl group of aniline.
Adducts of Ni(II) acetylacetonate with heterocyclic
bases have been reported and their preparation, char-
acterization and thermochemistry established [1].
Aniline and aniline derivatives are also known to form
adducts [2±4]. It is expected that aniline and aniline
derivatives will also form coordination compounds
with Ni(II) acetylacetonate involving coordination
through the nitrogen atom. The substitution of one
hydrogen atom in the phenyl group by the electron-
withdrawing groups will cause a decrease in the
electronic density in the aromatic ring and by an
inductive effect, also decrease the electronic density
on the nitrogen atom. Similarly the substitution of
hydrogen atoms by electron-donating groups should
cause an increase in the electronic density in the
2. Experimental
2.1. Chemicals
Ni(II) acetylacetonate was prepared by the Charles
and Pawlikouski method [5]. The compound was
recrystallized from methanol and dehydrated under
reduced pressure at 398 K. The product was green and
the results of the chemical analysis were: Ni, 22.61; C,
46.09; H, 5.46 mass percent (theoretical: Ni, 22.85; C,
*Tel.: +55-019-7883088; e-mail: dunstan@iqm.unicamp.br
0040-6031/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 9 9 ) 0 0 0 8 4 - 2

6
P.O. Dunstan / Thermochimica Acta 333 (1999) 5±11
Â
46.75; H, 5.49). Aniline p.a. (Veltec, Quõmica Fin);
2,6-dimethylaniline (99% Aldrich Chemical); o- and
m-chloroaniline (98% Aldrich Chemical) were pur-
i®ed by the method of Riddick [6]. Solvents used in
the synthesis of adducts were puri®ed by distillation
and stored over Linde 4A molecular sieves.
aluminium as a standard (mp 660.378C) and calcium
oxalate as a standard for weight calibration. DSC
calibration was made using metallic Indium as a
l
1
standard (mp 156.738C), Ás Hꢀ ˆ 28.4 Jg
.
2.6. Calorimetric measurements
2.2. Analytical
All the solution calorimetric determinations were
carried out in a LKB 8700-1 precision calorimetric
system as described before [8]. The solution calori-
metric determinations were performed by dissolving
the appropriate mass of samples (14±171 mg) of the
adduct or Ni(II) acetylacetonate in a 1 : 3 (v/v) mix-
ture of aqueous HCl 1.2 M and methanol. This mixture
was elected because the compounds dissolved quickly
and with good thermic effect. The aniline or aniline
derivatives were dissolved in this last solution main-
taining a molar relation equal to the stoichiometry of
the adduct. The accuracy of the calorimeter was
checked out by determining the heat of dissolution
Carbon, hydrogen and nitrogen contents were deter-
mined by microanalytical procedures. The nickel
content was determined by complexometric titration
with 0.01 M EDTA [7] in aqueous solutions of adducts
samples. The capillary melting points of the adducts
were determined using an UNIMELT equipment from
(Thomas Hover).
2.3. Adduct synthesis
The adducts were synthesised by the direct reaction
of Ni(II) acetylacetonate with excess of the ligands. A
typical procedure is given bellow.
To 1.2 g of Ni(acac)2 (4.7 mmol), 10 ml of aniline
was added with stirring. Gently warming dissolves the
chelate. The solution was cooled in a freezer for
several hours. The solid formed was ®ltered, washed
with three portions of 10 ml of petroleum ether and
dried for several hours in vacuo and stored in a
desiccator over calcium chloride.
of tris [(hydroxymethyl)amino methane in
3
0.1 mol dm
hydrochloric acid. The result
( 29.78 Æ 0.03 kJ mol 1) is in agreement with the
value
recommended
by
IUPAC
[9]
( 29.763 Æ 0.003 kJ mol 1).
2.7. Electronic spectra
Spectra of the solid adducts in the region 350±
2200 nm were obtained with a UV-VIS-NIR Varian-
Cary SG Spectrophotometer with a standard re¯ec-
tance attachment.
2.4. Infrared spectra
Spectra were obtained with samples in KBr
matrix for the adducts. For liquid ligands a ®lm of
the ligand sandwiched between NaCl Plates was
used. Spectra were recorded with a Perkin Elmer
3. Results and discussion
1600 series FTIR Spectrophotometer in the region
1
All the adducts obtained were solids. The yields
range from 27 to 88%. The yields, melting points,
colors, appearance and analytical data are summarized
in Table 1.
4000±400 cm
.
2.5. Thermal Studies
TG±DTG and DSC measurements were made in an
argon atmosphere in a Du Pont 951 TG Analyser with
samples varying in mass from 5.28 to 8.71 mg for
TGDTG and from 1.08 to 1.61 for DSC and a heating
rate of 10 K min1 in the temperature ranges 298±
1214 K for TG±DTG and 298±673 K for DSC. TG
calibration for temperature was made using metallic
3.1. Infrared Data
The more important i.r. bands are reported in
Table 2. Two bands are observed in the region
1
1600±1500 cm
(1604±1589 cm1) and C±C (1520±1515 cm
stretching vibrations [10,11]. The bands observed in
. These are assigned to C±O
1
)

P.O. Dunstan / Thermochimica Acta 333 (1999) 5±11
7
Table 1
Yields in % on preparation, melting points, appearance and analytical data of the adducts
Compound
Yield
M.P. (K)a Appearance
C
H
N
Nickel
Calcd. Found
Calcd. Found
Calcd. Found
Calcd. Found
[Ni(acac)2(an)2]
38
27
88
66
201±204
158±62
118±20
153±4
l.bl.pw
l.bl.pw
l.bl.cr
59.62
51.60
51.60
62.55
59.89
51.53
51.42
62.20
6.37
5.12
5.12
7.27
5.93
4.99
4.91
7.22
6.32
5.47
5.47
5.61
6.43
5.29
5.31
5.60
13.25
11.47
11.47
11.76
12.99
11.44
11.27
11.54
[Ni(acsac)2(o-clan)2]
[Ni(acac)2(m-clan)2]
[Ni(acac)2(dimean)2]
l.bl.pw
a Melting with decomposition.
b Key: I, light; bl, blue; pw., powder, and cr., crystals.
Table 2
1 a
)
Infrared data for ligands and their complexes (cm
Compound
ꢁ(C±O)
ꢁ(C±C)
ꢁ(Ni±O).
Ligands bands
ꢁ(N±H)
ꢂ(H±N±c)
Ni(acac)2
1605 sh
1604 vs
1602 vs
1601 vs
1589 vs
1520 vs
1515 vs
1519 vs
1519 vs
1519 vs
586 m
574 m
573 m
573 m
570 m
an
3437 m, 3354 m
3265 m, 3179 m
3442 m,3362m
3264 m, 3178 m
3457 m, 3362 m
3256 m, 3167 m
3471m,3386s
n.o.
[Ni(acac)2(an)2]
o-clan
n.o.
1617 s
n.o.
[Ni(acac)2(o-clan)2]
m-clan
1620 s,1597 s
n.o.
1623s
[Ni(acac)2(m-clan)2]
dimean
[Ni(acac)2(dimean)2]
3381 m, 3313 m
n.o.
a Key: n.o., not observed.
Intensity of bands: vs, very strong; s, strong; m, medium, and sh, shoulder.
the region 586±570 cm 1 are assigned to Ni±O modes
[12±15]. No bands could reasonably be assigned to the
stretching vibration of Ni±N bond. It has been
observed in related adducts of Co(II), Ni(II) and Zn(II)
1. [Ni(acac)2(an)2] ! [Ni(acac)2an] ‡ an
[Ni(acac)2an] ! Ni(acac)2 ‡ an
Ni(acac)2 ! pyrolysis
2. [Ni(acac)2
‡ 0.5(o-clan)
(o-clan)2] ! [Ni(acac)2(o-clan),1.5
]
1
that it lies bellow 200 cm [12] due to the low free
energy change accompanying adduct formation, that
1
is only of about 1.5 kcal mol for Co(II) acetyl-
[Ni(acac)2 (o-clan)1.5] ! [Ni(acac)2(o-clan)05]
‡ (o-clan)
acetonate [12]. The shifts to lower frequencies
observed in the adducts of ꢁ(CO); ꢁ(CC) and ꢁ(NiO)
relative to the free Ni(II) acetylacetonate, indicated
that the amines were coordinated to the nickel ion
[16]. Big shifts to lower frequencies of ꢁ(N±H) of
ligands after coordination were also observed, indi-
cating coordination of ligands through the nitrogen
atom of the NH group [17,18].
[Ni(acac)2.
(o-clan)
(o-clan)05] ! Ni(acac)2 ‡ 0.5
Ni(acac)2! pyrolysis
3. [Ni(acac)2(m-clan)2] ! [Ni(acac)2(m-clan)1.5] ‡
0.5 (m-clan)
[Ni(acac)2(m-clan)1.5] ! [Ni(acac)2(m-clan)075
‡ 0.75 (m-clan)
]
[Ni(acac)2(m-clan)0.75] ! 0.75(m-clan) ‡
3.2. Thermal studies
pyrolysis Ni(acac)2
TG±DTG studies show that the adducts followed
different processes of thermal dissociation:
4. [Ni(acac)2(dimean)2] ! [Ni(acac)2(dimean)0.25] -
‡ 1.75 dimean

8
P.O. Dunstan / Thermochimica Acta 333 (1999) 5±11
[Ni(acac)2(dimean)025] ! 0.25 dimean ‡ pyro-
were observed for some adducts. According to the
number and position of these bands and considering
the magnitude of the crystal ®eld parameters as com-
pared with that of Bolster [20] we can conclude that
the Ni(Il) ion is pseudo-octahedrally surrounded by
two nitrogen atoms and four oxygen atoms. Pseudo-
octahedral complexes of Ni(II) have been widely
studied by Reedijk et al. [19]. They concluded that
the ligand-®eld Oh is a good approaching for these
pseudo-octahedral complexes. The crystal ®eld para-
meters obtained for the compounds [Ni(acac)2L2] are
in agreement with these results.
lysis Ni(acac)2
The DSC curves of the adducts are consistent with
TG±DTG data. They present several endothermic
peaks due to the elimination of ligand, elimination
of ligand with melting, elimination of ligand with
pyrolysis of Ni(AcAc)2 and decomposition of the
product of the pyrolysis of Ni(acac)2. The Table 3
lists the thermoanalytical data of the adducts.
3.3. Electronic spectra
Table 4 presents the band maxima assignments and
calculated ligand ®eld parameters for the adducts. The
ligand ®eld parameters were calculated according to
Reedijk et al. [19]. The electronic spectra of the
3.4. Calorimetric measurements
The standard enthalpies of dissolution of Ni(II)
acetylactonate, ligands and adducts were obtained
as previously described [1]. Ni(acac)2 exists as a
trimeric structure in the solid state [21]. Thus a
hypothetical monomer for the calculation of the stan-
dard enthalpy of dissolution of Ni(acac)2 had to be
adducts present four absorption bands: ꢁ1 in the region
1
10469±12740 cm
1
; ꢁ2 in the region 16465±
and ꢁ3 in the region 27742±
16720 cm
1
29677 cm 1. ꢁ4 in the region 12778±12958 cm
Table 3
Thermoanalytical data of the compounds
Compound
% Mass lost
Calcd.
TG temperature Species lost
range (K)
DSC peak Enthalpy
temperature (K) (kg/mol
1
)
Obs.
[NI(acac)2(an)2]
21.01
21.01
20.96
23.04
50.12
3.65
455±662
662±459
459±634
634±689
-an
402
473
563
671
69.6
100.1
24.8
6.0
-an
a
-Ni(acac)2
2.23b
Ni(acac)2(o-clan)2]
12.46
24.91
12.46
50.18
16.80
22.00
13.40
25.80
13.54
6.53b
380±416
416±467
467±532
532±607
607±608
0.5(o-clan)
-(o-clan)
397
438
492
662
26.9
31.5
47.5
14.0
0.5(o-clan)
a
-Ni(acac)2
[Ni (acac)2 (m-clan)2]
12.46
18.68
68.84
11.07
17.51
34.28
30.71
4.46
306±378
378±409
409±479
479±592
592±677
0.5(m-clan)
393
489
630
28.1
73.8
16.4
0.7(m-clan)
a
0.75(m-Ni(acac)2
2.27b
41.09
51.23
4.69
[Ni (acac)2 (dimean)2]
42.47
57.53
322±426
426±641
641±700
1.75 dimean
429
531
659
69.7
27.1
77.9
a
0.25 dimean- Ni(acac)2
2.99b
a Pyrolysis of Ni(acac)2.
b Residue at 1273 K.

P.O. Dunstan / Thermochimica Acta 333 (1999) 5±11
9
Table 4
Band maximum assignments and calculated ligand-field parameters for the compounds
1
1
1
1
1
1
Compound
ꢁ1/cm
ꢁ4/cm
ꢁ2/cm
ꢁ3/cm
Dq/cm
B/cm
Dq/B
ꢃ*
[Ni(acac)2(an)2]
10174
10251
10470
10226
12845
12778
12958
12453
16465
16545
16692
16720
29.677
27879
27742
28527
1017
1025
1047
1023
914
871
818
958
1.11
1.18
1.28
1.07
0.89
0.85
0.79
0.93
[Ni(acac)2(o-clan)2]
[Ni(acac)2 (m-clan2)]
[Ni(acac)2 (dimen)2]
‡
ꢃ
1
ˆ B/Bo, Bo ˆ 1030 cm (Ni2‡).
3
3
1
3
3
3
3
3
ꢁ1 ˆ T2g A2g, ꢁ4 ˆ Eg A2g, ꢁ2 ˆ T1gꢀF† A2g, ꢁ3 ˆ T1gꢀP† A2g
assumed. The standard enthalpies of dissolution were
obtained according with the standard enthalpies of
reactions 1±4 in solution:
(Á2Hꢀ) and of the adducts (Á3Hꢀ). Uncertainty inter-
vals given in this table are twice the standard devia-
tions of the means of about ®ve replicate
measurements on each compound. Combined errors
were calculated from the square root of the sum of the
square of the component errors.
From the values obtained for the standard enthalpies
of the acid/base reactions and using appropriate
thermochemical cycles [22,23], the following thermo-
chemical parameters were determined: the standard
enthalpies of formation ꢀÁfHꢀ†, being equal to
ÁfHꢀ(adduct(s)) ˆ ÁrHꢀ ‡ ÁfHꢀ (Ni(acac)2(s))‡2
ÁfHꢀ(ligand(I)); the standard enthalpies of decompo-
sition (ÁDHꢀ), from the cycle
Niꢀacac†
‡ calorimetric solvent
2ꢀS†
! solutionA; Á1Hꢀ
(1)
(2)
2Lꢀl† ‡ solution A ! solutionB; Á2Hꢀ
‰Niꢀacac†2ꢀL† Š ‡ calorimetric solvent
2 ꢀS†
! solutionC; Á3Hꢀ
solutionB ! solutionC; Á4Hꢀ
(3)
(4)
The application of Hess'law to the series of reac-
tions Eqs. (1)±(4) gives the standard enthalpies of the
acid/base reactions (ÁmH%), according to the reaction
Eq. (5):
Niꢀacac† ‡ 2L ! ‰Niꢀacac†2L2Š;
2
ÁmÁ1Hꢀ ‡ Á2Hꢀ Á3Hꢀ;
(5)
since the ®nal B and C solutions are equivalent and
Á4Hꢀ ˆ 0: Table 5 gives the values obtained for the
enthalpies of dissolution of Ni(II) acetylacetonate
(Á1Hꢀ), ligands into the solution of Ni(acac)2
being equal to
ÁDHꢀ ˆ 2Ágl Hꢀ ÁrHꢀ;
the standard lattice enthalpies (ÁMHꢀ), from the cycle
Table 5
Enthalpies of dissolution at 298.15 K
1
Compound
Calorimetric solventa
Number of experiments
ÁiH8/kJ mol
Ni(acac)2
HCl 1.2M±methanol
19
5
(i ˆ 1) 3.73 Æ 0.13
(i ˆ 2) 50.39 Æ 0.42
(i ˆ 3) 3.51 Æ 0.18
(i ˆ 2) 29.67 Æ 0.29
(i ˆ 3) 18.96 Æ 0.36
(i ˆ 2) 36.05 Æ 0.58
(i ˆ 3) 3.31 Æ 0.06
(i ˆ 2) 41.84 Æ 1.12
(i ˆ 3) 2.40 Æ 0.11
an
2:1 Ni(acac)2±HCl 1.2M±methanol
HCl 1.2M±methanol
[Ni(acac)2(an)2]
o-clan
5
2:1 Ni(acac)2±HCl 1.2M±methanol
HCl 1.2M±methanol
4
[Ni(acac)2(o-clan)2]
m-clan
4
2:1 Ni(acac)2±HCl 1.2M±methanol
HCl 1.2M±methanol
6
[Ni(acac)2(m-clan)2]
dimean
[Ni(acac)2 (dimean)2]
4
2:1 Ni(acac)2±HCl1:2M±methanol
HCl 1.2M±methanol
5
4
a 1 : 3 mixture of 1.2 mol l aqueous hydrochloric acid and methanol.
1

10
P.O. Dunstan / Thermochimica Acta 333 (1999) 5±11
Based on the ÁrHꢀ values for the adducts of the
same stoichiometry we obtain the basicity sequence:
ꢀ
o-clan > an > dimean > m-clan. Using the D (Ni±N)
values we obtain the sequence o-clan > dimean >
an > m-clan. The expected order would be dimean >
an > m-clan ꢁ o-clan, due to an inductive effect of
substitution of one hydrogen atom in the phenyl group
of an by the electron withdrawing chlorine atom in o-
or m-clan. dimean is expected to be a stronger base
than an as two hydrogen atoms of the phenyl group of
an are substituted by two electron-donating methyl
groups. This leads to the decrease of the electronic
density available for bonding on the nitrogen atom in
the ®rst case and to the increase of that in the last case.
The same expected order is observed on the basis of
being equal to
ÁMHꢀ ˆ ÁrHꢀ Ágs Hꢀ 2ÁlgHꢀ
and the standard enthalpies of the Lewis acid/base
reactions in the gaseous phase (ÁrHꢀ(g)), from the
cycle
ꢀ
D(Ni±N) values with the exception of the position of
o-clan. This could be due to the contribution of
another kind of interaction like intramolecular hydro-
gen bonding between nitrogen and chlorine atoms in
o-clan.
Comparing the ligand ®eld parameters Dq with the
ꢀ
thermochemical parameters D(Ni±N) for the adducts
of an, m-clan and dimean, we observed that the Dq
Being equal to ÁrHꢀꢀg† ˆ ÁsgHꢀ 2ÁlgHꢀ‡
ÁrHꢀ ‡ Ágs Hꢀ These last values can be used to cal-
culate the standard enthalpies of the Ni±N bonds [23],
ꢀ
ꢀ
ꢀ
values decrease with the increase of D (Ni±N) values
being equal to D(Ni±N)ˆ ÁrH (g)/2. Table 6 lists
the values obtained for all these thermochemical
parameters for the adducts. For the determination of
(ÁrHꢀ(g)) it was necessary to assume that the molar
standard enthalpy of sublimation of each adduct was
equal to the enthalpy of sublimation or vaporization of
one mole of ligand [22,23,26,27], as melting points
and thermal studies showed that the adducts decom-
posed on heating and were not found in the liquid
phase and probably not in the gaseous phase.
indicating that the splitting of the d orbitals of Ni(II)
ion is not favored by stronger Ni±N bonds (Fig. 1).
The contrary was observed for Ni(II) acetylacetonate
‡
adducts with heterocyclic bases [1]. Comparing ꢃ
ꢀ
values with D(Ni±N) values we observed for the same
‡
adducts, that the ꢃ values increase with the increase
ꢀ
of D(Ni±N) values, indicating that the covalence of the
d orbitals of Ni(Il) ion is lower as the Ni±N bond is
stronger (Fig. 2). This is also the contrary of the
Table 6
1
Summary of the thermochemical results (kJ mol
)
ÁrHꢀ
ÁfHꢀ
Ágs (Hꢀ/Á` Hꢀ) ÁMHꢀ
ÁDHꢀ
ÁrHꢀ(g)
g
ꢀ
D (Ni±N)
Compound
Ni(acac)2(s)
an(l)
910.6 Æ 2.1a 95.4a
31.03 Æ 0.70b
6.8c
55.8 Æ 1.06b
o-clan(l)
62.2c
61.9c
66.9c
m-clan(l)
dimean(l)
11.8c
45.1c
[Ni(acac)2(an)2](s)
[Ni(acac)2(o-clan)2](s)
[Ni(acac)2(m-clan)2](s)
[Ni(acac)2(dimean)2](s)
50.61 Æ 0.48
899.2 Æ 2.3
949.4 Æ 2.9
970.7 Æ 4.6
1044.0 Æ 3.1
257.6 Æ 2.4 162.2 Æ 2.1
272.2 Æ 2.3 176.8 Æ 2.1
255.7 Æ 4.2 160.3 Æ 4.0
272.4 Æ 4.3 177.0 Æ 4.2
201.8 Æ 2.6 100.9 Æ 1.3
210,0 Æ 2.5 105.0 Æ 1.3
193.8 Æ 4.6 96.9 Æ 2.3
205.5 Æ 4.7 102.8 Æ 2.4
52.36 Æ 0.48
36.47 Æ 0.60
43.17 Æ 1.15
a Reference [24].
b Reference [25].
c Reference [1].

P.O. Dunstan / Thermochimica Acta 333 (1999) 5±11
11
increase in the sequence:py < b-pico < pipd < 3-cya-
nopy [1], whereas the Ni±N bonds become stronger.
References
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ꢀ
Fig. 1. Correlation of Dq values with D(Ni±N) values for the
adducts of Ni(acac)2 with (1) an, (3) m-clan and (4) dimean.
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‡
ꢀ
Fig. 2. Correlation of ꢃ values with D(Ni±N) values for the
adducts of Ni(acac)2 with (1) an, (3) m-clan and (4) dimean.