A strongly fluorescent NiII complex with 2-(2-hy­droxy­eth­yl)pyridine ligands: synthesis, characterization and theoretical analysis and comparison with a related polymeric CuII complex

Zeghouan, O.; Dems, M.A.E.; Sellami, S.; Merazig, H.; Daran, J.C.

doi:10.1107/S2056989018009301

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ISSN: 2056-9890

Volume 74| Part 8| August 2018| Pages 1042-1048

https://doi.org/10.1107/S2056989018009301

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A strongly fluorescent Ni^II complex with 2-(2-hydroxyethyl)pyridine ligands: synthesis, characterization and theoretical analysis and comparison with a related polymeric Cu^II complex

Ouahida Zeghouan,^a,^b ^* Mohamed AbdEsselem Dems,^c,^b Seifeddine Sellami,^d Hocine Merazig ^a and Jean Claude Daran ^e

^aUnité de Recherche Chimie de l'Environnement et Moléculaire Structurale, 'CHEMS', Faculté des Sciences Exactes, Campus Chaabet Ersas, Université Frères Mentouri Constantine 1, 25000 Constantine, Algeria, ^bCentre de Recherche en Biotechnologie, Constantine, Algeria, ^cLaboratoire de Chimie des Matériaux et des Vivants: Activité, Réactivité, Université Hadj-Lakhdar Batna, Algeria, ^dLaboratoire Pollution et Traitement des Eaux, Département de Chimie, Faculté des Sciences Exactes, Université Frères Mentouri Constantine 1, 25000 Constantine, Algeria, and ^eLaboratoire de Chimie de Coordination, UPR-CNRS 8241, 205 route de Narbonne, 31077 Toulouse Cedex 4, France
^*Correspondence e-mail: ouahida.zeghouan@gmail.com

Edited by A. Van der Lee, Université de Montpellier II, France (Received 5 June 2018; accepted 27 June 2018; online 6 July 2018)

The synthesis and characterization of diaquabis[2-(2-hydroxyethyl)pyridine-κ²N,O)nickel(II) dinitrate, [Ni(C₇H₉NO)₂(H₂O)₂](NO₃)₂, under ambient conditions is reported and compared with catena-poly[[bis[2-(2-hydroxyethyl)pyridine-κ²N,O]copper(II)]-μ-sulfato-κ²O:O′], [Cu(C₇H₉NO)₂(SO₄)]_n [Zeghouan et al. (2016 ). Private communication (refcode 1481676). CCDC, Cambridge, England]. In the two complexes, the 2-(2-hydroxyethyl)pyridine ligands coordinate the metal ions through the N atom of the pyridine ring and the O atom of the hydroxy group, creating a chelate ring. The Ni^II or Cu^II ion lies on an inversion centre and exhibits a slightly distorted MO₄N₂ octahedral coordination geometry, build up by O and N atoms from two 2-(2-hydroxyethyl)pyridine ligands and two water molecules or two O atoms belonging to sulfate anions. The sulfate anion bridges the Cu^II ions, forming a polymeric chain. The photoluminescence properties of these complexes have been studied on as-synthesized samples and reveal that both compounds display a strong blue-light emission with maxima around 497 nm. From DFT/TDDFT studies, the blue emission appears to be derived from the ligand-to-metal charge-transfer (LMCT) excited state. In addition, the IR spectroscopic properties and thermogravimetric behaviours of both complexes have been investigated.

Keywords: transition metal; fluorescence; blue-light emission; TDDFT; crystal structure.

CCDC reference: 1481640

1. Chemical context

A wide variety of nitrogen-containing heterocyclic ligands has been used to construct coordination complexes (Lin et al., 2015 ; Kim et al., 2015 ; Huang et al., 2015 ). In particular, pyridine alcohol derivatives and their metal complexes have been studied extensively in recent years, focusing on the rational design and synthesis of coordination monomers and polymers because of their intriguing structural features as well as potential applications in catalysis and fluorescence and as chemical sensors (Ley et al., 2010 ). Moreover, luminescent compounds have also attracted attention because of their applications, particularly in modern electronics, as materials for producing organic light-emitting diodes (OLEDs) (Kelley et al., 2004 ). The 2-(2-hydroxyethyl)pyridine (hep-H) ligand may adopt many coordinating variants because of its donating capabilities: N-monodentate (N) (Martínez et al., 2007 ), N,O-chelating (²N,O) (Antonioli et al., 2007 ); deprotonated chelating (²N,O) (Antonioli et al., 2007) and bridging (N:O) (Antonioli et al., 2007), ²N,O:O⁷and ²N,O:O:O (Wang et al., 2010 ) or simultaneously ²N,O:O and ²N,O:O:O bridging (Stamatatos, Boudalis et al., 2007 ).

We are in particular interested in the hep-H ligand, which has attracted much attention in biology and chemistry because it is a useful model and for its practical applications (Kong et al., 2009 ; Mobin et al., 2010 ). The hep-H ligand could be a good candidate to construct simultaneously nitrogen heteroaromatic alcohol coordination monomers and polymers with interesting magnetic behaviour. On the other hand, with Ni^II and Cu^II metals, the hep-H ligand could also be a desirable candidate for fluorescent materials. The flexible coordination sphere around the Ni^II and Cu^II ions, in combination with steric and packing forces, is one of the effects that gives rise to a wide structural diversity in Ni^II/Cu^II coordination chemistry (Comba & Remenyi, 2003 ).

The combination of multidentate ligands with suitable cations has led to a large number of novel mononuclear and polynuclear complexes. In this study, by reacting the flexible hep-H ligand with Ni(NO₃)₂·6H₂O, we have successfully obtained the monomeric Ni^II complex diaquabis[2-(2-hydroxyethyl)pyridine-κ²N,O)nickel(II) dinitrate, [Ni(C₇H₈NO)₂(H₂O)₂](NO₃)₂ (1). The related polymeric complex, catena-poly[[bis[2-(2-hydroxyethyl)pyridine-κ²N,O]copper(II)]-μ-sulfato-κ²O:O′], [Cu(C₇H₈NO)₂(SO₄)]_n (Zeghouan et al., 2016; Zienkiewicz-Machnik et al., 2016 ) had previously been obtained by reacting the hep-H ligand with Cu(SO₄)₂·6H₂O. Herein we compare their structures, IR spectra, thermostability, fluorescence and absorption properties and tge results of a theoretical study performed using TDDFT calculations.

2. Structural commentary

In the mononuclear title Ni^II complex 1 as well as in the polymeric Cu^II complex 2 (Zeghouan et al., 2016; Zienkiewicz-Machnik et al., 2016), the metal ions are located on inversion centers with the neutral hep-H molecule acting as a bidentate ligand in a ²N,O fashion and forming the equatorial plane of an octahedron, the apex of which is occupied by the water molecules in the case of the Ni^II complex or an O atom of an SO₄²⁻ anion in the Cu^II complex (Figs. 1 and 2). The main difference between the two structures is the occurrence of the SO₄²⁻ anion in 2, which links complex molecules, forming a polymeric chain. Moreover, in this structure the asymmetric unit contains two half molecules of the complex. In the Ni^II complex, two nitrate anions balance the charges. The coordination environment around the nickel ions can be described as a nearly perfect octahedron. The O1—Ni1—N1 [88.68 (3)°], N1—Ni1—O1W [90.00 (4)°] and O1—Ni1—O1W [89.26 (4)°] angles are all very close to 90° (Table 1). The two hep-H ligands are trans with respect to each other. The hydroxyl O atom and the pyridine N atoms define the equatorial plane while the water molecules occupy the apices. In the case of the Cu^II complex, the octahedron is slightly distorted with the angles around the metal ranging from 83.39 (5) to 96.62 (5)°. This distortion might result from the influence of the SO₄²⁻ linking the Cu complex to form a polymeric chain.

Table 1
Comparison of experimental and calculated distances and angles (Å, °) in 1 and 2

1
Ni1—O1	2.0622 (14)	2.07
Ni1—O1W	2.0831 (15)	2.10
Ni1—N1	2.1019 (14)	2.12
O2—N2	1.2520 (14)	1.23
O3—N2	1.2548 (12)	1.22
O4—N2	1.2537 (12)	1.27

O1—Ni1—O1W	90.74 (4)	93.00
O1—Ni1—N1	88.68 (3)	87.00
O1—Ni1—O1Wⁱ	89.26 (4)	91.8
O1—Ni1—N1ⁱ	91.32 (3)	92.3
O1W—Ni1—N1	90.00 (4)	92
O1ⁱ—Ni1—O1W	89.26 (4)	87.00
O1W—Ni1—N1ⁱ	90.00 (4)	91.8
O1ⁱ—Ni1—N1	91.32 (3)	92.3
O1Wⁱ—Ni1—N1	90.00 (4)	91.8
O1ⁱ—Ni1—O1Wⁱ	90.74 (4)	87.5

O1W—Ni1—O1—C2	−79.99 (10)	80.02
N1ⁱ—Ni1—O1—C2	−170.01 (10)	166.70
O1—Ni1—N1—C4	−29.33 (10)	31.30
O1—Ni1—N1—C8	151.96 (9)	−147.60
O1Wⁱ—Ni1—N1—C4	−118.59 (9)	114.9
O1Wⁱ—Ni1—N1—C8	62.70 (9)	−64.00

2
Cu1—O1	2.01	2.08
Cu1—N1	2.02	1.99
Cu1—O1ⁱ	2.01	2.08
Cu1—N1ⁱ	2.02	1.99
Cu2—O2	2.05	2.08

N2—Cu2—N2ⁱⁱ	180	180.00
O1—Cu1—N1	92.39	90.60
O1—Cu1—O1ⁱ	180	180.00

O3—Cu1—O1—C1	−93.9	−98
O1—Cu1—N1—C7	−151.03	−153
N2—Cu2—O2—C8	151.24	148
Cu1—O1—C1—C2	−37.55.	−40
C7—N1—C3—C2	177	179
C7—N1—C3—C4	−0.5	−0.4

Figure 1
View of the Ni complex, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as circles of arbitrary radii. Hydrogen bonds are shown as dashed lines. [Symmetry code: (i): − x + 1, −y + 1, −z + 2].

Figure 2
Partial view of the polymer chain in the Cu compound, with displacement ellipsoids drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines. [Symmetry code: (i) −x + 1, −y + 2, −z + 2; (ii) −x, −y + 1, −z + 1].

In both complexes, the chelate ring displays a twist-boat conformation with puckering parameters θ = 81.9° and φ = 162° for 1 and θ = 79.2° and φ = 159.9° and θ = 87.75° and φ= 176.08° for the two molecules of 2.

3. Supramolecular features

Although not coordinated to the Ni atom, the nitrate anion in 1 participates in the packing motif. The hydroxyl group and water molecules are involved in strong O—H⋯O hydrogen bonds (Table 2) with the O atoms of the nitrate anions, resulting in the formation of R₄⁴(12) and R₄⁴(16) graph-set motifs, as shown in Fig. 3, building up a three-dimensional network. C—H⋯O hydrogen bonds also occur.

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1W—H2W⋯O3ⁱ	0.84	1.95	2.7870 (16)	176
O1W—H2W⋯N2ⁱ	0.84	2.68	3.455 (2)	153
O1W—H1W⋯O4	0.85	1.93	2.7720 (19)	174
O1—H1⋯O2ⁱⁱ	0.82	1.88	2.6952 (15)	172
O1—H1⋯N2ⁱⁱ	0.82	2.65	3.4208 (17)	159
C2—H2B⋯O3ⁱⁱⁱ	0.97	2.64	3.378 (2)	133
C3—H3A⋯O1W	0.97	2.55	3.2278 (17)	127
C8—H8⋯O1^iv	0.93	2.49	3.0136 (19)	116
C8—H8⋯O4^iv	0.93	2.66	3.4448 (18)	143
C5—H5⋯O2^v	0.93	2.41	3.3076 (19)	163
Symmetry codes: (i) -x+2, -y+1, -z+2; (ii) -x+1, -y, -z+2; (iii) x-1, y, z; (iv) -x+1, -y+1, -z+2; (v) -x+1, -y, -z+1.

Figure 3
Partial view of the packing in the Ni^II complex showing the O—H⋯O hydrogen bonds (dashed lines) and the formation of the R₄⁴(12) and R₄⁴(16) graph-set motifs. [Symmetry codes: (i) − x + 2, −y + 1, −z + 2; (ii) −x + 1, −y, −z + 2].

4. Database survey

A search of the Cambridge Structural Database (CSD, Version 5.36; Groom et al., 2016 ) based on an Ni(hep-H)₂O₂ fragment gave 11 hits for closely related structures with an octahedral Ni complex, located on an inversion center, coordinated by two chelating N,O hep-H ligands in the equatorial plane and two O atoms of different ligands at the apices. A comparison of the Ni—N and Ni—O bond lengths as well as of the dihedral angles between the equatorial NiO₂N₂ plane and the pyridine ring is displayed in Table 3. There are no notable differences between the Ni—O(H) distances, which range from 2.057 (2) to 2.114 (1) Å, and the Ni—O(ligand) bonds, ranging from 2.052 (1) to 2.112 (2) Å. Clearly the organic substituent attached to the O atom in the axial position has no real influence on the Ni—O(R) bond length. The dihedral angles between the pryridine ring and the NiN₂O₂ basal square plane range from 28.3 to 37.6°. The largest angle is observed for two polymeric structures in which the succinato or adipato organic ligand bridge the Ni atoms, forming a chain; this is possibly related to steric effects. A similar search on the Cu(Hep-H)₂O₂ fragment gave seven hits. The major difference observed with the related Ni complexes is the large discrepancy in the Cu—O(H) bond lengths, which range from 2.012 (2) to 2.428 (2) Å and the Cu—O(R) lengths, ranging from 1.982 (1) to 2.387 (4) Å. The difference observed between the Cu—O(H) and Cu—O(R) bond lengths might be due to the Jahn–Teller effect. The dihedral angles between the pryridine ring and the CuN₂O₂ basal square plane, ranging from 26 to 38°, are close to those found in the Ni complexes. Similar twist-boat conformations are observed in all of the related Ni and Cu complexes bearing the hep-H ligand (Table 3).

Table 3
Comparison of selected geometrical parameters (%, Å, °) for Ni^II and Cu^II complexes bearing the hep-H ligand

Δ is the dihedral angle between the basal MO₂N₂ square plane and the pyridine ring.

Ref.	R-factor	M—N	M—OH	M—O(R)	Δ	θ	φ
1	1.80	2.102 (1)	2.062 (1)	2.083 (2)	28.28 (4)	81.9 (1)	162.6 (1)
BOZJAD^a	3.80	2.102 (2)	2.065 (3)	2.084 (3)	28.4 (1)	80.6 (3)	163.4 (3)
HULYAO^b	3.22	2.073 (1)	2.064 (1)	2.085 (1)	30.37 (6)	78.7 (1)	156.3 (1)
EJEZEZ^c	2.58	2.082 (1)	2.089 (1)	2.090 (1)	30.88 (6)	99.0 (1)	346.8 (1)
FEFWIY^d	3.13	2.100 (2)	2.088 (1)	2.072 (2)	30.4 (1)	96.8 (2)	349.7 (2)
FEFWIY01^d	3.05	2.090 (1)	2.104 (1)	2.064 (1)	31.86 (8)	95.9 (1)	354.6 (2)
FEFWIY02^d	2.59	2.096 (1)	2.085 (1)	2.064 (1)	30.51 (7)	97.9 (1)	346.1 (1)
BOZJOR^a	3.75	2.078 (2)	2.096 (1)	2.063 (2)	37.6 (1)	89.2 (2)	175.3 (2)
BOZJUX^a	3.03	2.083 (1)	2.114 (1)	2.052 (1)	35.43 (8)	94.3 (1)	352.5 (2)
BOZKAE^a	4.36	2.098 (2)	2.096 (2)	2.064 (2)	29.9 (1)	81.9 (2)	160.4 (2)
RAJQOL^e	4.07	2.083 (2)	2.057 (2)	2.112 (2)	31.9 (1)	84.5 (2)	167.7 (2)

2 NABBEA01^f	1.9	2.025 (2) 1.988 (2)	2.012 (2) 2.055 (1)	2.380 (1) 2.298 (1)	28.5 (1) 38.0 (1)	79.2 (1) 87.8 (1)	159.9 (1) 176.2 (1)
NABBEA^g	5.2	1.993 (4) 2.031 (4)	2.070 (4) 2.016 (4)	2.298 (4) 2.387 (4)	37.5 (2) 28.8 (2)	87.5 (3) 100.3 (4)	175.9 (3) 340.6 (4)
HAYHAS^h	2.8	2.032 (2)	2.422 (1)	1.982 (1)	29.50 (7)	81.9 (1)	171.9 (1)
IREREDⁱ	4.04	2.017 (2)	2.385 (2)	2.025 (2)	31.0 (1)	94.4 (2)	356.0 (2)
OJOBAQ^j	2.35	2.009 (1)	2.041 (1)	2.312 (1)	33.96 (4)	98.6 (1)	340.0 (1)
SOJGAB^k	3.52	2.029 (2)	2.428 (2)	1.998 (1)	25.97 (8)	101.4 (2)	346.6 (2)
UGAROK^l	3.44	2.021 (2) 2.030 (2)	2.019 (2) 2.024 (2)	2.357 (2) 2.346 (2)	31.4 (1) 32.5 (1)	95.9 (2) 80.6 (2)	345.3 (2) 167.0 (2)
Notes: (a) Trdin et al. (2015 ); (b) Hamamci et al. (2002 ); (c) Yilmaz et al. (2011 ); (d) Trdin & Lah (2012 ); (e) Çolak et al. (2017 ); (f) Zeghouan et al. (2016); (g) Zienkiewicz-Machnik et al. (2016); (h) Lapanje et al. (2012 ); (i) Pothiraja et al. (2011 ); (j) Yilmaz et al. (2003 ); (k) Caglar et al. (2014 ); (l) Yeşılel et al. (2009 ).

5. Thermogravimetric and differential thermal analysis

Thermal analyses were performed on a SETARM 92-16.18 PC/PG 1 instrument from 303 to 1273 K under a dynamic air atmosphere and under nitrogen at 200.0 ml min⁻¹ with a heating rate of 283 K min ⁻¹. The stability of the two complexes was measured by TGA and the experimental results are in agreement with the calculated data.

The TG curve for 1 (Fig. 4a) shows that the monomer is stable up to 424 K with the first weight loss of 33.55% (calculated 34.21%) at 303 −438 K corresponding to the loss of two coordinated water molecules and the organic hep-H ligand. The second loss of 47.51% (calculated 40.02%) at 438–488 K corresponds to the loss of the second hep-H ligand and the nitrate anion, and then the second nitrate anion decomposes (DP/P = 12.14%, calculated =13.34%). In addition, the corresponding endothermic and exothermic peaks (at 424.26, 475.06 and 631.85 K) in the differential scanning ATD curve also record the processes of weight loss. As illustrated in Fig. 4b, the TG curve for 2 shows that the polymer is stable up to 470 K with the first weight loss of 24.16% (calculated 23.66%) at 470–483 K corresponding to the loss of the sulfate anion and the second loss of 29.42% (calculated 30.30%) at 483–573 K to the loss of the first hep-H ligand, and then the second hep-H ligand decomposes (DP/P = 28.55%, calculated =30.30%). In addition, the corresponding endothermic and exothermic peaks (at 473, 558 and 773 K) in the differential scanning ATD curve also record the processes of weight loss.

Figure 4
The thermogravimetric (TG) and differential thermal analysis (DTA) curves for (a) the monomer and (b) the polymer.

6. Luminescence properties

Photoluminescence spectra were measured using a Cary Eclipse (Agilent Technologies) fluorescence spectrophotometer with quartz cell (1 × 1 cm² cross-section) equipped with a xenon lamp and a dual monochromator. The measurements were carried out at ambient temperature (298 K) with the slit_ex/em = 10 nm/10 nm. The photoluminescence properties of 1, 2 and free hep-H in an ethanol–water (v/v = 1:1) solution were investigated in the visible region. As shown in Fig. 5, free hep-H displays orange emission with a band at 496.06 nm (excited at 269.70 nm), which may be assigned to a π–π* electronic transition. When hep-H is combined with Ni^II or Cu^II in 1 or 2, an intense blue emission band is seen at λ_em/λ_ex = 498.03 nm/250.93 nm or 496.96 nm/250.00 nm respectively. This should probably be assigned to the π–π* charge-transfer interaction of the hep-H ligands. The observed blue shift of the emission maximum between 1, 2 and free hep-H is considered to originate mainly from the influence of the coordination of the metal atoms to the hep-H ligand (Leitl et al., 2016 ). Thus, these compounds may be candidates for blue-light luminescent materials which suggests that more transition metal, pyridine alcohol compounds with good luminescent properties can be developed.

Figure 5
The fluorescence spectrum of the hep-H ligand and the title compounds (excitation at 250 and 269.70 nm for the complexes and hep-H, respectively)

7. TDDFT calculations

In an effort to better understand the nature of the electronic transitions exhibited by compounds 1 and 2, DFT calculations using the Amsterdam density function (ADF) software (Baerends et al., 1973 ) along with generalized gradient approximations, exchange and correlation functional GGA (PBE) (Perdew et al., 1997 ), employing the TZP (triple zeta polarized) basis set. The singlet excited state was optimized using time-dependent density functional theory calculations (TDDFT) (Bauernschmitt & Ahlrichs, 1996 ; Gross & Kohn, 1990 ; Gross et al., 1996 ).

The ground-state geometry of 1 and 2 was adapted from the X-ray data. The calculated structural parameters show a good agreement with the original X-ray diffraction data (Table 1); the root-mean-square deviation f between the X-ray and the DFT structure for non-hydrogen atoms is 0.603 and 0.620 Å for 1 and 2, respectively. The computed absorption bands, dominant transitions, characters, and oscillator strengths (f) are given in Table 4. As shown in this table, two absorption features are predicted for the monomer; these mainly consist of absorption peaks located at λ = 286 and 280 nm, resulting from the HOMO-2 to LUMO transition and the HOMO-3 to LUMO transition, which is attributed to a ligand–metal charge transfer (LMTC) (Fig. 6a). Three absorption features are predicted in the polymer, consisting mainly of absorption peaks that are located at λ = 507, 443 and 244 nm, resulting from HOMO-4 to LUMO, HOMO-5 to LUMO and HOMO-2 to LUMO transitions, which are attributed to a ligand–metal charge transfer (LMTC) (Fig. 6b). The HOMO–LUMO energy gap was found to be 4.33, 4.42 for the transitions in 1 and 2.44, 4.03, 5.81 ev for the transitions in 2.

Table 4
The calculated optical transition energies (nm) and their corresponding oscillator strengths (f) (ev) for 1 and 2

λ	f	E	Transition	Type
1
286	0.03	4.33	HOMO-2 to LUMO	LMTC
280	0.01	4.42	HOMO-3 to LUMO	LMTC
2
507	0.009	2.44	HOMO-4 to LUMO	LMTC
443	0.08	4.03	HOMO-5 to LUMO	LMTC
244	0.07	5.81	HOMO-2 to LUMO+1	LLTC

Figure 6
Plots of the molecular orbitals dominating the contribution of the low-energy transitions for (a) the monomer and (b) the polymer.

8. Synthesis and crystallization

All chemicals and solvents were commercially purchased and used as received. The infrared spectra were recorded on a Perkin–Elmer spectrometer at room temperature in the range of 4000–500 cm⁻¹.

The hep-H ligand was obtained from commercial sources. The synthesis of the two compounds followed the same procedures as previously described for the Co^II analog (Zeghouan et al., 2013 ). (2-Hydroxyethyl)pyridine (10.0 mmol, 1.67 g) was reacted in a mixture of ethanol–water (v/v = 1:1) with Ni(NO₃)₂·6H₂O (10.0 mmol, 2.50 g) for the Ni^II analogue and with Cu(SO₄)₂·6H₂O (10.0 mmol, 2.3 g) for the Cu^II analogue. The solutions were maintained under agitation for 24 h at room temperature. Green prisms of the monomer and green prisms of the polymer were obtained by slow evaporation of the solvents within three weeks. The crystals formed were filtered and washed with 15 ml of water.

IR (cm⁻¹, pure crystals of compounds without KBr): Ni analogue: 3389 (vs), 3124 (vs), 2862 (m), 2764 (m), 2360 (m), 1658 (m), 1442 (m), 1371 (vs), 1306 (vs), 1084 (m), 1021 (m), 763 (m), 586 (m). Cu analogue: 3392 (vs), 3127 (s), 2911 (m), 1655 (m), 1609 (m), 1572 (w), 1493 (w), 1444 (w), 1373 (vs), 1356 (vs), 1313 (m), 1159 (m), 1082 (m), 1023 (m), 907 (w), 860 (s), 764 (m), 706 (s), 643 (s).

9. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 5. O-bound H atoms were located in a difference-Fourier map and refined with O—H restrained to 0.85 (1) Å, with U_i_so(H) = 1.5U_eq(O). For the water molecule a further H⋯H distance restraint of 1.39 (2) Å was used. C-bound H atoms were placed at calculated positions with C—H = 0.93 Å (aromatic H atoms) and 0.97 Å (methylene H atoms), and refined in riding mode with U_iso(H) = 1.2U_eq(C). Four reflections were omitted from the refinement.

Table 5
Experimental details

Crystal data
Chemical formula	[Ni(C₇H₉NO)₂(H₂O)₂](NO₃)₂
M_r	465.05
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	293
a, b, c (Å)	7.782 (5), 8.185 (5), 8.811 (5)
α, β, γ (°)	96.785 (5), 113.856 (5), 109.140 (5)
V (Å³)	464.0 (5)
Z	1
Radiation type	Mo Kα
μ (mm⁻¹)	1.11
Crystal size (mm)	0.18 × 0.11 × 0.08

Data collection
Diffractometer	Bruker APEXII
No. of measured, independent and observed [I > 2σ(I)] reflections	2478, 2478, 2471
R_int	0.019
(sin θ/λ)_max (Å⁻¹)	0.685

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.018, 0.051, 1.08
No. of reflections	2478
No. of parameters	133
No. of restraints	4
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	0.42, −0.29
Computer programs: APEX2 and SAINT (Bruker, 2006 ), SIR2002 (Burla et al., 2003 ), SHELXL (Sheldrick, 2015 ), ORTEPIII (Burnett & Johnson, 1996 ), ORTEP-3 for Windows and WinGX (Farrugia, 2012 ), PLATON (Spek, 2009 ) and Mercury (Macrae et al., 2006 ).

Supporting information

CCDC reference: 1481640

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989018009301/vn2135sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989018009301/vn2135Isup3.hkl

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT (Bruker, 2006); data reduction: SAINT (Bruker, 2006); program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: SHELXL (Sheldrick, 2015); molecular graphics: ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 for Windows (Farrugia, 2012), PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 2012) and Mercury (Macrae et al., 2006).

Diaquabis[2-(2-hydroxyethyl)pyridine-κ²N,O)nickel(II) dinitrate top

Crystal data top

[Ni(C₇H₉NO)₂(H₂O)₂](NO₃)₂	Z = 1
M_r = 465.05	F(000) = 242
Triclinic, P1	D_x = 1.664 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.782 (5) Å	Cell parameters from 1536 reflections
b = 8.185 (5) Å	θ = 2.8–33.8°
c = 8.811 (5) Å	µ = 1.11 mm⁻¹
α = 96.785 (5)°	T = 293 K
β = 113.856 (5)°	Prism, green
γ = 109.140 (5)°	0.18 × 0.11 × 0.08 mm
V = 464.0 (5) Å³

Data collection top

Bruker APEXII diffractometer	2471 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.019
Graphite monochromator	θ_max = 29.1°, θ_min = 3.0°
φ scans	h = −11→11
2478 measured reflections	k = −11→11
2478 independent reflections	l = −12→11

Refinement top

Refinement on F²	4 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F² > 2σ(F²)] = 0.018	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.051	w = 1/[σ²(F_o²) + (0.0235P)² + 0.1863P] where P = (F_o² + 2F_c²)/3
S = 1.08	(Δ/σ)_max < 0.001
2478 reflections	Δρ_max = 0.42 e Å⁻³
133 parameters	Δρ_min = −0.29 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Ni1	0.500000	0.500000	1.000000	0.01030 (6)
O1W	0.76119 (11)	0.49746 (9)	0.98827 (9)	0.01538 (14)
H2W	0.870471	0.591206	1.051410	0.023*
H1W	0.786623	0.405991	1.002286	0.023*
O1	0.36368 (11)	0.22139 (9)	0.92461 (9)	0.01563 (14)
H1	0.312496	0.167495	0.978813	0.023*
O3	0.88841 (12)	0.18215 (11)	0.80898 (10)	0.02212 (16)
O4	0.81394 (14)	0.18243 (11)	1.02219 (11)	0.02427 (17)
O2	0.77192 (14)	−0.06798 (10)	0.86796 (11)	0.02611 (18)
N1	0.36503 (12)	0.49127 (11)	0.73709 (10)	0.01265 (15)
N2	0.82483 (13)	0.09922 (11)	0.89982 (11)	0.01520 (16)
C2	0.26126 (17)	0.10590 (13)	0.75001 (13)	0.01930 (19)
H2B	0.116946	0.085298	0.694728	0.023*
H2A	0.268633	−0.009987	0.751370	0.023*
C3	0.36373 (16)	0.19383 (13)	0.64843 (13)	0.01691 (18)
H3A	0.511649	0.232402	0.715215	0.020*
H3B	0.315995	0.104372	0.541211	0.020*
C7	0.24432 (16)	0.64650 (14)	0.52920 (13)	0.01830 (19)
H7	0.220254	0.747349	0.506920	0.022*
C6	0.20270 (16)	0.50690 (15)	0.39547 (13)	0.01914 (19)
H6	0.151505	0.513073	0.281924	0.023*
C8	0.32254 (15)	0.63218 (13)	0.69660 (12)	0.01527 (17)
H8	0.346937	0.724379	0.785476	0.018*
C4	0.32151 (14)	0.35408 (13)	0.60574 (12)	0.01359 (17)
C5	0.23876 (16)	0.35837 (14)	0.43420 (12)	0.01737 (18)
H5	0.207865	0.261841	0.346023	0.021*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Ni1	0.01338 (8)	0.00887 (8)	0.00873 (8)	0.00453 (6)	0.00534 (6)	0.00257 (6)
O1W	0.0160 (3)	0.0134 (3)	0.0175 (3)	0.0064 (3)	0.0085 (3)	0.0041 (3)
O1	0.0221 (3)	0.0099 (3)	0.0129 (3)	0.0034 (3)	0.0092 (3)	0.0027 (2)
O3	0.0254 (4)	0.0203 (4)	0.0214 (4)	0.0055 (3)	0.0140 (3)	0.0093 (3)
O4	0.0394 (5)	0.0201 (4)	0.0242 (4)	0.0169 (3)	0.0210 (4)	0.0073 (3)
O2	0.0401 (5)	0.0120 (3)	0.0290 (4)	0.0060 (3)	0.0232 (4)	0.0038 (3)
N1	0.0150 (3)	0.0124 (3)	0.0109 (3)	0.0058 (3)	0.0062 (3)	0.0035 (3)
N2	0.0148 (4)	0.0143 (4)	0.0157 (4)	0.0055 (3)	0.0069 (3)	0.0042 (3)
C2	0.0266 (5)	0.0106 (4)	0.0149 (4)	0.0034 (4)	0.0088 (4)	0.0006 (3)
C3	0.0241 (5)	0.0144 (4)	0.0140 (4)	0.0097 (4)	0.0097 (4)	0.0026 (3)
C7	0.0214 (5)	0.0195 (5)	0.0160 (4)	0.0103 (4)	0.0081 (4)	0.0090 (4)
C6	0.0200 (4)	0.0248 (5)	0.0116 (4)	0.0086 (4)	0.0065 (4)	0.0072 (4)
C8	0.0186 (4)	0.0144 (4)	0.0136 (4)	0.0076 (3)	0.0075 (3)	0.0046 (3)
C4	0.0144 (4)	0.0139 (4)	0.0121 (4)	0.0049 (3)	0.0069 (3)	0.0026 (3)
C5	0.0188 (4)	0.0198 (4)	0.0111 (4)	0.0065 (4)	0.0067 (3)	0.0018 (3)

Geometric parameters (Å, º) top

Ni1—O1ⁱ	2.0622 (14)	C2—C3	1.5193 (15)
Ni1—O1	2.0622 (14)	C2—H2B	0.9700
Ni1—O1Wⁱ	2.0831 (15)	C2—H2A	0.9700
Ni1—O1W	2.0831 (15)	C3—C4	1.5063 (15)
Ni1—N1	2.1019 (14)	C3—H3A	0.9700
Ni1—N1ⁱ	2.1019 (14)	C3—H3B	0.9700
O1W—H2W	0.8426	C7—C8	1.3861 (15)
O1W—H1W	0.8451	C7—C6	1.3891 (16)
O1—C2	1.4374 (14)	C7—H7	0.9300
O1—H1	0.8184	C6—C5	1.3848 (16)
O3—N2	1.2548 (12)	C6—H6	0.9300
O4—N2	1.2537 (12)	C8—H8	0.9300
O2—N2	1.2520 (14)	C4—C5	1.3930 (15)
N1—C8	1.3485 (14)	C5—H5	0.9300
N1—C4	1.3570 (13)

O1ⁱ—Ni1—O1	180.0	O1—C2—C3	109.66 (9)
O1ⁱ—Ni1—O1Wⁱ	90.74 (4)	O1—C2—H2B	109.7
O1—Ni1—O1Wⁱ	89.26 (4)	C3—C2—H2B	109.7
O1ⁱ—Ni1—O1W	89.26 (4)	O1—C2—H2A	109.7
O1—Ni1—O1W	90.74 (4)	C3—C2—H2A	109.7
O1Wⁱ—Ni1—O1W	180.0	H2B—C2—H2A	108.2
O1ⁱ—Ni1—N1	91.32 (3)	C4—C3—C2	113.88 (9)
O1—Ni1—N1	88.68 (3)	C4—C3—H3A	108.8
O1Wⁱ—Ni1—N1	90.00 (4)	C2—C3—H3A	108.8
O1W—Ni1—N1	90.00 (4)	C4—C3—H3B	108.8
O1ⁱ—Ni1—N1ⁱ	88.68 (3)	C2—C3—H3B	108.8
O1—Ni1—N1ⁱ	91.32 (3)	H3A—C3—H3B	107.7
O1Wⁱ—Ni1—N1ⁱ	90.00 (4)	C8—C7—C6	118.53 (10)
O1W—Ni1—N1ⁱ	90.00 (4)	C8—C7—H7	120.7
N1—Ni1—N1ⁱ	180.0	C6—C7—H7	120.7
Ni1—O1W—H2W	114.9	C5—C6—C7	118.83 (10)
Ni1—O1W—H1W	117.1	C5—C6—H6	120.6
H2W—O1W—H1W	108.6	C7—C6—H6	120.6
C2—O1—Ni1	125.84 (6)	N1—C8—C7	123.30 (9)
C2—O1—H1	107.8	N1—C8—H8	118.3
Ni1—O1—H1	120.3	C7—C8—H8	118.3
C8—N1—C4	117.93 (9)	N1—C4—C5	121.60 (9)
C8—N1—Ni1	118.03 (6)	N1—C4—C3	118.57 (9)
C4—N1—Ni1	124.03 (7)	C5—C4—C3	119.83 (9)
O2—N2—O4	119.76 (9)	C6—C5—C4	119.75 (9)
O2—N2—O3	119.70 (9)	C6—C5—H5	120.1
O4—N2—O3	120.54 (9)	C4—C5—H5	120.1

Symmetry code: (i) −x+1, −y+1, −z+2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1W—H2W···O3ⁱⁱ	0.84	1.95	2.7870 (16)	176
O1W—H2W···N2ⁱⁱ	0.84	2.68	3.455 (2)	153
O1W—H1W···O4	0.85	1.93	2.7720 (19)	174
O1—H1···O2ⁱⁱⁱ	0.82	1.88	2.6952 (15)	172
O1—H1···N2ⁱⁱⁱ	0.82	2.65	3.4208 (17)	159
C2—H2B···O3^iv	0.97	2.64	3.378 (2)	133
C3—H3A···O1W	0.97	2.55	3.2278 (17)	127
C8—H8···O1ⁱ	0.93	2.49	3.0136 (19)	116
C8—H8···O4ⁱ	0.93	2.66	3.4448 (18)	143
C5—H5···O2^v	0.93	2.41	3.3076 (19)	163

Symmetry codes: (i) −x+1, −y+1, −z+2; (ii) −x+2, −y+1, −z+2; (iii) −x+1, −y, −z+2; (iv) x−1, y, z; (v) −x+1, −y, −z+1.

Comparison of distances and angles (Å, °) in 1 and 2 top

1
Ni1—O1	2.0622 (14)	2.07
Ni1—O1W	2.0831 (15)	2.10
Ni1—N1	2.1019 (14)	2.12
O2—N2	1.2520 (14)	1.23
O3—N2	1.2548 (12)	1.22
O4—N2	1.2537 (12)	1.27

O1—Ni1—O1W	90.74 (4)	93.00
O1—Ni1—N1	88.68 (3)	87.00
O1—Ni1—O1ⁱ	180	179.00
O1—Ni1—O1Wⁱ	89.26 (4)	91.8
O1—Ni1—N1ⁱ	91.32 (3)	92.3
O1W—Ni1—N1	90.00 (4)	92
O1ⁱ—Ni1—O1W	89.26 (4)	87.00
O1W—Ni1—O1Wⁱ	180	178.2
O1W—Ni1—N1ⁱ	90.00 (4)	91.8
O1ⁱ—Ni1—N1	91.32 (3)	92.3
O1Wⁱ—Ni1—N1	90.00 (4)	91.8
N1—Ni1—N1ⁱ	180	179
O1ⁱ—Ni1—O1Wⁱ	90.74 (4)	87.5

O1W—Ni1—O1—C2	-79.99 (10)	80.02
N1ⁱ—Ni1—O1—C2	-170.01 (10)	166.70
O1—Ni1—N1—C4	-29.33 (10)	31.30
O1—Ni1—N1—C8	151.96 (9)	-147.60
O1Wⁱ—Ni1—N1—C4	-118.59 (9)	114.9
O1Wⁱ—Ni1—N1—C8	62.70 (9)	-64.00
2
Cu1—O1	2.01	2.08
Cu1—N1	2.02	1.99
Cu1—O1ⁱ	2.01	2.08
Cu1—N1ⁱ	2.02	1.99
Cu2—O2	2.05	2.08

N2—Cu2—N2ⁱⁱ	180	180.00
O1—Cu1—N1	92.39	90.60
O1—Cu1—O1ⁱ	180	180.00

O3—Cu1—O1—C1	-93.9	-98
O1—Cu1—N1—C7	-151.03	-153
N2—Cu2—O2—C8	151.24	148
Cu1—O1—C1—C2	-37.55.	-40
C7—N1—C3—C2	177	179
C7—N1—C3—C4	-0.5	-0.4

Comparison of selected geometrical parameters (%, Å, °) for Ni^II and Cu^II complexes bearing the Hep-H ligand top

Δ is dihedral angle between the basal MO₂N₂ square plane and the pyridine ring.

Ref.	R-factor	M—N	M—OH	M—O(R)	Δ	θ	φ
1	1.80	2.102 (1)	2.062 (1)	2.083 (2)	28.28 (4)	81.9 (1)	162.6 (1)
BOZJAD^a	3.80	2.102 (2)	2.065 (3)	2.084 (3)	28.4 (1)	80.6 (3)	163.4 (3)
HULYAO^b	3.22	2.073 (1)	2.064 (1)	2.085 (1)	30.37 (6)	78.7 (1)	156.3 (1)
EJEZEZ^c	2.58	2.082 (1)	2.089 (1)	2.090 (1)	30.88 (6)	99.0 (1)	346.8 (1)
FEFWIY^d	3.13	2.100 (2)	2.088 (1)	2.072 (2)	30.4 (1)	96.8 (2)	349.7 (2)
FEFWIY01^d	3.05	2.090 (1)	2.104 (1)	2.064 (1)	31.86 (8)	95.9 (1)	354.6 (2)
FEFWIY02^d	2.59	2.096 (1)	2.085 (1)	2.064 (1)	30.51 (7)	97.9 (1)	346.1 (1)
BOZJOR^a	3.75	2.078 (2)	2.096 (1)	2.063 (2)	37.6 (1)	89.2 (2)	175.3 (2)
BOZJUX^a	3.03	2.083 (1)	2.114 (1)	2.052 (1)	35.43 (8)	94.3 (1)	352.5 (2)
BOZKAE^a	4.36	2.098 (2)	2.096 (2)	2.064 (2)	29.9 (1)	81.9 (2)	160.4 (2)
RAJQOL^e	4.07	2.083 (2)	2.057 (2)	2.112 (2)	31.9 (1)	84.5 (2)	167.7 (2)

2 NABBEA01^f	1.9	2.025 (2) 1.988 (2)	2.012 (2) 2.055 (1)	2.380 (1) 2.298 (1)	28.5 (1) 38.0 (1)	79.2 (1) 87.8 (1)	159.9 (1) 176.2 (1)
NABBEA^g	5.2	1.993 (4) 2.031 (4)	2.070 (4) 2.016 (4)	2.298 (4) 2.387 (4)	37.5 (2) 28.8 (2)	87.5 (3) 100.3 (4)	175.9 (3) 340.6 (4)
HAYHAS^h	2.8	2.032 (2)	2.422 (1)	1.982 (1)	29.50 (7)	81.9 (1)	171.9 (1)
IREREDⁱ	4.04	2.017 (2)	2.385 (2)	2.025 (2)	31.0 (1)	94.4 (2)	356.0 (2)
OJOBAQ^j	2.35	2.009 (1)	2.041 (1)	2.312 (1)	33.96 (4)	98.6 (1)	340.0 (1)
SOJGAB^k	3.52	2.029 (2)	2.428 (2)	1.998 (1)	25.97 (8)	101.4 (2)	346.6 (2)
UGAROK^l	3.44	2.021 (2) 2.030 (2)	2.019 (2) 2.024 (2)	2.357 (2) 2.346 (2)	31.4 (1) 32.5 (1)	95.9 (2) 80.6 (2)	345.3 (2) 167.0 (2)

Notes: (a) Trdin et al. (2015); (b) Hamamci et al. (2002); (c) Yilmaz et al. (2011); (d) Trdin & Lah (2012); (e) Çolak et al. (2017); (f) Zeghouan et al. (2016); (g) Zienkiewicz-Machnik et al. (2016); (h) Lapanje et al. (2012); (i) Pothiraja et al. (2011); (j) Yilmaz et al. (2003); (k) Caglar et al. (2014); (l) Yeşılel et al. (2009).

The calculated optical transition energies (nm) and their corresponding oscillator strengths (f) (ev) for 1 and 2 top

λ	f	E	Transition	Type
1
286	0.03	4.33	HOMO-2 to LUMO	LMTC
280	0.01	4.42	HOMO-3 to LUMO	LMTC
2
507	0.009	2.44	HOMO-4 to LUMO	LMTC
443	0.08	4.03	HOMO-5 to LUMO	LMTC
244	0.07	5.81	HOMO-2 to LUMO+1	LLTC

Funding information

This work was supported by the Unité de Recherche de Chimie de l'Environnement et Moléculaire Structurale (URCHEMS), Université Frères Mentouri Constantine, Algeria and the Biotechnology Research Center (CRBt), Constantine, Algeria. Thanks are due to MESRS and ATRST (Ministère de l'Enseignement Supérieur et de la Recherche Scientifique et l'Agence Thématique de Recherche en Sciences et Technologie, Algeria) for financial support via the PNR program.

References

Antonioli, B., Bray, D. J., Clegg, J. K., Jolliffe, K. A., Gloe, K., Gloe, K. & Lindoy, L. F. (2007). Polyhedron, 26, 673–678. Web of Science CSD CrossRef CAS Google Scholar
Baerends, E. J., Ellis, D. E. & Ros, P. (1973). J. Chem. Phys. 2(1), 41–51. Google Scholar
Bauernschmitt, R. & Ahlrichs, R. (1996). J. Chem. Phys. 104, 9047–9052. CrossRef CAS Web of Science Google Scholar
Bruker (2006). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA. Google Scholar
Burla, M. C., Camalli, M., Carrozzini, B., Cascarano, G. L., Giacovazzo, C., Polidori, G. & Spagna, R. (2003). J. Appl. Cryst. 36, 1103. CrossRef IUCr Journals Google Scholar
Burnett, M. N. & Johnson, C. K. (1996). ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA. Google Scholar
Caglar, S., Saykal, T., Buyukgungor, O. & Sahin, E. (2014). Synth. React. Inorg. Met.-Org. Nano-Met. Chem. 44, 1234–1242. Web of Science CrossRef Google Scholar
Çolak, A. T., Günay, H., Temel, E., Büyükgüngör, O. & Çolak, F. (2017). Transit. Met. Chem. 42, 85–93. Google Scholar
Comba, P. & Remenyi, R. (2003). Coord. Chem. Rev. 238, 9–20. Web of Science CrossRef Google Scholar
Farrugia, L. J. (2012). J. Appl. Cryst. 45, 849–854. Web of Science CrossRef CAS IUCr Journals Google Scholar
Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171–179. Web of Science CSD CrossRef IUCr Journals Google Scholar
Gross, E. U. K., Dobson, J. F. & Petersilka, M. (1996). Density Functional Theory of Time Dependent Phenomena in Topics in Current Chemistry – Density Functional Theory II, edited by K. Hafner, K. N. Houk, I. J. M. Lehn, K. N. Raymond, C. W. Rees, J. Thiem & F. Vogtle, pp. 81–172. Berlin: Springer. Google Scholar
Gross, E. K. U. & Kohn, W. (1990). Adv. Quantum Chem. 21, 255–291. CrossRef CAS Google Scholar
Hamamci, S., Yilmaz, V. T. & Thöne, C. (2002). Acta Cryst. E58, m700–m701. Web of Science CSD CrossRef IUCr Journals Google Scholar
Huang, Q.-Y., Yang, Y. & Meng, X.-R. (2015). Acta Cryst. C71, 701–705. Web of Science CSD CrossRef IUCr Journals Google Scholar
Kelley, T. W., Baude, P. F., Gerlach, C., Ender, D. E., Muyres, D., Haase, M. A., Vogel, D. E. & Theiss, S. D. (2004). Chem. Mater. 16, 4413–4422. Web of Science CrossRef CAS Google Scholar
Kim, Y.-I., Song, Y.-K., Kim, D. & Kang, S. K. (2015). Acta Cryst. C71, 908–911. Web of Science CrossRef IUCr Journals Google Scholar
Kong, L.-Q., Ju, X.-P. & Li, D.-C. (2009). Acta Cryst. E65, m1518. Web of Science CSD CrossRef IUCr Journals Google Scholar
Lapanje, K., Leban, I. & Lah, N. (2012). Acta Cryst. E68, m599. CSD CrossRef IUCr Journals Google Scholar
Leitl, M. J., Zink, D. M., Schinabeck, A., Baumann, T., Volz, D. & Yersin, H. (2016). Top Curr Chem (Z), 374, 25–68. Web of Science CrossRef Google Scholar
Ley, A. N., Dunaway, L. E., Brewster, T. P., Dembo, M. D., Harris, T. D., Baril-Robert, F., Li, X., Patterson, H. H. & Pike, R. D. (2010). Chem. Commun. 46, 4565–4567. Web of Science CrossRef Google Scholar
Lin, R.-G., Wang, Y.-L. & Liang, Q. (2015). Acta Cryst. C71, 44–47. Web of Science CrossRef IUCr Journals Google Scholar
Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453–457. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Martínez, A., Lorenzo, J., Prieto, M. J., Font-Bardia, M., Solans, X., Avilés, F. X. & Moreno, V. (2007). Bioorg. Med. Chem. 15, 969–979. Google Scholar
Mobin, Sh. M., Srivastava, A. K., Mathur, P. & Lahiri, G. K. (2010). Dalton Trans. 39, 1447–1449. Web of Science CrossRef Google Scholar
Perdew, J. P., Burke, K. & Ernzerhof, M. (1997). Phys. Rev. Lett. 78, 1396–1396. CrossRef CAS Web of Science Google Scholar
Pothiraja, R., Sathiyendiran, M., Steiner, A. & Murugavel, R. (2011). Inorg. Chim. Acta, 372, 347–352. Web of Science CSD CrossRef CAS Google Scholar
Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8. Web of Science CrossRef IUCr Journals Google Scholar
Spek, A. L. (2009). Acta Cryst. D65, 148–155. Web of Science CrossRef CAS IUCr Journals Google Scholar
Stamatatos, T. C., Boudalis, A. K., Pringouri, K. V., Raptopoulou, C. P., Terzis, A., Wolowska, J., McInnes, E. J. L. & Perlepes, S. P. (2007). Eur. J. Inorg. Chem. pp. 5098–5104. Web of Science CSD CrossRef Google Scholar
Trdin, M. & Lah, N. (2012). Acta Cryst. C68, m359–m362. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Trdin, M., Leban, I. & Lah, N. (2015). Acta Chim. Slov. 62, 249–254. Web of Science CrossRef Google Scholar
Wang, F.-M., Lu, C.-S., Li, Y.-Z. & Meng, Q.-J. (2010). Acta Cryst. E66, m594. Web of Science CSD CrossRef IUCr Journals Google Scholar
Yeşılel, O. Z., Erer, H., Soylu, M. S. & Büyükgüngör, O. (2009). J. Coord. Chem. 62, 2438–2448. Google Scholar
Yilmaz, V. T., Hamamci, S. & Thöne, C. (2003). J. Coord. Chem. 56, 787–795. Web of Science CSD CrossRef CAS Google Scholar
Yilmaz, V. T., Yilmaz, F., Guney, E. & Buyukgungor, O. (2011). J. Coord. Chem. 64, 159–169. Web of Science CrossRef CAS Google Scholar
Zeghouan, O., Bendjeddou, L., Dems, M. A. & Merazig, H. (2016). Private communication (refcode 1481676). CCDC, Cambridge, England. Google Scholar
Zeghouan, O., Guenifa, F., Hadjadj, N., Bendjeddou, L. & Merazig, H. (2013). Acta Cryst. E69, m439–m440. CrossRef IUCr Journals Google Scholar
Zienkiewicz-Machnik, M., Masternak, J., Kazimierczuk, K. & Barszcz, B. (2016). J. Mol. Struct. 1126, 37–46. Google Scholar

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