metal-organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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ISSN: 2056-9890

Di­chlorido(2-{[2-(piperazin-4-ium-1-yl)eth­yl]imino­meth­yl}phenolate)cadmium(II)

aDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
*Correspondence e-mail: khaledi@siswa.um.edu.my

(Received 8 August 2010; accepted 12 August 2010; online 18 August 2010)

In the title compound, [CdCl2(C13H19N3O)], the CdII ion is penta­coordinated with the N,N,O-tridentate Schiff base 2-{[2-(piperazin-4-ium-1-yl)eth­yl]imino­meth­yl}phenolate ligand and two Cl atoms in a highly distorted square-pyramidal geometry; the piperazine ring adopts a chair conformation. In the crystal structure, adjacent mol­ecules are linked together via N—H⋯O and N—H⋯Cl hydrogen bonds, forming infinite layers parallel to the ab plane. The layers are further connected through C—H⋯Cl inter­actions into a three-dimensional network.

Related literature

For related structures, see: Mukhopadhyay et al. (2003[Mukhopadhyay, S., Mandal, D., Ghosh, D., Goldberg, I. & Chaudhury, M. (2003). Inorg. Chem. 42, 8439-8445.]); Xu et al. (2008[Xu, R. B., Xu, X. Y., Wang, M. Y., Wang, D. Q., Yin, T., Xu, G. X., Yang, X. J., Lu, L. D., Wang, X. & Lei, Y. J. (2008). J. Coord. Chem. 61, 3306-3313.]).

[Scheme 1]

Experimental

Crystal data
  • [CdCl2(C13H19N3O)]

  • Mr = 416.61

  • Orthorhombic, P b c a

  • a = 14.7512 (16) Å

  • b = 13.1406 (15) Å

  • c = 16.6188 (19) Å

  • V = 3221.4 (6) Å3

  • Z = 8

  • Mo Kα radiation

  • μ = 1.69 mm−1

  • T = 100 K

  • 0.45 × 0.39 × 0.18 mm

Data collection
  • Bruker APEXII CCD diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996[Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.]) Tmin = 0.518, Tmax = 0.751

  • 38841 measured reflections

  • 3700 independent reflections

  • 3409 reflections with I > 2σ(I)

  • Rint = 0.041

Refinement
  • R[F2 > 2σ(F2)] = 0.017

  • wR(F2) = 0.045

  • S = 1.06

  • 3700 reflections

  • 187 parameters

  • 2 restraints

  • H atoms treated by a mixture of independent and constrained refinement

  • Δρmax = 0.44 e Å−3

  • Δρmin = −0.28 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N3—H3A⋯Cl1i 0.89 (2) 2.53 (2) 3.3108 (14) 146 (2)
N3—H3A⋯Cl2ii 0.89 (2) 2.78 (2) 3.2689 (14) 116 (2)
N3—H3B⋯O1ii 0.89 (2) 1.80 (2) 2.6743 (17) 167 (2)
C11—H11B⋯Cl2 0.99 2.70 3.6372 (16) 157
C13—H13B⋯Cl1 0.99 2.78 3.4302 (16) 124
C4—H4⋯Cl1iii 0.95 2.80 3.7165 (17) 161
C13—H13A⋯Cl1i 0.99 2.82 3.5851 (16) 134
Symmetry codes: (i) [-x+{\script{3\over 2}}, y+{\script{1\over 2}}, z]; (ii) [-x+2, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]; (iii) [x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}].

Data collection: APEX2 (Bruker, 2007[Bruker (2007). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2007[Bruker (2007). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: X-SEED (Barbour, 2001[Barbour, L. J. (2001). J. Supramol. Chem. 1, 189-191.]); software used to prepare material for publication: SHELXL97 and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information


Comment top

The title compound is a cadmium (II) complex of the Schiff base ligand, 1-(2-salicylaldiminoethyl)piperazine. The piperazinyl arm of the ligand can, in principle, have both boat and chair conformations that makes the molecule to display ambidentate coordination behavior. The ligand has been shown to act as a tetradentate or tridentate chelate with nickel(II) ions, depending on the piperazine ring conformation (Mukhopadhyay et al., 2003). In the title complex, the piperazine ring adopts the chair conformation and the ligand is bound to the metal ion in a NNO-tridentate fashion. The cadmium(II) atom is penta-coordinated by the Schiff base ligand and two chloride atoms in a highly distorted square planar geometry (index τ = 0.38). The piperzaine nitrogen atom, N3, which stays away from coordination, is protonated, implying the zwitterionic nature of the complex. In the crystal structure, intermolecular N—H···O, N—H···Cl and C—H···Cl hydrogen bonds connect the adjacent molecules into infinite three-dimensional network (Fig. 2). Morever, intramolecular C—H···Cl hydrogen bondings are observed. The crystal structure contains void spaces with the size of 199 Å-3 (6.2% of the cell volume) within which there is no evidence for included solvent.

Related literature top

For related structures, see: Mukhopadhyay et al. (2003); Xu et al. (2008).

Experimental top

The Schiff base ligand was prepared following the procedure reported previously (Mukhopadhyay et al., 2003). The cadmium (II) complex was synthesized by treatment of the ligand (0.233 g, 1 mmol) with cadmium (II) chloride (0.183 g, 1 mmol) in ethanol (20 ml). The mixture was stirred at room temperature for 10 min and then set aside for a few days whereupon the yellow crystals of the title compound were obtained.

Refinement top

The C-bound hydrogen atoms were placed at idealized positions (C—H = 0.95–0.99 Å) and were treated as riding on their parent atoms. The N-bound hydrogen atoms were located in a difference Fourier map and refined with distance restraint of N—H 0.88 (2) Å. The Uiso(H) were allowed at 1.2Ueq(C) or 1.5Ueq(N). The final difference map was essentially featurless.

Structure description top

The title compound is a cadmium (II) complex of the Schiff base ligand, 1-(2-salicylaldiminoethyl)piperazine. The piperazinyl arm of the ligand can, in principle, have both boat and chair conformations that makes the molecule to display ambidentate coordination behavior. The ligand has been shown to act as a tetradentate or tridentate chelate with nickel(II) ions, depending on the piperazine ring conformation (Mukhopadhyay et al., 2003). In the title complex, the piperazine ring adopts the chair conformation and the ligand is bound to the metal ion in a NNO-tridentate fashion. The cadmium(II) atom is penta-coordinated by the Schiff base ligand and two chloride atoms in a highly distorted square planar geometry (index τ = 0.38). The piperzaine nitrogen atom, N3, which stays away from coordination, is protonated, implying the zwitterionic nature of the complex. In the crystal structure, intermolecular N—H···O, N—H···Cl and C—H···Cl hydrogen bonds connect the adjacent molecules into infinite three-dimensional network (Fig. 2). Morever, intramolecular C—H···Cl hydrogen bondings are observed. The crystal structure contains void spaces with the size of 199 Å-3 (6.2% of the cell volume) within which there is no evidence for included solvent.

For related structures, see: Mukhopadhyay et al. (2003); Xu et al. (2008).

Computing details top

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. Displacement ellipsoid plot of the title compound at the 50% probability level. H atoms are drawn as spheres of arbitrary radius.
[Figure 2] Fig. 2. Unit-cell packing of the title compound, viewed down the b axis, showing the hydrogen-bonded polymeric network. H atoms not involved in hydrogen bonds have been omitted for clarity.
Dichlorido(2-{[2-(piperazin-4-ium-1-yl)ethyl]iminomethyl}phenolate)cadmium(II) top
Crystal data top
[CdCl2(C13H19N3O)]F(000) = 1664
Mr = 416.61Dx = 1.718 Mg m3
Orthorhombic, PbcaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2abCell parameters from 9877 reflections
a = 14.7512 (16) Åθ = 2.4–31.3°
b = 13.1406 (15) ŵ = 1.69 mm1
c = 16.6188 (19) ÅT = 100 K
V = 3221.4 (6) Å3Block, yellow
Z = 80.45 × 0.39 × 0.18 mm
Data collection top
Bruker APEXII CCD
diffractometer
3700 independent reflections
Radiation source: fine-focus sealed tube3409 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.041
φ and ω scansθmax = 27.5°, θmin = 2.4°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 1919
Tmin = 0.518, Tmax = 0.751k = 1717
38841 measured reflectionsl = 2121
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)] = 0.017Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.045H atoms treated by a mixture of independent and constrained refinement
S = 1.06 w = 1/[σ2(Fo2) + (0.0187P)2 + 2.1332P]
where P = (Fo2 + 2Fc2)/3
3700 reflections(Δ/σ)max = 0.002
187 parametersΔρmax = 0.44 e Å3
2 restraintsΔρmin = 0.28 e Å3
Crystal data top
[CdCl2(C13H19N3O)]V = 3221.4 (6) Å3
Mr = 416.61Z = 8
Orthorhombic, PbcaMo Kα radiation
a = 14.7512 (16) ŵ = 1.69 mm1
b = 13.1406 (15) ÅT = 100 K
c = 16.6188 (19) Å0.45 × 0.39 × 0.18 mm
Data collection top
Bruker APEXII CCD
diffractometer
3700 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
3409 reflections with I > 2σ(I)
Tmin = 0.518, Tmax = 0.751Rint = 0.041
38841 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0172 restraints
wR(F2) = 0.045H atoms treated by a mixture of independent and constrained refinement
S = 1.06Δρmax = 0.44 e Å3
3700 reflectionsΔρmin = 0.28 e Å3
187 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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
Cd10.915609 (7)0.521115 (8)0.335271 (6)0.01335 (4)
Cl10.80478 (3)0.46142 (3)0.23256 (2)0.02000 (8)
Cl21.05575 (2)0.57074 (3)0.26583 (2)0.01803 (8)
O10.98159 (7)0.37354 (9)0.37625 (7)0.0192 (2)
N10.87369 (9)0.52146 (10)0.46665 (8)0.0162 (3)
N20.83315 (8)0.68754 (10)0.35360 (8)0.0139 (2)
N30.88695 (9)0.83051 (10)0.22922 (8)0.0149 (2)
H3A0.8533 (12)0.8859 (13)0.2359 (11)0.022*
H3B0.9244 (12)0.8437 (16)0.1887 (11)0.022*
C10.95272 (10)0.31114 (12)0.43163 (9)0.0169 (3)
C20.96780 (11)0.20498 (12)0.42363 (10)0.0195 (3)
H20.99670.18020.37650.023*
C30.94174 (11)0.13662 (13)0.48221 (10)0.0220 (3)
H30.95230.06600.47420.026*
C40.90004 (11)0.16929 (13)0.55317 (10)0.0213 (3)
H40.88370.12210.59400.026*
C50.88317 (10)0.27220 (13)0.56245 (9)0.0194 (3)
H50.85500.29530.61050.023*
C60.90643 (10)0.34411 (12)0.50271 (9)0.0167 (3)
C70.87494 (10)0.44702 (13)0.51703 (9)0.0172 (3)
H70.85270.46110.56950.021*
C80.83000 (10)0.61616 (12)0.49269 (9)0.0178 (3)
H8A0.87660.66570.51000.021*
H8B0.78950.60240.53890.021*
C90.77532 (10)0.66006 (12)0.42318 (9)0.0172 (3)
H9A0.72960.60950.40580.021*
H9B0.74260.72140.44190.021*
C100.88602 (10)0.77994 (12)0.37278 (9)0.0164 (3)
H10A0.92540.76620.41980.020*
H10B0.84400.83570.38740.020*
C110.94408 (10)0.81319 (12)0.30220 (9)0.0158 (3)
H11A0.97650.87680.31620.019*
H11B0.98990.76020.29060.019*
C120.82875 (10)0.74064 (12)0.21146 (9)0.0166 (3)
H12A0.86740.68250.19540.020*
H12B0.78780.75670.16600.020*
C130.77292 (10)0.71146 (12)0.28467 (9)0.0158 (3)
H13A0.73210.76840.29920.019*
H13B0.73500.65140.27190.019*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd10.01279 (7)0.01314 (7)0.01412 (7)0.00111 (4)0.00214 (4)0.00129 (4)
Cl10.01838 (18)0.01817 (18)0.02346 (19)0.00298 (14)0.00124 (14)0.00369 (14)
Cl20.01453 (16)0.01461 (17)0.02495 (19)0.00003 (13)0.00517 (14)0.00176 (14)
O10.0201 (5)0.0189 (5)0.0186 (5)0.0057 (4)0.0045 (4)0.0040 (4)
N10.0132 (6)0.0189 (7)0.0164 (6)0.0015 (5)0.0010 (5)0.0002 (5)
N20.0117 (6)0.0146 (6)0.0153 (6)0.0007 (5)0.0005 (5)0.0009 (5)
N30.0153 (6)0.0127 (6)0.0166 (6)0.0006 (5)0.0005 (5)0.0007 (5)
C10.0134 (7)0.0180 (7)0.0192 (7)0.0003 (6)0.0030 (6)0.0024 (6)
C20.0174 (7)0.0190 (8)0.0222 (8)0.0013 (6)0.0020 (6)0.0017 (6)
C30.0178 (7)0.0175 (8)0.0306 (9)0.0017 (6)0.0083 (6)0.0054 (7)
C40.0167 (7)0.0244 (8)0.0229 (8)0.0052 (6)0.0065 (6)0.0098 (7)
C50.0147 (7)0.0273 (8)0.0161 (7)0.0045 (6)0.0034 (6)0.0050 (6)
C60.0143 (7)0.0198 (8)0.0158 (7)0.0019 (6)0.0024 (6)0.0034 (6)
C70.0128 (7)0.0241 (8)0.0147 (7)0.0013 (6)0.0000 (5)0.0003 (6)
C80.0183 (7)0.0195 (7)0.0156 (7)0.0017 (6)0.0035 (6)0.0006 (6)
C90.0139 (7)0.0179 (7)0.0198 (7)0.0011 (6)0.0040 (6)0.0009 (6)
C100.0153 (7)0.0168 (7)0.0172 (7)0.0021 (6)0.0004 (6)0.0023 (6)
C110.0139 (7)0.0155 (7)0.0179 (7)0.0019 (6)0.0009 (6)0.0003 (6)
C120.0164 (7)0.0157 (7)0.0177 (7)0.0023 (6)0.0025 (6)0.0004 (6)
C130.0124 (7)0.0157 (7)0.0192 (7)0.0007 (5)0.0020 (6)0.0009 (6)
Geometric parameters (Å, º) top
Cd1—N12.2693 (13)C4—C51.384 (2)
Cd1—O12.2740 (11)C4—H40.9500
Cd1—Cl22.4557 (4)C5—C61.413 (2)
Cd1—Cl12.4904 (4)C5—H50.9500
Cd1—N22.5209 (13)C6—C71.450 (2)
O1—C11.3042 (19)C7—H70.9500
N1—C71.288 (2)C8—C91.522 (2)
N1—C81.4667 (19)C8—H8A0.9900
N2—C101.4779 (19)C8—H8B0.9900
N2—C91.4816 (19)C9—H9A0.9900
N2—C131.4833 (19)C9—H9B0.9900
N3—C121.4897 (19)C10—C111.517 (2)
N3—C111.4943 (19)C10—H10A0.9900
N3—H3A0.889 (15)C10—H10B0.9900
N3—H3B0.887 (15)C11—H11A0.9900
C1—C21.419 (2)C11—H11B0.9900
C1—C61.432 (2)C12—C131.518 (2)
C2—C31.379 (2)C12—H12A0.9900
C2—H20.9500C12—H12B0.9900
C3—C41.398 (3)C13—H13A0.9900
C3—H30.9500C13—H13B0.9900
N1—Cd1—O180.22 (4)C5—C6—C7115.51 (14)
N1—Cd1—Cl2132.92 (3)C1—C6—C7124.80 (14)
O1—Cd1—Cl290.39 (3)N1—C7—C6127.33 (14)
N1—Cd1—Cl1118.77 (3)N1—C7—H7116.3
O1—Cd1—Cl1102.57 (3)C6—C7—H7116.3
Cl2—Cd1—Cl1108.309 (15)N1—C8—C9109.30 (12)
N1—Cd1—N275.55 (4)N1—C8—H8A109.8
O1—Cd1—N2155.52 (4)C9—C8—H8A109.8
Cl2—Cd1—N2103.45 (3)N1—C8—H8B109.8
Cl1—Cd1—N292.25 (3)C9—C8—H8B109.8
C1—O1—Cd1127.43 (9)H8A—C8—H8B108.3
C7—N1—C8117.32 (13)N2—C9—C8112.31 (12)
C7—N1—Cd1128.33 (11)N2—C9—H9A109.1
C8—N1—Cd1113.90 (9)C8—C9—H9A109.1
C10—N2—C9109.61 (12)N2—C9—H9B109.1
C10—N2—C13107.97 (12)C8—C9—H9B109.1
C9—N2—C13108.04 (11)H9A—C9—H9B107.9
C10—N2—Cd1118.96 (9)N2—C10—C11111.59 (12)
C9—N2—Cd199.25 (9)N2—C10—H10A109.3
C13—N2—Cd1112.30 (9)C11—C10—H10A109.3
C12—N3—C11111.41 (12)N2—C10—H10B109.3
C12—N3—H3A110.6 (13)C11—C10—H10B109.3
C11—N3—H3A109.8 (12)H10A—C10—H10B108.0
C12—N3—H3B111.3 (14)N3—C11—C10110.68 (12)
C11—N3—H3B107.1 (13)N3—C11—H11A109.5
H3A—N3—H3B106.4 (19)C10—C11—H11A109.5
O1—C1—C2120.06 (14)N3—C11—H11B109.5
O1—C1—C6123.22 (14)C10—C11—H11B109.5
C2—C1—C6116.72 (14)H11A—C11—H11B108.1
C3—C2—C1122.04 (16)N3—C12—C13110.73 (12)
C3—C2—H2119.0N3—C12—H12A109.5
C1—C2—H2119.0C13—C12—H12A109.5
C2—C3—C4121.21 (16)N3—C12—H12B109.5
C2—C3—H3119.4C13—C12—H12B109.5
C4—C3—H3119.4H12A—C12—H12B108.1
C5—C4—C3118.25 (15)N2—C13—C12110.34 (12)
C5—C4—H4120.9N2—C13—H13A109.6
C3—C4—H4120.9C12—C13—H13A109.6
C4—C5—C6122.12 (15)N2—C13—H13B109.6
C4—C5—H5118.9C12—C13—H13B109.6
C6—C5—H5118.9H13A—C13—H13B108.1
C5—C6—C1119.56 (15)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3A···Cl1i0.89 (2)2.53 (2)3.3108 (14)146 (2)
N3—H3A···Cl2ii0.89 (2)2.78 (2)3.2689 (14)116 (2)
N3—H3B···O1ii0.89 (2)1.80 (2)2.6743 (17)167 (2)
C11—H11B···Cl20.992.703.6372 (16)157
C13—H13B···Cl10.992.783.4302 (16)124
C4—H4···Cl1iii0.952.803.7165 (17)161
C13—H13A···Cl1i0.992.823.5851 (16)134
Symmetry codes: (i) x+3/2, y+1/2, z; (ii) x+2, y+1/2, z+1/2; (iii) x, y+1/2, z+1/2.

Experimental details

Crystal data
Chemical formula[CdCl2(C13H19N3O)]
Mr416.61
Crystal system, space groupOrthorhombic, Pbca
Temperature (K)100
a, b, c (Å)14.7512 (16), 13.1406 (15), 16.6188 (19)
V3)3221.4 (6)
Z8
Radiation typeMo Kα
µ (mm1)1.69
Crystal size (mm)0.45 × 0.39 × 0.18
Data collection
DiffractometerBruker APEXII CCD
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.518, 0.751
No. of measured, independent and
observed [I > 2σ(I)] reflections
38841, 3700, 3409
Rint0.041
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.017, 0.045, 1.06
No. of reflections3700
No. of parameters187
No. of restraints2
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.44, 0.28

Computer programs: APEX2 (Bruker, 2007), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), X-SEED (Barbour, 2001), SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2010).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N3—H3A···Cl1i0.889 (15)2.534 (16)3.3108 (14)146.4 (17)
N3—H3A···Cl2ii0.889 (15)2.775 (19)3.2689 (14)116.4 (15)
N3—H3B···O1ii0.887 (15)1.802 (15)2.6743 (17)167.4 (19)
C11—H11B···Cl20.992.703.6372 (16)157.4
C13—H13B···Cl10.992.783.4302 (16)123.9
C4—H4···Cl1iii0.952.803.7165 (17)161.2
C13—H13A···Cl1i0.992.823.5851 (16)134.4
Symmetry codes: (i) x+3/2, y+1/2, z; (ii) x+2, y+1/2, z+1/2; (iii) x, y+1/2, z+1/2.
 

Acknowledgements

The authors thank the University of Malaya for funding this study (FRGS grant No. FP009/2008 C).

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