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A new polymorph of a mononuclear nickel(II) acetate com­plex with 2-(pyridin-2-yl)ethanol ligands, [Ni(CH3COO)2(C7H9NO)2], has been prepared and structurally characterized. Its mol­ecular structure resembles the structures of two previously reported polymorphs in that the NiII atom is located on an inversion centre and is coordinated by pairs of acetate and 2-(pyridin-2-yl)ethanol ligands. The acetate anions are coordinated in a monodentate manner, while the 2-(pyridin-2-yl)ethanol ligands are coordinated in a bidentate chelating mode involving the endocyclic N atom and the hy­droxy O atom of the ligand side chain. A strong bifurcated intra­molecular hydrogen-bond inter­action was observed involving the hy­droxy O atom as donor and both acetate O atoms as acceptors. No classical inter­molecular hydrogen-bond contacts were observed. However, the crystal packing is effected through π–π and C—H...π inter­actions, giving rise to a different packing arrangement. A brief comparison of the three polymorphic forms is presented.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270112046422/sk3457sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270112046422/sk3457Isup2.hkl
Contains datablock I

CCDC reference: 915096

Comment top

The synthesis of new metal–organic hybrid materials remains one of the major trends in the field of coordination chemistry and crystal engineering (Liu et al., 2010; Perry et al., 2009; Robin & Fromm, 2006; Schubert, 2011). The successful preparation of such materials requires suitable ligands with the ability to link the metal centres into larger architectures. Simple pyridine alcohols are versatile N,O-coordinating ligands capable of binding to metal ions in a variety of coordination modes: (i) monodentate through the pyridine N atom only; (ii) bidentate chelating through the pyridine N atom and the hydroxy O atom; and (iii) bidentate bridging with the hydroxy O atom as a bridge between two metal centres. We are interested in the coordination behaviour of simple pyridine alcohols in general (Lah et al., 2006, 2010; Lapanje et al., 2012) and 2-(pyridin-2-yl)ethanol (2-pyEtOH) is an example. A search of the Cambridge Structural Database (Allen, 2002) reveals 39 structures of different transition metals with 2-pyEtOH in its neutral form. Among these, six are NiII complexes, five of which are mononuclear with an octahedral arrangement of ligands around the central NiII atom and the 2-pyEtOH ligand coordinated in a chelating manner (Kong et al., 2009; Yilmaz et al., 2011; Hamamci et al., 2002; Yesilel et al., 2008; Lv et al., 2010). Additionally, a trinuclear NiII complex was reported in which the metal centres are connected by deprotonated 2-pyEtOH ligands, while an additional neutral 2-pyEtOH molecule acts as a terminal ligand and is coordinated to a single NiII atom in a chelating manner (Kayser et al., 2010). Recently, we have reported the structures of two polymorphs of bis(acetato-κO)bis[2-(pyridin-2-yl)ethanol-κ2N,O]nickel(II), (I), that concomitantly crystallize from a mixture of nickel acetate and 2-pyEtOH in acetonitrile, viz. a monoclinic and a triclinic form, which are referred to as polymorphs A and B, respectively (Trdin et al. 2012). Our work has recently been devoted to the preparation of new coordination polymers with the intention of replacing acetate ligands with other multifunctional organic ligands. During attempts to prepare NiII–oxalate complexes with 2-pyEtOH, light-blue crystals were obtained and subsequently identified as a third polymorph of mononuclear (I), herein denoted as polymorph C. The molecular structure is shown in Fig. 1. The NiII atom is located on an inversion centre and is surrounded by two 2-pyEtOH ligands coordinated in a chelating manner and by two acetate anions coordinated as monodentate ligands through one of the two carboxylate O atoms. Thus, an almost perfect octahedral N2O4 geometry is achieved. The noncoordinated carboxylate O atom enhances the stability of the complex through a strong intramolecular hydrogen bond with the hydroxy group of the 2-pyEtOH ligand [O32···O1A = 2.533 (2) Å; Table 1]. An additional attractive intramolecular interaction exists between the hydroxy group and the coordinated acetate O atom [O31···O1A = 2.9585 (18) Å]. It should be noted that the coordination geometry and the overall molecular structure, including the bifurcated intramolecular hydrogen bond, is similar in all three polymorphs. A comparison of the crystal data for all three polymorphs is given in Table 2 and selected geometric parameters are listed in Table 3.

The three polymorphs differ primarily in their packing arrangement, which is governed by weak intermolecular interactions. Polymorph C crystallizes in the monoclinic space group P21/c with two molecules in the unit cell. The packing is dominated by ππ stacking interactions between the pyridine rings of neighbouring molecules related by an inversion centre [centroid–centroid distance = 4.236 (12) Å, interplanar distance = 3.4720 (11) Å and offset angle = 34.95°]. The mononuclear units are connected via these interactions into infinite chains running parallel to the ac diagonal. The chains interact to form two-dimensional layers through weak contacts between the methyl groups and the noncoordinated O atom of the acetate groups protruding from the chains (Fig. 2a).

The other monoclinic polymorph, A, also crystallizes in the space group P21/c with a unit-cell volume of 33.80 Å3 larger than that of polymorph C [951.76 (6) Å3]. Differences in the intermolecular interactions are reflected in the arrangement of the molecules in space: no ππ interactions were observed, well separated molecules are distributed as shown in Fig. 2(b.

Triclinic polymorph B crystallizes in the space group P1 with a unit-cell volume of 11.5 Å3 smaller than that of polymorph A and 22.3 Å3 larger that that of polymorph C. The structure contains two crystallographically distinct molecules, both possessing an inversion centre. Thus, the asymmetric unit consists of two halves of the monomeric molecules. The molecules are arranged in two types of layers; each layer contains a set of crystallographycally equivalent molecules related by translation only (Fig. 2c). Molecules in the first type of layer (denoted a) are brought closer by ππ interactions of the same type as observed in polymorph C. Molecules in the second type of layer (denoted b) are oriented with respect to each other with the methyl groups of the acetate ligands. Additionally, C—H···π interactions [point-to-face edge-on T-shaped geometry; see Janiak (2000) for details] are observed.

In summary, for monomeric (I), three polymorphic phases are known. Two of them (polymorphs A and B) crystallize concomitantly from the mixture of NiII acetate and 2-pyEtOH in acetonitrile. The polymorphic form C crystallizes from the mixture of NiII acetate, 2-pyEtOH and potassium oxalate in methanol. The oxalate anion did not participate in the coordination to the NiII centre but, apparently, plays a templating role. Crystals of all three polymorphic forms are stable but have significantly different densities. The `density rule' (Bernstein, 2002), often used as an indicator of thermodynamic stability of different polymorphic forms, is not obeyed in this particular case. Recently, the synthesis and structure of a copper analogue was reported (Lapanje et al., 2012). Its structure is isomorphic with polymorph A. No polymorphism has been detected in the case of a copper compound.

Related literature top

For related literature, see: Allen (2002); Bernstein (2002); Hamamci et al. (2002); Janiak (2000); Kayser et al. (2010); Kong et al. (2009); Lah & Leban (2010); Lah et al. (2006); Lapanje et al. (2012); Liu et al. (2010); Lv et al. (2010); Perry et al. (2009); Robin & Fromm (2006); Schubert (2011); Trdin et al. (2012); Yesilel et al. (2008); Yilmaz et al. (2011).

Experimental top

Potassium oxalate monohydrate (0.03 g, 0.16 mmol) was gradually added to a stirred solution of nickel(II) acetate tetrahydrate (0.2 g, 0.8 mmol) and 2-pyEtOH (0.2 ml, 1.8 mmol) in methanol (10 ml) at room temperature. Sodium methoxide (0.54 g, 1 mmol) was gradually added when the solution was heated to boiling point. The precipitate which formed was filtered off after 5 min of continuous stirring and heating. The remaining light-green solution was allowed to cool and was left to slowly evaporate under ambient conditions. Blue prismatic crystals were obtained from the green oil after a month.

Refinement top

All H atoms were initially found in a Fourier difference map, but were included in the final refinement cycles in calculated positions and refined as riding on their parent atoms. Aromatic H atoms were permitted to ride with C—H = 0.93 Å and Ueq(H) = 1.2UisoC, H atoms bonded to O atoms were permitted to ride with O—H = 0.82 Å and Ueq(H)=1.5iso(O), those of the CH2 groups with C—H = 0.97 Å and Ueq(H) = 1.2UisoC and those of the CH3 groups with C—H = 0.96 Å and Ueq(H) = 1.5UisoC.

Computing details top

Data collection: CrysAlis PRO (Agilent, 2011); cell refinement: CrysAlis PRO (Agilent, 2011); data reduction: CrysAlis PRO (Agilent, 2011); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009) and CrystalMaker (CrystalMaker, 2007).

Figures top
[Figure 1] Fig. 1. The molecular structure of polymorph C of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry code: (i) -x+1, -y, -z+1.]
[Figure 2] Fig. 2. Packing diagrams of (a) polymorph C, and (b) polymorph A, viewed along the b axis, and (c) polymorph B, viewed along the a axis.
Bis(acetato-κO)bis[2-(pyridin-2-yl)ethanol- κ2N,O]nickel(II) top
Crystal data top
[Ni(C2H3O2)2(C7H9NO)2]F(000) = 444
Mr = 423.10Dx = 1.476 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 2802 reflections
a = 8.4292 (3) Åθ = 2.8–30.4°
b = 12.4129 (4) ŵ = 1.06 mm1
c = 12.0850 (4) ÅT = 150 K
β = 131.175 (2)°Prismatic, blue
V = 951.76 (6) Å30.2 × 0.16 × 0.14 mm
Z = 2
Data collection top
Agilent SuperNova (Dual, Cu at zero, Atlas)
diffractometer
2178 independent reflections
Radiation source: SuperNova (Mo) X-ray Source1862 reflections with I > 2σ(I)
Mirror monochromatorRint = 0.032
Detector resolution: 10.4933 pixels mm-1θmax = 27.5°, θmin = 2.8°
ω scansh = 1010
Absorption correction: multi-scan
(CrysAlis PRO; Agilent, 2011)
k = 1612
Tmin = 0.812, Tmax = 1.000l = 1515
5104 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.031Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.075H-atom parameters constrained
S = 1.04 w = 1/[σ2(Fo2) + (0.0263P)2 + 0.3819P]
where P = (Fo2 + 2Fc2)/3
2178 reflections(Δ/σ)max = 0.025
126 parametersΔρmax = 0.32 e Å3
0 restraintsΔρmin = 0.34 e Å3
Crystal data top
[Ni(C2H3O2)2(C7H9NO)2]V = 951.76 (6) Å3
Mr = 423.10Z = 2
Monoclinic, P21/cMo Kα radiation
a = 8.4292 (3) ŵ = 1.06 mm1
b = 12.4129 (4) ÅT = 150 K
c = 12.0850 (4) Å0.2 × 0.16 × 0.14 mm
β = 131.175 (2)°
Data collection top
Agilent SuperNova (Dual, Cu at zero, Atlas)
diffractometer
2178 independent reflections
Absorption correction: multi-scan
(CrysAlis PRO; Agilent, 2011)
1862 reflections with I > 2σ(I)
Tmin = 0.812, Tmax = 1.000Rint = 0.032
5104 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0310 restraints
wR(F2) = 0.075H-atom parameters constrained
S = 1.04Δρmax = 0.32 e Å3
2178 reflectionsΔρmin = 0.34 e Å3
126 parameters
Special details top

Experimental. Absorption correction: CrysAlis PRO, Agilent Technologies, Version 1.171.35.11 (release 16–05-2011 CrysAlis171. NET) (compiled May 16 2011,17:55:39) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

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

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Ni10.50000.00000.50000.01492 (11)
N110.2163 (2)0.04986 (13)0.29641 (15)0.0169 (3)
C120.1659 (3)0.15434 (15)0.25796 (18)0.0199 (4)
C130.0312 (3)0.18454 (16)0.12683 (19)0.0243 (4)
H130.06490.25700.10330.029*
C140.1762 (3)0.10616 (17)0.03208 (19)0.0259 (4)
H140.30690.12510.05680.031*
C150.1241 (3)0.00049 (16)0.0713 (2)0.0230 (4)
H150.21910.05470.00920.028*
C160.0709 (3)0.02575 (16)0.20397 (19)0.0200 (4)
H160.10390.09780.23100.024*
C2A0.3283 (3)0.23731 (15)0.36254 (19)0.0247 (4)
H2A0.27430.30810.31890.030*
H2B0.45380.22500.37610.030*
C1A0.3889 (3)0.23659 (15)0.51194 (19)0.0262 (4)
H12A0.46880.30110.56560.031*
H12B0.26230.23710.49870.031*
O1A0.51246 (19)0.14359 (10)0.59543 (13)0.0224 (3)
H1A0.47080.11780.63480.034*
O310.32257 (18)0.07155 (10)0.54228 (13)0.0200 (3)
O320.3705 (2)0.04846 (13)0.70003 (14)0.0315 (3)
C310.2984 (3)0.03858 (16)0.62914 (18)0.0211 (4)
C320.1691 (3)0.10893 (19)0.6463 (2)0.0298 (5)
H32A0.17550.08060.72310.045*
H32B0.22450.18090.67110.045*
H32C0.02520.11000.55560.045*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ni10.01389 (17)0.01210 (17)0.01555 (17)0.00006 (11)0.00831 (14)0.00062 (11)
N110.0166 (7)0.0153 (8)0.0184 (7)0.0005 (6)0.0113 (6)0.0015 (6)
C120.0222 (9)0.0179 (10)0.0219 (8)0.0010 (7)0.0155 (8)0.0008 (7)
C130.0269 (9)0.0221 (10)0.0213 (9)0.0071 (8)0.0148 (8)0.0046 (7)
C140.0219 (9)0.0324 (12)0.0181 (8)0.0066 (8)0.0109 (8)0.0030 (8)
C150.0189 (9)0.0260 (11)0.0198 (9)0.0036 (7)0.0109 (8)0.0048 (7)
C160.0212 (9)0.0175 (9)0.0208 (9)0.0014 (7)0.0137 (8)0.0003 (7)
C2A0.0229 (9)0.0130 (9)0.0306 (10)0.0004 (7)0.0143 (8)0.0029 (7)
C1A0.0219 (9)0.0155 (10)0.0263 (9)0.0020 (7)0.0095 (8)0.0035 (7)
O1A0.0234 (6)0.0155 (7)0.0226 (6)0.0013 (5)0.0127 (5)0.0012 (5)
O310.0215 (6)0.0191 (7)0.0210 (6)0.0011 (5)0.0147 (5)0.0018 (5)
O320.0364 (8)0.0336 (9)0.0282 (7)0.0057 (7)0.0229 (7)0.0104 (6)
C310.0151 (8)0.0250 (10)0.0155 (8)0.0045 (7)0.0068 (7)0.0023 (7)
C320.0313 (10)0.0368 (13)0.0295 (10)0.0001 (9)0.0236 (9)0.0019 (9)
Geometric parameters (Å, º) top
Ni1—O31i2.0719 (12)C15—H150.9300
Ni1—O312.0719 (12)C16—H160.9300
Ni1—O1A2.0877 (13)C2A—C1A1.519 (3)
Ni1—O1Ai2.0877 (13)C2A—H2A0.9700
Ni1—N11i2.0996 (13)C2A—H2B0.9700
Ni1—N112.0996 (13)C1A—O1A1.432 (2)
N11—C121.349 (2)C1A—H12A0.9700
N11—C161.352 (2)C1A—H12B0.9700
C12—C131.395 (2)O1A—H1A0.8200
C12—C2A1.501 (2)O31—C311.262 (2)
C13—C141.381 (3)O32—C311.259 (2)
C13—H130.9300C31—C321.514 (3)
C14—C151.377 (3)C32—H32A0.9600
C14—H140.9300C32—H32B0.9600
C15—C161.379 (3)C32—H32C0.9600
O31i—Ni1—O31180.0C16—C15—H15120.5
O31—Ni1—O1A90.67 (5)N11—C16—C15122.76 (18)
O31i—Ni1—O1Ai90.67 (5)N11—C16—H16118.6
O31—Ni1—O1Ai89.33 (5)C15—C16—H16118.6
O31—Ni1—N1187.99 (5)C12—C2A—C1A113.79 (16)
O31i—Ni1—N11i87.99 (5)C12—C2A—H2A108.8
O31—Ni1—N11i92.01 (5)C1A—C2A—H2A108.8
O1A—Ni1—N1189.99 (5)C12—C2A—H2B108.8
O1Ai—Ni1—N11i89.99 (5)C1A—C2A—H2B108.8
O31i—Ni1—N1192.01 (5)H2A—C2A—H2B107.7
O31—Ni1—N1187.99 (5)O1A—C1A—C2A111.21 (15)
O1Ai—Ni1—N1190.01 (5)O1A—C1A—H12A109.4
N11i—Ni1—N11180.0C2A—C1A—H12A109.4
C12—N11—C16118.32 (15)O1A—C1A—H12B109.4
C12—N11—Ni1123.00 (11)C2A—C1A—H12B109.4
C16—N11—Ni1118.50 (12)H12A—C1A—H12B108.0
N11—C12—C13121.28 (16)C1A—O1A—H1A109.5
N11—C12—C2A117.64 (15)C31—O31—Ni1127.18 (12)
C13—C12—C2A121.07 (17)O32—C31—O31125.02 (18)
C14—C13—C12119.63 (18)O32—C31—C32118.08 (17)
C14—C13—H13120.2O31—C31—C32116.89 (17)
C12—C13—H13120.2C31—C32—H32A109.5
C15—C14—C13118.97 (17)C31—C32—H32B109.5
C15—C14—H14120.5H32A—C32—H32B109.5
C13—C14—H14120.5C31—C32—H32C109.5
C14—C15—C16118.99 (17)H32A—C32—H32C109.5
C14—C15—H15120.5H32B—C32—H32C109.5
Symmetry code: (i) x+1, y, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1A—H1A···O310.822.552.9585 (18)112
O1A—H1A···O320.821.722.533 (2)172

Experimental details

Crystal data
Chemical formula[Ni(C2H3O2)2(C7H9NO)2]
Mr423.10
Crystal system, space groupMonoclinic, P21/c
Temperature (K)150
a, b, c (Å)8.4292 (3), 12.4129 (4), 12.0850 (4)
β (°) 131.175 (2)
V3)951.76 (6)
Z2
Radiation typeMo Kα
µ (mm1)1.06
Crystal size (mm)0.2 × 0.16 × 0.14
Data collection
DiffractometerAgilent SuperNova (Dual, Cu at zero, Atlas)
diffractometer
Absorption correctionMulti-scan
(CrysAlis PRO; Agilent, 2011)
Tmin, Tmax0.812, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
5104, 2178, 1862
Rint0.032
(sin θ/λ)max1)0.649
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.031, 0.075, 1.04
No. of reflections2178
No. of parameters126
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.32, 0.34

Computer programs: CrysAlis PRO (Agilent, 2011), SHELXS97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1997), SHELXL97 (Sheldrick, 2008), PLATON (Spek, 2009) and CrystalMaker (CrystalMaker, 2007).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1A—H1A···O310.822.552.9585 (18)112
O1A—H1A···O320.821.722.533 (2)172
Comparison of crystal data for polymorphs A and B (Trdin et al., 2012) and C (this work). top
Polymorph APolymorph BPolymorph C
Crystal systemMonoclinicTriclinicMonoclinic
Space groupP21/cP1P21/c
Z424
a (Å)8.4777 (2)9.0784 (2)8.4292 (3)
b (Å)7.9182 (2)9.8113 (2)12.4129 (4)
c (°)15.1985 (3)12.3803 (2)12.0850 (4)
α (°)100.8972 (12)
β (°)104.983 (2)104.9007 (11)131.175 (2)
γ (°)107.3424 (12)
V3)985.56 (4)974.09 (3)951.76 (6)
Dcalc (Mg m-3)1.4261.4431.476
In order to retain the space group P21/c for comparison purposes, polymorph C is described using a nonreduced unit cell. The corresponding reduced cell is as follows: a = 8.4292 (3), b = 12.4129 (4), c = 9.1087 (3) Å and β = 92.976 (3)°.
Comparison of selected bond lengths (Å) and angles (°) in polymorphs A and B (Trdin et al.,2012) and C (this work). top
Polymorph A
Ni1—N112.0905 (14)O31—Ni1—N1188.09 (5)
Ni1—O1A2.1038 (12)O31—Ni1—O1A90.90 (5)
Ni1—O312.0643 (12)O1A—Ni1—N1188.93 (5)
Polymorph B
Ni1—N112.0955 (11)O31—Ni1—N1190.27 (4)
Ni1—O1A2.0850 (9)O31—Ni1—O1A90.03 (4)
Ni1—O312.0644 (10)O1A—Ni1—N1189.93 (4)
Ni2—N212.0833 (11)O41—Ni2—N2189.24 (4)
Ni2—O1B2.0828 (10)O41—Ni2—O1B89.71 (4)
Ni2—O412.0798 (10)O1B—Ni2—N2189.68 (4)
Polymorph C
Ni1—N112.0996 (13)O31—Ni1—N1187.99 (5)
Ni1—O1A2.0877 (13)O31—Ni1—O1A90.67 (5)
Ni1—O312.0719 (12)O1A—Ni1—N1189.99 (5)
 

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