The title compound, [Cd(C
3H
6NO
5P)(H
2O)
2]
n, is a three-dimensional polymeric complex. The asymmetric unit contains one Cd atom, one
N-(phosphonomethyl)glycine zwitterion [(O
−)
2OPCH
2NH
2+CH
2COO
−] and two water molecules. The coordination geometry is a distorted CdO
6 octahedron. Each
N-(phosphonomethyl)glycine ligand bridges four adjacent water-coordinated Cd cations through three phosphonate O atoms and one carboxylate O atom, like a regular PO
43− group in zeolite-type frameworks. One-dimensional zigzag (–O—P—C—N—C—C—O—Cd–)
n chains along the [101] direction are linked to one another
via Cd—O—P bridges and form a three-dimensional network motif with three types of channel systems. The variety of O—H
O and N—H
O hydrogen bonds is likely to be responsible for stabilizing the three-dimensional network structure and preventing guest molecules from entering into the channels.
Supporting information
CCDC reference: 607929
A mixture of cadmium(II) acetate dihydrate (0.134 g, 0.5 mmol),
N-(phosphonomethyl)glycine (0.078 g, 0.5 mmol) and deionized water (16 ml) was heated in a Teflon-lined stainless steel autoclave (25 ml) for 144 h
at 433 K, after which the autoclave was cooled to room temperature over a
period of 12 h at a rate of 10 K h-1. Colourless block single crystals of
(I) were collected in about 18% yield.
H atoms on C and N atoms were positioned geometrically and were included in the
refinement in the riding-model approximation, with C—H distances of 0.97 Å
and N—H distances of 0.90 Å, and with Uiso(H) =
1.2Ueq(C,N). The water H atoms were located in a difference
Fourier map and were refined subject to an O—H distance restraint of 0.82 (1) Å. The absolute structure could be determined by refining the Flack
parameter (Flack, 1983), using 616 Friedel pairs.
Data collection: CrystalClear (Rigaku, 1999); cell refinement: CrystalClear; data reduction: CrystalStructure (Rigaku/MSC, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 2000); software used to prepare material for publication: SHELXTL.
Poly[[diaquacadmium(II)]-µ
4-
N-(phosphonatomethyl)glycinato]
top
Crystal data top
[Cd(C3H6NO5P)(H2O)2] | F(000) = 616 |
Mr = 315.49 | Dx = 2.580 Mg m−3 |
MonoclinicCc | Mo Kα radiation, λ = 0.71070 Å |
Hall symbol: C -2yc | Cell parameters from 1695 reflections |
a = 9.827 (2) Å | θ = 3.6–25.3° |
b = 4.9326 (10) Å | µ = 2.90 mm−1 |
c = 16.795 (4) Å | T = 153 K |
β = 93.910 (4)° | Block, colourless |
V = 812.2 (3) Å3 | 0.30 × 0.25 × 0.07 mm |
Z = 4 | |
Data collection top
Rigaku Mercury diffractometer | 1359 independent reflections |
Radiation source: fine-focus sealed tube | 1348 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.021 |
Detector resolution: 7.31 pixels mm-1 | θmax = 25.4°, θmin = 4.2° |
ω scans | h = −11→11 |
Absorption correction: multi-scan (Jacobson, 1998) | k = −5→5 |
Tmin = 0.430, Tmax = 0.817 | l = −20→17 |
3642 measured reflections | |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.015 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.035 | w = 1/[σ2(Fo2) + (0.0137P)2 + 0.0465P] where P = (Fo2 + 2Fc2)/3 |
S = 1.09 | (Δ/σ)max < 0.001 |
1359 reflections | Δρmax = 0.60 e Å−3 |
127 parameters | Δρmin = −0.47 e Å−3 |
6 restraints | Absolute structure: Flack (1983), with 616 Friedel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: −0.03 (2) |
Crystal data top
[Cd(C3H6NO5P)(H2O)2] | V = 812.2 (3) Å3 |
Mr = 315.49 | Z = 4 |
MonoclinicCc | Mo Kα radiation |
a = 9.827 (2) Å | µ = 2.90 mm−1 |
b = 4.9326 (10) Å | T = 153 K |
c = 16.795 (4) Å | 0.30 × 0.25 × 0.07 mm |
β = 93.910 (4)° | |
Data collection top
Rigaku Mercury diffractometer | 1359 independent reflections |
Absorption correction: multi-scan (Jacobson, 1998) | 1348 reflections with I > 2σ(I) |
Tmin = 0.430, Tmax = 0.817 | Rint = 0.021 |
3642 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.015 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.035 | Δρmax = 0.60 e Å−3 |
S = 1.09 | Δρmin = −0.47 e Å−3 |
1359 reflections | Absolute structure: Flack (1983), with 616 Friedel pairs |
127 parameters | Absolute structure parameter: −0.03 (2) |
6 restraints | |
Special details top
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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Cd1 | 0.5379 | 0.42153 (3) | 0.6762 | 0.00723 (7) | |
P1 | 0.34039 (9) | −0.09619 (15) | 0.58567 (5) | 0.00563 (18) | |
O1 | 0.3806 (2) | 0.1080 (4) | 0.65054 (14) | 0.0105 (5) | |
O2 | 0.2009 (2) | −0.2227 (4) | 0.59649 (13) | 0.0087 (5) | |
O3 | 0.4490 (2) | −0.3069 (4) | 0.57244 (14) | 0.0095 (5) | |
O4 | 0.0635 (2) | 0.3449 (5) | 0.29362 (14) | 0.0111 (5) | |
O5 | 0.0289 (3) | 0.0494 (4) | 0.39180 (14) | 0.0125 (5) | |
O6 | 0.6839 (3) | 0.6951 (5) | 0.74746 (16) | 0.0139 (5) | |
H6A | 0.7570 | 0.6990 | 0.7267 | 0.021* | |
O7 | 0.3872 (3) | 0.6469 (5) | 0.76013 (15) | 0.0117 (5) | |
H7A | 0.4108 | 0.6157 | 0.8070 | 0.018* | |
N1 | 0.2003 (3) | 0.2953 (5) | 0.49885 (16) | 0.0078 (6) | |
H1A | 0.1267 | 0.2028 | 0.5127 | 0.009* | |
H1D | 0.2213 | 0.4188 | 0.5372 | 0.009* | |
C1 | 0.3176 (4) | 0.1030 (6) | 0.4940 (2) | 0.0094 (7) | |
H1B | 0.4003 | 0.2041 | 0.4861 | 0.011* | |
H1C | 0.3004 | −0.0174 | 0.4487 | 0.011* | |
C2 | 0.1664 (4) | 0.4381 (6) | 0.4218 (2) | 0.0082 (7) | |
H2B | 0.2500 | 0.4865 | 0.3977 | 0.010* | |
H2C | 0.1173 | 0.6039 | 0.4318 | 0.010* | |
C3 | 0.0799 (3) | 0.2599 (6) | 0.36479 (19) | 0.0097 (7) | |
H7B | 0.405 (4) | 0.807 (3) | 0.754 (3) | 0.022 (12)* | |
H6B | 0.652 (5) | 0.841 (5) | 0.760 (3) | 0.027 (13)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cd1 | 0.00718 (11) | 0.00720 (11) | 0.00730 (11) | −0.00118 (12) | 0.00049 (7) | −0.00046 (11) |
P1 | 0.0059 (4) | 0.0054 (5) | 0.0055 (4) | −0.0002 (3) | 0.0000 (3) | 0.0003 (3) |
O1 | 0.0101 (12) | 0.0102 (12) | 0.0112 (13) | −0.0028 (9) | 0.0001 (10) | −0.0018 (9) |
O2 | 0.0085 (11) | 0.0078 (11) | 0.0100 (11) | −0.0001 (9) | 0.0015 (8) | −0.0025 (9) |
O3 | 0.0102 (13) | 0.0087 (12) | 0.0097 (13) | 0.0028 (10) | 0.0024 (10) | 0.0024 (10) |
O4 | 0.0152 (12) | 0.0108 (11) | 0.0068 (12) | −0.0007 (10) | −0.0025 (10) | −0.0006 (10) |
O5 | 0.0180 (13) | 0.0106 (13) | 0.0085 (12) | −0.0052 (10) | −0.0010 (10) | −0.0001 (9) |
O6 | 0.0095 (13) | 0.0134 (15) | 0.0193 (14) | −0.0033 (11) | 0.0050 (10) | −0.0062 (11) |
O7 | 0.0145 (13) | 0.0109 (12) | 0.0096 (13) | −0.0005 (11) | −0.0003 (10) | 0.0011 (10) |
N1 | 0.0078 (13) | 0.0074 (14) | 0.0080 (14) | −0.0010 (11) | −0.0020 (10) | −0.0006 (11) |
C1 | 0.0085 (17) | 0.0074 (17) | 0.0125 (18) | 0.0020 (13) | 0.0012 (14) | 0.0006 (13) |
C2 | 0.0117 (17) | 0.0070 (18) | 0.0059 (18) | 0.0014 (11) | 0.0001 (14) | 0.0038 (12) |
C3 | 0.0083 (15) | 0.0089 (16) | 0.0117 (17) | 0.0026 (14) | −0.0001 (13) | 0.0017 (14) |
Geometric parameters (Å, º) top
Cd1—O1 | 2.208 (2) | O6—H6B | 0.82 (3) |
Cd1—O6 | 2.253 (2) | O7—H7A | 0.8200 |
Cd1—O2i | 2.271 (2) | O7—H7B | 0.820 (10) |
Cd1—O3ii | 2.321 (2) | N1—C2 | 1.491 (4) |
Cd1—O4iii | 2.369 (2) | N1—C1 | 1.500 (4) |
Cd1—O7 | 2.387 (2) | N1—H1A | 0.9000 |
P1—O1 | 1.516 (2) | N1—H1D | 0.9000 |
P1—O3 | 1.517 (2) | C1—H1B | 0.9700 |
P1—O2 | 1.528 (2) | C1—H1C | 0.9700 |
P1—C1 | 1.828 (4) | C2—C3 | 1.517 (5) |
O4—C3 | 1.267 (4) | C2—H2B | 0.9700 |
O5—C3 | 1.251 (4) | C2—H2C | 0.9700 |
O6—H6A | 0.8200 | | |
| | | |
O1—Cd1—O6 | 159.25 (9) | Cd1—O6—H6B | 115 (4) |
O1—Cd1—O2i | 100.24 (8) | H6A—O6—H6B | 116.7 |
O6—Cd1—O2i | 92.94 (9) | Cd1—O7—H7A | 109.5 |
O1—Cd1—O3ii | 92.01 (8) | Cd1—O7—H7B | 103 (3) |
O6—Cd1—O3ii | 104.27 (8) | H7A—O7—H7B | 105.1 |
O2i—Cd1—O3ii | 88.99 (8) | C2—N1—C1 | 112.3 (3) |
O1—Cd1—O4iii | 78.89 (9) | C2—N1—H1A | 109.2 |
O6—Cd1—O4iii | 82.10 (9) | C1—N1—H1A | 109.2 |
O2i—Cd1—O4iii | 106.12 (8) | C2—N1—H1D | 109.2 |
O3ii—Cd1—O4iii | 163.45 (8) | C1—N1—H1D | 109.2 |
O1—Cd1—O7 | 89.29 (9) | H1A—N1—H1D | 107.9 |
O6—Cd1—O7 | 78.81 (9) | N1—C1—P1 | 110.1 (2) |
O2i—Cd1—O7 | 169.98 (8) | N1—C1—H1B | 109.6 |
O3ii—Cd1—O7 | 87.58 (9) | P1—C1—H1B | 109.6 |
O4iii—Cd1—O7 | 78.59 (9) | N1—C1—H1C | 109.6 |
O1—P1—O3 | 114.13 (14) | P1—C1—H1C | 109.6 |
O1—P1—O2 | 112.20 (13) | H1B—C1—H1C | 108.1 |
O3—P1—O2 | 112.54 (13) | N1—C2—C3 | 110.9 (2) |
O1—P1—C1 | 105.04 (14) | N1—C2—H2B | 109.5 |
O3—P1—C1 | 106.97 (15) | C3—C2—H2B | 109.5 |
O2—P1—C1 | 105.10 (15) | N1—C2—H2C | 109.5 |
P1—O1—Cd1 | 138.63 (15) | C3—C2—H2C | 109.5 |
P1—O2—Cd1iv | 128.08 (12) | H2B—C2—H2C | 108.0 |
P1—O3—Cd1v | 121.19 (14) | O5—C3—O4 | 126.1 (3) |
C3—O4—Cd1vi | 127.0 (2) | O5—C3—C2 | 118.2 (3) |
Cd1—O6—H6A | 109.5 | O4—C3—C2 | 115.7 (3) |
| | | |
O3—P1—O1—Cd1 | 61.5 (2) | O2—P1—O3—Cd1v | −73.17 (17) |
O2—P1—O1—Cd1 | −168.99 (18) | C1—P1—O3—Cd1v | 171.90 (15) |
C1—P1—O1—Cd1 | −55.4 (2) | C2—N1—C1—P1 | −172.9 (2) |
O6—Cd1—O1—P1 | −150.1 (2) | O1—P1—C1—N1 | −64.9 (2) |
O2i—Cd1—O1—P1 | −21.5 (2) | O3—P1—C1—N1 | 173.5 (2) |
O3ii—Cd1—O1—P1 | 67.8 (2) | O2—P1—C1—N1 | 53.7 (2) |
O4iii—Cd1—O1—P1 | −126.1 (2) | C1—N1—C2—C3 | 80.9 (3) |
O7—Cd1—O1—P1 | 155.4 (2) | Cd1vi—O4—C3—O5 | −34.1 (4) |
O1—P1—O2—Cd1iv | 14.7 (2) | Cd1vi—O4—C3—C2 | 147.8 (2) |
O3—P1—O2—Cd1iv | 145.08 (14) | N1—C2—C3—O5 | 12.4 (4) |
C1—P1—O2—Cd1iv | −98.87 (17) | N1—C2—C3—O4 | −169.3 (3) |
O1—P1—O3—Cd1v | 56.19 (18) | | |
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x, y+1, z; (iii) x+1/2, −y+1/2, z+1/2; (iv) x−1/2, y−1/2, z; (v) x, y−1, z; (vi) x−1/2, −y+1/2, z−1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O3vii | 0.90 | 2.07 | 2.881 (4) | 149 |
N1—H1D···O2ii | 0.90 | 2.05 | 2.888 (4) | 155 |
O6—H6A···O1i | 0.82 | 1.88 | 2.646 (3) | 156 |
O6—H6A···O7i | 0.82 | 2.60 | 2.991 (3) | 111 |
O6—H6B···O4viii | 0.82 (3) | 1.88 (3) | 2.697 (3) | 174 (5) |
O7—H7A···O5iii | 0.82 | 1.95 | 2.710 (3) | 153 |
O7—H7B···O1ii | 0.82 (1) | 2.28 (3) | 2.924 (3) | 136 (4) |
O7—H7B···O4viii | 0.82 (1) | 2.38 (3) | 3.077 (3) | 143 (4) |
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x, y+1, z; (iii) x+1/2, −y+1/2, z+1/2; (vii) x−1/2, y+1/2, z; (viii) x+1/2, −y+3/2, z+1/2. |
Experimental details
Crystal data |
Chemical formula | [Cd(C3H6NO5P)(H2O)2] |
Mr | 315.49 |
Crystal system, space group | MonoclinicCc |
Temperature (K) | 153 |
a, b, c (Å) | 9.827 (2), 4.9326 (10), 16.795 (4) |
β (°) | 93.910 (4) |
V (Å3) | 812.2 (3) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 2.90 |
Crystal size (mm) | 0.30 × 0.25 × 0.07 |
|
Data collection |
Diffractometer | Rigaku Mercury diffractometer |
Absorption correction | Multi-scan (Jacobson, 1998) |
Tmin, Tmax | 0.430, 0.817 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3642, 1359, 1348 |
Rint | 0.021 |
(sin θ/λ)max (Å−1) | 0.602 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.015, 0.035, 1.09 |
No. of reflections | 1359 |
No. of parameters | 127 |
No. of restraints | 6 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.60, −0.47 |
Absolute structure | Flack (1983), with 616 Friedel pairs |
Absolute structure parameter | −0.03 (2) |
Selected geometric parameters (Å, º) topCd1—O1 | 2.208 (2) | Cd1—O3ii | 2.321 (2) |
Cd1—O6 | 2.253 (2) | Cd1—O4iii | 2.369 (2) |
Cd1—O2i | 2.271 (2) | Cd1—O7 | 2.387 (2) |
| | | |
O1—Cd1—O6 | 159.25 (9) | O2i—Cd1—O4iii | 106.12 (8) |
O1—Cd1—O2i | 100.24 (8) | O3ii—Cd1—O4iii | 163.45 (8) |
O6—Cd1—O2i | 92.94 (9) | O1—Cd1—O7 | 89.29 (9) |
O1—Cd1—O3ii | 92.01 (8) | O6—Cd1—O7 | 78.81 (9) |
O6—Cd1—O3ii | 104.27 (8) | O2i—Cd1—O7 | 169.98 (8) |
O2i—Cd1—O3ii | 88.99 (8) | O3ii—Cd1—O7 | 87.58 (9) |
O1—Cd1—O4iii | 78.89 (9) | O4iii—Cd1—O7 | 78.59 (9) |
O6—Cd1—O4iii | 82.10 (9) | | |
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x, y+1, z; (iii) x+1/2, −y+1/2, z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O3iv | 0.90 | 2.07 | 2.881 (4) | 148.9 |
N1—H1D···O2ii | 0.90 | 2.05 | 2.888 (4) | 155.2 |
O6—H6A···O1i | 0.82 | 1.88 | 2.646 (3) | 155.5 |
O6—H6A···O7i | 0.82 | 2.60 | 2.991 (3) | 111.2 |
O6—H6B···O4v | 0.82 (3) | 1.88 (3) | 2.697 (3) | 174 (5) |
O7—H7A···O5iii | 0.82 | 1.95 | 2.710 (3) | 153.3 |
O7—H7B···O1ii | 0.820 (10) | 2.28 (3) | 2.924 (3) | 136 (4) |
O7—H7B···O4v | 0.820 (10) | 2.38 (3) | 3.077 (3) | 143 (4) |
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x, y+1, z; (iii) x+1/2, −y+1/2, z+1/2; (iv) x−1/2, y+1/2, z; (v) x+1/2, −y+3/2, z+1/2. |
Metal complexes containing phosphonic acids attached to a variety of functional groups, such as aza-crown ethers (Sharma & Clearfield, 2000), amines (Kong et al., 2004; Jankovics et al., 2002) and carboxylic acid groups (Zhu et al., 2000; Mao et al., 2002), have shown many unusual structural and functional features. The N-(phosphonomethyl)glycine ligand has been reported as one of trifunctional aminocarboxylatephosphonates and features a diverse range of coordination modes in metal complexes (Stock, 2002; Ramstedt et al., 2004). Here, we report a new polymeric CdII complex using the trifunctional N-phosphonomethylglycine (PMG) ligand, (I), in which the coordination mode of PMG has not previously been reported in the literatures.
The structure of complex (I) is shown in Fig. 1. The asymmetric unit consists of one CdII ion, one PMG dianion and two water molecules. The CdII ion is six-coordinated and situated in a distorted CdO6 octahedral environment, involving three O atoms from phosphonate groups of three neighbouring ligands, one carboxylate O atom from another ligand and two water O atoms. The Cd—O bond distances are in the range 2.208 (2)–2.387 (2) Å (Table 1), which are similar to those reported for another CdII aminocarboxylatephosphonate (Yang et al., 2003). The equatorial plane of the coordination environment is defined by atoms O1, O3ii, O4iii and O6 [symmetry codes: (ii) ?; (iii) ? Please complete], with a mean standard deviation of 0.0454°. The trans-axial positions are occupied by atoms O7 and O2i [symmetry code: (i) ?; Please complete], with a O7—Cd1—O2i bond angle of 169.99 (9)°. The imino N atom is not coordinated. There are also O—H···O and N—H···O hydrogen-bonding interactions in the structure (Fig. 1 and Table 2).
The X-ray crystal structure reveals that compound (I) has a metal-to-ligand ratio of 1. It is also clear that both phosphonate and carboxylate groups of the ligand are deprotonated, whereas the Cd atom has an oxidation state of +2. Thus, the only way in which the neutrality of compound (I) can be achieved is by considering the possibility that the secondary amine may be 2H-protonated, including the –NH2+– group. Overall, the ligand coordinates to the sphere of CdII carrying a double negative charge, as the zwitterion [2-O3PCH2NH2+CH2COO-] (Stock, 2002). Three phosphonate O atoms and one terminal carboxylate O atom in one zwitterion are utilized to connect the Cd2+ site, and therefore each [2-O3PCH2NH2+CH2COO-] zwitterion in effect behaves like a regular PO43- group in zeolite-type frameworks (Zhu et al., 2000) and is four-connected to four Cd2+ sites. Such a coordination mode is different from those previously reported for PMG. To maintain a metal-to-ligand ratio of 1, each Cd2+ site is also four-connected to [O3PCH2NH2COO]2- sites (see scheme and Fig. 1).
A one-dimensional zigzag chain is formed in the structure of (I), containing a repeating (–O1—P1—C1—N1—C2—C3—O4—Cd1–) unit, with a distance of 9.586 Å (metal-to-metal) along the [101] direction. These chains are further linked to one another via two types of Cd1—O2—P1 and Cd1—O3—P1 bridges in a different direction, as the –PO3-– groups link to Cd atoms in different chains (Fig. 2), with O—Cd—O bond angles in the range 78.87 (8)–163.42 (7)° (Table 1). The result of cross-linking chains in this manner is the formation of a three-dimensional network motif containing three channel systems that are nearly perpendicular to one another. These channels are created by 12-, 20- and 20-membered rings, respectively. Each 12-membered ring (A) is formed of three Cd atoms and three phosphonate groups, (–O—P—O—Cd–)3. The two 20-membered rings (B and C) are similarly composed of two (–Cd—O—P—C—N—C—C—O—Cd–) units, sharing one Cd atom and one O—P—O bridge (Fig. 2).
Molecules of compound (I) show extensive hydrogen bonding between the coordinated water molecules and the phosphonate/carboxylate O atoms, between coordinated water molecules, and between the imino N atoms and the phosphonate O atoms. Such a complex hydrogen-bond network is likely to contribute to the overall stability of the crystal structure and prevents guest molecules entering into the above channels (Table 2 and Fig. 3).