In the title compound,
catena-poly[[aquazinc(II)]-
3-tyrosinato], [Zn(C
9H
7NO
3)(H
2O)]
n, each Zn atom has a distorted square-pyramidal geometry comprised of three O atoms and one N atom from three tyrosinate (tyr) ligands, and one aqua ligand. Two inversion-related Zn
2+ ions are bridged by two O atoms from the phenolate groups of two tyr ligands to form a centrosymmetric dimeric unit, which can be described as a planar Zn
2O
2 four-membered ring. These repeating dimeric units are arranged along the
c axis to give a one-dimensional chain coordination polymer, in which the tyr ligand adopts an unusual chelating/bridging coordination mode.
Supporting information
CCDC reference: 659116
Single crystals of the title complex suitable for X-ray crystallographic
analysis were obtained by solvothermal treatment of Zn(NO3)2·6H2O
(0.2 mmol), H2-tyr (0.1 mmol), CH3OH (5 ml) and NH3 (0.2 ml). The
reagents were placed in a thick Pyrex tube (ca 20 cm long). The tube
was cooled with liquid N2 and the air evacuated. The sealed tube was heated
at 413 k for 10 d to yield yellow block crystals in about 25% yield.
H atoms on C and N atoms were positioned geometrically and were allowed to ride
on their parent atoms, with C—H = 0.93 Å and N—H = 0.90 Å, and
Uiso(H) = 1.2Ueq(C) or 1.2Ueq(N). H atoms on O
atoms were located in a difference map and refined. High displacement
parameters suggest some disorder in the C8 atom of the tyr2- ligand, but
this could not be resolved.
Data collection: CrystalClear (Molecular Structure Corporation & Rigaku, 2001); cell refinement: CrystalClear; data reduction: CrystalStructure (Rigaku/MSC, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.
catena-poly[[aquazinc(II)]-µ
3-tyrosinato]
top
Crystal data top
[Zn(C9H7NO3)(H2O)] | V = 484.81 (17) Å3 |
Mr = 260.54 | Z = 2 |
Triclinic, P1 | F(000) = 264 |
Hall symbol: -P 1 | Dx = 1.785 Mg m−3 |
a = 5.8633 (12) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 9.681 (2) Å | θ = 2.3–26.0° |
c = 9.772 (2) Å | µ = 2.52 mm−1 |
α = 65.336 (3)° | T = 273 K |
β = 75.334 (3)° | Block, yellow |
γ = 78.440 (3)° | 0.14 × 0.10 × 0.06 mm |
Data collection top
Rigaku Mercury diffractometer | 1841 independent reflections |
Radiation source: fine-focus sealed tube | 1645 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.020 |
Detector resolution: 7.31 pixels mm-1 | θmax = 26.0°, θmin = 2.3° |
ω scans | h = −7→7 |
Absorption correction: multi-scan (Jacobson, 1998) | k = −11→11 |
Tmin = 0.719, Tmax = 0.863 | l = −12→12 |
3474 measured reflections | |
Refinement top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.044 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.109 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.06 | w = 1/[σ2(Fo2) + (0.0592P)2 + 0.676P] where P = (Fo2 + 2Fc2)/3 |
1841 reflections | (Δ/σ)max = 0.070 |
144 parameters | Δρmax = 0.61 e Å−3 |
2 restraints | Δρmin = −0.51 e Å−3 |
Crystal data top
[Zn(C9H7NO3)(H2O)] | γ = 78.440 (3)° |
Mr = 260.54 | V = 484.81 (17) Å3 |
Triclinic, P1 | Z = 2 |
a = 5.8633 (12) Å | Mo Kα radiation |
b = 9.681 (2) Å | µ = 2.52 mm−1 |
c = 9.772 (2) Å | T = 273 K |
α = 65.336 (3)° | 0.14 × 0.10 × 0.06 mm |
β = 75.334 (3)° | |
Data collection top
Rigaku Mercury diffractometer | 1841 independent reflections |
Absorption correction: multi-scan (Jacobson, 1998) | 1645 reflections with I > 2σ(I) |
Tmin = 0.719, Tmax = 0.863 | Rint = 0.020 |
3474 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.044 | 2 restraints |
wR(F2) = 0.109 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.06 | Δρmax = 0.61 e Å−3 |
1841 reflections | Δρmin = −0.51 e Å−3 |
144 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 | x | y | z | Uiso*/Ueq | |
N1 | 0.7359 (7) | 0.2206 (5) | 0.2087 (5) | 0.0400 (9) | |
H1B | 0.6048 | 0.2862 | 0.1883 | 0.048* | |
H1A | 0.6922 | 0.1362 | 0.2908 | 0.048* | |
Zn1 | 0.10104 (8) | −0.16052 (5) | 0.98560 (5) | 0.02613 (18) | |
O1 | 0.1409 (5) | 0.0629 (3) | 0.8754 (3) | 0.0317 (7) | |
O1W | 0.3249 (7) | −0.3060 (5) | 1.1269 (5) | 0.0491 (9) | |
H1W2 | 0.469 (6) | −0.292 (10) | 1.088 (9) | 0.12 (3)* | |
H1W1 | 0.296 (13) | −0.399 (3) | 1.158 (8) | 0.09 (2)* | |
O2 | 1.1516 (5) | 0.2756 (4) | 0.0164 (4) | 0.0344 (7) | |
O3 | 1.2600 (6) | 0.3971 (4) | 0.1327 (4) | 0.0464 (9) | |
C1 | 0.3115 (7) | 0.1270 (5) | 0.7566 (5) | 0.0274 (9) | |
C2 | 0.2607 (8) | 0.2616 (5) | 0.6356 (5) | 0.0383 (10) | |
H2 | 0.1059 | 0.3087 | 0.6380 | 0.046* | |
C3 | 0.4338 (10) | 0.3268 (6) | 0.5120 (5) | 0.0457 (12) | |
H3 | 0.3926 | 0.4169 | 0.4328 | 0.055* | |
C4 | 0.6654 (9) | 0.2635 (6) | 0.5017 (5) | 0.0436 (12) | |
C5 | 0.7176 (8) | 0.1297 (6) | 0.6229 (6) | 0.0447 (12) | |
H5 | 0.8733 | 0.0840 | 0.6201 | 0.054* | |
C6 | 0.5454 (8) | 0.0622 (5) | 0.7478 (6) | 0.0374 (10) | |
H6 | 0.5870 | −0.0279 | 0.8269 | 0.045* | |
C7 | 0.8563 (12) | 0.3332 (9) | 0.3650 (7) | 0.075 (2) | |
H7 | 0.9452 | 0.4037 | 0.3631 | 0.091* | |
C8 | 0.8947 (11) | 0.2886 (10) | 0.2421 (8) | 0.089 (3) | |
C9 | 1.1178 (7) | 0.3254 (5) | 0.1217 (5) | 0.0310 (9) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.030 (2) | 0.056 (3) | 0.043 (2) | −0.0176 (18) | 0.0080 (17) | −0.030 (2) |
Zn1 | 0.0231 (3) | 0.0286 (3) | 0.0269 (3) | −0.00491 (18) | 0.00178 (19) | −0.0137 (2) |
O1 | 0.0320 (16) | 0.0268 (15) | 0.0299 (16) | −0.0078 (12) | 0.0120 (13) | −0.0130 (13) |
O1W | 0.038 (2) | 0.050 (2) | 0.055 (2) | −0.0049 (17) | −0.0040 (18) | −0.0190 (19) |
O2 | 0.0234 (14) | 0.0477 (18) | 0.0370 (17) | −0.0099 (13) | 0.0062 (13) | −0.0253 (15) |
O3 | 0.0335 (18) | 0.063 (2) | 0.056 (2) | −0.0206 (16) | 0.0110 (16) | −0.0400 (19) |
C1 | 0.026 (2) | 0.030 (2) | 0.029 (2) | −0.0093 (17) | 0.0047 (17) | −0.0162 (18) |
C2 | 0.035 (2) | 0.041 (3) | 0.034 (2) | −0.006 (2) | −0.002 (2) | −0.011 (2) |
C3 | 0.054 (3) | 0.051 (3) | 0.025 (2) | −0.023 (2) | −0.001 (2) | −0.003 (2) |
C4 | 0.047 (3) | 0.066 (3) | 0.028 (2) | −0.032 (3) | 0.010 (2) | −0.026 (2) |
C5 | 0.025 (2) | 0.063 (3) | 0.054 (3) | −0.012 (2) | 0.009 (2) | −0.036 (3) |
C6 | 0.034 (2) | 0.035 (2) | 0.037 (3) | −0.0042 (19) | 0.000 (2) | −0.013 (2) |
C7 | 0.083 (4) | 0.123 (6) | 0.047 (3) | −0.080 (4) | 0.042 (3) | −0.058 (4) |
C8 | 0.059 (4) | 0.185 (8) | 0.072 (4) | −0.087 (5) | 0.047 (3) | −0.100 (5) |
C9 | 0.025 (2) | 0.036 (2) | 0.034 (2) | −0.0082 (18) | 0.0033 (18) | −0.018 (2) |
Geometric parameters (Å, º) top
N1—C8 | 1.409 (6) | O3—C9 | 1.236 (5) |
N1—Zn1i | 2.154 (4) | C1—C2 | 1.386 (6) |
N1—H1B | 0.9000 | C1—C6 | 1.387 (6) |
N1—H1A | 0.9000 | C2—C3 | 1.374 (7) |
Zn1—O1 | 2.006 (3) | C2—H2 | 0.9300 |
Zn1—O2i | 2.032 (3) | C3—C4 | 1.370 (8) |
Zn1—O1W | 2.041 (4) | C3—H3 | 0.9300 |
Zn1—O1ii | 2.075 (3) | C4—C5 | 1.385 (8) |
Zn1—N1i | 2.154 (4) | C4—C7 | 1.512 (7) |
O1—C1 | 1.339 (5) | C5—C6 | 1.383 (7) |
O1—Zn1ii | 2.075 (3) | C5—H5 | 0.9300 |
O1W—H1W2 | 0.85 (5) | C6—H6 | 0.9300 |
O1W—H1W1 | 0.86 (5) | C7—C8 | 1.392 (7) |
O2—C9 | 1.267 (5) | C7—H7 | 0.9300 |
O2—Zn1i | 2.032 (3) | C8—C9 | 1.510 (6) |
| | | |
C8—N1—Zn1i | 110.5 (3) | C2—C1—C6 | 116.9 (4) |
C8—N1—H1B | 109.5 | C3—C2—C1 | 121.5 (5) |
Zn1i—N1—H1B | 109.5 | C3—C2—H2 | 119.2 |
C8—N1—H1A | 109.5 | C1—C2—H2 | 119.2 |
Zn1i—N1—H1A | 109.5 | C4—C3—C2 | 122.1 (5) |
H1B—N1—H1A | 108.1 | C4—C3—H3 | 119.0 |
O1—Zn1—O2i | 128.61 (13) | C2—C3—H3 | 119.0 |
O1—Zn1—O1W | 121.18 (15) | C3—C4—C5 | 116.7 (4) |
O2i—Zn1—O1W | 110.19 (15) | C3—C4—C7 | 122.4 (6) |
O1—Zn1—O1ii | 76.84 (12) | C5—C4—C7 | 120.9 (5) |
O2i—Zn1—O1ii | 91.12 (12) | C6—C5—C4 | 122.0 (5) |
O1W—Zn1—O1ii | 103.19 (14) | C6—C5—H5 | 119.0 |
O1—Zn1—N1i | 95.71 (14) | C4—C5—H5 | 119.0 |
O2i—Zn1—N1i | 79.16 (13) | C5—C6—C1 | 120.8 (5) |
O1W—Zn1—N1i | 96.35 (16) | C5—C6—H6 | 119.6 |
O1ii—Zn1—N1i | 160.22 (15) | C1—C6—H6 | 119.6 |
C1—O1—Zn1 | 127.1 (2) | C8—C7—C4 | 117.9 (5) |
C1—O1—Zn1ii | 128.8 (2) | C8—C7—H7 | 121.1 |
Zn1—O1—Zn1ii | 103.16 (12) | C4—C7—H7 | 121.1 |
Zn1—O1W—H1W2 | 113 (6) | C7—C8—N1 | 126.7 (5) |
Zn1—O1W—H1W1 | 111 (5) | C7—C8—C9 | 119.2 (4) |
H1W2—O1W—H1W1 | 114 (7) | N1—C8—C9 | 114.0 (4) |
C9—O2—Zn1i | 118.6 (3) | O3—C9—O2 | 123.6 (4) |
O1—C1—C2 | 121.1 (4) | O3—C9—C8 | 119.4 (4) |
O1—C1—C6 | 122.0 (4) | O2—C9—C8 | 117.0 (4) |
| | | |
O2i—Zn1—O1—C1 | −109.6 (3) | C3—C4—C5—C6 | 0.5 (7) |
O1W—Zn1—O1—C1 | 72.1 (4) | C7—C4—C5—C6 | −178.8 (4) |
O1ii—Zn1—O1—C1 | 169.7 (4) | C4—C5—C6—C1 | −0.2 (7) |
N1i—Zn1—O1—C1 | −28.9 (3) | O1—C1—C6—C5 | 179.2 (4) |
O2i—Zn1—O1—Zn1ii | 80.73 (17) | C2—C1—C6—C5 | −0.3 (7) |
O1W—Zn1—O1—Zn1ii | −97.61 (17) | C3—C4—C7—C8 | −89.0 (9) |
O1ii—Zn1—O1—Zn1ii | 0.0 | C5—C4—C7—C8 | 90.3 (8) |
N1i—Zn1—O1—Zn1ii | 161.41 (15) | C4—C7—C8—N1 | 19.8 (14) |
Zn1—O1—C1—C2 | 139.5 (4) | C4—C7—C8—C9 | −165.6 (7) |
Zn1ii—O1—C1—C2 | −53.4 (5) | Zn1i—N1—C8—C7 | −175.7 (8) |
Zn1—O1—C1—C6 | −39.9 (5) | Zn1i—N1—C8—C9 | 9.4 (8) |
Zn1ii—O1—C1—C6 | 127.2 (4) | Zn1i—O2—C9—O3 | −179.8 (4) |
O1—C1—C2—C3 | −178.9 (4) | Zn1i—O2—C9—C8 | 2.6 (6) |
C6—C1—C2—C3 | 0.5 (7) | C7—C8—C9—O3 | −1.4 (11) |
C1—C2—C3—C4 | −0.3 (8) | N1—C8—C9—O3 | 173.8 (6) |
C2—C3—C4—C5 | −0.2 (7) | C7—C8—C9—O2 | 176.3 (7) |
C2—C3—C4—C7 | 179.0 (5) | N1—C8—C9—O2 | −8.4 (9) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x, −y, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1B···O3iii | 0.90 | 2.18 | 3.056 (6) | 165 |
O1W—H1W1···O3iv | 0.86 (5) | 2.15 (5) | 2.950 (6) | 156 (6) |
O1W—H1W2···O2v | 0.85 (5) | 2.21 (5) | 3.051 (6) | 175 (9) |
Symmetry codes: (iii) x−1, y, z; (iv) x−1, y−1, z+1; (v) −x+2, −y, −z+1. |
Experimental details
Crystal data |
Chemical formula | [Zn(C9H7NO3)(H2O)] |
Mr | 260.54 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 273 |
a, b, c (Å) | 5.8633 (12), 9.681 (2), 9.772 (2) |
α, β, γ (°) | 65.336 (3), 75.334 (3), 78.440 (3) |
V (Å3) | 484.81 (17) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 2.52 |
Crystal size (mm) | 0.14 × 0.10 × 0.06 |
|
Data collection |
Diffractometer | Rigaku Mercury diffractometer |
Absorption correction | Multi-scan (Jacobson, 1998) |
Tmin, Tmax | 0.719, 0.863 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3474, 1841, 1645 |
Rint | 0.020 |
(sin θ/λ)max (Å−1) | 0.617 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.044, 0.109, 1.06 |
No. of reflections | 1841 |
No. of parameters | 144 |
No. of restraints | 2 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.61, −0.51 |
Selected geometric parameters (Å, º) topZn1—O1 | 2.006 (3) | Zn1—O1ii | 2.075 (3) |
Zn1—O2i | 2.032 (3) | Zn1—N1i | 2.154 (4) |
Zn1—O1W | 2.041 (4) | | |
| | | |
O1—Zn1—O2i | 128.61 (13) | O1W—Zn1—O1ii | 103.19 (14) |
O1—Zn1—O1W | 121.18 (15) | O1—Zn1—N1i | 95.71 (14) |
O2i—Zn1—O1W | 110.19 (15) | O2i—Zn1—N1i | 79.16 (13) |
O1—Zn1—O1ii | 76.84 (12) | O1W—Zn1—N1i | 96.35 (16) |
O2i—Zn1—O1ii | 91.12 (12) | O1ii—Zn1—N1i | 160.22 (15) |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x, −y, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1B···O3iii | 0.90 | 2.18 | 3.056 (6) | 165 |
O1W—H1W1···O3iv | 0.86 (5) | 2.15 (5) | 2.950 (6) | 156 (6) |
O1W—H1W2···O2v | 0.85 (5) | 2.21 (5) | 3.051 (6) | 175 (9) |
Symmetry codes: (iii) x−1, y, z; (iv) x−1, y−1, z+1; (v) −x+2, −y, −z+1. |
The rational design and assembly of metal–organic coordination frameworks have received much attention in recent years, owing to their intriguing structural topologies and potential or practical applications in the areas of catalysis, magnetism, gas storage, nonlinear optics, electronics and others (Bernhard et al., 2003; Lin et al., 1998; Sun et al., 2005; Zhu et al., 2005; Wu et al., 2007). A number of fascinating metal–organic coordination polymers are known to be constructed by the combination of symmetrical or asymmetrical bridging ligands as the 'spacer', and metal ions or a metal cluster as the 'node'. Carboxylate-containing ligands acting as the 'spacer' have attracted much attention because of the diversity of the binding modes of the carboxylate group (Zhu et al., 2005; Shi et al., 2005). The tyr ligand, with a carboxylate group, and its derivatives are good spacers because they often behave similarly to isonicotinic acid, acting as a chelating/bridging ligand via the N and O atoms. Diverse topologies can be achieved with the tyr ligand (Ayyappan et al., 2001; Lu & Babb, 2001; Lu et al., 2003). However, the reported complexes of the tyr ligand are generally mononuclear (Emseis et al., 2004; Harrowfield et al., 1983; Majumder et al., 2002), with only two coordination polymers being described in the literature, namely [Cu(H-tyr)2]n and {[Cu2(H-tyr)2(4,4-bipy). 2H2O].2 ClO4}n (Weng et al., 2002). Interestingly, the phenolate O atom in these two complexes is uncoordinated. In order to learn more about the coordination mode of the tyrosinato ligand, we have chosen the zinc(II) salts as the node. The zinc coordination polymers exhibit rich structural diversity because of the variable coordination behaviours of the d10 metal ion ZnII. We have successfully obtained the 1-D zinc(II) polymer [Zn(C9H7NO3)(H2O)]n, (I), containing the unusual coordinating phenolate O atom, via synthesis under solvothermal conditions.
The crystal structure of (I) consists of neutral [Zn(C9H7NO3) (H2O)] 1-D chains (see Fig. 1). Two Zn2+ ions are linked by two O atoms of the phenolate groups to give rise to a dimeric unit, which displays an inversion centre sited in the middle of the Zn2O2 cores. The Zn1—Zn1ii [symmetry code: (ii) -x, -y, -z + 2] intramolecular separation is 3.1981 (9) Å. Each zinc(II) centre in the dimeric unit is coordinated to three O atoms and one N atom from three tyr ligands, and one aqua ligand in a distorted square-pyramidal coordination geometry. These dimeric units are connected by tyr ligands to form a 1-D chain coordination polymer propagating along the crystallographic c axis. The Zn—O bonds, varying from 2.006 (3) to 2.075 (3) Å, are in good agreement with the corresponding bond lengths in [Zn2(Rsala)2 (H2O)2]·2H2O (Vittal & Yang, 2002), [Zn(BTZ)2]2 (Yu et al., 2003), Zn2(H2SB)2·3H2O·Me2CO (Matalobos et al., 2004) and [Zn2C22H20N4O2(H2O)2] (ClO4)2 (Huang et al., 2001). The Zn1—N1i [symmetry code: (i) -x + 1, -y, -z + 1] bond length is 2.154 (4) Å, comparable with those reported for [M(en)3]2Sn2S6 [2.14 (3)–2.23 (1) Å; Jia et al., 2004] and [Zn(en)3]4In16(Te2)4(Te3)Te22 [2.12 (3)–2.32 (3) Å; Chen et al., 2001]. The hydrogen bonds between the O atoms of the carboxylate groups and the H atoms of the water molecules [O1W—H···O3iv, symmetry code: (iv) x - 1, y - 1, z + 1] link the adjacent chains to form a 2-D sheet within the (100) plane (Fig. 2); the chains further interact via the formation of N1—H···O3iii and O1W—H···O2v [symmetry code: (iii) x - 1, y, z; (v) -x + 2, -y, -z + 1] hydrogen bonds, resulting in a three-dimensional H-bonding network structure.
The possible coordination modes of tyr2- and H-tyr- are shown in the scheme below. The usual chelating mode is (b), as exemplified by [Co(en)(2-N-eth-en) (H-tyr)]·2ClO4·2H2O (Harrowfield et al., 1983), [Cu(hista)(H-tyr) (ClO4)] (Yamauchi et al., 1989), [Ru(bpy)2 (H-tyr)]ClO4 (Majumder et al., 2002), [Cu(H-tyr)(phen)ClO4]·2.5H2O (Sugimori et al., 1997) and [Co(picchxn)(H-tyr)] Br2·3.5H2O (Emseis et al., 2004). The bridging mode (c) is less common, with only two examples found, [Cu(H-tyr)2]n and {[Cu2(H-tyr)2(4,4-bipy). 2H2O].2 ClO4}n (Weng et al., 2002). The most remarkable feature of (I) is the unusual coordination mode (a) of the tyr2- ligand. The tyr ligand adopts a chelating/bridging coordination mode, in which its amino and carboxylate bind a Zn2+ ion to form a chelating five-membered ring. In addition, the phenolate –OH bridges another two Zn2+ ions, resulting in the formation of a planar Zn2O2 four-membered ring which contributes to the distortion of the square-pyramidal geometry around the metal ion.