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Acta Cryst. (2007). E63, m2235-m2236    [ doi:10.1107/S1600536807036604 ]

Diaquabis(pyridine-2-carboxylato)magnesium(II) 0.15-hydrate

M. A. Sharif, H. Aghabozorg, E. Motyeian, M. Ghadermazi and J. Attar Gharamaleki

Abstract top

The reaction of magnesium(II) chloride tetrahydrate with the proton-transfer compound piperazinediium pyridine-2-carboxylate, (pipzH2)(pyc)2 (pipz is pirerazine and pycH is pyridine-2-carboxylic acid) in aqueous solution leads to the formation of the title compound, [Mg(C6H4NO2)2(H2O)2]·0.15H2O. The Mg atom is six-coordinated in a distorted octahedral environment by two bidentate pyridine-2-carboxylate groups and two O atoms of coordinated water molecules, which are located in cis positions. In the crystal structure, intermolecular O-H...O and C-H...O hydrogen bonds, and [pi]-[pi] [[pi]-[pi] distance = 3.5616 (8) Å for pyridine rings; symmetry code: 2-x, 1-y, 1-z] and C-H...[pi] stacking, connect the various components into a supramolecular structure.

Comment top

Intermolecular interactions, such as hydrogen bonding, π–π stacking, ion pairing and donor acceptor interactions, are famous for making aggregates of molecules. One or more of these interactions may result in the formation of specific and spontaneous self-associations or self-assemblies of compounds. Research has shown that hydrogen bonding plays the key role in the preparation of self-assembled or self-associated compounds. There is a very close relationship between hydrogen bonding and formation of proton-transfer compounds (Aghabozorg et al., 2006). In order to develop new types of proton transfer compounds and hydrogen bonding systems, our research group has already selected pyridine-2,6-dicarboxylic acid (pydcH2) and 1,10-phenanthroline-2,9-dicarboxylic acid (phendcH2) as proton donors and pyridine-2,6-diamine (pyda), creatinine (creat) and propane-1,3-diamine (pda) as proton acceptors. These resulted in the formation of new proton transfer compounds (pydcH)(pydaH) (Aghabozorg et al., 2005), (creatH)(phendcH)·H2O (Soleimannejad et al., 2005) and (pda)(pydc)(pydcH2) (Aghabozorg, Ghadermazi & Ramezanipour, 2006). Here, we report the synthesis and X-ray crystal structure of the title compound, (I). The asymmetric unit of compound (I) contains a neutral complex and one water molecule (Fig. 1). The MgII atom is six-coordinated by two pyridine-2-carboxylate, (pyc)−, groups and two coordinated water molecules. The O6—Mg1—O7 angel is 86.90 (4)°, showing that the two coordinated water molecules are located at cis to each other. Also, torsion angels show that the two (pyc)− fragments are almost perpendicular to each other. Therefore, the coordination around MgII is distorted octahedral. A considerable feature of the compound (I) is the presence of π–π and C—H···π stacking interactions. The average distance between the planes are 3.5616 (8) Å (2 − x, 1 − y, 1 − z). The C—H···π distances (measured to the centre of phenyl ring) are 3.225 (1) Å and 3.417 (1) Å and the C–H···π angles are 156.3 (1)° and 136.9 (1)°, respectively (Figs 2 and 3). Intermolecular O—H···O and C—H···O hydrogen bonds ranging from 2.669 (1) to 3.328 (2) Å (Table 2) seem to be effective in the stabilization of the crystal structure, resulting in the formation of an interesting supramolecular structure (Fig. 4).

Related literature top

In order to develop new types of proton-transfer compounds and hydrogen-bonding systems, our research group has already selected pyridine-2,6-dicarboxylic acid (pydcH2) and 1,10-phenanthroline-2,9-dicarboxylic acid (phendcH2) as proton donors and pyridine-2,6-diamine (pyda), creatinine (creat) and propane-1,3-diamine (pda) as proton acceptors. These resulted in the formation of the new proton-transfer compounds (pydcH)(pydaH) (Aghabozorg et al., 2005), (creatH)(phendcH)·H2O (Soleimannejad et al., 2005) and (pda)(pydc)(pydcH2) (Aghabozorg, Ghadermazi & Ramezanipour, 2006). For further details, see: Aghabozorg, Zabihi et al. (2006); Aghabozorg, Ghasemikhah et al. (2006).

Experimental top

A solution of MgCl2·4H2O (143 mg, 0.5 mmol) in water (20 ml) was added to an aqueous solution of (pipzH2)(pyc)2 (253 mg, 1.0 mmol) in water (20 ml) in a 1:2 molar ratio. Colorless crystals of (I) were obtained after allowing the mixture to stand for two weeks at room temperature.

Refinement top

The hydrogen atoms of water molecules were found in difference Fourier synthesis. The H(C) atom positions were calculated. All hydrogen atoms were refined in isotropic approximation in riding model with with the Uiso(H) parameters equal to 1.2 Ueq(Ci) and 1.2 Ueq(Oi) where U(Ci) and U(Oi) are respectively the equivalent thermal parameters of the carbon and oxygen atoms to which corresponding H atoms are bonded.

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2005); software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. The structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. π–π Stacking interactions between two aromatic rings of (I), The average distance between the planes are 3.5616 (8) Å.
[Figure 3] Fig. 3. The C—H···π distances (measured to the centre of phenyl ring) are 3.225 and 3.417 Å and the C–H···π angles are 156.26° and 136.86°, respectively.
[Figure 4] Fig. 4. A packing diagram of (I). Hydrogen bonds are shown as dashed lines.
Diaquabis(pyridine-2-carboxylato)magnesium(II) 0.15-hydrate top
Crystal data top
[Mg(C6H4NO2)2(H2O)2]·0.15H2OF(000) = 638
Mr = 307.25Dx = 1.397 Mg m−3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 290 reflections
a = 11.6385 (6) Åθ = 3–28°
b = 8.7955 (5) ŵ = 0.15 mm−1
c = 14.9357 (8) ÅT = 100 K
β = 107.221 (1)°Prism, colourless
V = 1460.37 (14) Å30.23 × 0.20 × 0.19 mm
Z = 4
Data collection top
Bruker APEXII CCD area-detector
diffractometer		3487 independent reflections
Radiation source: fine-focus sealed tube2879 reflections with I > 2σ(I)
graphiteRint = 0.029
ω scansθmax = 28.0°, θmin = 2.0°
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		h = −15→15
Tmin = 0.954, Tmax = 0.966k = −11→11
20864 measured reflectionsl = −19→19
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)] = 0.032Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.090H atoms treated by a mixture of independent and constrained refinement
S = 1.04 w = 1/[σ2(Fo2) + (0.0495P)2 + 0.273P]
where P = (Fo2 + 2Fc2)/3
3487 reflections(Δ/σ)max < 0.001
194 parametersΔρmax = 0.82 e Å−3
0 restraintsΔρmin = −0.23 e Å−3
Crystal data top
[Mg(C6H4NO2)2(H2O)2]·0.15H2OV = 1460.37 (14) Å3
Mr = 307.25Z = 4
Monoclinic, P21/nMo Kα radiation
a = 11.6385 (6) ŵ = 0.15 mm−1
b = 8.7955 (5) ÅT = 100 K
c = 14.9357 (8) Å0.23 × 0.20 × 0.19 mm
β = 107.221 (1)°
Data collection top
Bruker APEXII CCD area-detector
diffractometer		3487 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2005)		2879 reflections with I > 2σ(I)
Tmin = 0.954, Tmax = 0.966Rint = 0.029
20864 measured reflectionsθmax = 28.0°
Refinement top
R[F2 > 2σ(F2)] = 0.032H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.090Δρmax = 0.82 e Å−3
S = 1.04Δρmin = −0.23 e Å−3
3487 reflectionsAbsolute structure: ?
194 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
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*/UeqOcc. (<1)
Mg10.75274 (4)0.14609 (4)0.36741 (3)0.01536 (11)
O10.95964 (8)0.13410 (10)0.64227 (6)0.0212 (2)
O20.84302 (8)0.07036 (10)0.49940 (6)0.01827 (19)
O30.68286 (8)−0.06450 (10)0.32554 (6)0.01797 (19)
O40.53051 (9)−0.22785 (11)0.30834 (7)0.0281 (2)
N10.80774 (9)0.35929 (11)0.44608 (7)0.0164 (2)
N20.57295 (10)0.15093 (12)0.39090 (8)0.0195 (2)
C10.78783 (11)0.50379 (14)0.41751 (9)0.0189 (3)
H1A0.74320.52320.35420.023*
C20.82985 (11)0.62649 (14)0.47670 (9)0.0201 (3)
H2A0.81480.72770.45410.024*
C30.89413 (12)0.59849 (15)0.56922 (9)0.0217 (3)
H3A0.92350.68030.61140.026*
C40.91508 (11)0.44843 (15)0.59947 (9)0.0211 (3)
H4A0.95860.42610.66260.025*
C50.87139 (10)0.33242 (14)0.53592 (9)0.0161 (2)
C60.89342 (10)0.16539 (14)0.56167 (9)0.0164 (2)
C70.51747 (14)0.26405 (16)0.42112 (11)0.0292 (3)
H7C0.55880.35780.43790.035*
C80.40216 (15)0.25093 (18)0.42914 (13)0.0382 (4)
H8A0.36540.33430.45040.046*
C90.34146 (15)0.11477 (18)0.40569 (13)0.0358 (4)
H9A0.26270.10250.41110.043*
C100.39795 (13)−0.00355 (16)0.37412 (10)0.0278 (3)
H10A0.3584−0.09840.35710.033*
C110.51309 (11)0.01883 (14)0.36780 (9)0.0194 (3)
C120.57951 (11)−0.10300 (15)0.33120 (8)0.0183 (3)
O60.90157 (8)0.11746 (10)0.32355 (6)0.0194 (2)
H6A0.91510.16020.27890.023*
H6B0.94650.04360.33600.023*
O70.67881 (8)0.25894 (10)0.24522 (6)0.01865 (19)
H7A0.72090.30190.21770.022*
H7B0.60880.27540.21490.022*
O1S0.3507 (12)−0.3966 (16)0.3526 (9)0.089 (4)*0.15
H1SA0.4061−0.34240.34810.106*0.15
H1SB0.2825−0.36120.33590.106*0.15
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Mg10.0147 (2)0.0129 (2)0.0172 (2)−0.00015 (15)0.00268 (16)−0.00011 (15)
O10.0191 (4)0.0191 (5)0.0207 (4)0.0034 (4)−0.0013 (4)0.0011 (3)
O20.0178 (4)0.0149 (4)0.0195 (4)−0.0010 (3)0.0016 (3)0.0001 (3)
O30.0158 (4)0.0158 (4)0.0223 (4)−0.0012 (3)0.0057 (3)−0.0022 (3)
O40.0286 (5)0.0225 (5)0.0384 (6)−0.0104 (4)0.0178 (4)−0.0118 (4)
N10.0143 (5)0.0155 (5)0.0186 (5)0.0002 (4)0.0037 (4)0.0001 (4)
N20.0209 (5)0.0165 (5)0.0222 (5)0.0010 (4)0.0081 (4)0.0001 (4)
C10.0189 (6)0.0179 (6)0.0198 (6)0.0005 (5)0.0058 (5)0.0015 (5)
C20.0197 (6)0.0152 (6)0.0275 (7)0.0005 (5)0.0101 (5)0.0002 (5)
C30.0191 (6)0.0177 (6)0.0271 (7)−0.0019 (5)0.0049 (5)−0.0064 (5)
C40.0187 (6)0.0208 (6)0.0204 (6)0.0020 (5)0.0009 (5)−0.0021 (5)
C50.0116 (5)0.0172 (6)0.0191 (6)0.0009 (4)0.0038 (4)0.0001 (5)
C60.0119 (5)0.0168 (6)0.0200 (6)0.0013 (5)0.0039 (4)0.0006 (5)
C70.0312 (8)0.0181 (6)0.0443 (8)−0.0009 (6)0.0205 (7)−0.0032 (6)
C80.0385 (9)0.0256 (8)0.0621 (11)0.0027 (7)0.0328 (8)−0.0044 (7)
C90.0287 (8)0.0309 (8)0.0567 (10)−0.0015 (6)0.0263 (7)−0.0011 (7)
C100.0258 (7)0.0238 (7)0.0379 (8)−0.0043 (6)0.0159 (6)−0.0021 (6)
C110.0200 (6)0.0191 (6)0.0202 (6)−0.0008 (5)0.0075 (5)0.0005 (5)
C120.0195 (6)0.0185 (6)0.0169 (6)−0.0014 (5)0.0054 (5)−0.0009 (5)
O60.0175 (4)0.0164 (4)0.0244 (5)0.0028 (3)0.0066 (4)0.0045 (3)
O70.0139 (4)0.0201 (4)0.0199 (4)−0.0002 (3)0.0019 (3)0.0044 (3)
Geometric parameters (Å, °) top
Mg1—O72.0313 (9)C3—H3A0.9500
Mg1—O62.0408 (10)C4—C51.3837 (18)
Mg1—O32.0449 (9)C4—H4A0.9500
Mg1—O22.0512 (9)C5—C61.5210 (17)
Mg1—N12.2049 (11)C7—C81.387 (2)
Mg1—N22.2222 (12)C7—H7C0.9500
O1—C61.2529 (15)C8—C91.382 (2)
O2—C61.2588 (15)C8—H8A0.9500
O3—C121.2763 (15)C9—C101.386 (2)
O4—C121.2379 (16)C9—H9A0.9500
N1—C11.3389 (16)C10—C111.3851 (19)
N1—C51.3478 (16)C10—H10A0.9500
N2—C71.3354 (17)C11—C121.5149 (18)
N2—C111.3461 (16)O6—H6A0.8199
C1—C21.3890 (18)O6—H6B0.8200
C1—H1A0.9500O7—H7A0.8196
C2—C31.3848 (19)O7—H7B0.8197
C2—H2A0.9500O1S—H1SA0.8200
C3—C41.3930 (18)O1S—H1SB0.8200
O7—Mg1—O686.90 (4)C5—C4—H4A120.6
O7—Mg1—O398.25 (4)C3—C4—H4A120.6
O6—Mg1—O395.08 (4)N1—C5—C4122.39 (11)
O7—Mg1—O2169.21 (4)N1—C5—C6115.01 (10)
O6—Mg1—O291.52 (4)C4—C5—C6122.59 (11)
O3—Mg1—O292.52 (4)O1—C6—O2125.70 (11)
O7—Mg1—N192.42 (4)O1—C6—C5117.70 (11)
O6—Mg1—N197.81 (4)O2—C6—C5116.60 (11)
O3—Mg1—N1163.68 (4)N2—C7—C8122.97 (13)
O2—Mg1—N177.21 (4)N2—C7—H7C118.5
O7—Mg1—N287.95 (4)C8—C7—H7C118.5
O6—Mg1—N2168.95 (4)C9—C8—C7119.04 (14)
O3—Mg1—N275.99 (4)C9—C8—H8A120.5
O2—Mg1—N295.33 (4)C7—C8—H8A120.5
N1—Mg1—N292.17 (4)C8—C9—C10118.59 (14)
C6—O2—Mg1119.25 (8)C8—C9—H9A120.7
C12—O3—Mg1121.15 (8)C10—C9—H9A120.7
C1—N1—C5118.42 (11)C11—C10—C9118.84 (13)
C1—N1—Mg1129.94 (9)C11—C10—H10A120.6
C5—N1—Mg1111.64 (8)C9—C10—H10A120.6
C7—N2—C11117.67 (11)N2—C11—C10122.89 (12)
C7—N2—Mg1129.78 (9)N2—C11—C12114.98 (11)
C11—N2—Mg1112.52 (8)C10—C11—C12122.10 (12)
N1—C1—C2122.66 (12)O4—C12—O3125.68 (12)
N1—C1—H1A118.7O4—C12—C11118.98 (11)
C2—C1—H1A118.7O3—C12—C11115.33 (11)
C3—C2—C1118.77 (12)Mg1—O6—H6A126.1
C3—C2—H2A120.6Mg1—O6—H6B124.7
C1—C2—H2A120.6H6A—O6—H6B106.6
C2—C3—C4118.89 (12)Mg1—O7—H7A121.3
C2—C3—H3A120.6Mg1—O7—H7B132.1
C4—C3—H3A120.6H7A—O7—H7B106.6
C5—C4—C3118.86 (12)H1SA—O1S—H1SB117.9
O7—Mg1—O2—C612.0 (3)N1—C1—C2—C3−0.53 (19)
O6—Mg1—O2—C693.42 (9)C1—C2—C3—C40.44 (19)
O3—Mg1—O2—C6−171.42 (9)C2—C3—C4—C50.28 (19)
N1—Mg1—O2—C6−4.24 (9)C1—N1—C5—C40.92 (18)
N2—Mg1—O2—C6−95.27 (9)Mg1—N1—C5—C4−179.50 (10)
O7—Mg1—O3—C12−87.16 (9)C1—N1—C5—C6−178.05 (10)
O6—Mg1—O3—C12−174.75 (9)Mg1—N1—C5—C61.53 (13)
O2—Mg1—O3—C1293.50 (9)C3—C4—C5—N1−0.99 (19)
N1—Mg1—O3—C1243.15 (19)C3—C4—C5—C6177.90 (11)
N2—Mg1—O3—C12−1.37 (9)Mg1—O2—C6—O1−173.57 (10)
O7—Mg1—N1—C13.61 (11)Mg1—O2—C6—C56.37 (14)
O6—Mg1—N1—C190.82 (11)N1—C5—C6—O1174.80 (11)
O3—Mg1—N1—C1−127.33 (15)C4—C5—C6—O1−4.17 (18)
O2—Mg1—N1—C1−179.40 (11)N1—C5—C6—O2−5.15 (16)
N2—Mg1—N1—C1−84.43 (11)C4—C5—C6—O2175.89 (11)
O7—Mg1—N1—C5−175.91 (8)C11—N2—C7—C8−0.2 (2)
O6—Mg1—N1—C5−88.71 (8)Mg1—N2—C7—C8177.65 (12)
O3—Mg1—N1—C553.15 (18)N2—C7—C8—C90.5 (3)
O2—Mg1—N1—C51.08 (8)C7—C8—C9—C10−0.6 (3)
N2—Mg1—N1—C596.05 (8)C8—C9—C10—C110.4 (2)
O7—Mg1—N2—C7−78.27 (13)C7—N2—C11—C100.0 (2)
O6—Mg1—N2—C7−140.6 (2)Mg1—N2—C11—C10−178.22 (11)
O3—Mg1—N2—C7−177.30 (13)C7—N2—C11—C12178.16 (12)
O2—Mg1—N2—C791.43 (13)Mg1—N2—C11—C12−0.08 (14)
N1—Mg1—N2—C714.08 (13)C9—C10—C11—N2−0.1 (2)
O7—Mg1—N2—C1199.71 (9)C9—C10—C11—C12−178.10 (14)
O6—Mg1—N2—C1137.4 (3)Mg1—O3—C12—O4−179.40 (10)
O3—Mg1—N2—C110.68 (9)Mg1—O3—C12—C111.73 (14)
O2—Mg1—N2—C11−90.59 (9)N2—C11—C12—O4−179.95 (12)
N1—Mg1—N2—C11−167.95 (9)C10—C11—C12—O4−1.79 (19)
C5—N1—C1—C2−0.15 (18)N2—C11—C12—O3−1.00 (16)
Mg1—N1—C1—C2−179.64 (9)C10—C11—C12—O3177.16 (12)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O6—H6A···O4i0.821.892.697 (1)170
O6—H6B···O1ii0.821.882.697 (1)176
O7—H7A···O3i0.821.872.669 (1)167
O7—H7B···O1iii0.821.932.726 (1)165
C9—H9A···O2iv0.952.573.328 (2)137
C7—H7C···Cg0.953.224.112 (1)156
C8—H8A···Cg0.953.424.162 (1)137
Symmetry codes: (i) −x+3/2, y+1/2, −z+1/2; (ii) −x+2, −y, −z+1; (iii) x−1/2, −y+1/2, z−1/2; (iv) −x+1, −y, −z+1.
Table 1
Selected geometric parameters (Å, °) top
Mg1—O72.0313 (9)Mg1—O22.0512 (9)
Mg1—O62.0408 (10)Mg1—N12.2049 (11)
Mg1—O32.0449 (9)Mg1—N22.2222 (12)
O7—Mg1—O686.90 (4)O3—Mg1—N1163.68 (4)
O7—Mg1—O2169.21 (4)O6—Mg1—N2168.95 (4)
O2—Mg1—O3—C1293.50 (9)O2—Mg1—N2—C791.43 (13)
Table 2
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O6—H6A···O4i0.821.892.697 (1)170
O6—H6B···O1ii0.821.882.697 (1)176
O7—H7A···O3i0.821.872.669 (1)167
O7—H7B···O1iii0.821.932.726 (1)165
C9—H9A···O2iv0.952.573.328 (2)137
C7—H7C···Cg0.953.224.112 (1)156
C8—H8A···Cg0.953.424.162 (1)137
Symmetry codes: (i) −x+3/2, y+1/2, −z+1/2; (ii) −x+2, −y, −z+1; (iii) x−1/2, −y+1/2, z−1/2; (iv) −x+1, −y, −z+1.
Acknowledgements top

Financial support by the Islamic Azad University, Qom Branch, and the Teacher Training University is gratefully acknowledged.

references
References top

Aghabozorg, Ghasemikhah et al. (2006). [Please give full details for missing reference]

Aghabozorg, H., Akbari Saei, A. & Ramezanipour, F. (2005). Acta Cryst. E61, o3242–o3244.

Aghabozorg, H., Ghadermazi, M. & Attar Gharamaleki, J. (2006). Acta Cryst. E62, o3174–o3176. [Reference not uniquely cited - please check]

Aghabozorg, H., Ghadermazi, M. & Ramezanipour, F. (2006). Acta Cryst. E62, o1143–o1146.

Aghabozorg, Zabihi et al. (2006). [Please give full details for missing reference]

Bruker (2005). APEX2 (Version 2.0-1), SAINT (Version 7.23A), SADABS (Version 2004/1), XPREP (Version 2005/2) and SHELXTL (Version 6.10). Bruker AXS Inc., Madison, Wisconsin, USA. [XPREP not cited - may it be removed?]

Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.

Soleimannejad, J., Sharif, M. A., Sheshmani, S., Alizadeh, R., Moghimi, A. & Aghabozorg, H. (2005). Anal. Sci. 21, x49–x50.