Related literature {#sec1}
==================

For the synthesis and properties of azo dyes, see: Wenker (1935[@bb7]); Ledoux *et al.* (2000[@bb3]); Viscardi *et al.* (2002[@bb6]). For a related structure, see: Sasaki *et al.* (2004[@bb4]).

Experimental {#sec2}
============

 {#sec2.1}

### Crystal data {#sec2.1.1}

C~18~H~18~N~6~O~2~S*M* *~r~* = 382.45Triclinic,*a* = 7.8093 (16) Å*b* = 11.035 (2) Å*c* = 11.776 (3) Åα = 94.268 (4)°β = 106.544 (4)°γ = 104.568 (5)°*V* = 929.8 (3) Å^3^*Z* = 2Mo *K*α radiationμ = 0.20 mm^−1^*T* = 295 K0.30 × 0.23 × 0.03 mm

### Data collection {#sec2.1.2}

Siemens--Bruker APEX diffractometerAbsorption correction: multi-scan (*SORTAV*; Blessing, 1995[@bb1]) *T* ~min~ = 0.93, *T* ~max~ = 1.009271 measured reflections4100 independent reflections1577 reflections with *I* \> 2σ(*I*)*R* ~int~ = 0.04015 standard reflections every 60 min intensity decay: none

### Refinement {#sec2.1.3}

*R*\[*F* ^2^ \> 2σ(*F* ^2^)\] = 0.050*wR*(*F* ^2^) = 0.055*S* = 0.864100 reflections244 parametersH atoms treated by a mixture of independent and constrained refinementΔρ~max~ = 0.40 e Å^−3^Δρ~min~ = −0.48 e Å^−3^

 {#d5e452}

Data collection: *SMART* (Bruker, 2007[@bb2]); cell refinement: *SAINT* (Bruker, 2007[@bb2]); data reduction: *SAINT*; program(s) used to solve structure: *SHELXS97* (Sheldrick, 2008[@bb5]); program(s) used to refine structure: *SHELXL97* (Sheldrick, 2008[@bb5]); molecular graphics: *XP* in *SHELXTL* (Sheldrick, 2008[@bb5]); software used to prepare material for publication: *SHELXL97*.

Supplementary Material
======================

Crystal structure: contains datablocks I, global. DOI: [10.1107/S1600536810053158/rz2541sup1.cif](http://dx.doi.org/10.1107/S1600536810053158/rz2541sup1.cif)

Structure factors: contains datablocks I. DOI: [10.1107/S1600536810053158/rz2541Isup2.hkl](http://dx.doi.org/10.1107/S1600536810053158/rz2541Isup2.hkl)

Additional supplementary materials: [crystallographic information](http://scripts.iucr.org/cgi-bin/sendsupfiles?rz2541&file=rz2541sup0.html&mime=text/html); [3D view](http://scripts.iucr.org/cgi-bin/sendcif?rz2541sup1&Qmime=cif); [checkCIF report](http://scripts.iucr.org/cgi-bin/paper?rz2541&checkcif=yes)

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: [RZ2541](http://scripts.iucr.org/cgi-bin/sendsup?rz2541)).

We thank Dr C. Barolo for supplying crystals of the title compound.

Comment
=======

The blood gas (CO~2~ or O~2~) measurement is often required in modern diagnosis and the indicator properties of azo dyestuff have been proved very informative in this field, as proposed in the pioneering work of Wenker (1935). The title compound, 4-diethylcyanoamino-4\'-sulfonylamino-azobenzene (Fig. 1), is part of this study and has been synthesized according to a modification of a standard procedure (Ledoux *et al.*, 2000; Viscardi *et al.*, 2002). Bond lengths and angles agree with those of a similar compound reported by Sasaki *et al.* (2004). The two phenyl rings form a dihedral angle of 26.16 (7)°. In the crystal packing, double chains of molecules parallel to the *a* axis are generated by weak C---H···N and N---H···N hydrogen bonds, where N acceptor atoms are the azo (N12) or cyano (N27) atoms (Table 1).

Experimental {#experimental}
============

The title compound has been obtained according to Ledoux *et al.* (2000) and Viscardi *et al.* (2002), and prepared by a modification of a standard procedure in analogy to similar compounds previously reported. Crystals suitable for X-ray analysis were obtained by slow evaporation of an ethanol solution.

Refinement {#refinement}
==========

All H atoms, except those of the NH~2~ group, have been placed in geometrically idealized positions and refined as riding, with C---H = 0.93--0.97 Å and with *U*~iso~(H) = 1.2 *U*~eq~(C). The NH~2~ hydrogen atoms have been located in the final Fourier map and refined freely with *U*~iso~(H) = 1.2 *U*~eq~(N). A small and poorly diffracting crystal has been used in the analysis.

Figures
=======

![The molecular structure of the title compound showing the atomic numbering and 50% probability displacements ellipsoids.](e-67-0o231-fig1){#Fap1}

Crystal data {#tablewrapcrystaldatalong}
============

  ---------------------- -------------------------------------
  C~18~H~18~N~6~O~2~S    *Z* = 2
  *M~r~* = 382.45        *F*(000) = 400
  Triclinic, *P*1        *D*~x~ = 1.359 Mg m^−3^
  Hall symbol: -P 1      Mo *K*α radiation, λ = 0.71073 Å
  *a* = 7.8093 (16) Å    Cell parameters from 52 reflections
  *b* = 11.035 (2) Å     θ = 1.9--20.2°
  *c* = 11.776 (3) Å     µ = 0.20 mm^−1^
  α = 94.268 (4)°        *T* = 295 K
  β = 106.544 (4)°       Plate, red
  γ = 104.568 (5)°       0.30 × 0.23 × 0.03 mm
  *V* = 929.8 (3) Å^3^   
  ---------------------- -------------------------------------

Data collection {#tablewrapdatacollectionlong}
===============

  -------------------------------------------------------------- --------------------------------------
  Siemens--Bruker APEX diffractometer                            1577 reflections with *I* \> 2σ(*I*)
  Radiation source: fine-focus sealed tube                       *R*~int~ = 0.040
  graphite                                                       θ~max~ = 28.4°, θ~min~ = 1.8°
  φ scans                                                        *h* = −10→10
  Absorption correction: multi-scan (*SORTAV*; Blessing, 1995)   *k* = −14→14
  *T*~min~ = 0.93, *T*~max~ = 1.00                               *l* = −14→15
  9271 measured reflections                                      15 standard reflections every 60 min
  4100 independent reflections                                   intensity decay: none
  -------------------------------------------------------------- --------------------------------------

Refinement {#tablewraprefinementdatalong}
==========

  ------------------------------------- ------------------------------------------------------------------------
  Refinement on *F*^2^                  Primary atom site location: structure-invariant direct methods
  Least-squares matrix: full            Secondary atom site location: difference Fourier map
  *R*\[*F*^2^ \> 2σ(*F*^2^)\] = 0.050   Hydrogen site location: inferred from neighbouring sites
  *wR*(*F*^2^) = 0.055                  H atoms treated by a mixture of independent and constrained refinement
  *S* = 0.86                            *w* = 1/\[σ^2^(*F*~o~^2^)\] where *P* = (*F*~o~^2^ + 2*F*~c~^2^)/3
  4100 reflections                      (Δ/σ)~max~ \< 0.001
  244 parameters                        Δρ~max~ = 0.40 e Å^−3^
  0 restraints                          Δρ~min~ = −0.48 e Å^−3^
  ------------------------------------- ------------------------------------------------------------------------

Special details {#specialdetails}
===============

  -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  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 *F*^2^ against ALL reflections. The weighted *R*-factor *wR* and goodness of fit *S* are based on *F*^2^, conventional *R*-factors *R* are based on *F*, with *F* set to zero for negative *F*^2^. The threshold expression of *F*^2^ \> σ(*F*^2^) is used only for calculating *R*-factors(gt) *etc*. and is not relevant to the choice of reflections for refinement. *R*-factors based on *F*^2^ 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 (Å^2^) {#tablewrapcoords}
==================================================================================================

  ------ --------------- -------------- --------------- -------------------- --
         *x*             *y*            *z*             *U*~iso~\*/*U*~eq~   
  C1     −0.4369 (3)     0.3324 (2)     0.1462 (2)      0.0329 (7)           
  C2     −0.3729 (3)     0.2269 (2)     0.1422 (2)      0.0385 (7)           
  H2A    −0.4475         0.1532         0.0896          0.046\*              
  C3     −0.1985 (3)     0.2304 (2)     0.2160 (2)      0.0397 (7)           
  H3A    −0.1535         0.1603         0.2117          0.048\*              
  C4     −0.0912 (3)     0.3396 (2)     0.2967 (2)      0.0338 (7)           
  C5     −0.1585 (3)     0.4427 (2)     0.3021 (2)      0.0474 (8)           
  H5A    −0.0880         0.5146         0.3582          0.057\*              
  C6     −0.3308 (3)     0.4404 (2)     0.2245 (2)      0.0438 (8)           
  H6A    −0.3735         0.5118         0.2258          0.053\*              
  S7     −0.66133 (10)   0.32583 (7)    0.05031 (7)     0.0441 (2)           
  O8     −0.6950 (2)     0.44536 (15)   0.07477 (14)    0.0586 (6)           
  O9     −0.6729 (2)     0.27865 (16)   −0.06983 (13)   0.0548 (6)           
  N10    −0.8133 (3)     0.2210 (2)     0.0862 (2)      0.0468 (7)           
  H10A   −0.817 (3)      0.243 (2)      0.1638 (18)     0.056\*              
  H10B   −0.799 (3)      0.1427 (19)    0.0698 (19)     0.056\*              
  N11    0.0845 (3)      0.34976 (19)   0.38119 (16)    0.0416 (6)           
  N12    0.1748 (3)      0.28313 (18)   0.34648 (16)    0.0402 (6)           
  C13    0.3437 (3)      0.2869 (2)     0.4342 (2)      0.0343 (7)           
  C14    0.4404 (3)      0.2039 (2)     0.4088 (2)      0.0406 (8)           
  H14A   0.3980          0.1541         0.3336          0.049\*              
  C15    0.5974 (3)      0.1942 (2)     0.4928 (2)      0.0416 (8)           
  H15A   0.6601          0.1382         0.4737          0.050\*              
  C16    0.6644 (3)      0.2679 (2)     0.6072 (2)      0.0373 (7)           
  C17    0.5725 (3)      0.3570 (2)     0.6288 (2)      0.0388 (7)           
  H17A   0.6186          0.4110         0.7019          0.047\*              
  C18    0.4168 (3)      0.3660 (2)     0.5447 (2)      0.0365 (7)           
  H18A   0.3586          0.4259         0.5614          0.044\*              
  N19    0.8150 (3)      0.2551 (2)     0.69548 (18)    0.0471 (7)           
  C20    0.9028 (4)      0.1477 (3)     0.6819 (2)      0.0713 (10)          
  H20A   0.9460          0.1199         0.7584          0.086\*              
  H20B   0.8126          0.0760         0.6252          0.086\*              
  C21    1.0583 (4)      0.1988 (3)     0.6383 (2)      0.0766 (10)          
  H21A   1.1448          0.2737         0.6924          0.092\*              
  H21B   1.0145          0.2216         0.5594          0.092\*              
  C22    1.1544 (4)      0.0919 (3)     0.6327 (3)      0.0738 (11)          
  N23    1.2304 (4)      0.0229 (2)     0.6272 (2)      0.0917 (10)          
  C24    0.8777 (3)      0.3258 (2)     0.8154 (2)      0.0445 (8)           
  H24A   0.8795          0.4133         0.8098          0.053\*              
  H24B   1.0046          0.3248         0.8548          0.053\*              
  C25    0.7577 (3)      0.2751 (2)     0.8932 (2)      0.0538 (8)           
  H25A   0.8088          0.3273         0.9717          0.065\*              
  H25B   0.6327          0.2814         0.8571          0.065\*              
  C26    0.7480 (4)      0.1423 (3)     0.9075 (3)      0.0547 (9)           
  N27    0.7442 (3)      0.0422 (2)     0.9183 (2)      0.0735 (9)           
  ------ --------------- -------------- --------------- -------------------- --

Atomic displacement parameters (Å^2^) {#tablewrapadps}
=====================================

  ----- ------------- ------------- ------------- ------------- -------------- --------------
        *U*^11^       *U*^22^       *U*^33^       *U*^12^       *U*^13^        *U*^23^
  C1    0.0227 (18)   0.0427 (19)   0.0314 (16)   0.0090 (15)   0.0055 (14)    0.0084 (14)
  C2    0.0346 (19)   0.0360 (18)   0.0405 (17)   0.0106 (15)   0.0069 (15)    −0.0041 (14)
  C3    0.040 (2)     0.041 (2)     0.0427 (17)   0.0215 (16)   0.0118 (15)    0.0065 (15)
  C4    0.030 (2)     0.0396 (19)   0.0351 (17)   0.0149 (16)   0.0098 (14)    0.0099 (15)
  C5    0.039 (2)     0.045 (2)     0.0466 (18)   0.0112 (16)   −0.0015 (16)   −0.0058 (15)
  C6    0.038 (2)     0.041 (2)     0.0496 (18)   0.0204 (16)   0.0025 (16)    −0.0011 (16)
  S7    0.0330 (5)    0.0526 (6)    0.0437 (5)    0.0171 (4)    0.0030 (4)     0.0080 (4)
  O8    0.0472 (14)   0.0501 (14)   0.0769 (14)   0.0306 (11)   0.0030 (11)    0.0080 (11)
  O9    0.0463 (14)   0.0874 (16)   0.0290 (11)   0.0259 (11)   0.0041 (10)    0.0059 (11)
  N10   0.0328 (15)   0.0556 (18)   0.0497 (16)   0.0109 (14)   0.0127 (13)    0.0012 (15)
  N11   0.0277 (15)   0.0549 (17)   0.0401 (14)   0.0191 (13)   0.0017 (12)    0.0056 (12)
  N12   0.0299 (15)   0.0549 (17)   0.0363 (14)   0.0157 (12)   0.0074 (12)    0.0094 (12)
  C13   0.0276 (19)   0.0417 (19)   0.0362 (17)   0.0148 (15)   0.0094 (15)    0.0078 (15)
  C14   0.039 (2)     0.051 (2)     0.0302 (16)   0.0160 (16)   0.0076 (15)    −0.0014 (15)
  C15   0.043 (2)     0.054 (2)     0.0379 (17)   0.0302 (17)   0.0143 (15)    0.0024 (16)
  C16   0.0285 (19)   0.049 (2)     0.0380 (18)   0.0181 (15)   0.0089 (15)    0.0108 (15)
  C17   0.0333 (19)   0.0476 (19)   0.0336 (17)   0.0197 (15)   0.0023 (14)    −0.0012 (14)
  C18   0.0327 (19)   0.0416 (19)   0.0376 (17)   0.0182 (15)   0.0089 (15)    0.0028 (15)
  N19   0.0448 (17)   0.0643 (18)   0.0404 (15)   0.0410 (15)   0.0056 (13)    0.0005 (13)
  C20   0.049 (2)     0.107 (3)     0.044 (2)     0.001 (2)     0.0126 (18)    0.0098 (19)
  C21   0.078 (3)     0.073 (3)     0.064 (2)     0.006 (2)     0.013 (2)      0.016 (2)
  C22   0.078 (3)     0.079 (3)     0.080 (2)     0.052 (2)     0.024 (2)      0.008 (2)
  N23   0.113 (3)     0.094 (2)     0.121 (2)     0.076 (2)     0.069 (2)      0.040 (2)
  C24   0.043 (2)     0.059 (2)     0.0342 (17)   0.0288 (16)   0.0034 (15)    0.0058 (16)
  C25   0.064 (2)     0.061 (2)     0.0455 (19)   0.0304 (18)   0.0190 (17)    0.0099 (17)
  C26   0.051 (2)     0.061 (2)     0.054 (2)     0.015 (2)     0.0202 (17)    0.005 (2)
  N27   0.069 (2)     0.055 (2)     0.095 (2)     0.0141 (18)   0.0277 (17)    0.0099 (18)
  ----- ------------- ------------- ------------- ------------- -------------- --------------

Geometric parameters (Å, °) {#tablewrapgeomlong}
===========================

  ------------------- ------------- ------------------- -------------
  C1---C6             1.364 (3)     C15---C16           1.405 (3)
  C1---C2             1.381 (3)     C15---H15A          0.9300
  C1---S7             1.775 (2)     C16---N19           1.376 (3)
  C2---C3             1.381 (3)     C16---C17           1.403 (3)
  C2---H2A            0.9300        C17---C18           1.363 (3)
  C3---C4             1.387 (3)     C17---H17A          0.9300
  C3---H3A            0.9300        C18---H18A          0.9300
  C4---C5             1.373 (3)     N19---C24           1.447 (3)
  C4---N11            1.419 (3)     N19---C20           1.530 (3)
  C5---C6             1.388 (3)     C20---C21           1.452 (3)
  C5---H5A            0.9300        C20---H20A          0.9700
  C6---H6A            0.9300        C20---H20B          0.9700
  S7---O8             1.4326 (15)   C21---C22           1.556 (3)
  S7---O9             1.4403 (15)   C21---H21A          0.9700
  S7---N10            1.610 (2)     C21---H21B          0.9700
  N10---H10A          0.939 (19)    C22---N23           1.085 (3)
  N10---H10B          0.913 (19)    C24---C25           1.527 (3)
  N11---N12           1.259 (2)     C24---H24A          0.9700
  N12---C13           1.414 (3)     C24---H24B          0.9700
  C13---C14           1.390 (3)     C25---C26           1.472 (3)
  C13---C18           1.393 (3)     C25---H25A          0.9700
  C14---C15           1.372 (3)     C25---H25B          0.9700
  C14---H14A          0.9300        C26---N27           1.116 (3)
                                                        
  C6---C1---C2        120.7 (2)     N19---C16---C17     120.6 (2)
  C6---C1---S7        119.93 (19)   N19---C16---C15     121.9 (2)
  C2---C1---S7        119.4 (2)     C17---C16---C15     117.5 (2)
  C1---C2---C3        120.2 (2)     C18---C17---C16     121.3 (2)
  C1---C2---H2A       119.9         C18---C17---H17A    119.4
  C3---C2---H2A       119.9         C16---C17---H17A    119.4
  C2---C3---C4        119.3 (2)     C17---C18---C13     121.0 (2)
  C2---C3---H3A       120.4         C17---C18---H18A    119.5
  C4---C3---H3A       120.4         C13---C18---H18A    119.5
  C5---C4---C3        120.0 (2)     C16---N19---C24     122.0 (2)
  C5---C4---N11       116.5 (2)     C16---N19---C20     122.3 (2)
  C3---C4---N11       123.5 (2)     C24---N19---C20     114.63 (19)
  C4---C5---C6        120.5 (2)     C21---C20---N19     106.4 (3)
  C4---C5---H5A       119.7         C21---C20---H20A    110.4
  C6---C5---H5A       119.7         N19---C20---H20A    110.4
  C1---C6---C5        119.3 (2)     C21---C20---H20B    110.4
  C1---C6---H6A       120.3         N19---C20---H20B    110.4
  C5---C6---H6A       120.3         H20A---C20---H20B   108.6
  O8---S7---O9        119.73 (10)   C20---C21---C22     106.0 (3)
  O8---S7---N10       106.68 (11)   C20---C21---H21A    110.5
  O9---S7---N10       106.08 (12)   C22---C21---H21A    110.5
  O8---S7---C1        108.04 (11)   C20---C21---H21B    110.5
  O9---S7---C1        107.70 (11)   C22---C21---H21B    110.5
  N10---S7---C1       108.15 (12)   H21A---C21---H21B   108.7
  S7---N10---H10A     112.7 (14)    N23---C22---C21     175.3 (4)
  S7---N10---H10B     109.6 (15)    N19---C24---C25     114.2 (2)
  H10A---N10---H10B   116 (2)       N19---C24---H24A    108.7
  N12---N11---C4      114.1 (2)     C25---C24---H24A    108.7
  N11---N12---C13     113.8 (2)     N19---C24---H24B    108.7
  C14---C13---C18     118.2 (2)     C25---C24---H24B    108.7
  C14---C13---N12     117.5 (2)     H24A---C24---H24B   107.6
  C18---C13---N12     124.3 (2)     C26---C25---C24     112.5 (2)
  C15---C14---C13     121.2 (2)     C26---C25---H25A    109.1
  C15---C14---H14A    119.4         C24---C25---H25A    109.1
  C13---C14---H14A    119.4         C26---C25---H25B    109.1
  C14---C15---C16     120.6 (2)     C24---C25---H25B    109.1
  C14---C15---H15A    119.7         H25A---C25---H25B   107.8
  C16---C15---H15A    119.7         N27---C26---C25     178.6 (3)
  ------------------- ------------- ------------------- -------------

Hydrogen-bond geometry (Å, °) {#tablewraphbondslong}
=============================

  ----------------------- ---------- ---------- ----------- ---------------
  *D*---H···*A*           *D*---H    H···*A*    *D*···*A*   *D*---H···*A*
  C15---H15A···N23^i^     0.93       2.52       3.427 (4)   166
  N10---H10B···N27^ii^    0.91 (2)   2.19 (2)   3.084 (2)   165
  N10---H10A···N12^iii^   0.94 (2)   2.19 (2)   3.124 (2)   176
  ----------------------- ---------- ---------- ----------- ---------------

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

###### Hydrogen-bond geometry (Å, °)

  *D*---H⋯*A*             *D*---H    H⋯*A*      *D*⋯*A*     *D*---H⋯*A*
  ----------------------- ---------- ---------- ----------- -------------
  C15---H15*A*⋯N23^i^     0.93       2.52       3.427 (4)   166
  N10---H10*B*⋯N27^ii^    0.91 (2)   2.19 (2)   3.084 (2)   165
  N10---H10*A*⋯N12^iii^   0.94 (2)   2.19 (2)   3.124 (2)   176

Symmetry codes: (i) ; (ii) ; (iii) .
