4,4'-Imino-dipyridinium bis-(hydrogen phthalate).

In the title salt, C(10)H(11)N(3) (2+)·2C(8)H(5)O(4) (-), doubly protonated 4,4'-dipyridylamine (dpa) cations participate in N-H⋯O hydrogen bonding with two hydrogen phthalate anions to form a neutral unit. Both anions contain an intramolecular O-H⋯O hydrogen bond. In the crystal structure, these units form two-dimensional layers through π-π stacking inter-actions with a centroid-to-centroid distance of 3.763 (3) Å. In turn, these layers aggregate in three dimensions by additional N-H⋯O hydrogen bonding. The assignment to the noncentrosymmetric space group P1 is corroborated by chemically unreasonable aromatic ring bond distances and poor K scale factor distributions for a disordered model in the centrosymmetric P space group.

Related literature

For the crystal structure of dpa, see: Cordes et al. (2006 ▶). For a chiral dpa-containing coordination polymer, see: Montney et al. (2007 ▶). For carboxylic acid/imine co-crystals, see: Horiuchi et al. (2005 ▶); Bhogala & Nangia (2003 ▶). For charge-separated hydrogen bonding, see: Steiner (2002 ▶). For the preparation of dpa, see: Zapf et al. (1998 ▶).

Experimental

Crystal data

C10H11N3 2+·2C8H5O4 −

M = 503.46

Triclinic,

a = 7.858 (2) Å

b = 8.101 (2) Å

c = 9.601 (3) Å

α = 85.673 (5)°

β = 85.186 (5)°

γ = 68.834 (4)°

V = 567.3 (3) Å3

Z = 1

Mo Kα radiation

μ = 0.11 mm−1

T = 293 (2) K

0.75 × 0.60 × 0.30 mm

Data collection

Bruker SMART 1K diffractometer

Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ▶) T min = 0.831, T max = 0.967

6282 measured reflections

2513 independent reflections

2269 reflections with I > 2σ(I)

R int = 0.014

Refinement

R[F 2 > 2σ(F 2)] = 0.060

wR(F 2) = 0.170

S = 1.06

2513 reflections

349 parameters

6 restraints

H atoms treated by a mixture of independent and constrained refinement

Δρmax = 0.56 e Å−3

Δρmin = −0.32 e Å−3

Data collection: SMART (Bruker, 2001 ▶); cell refinement: SAINT-Plus (Bruker, 2003 ▶); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: CrystalMaker (Palmer, 2005 ▶); software used to prepare material for publication: SHELXL97.

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808031681/lh2702sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808031681/lh2702Isup2.hkl

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

C10H11N32+·2C8H5O4−	Z = 1
Mr = 503.46	F(000) = 262
Triclinic, P1	Dx = 1.474 Mg m−3
Hall symbol: P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.858 (2) Å	Cell parameters from 6282 reflections
b = 8.101 (2) Å	θ = 2.1–28.0°
c = 9.601 (3) Å	µ = 0.11 mm−1
α = 85.673 (5)°	T = 293 K
β = 85.186 (5)°	Block, colourless
γ = 68.834 (4)°	0.75 × 0.60 × 0.30 mm
V = 567.3 (3) Å3

Bruker SMART 1K diffractometer	2513 independent reflections
Radiation source: fine-focus sealed tube	2269 reflections with I > 2σ(I)
graphite	Rint = 0.014
ω scans	θmax = 28.0°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −10→10
Tmin = 0.831, Tmax = 0.967	k = −10→10
6282 measured reflections	l = −12→12

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)] = 0.060	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.170	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ2(Fo2) + (0.0871P)2 + 0.2863P] where P = (Fo2 + 2Fc2)/3
2513 reflections	(Δ/σ)max < 0.001
349 parameters	Δρmax = 0.56 e Å−3
6 restraints	Δρmin = −0.32 e Å−3

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.

	x	y	z	Uiso*/Ueq
O1	−0.9711 (7)	0.8965 (7)	1.1049 (4)	0.0832 (14)
O2	−0.7469 (5)	0.7612 (6)	1.2383 (5)	0.0712 (12)
O3	−0.6750 (5)	0.5656 (7)	1.4411 (6)	0.0824 (14)
H3A	−0.691 (11)	0.624 (10)	1.337 (9)	0.099*
O4	−0.8021 (6)	0.3983 (6)	1.5649 (5)	0.0780 (13)
O5	0.3019 (7)	1.2225 (8)	0.2453 (5)	0.0926 (17)
O6	0.0684 (5)	1.3566 (6)	0.1220 (5)	0.0709 (12)
H7A	0.043 (9)	1.430 (9)	0.028 (8)	0.085*
O7	−0.0087 (5)	1.5473 (6)	−0.0843 (5)	0.0802 (13)
O8	0.1036 (5)	1.7269 (5)	−0.2062 (4)	0.0654 (10)
N1	−0.6896 (8)	0.9599 (7)	0.9469 (5)	0.0655 (14)
H1N	−0.780 (6)	0.944 (9)	0.995 (6)	0.079*
N2	−0.0792 (9)	1.2304 (7)	0.3688 (5)	0.0760 (18)
H2N	−0.047 (10)	1.285 (8)	0.299 (5)	0.091*
N3	−0.2299 (5)	0.9798 (5)	0.7185 (4)	0.0495 (8)
H3N	−0.121 (5)	0.902 (6)	0.751 (6)	0.059*
C1	−0.7118 (7)	1.0624 (9)	0.8305 (7)	0.0714 (17)
H1	−0.8289	1.1282	0.8031	0.086*
C2	−0.5601 (8)	1.0716 (7)	0.7497 (5)	0.0605 (14)
H2	−0.5747	1.1424	0.6674	0.073*
C3	−0.3924 (6)	0.9770 (7)	0.7916 (5)	0.0533 (12)
C4	−0.3767 (8)	0.8754 (8)	0.9177 (6)	0.0689 (16)
H4	−0.2625	0.8122	0.9517	0.083*
C5	−0.5320 (10)	0.8709 (8)	0.9894 (6)	0.0713 (16)
H5	−0.5226	0.8009	1.0718	0.086*
C6	0.0413 (8)	1.1117 (8)	0.4402 (7)	0.0668 (15)
H6	0.1643	1.0811	0.4115	0.080*
C7	−0.0060 (7)	1.0321 (7)	0.5539 (6)	0.0607 (13)
H7	0.0843	0.9471	0.6042	0.073*
C8	−0.1878 (8)	1.0729 (6)	0.5996 (5)	0.0517 (11)
C9	−0.3186 (7)	1.1998 (8)	0.5237 (6)	0.0618 (14)
H9	−0.4424	1.2313	0.5500	0.074*
C10	−0.2574 (9)	1.2797 (8)	0.4051 (6)	0.0697 (15)
H10	−0.3414	1.3673	0.3517	0.084*
C11	−1.0440 (6)	0.7547 (6)	1.3134 (4)	0.0392 (9)
C12	−1.2276 (6)	0.8392 (7)	1.2857 (5)	0.0508 (11)
H12	−1.2573	0.9150	1.2065	0.061*
C13	−1.3670 (7)	0.8140 (8)	1.3720 (7)	0.0642 (14)
H13	−1.4881	0.8714	1.3502	0.077*
C14	−1.3265 (7)	0.7059 (8)	1.4877 (6)	0.0639 (15)
H14	−1.4203	0.6922	1.5477	0.077*
C15	−1.1462 (7)	0.6149 (7)	1.5178 (5)	0.0547 (12)
H15	−1.1207	0.5380	1.5967	0.066*
C16	−1.0025 (6)	0.6360 (5)	1.4328 (4)	0.0384 (9)
C17	−0.9122 (7)	0.8067 (6)	1.2125 (5)	0.0493 (11)
C18	−0.8166 (7)	0.5225 (7)	1.4825 (6)	0.0586 (12)
C21	0.3638 (5)	1.3702 (5)	0.0345 (4)	0.0391 (9)
C22	0.5473 (7)	1.2878 (7)	0.0605 (5)	0.0535 (12)
H22	0.5797	1.2125	0.1396	0.064*
C23	0.6836 (7)	1.3158 (8)	−0.0294 (7)	0.0640 (14)
H23	0.8060	1.2567	−0.0120	0.077*
C24	0.6362 (7)	1.4317 (9)	−0.1449 (6)	0.0632 (14)
H24	0.7259	1.4535	−0.2048	0.076*
C25	0.4570 (7)	1.5131 (7)	−0.1694 (5)	0.0539 (12)
H25	0.4265	1.5892	−0.2483	0.065*
C26	0.3158 (6)	1.4886 (6)	−0.0825 (4)	0.0420 (9)
C27	0.2367 (8)	1.3142 (7)	0.1443 (5)	0.0548 (12)
C28	0.1238 (6)	1.5967 (6)	−0.1279 (5)	0.0488 (10)

	U11	U22	U33	U12	U13	U23
O1	0.080 (3)	0.110 (4)	0.055 (2)	−0.037 (3)	0.000 (2)	0.034 (2)
O2	0.044 (2)	0.090 (3)	0.076 (3)	−0.0278 (18)	0.0088 (17)	0.023 (2)
O3	0.0427 (19)	0.099 (3)	0.106 (3)	−0.030 (2)	−0.022 (2)	0.032 (3)
O4	0.081 (3)	0.072 (3)	0.072 (3)	−0.020 (2)	−0.018 (2)	0.032 (2)
O5	0.083 (3)	0.134 (5)	0.058 (2)	−0.047 (3)	0.000 (2)	0.048 (3)
O6	0.046 (2)	0.083 (3)	0.079 (3)	−0.0271 (18)	0.0162 (18)	0.022 (2)
O7	0.0424 (18)	0.088 (3)	0.108 (3)	−0.0269 (18)	−0.0145 (19)	0.040 (2)
O8	0.054 (2)	0.064 (2)	0.071 (2)	−0.0164 (17)	−0.0107 (17)	0.0269 (18)
N1	0.071 (3)	0.081 (3)	0.061 (3)	−0.051 (3)	0.032 (2)	−0.020 (2)
N2	0.125 (5)	0.062 (3)	0.051 (2)	−0.054 (3)	0.037 (3)	0.000 (2)
N3	0.0458 (17)	0.056 (2)	0.0426 (18)	−0.0175 (15)	0.0023 (14)	0.0135 (15)
C1	0.040 (3)	0.084 (4)	0.082 (4)	−0.008 (3)	−0.013 (2)	−0.014 (3)
C2	0.084 (4)	0.056 (3)	0.039 (2)	−0.024 (3)	−0.011 (2)	0.018 (2)
C3	0.045 (2)	0.070 (3)	0.050 (3)	−0.028 (2)	0.0135 (19)	−0.015 (2)
C4	0.063 (3)	0.066 (3)	0.051 (3)	0.006 (2)	−0.005 (2)	0.010 (2)
C5	0.098 (5)	0.059 (3)	0.049 (3)	−0.025 (3)	0.005 (3)	0.018 (2)
C6	0.054 (3)	0.066 (3)	0.083 (4)	−0.028 (2)	0.018 (3)	−0.015 (3)
C7	0.049 (3)	0.067 (3)	0.057 (3)	−0.009 (2)	−0.007 (2)	−0.003 (2)
C8	0.076 (3)	0.043 (2)	0.038 (2)	−0.027 (2)	0.011 (2)	0.0008 (17)
C9	0.044 (2)	0.078 (4)	0.063 (3)	−0.021 (2)	0.007 (2)	−0.014 (3)
C10	0.082 (4)	0.058 (3)	0.058 (3)	−0.012 (3)	−0.018 (3)	0.014 (2)
C11	0.037 (2)	0.048 (2)	0.0359 (19)	−0.0200 (17)	−0.0010 (16)	0.0031 (16)
C12	0.040 (2)	0.059 (3)	0.051 (3)	−0.016 (2)	−0.0064 (19)	0.009 (2)
C13	0.036 (2)	0.077 (4)	0.077 (4)	−0.018 (2)	−0.004 (2)	0.002 (3)
C14	0.047 (3)	0.078 (4)	0.076 (4)	−0.037 (3)	0.015 (2)	−0.001 (3)
C15	0.060 (3)	0.065 (3)	0.048 (3)	−0.036 (2)	0.006 (2)	0.009 (2)
C16	0.041 (2)	0.041 (2)	0.038 (2)	−0.0194 (17)	−0.0055 (16)	0.0053 (16)
C17	0.054 (3)	0.055 (3)	0.041 (2)	−0.025 (2)	0.0030 (19)	0.0045 (19)
C18	0.054 (3)	0.057 (3)	0.064 (3)	−0.019 (2)	−0.012 (2)	0.009 (2)
C21	0.038 (2)	0.040 (2)	0.039 (2)	−0.0150 (16)	−0.0002 (16)	0.0020 (16)
C22	0.051 (3)	0.058 (3)	0.052 (3)	−0.020 (2)	−0.016 (2)	0.014 (2)
C23	0.034 (2)	0.077 (3)	0.083 (4)	−0.024 (2)	−0.004 (2)	0.002 (3)
C24	0.047 (3)	0.088 (4)	0.061 (3)	−0.037 (3)	0.015 (2)	0.004 (3)
C25	0.050 (3)	0.065 (3)	0.049 (3)	−0.027 (2)	−0.001 (2)	0.014 (2)
C26	0.0350 (19)	0.052 (2)	0.041 (2)	−0.0199 (17)	0.0055 (16)	−0.0010 (18)
C27	0.062 (3)	0.058 (3)	0.045 (2)	−0.026 (2)	0.015 (2)	0.004 (2)
C28	0.042 (2)	0.051 (2)	0.051 (2)	−0.0165 (18)	−0.0068 (18)	0.013 (2)

O1—C17	1.238 (6)	C7—C8	1.385 (7)
O2—C17	1.257 (6)	C7—H7	0.9300
O2—H3A	1.37 (9)	C8—C9	1.376 (8)
O3—C18	1.305 (7)	C9—C10	1.403 (8)
O3—H3A	1.07 (9)	C9—H9	0.9300
O4—C18	1.210 (6)	C10—H10	0.9300
O5—C27	1.206 (7)	C11—C12	1.395 (6)
O6—C27	1.273 (7)	C11—C16	1.420 (6)
O6—H7A	1.03 (8)	C11—C17	1.507 (6)
O7—C28	1.273 (6)	C12—C13	1.383 (7)
O7—H7A	1.37 (8)	C12—H12	0.9300
O8—C28	1.218 (6)	C13—C14	1.347 (8)
N1—C5	1.271 (9)	C13—H13	0.9300
N1—C1	1.325 (9)	C14—C15	1.385 (8)
N1—H1N	0.86 (6)	C14—H14	0.9300
N2—C6	1.282 (9)	C15—C16	1.391 (6)
N2—C10	1.333 (9)	C15—H15	0.9300
N2—H2N	0.85 (6)	C16—C18	1.513 (7)
N3—C8	1.403 (5)	C21—C22	1.388 (6)
N3—C3	1.411 (5)	C21—C26	1.404 (6)
N3—H3N	0.92 (5)	C21—C27	1.547 (6)
C1—C2	1.389 (9)	C22—C23	1.391 (7)
C1—H1	0.9300	C22—H22	0.9300
C2—C3	1.342 (8)	C23—C24	1.382 (9)
C2—H2	0.9300	C23—H23	0.9300
C3—C4	1.400 (7)	C24—C25	1.355 (8)
C4—C5	1.361 (9)	C24—H24	0.9300
C4—H4	0.9300	C25—C26	1.394 (6)
C5—H5	0.9300	C25—H25	0.9300
C6—C7	1.321 (9)	C26—C28	1.527 (6)
C6—H6	0.9300
C17—O2—H3A	114 (4)	C13—C12—C11	122.2 (4)
C18—O3—H3A	110 (4)	C13—C12—H12	118.9
C27—O6—H7A	109 (4)	C11—C12—H12	118.9
C28—O7—H7A	109 (3)	C14—C13—C12	119.7 (5)
C5—N1—C1	121.9 (5)	C14—C13—H13	120.2
C5—N1—H1N	116 (5)	C12—C13—H13	120.2
C1—N1—H1N	122 (5)	C13—C14—C15	120.4 (5)
C6—N2—C10	122.0 (5)	C13—C14—H14	119.8
C6—N2—H2N	120 (5)	C15—C14—H14	119.8
C10—N2—H2N	118 (5)	C14—C15—C16	121.4 (5)
C8—N3—C3	135.3 (4)	C14—C15—H15	119.3
C8—N3—H3N	108 (4)	C16—C15—H15	119.3
C3—N3—H3N	117 (4)	C15—C16—C11	118.6 (4)
N1—C1—C2	119.9 (5)	C15—C16—C18	113.1 (4)
N1—C1—H1	120.0	C11—C16—C18	128.3 (4)
C2—C1—H1	120.0	O1—C17—O2	121.0 (5)
C3—C2—C1	119.2 (5)	O1—C17—C11	118.5 (5)
C3—C2—H2	120.4	O2—C17—C11	120.5 (4)
C1—C2—H2	120.4	O4—C18—O3	120.8 (5)
C2—C3—C4	118.6 (5)	O4—C18—C16	119.8 (5)
C2—C3—N3	123.6 (5)	O3—C18—C16	119.3 (5)
C4—C3—N3	117.8 (5)	C22—C21—C26	118.9 (4)
C5—C4—C3	118.6 (5)	C22—C21—C27	112.6 (4)
C5—C4—H4	120.7	C26—C21—C27	128.5 (4)
C3—C4—H4	120.7	C21—C22—C23	121.3 (4)
N1—C5—C4	121.8 (5)	C21—C22—H22	119.4
N1—C5—H5	119.1	C23—C22—H22	119.4
C4—C5—H5	119.1	C24—C23—C22	119.6 (5)
N2—C6—C7	121.3 (5)	C24—C23—H23	120.2
N2—C6—H6	119.4	C22—C23—H23	120.2
C7—C6—H6	119.4	C25—C24—C23	118.9 (4)
C6—C7—C8	121.1 (5)	C25—C24—H24	120.5
C6—C7—H7	119.4	C23—C24—H24	120.5
C8—C7—H7	119.4	C24—C25—C26	123.4 (4)
C9—C8—C7	118.2 (4)	C24—C25—H25	118.3
C9—C8—N3	123.2 (5)	C26—C25—H25	118.3
C7—C8—N3	118.5 (5)	C25—C26—C21	117.8 (4)
C8—C9—C10	117.3 (5)	C25—C26—C28	114.7 (4)
C8—C9—H9	121.4	C21—C26—C28	127.5 (3)
C10—C9—H9	121.4	O5—C27—O6	121.4 (5)
N2—C10—C9	120.1 (5)	O5—C27—C21	119.0 (5)
N2—C10—H10	119.9	O6—C27—C21	119.4 (4)
C9—C10—H10	119.9	O8—C28—O7	122.3 (5)
C12—C11—C16	117.7 (4)	O8—C28—C26	118.4 (4)
C12—C11—C17	114.6 (4)	O7—C28—C26	119.3 (4)
C16—C11—C17	127.7 (4)
C5—N1—C1—C2	1.5 (9)	C12—C11—C16—C18	177.2 (5)
N1—C1—C2—C3	−0.6 (9)	C17—C11—C16—C18	−4.8 (8)
C1—C2—C3—C4	−1.4 (8)	C12—C11—C17—O1	−10.2 (7)
C1—C2—C3—N3	−178.7 (5)	C16—C11—C17—O1	171.7 (5)
C8—N3—C3—C2	3.8 (8)	C12—C11—C17—O2	169.0 (5)
C8—N3—C3—C4	−173.6 (5)	C16—C11—C17—O2	−9.0 (8)
C2—C3—C4—C5	2.7 (9)	C15—C16—C18—O4	17.3 (7)
N3—C3—C4—C5	−179.9 (5)	C11—C16—C18—O4	−162.1 (5)
C1—N1—C5—C4	−0.2 (10)	C15—C16—C18—O3	−159.4 (5)
C3—C4—C5—N1	−1.9 (10)	C11—C16—C18—O3	21.3 (8)
C10—N2—C6—C7	0.1 (10)	C26—C21—C22—C23	−2.2 (8)
N2—C6—C7—C8	0.5 (9)	C27—C21—C22—C23	177.6 (5)
C6—C7—C8—C9	−0.4 (8)	C21—C22—C23—C24	1.9 (9)
C6—C7—C8—N3	178.0 (5)	C22—C23—C24—C25	−1.3 (10)
C3—N3—C8—C9	1.6 (8)	C23—C24—C25—C26	1.2 (10)
C3—N3—C8—C7	−176.7 (5)	C24—C25—C26—C21	−1.4 (8)
C7—C8—C9—C10	−0.3 (8)	C24—C25—C26—C28	178.6 (5)
N3—C8—C9—C10	−178.6 (5)	C22—C21—C26—C25	1.9 (7)
C6—N2—C10—C9	−0.8 (9)	C27—C21—C26—C25	−177.9 (5)
C8—C9—C10—N2	0.9 (9)	C22—C21—C26—C28	−178.1 (5)
C16—C11—C12—C13	1.7 (7)	C27—C21—C26—C28	2.1 (8)
C17—C11—C12—C13	−176.5 (5)	C22—C21—C27—O5	6.8 (7)
C11—C12—C13—C14	0.6 (9)	C26—C21—C27—O5	−173.4 (6)
C12—C13—C14—C15	−2.4 (9)	C22—C21—C27—O6	−168.9 (5)
C13—C14—C15—C16	1.9 (9)	C26—C21—C27—O6	10.9 (8)
C14—C15—C16—C11	0.4 (7)	C25—C26—C28—O8	−20.4 (7)
C14—C15—C16—C18	−179.0 (5)	C21—C26—C28—O8	159.6 (5)
C12—C11—C16—C15	−2.2 (6)	C25—C26—C28—O7	158.8 (5)
C17—C11—C16—C15	175.9 (5)	C21—C26—C28—O7	−21.2 (8)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H3A···O2	1.07 (9)	1.37 (9)	2.386 (6)	155 (7)
O6—H7A···O7	1.03 (8)	1.37 (8)	2.396 (6)	172 (7)
N1—H1N···O1	0.86 (6)	1.90 (6)	2.757 (6)	177 (7)
N2—H2N···O6	0.85 (6)	2.00 (6)	2.834 (5)	167 (7)
N3—H3N···O8i	0.92 (5)	1.88 (5)	2.794 (5)	172 (5)

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O3—H3A⋯O2	1.07 (9)	1.37 (9)	2.386 (6)	155 (7)
O6—H7A⋯O7	1.03 (8)	1.37 (8)	2.396 (6)	172 (7)
N1—H1N⋯O1	0.86 (6)	1.90 (6)	2.757 (6)	177 (7)
N2—H2N⋯O6	0.85 (6)	2.00 (6)	2.834 (5)	167 (7)
N3—H3N⋯O8i	0.92 (5)	1.88 (5)	2.794 (5)	172 (5)

Symmetry code: (i) .