Group III quinaldates: synthesis, structure and photoluminescence

Article abstract of DOI:10.1080/00958972.2017.1283416

The reactions of Al(III), Ga(III) and In(III) nitrates with 2-quinaldic acid (qaH) afforded [Al₂(OH)₂(qa)₄]·2H₂O (1), [Ga(qa)₂(H₂O)₂]NO₃ (2) and [In(qa)₂(NO₃)(H₂O)] (3), respectively, in high yields. The crystal structures of 1, 2 and 3 have been determined by single-crystal X-ray crystallography. The structure of 1 features a di-hydroxo bridged [Al₂(μ-OH)₂]⁴⁺ dimer in which each Al(III) is further ligated by two bidentate chelate qa^? ligands. Complexes 2 and 3 are mononuclear with the M(III) ions in octahedral environments surrounded by two bidentate chelate qa^? and two H₂O in 2 or one H₂O and a terminal NO₃ ^? in 3. Characteristic IR as well as thermal analysis and solid-state fluorescence are discussed.

Full text of DOI:10.1080/00958972.2017.1283416

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Group III quinaldates: synthesis, structure and
photoluminescence
Christiana Birnara, Vadim G. Kessler & Giannis S. Papaefstathiou
To cite this article: Christiana Birnara, Vadim G. Kessler & Giannis S. Papaefstathiou (2017)
Group III quinaldates: synthesis, structure and photoluminescence, Journal of Coordination
Chemistry, 70:6, 997-1007, DOI: 10.1080/00958972.2017.1283416
To link to this article: http://dx.doi.org/10.1080/00958972.2017.1283416
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Date: 21 February 2017, At: 02:54

Journal of Coordination Chemistry, 2017
Vol. 70, no. 6, 997–1007
ꢀꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/10.1080/00958972.2017.1283416
Group III quinaldates: synthesis, structure and
photoluminescence
a
b
a
Christiana Birnara , Vadim G. Kessler and Giannis S. Papaefstathiou
ꢆ
lꢆbꢃꢅꢆꢁꢃꢅꢇ ꢃꢈ iꢉꢃꢅgꢆꢉꢄc Cꢀꢊꢋꢄꢌꢁꢅꢇ, dꢊpꢆꢅꢁꢋꢊꢉꢁ ꢃꢈ Cꢀꢊꢋꢄꢌꢁꢅꢇ, nꢆꢁꢄꢃꢉꢆꢍ ꢆꢉꢂ Kꢆpꢃꢂꢄꢌꢁꢅꢄꢆꢉ uꢉꢄvꢊꢅꢌꢄꢁꢇ ꢃꢈ aꢁꢀꢊꢉꢌ,
b
Zꢃgꢅꢆꢈꢃꢎ, Gꢅꢊꢊcꢊ; dꢊpꢆꢅꢁꢋꢊꢉꢁ ꢃꢈ Cꢀꢊꢋꢄꢌꢁꢅꢇ, swꢊꢂꢄꢌꢀ uꢉꢄvꢊꢅꢌꢄꢁꢇ ꢃꢈ agꢅꢄcꢎꢍꢁꢎꢅꢆꢍ scꢄꢊꢉcꢊꢌ, uppꢌꢆꢍꢆ, swꢊꢂꢊꢉ
ABSTRACT
ARTICLE HISTORY
The reactions of Al(III), Ga(III) and In(III) nitrates with 2-quinaldic
acid (qaH) afforded [Al (OH) (qa) ]·2H O (1), [Ga(qa) (H O) ]NO (2)
rꢊcꢊꢄvꢊꢂ 30 ocꢁꢃbꢊꢅ 2016
accꢊpꢁꢊꢂ 5 dꢊcꢊꢋbꢊꢅ 2016
2
2
4
2
2
2
2
3
and [In(qa) (NO )(H O)] (3), respectively, in high yields. The crystal
2
3
2
KEYWORDS
structures of 1, 2 and 3 have been determined by single-crystal X-ray
aꢍ(iii) cꢃꢋpꢍꢊxꢊꢌ; cꢅꢇꢌꢁꢆꢍ
ꢌꢁꢅꢎcꢁꢎꢅꢊꢌ; Gꢆ(iii) cꢃꢋpꢍꢊxꢊꢌ;
iꢉ(iii) cꢃꢋpꢍꢊxꢊꢌ; qꢎꢄꢉꢆꢍꢂꢄc
ꢆcꢄꢂ; ꢌꢃꢍꢄꢂ-ꢌꢁꢆꢁꢊ flꢎꢃꢅꢊꢌcꢊꢉcꢊ
crystallography. The structure of 1 features a di-hydroxo bridged
4
+
[
Al (μ-OH) ] dimer in which each Al(III) is further ligated by two
2 2
−
bidentate chelate qa ligands. Complexes 2 and 3 are mononuclear
with the M(III) ions in octahedral environments surrounded by two
−
bidentate chelate qa and two H O in 2 or one H O and a terminal
2
2
−
NO in 3. Characteristic IR as well as thermal analysis and solid-state
3
fluorescence are discussed.
1
. Introduction
Quinaldic acid (qaH), which is a biologically relevant molecule since it has been involved in
the tryptophan’s metabolism [1–3], is also a well-known organic precipitant for several,
CONTACT Gꢄꢆꢉꢉꢄꢌ s. Pꢆpꢆꢊꢈꢌꢁꢆꢁꢀꢄꢃꢎ
gꢌpꢆpꢆꢊꢈ@cꢀꢊꢋ.ꢎꢃꢆ.gꢅ
sꢎppꢍꢊꢋꢊꢉꢁꢆꢍ ꢂꢆꢁꢆ ꢈꢃꢅ ꢁꢀꢄꢌ ꢆꢅꢁꢄcꢍꢊ cꢆꢉ bꢊ ꢆccꢊꢌꢌꢊꢂ ꢆꢁ ꢀꢁꢁp://ꢂx.ꢂꢃꢄ.ꢃꢅg/10.1080/00958972.2017.1283416.
©
2017 iꢉꢈꢃꢅꢋꢆ uK lꢄꢋꢄꢁꢊꢂ, ꢁꢅꢆꢂꢄꢉg ꢆꢌ tꢆꢇꢍꢃꢅ & fꢅꢆꢉcꢄꢌ Gꢅꢃꢎp

998
C. BIRNARA ET AL.
mainly divalent, metal ions [4]. The ability of quinaldic acid to give insoluble or sparingly
soluble metal complexes has been found useful for gravimetric analysis of such metal ions
and/or for removing metal ions from aqueous solutions [4, 5]. To this end, several divalent
II
II
II
II
II
II
II
II
II
II
II
quinaldate metal complexes (i.e. Mn , Fe , Co , Ni , Cu , Zn , Ru , Pd , Cd , Hg and Pb ) have
been synthesized and characterized by single-crystal X-ray crystallography [6–31]. The anion
−
I
of quinaldic acid (qa ) has also been found to stabilize several low valent metal ions (i.e. Cu ,
I
I
III
III
III
Rh and Ag ) [32–37], lanthanide [38–40] and other trivalent metal ions (i.e. Cr , Fe , Bi and
III
IV
V
V
V
VI
V
IV
Os ) [41–44] as well as several high valent metal ions (i.e. V , V , Mn , Nb , W , Re and Os )
45–52]. Among them, only two group III quinaldate metal complexes have been structurally
characterized, the mononuclear [Ga(qa) Cl] [53] and the dinuclear [Ga (OH) (qa) ]·4py [5].
[
2
2
2
4
The first exhibits moderate antiproliferative activity against several human cancer cell lines
and mouse fibroblasts while the second was isolated in an attempt to selectively remove
3
+
3+
Al ions from acidic solutions containing a variety of other divalent metal ions and Cr .
−
Despite the extended π-system of qaH and its monoanion qa there is only a handful of
metal quinaldates where photophysical properties have been studied. These include few
lanthanide [40, 54–57] and some metal(II) quinaldates [30].
Continuing our previous work on the coordination chemistry of group III metal complexes,
which is focused on synthesis, structural characterization, spectroscopic study, evaluation
of the biological activity and study of their photophysical properties [58–67], we report
herein the synthesis, structural, spectroscopic characterization, thermal analysis and sol-
id-state photoluminescence of three group III metal complexes, [Al (OH) (qa) ]·2H O (1),
2
2
4
2
[
Ga(qa) (H O) ]NO (2) and [In(qa) (NO )(H O)] (3). Complexes 1 and 3 represent the first
2 2 2 3 2 3 2
structurally characterized Al(III) and In(III) quinaldate complexes, while 2 is only the third
structurally characterized quinaldate Ga(III) complex [5, 53].
2
. Experimental
2
.1. General and physical measurements
All manipulations were performed under aerobic conditions, using materials as received.
Ga(NO ) ·9H O was prepared following literature procedures [60]. Microanalyses (C, H and
3
3
2
N) were performed with an EA 1108 Carlo Erba analyzer. IR spectra were recorded on a
Shimadzu FT/IR IRAffinity-1 spectrometer with samples prepared as KBr pellets. TGA diagrams
were recorded on a Mettler-Toledo TGA/DSC1 instrument under a N flow of 50 ml/min.
2
Emission and excitation spectra were recorded on a Shimadzu RF-5301PC spectrofluoro-
photometer on powdered samples dispersed and squeezed on a quartz plate.
2
.2. Compound preparation
2
.2.1. Synthesis of [Al (OH) (qa) ]·2H O (1)
2
2
4
2
A solution of Al(NO ) ·9H O (90 mg, 0.24 mmol) in 10 mL DMF was added dropwise to a
3
3
2
stirred solution of qaH (124 mg, 0.72 mmol) in DMF (10 mL). The resultant colorless solution
was further stirred for 30 min and then left undisturbed at room temperature. Upon standing,
X-ray quality colorless crystals of 1 formed over a period of one week. The crystals were
collected by filtration, washed with DMF (1 × 5 mL) and Et O (1 × 5 mL) and dried in vacuum.
2
Yield: 45 mg (46%), based on Al. Anal. Calcd for C H N O Al : C, 59.12; H, 3.72; N, 6.89.
4
0
30
4
12
2

JOURNAL OF COORDINATION CHEMISTRY
999
−1
Found: C, 59.23; H, 3.60; N, 6.94%. IR data (KBr pellets, cm ): 3547 m, 3447 br, 1683 s, 1661
s, 1618 m, 1596 m, 1515 w, 1461 m, 1375 s, 1342 s, 1189 m, 908 m, 820 m, 770 s.
2
.2.2. Synthesis of [Ga(qa) (H O) ]NO (2)
2 2 2 3
A solution of Ga(NO ) ·9H O (109 mg, 0.26 mmol) in 15 mL MeOH was added dropwise to a
3
3
2
stirred solution of qaH (128 mg, 0.74 mmol) in MeOH (10 mL). The resultant colorless solution
was further stirred for 30 min and then left undisturbed at room temperature. Upon slow
evaporation, X-ray quality colorless crystals of 2 formed over a period of three days. The
crystals were collected by filtration, washed with MeOH (1 × 5 mL) and Et O (1 × 5 mL) and
2
dried in vacuum. Yield: 130 mg (97%), based on Ga. Anal. Calcd for C H N O Ga: C, 46.91;
2
0
16
3
1
9
−
H, 3.15; N, 8.21. Found: C, 46.80; H, 3.02; N, 8.33%. IR data (KBr pellets, cm ): 3397 br, 3118
s, 3019 br, 1666 br, 1652 br, 1593 m, 1566 s, 1515 m, 1464 m, 1381 br, 1347 s, 1275 m, 1219
w, 1188 w, 1161 w, 972 s, 865 s, 779 s.
2
.2.3. Synthesis of [In(qa) (NO )(H O)] (3)
2 3 2
A solution of In(NO ) ·5H O (80 mg, 0.20 mmol) in 10 mL MeOH was added dropwise to a
3
3
2
stirred solution of qaH (100 mg, 0.58 mmol) in MeOH (10 mL). The resultant colorless solution
was gently heated below the boiling point of MeOH (~50 C) and stirred for 15 min and then
left undisturbed at room temperature. Upon slow evaporation, X-ray quality colorless crystals
of 3 formed over a period of two days. The crystals were collected by filtration, washed with
MeOH (1 × 5 mL) and Et O (1 × 5 mL) and dried in vacuum. Yield: 34 mg (31%), based on In.
2
Anal. Calcd for C H N O In: C, 44.55; H, 2.62; N, 7.79. Found: C, 44.46; H, 2.50; N, 7.83%. IR
2
0
14
−
3
8
1
data (KBr pellets, cm ): 3446 br, 3071 w, 1639 s, 1566 w, 1515 w, 1492 m, 1383 s, 1358 w,
283 w, 1166 w, 902 w, 852 w, 805 w, 772 w.
1
2
.3. Single-crystal X-ray crystallography
The data collections for single crystals of 1–3 were carried out at room temperature using
MoKα radiation (λ = 0.71073 Å) on a Bruker SMART Apex-II diffractometer. Complete crystal
data and parameters for data collection and processing are reported in table 1. The structures
were solved by direct methods using SHELXS-97 [68] and refined by full-matrix least-squares
2
techniques on F with SHELXL-2014/7 [69].
3
. Results and discussion
3
.1. Brief synthetic comments
Complexes 2 and 3 were prepared by mixing a methanolic solution of qaH with a methanolic
solution of a M(III) nitrate salt. The concentration of the resultant mixtures as well as the
metal to ligand ratio do not seem to affect the identity of the products but they do change
the reaction yields and most importantly the quality of the crystals. Complex 1 was prepared
in the form of single-crystals in a similar fashion from a DMF solution. Although no base was
added to the reaction mixtures, the quinaldic acid deprotonates to give quinaldate com-
plexes most probably due to hydrolysis of the group III metal ions at very low pH [70]. Other
attempts to obtain crystalline materials from aqueous solutions with or without the presence

1000
C. BIRNARA ET AL.
Table 1. Cꢅꢇꢌꢁꢆꢍ ꢆꢉꢂ ꢌꢁꢅꢎcꢁꢎꢅꢊ ꢅꢊfiꢉꢊꢋꢊꢉꢁ ꢂꢆꢁꢆ ꢈꢃꢅ 1ꢏ3.
Compound reference
1
2
3
eꢋpꢄꢅꢄcꢆꢍ ꢈꢃꢅꢋꢎꢍꢆ
tꢊꢋpꢊꢅꢆꢁꢎꢅꢊ
Wꢆvꢊꢍꢊꢉgꢁꢀ
Cꢅꢇꢌꢁꢆꢍ ꢌꢇꢌꢁꢊꢋ
spꢆcꢊ gꢅꢃꢎp
uꢉꢄꢁ cꢊꢍꢍ ꢂꢄꢋꢊꢉꢌꢄꢃꢉꢌ
C h aꢍ n o
296(2) K
0.71073 Å
C h Gꢆn o
296(2) K
0.71073 Å
mꢃꢉꢃcꢍꢄꢉꢄc
C h iꢉn o
4
0
30
2
4
12
20 16
3
9
20 14
3 8
296(2) K
0.71073 Å
mꢃꢉꢃcꢍꢄꢉꢄc
mꢃꢉꢃcꢍꢄꢉꢄc
C2/c
P2 /n
P2 /c
1
1
a = 8.9299(11) Å, α = 90°
a = 9.0096(17) Å, α = 90°
a = 10.271(2) Å, α = 90°
b = 28.966(4) Å,
b = 5.9954(11) Å,
b = 9.905(2) Å,
β = 101.488(2)°
β = 98.313(2)°
β = 95.542(3)°
c = 14.0526(18) Å, γ = 90°
c = 20.335(4) Å, γ = 90°
c = 19.528(4) Å, γ = 90°
3
3
3
Vꢃꢍꢎꢋꢊ
3562.1(8) Å
1086.9(4) Å
1977.4(7) Å
Z
4
2
4
−
3
−3
−3
dꢊꢉꢌꢄꢁꢇ (cꢆꢍcꢎꢍꢆꢁꢊꢂ)
abꢌꢃꢅpꢁꢄꢃꢉ cꢃꢊfficꢄꢊꢉꢁ
F(0 0 0)
1.515 g cꢋ
1.565 g cꢋ
1.323 ꢋꢋ
1.811 g cꢋ
1.252 ꢋꢋ
0.158 ꢋꢋ−
1680
1
−1
−1
520
1072
3
3
3
Cꢅꢇꢌꢁꢆꢍ ꢌꢄzꢊ
θ ꢅꢆꢉgꢊ ꢈꢃꢅ ꢂꢆꢁꢆ cꢃꢍꢍꢊcꢁꢄꢃꢉ
iꢉꢂꢊx ꢅꢆꢉgꢊꢌ
0.30 × 0.14 × 0.12 ꢋꢋ
2.431 ꢁꢃ 25.295°
−10 ≤ h ≤ 10, −34 ≤ k ≤ 34,
16 ≤ l ≤ 16
15,216
3223 [Rꢄꢉꢁ = 0.0544]
fꢎꢍꢍ-ꢋꢆꢁꢅꢄx ꢍꢊꢆꢌꢁ-ꢌqꢎꢆꢅꢊꢌ
0.39 × 0.22 × 0.08 ꢋꢋ
0.32 × 0.23 × 0.19 ꢋꢋ
3.546 ꢁꢃ 25.245°
−10 ≤ h ≤ 10, −7 ≤ k ≤ 7,
−24 ≤ l ≤ 24
9540
1878 [Rꢄꢉꢁ = 0.0381]
fꢎꢍꢍ-ꢋꢆꢁꢅꢄx ꢍꢊꢆꢌꢁ-ꢌqꢎꢆꢅꢊꢌ
2.863 ꢁꢃ 25.250°
−12 ≤ h ≤ 12, −11 ≤ k ≤ 11,
−23 ≤ l ≤ 23
19,351
3554 [Rꢄꢉꢁ = 0.0286]
fꢎꢍꢍ-ꢋꢆꢁꢅꢄx ꢍꢊꢆꢌꢁ-ꢌqꢎꢆꢅꢊꢌ
−
rꢊflꢊcꢁꢄꢃꢉꢌ cꢃꢍꢍꢊcꢁꢊꢂ
iꢉꢂꢊpꢊꢉꢂꢊꢉꢁ ꢅꢊflꢊcꢁꢄꢃꢉꢌ
rꢊfiꢉꢊꢋꢊꢉꢁ ꢋꢊꢁꢀꢃꢂ
2
2
2
ꢃꢉ F
ꢃꢉ F
ꢃꢉ F
dꢆꢁꢆ / ꢅꢊꢌꢁꢅꢆꢄꢉꢁꢌ / pꢆꢅꢆꢋꢊꢁꢊꢅꢌ
Gꢃꢃꢂꢉꢊꢌꢌ-ꢃꢈ-fiꢁ
fꢄꢉꢆꢍ R ꢄꢉꢂꢄcꢊꢌ [I > 2σ(I)]
3223 / 2 / 274
1.054
Rꢃbꢌ = 0.0410,
wRꢃbꢌ = 0.0877
1878 / 180 / 169
1.132
Rꢃbꢌ = 0.0636,
wRꢃbꢌ = 0.1685
3554 / 1 / 297
1.033
Rꢃbꢌ = 0.0199,
wRꢃbꢌ = 0.0481
R ꢄꢉꢂꢄcꢊꢌ [ꢆꢍꢍ ꢂꢆꢁꢆ]
CCdC
Rꢆꢍꢍ = 0.0661, wRꢆꢍꢍ = 0.0977 Rꢆꢍꢍ = 0.0694, wRꢆꢍꢍ = 0.1724 Rꢆꢍꢍ = 0.0264, wRꢆꢍꢍ = 0.0498
1,512,454 1,512,455 1,512,456
of a base (0.1 M NaOH) resulted in cloudy/milky suspensions from which we were not able
to isolate any solid material by filtration.
3
.2. Description of structures
Complex 1 crystallizes in the monoclinic space group C2/c and comprises a di-hydroxo
4
+
3+
−
bridged [Al(μ-OH) Al] core (figure 1). The Al centers and the μ-OH ligands are identical
2
since a crystallographic twofold axis is passing through the center of the Al⋯Al distance,
4
+
perpendicular to the [Al(μ-OH) Al] mean plane. The di-hydroxo core is almost planar with
2
3
+
both Al and O being ~0.29 Å above or below the AlO Al mean plane with the AlOAlO
2
torsion angle being 3.67°. The distorted octahedral environment around each metal center
−
is completed by two N,O-chelate qa ligands having their nitrogens in trans orientation and
their oxygens in cis orientation with respect to each other. The hydroxo O are trans and cis
−
to the qa O and N, respectively. The Al⋯Al distance is 2.944(1) Å while the Al–O and Al–N
distances are 1.844(2)–1.858(2) and 2.120(2)–2.132(2) Å, respectively. These values are com-
parable to previously characterized [(LO,N)2Al(μ-OH) Al(LO,N)2] dimers [71–75], where LN,O− is
2
the monoanion of a N,O-chelate ligand and shorter compared to the Ga⋯Ga, Ga–O and
3
+
Ga–N distances in [Ga (OH) (qa) ]·4py [5] due to the smaller effective ionic radius of Al
2
2
4
3
+
3+
(
Ga 0.620 and Al 0.535 Å) in an octahedral geometry [70]. Owing to their position around
−
the dimer the qa ligands participate in intra-dimer π–π stacking interactions with the fol-
lowing parameters: centroidC5–C10⋯centroidC5–C10 (−x, y, 0.5−z) 3.770(1) Å and centroidN2–
C20⋯centroidC15–C20 (−x, y, 0.5−z) 3.515(1) Å.

JOURNAL OF COORDINATION CHEMISTRY
1001
Figure 1. tꢀꢊ (Λ,Λ) ꢄꢌꢃꢋꢊꢅ ꢃꢈ ꢁꢀꢊ [aꢍ (oh) (qꢆ) ] ꢂꢄꢋꢊꢅ ꢄꢉ 1. dꢆꢌꢀꢊꢂ ꢍꢄꢉꢊꢌ ꢅꢊpꢅꢊꢌꢊꢉꢁ ꢁꢀꢊ πꢏπ ꢄꢉꢁꢊꢅꢆcꢁꢄꢃꢉꢌ
2
2
4
(ꢌꢊꢊ ꢁꢊxꢁ ꢈꢃꢅ ꢂꢊꢁꢆꢄꢍꢌ). mꢃꢌꢁ ꢀꢇꢂꢅꢃgꢊꢉꢌ ꢀꢆvꢊ bꢊꢊꢉ ꢃꢋꢄꢁꢁꢊꢂ ꢈꢃꢅ cꢍꢆꢅꢄꢁꢇ. Cꢃꢍꢃꢅ cꢃꢂꢊ: aꢍ gꢅꢊꢊꢉ, o ꢅꢊꢂ, n bꢍꢎꢊ,
C gꢅꢆꢇ, h cꢇꢆꢉ. sꢇꢋꢋꢊꢁꢅꢇ cꢃꢂꢊ: (’) −x, y, 0.5−z.
Scheme 1. tꢀꢊ ꢌqꢎꢆꢅꢊ ꢆꢉꢂ gꢅꢆꢉꢉꢇ kꢉꢃꢁꢌ (ꢁꢃp) ꢆꢉꢂ ꢁꢀꢊꢄꢅ ꢆꢉꢆꢍꢃgꢇ ꢁꢃ ꢁꢀꢊ ꢁꢀꢅꢊꢊ pꢃꢌꢌꢄbꢍꢊ ꢄꢌꢃꢋꢊꢅꢌ ꢃꢈ
[
(l ) m(μ-oh) m(lo,n)2] (bꢃꢁꢁꢃꢋ).
o,n 2 2
Symmetric dimers such as [(LO,N)2Al(μ-OH) Al(LO,N)2] have three possible isomers, the meso
2
(Λ,Δ) and the rac (Δ,Δ or Λ,Λ) forms (scheme 1). The first is related to the square knot and is
achiral, while the latter are related to the topological chiral granny knot that has two enan-
tiomorphs [76]. Complex 1 comprises the rac form where both (Λ,Λ) and (Δ,Δ) enantiomorphs
exist in the lattice. This is also the case in all other previously reported [(LO,N)2Al(μ-OH) Al(L ) ]
2
O,N 2
dimers [71–74] except in one that comprises only one enantiomorph (the Δ,Δ) in its lattice
75]. The latter might precipitate as a conglomerate, but that has not been realized.
[

1002
C. BIRNARA ET AL.
8
4
3
Figure 2. rꢊpꢅꢊꢌꢊꢉꢁꢆꢁꢄꢃꢉ ꢃꢈ ꢁꢀꢊ ꢅꢊꢆꢍ (4 .5 .6 )-bsn ꢉꢊꢁwꢃꢅk ꢆꢂꢃpꢁꢊꢂ bꢇ 1. Bꢍꢆck ꢌpꢀꢊꢅꢊꢌ ꢅꢊpꢅꢊꢌꢊꢉꢁ ꢁꢀꢊ
aꢍ (oh) (qꢆ) ] ꢂꢄꢋꢊꢅꢌ, ꢃꢅꢆꢉgꢊ ꢍꢄꢉꢊꢌ ꢅꢊpꢅꢊꢌꢊꢉꢁ cꢃꢉꢉꢊcꢁꢄꢃꢉꢌ vꢄꢆ πꢏπ ꢌꢁꢆckꢄꢉg ꢄꢉꢁꢊꢅꢆcꢁꢄꢃꢉꢌ ꢆꢉꢂ ꢂꢆꢌꢀꢊꢂ bꢍꢆck
[
2
2
4
ꢍꢄꢉꢊꢌ ꢅꢊpꢅꢊꢌꢊꢉꢁ cꢃꢉꢉꢊcꢁꢄꢃꢉꢌ ꢁꢀꢅꢃꢎgꢀ ꢁꢀꢊ ꢀꢇꢂꢅꢃgꢊꢉ bꢃꢉꢂꢄꢉg ꢄꢉꢁꢊꢅꢆcꢁꢄꢃꢉꢌ.
Figure 3. tꢀꢊ ꢋꢃꢍꢊcꢎꢍꢆꢅ ꢌꢁꢅꢎcꢁꢎꢅꢊ ꢆꢉꢂ ꢁꢀꢊ ꢀꢇꢂꢅꢃgꢊꢉ bꢃꢉꢂꢄꢉg ꢄꢉꢁꢊꢅꢆcꢁꢄꢃꢉꢌ ꢄꢉ 2. Cꢃꢍꢃꢅ cꢃꢂꢊ: Gꢆ gꢅꢊꢊꢉ, o
ꢅꢊꢂ, n bꢍꢎꢊ, C gꢅꢆꢇ, h cꢇꢆꢉ. sꢇꢋꢋꢊꢁꢅꢇ cꢃꢂꢊ: (’) 1−x, 1−y, −z, (”) 1−x, 2−y, −z.
In the lattice, the molecules of 1 are connected with four neighboring molecules through
intermolecular π–π interactions and to two other dimers via hydrogen bonding interactions
−
that involve the bridging OH , the uncoordinated carboxylate O4 and the lattice H O mol-
2
ecules (figure S1). In this arrangement, each dinuclear unit connects to six neighboring
8
4
3
dimers creating a bsn network with point symbol (4 .5 .6 ) (figure 2).
3+
The mononuclear complex 2 crystallizes in the monoclinic space group P2 /n. The Ga is
1
situated on a center of inversion and is in a distorted octahedral geometry surrounded by
−
−
two bidentate chelate qa ligands and two terminal water molecules (figure 3). The qa ligands
have both their N and O atoms in trans orientation forming the basal plane of the distorted
octahedron with the terminal water molecules occupying the apical positions. The Ga–Oqa,
Ga–N and Ga–Owater distances are 1.910(3), 2.123(4) and 1.987(4) Å, respectively. All transoid

JOURNAL OF COORDINATION CHEMISTRY
1003
Figure 4. tꢀꢊ ꢋꢃꢍꢊcꢎꢍꢆꢅ ꢌꢁꢅꢎcꢁꢎꢅꢊ ꢆꢉꢂ ꢁꢀꢊ wꢊꢆk ꢄꢉꢁꢊꢅꢆcꢁꢄꢃꢉꢌ ꢄꢉ 3. Cꢃꢍꢃꢅ cꢃꢂꢊ: iꢉ gꢅꢊꢊꢉ, o ꢅꢊꢂ, n bꢍꢎꢊ, C
gꢅꢆꢇ, h cꢇꢆꢉ. mꢃꢌꢁ ꢀꢇꢂꢅꢃgꢊꢉꢌ ꢀꢆvꢊ bꢊꢊꢉ ꢃꢋꢄꢁꢁꢊꢂ ꢈꢃꢅ cꢍꢆꢅꢄꢁꢇ. sꢇꢋꢋꢊꢁꢅꢇ cꢃꢂꢊ: (’) 2−x, 0.5 + y, 0.5−z, (”)
2−x, 0.5−y, 0.5−z.
−
angles are 180°, but the cisoid angles related to the bite of the chelate qa ligand are acute
(
82.55°) with the rest around the basal plane being obtuse (97.45°). The water molecule forms
−
almost right angles which range between 88.22° and 91.78° with the N and O of the qa lig-
ands. In the lattice, the [Ga(qa) (H O) ] ions form a 1-D hydrogen-bonded chain along the b
axis that involves the water molecule and the uncoordinated carboxylate O2 of the qa ligand
with the following parameters: O3⋯O2 (1−x, 2−y, −z) 2.659(5) Å, H3B⋯O2 2.13 Å and ∠O3–
H3B⋯O2 115°. The second hydrogen of the terminal water, H3A, is hydrogen bonded to the
+
2
2
2
−
−
3
NO with the following parameters: O3⋯O4 2.562(9) Å, H3A⋯O4 2.18 Å and ∠O3–H3A⋯O4
104°. There are no other intermolecular interactions or π–π stacking in the crystal of 2.
Complex 3 crystallizes in the monoclinic space group P2 /c. It is also a mononuclear
1
3+
−
complex with the In in a distorted octahedral geometry. Two bidentate chelate qa ligands
having their N and O atoms in trans orientation, respectively, form the basal plane of the
−
octahedron with the O atoms of a terminal NO and a terminal water molecule occupying
3
the apical positions (figure 4). The In–O , In–N, In–O
and In–Owater distances are 2.114(2),
qa
nitrate
2
.099(2), 2.253(2), 2.283(2), 2.196(2) and 2.169(2) Å, respectively. These distances are longer
3
+
than the respective bond distances in 2 due to the larger effective ionic radius of In(III) (In
3
+
0
1
.80 and Ga 0.620 Å) in an octahedral geometry [70]. The transoid angles are within the
65.99° to 176.82° range while the cisoid angles fall within the range of 75.94° to 105.33°. In
the lattice, the [In(qa) (NO )(H O)] molecules form a 1-D hydrogen-bonded chain along the
2
3
2
b axis that involves the hydrogens of the terminal water and both the uncoordinated car-
−
boxylate O atoms of qa ligands with the following parameters: O5⋯O2 (2−x, 0.5 + y, 0.5−z)
2
2
.668(3) Å, H5B⋯O2 1.92(3) Å and ∠O5–H5B⋯O2 166(3)° and O5⋯O4 (2−x, y–0.5, 0.5–z)
.692(3) Å, H5A⋯O2 1.93(2) Å and ∠O5–H5A⋯O4 170(4)°. The chain is further stabilized by
intramolecular, intra-chain π–π interactions with the following parameters: centroidC5–
C10⋯centroidC15–C20 (2−x, 0.5 + y, 0.5−z) 3.588(1) Å. Surprisingly, 2 and 3 are the first

1004
C. BIRNARA ET AL.
octahedral Ga(III) and In(III) complexes of any nuclearity comprising two N,O-chelate ligands
with both N and O in trans orientation.
3
.3. IR spectra
−1
The IR spectrum of quinaldic acid exhibits a medium intensity band at ~1996 cm which is
assigned to ν(C=O) since qaH in the solid-state exists in two tautomeric forms, the neutral
−1
and the zwitterionic [77]. This band is apparent in the IR spectrum of 1 (1683 cm ) but not
in the spectra of 2 and 3 (figure S2). The C–O distances of the uncoordinated carboxylate O
in both crystallographically independent carboxylate units in 1 are shorter (1.214 Å) than
the respective C–O distances of the uncoordinated carboxylate O in 2 (1.231 Å) and 3
(
1.225 Å), implying a stronger character of the C=O bond in 1. Quinaldic acid tautomers
−1
exhibit two ν (COO) and two ν (COO) bands at 1642, 1585, 1383, and 1317 cm , respectively
[
at 1375 cm and 1342 cm for ν (COO), respectively, while the IR spectra of 2 and 3 exhibit
one antisymmetric (1662 cm in 2 and 1639 cm in 3) and one symmetric (1347 cm in 2
and 1359 cm in 3). The existence of the nitrates in the crystals of 2 and 3 is reflected in the
appearance of a strong band at ~1384 cm− [78]. The latter is absent in the spectrum of 1
due to the absence of nitrate ions in the crystal.
as
s
−1
−1
26]. In the IR spectrum of 1 these bands are at 1661 cm and 1573 cm for ν (COO) and
as
−
1
−1
s
−
1
−1
−1
−
1
1
3
.4. Thermal analysis
Thermogravimetric analysis (figure S3) reveals that 1 loses solvate water molecules from 65
to 135°C and degrades above 200°C. The residue at 600°C, 24.32%, is more than what is
expected for Al O (theoretical value 12.54%). Complex 2 loses coordinated water molecules
2
3
from 130 to 145°C and degrades immediately after that. The residue at 600°C, 18.34%, cor-
responds to Ga O (theoretical value 18.30%). Complex 3 loses coordinated water molecules
2
3
Figure 5. excꢄꢁꢆꢁꢄꢃꢉ ꢆꢉꢂ ꢊꢋꢄꢌꢌꢄꢃꢉ ꢌpꢊcꢁꢅꢆ ꢃꢈ 1ꢏ3 ꢄꢉ ꢁꢀꢊ ꢌꢃꢍꢄꢂ-ꢌꢁꢆꢁꢊ.

JOURNAL OF COORDINATION CHEMISTRY
1005
at 175–215°C and degrades above 300°C. The residue at 600°C, 36.82%, is more than what
is expected for In O (theoretical value 25.74%).
2
3
3
.5. Solid-state photoluminescence measurements
The solid-state excitation and emission spectra of quinaldic acid and of 1–3 are shown in
figure S4 and figure 5, respectively. Emission spectra were obtained after excitation at the
peak maximum of the relevant excitation spectrum. Quinaldic acid exhibits an emission band
with a maximum at 427 nm upon excitation at 366 nm. Complexes 1, 2 and 3 exhibit emission
maxima at 428 nm (λ = 327 nm), 425 nm (λ = 370 nm) and 436 nm (λ = 369 nm), respec-
ex
ex
ex
tively, which are all within the blue light region. The maxima in the emission spectra of 1–3
are less broad but they are not significantly shifted compared to the emission of the free
ligand. Since the emission of the complexes is ligand-based [30], the role of the M(III) atom
is to impose conformational rigidity that restricts the energy loss via non-radiative decay [58].
4
. Conclusion
A family of group III metal complexes based on the anion of quinaldic acid has been synthe-
sized and structurally characterized. The Al(III) complex comprises a bis-hydroxo bridged
−
core, surrounded by four chelate qa anions. The Ga(III) and In(III) complexes are mononuclear
−
comprising an octahedral M(III) surrounded by two chelate qa ligands in trans orientation
−
and solvent (H O for Ga) or H O and NO (for In). All complexes were also characterized by
2
2
3
IR spectroscopy and thermal techniques. Both IR spectra and TGA are in agreement with the
structures of the complexes. All complexes display ligand-based photoluminescence in the
solid-state in the visible (blue) region. The emission maxima of all complexes are quite close
to the ligand emission maximum, nevertheless, the intensity of the emission of the com-
plexes is much higher than that of the free ligand. Complexes 1 and 3 are the first structurally
characterized Al(III) and In(III) quinaldates while 2 is only the third structurally characterized
Ga(III) quinaldate.
Supplementary material
CIF files of complexes 1–3 and figures.
Acknowledgements
The Special Account for Research Grants (SARG) of the National and Kapodistrian University of
Athens (UoA) is gratefully acknowledged for partial support of this work. We also thank the Bodossaki
Foundation for donating the TGA to UoA.
Disclosure statement
No potential conflict of interest was reported by the authors.
ORCID
Giannis S. Papaefstathiou
http://orcid.org/0000-0001-5514-6371

1006
C. BIRNARA ET AL.
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