The coordination geometry of the ZnII atom in the title complex, [Zn2(NCS)4(C6H8N6)2], is that of a distorted tetrahedron, in which the ZnII atom is coordinated by four N atoms from the triazole rings of two symmetry-related 1,2-bis(1,2,4-triazol-1-yl)ethane ligands and two thiocyanate ligands. Two ZnII atoms are bridged by two organic ligands to form a dimer. The dimer lies about an inversion center.
Supporting information
CCDC reference: 274706
A 25 ml water/MeOH solution (1:1 v/v) of Zn(NO3)2.6H2O
(0.5 mmol) was added to one leg of an H-shaped tube, and a 25 ml water/MeOH
(1:1 v/v) solution of 1,2-bis(1,2,4-triazol-1-yl)ethane (bte)
(0.5 mmol) and KSCN (1.0 mmol) was added to another leg of the tube.
Colourless crystals were obtained after about two months. Analysis calculated
for C16H16N16S4Zn2: C 27.79, H 2.33, N 32.42%; found: C 27.75, H
2.31, N 32.36%.
H atoms were placed in idealized positions and refined as riding, with C—H
distances of 0.95 (triazole) and 0.99 Å (ethane), and with Uiso(H)
= 1.2Ueq(C).
Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: SHELXTL.
bis[µ-1,2-bis(1
H-1,2,4-triazol-1-yl)ethane-
κ2N4:
N4']bis[diisothiocyanatozinc(II)]
top
Crystal data top
[Zn2(NCS)4(C6H8N6)2] | Z = 1 |
Mr = 691.51 | F(000) = 348 |
Triclinic, P1 | Dx = 1.697 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 8.3859 (14) Å | Cell parameters from 2682 reflections |
b = 8.7715 (19) Å | θ = 3.4–25.4° |
c = 10.0402 (10) Å | µ = 2.12 mm−1 |
α = 80.784 (13)° | T = 193 K |
β = 68.195 (11)° | Block, colorless |
γ = 87.373 (14)° | 0.30 × 0.24 × 0.14 mm |
V = 676.8 (2) Å3 | |
Data collection top
Rigaku Mercury CCD diffractometer | 2462 independent reflections |
Radiation source: fine-focus sealed tube | 2192 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.025 |
ω scans | θmax = 25.3°, θmin = 3.4° |
Absorption correction: multi-scan (Jacobson, 1998) | h = −10→9 |
Tmin = 0.546, Tmax = 0.748 | k = −10→10 |
6769 measured reflections | l = −12→11 |
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)] = 0.032 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.083 | H-atom parameters constrained |
S = 1.01 | w = 1/[σ2(Fo2) + (0.0453P)2 + 0.3766P] where P = (Fo2 + 2Fc2)/3 |
2462 reflections | (Δ/σ)max = 0.001 |
172 parameters | Δρmax = 0.55 e Å−3 |
0 restraints | Δρmin = −0.39 e Å−3 |
Crystal data top
[Zn2(NCS)4(C6H8N6)2] | γ = 87.373 (14)° |
Mr = 691.51 | V = 676.8 (2) Å3 |
Triclinic, P1 | Z = 1 |
a = 8.3859 (14) Å | Mo Kα radiation |
b = 8.7715 (19) Å | µ = 2.12 mm−1 |
c = 10.0402 (10) Å | T = 193 K |
α = 80.784 (13)° | 0.30 × 0.24 × 0.14 mm |
β = 68.195 (11)° | |
Data collection top
Rigaku Mercury CCD diffractometer | 2462 independent reflections |
Absorption correction: multi-scan (Jacobson, 1998) | 2192 reflections with I > 2σ(I) |
Tmin = 0.546, Tmax = 0.748 | Rint = 0.025 |
6769 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.032 | 0 restraints |
wR(F2) = 0.083 | H-atom parameters constrained |
S = 1.01 | Δρmax = 0.55 e Å−3 |
2462 reflections | Δρmin = −0.39 e Å−3 |
172 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 | |
Zn1 | 0.13787 (4) | 0.25826 (4) | 0.60212 (3) | 0.03123 (13) | |
S1 | −0.35612 (10) | 0.15645 (10) | 0.52657 (9) | 0.0405 (2) | |
S2 | −0.10257 (10) | 0.65350 (10) | 0.86288 (9) | 0.0411 (2) | |
N1 | 0.4950 (3) | 0.3109 (3) | 0.1842 (2) | 0.0257 (5) | |
N2 | 0.5188 (3) | 0.4511 (3) | 0.2172 (2) | 0.0332 (6) | |
N3 | 0.3254 (3) | 0.3067 (3) | 0.4078 (2) | 0.0285 (5) | |
N4 | 0.7652 (3) | 0.0662 (3) | 0.0910 (2) | 0.0264 (5) | |
N5 | 0.6985 (3) | −0.0600 (3) | 0.0645 (3) | 0.0349 (6) | |
N6 | 0.8002 (3) | −0.1243 (3) | 0.2427 (2) | 0.0272 (5) | |
N7 | −0.0638 (4) | 0.1722 (3) | 0.5900 (3) | 0.0451 (7) | |
N8 | 0.0852 (4) | 0.4535 (3) | 0.6766 (3) | 0.0474 (7) | |
C1 | 0.4128 (4) | 0.4427 (3) | 0.3526 (3) | 0.0336 (7) | |
H1 | 0.3986 | 0.5248 | 0.4071 | 0.040* | |
C2 | 0.3803 (4) | 0.2279 (3) | 0.2972 (3) | 0.0302 (6) | |
H2 | 0.3424 | 0.1268 | 0.2993 | 0.036* | |
C3 | 0.7233 (4) | −0.1712 (3) | 0.1583 (3) | 0.0324 (6) | |
H3 | 0.6904 | −0.2756 | 0.1666 | 0.039* | |
C4 | 0.8238 (3) | 0.0256 (3) | 0.1965 (3) | 0.0279 (6) | |
H4 | 0.8753 | 0.0940 | 0.2338 | 0.034* | |
C5 | 0.5807 (4) | 0.2739 (3) | 0.0379 (3) | 0.0313 (6) | |
H5A | 0.5830 | 0.3670 | −0.0331 | 0.038* | |
H5B | 0.5131 | 0.1928 | 0.0234 | 0.038* | |
C6 | 0.7627 (4) | 0.2185 (3) | 0.0076 (3) | 0.0311 (6) | |
H6A | 0.8203 | 0.2134 | −0.0973 | 0.037* | |
H6B | 0.8274 | 0.2933 | 0.0332 | 0.037* | |
C7 | −0.1837 (4) | 0.1664 (3) | 0.5632 (3) | 0.0316 (6) | |
C8 | 0.0083 (4) | 0.5370 (3) | 0.7532 (3) | 0.0307 (6) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Zn1 | 0.0315 (2) | 0.0317 (2) | 0.0273 (2) | 0.00030 (14) | −0.00921 (14) | 0.00043 (13) |
S1 | 0.0343 (4) | 0.0414 (5) | 0.0491 (5) | −0.0014 (3) | −0.0194 (4) | −0.0060 (4) |
S2 | 0.0343 (4) | 0.0438 (5) | 0.0470 (5) | 0.0038 (3) | −0.0139 (4) | −0.0152 (4) |
N1 | 0.0277 (12) | 0.0249 (12) | 0.0244 (11) | 0.0036 (9) | −0.0111 (10) | −0.0009 (9) |
N2 | 0.0420 (15) | 0.0260 (13) | 0.0288 (12) | −0.0059 (11) | −0.0103 (11) | −0.0016 (10) |
N3 | 0.0309 (12) | 0.0265 (13) | 0.0275 (12) | 0.0009 (10) | −0.0123 (10) | 0.0007 (9) |
N4 | 0.0268 (12) | 0.0240 (12) | 0.0250 (11) | 0.0036 (9) | −0.0067 (9) | −0.0023 (9) |
N5 | 0.0434 (15) | 0.0294 (14) | 0.0369 (13) | 0.0015 (11) | −0.0205 (12) | −0.0059 (11) |
N6 | 0.0263 (12) | 0.0276 (13) | 0.0245 (11) | 0.0005 (10) | −0.0064 (9) | −0.0023 (9) |
N7 | 0.0403 (16) | 0.0459 (17) | 0.0499 (16) | −0.0019 (13) | −0.0200 (13) | −0.0008 (13) |
N8 | 0.0597 (18) | 0.0341 (15) | 0.0416 (15) | 0.0012 (13) | −0.0117 (14) | −0.0044 (12) |
C1 | 0.0411 (17) | 0.0276 (16) | 0.0316 (15) | −0.0013 (13) | −0.0138 (13) | −0.0022 (12) |
C2 | 0.0346 (16) | 0.0234 (15) | 0.0322 (14) | 0.0024 (12) | −0.0135 (12) | −0.0008 (11) |
C3 | 0.0384 (16) | 0.0267 (15) | 0.0323 (15) | −0.0008 (12) | −0.0131 (13) | −0.0051 (12) |
C4 | 0.0256 (14) | 0.0287 (15) | 0.0277 (14) | −0.0012 (11) | −0.0073 (11) | −0.0050 (11) |
C5 | 0.0382 (16) | 0.0295 (16) | 0.0263 (14) | 0.0075 (13) | −0.0133 (12) | −0.0030 (11) |
C6 | 0.0343 (15) | 0.0265 (15) | 0.0261 (14) | 0.0017 (12) | −0.0060 (12) | 0.0014 (11) |
C7 | 0.0323 (16) | 0.0253 (15) | 0.0317 (14) | −0.0055 (12) | −0.0058 (13) | −0.0024 (11) |
C8 | 0.0360 (16) | 0.0246 (15) | 0.0331 (15) | −0.0069 (13) | −0.0173 (13) | 0.0043 (12) |
Geometric parameters (Å, º) top
Zn1—N7 | 1.935 (3) | N5—C3 | 1.309 (4) |
Zn1—N8 | 1.945 (3) | N6—C4 | 1.321 (4) |
Zn1—N3 | 1.994 (2) | N6—C3 | 1.358 (4) |
Zn1—N6i | 2.009 (2) | N6—Zn1i | 2.009 (2) |
S1—C7 | 1.628 (3) | N7—C7 | 1.139 (4) |
S2—C8 | 1.623 (3) | N8—C8 | 1.146 (4) |
N1—C2 | 1.315 (4) | C1—H1 | 0.9500 |
N1—N2 | 1.365 (3) | C2—H2 | 0.9500 |
N1—C5 | 1.458 (3) | C3—H3 | 0.9500 |
N2—C1 | 1.311 (4) | C4—H4 | 0.9500 |
N3—C2 | 1.326 (4) | C5—C6 | 1.515 (4) |
N3—C1 | 1.354 (4) | C5—H5A | 0.9900 |
N4—C4 | 1.320 (4) | C5—H5B | 0.9900 |
N4—N5 | 1.367 (3) | C6—H6A | 0.9900 |
N4—C6 | 1.462 (3) | C6—H6B | 0.9900 |
| | | |
N7—Zn1—N8 | 110.66 (12) | N3—C1—H1 | 123.0 |
N7—Zn1—N3 | 112.05 (11) | N1—C2—N3 | 109.8 (3) |
N8—Zn1—N3 | 105.54 (11) | N1—C2—H2 | 125.1 |
N7—Zn1—N6i | 109.15 (10) | N3—C2—H2 | 125.1 |
N8—Zn1—N6i | 102.35 (11) | N5—C3—N6 | 114.1 (3) |
N3—Zn1—N6i | 116.53 (9) | N5—C3—H3 | 123.0 |
C2—N1—N2 | 110.2 (2) | N6—C3—H3 | 123.0 |
C2—N1—C5 | 128.4 (2) | N4—C4—N6 | 109.9 (2) |
N2—N1—C5 | 121.2 (2) | N4—C4—H4 | 125.1 |
C1—N2—N1 | 102.5 (2) | N6—C4—H4 | 125.1 |
C2—N3—C1 | 103.5 (2) | N1—C5—C6 | 113.4 (2) |
C2—N3—Zn1 | 130.4 (2) | N1—C5—H5A | 108.9 |
C1—N3—Zn1 | 125.69 (19) | C6—C5—H5A | 108.9 |
C4—N4—N5 | 110.1 (2) | N1—C5—H5B | 108.9 |
C4—N4—C6 | 129.6 (2) | C6—C5—H5B | 108.9 |
N5—N4—C6 | 120.4 (2) | H5A—C5—H5B | 107.7 |
C3—N5—N4 | 102.5 (2) | N4—C6—C5 | 111.3 (2) |
C4—N6—C3 | 103.5 (2) | N4—C6—H6A | 109.4 |
C4—N6—Zn1i | 129.92 (19) | C5—C6—H6A | 109.4 |
C3—N6—Zn1i | 126.59 (19) | N4—C6—H6B | 109.4 |
C7—N7—Zn1 | 159.1 (3) | C5—C6—H6B | 109.4 |
C8—N8—Zn1 | 156.4 (3) | H6A—C6—H6B | 108.0 |
N2—C1—N3 | 114.1 (3) | N7—C7—S1 | 179.3 (3) |
N2—C1—H1 | 123.0 | N8—C8—S2 | 179.2 (3) |
| | | |
C2—N1—N2—C1 | −0.1 (3) | N2—N1—C2—N3 | −0.6 (3) |
C5—N1—N2—C1 | 175.6 (2) | C5—N1—C2—N3 | −175.9 (2) |
N7—Zn1—N3—C2 | −41.1 (3) | C1—N3—C2—N1 | 0.9 (3) |
N8—Zn1—N3—C2 | −161.6 (2) | Zn1—N3—C2—N1 | 173.22 (17) |
N6i—Zn1—N3—C2 | 85.6 (2) | N4—N5—C3—N6 | 0.3 (3) |
N7—Zn1—N3—C1 | 129.6 (2) | C4—N6—C3—N5 | −0.1 (3) |
N8—Zn1—N3—C1 | 9.1 (2) | Zn1i—N6—C3—N5 | −179.51 (18) |
N6i—Zn1—N3—C1 | −103.7 (2) | N5—N4—C4—N6 | 0.3 (3) |
C4—N4—N5—C3 | −0.4 (3) | C6—N4—C4—N6 | 179.7 (2) |
C6—N4—N5—C3 | −179.8 (2) | C3—N6—C4—N4 | −0.1 (3) |
N8—Zn1—N7—C7 | 48.1 (8) | Zn1i—N6—C4—N4 | 179.24 (17) |
N3—Zn1—N7—C7 | −69.3 (8) | C2—N1—C5—C6 | −102.0 (3) |
N6i—Zn1—N7—C7 | 160.0 (7) | N2—N1—C5—C6 | 83.1 (3) |
N7—Zn1—N8—C8 | 47.0 (7) | C4—N4—C6—C5 | −114.0 (3) |
N3—Zn1—N8—C8 | 168.5 (7) | N5—N4—C6—C5 | 65.4 (3) |
N6i—Zn1—N8—C8 | −69.2 (7) | N1—C5—C6—N4 | 69.1 (3) |
N1—N2—C1—N3 | 0.7 (3) | Zn1—N7—C7—S1 | −151 (25) |
C2—N3—C1—N2 | −1.1 (3) | Zn1—N8—C8—S2 | −4 (23) |
Zn1—N3—C1—N2 | −173.83 (19) | | |
Symmetry code: (i) −x+1, −y, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C1—H1···S1ii | 0.95 | 2.95 | 3.853 (3) | 159 |
C2—H2···S1iii | 0.95 | 2.82 | 3.525 (3) | 131 |
C4—H4···S2iv | 0.95 | 2.79 | 3.574 (3) | 140 |
C6—H6B···S2iv | 0.99 | 2.95 | 3.819 (3) | 148 |
Symmetry codes: (ii) −x, −y+1, −z+1; (iii) −x, −y, −z+1; (iv) −x+1, −y+1, −z+1. |
Experimental details
Crystal data |
Chemical formula | [Zn2(NCS)4(C6H8N6)2] |
Mr | 691.51 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 193 |
a, b, c (Å) | 8.3859 (14), 8.7715 (19), 10.0402 (10) |
α, β, γ (°) | 80.784 (13), 68.195 (11), 87.373 (14) |
V (Å3) | 676.8 (2) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 2.12 |
Crystal size (mm) | 0.30 × 0.24 × 0.14 |
|
Data collection |
Diffractometer | Rigaku Mercury CCD diffractometer |
Absorption correction | Multi-scan (Jacobson, 1998) |
Tmin, Tmax | 0.546, 0.748 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6769, 2462, 2192 |
Rint | 0.025 |
(sin θ/λ)max (Å−1) | 0.602 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.032, 0.083, 1.01 |
No. of reflections | 2462 |
No. of parameters | 172 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.55, −0.39 |
Selected geometric parameters (Å, º) topZn1—N7 | 1.935 (3) | Zn1—N3 | 1.994 (2) |
Zn1—N8 | 1.945 (3) | Zn1—N6i | 2.009 (2) |
| | | |
N7—Zn1—N8 | 110.66 (12) | N3—Zn1—N6i | 116.53 (9) |
N7—Zn1—N3 | 112.05 (11) | C7—N7—Zn1 | 159.1 (3) |
N8—Zn1—N3 | 105.54 (11) | C8—N8—Zn1 | 156.4 (3) |
N7—Zn1—N6i | 109.15 (10) | N7—C7—S1 | 179.3 (3) |
N8—Zn1—N6i | 102.35 (11) | N8—C8—S2 | 179.2 (3) |
Symmetry code: (i) −x+1, −y, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C1—H1···S1ii | 0.95 | 2.95 | 3.853 (3) | 159 |
C2—H2···S1iii | 0.95 | 2.82 | 3.525 (3) | 131 |
C4—H4···S2iv | 0.95 | 2.79 | 3.574 (3) | 140 |
C6—H6B···S2iv | 0.99 | 2.95 | 3.819 (3) | 148 |
Symmetry codes: (ii) −x, −y+1, −z+1; (iii) −x, −y, −z+1; (iv) −x+1, −y+1, −z+1. |
1,2,4-Triazole and its derivatives are very interesting ligands, because they combine the coordination geometry of both pyrazole and imidazole with regard to the arrangement of their three heteroatoms. A large number of mononuclear, oligonuclear and polynuclear transition metal complexes of 1,2,4-triazole derivatives have been synthesized and characterized because of their magnetic properties and novel topologies (Haasnoot, 2000). However, the complexes of the flexible bis(triazole) ligands have not been well explored (Haasnoot, 2000; Albada et al., 2000; Zhao et al., 2002; Meng et al., 2004; Li et al., 2005).
In our previous studies, we synthesized several coordination polymers with the flexible ligand 1,2-bis(1,2,4-triazol-1-yl)ethane (bte; Li et al., 1999, 2003; Zhu et al., 2004; Wang et al., 2005). In order to extend our work, in the present paper, we report the preparation and crystal structure of a novel dimeric ZnII complex [Zn(bte)(NCS)2]2, (I).
The crystal structure of (I) is made of a neutral dimeric metallocycle. The dimer is centrosymmetric. As shown in Fig. 1, in each dimer, two zinc(II) centers are connected by two bte ligands, resulting in a discrete Zn2(bte)2 18-membered binuclear metallocycle. Wilke (1978) reported many binuclear complexes containing 3-, 4-, 5-, 7-, 9-, 11-, 12-, 13- and 14-membered binuclear metallocycles. Previously, we synthesized a dimeric copper(II) complex {[Cu(TTA)2]2(bte)} in which bte acts as a bridge, linking two [Cu(TTA)2] units and forming a dimer structure (TTA is1,1,1-trifluoro-3-(2-thenoyl)acetone; Li et al., 1999). Complex (I) is the second dimer complex constructed from bte.
Each zinc(II) center is four-coordinated by two N atoms of bte ligands and two N atoms of two thiocyanate ligands (Table 1), forming a distorted tetrahedral geometry. The Zn—N (triazole) bond lengths in (I) are shorter than those in the similar compounds [Zn(bte)(N3)2]n (Zhu et al., 2004) and [Zn(bte)2(dca)2]n (dca is dicyanamide; Li et al., 2003). The N—Zn—N bond angles are in the range 102.35 (11)–116.53 (9)°. The monodentate N-bound NCS- ligands are almost linear (Table 1).
However, the zinc(II) centers have different coordination geometry in the previously reported bte complexes. For example, the coordination environment of the zinc(II) center is distorted octahedral in [Zn(bte)2(dca)2]n, which has a one-dimensional double chain containing a Zn2(bte)2 18-membered metallocycle (Li et al., 2003). The coordination environment of the zinc(II) center is a distorted trigonal bipyramid in [Zn(bte)(N3)2]n, which forms an infinite one-dimensional chain containing both 18-membered Zn2(bte)2 and four-membered Zn2(µ-1,1-N3)2 rings (Zhu et al., 2004).
Each bte ligand exhibits the gauche conformation in (I) and the above two cited compounds, in contrast to the anti conformation of the free bte molecule (Li et al., 2004). The N1—C5—C6—N4 torsion angles are 69.1 (3)° in (I), 58.1 (2)° in [Zn(bte)2(dca)2]n (Li et al., 2003) and 62.6 (2)° in [Zn(bte)(N3)2]n (Zhu et al., 2004). The dihedral angles between two triazole rings are 60.03 (10)° in (I), 58.05 (6)° in [Zn(bte)2(dca)2]n and 51.65 (6)° in [Zn(bte)(N3)2]n. The Zn···Zn separation via the bridging bte ligand is 7.268 (2) Å in (I), compared with the corresponding values 8.369 (4) Å in [Zn(bte)2(dca)2]n and 6.722 (2) Å in [Zn(bte)(N3)2]n.
The π–π stacking interactions and weak hydrogen bonding play an important role in formation of the crystal structure. The dimers superpose together along [010] and form the channels with the dimensions 6.4 × 5.5 Å. The S atoms of adjacent dimers along [100] insert into the channels. The N4–N6/C3/C4 triazole ring and its symmetry-related (2 - x, -y, -z) triazole ring are absolutely parallel, with the centroid-to-centroid distance 4.048 Å and the perpendicular distance 3.723 Å, exhibiting obvious π–π stacking interactions (Fig. 2). There are weak C—H···S hydrogen-bonding interactions between the H atoms of the bte molecules and S atoms of the thiocyanate groups of adjacent dimers (Table 2).