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ISSN: 2056-9890

Crystal structure of melaminium cyano­acetate monohydrate

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aDepartment of Chemistry and Biochemistry, University of North Georgia, Oakwood, Georgia, USA, bOklahoma State University, Stillwater, Oklahoma, USA, and cUniversity of Oklahoma, Norman, Oklahoma, USA
*Correspondence e-mail: bsigdelregmi@ung.edu

Edited by H. Ishida, Okayama University, Japan (Received 3 August 2020; accepted 8 September 2020; online 11 September 2020)

The asymmetric unit of the title compound, 2,4,6-tri­amino-1,3,5-triazin-1-ium cyano­acetate monohydrate, C3H7N6+·NCCH2COO·H2O, consists of a melaminium cation, a cyano­acetate anion and a water mol­ecule, which are connected to each other via N—H⋯O and O—H⋯O hydrogen bonds, generating an eight-membered ring. In the crystal, the melaminium cations are connected by two pairs of N—H⋯N hydrogen bonds, forming tapes along [110]. These tapes develop a three-dimensional network through N—H⋯O, O—H⋯O, N—H⋯N and C—H⋯O hydrogen bonds between the cations, anions and water mol­ecules.

1. Chemical context

Melamine (systematic name: 2,4,6-tri­amino-1,3,5-triazine), a trimer of cyanamide, has many industrial applications. The cross-linked resins of melamine with formaldehyde have applications in adhesive coatings, laminations and flame retardants (Billmeyer, 1984[Billmeyer, F. W. (1984). Science, 3rd ed. New York: Wiley-Interscience.]). In the past, various organic melamine salts were tested as potential melamine substitutes for melamine urea formaldehyde resins (Weinstabl et al., 2001[Weinstabl, A., Binder, W. H., Gruber, H. & Kantner, W. (2001). J. Appl. Polym. Sci. 81, 1654-1661.]). In general, protonation of melamine with organic and inorganic acids has been found to yield compounds with extensive hydrogen-bonding networks involving both N—H⋯O and O—H⋯O hydrogen bonds. This paper is a part of our investigation of the chemistry of cyano­acetate with nitro­gen-based cations and their potential application as flame retardants since cyano­acetic acid is an analogue to polyacrylo­nitrile. It is well known that polyacrylo­nitrile is used in industry to manufacture carbon fibers because of its ability to produce carbon char (Bacon & Hoses, 1986[Bacon, R. & Hoses, T. N. (1986). High Performance Polymers, Their Origin and Development, edited by R. B. Saymour and G. S. Kirshambaum, p .342. New York/Amsterdam/London: Elsevier.]). Cyano­acetic acid has a nitrile group and also can act as acid source, both of which could enhance the flame-retarding properties.

[Scheme 1]

2. Structural commentary

The asymmetric unit of the title compound consists of a melaminium cation, a cyano­acetate anion and a water mol­ecule, which are connected to each other via N—H⋯O and O—H⋯O hydrogen bonds, generating an eight-membered ring (Fig. 1[link]). The six-membered ring of the melaminium cation shows significant distortion from a hexa­gonal shape. The bond distances [C—N = 1.322 (2)–1.368 (2) Å] and the angles [C—N—C = 115.76 (15)–119.08 (14)° and N—C—N = 121.44 (15)–125.42 (15)°] fall within similar ranges to those reported for similar singly protonated melaminium salts of simple alkyl mono- and di­carb­oxy­lic acids, namely, melaminium acetate acetic acid solvate (Perpétuo & Janczak, 2002[Perpétuo, G. J. & Janczak, J. (2002). Acta Cryst. C58, o112-o114.]), melaminium maleate (Janczak & Perpétuo, 2004[Janczak, J. & Perpétuo, G. J. (2004). Acta Cryst. C60, o211-o214.]), melaminium formate (Perpétuo et al., 2005[Perpétuo, G. J., Ribeiro, M. A. & Janczak, J. (2005). Acta Cryst. E61, o1818-o1820.]), melaminium tartarate (Su et al., 2009[Su, H., Lv, Y.-K. & Feng, Y.-L. (2009). Acta Cryst. E65, o933.]), bis­(melaminium) succinate (Froschauer & Weil, 2012a[Froschauer, B. & Weil, M. (2012a). Acta Cryst. E68, o2553-o2554.]) and melaminium hydrogen malonate (Froschauer & Weil, 2012b[Froschauer, B. & Weil, M. (2012b). Acta Cryst. E68, o2555.]). On the other hand, the angles in the six-membered ring of unprotonated melamine (Adam et al., 2010[Adam, F., Lin, S. K., Quah, C. K., Hemamalini, M. & Fun, H.-K. (2010). Acta Cryst. E66, o3033-o3034.]) are in the range 124.86 (17) to 125.51 (17)°.

[Figure 1]
Figure 1
Mol­ecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Hydrogen atoms are shown as spheres of arbitrary radius and hydrogen bonds as dashed lines.

In the anion, both O atoms of the carboxyl­ate group are involved in hydrogen bonds to amino groups of adjacent melaminium ions. The nitrile group has a bond length of 1.145 (2) Å that is typical of a nitrile (Kanters et al., 1978[Kanters, J. A., Roelofsen, G. & Straver, L. H. (1978). Acta Cryst. B34, 1393-1395.]). The angle at the nitrile carbon, N≡C—C, is 179.30 (19)° which is close to the theoretical value of 180°. The O atom of the water mol­ecule acts as a lone-pair donor to the protonated nitro­gen of the melaminium ion that is present in the same eight-membered ring. The presence of the water mol­ecule in the structure of melaminium cyano­acetate can be expected to contribute to fire retardancy as its release and evaporation will provide cooling.

3. Supra­molecular features

The melaminium cation in the crystal is involved in altogether nine hydrogen bonds: for each melaminium cation, seven of them are of the hydrogen-bond donor type while the remaining two are of the acceptor type (Table 1[link]). Neighbouring cations are connected by two pairs of N—H⋯N hydrogen bonds (N8—H8B⋯N4iii and N9—H9B⋯N6iv; symmetry codes as in Table 1[link]) to form a tape-like structure propagating along [110] and running between the cyano­acetate anions. Three N—H⋯O hydrogen bonds (N7—H7A⋯O13i, N8—H8A⋯O11 and N9—H9A⋯O13iii; Table 1[link]) link the cation with three different cyano­acetate anions. Furthermore, the cation is also connected with a water mol­ecule via an N—H⋯O hydrogen bond (N2—H2⋯O1S) between the protonated imine and the water O atom. Finally, the cation is linked with the nitrile group of the anion via an N—H⋯N hydrogen bond (N7—H7B⋯N16ii; Table 1[link]). There also exist O—H⋯O (O1S—H1SA⋯O11 and O1S—H1SB⋯O11vi) hydrogen bonds between the water mol­ecule and the anion. In addition, a C—H⋯O hydrogen bond between the methyl­ene H and water O atoms is observed as the C—H group is activated because of the electron-withdrawing cyano group adjacent to it. Altogether, these hydrogen bonds existing between the cations, anions and water mol­ecules generate a three-dimensional network (Fig. 2[link]).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N2—H2⋯O1S 0.90 (2) 1.81 (2) 2.7067 (19) 176.4 (19)
N7—H7A⋯O13i 0.89 (2) 2.00 (2) 2.881 (2) 168 (2)
N7—H7B⋯N16ii 0.92 (2) 2.13 (2) 3.001 (2) 155.6 (18)
N8—H8A⋯O11 0.91 (2) 2.01 (2) 2.891 (2) 164.6 (19)
N8—H8B⋯N4iii 0.88 (2) 2.07 (2) 2.952 (2) 176 (2)
N9—H9A⋯O13iii 0.90 (2) 2.08 (2) 2.792 (2) 135.7 (19)
N9—H9B⋯N6iv 0.90 (2) 2.08 (2) 2.980 (2) 174 (2)
C14—H14B⋯O1Sv 0.99 2.46 3.233 (2) 134
O1S—H1SA⋯O11 0.93 (2) 1.78 (2) 2.6860 (19) 163.3 (19)
O1S—H1SB⋯O11vi 0.87 (2) 1.97 (2) 2.8351 (19) 178 (2)
Symmetry codes: (i) x-1, y-1, z; (ii) [-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]; (iii) -x+2, -y+1, -z+1; (iv) -x+1, -y, -z+1; (v) [-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]; (vi) x-1, y, z.
[Figure 2]
Figure 2
A packing diagram of the title compound, viewed down the a axis, showing the O—H⋯O and N—H⋯O hydrogen bonds (green dashed lines), the N—H⋯N hydrogen bonds (blue dashed lines) and the C—H⋯O hydrogen bonds (magenta dashed lines).

4. Database survey

A search of the Cambridge Structural Database (Version 5.40, update of May 2020; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) for 2,4,6-tri­amino-1,3,5-triazin-1-ium showed more than 30 records; however, for 2,4,6-tri­amino-1,3,5-triazin-1-ium forming only single protonated salts with purely organic aliphatic carb­oxy­lic acids the search gave the following crystal structures: melamine with maleic acid (refcode ARUDAS; Janczak & Perpétuo, 2004[Janczak, J. & Perpétuo, G. J. (2004). Acta Cryst. C60, o211-o214.]), with formic acid (FONMEB; Perpétuo et al., 2005[Perpétuo, G. J., Ribeiro, M. A. & Janczak, J. (2005). Acta Cryst. E61, o1818-o1820.]), with acetic acid (EFAZOA; Perpétuo & Janczak, 2002[Perpétuo, G. J. & Janczak, J. (2002). Acta Cryst. C58, o112-o114.]), with malonic acid (HOWRIV01; Froschauer & Weil, 2012b[Froschauer, B. & Weil, M. (2012b). Acta Cryst. E68, o2555.]), with succinic acid (LEGZEE; Froschauer & Weil, 2012a[Froschauer, B. & Weil, M. (2012a). Acta Cryst. E68, o2553-o2554.]), with nitrilo­tri­acetic acid (MIHYAF; Hoxha et al., 2013[Hoxha, K. & Prior, T. J. (2013). Acta Cryst. E69, o1674-o1675.]) and with tartaric acid (VORSUR; Su et al., 2009[Su, H., Lv, Y.-K. & Feng, Y.-L. (2009). Acta Cryst. E65, o933.]). A search for organic co-crystals/salts of cyano­acetic acid gave one structure, 4,4′-bi­pyridine bis­(cyano­acetic acid) (Song et al., 2008[Song, G., Hao, E.-J. & Li, W. (2008). Acta Cryst. E64, o2058.]). For metal complexes with cyano­acetic acid or cyano­acetate, 24 structures were reported, such as silver cyano­acetate (Edwards et al., 1997[Edwards, D. A., Mahon, M. F. & Paget, T. J. (1997). Polyhedron, 16, 25-31.]) and cadmium cyano­acetate (Post & Trotter, 1974[Post, M. L. & Trotter, J. (1974). J. Chem. Soc. Dalton Trans. pp. 285-288.]). In these metal salts, the metal is coordinated by the acetate group as well as the cyano group.

5. Synthesis and crystallization

A solution of cyano­acetic acid (1.7g, 20 mmol) in 100 ml of deionized water was added to a solution of melamine (2.5 g, 20 mmol) in 100 ml of deionized water. The reaction mixture was heated to 353 K for 3 h. The resulting clear solution was cooled to room temperature and then was allowed to slowly evaporate. Single crystals of the title compound formed after several days.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. C-bound H atoms were initially determined by geometry (C—H = 0.99 Å) and were refined using a riding model, with Uiso(H) = 1.2Ueq(C). H atoms bonded to N and O were located in a difference map, and their positions were refined freely, with Uiso(H) = 1.2Ueq(N or O).

Table 2
Experimental details

Crystal data
Chemical formula C3H7N6+·C3H2NO2·H2O
Mr 229.22
Crystal system, space group Monoclinic, P21/c
Temperature (K) 100
a, b, c (Å) 4.6928 (6), 9.3881 (13), 22.918 (3)
β (°) 91.646 (3)
V3) 1009.3 (2)
Z 4
Radiation type Mo Kα
μ (mm−1) 0.12
Crystal size (mm) 0.44 × 0.17 × 0.04
 
Data collection
Diffractometer Bruker APEX CCD
Absorption correction Multi-scan (SADABS; Bruker, 2007[Bruker (2007). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.])
Tmin, Tmax 0.948, 0.995
No. of measured, independent and observed [I > 2σ(I)] reflections 12615, 2517, 1856
Rint 0.058
(sin θ/λ)max−1) 0.668
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.047, 0.126, 1.00
No. of reflections 2517
No. of parameters 172
H-atom treatment H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3) 0.28, −0.29
Computer programs: SMART and SAINT (Bruker, 2007[Bruker (2007). SMART, SAINT and SADABS. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXT (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2018/3 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]), SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]) and CrystalMaker (Palmer, 2014[Palmer, D. C. (2014). CrystalMaker. CrystalMaker Software Ltd, Begbroke, England.]).

Supporting information


Computing details top

Data collection: SMART (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008) and CrystalMaker (Palmer, 2014); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

2,4,6-Triamino-1,3,5-triazin-1-ium cyanoacetate monohydrate top
Crystal data top
C3H7N6+·C3H2NO2·H2OF(000) = 480
Mr = 229.22Dx = 1.509 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 4.6928 (6) ÅCell parameters from 3720 reflections
b = 9.3881 (13) Åθ = 2.3–28.1°
c = 22.918 (3) ŵ = 0.12 mm1
β = 91.646 (3)°T = 100 K
V = 1009.3 (2) Å3Needle, colourless
Z = 40.44 × 0.17 × 0.04 mm
Data collection top
Bruker APEX CCD
diffractometer
1856 reflections with I > 2σ(I)
φ and ω scansRint = 0.058
Absorption correction: multi-scan
(SADABS; Bruker, 2007)
θmax = 28.4°, θmin = 1.8°
Tmin = 0.948, Tmax = 0.995h = 56
12615 measured reflectionsk = 1212
2517 independent reflectionsl = 3030
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)] = 0.047Hydrogen site location: mixed
wR(F2) = 0.126H atoms treated by a mixture of independent and constrained refinement
S = 1.00 w = 1/[σ2(Fo2) + (0.064P)2 + 0.320P]
where P = (Fo2 + 2Fc2)/3
2517 reflections(Δ/σ)max = 0.001
172 parametersΔρmax = 0.28 e Å3
0 restraintsΔρmin = 0.29 e Å3
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.3297 (4)0.25701 (18)0.41214 (7)0.0117 (4)
N20.4321 (3)0.39286 (15)0.40750 (6)0.0121 (3)
H20.359 (4)0.453 (2)0.3804 (9)0.014*
C30.6562 (4)0.43434 (17)0.44283 (7)0.0111 (4)
N40.7614 (3)0.35064 (14)0.48477 (6)0.0126 (3)
C50.6396 (4)0.21954 (17)0.48861 (8)0.0125 (4)
N60.4316 (3)0.16816 (15)0.45231 (6)0.0135 (3)
N70.1226 (3)0.21696 (16)0.37493 (7)0.0151 (3)
H7A0.059 (4)0.128 (2)0.3786 (9)0.018*
H7B0.055 (4)0.277 (2)0.3458 (9)0.018*
N80.7672 (3)0.56251 (15)0.43490 (7)0.0137 (3)
H8A0.711 (4)0.617 (2)0.4041 (9)0.016*
H8B0.914 (5)0.586 (2)0.4577 (9)0.016*
N90.7332 (4)0.13535 (16)0.53094 (7)0.0202 (4)
H9A0.870 (5)0.163 (2)0.5569 (10)0.024*
H9B0.673 (5)0.044 (3)0.5337 (9)0.024*
O110.6998 (3)0.73778 (13)0.33172 (5)0.0157 (3)
C120.7511 (4)0.87001 (18)0.33632 (8)0.0129 (4)
O130.9314 (3)0.92554 (14)0.36958 (6)0.0224 (3)
C140.5789 (4)0.97232 (18)0.29669 (8)0.0163 (4)
H14A0.4652261.0358610.3214670.020*
H14B0.7132481.0326420.2751420.020*
C150.3874 (4)0.90159 (18)0.25472 (8)0.0156 (4)
N160.2366 (4)0.84731 (17)0.22144 (7)0.0237 (4)
O1S0.2181 (3)0.58309 (13)0.32906 (6)0.0163 (3)
H1SA0.363 (5)0.650 (2)0.3269 (9)0.020*
H1SB0.059 (5)0.630 (2)0.3289 (9)0.020*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0117 (8)0.0117 (8)0.0118 (8)0.0003 (6)0.0012 (6)0.0011 (6)
N20.0141 (8)0.0088 (7)0.0131 (7)0.0006 (6)0.0040 (6)0.0023 (6)
C30.0116 (9)0.0105 (8)0.0110 (8)0.0009 (6)0.0005 (6)0.0011 (6)
N40.0140 (8)0.0095 (7)0.0141 (7)0.0014 (6)0.0023 (6)0.0011 (5)
C50.0123 (9)0.0104 (7)0.0148 (9)0.0017 (6)0.0024 (7)0.0005 (6)
N60.0161 (8)0.0099 (7)0.0144 (8)0.0012 (6)0.0048 (6)0.0016 (6)
N70.0184 (8)0.0109 (7)0.0155 (8)0.0025 (6)0.0063 (6)0.0025 (6)
N80.0148 (8)0.0108 (7)0.0152 (8)0.0039 (6)0.0036 (6)0.0036 (6)
N90.0257 (9)0.0117 (7)0.0222 (9)0.0067 (7)0.0141 (7)0.0064 (6)
O110.0150 (7)0.0108 (6)0.0208 (7)0.0009 (5)0.0040 (5)0.0034 (5)
C120.0135 (9)0.0115 (8)0.0136 (9)0.0024 (7)0.0013 (7)0.0022 (6)
O130.0269 (8)0.0163 (6)0.0231 (7)0.0048 (6)0.0135 (6)0.0034 (5)
C140.0197 (10)0.0113 (8)0.0174 (9)0.0010 (7)0.0069 (7)0.0001 (7)
C150.0164 (9)0.0128 (8)0.0174 (9)0.0025 (7)0.0027 (7)0.0037 (7)
N160.0273 (10)0.0198 (8)0.0235 (9)0.0010 (7)0.0104 (7)0.0012 (7)
O1S0.0129 (7)0.0126 (6)0.0232 (7)0.0003 (5)0.0031 (5)0.0052 (5)
Geometric parameters (Å, º) top
C1—N61.322 (2)N8—H8B0.88 (2)
C1—N71.329 (2)N9—H9A0.90 (2)
C1—N21.368 (2)N9—H9B0.90 (2)
N2—C31.365 (2)O11—C121.268 (2)
N2—H20.90 (2)C12—O131.238 (2)
C3—N41.326 (2)C12—C141.536 (2)
C3—N81.326 (2)C14—C151.458 (2)
N4—C51.361 (2)C14—H14A0.9900
C5—N91.317 (2)C14—H14B0.9900
C5—N61.353 (2)C15—N161.145 (2)
N7—H7A0.89 (2)O1S—H1SA0.93 (2)
N7—H7B0.92 (2)O1S—H1SB0.87 (2)
N8—H8A0.91 (2)
N6—C1—N7120.78 (16)C3—N8—H8A121.0 (13)
N6—C1—N2121.44 (15)C3—N8—H8B117.0 (14)
N7—C1—N2117.77 (15)H8A—N8—H8B121.5 (19)
C3—N2—C1119.08 (14)C5—N9—H9A122.0 (14)
C3—N2—H2120.1 (13)C5—N9—H9B121.5 (14)
C1—N2—H2120.8 (13)H9A—N9—H9B116 (2)
N4—C3—N8119.86 (16)O13—C12—O11126.04 (16)
N4—C3—N2121.68 (15)O13—C12—C14116.09 (15)
N8—C3—N2118.45 (15)O11—C12—C14117.87 (15)
C3—N4—C5115.76 (15)C15—C14—C12114.17 (14)
N9—C5—N6117.29 (15)C15—C14—H14A108.7
N9—C5—N4117.30 (16)C12—C14—H14A108.7
N6—C5—N4125.42 (15)C15—C14—H14B108.7
C1—N6—C5116.32 (15)C12—C14—H14B108.7
C1—N7—H7A116.4 (13)H14A—C14—H14B107.6
C1—N7—H7B121.4 (13)N16—C15—C14179.30 (19)
H7A—N7—H7B122.1 (19)H1SA—O1S—H1SB106.4 (19)
N6—C1—N2—C34.1 (2)C3—N4—C5—N62.5 (3)
N7—C1—N2—C3176.16 (16)N7—C1—N6—C5179.16 (16)
C1—N2—C3—N45.8 (2)N2—C1—N6—C50.6 (2)
C1—N2—C3—N8174.98 (16)N9—C5—N6—C1176.40 (17)
N8—C3—N4—C5178.19 (16)N4—C5—N6—C14.1 (3)
N2—C3—N4—C52.6 (2)O13—C12—C14—C15174.83 (17)
C3—N4—C5—N9177.98 (17)O11—C12—C14—C154.3 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H2···O1S0.90 (2)1.81 (2)2.7067 (19)176.4 (19)
N7—H7A···O13i0.89 (2)2.00 (2)2.881 (2)168 (2)
N7—H7B···N16ii0.92 (2)2.13 (2)3.001 (2)155.6 (18)
N8—H8A···O110.91 (2)2.01 (2)2.891 (2)164.6 (19)
N8—H8B···N4iii0.88 (2)2.07 (2)2.952 (2)176 (2)
N9—H9A···O13iii0.90 (2)2.08 (2)2.792 (2)135.7 (19)
N9—H9B···N6iv0.90 (2)2.08 (2)2.980 (2)174 (2)
C14—H14B···O1Sv0.992.463.233 (2)134
O1S—H1SA···O110.93 (2)1.78 (2)2.6860 (19)163.3 (19)
O1S—H1SB···O11vi0.87 (2)1.97 (2)2.8351 (19)178 (2)
Symmetry codes: (i) x1, y1, z; (ii) x, y1/2, z+1/2; (iii) x+2, y+1, z+1; (iv) x+1, y, z+1; (v) x+1, y+1/2, z+1/2; (vi) x1, y, z.
 

References

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