• No results found

Poly­[[cis di­aqua(2,2′ bi­pyridine)copper(II)] μ 3 carboxyl­ato 4 hy­droxy­benzene­sulfonato]

N/A
N/A
Protected

Academic year: 2020

Share "Poly­[[cis di­aqua(2,2′ bi­pyridine)copper(II)] μ 3 carboxyl­ato 4 hy­droxy­benzene­sulfonato]"

Copied!
8
0
0

Loading.... (view fulltext now)

Full text

(1)

metal-organic papers

Acta Cryst.(2005). E61, m509–m511 doi:10.1107/S1600536805004022 Fanet al. [Cu(C

7H4O6S)(C10H8N2)(H2O)2]

m509

Acta Crystallographica Section E

Structure Reports Online

ISSN 1600-5368

Poly[[

cis

-diaqua(2,2

000

-bipyridine)copper(II)]-l

-3-carboxylato-4-hydroxybenzenesulfonato]

Sai-Rong Fan,aLong-Guan Zhu,a* Hong-Ping Xiaoband

Seik Weng Ngc

aDepartment of Chemistry, Zhejiang University,

Hangzhou 310007, People’s Republic of China,

bSchool of Chemistry and Materials Science,

Wenzhou Normal College, Wenzhou 325027, People’s Republic of China, andcDepartment of

Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia

Correspondence e-mail: chezlg@zju.edu.cn

Key indicators

Single-crystal X-ray study

T= 295 K

Mean(C–C) = 0.005 A˚

Rfactor = 0.052

wRfactor = 0.112

Data-to-parameter ratio = 15.1

For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e.

#2005 International Union of Crystallography

Printed in Great Britain – all rights reserved

The title complex, [Cu(C7H4O6S)(C10H8N2)(H2O)2]n, consists

of a polymeric neutral chain involving the 3-carboxylato-4-hydroxybenzenesulfonate ligand. The Cu atom shows a distorted octahedral coordination geometry, defined by two N atoms of the bipyridine, two O atoms of water molecules and the carboxyl O atom as well as one sulfonyl O atom of a symmetry-related bridging ligand. H atoms of water molecules

are involved in O—H O hydrogen bonding, building a three

dimensional network.

Comment

In a recent report on metal 3-carboxy-4-hydroxybenzene-sufonates, the authors reacted copper(II)

bis(3-carboxy-4-hydroxybenzenesulfonate) (prepared in situ) with two molar

equivalents of 2,20-bipyridine and obtained the expected bis-chelated compound but, of the two monoanions, only one is coordinated to the Cu atom, which is only five-coordinate (Gao et al., 2005). Without an abstracting reagent, a similar synthesis yielded the monochelated compound, but the

3-carboxy-4-hydroxybenzenesulfonate behaves here as a

dianion (Fig. 1).

In the title compound, (I), the doubly deprotonated

3-carboxylato-4-hydroxybenzenesulfonate group acts as a 2

-bridging ligand linking Cu atoms, forming a polymeric zigzag chain. The compound is isostructural with the cobalt(II) analog, whose structure has been described recently (Fanet al., 2005). H atoms of water molecules are involved in

inter-molecular O—H O hydrogen bonding, building a

three-dimensional network (Table 1 and Fig. 2). There are also

intramolecular O—H O hydrogen bonds between the

hydroxyl group and the carboxyl O atom coordinated to copper, and between one of the water molecules and the second carboxyl O atom (Table 1).

(2)

Experimental

A solution of copper acetate hydrate (0.041 g, 0.2 mmol) and 5-sulfosalicylic acid dihydrate (0.103 g, 0.4 mmol) dissolved in water (20 ml) was added to a methanol solution (5 ml) of 2,20-bipyridyl

(0.030 g, 0.2 mmol). The clear blue solution was left to stand for a day to allow the solvent to evaporate. Blue block-shaped crystals were

obtained. Analysis calculated for C17H16CuN2O8S: C 43.26, H 3.42, N

5.94%; found: C 42.63, H 3.47, N 5.96%.

Crystal data

[Cu(C7H4O6S)(C10H8N2)(H2O)2] Mr= 471.92

Monoclinic,P21=n a= 14.2339 (8) A˚

b= 7.7622 (4) A˚

c= 17.801 (1) A˚

= 110.940 (1) V= 1836.87 (17) A˚3

Z= 4

Dx= 1.707 Mg m

3

MoKradiation Cell parameters from 4713

reflections

= 2.3–28.3 = 1.35 mm1

T= 295 (2) K Block, blue

0.280.260.12 mm

Data collection

Bruker SMART APEX area-detector diffractometer

’and!scans

Absorption correction: multi-scan (SADABS; Bruker, 2002)

Tmin= 0.703,Tmax= 0.854

10938 measured reflections

4143 independent reflections 3855 reflections withI> 2(I)

Rint= 0.024 max= 27.5

h=18!18

k=9!10

l=23!14

Refinement

Refinement onF2 R[F2> 2(F2)] = 0.052

wR(F2) = 0.112 S= 1.20 4143 reflections 275 parameters

H atoms treated by a mixture of independent and constrained refinement

w= 1/[2(F

o2) + (0.0379P)2

+ 2.6968P]

whereP= (Fo2+ 2Fc2)/3

(/)max= 0.001

max= 0.63 e A˚ 3

min=0.40 e A˚ 3

Table 1

Hydrogen-bonding geometry (A˚ ,).

D—H A D—H H A D A D—H A

O1W—H1W1 O2i

0.821 (18) 1.870 (19) 2.688 (3) 174 (4) O1W—H1W2 O2ii

0.83 (4) 1.89 (4) 2.717 (3) 178 (4) O2W—H2W1 O3i 0.848 (17) 2.001 (19) 2.810 (4) 159 (3) O2W—H2W2 O4 0.852 (18) 1.99 (2) 2.738 (4) 146 (3) O6—H6 O5 0.82 1.89 2.599 (3) 143

Symmetry codes: (i)x1 2;

3 2y;z

1

2; (ii) 1x;1y;2z.

Aromatic H atoms were positioned geometrically and were included in the refinement in the riding-model approximation [C— H = 0.93 A˚ andUiso(H) = 1.2Ueq(C)]. The water and hydroxy H atoms

were located in a difference Fourier map and refined with distance restraints of O—H = 0.85 (1) A˚ and H H = 1.39 (1) A˚ , and

Uiso(H) = 1.2Ueq(O).

Data collection:SMART(Bruker, 2002); cell refinement:SAINT

(Bruker, 2002); data reduction:SAINT; program(s) used to solve structure:SHELXS97(Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics:

ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication:SHELXL97.

We thank the National Natural Science Foundation of China (No. 50073019) and the University of Malaya for supporting this study.

References

Bruker (2002).SADABS, SAINTandSMART. Bruker AXS Inc., Madison, Wisconsin, USA.

Burnett, M. N. & Johnson, C. K. (1996).ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA.

metal-organic papers

m510

Fanet al. [Cu(C

[image:2.610.45.295.76.191.2]

7H4O6S)(C10H8N2)(H2O)2] Acta Cryst.(2005). E61, m509–m511 Figure 2

CAMERON(Watkinet al., 1993) view of the packing, showing the O—

H O hydrogen-bonded (dashed lines) three-dimensional network. H

atoms not involved in hydrogen bonding have been omitted.

Figure 1

ORTEPIII(Burnett & Johnson, 1996) plot of a fragment of the polymeric chain of (I). Displacement ellipsoids are drawn at the 30% probability

level. H atoms have been omitted for clarity. [Symmetry codes: (i)x1

2, 1

2y, z 1 2; (ii)

1 2+x,

1 2y,

[image:2.610.45.296.253.622.2]
(3)

Fan, S.-R., Zhu, L.-G., Xiao, H.-P. & Ng, S. W. (2005).Acta Cryst.E61, m435– m436.

Gao, S., Huo, L.-H., Zhao, H. & Ng, S. W. (2005).Acta Cryst.E61, m290– m292.

Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Go¨ttingen, Germany.

Watkin, D. M., Pearce, L. & Prout, C. K. (1993).CAMERON. Chemical Crystallography Laboratory, University of Oxford, England.

metal-organic papers

Acta Cryst.(2005). E61, m509–m511 Fanet al. [Cu(C

(4)

supporting information

sup-1

Acta Cryst. (2005). E61, m509–m511

supporting information

Acta Cryst. (2005). E61, m509–m511 [https://doi.org/10.1107/S1600536805004022]

Poly[[

cis

-diaqua(2,2

-bipyridine)copper(II)]-µ-3-carboxylato-4-hydroxybenzene-sulfonato]

Sai-Rong Fan, Long-Guan Zhu, Hong-Ping Xiao and Seik Weng Ng

Poly[[cis-diaqua(2,2′-bipyridine)copper(II)]-µ-3-carboxylato-4- hydroxybenzenesulfonato]

Crystal data

[Cu(C7H4O6S)(C10H8N2)(H2O)2] Mr = 471.92

Monoclinic, P21/n

Hall symbol: -P 2yn

a = 14.2339 (8) Å

b = 7.7622 (4) Å

c = 17.801 (1) Å

β = 110.940 (1)°

V = 1836.87 (17) Å3 Z = 4

F(000) = 964

Dx = 1.707 Mg m−3

Mo radiation, λ = 0.71073 Å Cell parameters from 4713 reflections

θ = 2.3–28.3°

µ = 1.35 mm−1 T = 295 K Block, blue

0.28 × 0.26 × 0.12 mm

Data collection

Bruker APEX area-detector diffractometer

Radiation source: fine-focus sealed tube Graphite monochromator

φ and ω scans

Absorption correction: multi-scan (SADABS; Bruker, 2002)

Tmin = 0.703, Tmax = 0.854

10938 measured reflections 4143 independent reflections 3855 reflections with I > 2σ(I)

Rint = 0.024

θmax = 27.5°, θmin = 2.3° h = −18→18

k = −9→10

l = −23→14

Refinement

Refinement on F2

Least-squares matrix: full

R[F2 > 2σ(F2)] = 0.052 wR(F2) = 0.112 S = 1.20 4143 reflections 275 parameters 6 restraints

Primary atom site location: structure-invariant direct methods

Secondary atom site location: difference Fourier map

Hydrogen site location: inferred from neighbouring sites

H atoms treated by a mixture of independent and constrained refinement

w = 1/[σ2(F

o2) + (0.0379P)2 + 2.6968P]

where P = (Fo2 + 2Fc2)/3

(Δ/σ)max = 0.001

Δρmax = 0.63 e Å−3

(5)

supporting information

sup-2

Acta Cryst. (2005). E61, m509–m511 Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2)

x y z Uiso*/Ueq

Cu1 0.41473 (3) 0.43810 (5) 0.67992 (2) 0.02594 (12) S1 0.79903 (5) 0.47741 (9) 1.14844 (4) 0.02252 (17) O1 0.84091 (17) 0.3277 (3) 1.19711 (13) 0.0332 (5) H1W1 0.298 (3) 0.659 (2) 0.699 (2) 0.040* H1W2 0.283 (3) 0.503 (4) 0.732 (2) 0.040* O2 0.76904 (17) 0.6060 (3) 1.19620 (14) 0.0312 (5) H2W1 0.477 (2) 0.794 (3) 0.669 (2) 0.037* H2W2 0.552 (2) 0.711 (4) 0.7302 (13) 0.037* O3 0.86249 (17) 0.5509 (3) 1.10858 (14) 0.0381 (6) O4 0.5985 (2) 0.6006 (4) 0.83827 (15) 0.0504 (7) O5 0.48314 (18) 0.3947 (3) 0.79452 (13) 0.0366 (6) O6 0.43908 (19) 0.1997 (3) 0.89597 (15) 0.0418 (6)

H6 0.4286 0.2432 0.8517 0.063*

O1W 0.3048 (2) 0.5534 (3) 0.70075 (16) 0.0374 (6) O2W 0.5126 (2) 0.7034 (4) 0.68134 (16) 0.0492 (7) N1 0.5126 (2) 0.3111 (4) 0.64346 (17) 0.0330 (6) N2 0.3418 (2) 0.4546 (4) 0.56064 (16) 0.0297 (6) C1 0.5980 (3) 0.2396 (6) 0.6905 (3) 0.0512 (10)

H1 0.6175 0.2524 0.7459 0.061*

C2 0.6591 (4) 0.1463 (7) 0.6598 (3) 0.0663 (14)

H2 0.7188 0.0975 0.6940 0.080*

C3 0.6302 (4) 0.1275 (6) 0.5784 (3) 0.0615 (13)

H3 0.6696 0.0637 0.5566 0.074*

C4 0.5433 (3) 0.2024 (5) 0.5290 (3) 0.0484 (10)

H4 0.5237 0.1923 0.4735 0.058*

C5 0.4847 (3) 0.2939 (4) 0.5629 (2) 0.0339 (8) C6 0.3882 (3) 0.3768 (4) 0.5159 (2) 0.0321 (7) C7 0.3473 (3) 0.3769 (6) 0.4324 (2) 0.0485 (10)

H7 0.3798 0.3221 0.4021 0.058*

C8 0.2571 (3) 0.4608 (6) 0.3959 (2) 0.0559 (12)

H8 0.2286 0.4640 0.3400 0.067*

C9 0.2092 (3) 0.5391 (6) 0.4407 (2) 0.0503 (10)

H9 0.1480 0.5949 0.4161 0.060*

(6)

supporting information

sup-3

Acta Cryst. (2005). E61, m509–m511

C14 0.5193 (2) 0.2755 (4) 0.95086 (19) 0.0273 (6) C15 0.5455 (2) 0.2172 (4) 1.02982 (19) 0.0295 (7) H15 0.5055 0.1353 1.0421 0.035* C16 0.6298 (2) 0.2792 (4) 1.08982 (18) 0.0273 (6) H16 0.6478 0.2367 1.1419 0.033* C17 0.5521 (2) 0.4770 (4) 0.84987 (19) 0.0285 (7)

Atomic displacement parameters (Å2)

U11 U22 U33 U12 U13 U23

Cu1 0.0293 (2) 0.0303 (2) 0.01867 (19) 0.00308 (15) 0.00907 (15) −0.00059 (15) S1 0.0235 (4) 0.0244 (4) 0.0182 (3) −0.0007 (3) 0.0058 (3) −0.0005 (3) O1 0.0349 (12) 0.0303 (12) 0.0265 (12) 0.0063 (10) 0.0014 (10) −0.0012 (10) O2 0.0404 (13) 0.0233 (11) 0.0307 (12) −0.0025 (9) 0.0136 (10) −0.0042 (9) O3 0.0314 (12) 0.0561 (16) 0.0271 (12) −0.0118 (11) 0.0109 (10) −0.0018 (11) O4 0.0543 (17) 0.0612 (18) 0.0249 (12) −0.0283 (14) 0.0012 (12) 0.0110 (12) O5 0.0422 (14) 0.0403 (13) 0.0185 (11) −0.0127 (11) 0.0002 (10) −0.0006 (10) O6 0.0397 (14) 0.0434 (14) 0.0307 (13) −0.0179 (11) −0.0018 (11) 0.0066 (11) O1W 0.0554 (16) 0.0252 (12) 0.0456 (15) 0.0100 (11) 0.0351 (13) 0.0075 (11) O2W 0.0594 (19) 0.0525 (17) 0.0351 (14) 0.0176 (14) 0.0161 (14) 0.0080 (13) N1 0.0354 (15) 0.0347 (15) 0.0344 (15) 0.0058 (12) 0.0192 (13) 0.0051 (12) N2 0.0340 (15) 0.0338 (14) 0.0231 (13) −0.0035 (12) 0.0126 (12) 0.0008 (11) C1 0.048 (2) 0.063 (3) 0.046 (2) 0.018 (2) 0.0217 (19) 0.013 (2) C2 0.056 (3) 0.068 (3) 0.087 (4) 0.031 (2) 0.041 (3) 0.026 (3) C3 0.068 (3) 0.056 (3) 0.085 (4) 0.013 (2) 0.057 (3) 0.002 (3) C4 0.061 (3) 0.045 (2) 0.056 (3) −0.0074 (19) 0.041 (2) −0.0097 (19) C5 0.0424 (19) 0.0317 (17) 0.0369 (19) −0.0076 (15) 0.0254 (16) −0.0027 (14) C6 0.0411 (19) 0.0336 (17) 0.0263 (16) −0.0126 (15) 0.0178 (15) −0.0045 (14) C7 0.062 (3) 0.058 (2) 0.0311 (19) −0.013 (2) 0.0238 (19) −0.0107 (18) C8 0.063 (3) 0.071 (3) 0.0244 (18) −0.019 (2) 0.0043 (19) 0.000 (2) C9 0.042 (2) 0.064 (3) 0.034 (2) −0.0045 (19) 0.0002 (17) 0.0100 (19) C10 0.0359 (18) 0.043 (2) 0.0327 (18) 0.0013 (15) 0.0108 (15) 0.0067 (16) C11 0.0214 (14) 0.0246 (14) 0.0189 (14) −0.0001 (11) 0.0038 (11) −0.0027 (11) C12 0.0238 (14) 0.0254 (15) 0.0223 (14) −0.0019 (12) 0.0072 (12) 0.0019 (12) C13 0.0249 (14) 0.0262 (15) 0.0194 (14) 0.0001 (12) 0.0064 (12) −0.0005 (12) C14 0.0235 (15) 0.0261 (15) 0.0286 (16) −0.0011 (12) 0.0048 (13) −0.0008 (13) C15 0.0298 (16) 0.0284 (16) 0.0297 (17) −0.0057 (13) 0.0100 (14) 0.0041 (13) C16 0.0294 (16) 0.0307 (16) 0.0204 (14) 0.0008 (13) 0.0073 (13) 0.0051 (13) C17 0.0272 (15) 0.0337 (17) 0.0226 (15) 0.0002 (13) 0.0062 (13) 0.0017 (13)

Geometric parameters (Å, º)

Cu1—O1W 1.950 (2) C2—H2 0.9300

Cu1—O5 1.950 (2) C3—C4 1.365 (6)

Cu1—N1 1.994 (3) C3—H3 0.9300

Cu1—N2 2.007 (3) C4—C5 1.387 (5)

Cu1—O1i 2.384 (2) C4—H4 0.9300

(7)

supporting information

sup-4

Acta Cryst. (2005). E61, m509–m511

S1—O3 1.450 (2) C6—C7 1.389 (5)

S1—O2 1.470 (2) C7—C8 1.377 (6)

S1—C11 1.768 (3) C7—H7 0.9300

O1—Cu1ii 2.384 (2) C8—C9 1.364 (6)

O4—C17 1.223 (4) C8—H8 0.9300

O5—C17 1.285 (4) C9—C10 1.381 (5)

O6—C14 1.344 (4) C9—H9 0.9300

O6—H6 0.8200 C10—H10 0.9300

O1W—H1W1 0.821 (18) C11—C12 1.379 (4) O1W—H1W2 0.83 (4) C11—C16 1.389 (4) O2W—H2W1 0.848 (17) C12—C13 1.396 (4) O2W—H2W2 0.852 (18) C12—H12 0.9300

N1—C1 1.327 (5) C13—C14 1.402 (4)

N1—C5 1.350 (4) C13—C17 1.500 (4)

N2—C10 1.339 (4) C14—C15 1.395 (4)

N2—C6 1.346 (4) C15—C16 1.377 (4)

C1—C2 1.386 (6) C15—H15 0.9300

C1—H1 0.9300 C16—H16 0.9300

C2—C3 1.366 (7)

O1W—Cu1—O5 90.85 (11) C5—C4—H4 120.5 O1W—Cu1—N1 171.82 (12) N1—C5—C4 121.2 (4) O5—Cu1—N1 96.28 (11) N1—C5—C6 114.8 (3) O1W—Cu1—N2 91.43 (11) C4—C5—C6 124.0 (3) O5—Cu1—N2 173.69 (11) N2—C6—C7 121.7 (3) N1—Cu1—N2 81.07 (11) N2—C6—C5 114.5 (3) O1W—Cu1—O1i 87.27 (9) C7—C6—C5 123.8 (3)

O5—Cu1—O1i 78.14 (9) C8—C7—C6 118.0 (4)

N1—Cu1—O1i 90.29 (10) C8—C7—H7 121.0

N2—Cu1—O1i 96.09 (9) C6—C7—H7 121.0

O1—S1—O3 114.48 (15) C9—C8—C7 120.7 (4) O1—S1—O2 110.01 (13) C9—C8—H8 119.6 O3—S1—O2 112.10 (14) C7—C8—H8 119.6 O1—S1—C11 105.73 (14) C8—C9—C10 118.4 (4) O3—S1—C11 106.94 (14) C8—C9—H9 120.8 O2—S1—C11 107.07 (14) C10—C9—H9 120.8 S1—O1—Cu1ii 136.51 (14) N2—C10—C9 122.2 (4)

C17—O5—Cu1 132.5 (2) N2—C10—H10 118.9

C14—O6—H6 109.5 C9—C10—H10 118.9

(8)

supporting information

sup-5

Acta Cryst. (2005). E61, m509–m511

C6—N2—Cu1 114.8 (2) O6—C14—C15 116.3 (3) N1—C1—C2 122.2 (4) O6—C14—C13 124.1 (3) N1—C1—H1 118.9 C15—C14—C13 119.7 (3) C2—C1—H1 118.9 C16—C15—C14 120.9 (3) C3—C2—C1 118.7 (4) C16—C15—H15 119.5

C3—C2—H2 120.6 C14—C15—H15 119.5

C1—C2—H2 120.6 C15—C16—C11 119.7 (3) C4—C3—C2 119.8 (4) C15—C16—H16 120.2

C4—C3—H3 120.1 C11—C16—H16 120.2

C2—C3—H3 120.1 O4—C17—O5 124.8 (3)

C3—C4—C5 119.1 (4) O4—C17—C13 120.6 (3) C3—C4—H4 120.5 O5—C17—C13 114.6 (3)

Symmetry codes: (i) x−1/2, −y+1/2, z−1/2; (ii) x+1/2, −y+1/2, z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A D—H H···A D···A D—H···A

O1W—H1W1···O2iii 0.82 (2) 1.87 (2) 2.688 (3) 174 (4)

O1W—H1W2···O2iv 0.83 (4) 1.89 (4) 2.717 (3) 178 (4)

O2W—H2W1···O3iii 0.85 (2) 2.00 (2) 2.810 (4) 159 (3)

O2W—H2W2···O4 0.85 (2) 1.99 (2) 2.738 (4) 146 (3)

O6—H6···O5 0.82 1.89 2.599 (3) 143

Figure

Figure 2

References

Related documents

The geometry around each Cd(II) ion is distorted octahedral, in which three positions are occupied by two N atoms and one O atom from the Schiff base ligand, two positions by

In the title polymer, [Mn(C8H8O5)(H2O)2]n, the Mn II atom is in a distorted octahedral coordination mode, binding to the bridging O atom of the bicycloheptane unit, two O atoms

One Ni II ion is in a slightly-distorted octahedral coordination environment formed by three O atoms from two adjacent pydc ligands, two N atoms from bpt and pydc ligands, and one

from one 2,2′-bipyridine ligand and four O atoms that belong to two oxalate dianions (Table 1) in a distorted octahedral geometry, as shown in Fig. Two neighboring Co centers

Within the cationic chain, atom Ag1 adopts a distorted trigonal coordination geometry, defined by two N donors from two 4,4′-bipyridine ligands and one water molecule, while in

The coordination geometry of the nickel(II) atom is distorted octahedral, being coordinated by four N atoms of four symmetry-related dca ligands in the equatorial plane and two O

The Ni II atom is coordinated by two N atoms from two distinct ligands ( L ) and four O atoms from water molecules, giving a slightly distorted octahedral coordination geometry with

The coordination of Mn1 can be described as octahedral, with two O atoms from different monodentate carboxyl groups and four water molecules, while atom Mn2 exists in a