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

For related structures of 1*H*-benzimidazole-5,6-dicarboxyl­ate complexes, see: Song, Wang, Hu *et al.* (2009[@bb5]); Song, Wang, Li *et al.* (2009[@bb6]); Song, Wang, Qin *et al.* (2009[@bb7]); Wang *et al.* (2009[@bb8]).

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

 {#sec2.1}

### Crystal data {#sec2.1.1}

\[Cd(C~9~H~4~N~2~O~4~)(C~3~H~7~NO)(H~2~O)\]·2H~2~O*M* *~r~* = 443.69Triclinic,*a* = 7.7729 (16) Å*b* = 9.1648 (18) Å*c* = 11.458 (2) Åα = 102.76 (3)°β = 97.70 (3)°γ = 94.96 (3)°*V* = 783.2 (3) Å^3^*Z* = 2Mo *K*α radiationμ = 1.44 mm^−1^*T* = 293 K0.29 × 0.25 × 0.21 mm

### Data collection {#sec2.1.2}

Rigaku/MSC Mercury CCD diffractometerAbsorption correction: multi-scan (REQAB; Jacobson, 1998[@bb1]) *T* ~min~ = 0.680, *T* ~max~ = 0.7526197 measured reflections2800 independent reflections1539 reflections with *I* \> 2σ(*I*)*R* ~int~ = 0.121

### Refinement {#sec2.1.3}

*R*\[*F* ^2^ \> 2σ(*F* ^2^)\] = 0.086*wR*(*F* ^2^) = 0.223*S* = 1.142800 reflections219 parameters9 restraintsH-atom parameters constrainedΔρ~max~ = 2.12 e Å^−3^Δρ~min~ = −1.80 e Å^−3^

 {#d5e678}

Data collection: *CrystalStructure* (Rigaku/MSC, 2002[@bb3]); cell refinement: *CrystalStructure*; data reduction: *CrystalStructure*; program(s) used to solve structure: *SHELXS97* (Sheldrick, 2008[@bb4]); program(s) used to refine structure: *SHELXL97* (Sheldrick, 2008[@bb4]); molecular graphics: *ORTEPII* (Johnson, 1976[@bb2]); software used to prepare material for publication: *SHELXL97*.

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

Crystal structure: contains datablocks I, global. DOI: [10.1107/S1600536810003065/hy2275sup1.cif](http://dx.doi.org/10.1107/S1600536810003065/hy2275sup1.cif)

Structure factors: contains datablocks I. DOI: [10.1107/S1600536810003065/hy2275Isup2.hkl](http://dx.doi.org/10.1107/S1600536810003065/hy2275Isup2.hkl)

Additional supplementary materials: [crystallographic information](http://scripts.iucr.org/cgi-bin/sendsupfiles?hy2275&file=hy2275sup0.html&mime=text/html); [3D view](http://scripts.iucr.org/cgi-bin/sendcif?hy2275sup1&Qmime=cif); [checkCIF report](http://scripts.iucr.org/cgi-bin/paper?hy2275&checkcif=yes)

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: [HY2275](http://scripts.iucr.org/cgi-bin/sendsup?hy2275)).

The authors acknowledge Guang Dong Ocean University for supporting this work.

Comment
=======

From the structural point of view, 1*H*-benzimidazole-5,6-dicarboxylic acid (H~3~bidc) possesses two N atoms of imidazole ring and four O atoms of carboxylate groups and might be used as versatile linker in constructing coordination polymers with abundant hydrogen bonds. Based on this idea, a series of coordination polymers fomed by this ligand have been reported by us: *catena*-poly\[\[diaqua(1,10-phenanthroline-κ^2^N,N\')nickel(II)\]- µ-Hbidc-κ^2^N^3^:O^6^\] (Song, Wang, Hu *et al.*, 2009), pentaaqua(Hbidc-κN^3^)cobalt(II) pentahydrate (Song, Wang, Li *et al.*, 2009), pentaaqua(Hbidc-κN^3^)nickel(II) pentahydrate (Song, Wang, Qin *et al.*, 2009), and tetraaquabis(Hbidc-κN^3^)cobalt(II) dimethylformamide disolvate dihydrate (Wang *et al.*, 2009). In the present paper, we report the title complex.

As shown in Fig. 1, the Cd^II^ atom exhibits an octahedral coordination geometry, defined by three O atoms from three different Hbidc ligands, one N atom from another Hbidc ligand, one O atom from a dimethylformamide ligand and one O atom from a water molecule. The equatorial plane is defined by O1W, O10, N1^i^ and O3^iii^ atoms, while O1 and O4^ii^ occupy the axial positions \[symmetry codes: (i) -*x*, 1-*y*, 1-*z*; (ii) 1+*x*, *y*, *z*; (iii) -*x*, -*y*, 1-*z*\]. Two solvent water molecules are present in the asymmetic unit. O---H···O and N---H···O hydrogen bonds are observed in the crystal structure with hydrogen-bond geometry in the normal range (Fig. 2 and Table 1).

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

A dimethylformamide solution (20 ml) containing CdCl~2~(0.1 mmol) and H~3~bidc (0.2 mmol) was stirred for a few minutes in air, and then left to stand at room temperature. Colorless crystals were obtained in a few weeks.

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

C- and N-bound H atoms were placed at calculated positions and treated as riding on the parent atoms, with C---H = 0.93 (CH), 0.96 (CH~3~), N---H = 0.86 Å and with *U*~iso~(H) = 1.2(1.5 for methyl)*U*~eq~(C, N). The water H-atoms were located in a difference Fourier map and refined as riding, with a distance restraint of O---H = 0.84 Å and with *U*~iso~(H) = 1.5*U*~eq~(O). The highest residual electron density was found 1.07 Å from Cd1 and the deepest hole 0.97 Å from Cd1.

Figures
=======

![The asymmetric unit of the title compound, showing the 30% probability displacement ellipsoids. \[Symmetry codes: (i) -x, 1-y, 1-z; (ii) 1+x, y, z; (iii) -x, -y,1-z.\]](e-66-0m209-fig1){#Fap1}

![A view of the crystal packing. Hydrogen bonds are shown as dashed lines.](e-66-0m209-fig2){#Fap2}

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

  ---------------------------------------------------- ---------------------------------------
  \[Cd(C~9~H~4~N~2~O~4~)(C~3~H~7~NO)(H~2~O)\]·2H~2~O   *Z* = 2
  *M~r~* = 443.69                                      *F*(000) = 444
  Triclinic, *P*1                                      *D*~x~ = 1.881 Mg m^−3^
  Hall symbol: -P 1                                    Mo *K*α radiation, λ = 0.71073 Å
  *a* = 7.7729 (16) Å                                  Cell parameters from 3441 reflections
  *b* = 9.1648 (18) Å                                  θ = 3.3--27.4°
  *c* = 11.458 (2) Å                                   µ = 1.44 mm^−1^
  α = 102.76 (3)°                                      *T* = 293 K
  β = 97.70 (3)°                                       Block, colorless
  γ = 94.96 (3)°                                       0.29 × 0.25 × 0.21 mm
  *V* = 783.2 (3) Å^3^                                 
  ---------------------------------------------------- ---------------------------------------

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

  ----------------------------------------------------------- --------------------------------------
  Rigaku/MSC Mercury CCD diffractometer                       2800 independent reflections
  Radiation source: fine-focus sealed tube                    1539 reflections with *I* \> 2σ(*I*)
  graphite                                                    *R*~int~ = 0.121
  ω scans                                                     θ~max~ = 25.2°, θ~min~ = 3.3°
  Absorption correction: multi-scan (REQAB; Jacobson, 1998)   *h* = −9→7
  *T*~min~ = 0.680, *T*~max~ = 0.752                          *k* = −10→10
  6197 measured reflections                                   *l* = −13→13
  ----------------------------------------------------------- --------------------------------------

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*\[*F*^2^ \> 2σ(*F*^2^)\] = 0.086   Hydrogen site location: inferred from neighbouring sites
  *wR*(*F*^2^) = 0.223                  H-atom parameters constrained
  *S* = 1.14                            *w* = 1/\[σ^2^(*F*~o~^2^) + (0.0683*P*)^2^ + 2.7388*P*\] where *P* = (*F*~o~^2^ + 2*F*~c~^2^)/3
  2800 reflections                      (Δ/σ)~max~ \< 0.001
  219 parameters                        Δρ~max~ = 2.12 e Å^−3^
  9 restraints                          Δρ~min~ = −1.80 e Å^−3^
  ------------------------------------- -------------------------------------------------------------------------------------------------

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^2^) {#tablewrapcoords}
==================================================================================================

  ------ -------------- -------------- ------------- -------------------- --
         *x*            *y*            *z*           *U*~iso~\*/*U*~eq~   
  Cd1    0.32811 (14)   0.19007 (13)   0.58926 (9)   0.0427 (4)           
  O1     0.1397 (12)    0.1778 (11)    0.7248 (7)    0.043 (2)            
  O2     −0.1244 (11)   0.1608 (11)    0.7803 (8)    0.043 (2)            
  O1W    0.5202 (9)     0.0812 (8)     0.7112 (7)    0.045 (3)            
  O10    0.4501 (13)    0.4197 (11)    0.7028 (8)    0.048 (3)            
  N1     −0.1716 (14)   0.7274 (13)    0.5549 (9)    0.037 (3)            
  N2     0.0418 (16)    0.7573 (12)    0.7100 (10)   0.046 (3)            
  H2     0.1247         0.8019         0.7676        0.055\*              
  N3     0.6296 (17)    0.5826 (15)    0.8605 (11)   0.057 (4)            
  C1     −0.0542 (18)   0.8220 (17)    0.6334 (13)   0.044 (4)            
  H1     −0.0382        0.9245         0.6362        0.053\*              
  C2     −0.1506 (16)   0.5900 (15)    0.5837 (12)   0.035 (3)            
  C3     −0.2450 (15)   0.4482 (15)    0.5278 (10)   0.031 (3)            
  H3     −0.3353        0.4370         0.4633        0.037\*              
  C4     −0.1988 (17)   0.3261 (16)    0.5722 (11)   0.037 (3)            
  C5     −0.0634 (17)   0.3421 (14)    0.6700 (11)   0.033 (3)            
  C6     0.0295 (17)    0.4860 (17)    0.7241 (12)   0.045 (4)            
  H6     0.1203         0.4999         0.7887        0.054\*              
  C7     −0.0192 (16)   0.6032 (16)    0.6778 (10)   0.033 (3)            
  C8     −0.0144 (18)   0.2164 (15)    0.7258 (12)   0.039 (3)            
  C11    0.758 (3)      0.606 (2)      0.9664 (14)   0.086 (6)            
  H11A   0.7649         0.5123         0.9907        0.128\*              
  H11B   0.7250         0.6793         1.0306        0.128\*              
  H11C   0.8693         0.6407         0.9491        0.128\*              
  C12    0.587 (2)      0.713 (2)      0.8183 (16)   0.077 (6)            
  H12A   0.5613         0.6868         0.7313        0.116\*              
  H12B   0.6835         0.7907         0.8445        0.116\*              
  H12C   0.4859         0.7477         0.8506        0.116\*              
  C10    0.560 (2)      0.4477 (19)    0.7957 (13)   0.054 (4)            
  H10    0.5975         0.3655         0.8226        0.065\*              
  O3W    0.7681 (13)    0.2252 (9)     1.0089 (11)   0.127 (6)            
  H5W    0.8465         0.2124         0.9650        0.190\*              
  H6W    0.6998         0.1446         0.9891        0.190\*              
  O2W    0.2935 (7)     0.0032 (12)    0.8739 (9)    0.080 (4)            
  H3W    0.3906         0.0207         0.8522        0.120\*              
  H4W    0.2273         0.0510         0.8364        0.120\*              
  C9     −0.2912 (17)   0.1756 (17)    0.5120 (11)   0.036 (3)            
  O3     −0.2155 (12)   0.0562 (10)    0.5048 (7)    0.041 (2)            
  O4     −0.4532 (9)    0.1698 (8)     0.4625 (7)    0.043 (2)            
  H1W    0.6279         0.1081         0.7315        0.065\*              
  H2W    0.4982         −0.0084        0.6711        0.065\*              
  ------ -------------- -------------- ------------- -------------------- --

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

  ----- ------------ ------------ ------------ ------------- ------------- -------------
        *U*^11^      *U*^22^      *U*^33^      *U*^12^       *U*^13^       *U*^23^
  Cd1   0.0451 (7)   0.0367 (7)   0.0457 (6)   −0.0036 (5)   0.0070 (4)    0.0115 (5)
  O1    0.040 (6)    0.042 (6)    0.043 (5)    −0.015 (5)    0.005 (4)     0.013 (4)
  O2    0.033 (5)    0.041 (6)    0.059 (6)    −0.002 (5)    0.007 (4)     0.024 (5)
  O1W   0.040 (5)    0.038 (6)    0.049 (5)    −0.017 (5)    0.006 (4)     0.004 (5)
  O10   0.054 (6)    0.044 (7)    0.039 (5)    −0.003 (5)    −0.005 (5)    0.006 (5)
  N1    0.035 (6)    0.030 (7)    0.042 (6)    0.000 (6)     0.000 (5)     0.006 (5)
  N2    0.056 (8)    0.023 (7)    0.053 (7)    −0.007 (6)    0.011 (6)     0.002 (6)
  N3    0.062 (9)    0.034 (8)    0.064 (8)    0.003 (7)     −0.009 (7)    0.004 (7)
  C1    0.048 (9)    0.035 (9)    0.064 (9)    0.014 (7)     0.021 (8)     0.031 (8)
  C2    0.030 (7)    0.029 (8)    0.057 (8)    0.011 (6)     0.020 (6)     0.020 (7)
  C3    0.025 (6)    0.043 (9)    0.023 (6)    −0.010 (6)    0.001 (5)     0.010 (6)
  C4    0.035 (8)    0.040 (9)    0.034 (7)    −0.009 (7)    0.003 (6)     0.009 (6)
  C5    0.045 (8)    0.022 (7)    0.033 (7)    0.002 (6)     0.006 (6)     0.008 (6)
  C6    0.032 (8)    0.055 (10)   0.043 (8)    −0.006 (7)    −0.007 (6)    0.016 (7)
  C7    0.029 (7)    0.047 (9)    0.029 (7)    0.016 (7)     0.003 (5)     0.016 (6)
  C8    0.041 (9)    0.027 (8)    0.043 (8)    −0.011 (7)    0.010 (6)     −0.002 (6)
  C11   0.105 (16)   0.080 (15)   0.052 (10)   0.008 (12)    −0.028 (10)   0.001 (10)
  C12   0.083 (14)   0.063 (14)   0.078 (12)   0.011 (11)    0.036 (10)    −0.013 (10)
  C10   0.065 (11)   0.049 (11)   0.049 (9)    0.012 (9)     0.009 (8)     0.009 (8)
  O3W   0.171 (17)   0.126 (15)   0.085 (10)   −0.006 (12)   0.049 (10)    0.020 (10)
  O2W   0.075 (8)    0.090 (10)   0.088 (8)    0.009 (7)     0.027 (7)     0.041 (8)
  C9    0.037 (8)    0.044 (9)    0.030 (7)    0.006 (7)     0.008 (6)     0.015 (6)
  O3    0.056 (6)    0.028 (6)    0.039 (5)    0.000 (5)     0.011 (4)     0.005 (4)
  O4    0.044 (6)    0.037 (6)    0.041 (5)    −0.009 (5)    0.008 (4)     −0.001 (4)
  ----- ------------ ------------ ------------ ------------- ------------- -------------

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

  ------------------------ ------------ ------------------- ------------
  Cd1---N1^i^              2.226 (11)   C3---C4             1.382 (19)
  Cd1---O10                2.266 (9)    C3---H3             0.9300
  Cd1---O1                 2.287 (8)    C4---C5             1.404 (18)
  Cd1---O3^ii^             2.314 (9)    C4---C9             1.472 (18)
  Cd1---O1W                2.344 (9)    C5---C6             1.414 (18)
  Cd1---O4^iii^            2.373 (7)    C5---C8             1.489 (19)
  O1---C8                  1.278 (16)   C6---C7             1.359 (19)
  O2---C8                  1.261 (14)   C6---H6             0.9300
  O1W---H1W                0.8380       C11---H11A          0.9600
  O1W---H2W                0.8382       C11---H11B          0.9600
  O10---C10                1.236 (17)   C11---H11C          0.9600
  N1---C1                  1.301 (17)   C12---H12A          0.9600
  N1---C2                  1.388 (17)   C12---H12B          0.9600
  N2---C1                  1.346 (17)   C12---H12C          0.9600
  N2---C7                  1.400 (17)   C10---H10           0.9300
  N2---H2                  0.8600       O3W---H5W           0.8411
  N3---C10                 1.320 (19)   O3W---H6W           0.8398
  N3---C11                 1.426 (19)   O2W---H3W           0.8389
  N3---C12                 1.43 (2)     O2W---H4W           0.8393
  C1---H1                  0.9300       C9---O3             1.279 (16)
  C2---C7                  1.359 (18)   C9---O4             1.302 (14)
  C2---C3                  1.407 (17)                       
                                                            
  N1^i^---Cd1---O10        96.6 (4)     C3---C4---C9        118.6 (11)
  N1^i^---Cd1---O1         103.1 (4)    C5---C4---C9        119.8 (13)
  O10---Cd1---O1           89.6 (3)     C4---C5---C6        119.5 (13)
  N1^i^---Cd1---O3^ii^     90.6 (4)     C4---C5---C8        123.9 (12)
  O10---Cd1---O3^ii^       172.6 (3)    C6---C5---C8        116.6 (12)
  O1---Cd1---O3^ii^        86.9 (3)     C7---C6---C5        117.3 (12)
  N1^i^---Cd1---O1W        169.1 (3)    C7---C6---H6        121.3
  O10---Cd1---O1W          88.5 (3)     C5---C6---H6        121.3
  O1---Cd1---O1W           86.5 (3)     C6---C7---C2        124.0 (13)
  O3^ii^---Cd1---O1W       84.8 (3)     C6---C7---N2        132.0 (12)
  N1^i^---Cd1---O4^iii^    85.9 (3)     C2---C7---N2        103.9 (12)
  O10---Cd1---O4^iii^      93.7 (3)     O2---C8---O1        123.0 (14)
  O1---Cd1---O4^iii^       170.0 (3)    O2---C8---C5        117.4 (13)
  O3^ii^---Cd1---O4^iii^   88.7 (3)     O1---C8---C5        119.3 (11)
  O1W---Cd1---O4^iii^      84.1 (3)     N3---C11---H11A     109.5
  C8---O1---Cd1            130.4 (8)    N3---C11---H11B     109.5
  H1W---O1W---H2W          112.2        H11A---C11---H11B   109.5
  C10---O10---Cd1          127.5 (11)   N3---C11---H11C     109.5
  C1---N1---C2             103.9 (12)   H11A---C11---H11C   109.5
  C1---N1---Cd1^i^         118.8 (10)   H11B---C11---H11C   109.5
  C2---N1---Cd1^i^         137.1 (9)    N3---C12---H12A     109.5
  C1---N2---C7             106.8 (11)   N3---C12---H12B     109.5
  C1---N2---H2             126.6        H12A---C12---H12B   109.5
  C7---N2---H2             126.6        N3---C12---H12C     109.5
  C10---N3---C11           123.2 (15)   H12A---C12---H12C   109.5
  C10---N3---C12           119.1 (14)   H12B---C12---H12C   109.5
  C11---N3---C12           117.5 (15)   O10---C10---N3      126.5 (16)
  N1---C1---N2             113.5 (13)   O10---C10---H10     116.7
  N1---C1---H1             123.2        N3---C10---H10      116.7
  N2---C1---H1             123.2        H5W---O3W---H6W     105.9
  C7---C2---N1             111.8 (12)   H3W---O2W---H4W     103.7
  C7---C2---C3             120.0 (13)   O3---C9---O4        121.1 (12)
  N1---C2---C3             128.2 (13)   O3---C9---C4        122.1 (12)
  C4---C3---C2             117.7 (11)   O4---C9---C4        116.8 (13)
  C4---C3---H3             121.2        C9---O3---Cd1^ii^   128.7 (8)
  C2---C3---H3             121.2        C9---O4---Cd1^iv^   118.5 (7)
  C3---C4---C5             121.6 (12)                       
  ------------------------ ------------ ------------------- ------------

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

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

  --------------------- --------- --------- ------------ ---------------
  *D*---H···*A*         *D*---H   H···*A*   *D*···*A*    *D*---H···*A*
  O1W---H1W···O2^iii^   0.84      1.92      2.757 (11)   177
  O1W---H2W···O4^ii^    0.84      1.85      2.649 (12)   159
  O2W---H3W···O1W       0.84      2.16      2.888 (9)    145
  O2W---H4W···O1        0.84      2.00      2.811 (11)   162
  O3W---H5W···O2^iii^   0.84      2.11      2.810 (12)   140
  O3W---H6W···O2W^v^    0.84      2.29      2.766 (14)   117
  N2---H2···O2W^vi^     0.86      2.18      2.970 (16)   152
  --------------------- --------- --------- ------------ ---------------

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

###### Hydrogen-bond geometry (Å, °)

  *D*---H⋯*A*                *D*---H   H⋯*A*   *D*⋯*A*      *D*---H⋯*A*
  -------------------------- --------- ------- ------------ -------------
  O1*W*---H1*W*⋯O2^i^        0.84      1.92    2.757 (11)   177
  O1*W*---H2*W*⋯O4^ii^       0.84      1.85    2.649 (12)   159
  O2*W*---H3*W*⋯O1*W*        0.84      2.16    2.888 (9)    145
  O2*W*---H4*W*⋯O1           0.84      2.00    2.811 (11)   162
  O3*W*---H5*W*⋯O2^i^        0.84      2.11    2.810 (12)   140
  O3*W*---H6*W*⋯O2*W*^iii^   0.84      2.29    2.766 (14)   117
  N2---H2⋯O2*W*^iv^          0.86      2.18    2.970 (16)   152

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