An indium(III)-water chain based on an unusual acyclic water pentamer

An in situ reaction under hydro­thermal conditions leads to the formation of the title compound, diaqua­(pyridine-2-carboxyl­ato)­(pyridine-2,6-dicarboxyl­ato)indium(II) trihydrate, [In(C₆H₄NO₂)(C₇H₃NO₄)(H₂O)₂]·3H₂O, in which the central In^III atom is seven-coordinated by one pyridine-2,6-di­carboxyl­ate ligand, one pyridine-2-carboxyl­ate ligand and two water mol­ecules in a penta­gonal-bipyramidal coordination environment. An indium(III)-water chain based on an unusual water pentamer is observed.

S1. Comment

The study of water clusters is important to an understanding of the structures and characteristics of liquid water and ice (Ludwig, 2001). Thus, the search for the experimental models of small water clusters is very important to improve our studies of liquid water and ice (Ye et al., 2004). So far, a variety of water clusters, including tetramers, hexamers, octamers and decamers, found in a number of crystalline hosts have been structurally characterized and display different configurations (Ghosh & Bharadwaj, 2004). Curiously, odd-membered water clusters are known to occur very rarely (Infantes & Motherwell, 2002). Few reports of structural characterization of the cyclic water pentamer are relatively recent (Naskar et al., 2005). Theoretically, the cyclic water pentamer is much more stable than the acyclic version because of cooperative hydrogen bonding in the cyclic moiety (Cruzan et al., 1996). To the best of our knowledge, no organic or metallo-organic compound is known in which an isolated acyclic water pentamer has been detected (Infantes & Motherwell, 2002). We report here for the first time the formation and structure of an acyclic water pentamer in the title compound, [In(pdc)(pc)(H₂O)₂]·3H₂O, (I), where pdc is pyridine-2,6-dicarboxylate and pc is pyridine-2-carboxylate.

Selected bond lengths and angles for (I) are given in Table 1. Compound (I) was obtained under hydrothermal conditions at 433 K. The compound once formed is insoluble in most solvents, including water. The structure of (I) can be described as a three-dimensional hydrogen-bonding superamolecular structure. The asymmetric unit for (I) is shown in Fig. 1. The central In^III atom is seven-coordinated by one pdc ligand, one pc ligand and two water molecules in a pentagonal bipyramidal coordination environment, in which the three carboxylate O atoms (O1, O4 and O5) and two N atoms (N1 and N2) from the pdc and pc anions make up the basal plane, while the axial positions are occupied by two water molecules (O1W and O2W). The In—O (carboxylate) bond lengths range from 2.1897 (17) to 2.3093 (17) Å, and the In—O1W and In—O2W distances are 2.147 (2) and 2.1484 (19) Å, respectively.

A new in situ reaction occurs in the InCl₃·6H₂O/H₂pdc system under hydrothermal conditions. In the reaction process, some of the pdc is transformed into pc via decarboxylation. A similar reaction process, in which quinolinic acid is transformed into pc via decarboxylation, has been observed recently (Yu et al., 2003). So far, a few novel in situ reactions, such as ligand oxidative coupling, hydrolysis and substitution, have been uncovered during the hydrothermal process (Zheng et al., 2004), in which many factors, including the nature of the metal ion and the temperature, pressure and pH, have been found to influence significantly the reaction outcome. As far as our system is concerned, the pH value may play a key role in the decarboxylation of pdc. When the pH value was adjusted to higher or lower than 5.5, no crystals of (I) were obtained under hydrothermal conditions at 433 K. To the best of our knowledge, the in situ transformation from pdc to pc has not been observed before.

An interesting feature of (I) is the presence of an In^III—water chain based on an unusual acyclic water pentamer (Figs. 2 and 3; Li et al., 2005). Within the water pentamer, three water molecules (O3W, O4W and O5W) act as both hydrogen-bond donors and acceptors, while another two water molecules (O1W and O2W) act only as hydrogen-bond acceptors. The hydrogen-bond parameters are given in Table 2. The average hydrogen-bond distance is 2.73 (5) Å, which is slightly shorter than the average hydrogen-bond distance of the liquid water pentamer (2.78 Å; Naskar et al., 2005). Interestingly, the water molecules of the pentamer are hydrogen bonded to the carboxylate O atoms (O2^v, O3, O3^vi, O5^vi and O6ⁱ) from the pdc and pc ligands. Meanwhile, two water molecules (O1W^vii and O2W^viii; symmetry codes as in Fig. 2) bind to the In^III atoms in the water pentamer, resulting in three-dimensional supramolecular structure. This observation indicates that the water pentamer is stabilized not only by hydrogen bonds but also by coordination interactions. The water molecule, the pdc and pc ligands, and the In^III atom play a crucial role in the formation of the water clusters.

In summary, a new In^III compound with three-dimensional supramolecular structure was synthesized through the hydrothermal method at 4333 K. In this compound, an In^III–water chain based on an unusual acyclic water pentamer was observed. In addition, a new in situ reaction under hydrothermal conditions leads to the formation of (I).

S2. Experimental

InCl₃·6H₂O (0.38 g, 1.0 mmol) and H₂pdc (0.246 g, 1.5 mmol) were dissolved in distilled water (20 ml) and the pH value was adjusted to 5.5 with dilute aqueous NaOH solution. The solution was heated in a 25 ml Teflon-lined reaction vessel at 433 K for 90 h and then cooled to room temperature over a period of 12 h. Colorless crystals of (I) were collected with a yield of 75%.

S3. Refinement

All H atoms on C atoms were positioned geometrically and refined as riding atoms with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C). H atoms of water molecules were located from difference Fourier maps and refined freely.

Computing details

Data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO; data reduction: PROCESS-AUTO; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-Plus (Sheldrick, 1990); software used to prepare material for publication: SHELXTL-Plus.

Figures

Scheme (I). Chemical structure Fig. 1: An ORTEPIII (Burnett & Johnson, 1996) view of the local coordination of In^III with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Fig. 2: An ORTEPIII (Burnett & Johnson, 1996) view showing the water pentamer of (I) and its coordination environment. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 2 − x, 2 − y, 1 − z; (v) 1 − x, 2 − y, −z; (vi) 1 − x, 1 − y, 1 − z; (vii) x − 1, y, z; (viii) x, y − 1, z.] Fig. 3: An ORTEPIII (Burnett & Johnson, 1996) view showing the structure of an In^III-water chain based on an unusual acyclic water pentamer. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) 2 − x, 2 − y, 1 − z; (v) 1 − x, 2 − y, −z; (vi) 1 − x, 1 − y, 1 − z; (vii) x − 1, y, z; (viii) x, y − 1, z.]

diaqua(pyridine-2-carboxylato)(pyridine-2,6-dicarboxylato)indium(II) trihydrate, [In(C₆H₄NO₂)(C₇H₃NO₄)(H₂O)₂]·3H₂O

Crystal data

[In(C6H4NO2)(C7H3NO4)(H2O)2]·3H2O	Z = 2
Mr = 492.11	F(000) = 492
Triclinic, P1	Dx = 1.827 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 8.0818 (16) Å	Cell parameters from 8707 reflections
b = 11.129 (2) Å	θ = 3.1–27.5°
c = 11.626 (2) Å	µ = 1.38 mm^−1
α = 67.56 (3)°	T = 292 K
β = 74.48 (3)°	Block, colorless
γ = 69.55 (3)°	0.39 × 0.33 × 0.28 mm
V = 894.6 (4) Å^3

Data collection

Rigaku R-AXIS RAPID diffractometer	4000 independent reflections
Radiation source: rotor-target	3457 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.035
Detector resolution: 10.0 pixels mm^-1	θmax = 27.5°, θmin = 3.1°
ω scan	h = −10→10
Absorption correction: multi-scan (ABSCOR; Higashi, 1995)	k = −14→14
Tmin = 0.528, Tmax = 0.670	l = −15→15
8707 measured reflections

Refinement

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)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.057	H atoms treated by a mixture of independent and constrained refinement
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0254P)^2] where P = (Fo^2 + 2Fc^2)/3
4000 reflections	(Δ/σ)max = 0.001
280 parameters	Δρmax = 0.60 e Å^−3
14 restraints	Δρmin = −0.44 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.6112 (3)	0.7708 (3)	0.3402 (2)	0.0287 (6)
C2	0.6446 (3)	0.8138 (2)	0.1983 (2)	0.0269 (5)
C3	0.6193 (4)	0.7425 (3)	0.1327 (3)	0.0399 (7)
H3	0.5766	0.6670	0.1756	0.048*
C4	0.6582 (4)	0.7848 (3)	0.0029 (3)	0.0464 (8)
H4	0.6413	0.7384	−0.0428	0.056*
C5	0.7223 (4)	0.8967 (3)	−0.0582 (3)	0.0401 (7)
H5	0.7499	0.9267	−0.1456	0.048*
C6	0.7447 (4)	0.9630 (3)	0.0126 (2)	0.0350 (6)
H6	0.7894	1.0378	−0.0287	0.042*
C7	0.8131 (4)	1.2836 (3)	0.0699 (2)	0.0317 (6)
C8	0.8440 (3)	1.2933 (3)	0.1880 (2)	0.0289 (6)
C9	0.9006 (4)	1.3944 (3)	0.1940 (3)	0.0406 (7)
H9	0.9259	1.4633	0.1214	0.049*
C10	0.9186 (4)	1.3905 (3)	0.3100 (3)	0.0465 (8)
H10	0.9554	1.4579	0.3163	0.056*
C11	0.8817 (4)	1.2861 (3)	0.4179 (3)	0.0392 (7)
H11	0.8928	1.2831	0.4966	0.047*
C12	0.8283 (3)	1.1873 (2)	0.4051 (2)	0.0262 (5)
C13	0.7850 (3)	1.0672 (3)	0.5134 (2)	0.0243 (5)
N1	0.7047 (3)	0.9243 (2)	0.13962 (18)	0.0262 (5)
N2	0.8097 (3)	1.1917 (2)	0.29297 (18)	0.0236 (4)
O1	0.7636 (2)	1.18133 (18)	0.08325 (16)	0.0329 (4)
O2	0.8395 (3)	1.3754 (2)	−0.03180 (17)	0.0435 (5)
O3	0.5622 (3)	0.66632 (19)	0.39969 (17)	0.0456 (5)
O4	0.6382 (2)	0.84340 (17)	0.39065 (15)	0.0303 (4)
O5	0.7351 (2)	0.98725 (16)	0.48387 (15)	0.0263 (4)
O6	0.8019 (2)	1.05038 (19)	0.62137 (16)	0.0342 (4)
O1W	1.0025 (2)	0.91200 (19)	0.25742 (18)	0.0299 (4)
O2W	0.4499 (2)	1.13989 (19)	0.29456 (18)	0.0322 (4)
O3W	0.0761 (3)	0.6636 (2)	0.2627 (2)	0.0510 (6)
O5W	0.4143 (4)	0.4041 (2)	0.1825 (2)	0.0605 (6)
In1	0.72576 (2)	1.024842 (16)	0.275845 (15)	0.02134 (6)
O4W	0.3866 (4)	0.5110 (2)	0.3684 (2)	0.0561 (6)
HW11	1.034 (4)	0.828 (2)	0.265 (3)	0.063 (11)*
HW12	1.069 (4)	0.911 (3)	0.305 (2)	0.048 (9)*
HW21	0.418 (4)	1.2262 (18)	0.275 (3)	0.054 (10)*
HW22	0.393 (5)	1.105 (3)	0.367 (2)	0.098 (15)*
HW31	0.170 (4)	0.614 (4)	0.302 (5)	0.147*
HW32	0.114 (6)	0.667 (5)	0.181 (2)	0.100 (16)*
HW51	0.402 (7)	0.438 (5)	0.243 (3)	0.150*
HW52	0.355 (7)	0.472 (4)	0.122 (3)	0.150*
HW41	0.385 (7)	0.448 (4)	0.443 (3)	0.150*
HW42	0.443 (5)	0.565 (3)	0.377 (3)	0.078 (12)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0390 (14)	0.0255 (13)	0.0249 (13)	−0.0132 (12)	−0.0075 (11)	−0.0061 (11)
C2	0.0356 (13)	0.0233 (13)	0.0242 (13)	−0.0111 (11)	−0.0088 (10)	−0.0046 (10)
C3	0.0622 (19)	0.0364 (16)	0.0285 (14)	−0.0246 (15)	−0.0082 (13)	−0.0076 (12)
C4	0.067 (2)	0.0523 (19)	0.0356 (16)	−0.0266 (17)	−0.0095 (15)	−0.0201 (14)
C5	0.0486 (16)	0.0503 (18)	0.0248 (14)	−0.0187 (15)	−0.0036 (12)	−0.0125 (13)
C6	0.0414 (15)	0.0365 (15)	0.0267 (14)	−0.0199 (13)	0.0002 (11)	−0.0052 (12)
C7	0.0376 (14)	0.0291 (14)	0.0265 (14)	−0.0123 (12)	−0.0035 (11)	−0.0053 (11)
C8	0.0356 (13)	0.0246 (13)	0.0246 (13)	−0.0121 (12)	−0.0019 (11)	−0.0043 (10)
C9	0.0593 (18)	0.0327 (15)	0.0339 (15)	−0.0259 (15)	−0.0026 (13)	−0.0064 (12)
C10	0.069 (2)	0.0397 (17)	0.0457 (18)	−0.0350 (17)	−0.0081 (15)	−0.0121 (14)
C11	0.0560 (17)	0.0378 (16)	0.0363 (16)	−0.0251 (15)	−0.0075 (13)	−0.0140 (13)
C12	0.0306 (12)	0.0257 (13)	0.0248 (13)	−0.0113 (11)	−0.0050 (10)	−0.0073 (10)
C13	0.0215 (11)	0.0313 (14)	0.0215 (12)	−0.0102 (11)	−0.0011 (9)	−0.0086 (10)
N1	0.0321 (11)	0.0257 (11)	0.0236 (11)	−0.0124 (10)	−0.0049 (9)	−0.0064 (9)
N2	0.0277 (10)	0.0237 (11)	0.0210 (10)	−0.0103 (9)	−0.0031 (8)	−0.0064 (8)
O1	0.0493 (11)	0.0308 (10)	0.0239 (9)	−0.0201 (9)	−0.0060 (8)	−0.0062 (8)
O2	0.0696 (13)	0.0351 (11)	0.0244 (10)	−0.0259 (11)	−0.0093 (9)	0.0036 (8)
O3	0.0849 (15)	0.0373 (11)	0.0265 (10)	−0.0420 (12)	−0.0117 (10)	0.0016 (8)
O4	0.0452 (10)	0.0317 (10)	0.0211 (9)	−0.0220 (9)	−0.0039 (8)	−0.0065 (7)
O5	0.0354 (9)	0.0281 (9)	0.0205 (8)	−0.0177 (8)	−0.0036 (7)	−0.0055 (7)
O6	0.0444 (11)	0.0465 (12)	0.0223 (9)	−0.0251 (10)	−0.0079 (8)	−0.0091 (8)
O1W	0.0302 (9)	0.0310 (11)	0.0349 (11)	−0.0073 (9)	−0.0099 (8)	−0.0152 (9)
O2W	0.0306 (9)	0.0277 (10)	0.0328 (11)	−0.0091 (9)	−0.0020 (8)	−0.0047 (8)
O3W	0.0631 (14)	0.0438 (13)	0.0521 (15)	−0.0093 (11)	−0.0131 (12)	−0.0238 (11)
O5W	0.0793 (17)	0.0348 (13)	0.0609 (16)	−0.0026 (12)	−0.0187 (14)	−0.0149 (11)
In1	0.02779 (10)	0.02061 (10)	0.01840 (9)	−0.01152 (7)	−0.00376 (6)	−0.00473 (6)
O4W	0.0901 (17)	0.0515 (14)	0.0413 (13)	−0.0393 (14)	−0.0316 (12)	0.0019 (10)

Geometric parameters (Å, º)

C1—O3	1.245 (3)	C11—H11	0.9300
C1—O4	1.264 (3)	C12—N2	1.333 (3)
C1—C2	1.507 (3)	C12—C13	1.516 (3)
C2—N1	1.346 (3)	C13—O6	1.235 (3)
C2—C3	1.382 (4)	C13—O5	1.276 (3)
C3—C4	1.381 (4)	N1—In1	2.328 (2)
C3—H3	0.9300	N2—In1	2.277 (2)
C4—C5	1.379 (4)	O1—In1	2.2734 (19)
C4—H4	0.9300	O4—In1	2.1897 (17)
C5—C6	1.376 (4)	O5—In1	2.3093 (17)
C5—H5	0.9300	O1W—In1	2.147 (2)
C6—N1	1.351 (3)	O1W—HW11	0.855 (18)
C6—H6	0.9300	O1W—HW12	0.863 (18)
C7—O2	1.258 (3)	O2W—In1	2.1484 (19)
C7—O1	1.277 (3)	O2W—HW21	0.855 (17)
C7—C8	1.508 (4)	O2W—HW22	0.858 (18)
C8—N2	1.352 (3)	O3W—HW31	0.89 (4)
C8—C9	1.384 (4)	O3W—HW32	0.903 (19)
C9—C10	1.378 (4)	O5W—HW51	0.89 (5)
C9—H9	0.9300	O5W—HW52	0.90 (4)
C10—C11	1.393 (4)	O4W—HW41	0.882 (19)
C10—H10	0.9300	O4W—HW42	0.92 (4)
C11—C12	1.382 (3)
O3—C1—O4	124.4 (2)	C2—N1—C6	117.9 (2)
O3—C1—C2	118.6 (2)	C2—N1—In1	113.87 (15)
O4—C1—C2	117.0 (2)	C6—N1—In1	128.28 (16)
N1—C2—C3	122.2 (2)	C12—N2—C8	120.6 (2)
N1—C2—C1	115.7 (2)	C12—N2—In1	120.08 (15)
C3—C2—C1	122.2 (2)	C8—N2—In1	119.28 (16)
C4—C3—C2	119.2 (2)	C7—O1—In1	120.85 (16)
C4—C3—H3	120.4	C1—O4—In1	121.10 (15)
C2—C3—H3	120.4	C13—O5—In1	120.29 (14)
C5—C4—C3	119.2 (3)	In1—O1W—HW11	121.2 (19)
C5—C4—H4	120.4	In1—O1W—HW12	119 (2)
C3—C4—H4	120.4	HW11—O1W—HW12	100 (3)
C6—C5—C4	118.7 (3)	In1—O2W—HW21	122 (2)
C6—C5—H5	120.6	In1—O2W—HW22	111 (3)
C4—C5—H5	120.6	HW21—O2W—HW22	110 (3)
N1—C6—C5	122.9 (2)	HW31—O3W—HW32	106 (5)
N1—C6—H6	118.6	HW51—O5W—HW52	106 (3)
C5—C6—H6	118.6	O1W—In1—O2W	179.22 (7)
O2—C7—O1	126.2 (3)	O1W—In1—O4	92.87 (8)
O2—C7—C8	117.6 (2)	O2W—In1—O4	87.73 (8)
O1—C7—C8	116.2 (2)	O1W—In1—O1	92.62 (8)
N2—C8—C9	121.0 (2)	O2W—In1—O1	87.13 (8)
N2—C8—C7	113.5 (2)	O4—In1—O1	147.99 (7)
C9—C8—C7	125.5 (2)	O1W—In1—N2	88.48 (7)
C10—C9—C8	118.4 (2)	O2W—In1—N2	90.74 (8)
C10—C9—H9	120.8	O4—In1—N2	141.55 (7)
C8—C9—H9	120.8	O1—In1—N2	70.10 (7)
C9—C10—C11	120.2 (2)	O1W—In1—O5	88.45 (8)
C9—C10—H10	119.9	O2W—In1—O5	91.26 (8)
C11—C10—H10	119.9	O4—In1—O5	72.02 (6)
C12—C11—C10	118.4 (3)	O1—In1—O5	139.66 (6)
C12—C11—H11	120.8	N2—In1—O5	69.61 (7)
C10—C11—H11	120.8	O1W—In1—N1	84.52 (7)
N2—C12—C11	121.3 (2)	O2W—In1—N1	96.14 (8)
N2—C12—C13	114.2 (2)	O4—In1—N1	72.27 (7)
C11—C12—C13	124.5 (2)	O1—In1—N1	76.91 (7)
O6—C13—O5	124.2 (2)	N2—In1—N1	145.90 (7)
O6—C13—C12	120.1 (2)	O5—In1—N1	143.15 (6)
O5—C13—C12	115.7 (2)	HW41—O4W—HW42	103 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1W—HW12···O6^i	0.86 (2)	1.76 (2)	2.601 (2)	166 (3)
O1W—HW11···O3W^ii	0.86 (2)	1.75 (2)	2.596 (3)	171 (3)
O2W—HW22···O5^iii	0.86 (2)	1.89 (2)	2.740 (3)	173 (4)
O2W—HW21···O5W^iv	0.86 (2)	1.85 (2)	2.667 (3)	159 (3)
O3W—HW32···O2^v	0.90 (2)	1.88 (2)	2.750 (3)	160 (4)
O3W—HW31···O4W	0.89 (4)	1.90 (2)	2.788 (4)	174 (5)
O4W—HW42···O3	0.92 (4)	1.84 (4)	2.758 (3)	177 (3)
O4W—HW41···O3^vi	0.88 (2)	1.85 (3)	2.701 (3)	162 (4)
O5W—HW52···O2^v	0.90 (4)	2.03 (3)	2.902 (3)	162 (5)
O5W—HW51···O4W	0.89 (5)	1.88 (4)	2.766 (4)	177 (5)

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