Syntheses and solid state structures of zinc (II) complexes with Bi-dentate N-(Aryl)imino-acenapthenone (Ar-BIAO) ligands

Article abstract of DOI:10.1007/s12039-014-0756-z

We have synthesized five zinc complexes of molecular formulae [ZnCl₂(2,6-dimethylphenyl-BIAO)]₂ (1a), [ZnBr₂(2,6-dimethylphenyl-BIAO)]₂ (1b), [ZnI₂(2,6-dimethylphenyl-BIAO)]₂(1c), [ZnBr

Full text of DOI:10.1007/s12039-014-0756-z

c
J. Chem. Sci. Vol. 127, No. 1, January 2015, pp. 1–11. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-014-0756-z
Syntheses and solid state structures of zinc (II) complexes with
Bi-dentate N-(Aryl)imino-acenapthenone (Ar-BIAO) ligands
SRINIVAS ANGA, SUPRIYA REJ, KISHOR NAKTODE, TIGMANSU PAL and
TARUN K PANDA∗
Department of Chemistry, Indian Institute of Technology Hyderabad, Ordnance Factory Estate,
Yeddumailaram 502 205, Telangana, India
e-mail: tpanda@iith.ac.in
MS received 19 May 2014; revised 18 June 2014; accepted 19 June 2014
Abstract. We have synthesized five zinc complexes of molecular formulae [ZnCl2(2,6-dimethylphenyl-
BIAO)]2 (1a), [ZnBr2(2,6-dimethylphenyl-BIAO)]2 (1b), [ZnI2(2,6-dimethylphenyl-BIAO)]2(1c), [ZnBr2(mes-
BIAO)]2(2b) and [ZnBr2(dipp-BIAO)] (3b) with rigid unsymmetrical iminoacenaphthenone ligands, (2,6-
dimethylphenyl-BIAO) (1), (mesityl-BIAO) (2) and (2,6-diisopropylphenyl-BIAO) (3). The zinc complex 1a
was prepared by the reaction of ZnCl2 and neutral (mesityl-BIAO) (1). However, complexes 1b, 2b and 3b were
obtained by the treatment of ZnBr2 and neutral ligands 1–3 respectively in 1:1 molar ratio in dichloromethane
at ambient temperature. In a similar reaction of ZnI2 with (2,6-dimethylphenyl-BIAO) (1) in dichloromethane
the corresponding iodo-complex 1c was obtained in good yield. All the zinc (II) complexes are characterized
by FT-IR, 1H and 13C{1H} NMR spectroscopic techniques. The solid state structures of the complexes 1a, 1b,
1c, 2b and 3b are confirmed by single crystal X-ray diffraction analysis. The molecular structures of com-
plexes 1a, 1b, 1c and 2b reveal the dimeric nature of the complexes and subsequently the centre atom zinc is
penta-coordinated to adopt distorted trigonal bipyramidal geometry around it. In contrast, the complex 3b is
in monomeric in nature due to bulkier size of the ligand and zinc ion is tetra coordinated to adopt distorted
tetrahedral geometry.
Keywords. Zinc(II); iminoacenathenone; penta- and tetra- coordinated; metallacycle; chelating ligands;
steric crowding
1. Introduction
already reported the reduction of alkyl and aryl car-
bonyl by using zinc complex as a catalyst using Poly-
methylhydrosiloxane (PMHS).17 Besides the reduction
of carbonyl, zinc complexes can also catalyze hydrosi-
lylation and exhibit polymerization of olefins. In recent
years, we have developed a series of rigid bi-dentate
[NO]-based N-(aryl) imino-acenapthenone (Ar-BIAO)
ligands.18 This class of ligands can be obtained from
the single condensation of acenaphthequinone and aryl
amine moiety in 1:1 ratio in acidic medium (scheme 1)
as a major product. In comparison with doubly con-
densed product (Ar-BIAN) first introduced by van
Asselt and Elsevier,19 the Ar-BIAO ligand contains
conjugated exocyclic carbonyl and imine groups. Sec-
ondly, the rigidity of the acenaphthene backbone forces
the imine N-atoms to remain in a fixed cis orienta-
tion with the exocyclic carbonyl group which favours
the chelating coordination to a metal centre. Similar
to Ar-BIAN, 2,2ꢁ-bipyridine and 1,10-phenanthroline
ligands,20–22 the σ-donating and π-accepting properties
of the Ar-BIAO ligands are observed due to the pres-
ence of exocyclic carbonyl and exocyclic imine groups
Zinc (II) complexes have been widely studied by seve-
ral research groups for the past decades. The growing
interest in the development of zinc catalysts for lactide
polymerization1 –9 is one of the driving force. Recently
N Zhao et al. have successfully reported some tri-
dentate [NO] based ligands and their Zn(II), Ta(IV),
Ti(IV), Zr(IV) complexes along with lanthanides,
which are implemented as useful catalysts for a range of
organic transformations.10–16 As an alternative method,
by switching the ligand systems from tridentate to
bidentate nature, tuning of catalytic activity of the
metal complexes can be anticipated. Clearly, most of
the applied metals (e.g., Pd, Rh, Ru, Ir) displayed dif-
ficulties by their low abundance, high price or toxicity.
But zinc complexes are less toxic, has high abundance
and low price. On the basis of that, research groups are
now focusing on different zinc complexes for catalytic
activity in organic transformations. V Bette et al. have
∗For correspondence
1

2
Srinivas Anga et al.
Scheme 1. Synthesis of (Ar-BIAO).
attached with rigid acenaphthene backbone. Herein, Yield: 239 mg (81%). FT-IR (selected frequency):
we present the full accounts of the synthesis and struc- ν = 3057 (Ar-H), 2918 (C-H), 2854 (C-H), 1725
tural studies of five zinc complexes with Ar-BIAO (C=O), 1645 (C=N), 1584, 1420, 1280, 1221, 840,
1
ligands, [ZnCl2(2,6-dimethylphenyl-BIAO)]2 (1a), 785 cm−1. H NMR (400 MHz, CDCl3, 25◦C): δ =
[ZnBr2(2,6-dimethylphenyl-BIAO)]2 (1b), [ZnI2(2,6- 8.38 (t, 2H, An-H), 8.21 (t, 1H, An-H), 7.96 (t, 1H,
dimethylphenyl-BIAO)]2 (1c), [ZnBr2(mes-BIAO)]2 An-H), 7.56 (t, 1H, An-H), 7.19 (m, 3H, Ar-H),
(2b) and [ZnBr2(dipp-BIAO)] (3b) and their UV-vis 6.78 (d, 1H, An-H), 2.21 (s, 6H, CH3) ppm; 13C{1H}
spectroscopic properties in solution and in solid state.
NMR (100 MHz, CDCl3, 25◦C): δ 189.3 (C=O),
161.2 (C=N), 147.4 (Ar-C), 140.9 (Ar-C), 135.0 (Ar-
C), 132.1 (Ar-C), 130.0 (Ar-C), 128.8 (Ar-C), 128.4
(Ar-C), 127.4 (Ar-C), 127.3 (Ar-C), 127.0 (Ar-C),
126.8 (Ar-C), 126.5 (Ar-C), 125.4 (Ar-C), 124.6
(Ar-C), 122.6 (Ar-C), 19.7 (CH3) ppm. Elemental anal-
ysis: (C42H32Cl10N2O2Zn2) (1a.CHCl3) Calc. C 46.62,
H 2.98, N 2.59; found C 46.22, H 2.61, N 2.33.
2. Experimental
2.1 General Information
All manipulations involving air- and moisture-sensitive
compounds were carried out under argon using the
standard Schlenk technique or argon-filled glove box.
Dichloromethane and pentane were dried by standard
methods and kept under molecular sieves prior to use.
1H NMR (400 MHz) and 13C {1H} NMR (100 MHz)
spectra were recorded on a BRUKER AVANCE III-
400 spectrometer. BRUKER ALPHA FT-IR was used
for FT-IR measurement. Elemental analyses were per-
formed on a BRUKER EURO EA at the Indian Insti-
tute of Technology Hyderabad. Ar-BIAO ligands 1-3
were prepared according to the literature method18,23
and anhydrous ZnCl2, ZnBr2 and ZnI2 were pur-
chased from Sigma Aldrich and used without further
purification.
2.3 Synthesis of [ZnBr2(2,6-dimethylphenyl-BIAO)]2
(1b)
In a dry degassed Schlenk tube, ligand 1 (200 mg, 0.70
mmol) was placed and about 10 mL of CH2Cl2 was
added on to it. The solution was charged with anhy-
drous ZnBr2 (158 mg, 0.70 mmol) at ambient tem-
perature under inert atmosphere. The reaction mixture
was stirred for another 12 h and then the reaction mix-
ture was filtered using cannula filtration. Deep reddish-
orange coloured filtrate was concentrated to 2 mL and
pentane (2 mL) was layered on to it and kept for crystal-
lization at −40◦C. Single crystals of light orange colour
were obtained after 2–3 days. Yield: 271 mg (76%).
FT-IR (selected frequency): ν = 3065, 2919, 2851,
1726 (C=O), 1650 (C=N), 1587, 1434, 1280, 1221,
2.2 Synthesis of [ZnCl2(2,6-dimethylphenyl-BIAO)]2
(1a)
1
777, 730 cm−1. H NMR (400 MHz, CDCl3, 25◦C):
In a dry degassed Schlenk tube, ligand 1 (200 mg, δ 8.47 (t, 2H, An-H), 8.27 (d, 1H, An-H), 8.05 (dd,
0.70 mmol) was placed and about 10 mL of CH2Cl2 1H, An-H), 7.65 (dd, 1H, An-H), 7.30 (m, 3H, Ar-H),
was added on to it. The solution was charged with 6.86 (d, 1H, An-H), 2.29 (s, 6H, CH3) ppm; 13C{1H}
anhydrous ZnCl2 (96 mg, 0.70 mmol) at ambient tem- NMR (100 MHz, CDCl3, 25◦C): δ = 190.7 (C=O),
perature under inert atmosphere. The reaction mixture 162.7 (C=N), 147.8 (Ar-C), 142.2 (Ar-C), 135.8
was stirred for another 12 h and then the reaction mix- (Ar-C), 133.0 (Ar-C), 132.6 (Ar-C), 130.9 (Ar-C),
ture was filtered using cannula filtration. Deep reddish- 129.7 (Ar-C), 129.5 (Ar-C), 129.3 (Ar-C), 128.4 (Ar-
orange coloured filtrate was evaporated to dryness C), 128.1 (Ar-C), 128.0 (Ar-C), 127.8 (Ar-C), 127.5
under vacuo. The residue was re-dissolved in 2 mL (Ar-C), 127.0 (Ar-C), 126.6 (Ar-C), 125.6 (Ar-C),
chloroform and pentane (2 mL) was layered on to it 123.7 (Ar-C), 18.9 (CH3) ppm. Elemental analysis:
and kept for crystallization at −40◦C. Single crystals of (C44H40Br4Cl8N2O2Zn2) (1b.2CH2Cl2) Calc. C 38.78,
light orange colour were obtained after 2–3 days.
H 2.96, N 2.06; found C 38.53 H 2.59, N 1.89.

Zinc complexes with Ar-BIAO ligands
3
2.4 Synthesis of [ZnI2(2,6-dimethylphenyl-BIAO)]2
(1c)
(Ar-C), 129.3 (Ar-C), 128.3 (Ar-C), 127.1 (Ar-C),
126.4 (Ar-C), 125.8, (Ar-C) 125.7 (Ar-C), 125.6 (Ar-
C), 21.0 (CH3), 18.9 (CH3) ppm. Elemental analysis:
(C46H42Br4Cl8N2O2Zn2) (2b.2CH2Cl2) Calc. C 39.78,
H 3.05, N 2.02; found C 39.31, H 2.79, N 1.89.
In a dry degassed Schlenk tube, ligand 1 (200 mg, 0.70
mmol) was placed and about 10 mL of CH2Cl2 was
added on to it. The solution was charged with anhy-
drous ZnI2 (224 mg, 0.70 mmol) at ambient tempera-
ture under inert atmosphere. The reaction mixture was
stirred for another 12 h and then the reaction mix-
ture was filtered using cannula filtration. Deep reddish-
orange coloured filtrate was concentrated to 2 mL and
pentane (2 mL) was layered on to it and kept for crystal-
lization at −40◦C. Single crystals of light orange colour
were obtained after 2–3 days. Yield: 355 mg, 84%. FT-
IR (selected frequency): ν = 3053, 2918, 2850, 1705
(C=O), 1645 (C=N), 1584, 1420, 1288, 1221, 833, 775
cm−1. 1H NMR (400 MHz, CDCl3, 25◦C): δ = 8.48 ( q,
2H, An-H), 8.28 (d, 1H, An-H), 8.05 (t, 1H, An-H),
7.65 (t, 1H, An-H), 7.29 (m, 3H, Ar-H), 6.87 (d, 1H,
An-H), 2.36 (s, 6H, CH3) ppm; 13C{1H} NMR (100
MHz, CDCl3, 25◦C): δ 189.7 (C=O), 161.7 (C=N),
147.1 (Ar-C), 140.9 (Ar-C), 135.0 (Ar-C), 132.1 (Ar-
C), 130.0 (Ar-C), 128.8 (Ar-C), 128.4 (Ar-C), 127.4
(Ar-C), 127.3 (Ar-C), 127.0 (Ar-C), 126.8 (Ar-C),
126.5 (Ar-C), 126.3 (Ar-C), 125.4 (Ar-C), 124.6
(Ar-C), 122.6 (Ar-C), 19.7 (CH3) ppm. Elemental
analysis: (C42H34Cl4I4N2O2Zn2) (1c.CH2Cl2) Calc. C
36.58, H 2.49, N 2.03; found C 35.98, H 2.13, N 1.85.
2.6 Synthesis of [ZnBr2(Dipp-BIAO)] (3b)
In a dry degassed Schlenk tube, ligand 3 (200 mg, 0.58
mmol) was placed and about 10 mL of CH2Cl2 was
added on to it. The solution was charged with anhy-
drous ZnBr2 (132 mg, 0.58 mmol) at ambient tem-
perature under inert atmosphere. The reaction mixture
was stirred for another 12 h and then the reaction mix-
ture was filtered using cannula filtration. Deep reddish-
orange coloured filtrate was concentrated to 2 mL and
pentane (2 mL) was layered on to it and kept for crystal-
lization at −40◦C. Single crystals of light orange colour
were obtained after 2–3 days. Yield: 259 mg 78%. FT-
IR (selected frequency): ν = 3063, 2963, 2927, 1726
(C=O), 1649 (C=N), 1586, 1434, 1274, 778, 725 cm−1.
1H NMR (400 MHz, CDCl3, 25◦C): δ 8.40 (t, 2H, An-
H), 8.21 (d, 1H, An-H), 7.98 (t, 1H, An-H), 7.55 (q,
1H, An-H), 7.41 (t, 1H, Ar-H), 7.32 (d, 2H, Ar-H),
6.68 (d, 1H, An-H), 3.01 (sept, 2H, CH(CH3)), 1.22 (d,
6H, CH(CH3)), 0.75 (d, 6H, CH(CH3)) ppm; 13C{1H}
NMR (100 MHz, CDCl3, 25◦C): δ 189.8 (C=O), 162.3
(C=N), 146.9 (Ar-C), 138.4 (Ar-C), 138.2 (Ar-C),
135.1 (Ar-C), 132.1 (Ar-C), 129.9 (Ar-C), 128.8 (Ar-
C), 128.0 (Ar-C), 127.8 (Ar-C), 126.2 (Ar-C), 125.7
(Ar-C), 125.4 (Ar-C), 124.1 (Ar-C), 122.6 (Ar-C), 27.9
(C-H), 23.9 (CH3), 23.7 (CH3) ppm. Elemental analy-
sis: (C25H25Br2Cl2NO Zn) (3b.2CH2Cl2) Calc. C 46.08,
H 3.87, N 2.15; found C 45.71, H 3.43, N 1.99.
2.5 Synthesis of [ZnBr2(Mes-BIAO)]2 (2b)
In a dry degassed Schlenk tube, ligand 2 (200 mg, 0.67
mmol) was placed and about 10 mL of CH2Cl2 was
added on to it. The solution was charged with anhy-
drous ZnBr2 (150 mg, 0.67 mmol) at ambient tem-
perature under inert atmosphere. The reaction mixture
was stirred for another 12 h and the reaction mix-
ture was filtered using cannula filtration. Deep reddish-
2.7 Single-crystal x-ray structure determinations
orange coloured filtrate was concentrated to 2 mL Single crystals of compound 1a, 1b, 1c, 2b and 3b
and pentane (2 mL) was layered on to it and kept were grown from a solution of CH2Cl2 (CHCl3 for
for crystallization at −40◦C. Single crystals of light 1a) and pentane under argon atmosphere at a tem-
orange colour were obtained after 2–3 days. Yield: perature of −40◦C. In each case a crystal of suitable
280 mg 80%. FT-IR (selected frequency): ν = 2920, dimensions was mounted on a CryoLoop (Hampton
2851, 1729 (C=O), 1648 (C=N), 1587, 1435, 1290, Research Corp.) with a layer of light mineral oil and
1
1224, 779, 730 cm−1. H NMR (400 MHz, CDCl3 placed in a nitrogen stream at 150(2) K. All measure-
25◦C): δ 8.46 (q, 2H, An-H), 8.28 (d, 1H, An- ments were made on a Agilent Supernova X-calibur
H), 8.03 (d, 1H, An-H), 7.60 (q, 1H, An-H), 6.96 Eos CCD detector with graphite-monochromatic CuKα
(d, 1H, An-H), 6.91 (d, 2H, Ar-H), 2.40 (s,3H, p- (1.54184 Å) and MoKα (0.71073 Å, for 2b) radia-
CH3), 2.34 (s, 3H, o-CH3), 2.25 (s, 3H, o-CH3) ppm; tion. Crystal data and structure refinement parameters
13C{1H} NMR (100 MHz, CDCl3, 25◦C): δ 190.1 are summarized in the table 1. The structures were
(C=O), 164.32 (C=N), 140.2 (Ar-C), 138.1 (Ar-C), solved by direct methods (SIR92)24 and refined on F2
137.3 (Ar-C), 136.0 (Ar-C), 133.1 (Ar-C), 132.4 (Ar- by full-matrix least-squares methods; using SHELXL-
C), 130.9 (Ar-C), 130.0 (Ar-C), 129.7 (Ar-C), 129.6 97.25 Non-hydrogen atoms were anisotropically refined.

4
Srinivas Anga et al.

Zinc complexes with Ar-BIAO ligands
5
H-atoms were included in the refinement on calcu- analytical techniques. The solid state structures of all
lated positions riding on their carrier atoms. The func- the complexes 1a–c, 2b and 3b were characterized by
ꢀ
tion minimized was [ w(Fo2 − Fc2)2] (w = 1 / single crystal X-ray diffraction analysis.
2Fc2) / 3 with σ2(Fo2) from counting statistics. The 3b show strong absorption bands at 1725, 1726, 1705,
function R1 and wR2 were (ꢀꢂFo| − |Fcꢂ) / ꢀ|Fo| 1729 and 1726 cm−1 respectively for respective C=O
and [ꢀw(Fo2 − Fc2)2 / ꢀ(wFo4)],1/2 respectively. The bond stretching, which is slightly deviated from the
[σ2 (Fo2)+ (aP)2 + bP]), where P = (Max(Fo2,0) +
In FT-IR spectra, all the compounds 1a–c, 2b and
ORTEP-3 program was used to draw the molecule.
C=O bond stretching frequencies of the corresponding
ligands.18,23 The strong absorption bands at 1645 (1a),
1650 (1b), 1645 (1c),1648 (2b) and 1649 (3b) cm−1 can
be assigned to C=N bond stretching of the iminoace-
napthenone moiety. In the 1H NMR spectrum measured
in CDCl3, compound 1a shows a sharp singlet signal
at 2.21 ppm which can be assigned to six protons from
two methyl group at o-position of the phenyl group.
For zinc dibromo and diiodo complexes 1b and 1c, the
respective methyl protons appeared as sharp singlet at
2.29 and 2.36 ppm which is slightly low field shifted
compared to that of 1a. However, the chemical shift val-
ues are in similar ranges and the slight differences can
be accounted for by the gradual increase in sizes from
chlorine to iodine atom attached to the zinc atom.
3. Results and Discussion
The 2, 6-dimethylphenyl-BIAO ligand (1) was treated
with anhydrous zinc dichloride in dichloromethane in
a 1:1 molar ratio to afford [ZnCl2(2,6-dimethylphenyl-
BIAO)]2 (1a) as orange solid in good yield (scheme 2).
Other zinc complexes 1b, 1c, 2b and 3b were
also isolated in similar reactions with respective Ar-
BIAO ligands and zinc halides (scheme 2). The
zinc complexes are soluble in THF, toluene, benzene
and dichloromethane at room temperature. All the
complexes were characterized by spectroscopic and
Scheme 2. Synthesis of zinc complexes of 1a–c, 2b and 3b.

6
Srinivas Anga et al.
However, these chemical shift values are slightly group C2/c with four molecules in unit cell along with
high field shifted with respect to the corresponding val- one chloroform molecule as solvate. In contrast, com-
ues of ligand 1 (δ 2.04 ppm). The multiplets in the plexes 1b, 1c and 2b crystallize in triclinic space group
range of 6.68–8.48 ppm for the complexes 1a–c are due P −1 having only one molecule in their respective unit
to the aromatic protons present in the phenyl group as cell along with dichloromethane molecule (two for 1b
well in the acenapthene moiety. Compound 2b which and 2b and one for 1c) as solvents. The details of
has mesityl-BIAO ligand, shows two sharp singlets at structural and refinement parameters of all the com-
2.34 and 2.25 ppm in a 1:1 ratio and can be assigned to plexes 1a–c and 2b are given in table 1. The molecu-
each of three methyl protons at o-positions of the phenyl lar structures of complexes 1a–c and 2b are shown in
group indicating the free rotation around the N(imine)- figure 1a–d respectively.
C(mesityl) is restricted in NMR time scale. The sin-
The complexes 1a–c and 2b are dimeric in nature
glet resonance signal at 2.40 ppm for compound 2b and two zinc ions are bridged through two μ2-halide
is assigned to the three methyl protons of the mesityl ions in each case. In complexes 1a–c, the coordination
group at p-position. These chemical shifts are in the polyhedron in each case is formed by the chelation
similar range with that of free ligand 2 (δ 2.04, six o- of imine nitrogen, carbonyl oxygen atoms of the 2,6-
protons) and 2.35 (three p-protons)23. The resonances dimethyl-BIAO ligand and the halide atoms (three
of the aryl protons present in acenaphthene back bone chloride for 1a, three bromide for 1b and three iodide
and aryl ring are in the expected region in between ions for 1c) attached to the zinc ion. In similar fash-
6.91–8.46 ppm similar with the corresponding values ion, the coordination polyhedron of compound 2b is
of complexes 1a–c and in well agreement with the free formed by the ligation of nitrogen and oxygen atoms
ligand 2. For compound 3b, where more bulky 2,6- present in mesityl-BIAO ligand and chloride ions. The
disopropyl-BIAO ligand is present, two doublet signals complexes 1a–c and 2b are centrosymmetric due the
at 0.74 and 1.22 ppm in 1:1 ratio and the coupling con- presence of an inversion center in the middle of each of
stants of (12 Hz) can be assigned to the methyl protons the molecule each of them form a four membered core
attached to the isopropyl groups and this is in similar Zn1-Cl1-Zn1i-Cl1i (1a), Zn1-Br1-Zn1i-Br1i (1b and
range with that of free ligand 3 (δ 0.8 and 1.1 ppm).18 2b), and Zn1-I1-Zn1i-I1i (1c). In addition, two more
The characteristic septet at 3.01 ppm corresponds to the metallacycles are formed in each case Zn1-N1-C2-C1-
resonance of the CH proton present in the isopropyl O1 and Zn1i-N1i-C2i-C1i-O1i (1a), Zn1-N1-C1-C2-O1
group is also observed slightly down field shifted than and Zn1i-N1i-C1i-C2i-O1i (1b), Zn1-N1-C9-C10-O1
the corresponding value (2.80 ppm) of ligand 3. The and Zn1i-N1i-C9i-C10i-O1i (1c) and Zn1-N1-C1-C2-
resonances of the protons of acenaphthene back bone O1 and Zn1i-N1i-C1i-C2i-O1i (2b). In these com-
and aryl ring for compound 3b are also in the expected plexes, the geometry around each zinc ion can be best
region between 6.68-8.40 ppm and in good agreement described either a distorted square pyramidal having
with the free ligand 3. In 13C {1H} NMR spectra of N1, O1, Cl1, Cl1i atoms for 1a, N1, O1, Br2, Br2i for
the compounds 1a–c, 2b and 3b, carbonyl carbon is 1b and 2b, N1, O1, I1, I1i for 1c in the basal position
mostly de-shielded and appear at δ = 189.3, 190.7, and Cl2 (1a), Br1 (1b and 2b) and I1 (1c) atoms in the
189.7, 189.7 and 189.8 ppm respectively. The imine car- apical position or distorted trigonal bipyramidal having
bon is observed at 161.2, 162.7, 161.7, 164.3 and 162.3 N1 Cl1 Cl2 atoms (for 1a), N1 Br1 Br2 (for 1b and 2b)
ppm respectively and the ipso carbon attached to nitro- and N1 I1 I2 (for 1c) are in the equatorial position and
gen atom is observed at 147.4, 147.8, 147.1, 147.0 and O1, Cl1i (1a), O1, Br2i (1b and 2b), O1, I1i (1c), atoms
146.9 ppm respectively for complex 1a–c, 2b and 3b. are in the apical position. Thus, all three complexes
These values are slightly shifted to the high field region 1a–c and 2b are examples of unusual penta- coordi-
compared to the respective Ar-BIAO ligands18,23 due to nated zinc atom. Such kind of unusual zinc complexes
the attachment of zinc ion.
are rare in literature.26,27 The Zn-O distances [2.469(2)
Å (1a), 2.484(3) Å (1b), 2.392(8) Å (1c) and 2.414(3) Å
(2b)] which are well in agreement with the zinc oxy-
gen coordination bond rather covalent bond (Zn-O
1.976 (2) Å for covalent bond.27 The Zn1-N1 distances
2.087(3) Å (for 1a), 2.073(3) Å (for 1b), 2.104(8) Å
(for 1c and 2b) are in the range of the zinc nitro-
gen coordination bond as the similar Zn-N distance
2.023(3) -2.34(3) Å is observed for Zn(mmpcd)]ClO4
(mmpcd = Me2pzCH2)2NC2H3MeNHC5H6CSSCH3)
3.1 Solid state structures
The compounds 1a–c, 2b and 3b were re-crystallized
from dichloromethane (CHCl3 for 1a) and pentane (1:1)
mixture and their molecular structures in the solid state
were established by single crystal X-ray diffraction
analysis. Compound 1a crystallizes in monoclinic space

Zinc complexes with Ar-BIAO ligands
7
Figure 1. a–d Solid-state structures of 1a–c and 2a showing the atom
labelling scheme omitting hydrogen atoms for clarity. Selected bond
lengths in [Å]: 1a. Zn(1)-N(1) 2.087(3), Zn(1)-Cl(2) 2.2103(15), Zn(1)-
Cl(1) 2.3091(14), Zn(1)-Cl(1)i 2.4404(13), Zn(1)-O(1) 2.468(3), Cl(1)-Zn(1)i
2.4404(13), O(1)-C(1) 1.225(5), N(1)-C(2) 1.277(5), N(1)-C(13) 1.459(5),
C(2)-C(3) 1.462(5), C(2)-C(1) 1.522(6), C(1)-C(11) 1.469(6); Selected bond
angles in [o]: N(1)-Zn(1)-Cl(2) 116.30(12), N(1)-Zn(1)-Cl(1) 115.46(11),
Cl(2)-Zn(1)-Cl(1) 124.18(5), N(1)-Zn(1)-Cl(1)i 96.67(10,) Cl(2)-Zn(1)-Cl(1)i
104.78(5), Cl(1)-Zn(1)-Cl(1)i 88.50(4), N(1)-Zn(1)-O(1) 74.84(12), Cl(2)-
Zn(1)-O(1) 89.41(9), Cl(1)-Zn(1)-O(1) 84.97(9), Cl(1)i-Zn(1)-O(1) 165.68(9,)
Zn(1)-Cl(1)-Zn(1)i 91.50(4), C(1)-O(1)-Zn(1) 105.5(3), C(2)-N(1)-C(13)
119.9(3), C(2)-N(1)-Zn(1) 118.9(3), C(13)-N(1)-Zn(1) 121.2(2), N(1)-C(2)-
C(3) 134.5(4), N(1)-C(2)-C(1) 117.8(4), C(3)-C(2)-C(1) 107.7(4), O(1)-
C(1)-C(11) 130.7(5), O(1)-C(1)-C(2) 122.7(4), C(11)-C(1)-C(2) 106.5(4),
C(10)-C(11)-C(1) 132.9(5), C(12)-C(11)-C(1) 105.8(4). 1b. Br(1)-Zn(1)
2.3266(6), Br(2)-Zn(1)i1 2.4243(6), Br(2)-Zn(1) 2.5980(7), Zn(1)-N(1)
2.073(3), Zn(1)-Br(2)i1 2.4243(6), Zn(1)-O(1) 2.483(3), O(1)-C(2) 1.223(5),
N(1)-C(1) 1.274(5), N(1)-C(13) 1.455(5), C(1)-C(11) 1.464(5), C(1)-C(2)
1.536(5); Selected Bond Angles in [o]: Zn(1)i1-Br(2)-Zn(1) 88.50(2), N(1)-
Zn(1)-Br(1) 116.29(9), N(1)-Zn(1)-Br(2)i1 117.64(9), Br(1)-Zn(1)-Br(2)i1
121.54(2), N(1)-Zn(1)-O(1) 74.91(11), Br(1)-Zn(1)-O(1) 89.52(7), Br(2)i1-
Zn(1)-O(1) 84.01(7), N(1)-Zn(1)-Br(2)96.30(9), Br(1)-Zn(1)-Br(2)103.50(2),
Br(2)i1-Zn(1)-Br(2) 91.50(2), O(1)-Zn(1)-Br(2) 166.65(7), C(2)-O(1)-Zn(1)
105.8(3), C(1)-N(1)-C(13) 118.8(3), C(1)-N(1)-Zn(1) 118.6(3), C(13)-N(1)-
Zn(1) 122.4(2) N(1)-C(1)-C(11) 134.2(4), N(1)-C(1)-C(2) 119.0(3), C(11)-
C(1)-C(2) 106.9(3), O(1)-C(2)-C(3) 132.7(4), O(1)-C(2)-C(1) 121.4(4).

8
Srinivas Anga et al.
(c)
(d)
Figure 1. 1c. I(1)-Zn(1) 2.6529(13), I(1)-Zn(1)i1 2.8263(15), I(2)-
Zn(1) 2.5377(13), Zn(1)-N(1) 2.104(8), Zn(1)-O(1) 2.392(8), Zn(1)-I(1)i1
2.8263(15), O(1)-C(10) 1.222(14), N(1)-C(9) 1.259(13), N(1)-C(1) 1.452(11),
C(2)-C(1) 1.409(14); Selected Bond Angles in [o]: Zn(1)-I(1)-Zn(1)i1
87.89(4), N(1)-Zn(1)-O(1) 76.0(3), N(1)-Zn(1)-I(2) 118.0(2), O(1)-Zn(1)-I(2)
91.63(19), N(1)-Zn(1)-I(1) 111.4(2), O(1)-Zn(1)-I(1) 80.23(18), I(2)-Zn(1)-
I(1) 126.07(5), N(1)-Zn(1)-I(1)i1 95.6(2), O(1)-Zn(1)-I(1)i1 165.42(19),
I(2)-Zn(1)-I(1)i1 102.89(5), I(1)-Zn(1)-I(1)i1 92.11(4), C(10)-O(1)-Zn(1)
106.7(6), C(9)-N(1)-C(1) 119.0(8), C(9)-N(1)-Zn(1) 117.2(6), C(1)-N(1)-
Zn(1) 123.8(6). 1d. Br(2)-Zn(1) 2.4512(7), Br(2)-Zn(1)i1 2.5639(7), Br(1)-
Zn(1) 2.3435(7), Zn(1)-N(1) 2.104(4), Zn(1)-O(1) 2.414(3), Zn(1)-Br(2)i1
2.5639(7), O(1)-C(2) 1.212(6), N(1)-C(1) 1.286(6), N(1)-C(13) 1.442(5),
C(1)-C(11) 1.466(6), C(1)-C(2) 1.535(6), C(2)-C(3) 1.466(6); Selected bond
Angles in [o]: Zn(1)-Br(2)-Zn(1)i1 89.08(2), N(1)-Zn(1)-Br(1) 114.62(10),
N(1)-Zn(1)-O(1) 75.58(12), Br(1)-Zn(1)-O(1) 87.64(8), N(1)-Zn(1)-Br(2)
117.29(10), Br(1)-Zn(1)-Br(2) 122.18(3), O(1)-Zn(1)-Br(2) 82.14(8), N(1)-
Zn(1)-Br(2)i1 96.74(10), Br(1)-Zn(1)-Br(2)i1 106.71(3), O(1)-Zn(1)-Br(2)i1
165.60(8), Br(2)-Zn(1)-Br(2)i1 90.92(2), C(2)-O(1)-Zn(1) 107.3(3), C(1)-
N(1)-C(13) 118.9(4), C(1)-N(1)-Zn(1) 117.3(3), C(13)-N(1)-Zn(1) 123.7(3),
N(1)-C(1)-C(2) 117.6(4), O(1)-C(2)-C(3) 131.4(4), O(1)-C(2)-C(1) 122.1(4),
C(3)-C(2)-C(1) 106.5(4).

Zinc complexes with Ar-BIAO ligands
9
(pz = pyrazole) reported by Chaudhury et al.28 and
1.994(2) - 2.050(2) Å observed for [{CH(Ph2PNSiMe3)2}
ZnN(SiMe3)2] reported by Roesky et al.29 Three dif-
ferent Zn-halide distances in each complex [Zn-Cl
2.210(2), 2.309(2), 2.440(1), Å for 1a; Zn-Br 2.327(6),
2.424(6), 2.598(7) Å for 1b; Zn-I 2.536(1), 2.653(1),
2.826(2) Å for 1c and Zn-Br 2.343(7), 2.451(7),
2.564(7) Å for 2b] indicate that one halide ion is
purely covalent bonded, whereas second halide ion
is bonded covalently as well as in bridging fashion
which elongate Zn-halide distance slightly, and the
third halide ion is purely a coordination bond and has
the longest Zn-halide distance. Thus, an asymmetric
attachment of the halide ions to the zinc centres are
observed in each complexes. The average distance
of 2.217(7) Å was observed as Zn-Cl distance in
BIANZnCl230 and 2.337–2.347 Å was reported as Zn-Br
distance (ZrBr2(TEEDA)) (tetraethylethylenediamine)
in literature.31 The Zn-I bond distance of 2.550(8)–
2.553(7) Å is reported for BIANZnI2 by Schumann et al.30
The monomeric zinc complex 3b crystallizes in
monoclinic space group P 21/c having two indepen-
dent molecules in the unit cell along with two
dichloromethane molecules. The details of structural
and refinement parameters of the complex 3b are given
in table 1. The molecular structure of complex 3b
is shown in figure 2. The central ion zinc is tetra-
coordinated through nitrogen and oxygen atoms present
in the 2,6-diisopropylphenyl-BIAO ligand and two bro-
mide ions attached to zinc. The geometry around the
zinc can be best described as distorted tetrahedral. With
respect to the dimeric complexes 1a–c and 2b, the
monomeric form of 3b can be understood due to the
presence of 2,6-isopropylphenyl group on the iminoa-
cenapthenone moiety which prevents the formation of
dimer. The Zn-O distances [2.162(2) and 2.154(2) Å
0.5
(1)
(2)
(3)
0.4
0.3
0.2
0.1
0.0
200
300
400
(a)
Wavelength (nm)
1a
1b
1c
2b
3b
0.5
0.4
0.3
0.2
0.1
0.0
Figure 2. Solid-state structure of 3b showing the atom
labelling scheme omitting hydrogen atoms for clar-
ity. Selected bond lengths in [Å]: Zn(1)-N(1) 2.086(2),
Zn(1)-O(1) 2.162(2), Zn(1)-Br(1) 2.3181(6), Zn(1)-Br(2)
2.3280(6), O(1)-C(2) 1.227(4), N(1)-C(1) 1.278(4), N(1)-
C(13) 1.460(4), C(1)-C(11) 1.460(4), C(1)-C(2) 1.539(4),
C(2)-C(3) 1.463(4); Selected bond angles in [o]: N(1)-Zn(1)-
O(1) 81.03(9), N(1)-Zn(1)-Br(1) 114.77(7), O(1)-Zn(1)-
Br(1) 107.52(6), N(1)-Zn(1)-Br(2) 113.13(7), O(1)-Zn(1)-
Br(2) 104.90(6), Br(1)-Zn(1)-Br(2) 125.08(2), C(2)-O(1)-
Zn(1) 109.00(19), C(1)-N(1)-C(13) 118.1(3), C(1)-N(1)-
Zn(1) 111.5(2), C(13)-N(1)-Zn(1) 130.30(19), N(1)-C(1)-
C(11) 135.3(3), N(1)-C(1)-C(2) 117.4(3), O(1)-C(2)-C(3)
132.4(3), O(1)-C(2)-C(1) 121.0(3), C(3)-C(2)-C(1) 106.5(3).
200
300
400
Wavelength (nm)
(b)
Figure 3. a-b. The UV-vis absorption spectra of ligands 1–
3 and zinc complexes 1a–c, 2b and 3b in CH2Cl2 at room
temperature (3.207 × 10−6 M) respectively.

10
Srinivas Anga et al.
(figure 4). In the solid-state UV-visible absorption spec-
1a
1b
1c
2b
3b
tra of 1a, 1b, 1c, 2b, 3b a broad absorption peak from
250 to 500 nm were attributed to the π to π* transi-
tion of ligand. In the solid-state UV-visible absorption
spectra of all zinc (II) complexes, the π → π* transi-
tion intensity is in the same order for complexes 1a, 1b,
2b and 3b but for complex 1c, the intensity drastically
decreases compared to that of other complexes.
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
4. Conclusion
We have successfully synthesized and character-
ized four dimeric penta-coordinated zinc complexes
[ZnCl2(2,6-dimethylphenyl-BIAO)]2 (1a), [ZnBr2(2,6-
dimethylphenyl-BIAO)]2 (1b), [ZnI2(2,6-dimethylphenyl-
BIAO)]2 (1c) and [ZnBr2(Mes-BIAO)]2 (2b) along
with one tetra-coordinated monomeric zinc complex
[ZnBr2(Dipp-BIAO)] (3b). The molecular structures of
all the complexes were established and they revealed
a bidentate ligation from the Ar-BIAO ligands in each
case through lone pairs of nitrogen and oxygen atoms.
Thus, it was observed that by changing the steric crowd-
ing on the Ar-BIAO ligand, the nuclearity of the zinc
complexes can be changed.
200
300
400
500
600
700
800
900
Wavelength (nm)
Figure 4. The solid state UV-vis absorption spectra of
complexes 1a–c, 2b and 3b.
for molecule 1 and 2 respectively] are slightly shorter
than that of complexes 1a–c and 2b (see above). This
can be explained due to expansion of coordination
number from four to five for zinc ion as we move
from tetrahedral geometry of 3b to trigonal bipyra-
midal geometry of 1a–c and 2b. Nevertheless, the
Zn-N distances [2.086(2) and 2.105(2) Å for molecule
1 and 2 respectively] are in the similar range with
that of 1a–c and 2b. The Zn-Br distances [2.318(6)
and 2.328(6) Å for molecule 1 and 2.307(6) and 2.332
(6) Å for molecule 2) are also similar with that of
zinc complexes 1b and 2b. In 3b, the four membered
zinc metallacycles Zn1-N1-C1-C2-O1 (molecule 1) and
Zn2-N2-C25-C26-O1 (molecule 2) are formed and
almost co-planar with the acenapthene plane (dihedral
angle 6.79◦).
Supplementary Information
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre
as a supplementary publication no. CCDC 1003687-
1003691. Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road,
Cambridge CB21EZ, UK (fax: + (44)1223-336-033;
email: deposit@ccdc.cam.ac.uk).
3.2 UV-visible spectra
UV-visible absorption spectra of Ar-BIAO ligands 1,
2 and 3 (figure 3a) were measured in dichloromethane
at room temperature and displayed a nearly compa-
rable absorption pattern at 230, 303 nm. The absorp-
tion spectra of the ligands 1, 2 and 3 can be attributed
to the π → π* transitions and n → π* transi-
tions respectively. The UV-visible absorption spectra
of complexes 1a, 1b, 1c, 2b and 3b (figure 3b) were
also measured in dichloromethane at room temperature
and displayed a similar kind of absorption pattern at
230 nm for π → π* transition. Upon coordination with
zinc (II) ion, the absorption peaks are slightly shifted
compared to that of the respective ligands. The solid-
state UV-visible absorption spectra of 1a, 1b, 1c, 2b,
3b were significantly different from that of solution
Acknowledgements
This work was supported by the Council of Scien-
tific and Industrial Research (CSIR) scheme ((No.
01(2530)/11/EMRII)) and start-up grant from IIT
Hyderabad. S.A. thanks CSIR, India and K. N. thanks
University Grant Commission (UGC), India for their
PhD fellowship.
References
1. Sun H, Ritch J S and Hayes P G 2011 Inorg. Chem. 50
8063
2. Pastor M F, Whitehorne T J J, Oguadinma P O and
Schaper F 2011 Inorg. Chem. Commun. 14 1737

Zinc complexes with Ar-BIAO ligands
11
3. Drouin F, Oguadinma P O, Whitehorne T J J,
Prud’homme R E and Schaper F 2010 Organometallics
29 2139
2013 Can. Chem. Trans. 1 105; (c) Anga S, Biswas S,
Kottalanka R K, Mallik B S and Panda T K 2014 Can.
Chem. Trans. 2 72
4. Boerner J, Floerke U, Doering A, Kuckling D, Jones 19. van Asselt R and Elsevier C J 1992 Organometallics 11
M D, Steiner M, Breuning M and Herres-Pawlis S 2010
Inorg. Chem. Commun. 13 369
5. Darensbourg D J and Karroonnirun O 2010 Inorg.
Chem. 49 2360
6. Howard R H, Alonso-Moreno C, Broomfield L M,
1999
20. Cavell K J, Stufkens D J and Vrieze K 1980 Inorg. Chim.
Acta 47 672
21. Reinhold J, Benedix R, Birner P and Hennig H 1979
Inorg. Chim. Acta 33 209
Hughes D L, Wright J A and Bochmann M 2009 Dalton 22. (a) Jeon M, Han C J and Kim S Y 2006 Macromol. Res.
Trans. 8667
14 306; (b) Small B L, Rios R, Fernandez E R, Gerlach
D L, Halfen J A and Carney M J 2010 Organometallics
29 6723; (c) Schmiege B M, Carney M J, Small B L,
Gerlach D L and Halfen J A 2001 Dalton Trans. 2547
7. Labourdette G, Lee D J, Patrick B O, Ezhova M B and
Mehrkhodavandi P 2009 Organometallics 28 1309
8. Chisholm M H, Eilerts N W, Huffman J C, Iyer S S,
Pacold M and Phomphrai K 2000 J. Am. Chem. Soc. 122 23. Kovach J, Peralta M, Brennessel W W and Jones W D
11845
2011 J. Mol. Struct. 992 33
9. Chakraborty D and Chen E Y -X 2003 Organometallics 24. Sheldrick G M SHELXS-97 Program of Crystal Struc-
22 769
ture Solution University of Göttingen, Germany 1997
10. Zhao N, Chen L, Ren W, Song H and Zi G 2012 J. 25. Sheldrick G M SHELXL-97 Program of Crystal Struc-
Organomet. Chem 712 29
11. Zi G 2009 Dalton Trans. 9101
12. Zi G 2011 J. Organomet. Chem. 696 68.
ture Refinement University of Göttingen, Germany 1997
26. Guru S and Ramana Rao D V 1968 Z. Anorg. Allg.
Chem. 362 108
13. Xiang L, Wang Q, Song
H
and Zi
G
2007 27. Bhattacharyya S, Kumar S B, Dutta S K, Tiekink E R T
and Chaudhury M 1996 Inor. Chem. 35 1967
Organometallics 26 5323
14. Wang Q, Xiang L, Song H and Zi G 2008 Inorg. Chem. 28. Seetawan U, Jugsujinda S, Seetawan T, Ratchasin
47 4319
A, Euvananont C, Junin C, Thanachayanot C and
Chainaronk P 2011 Mater. Sci. Appl. 2 1302
29. Marks S, Köppe R, Panda T K and Roesky P W 2010
Chem. Eur. J. 16 7096
30. Fedushkin I L, Skatova A A, Eremenko O V, Hummert
M and Schumann H 2007 Z. Anorg. Allg. Chem. 633
1739
15. Zi G, Xiang L and Song H 2008 Organometallics 27
1242
16. Xiang L, Song H and Zi G 2008 Eur. J. Inorg. Chem.
1135
17. Bette V, Mortreux A, Savoia D and Carpentier J F 2004
Tetrahedron 60 2837
18. (a) Anga S, Paul M, Naktode K, Kottalanka R K and 31. Eckert P K, Vieira I S, Gessner V H, Börner J,
Panda T K 2012 Z. Anorg. Allg. Chem. 637 1311; (b)
Anga S, Pal T, Kottalanka R K, Paul M and Panda T K
Strohmann C and Herres-Pawlis S 2013 Polyhedron 49
151