New iron(III) nitrate hydrates: Fe(NO₃)₃·xH₂O with x = 4, 5 and 6

Crystals of the title compounds were grown from their hydrous melts or solutions. The crystal structure of iron(III) trinitrate hexa­hydrate {hexa­aqua­iron(III) trinitrate, [Fe(H₂O)₆](NO₃)₃} is built up from [Fe(H₂O)₆]²⁺ octa­hedra and nitrate anions connected via hydrogen bonds. In iron(III) trinitrate penta­hydrate {penta­aqua­nitratoiron(III) dinitrate, [Fe(NO₃)(H₂O)₅](NO₃)₂}, one water mol­ecule in the coordination octa­hedron of the Fe^III atom is substituted by an O atom of a nitrate group. Iron(III) trinitrate tetra­hydrate {triaqua­dinitratoiron(III) nitrate monohydrate, [Fe(NO₃)₂(H₂O)₃]NO₃·H₂O} represents the first example of a simple iron(III) nitrate with penta­gonal-bipyramidal coordination geometry, where two bidentate nitrate anions and one water mol­ecule form a penta­gonal plane.

S1. Comment

From aqueous solutions of iron(III) nitrate crystallizes the nonahydrate Fe(NO₃)₃·9H₂O. Its crystal structure was reported by Hair & Beattie (1977). Because of the strong hygroscopicity and the tendency of iron(III) nitrate to hydrolyze and precipitate basic salts, neutral hydrates containing less than 9 mol water per mol salt do not crystallize from simple aqueous solutions. To prevent hydrolysis lower hydrates can be crystallized only in the presence of high concentrations of nitric acid. Reports on the existence and stability of lower hydrates are contradictory. According to Cameron & Robinson (1909) the hexahydrate crystallizes from a solution of nonahydrate in nitric acid. Malquori (1929a,b) proposed addition of N₂O₅. Hathaway & Underhill (1960) declared to have synthesized a dihydrate by means of a reaction of anhydrous iron(III) chloride in pure nitric acid. Rodenko & Panov (1994) performed solubility determinations at temperatures in the range 283–313 K in the system Fe(NO₃)₃–HNO₃–H₂O. Graphically presented solubility isotherms were interpreted as branches from hexa- and tetrahydrate at nitric acid concentrations of 56–77% HNO₃ and 77–85% HNO₃, respectively. El Goundali & Kaddami (2006, 2007, 2008) claimed the formation of an iron(III) nitrate hexahydrate within the system Fe(NO₃)₃–Co(NO₃)₂–HNO₃ at 303 K. Addison (1980) and Addison & Chapman (1965) thoroughly investigated reactions of liquid N₂O₄ with hydrated nitrates and metals. Addison stated that iron(III) nitrate nonahydrate reacted with N₂O₄ to yield a yellow–brown pentahydrate (Addison & Chapman, 1965). The same authors supposed that the reaction product of metallic iron with an N₂O₄/HNO₃ mixture was a dihydrate after 2 weeks' evacuation. For all these phases, no X-ray pattern was recorded. The chemical formulas were derived from chemical analyses of the wet solid residues.

Crystals of the title compounds were grown from their hydrous melts or solutions in highly concentrated nitric acid. Iron(III) nitrate pentahydrate, (II), was prepared through the reaction of liquid N₂O₄ with iron(III) nitrate nonahydrate. The hexa-, (I), and tetrahydrate, (III), were obtained by dissolving the pentahydrate in highly concentrated nitric acid and subsequent evaporation at reduced pressure. With the successful preparation of single crystals and their structure determination in this work, the existence and stoichiometry of at least three lower hydrates could [can] be confirmed unequivocally.

As expected, the crystal structure of the hexahydrate consists of Fe(H₂O)₆ octahedra (see Fig. 1a). The Fe(H₂O)₆ octahedra are connected via hydrogen bonds to nitrate ions, where every H atom of a water molecule is in contact with another nitrate group at distances of 1.89 Å, thus arranging 12 NO₃^- anions around an octahedron unit (Fig. 1b). The result is a complex but highly symmetric hydrogen-bond network, as shown in Fig. 2.

With a further decrease of the water content, nitrate ions enter the coordination sphere of iron. In Fe(NO₃)₃·5H₂O, the Fe^III atom is still coordinated by six ligands (see Fig. 3) completing the coordination sphere with a monodentate bound nitrate ligand. One of the other O atoms of the coordinated nitrate ion forms a hydrogen bond to a water molecule of an adjacent octahedron unit (Fig. 4). This yields two NO₃^- octahedral chains approximately in the [110] direction (Fig. 4). These chains are connected by the noncoordinated nitrate ions via hydrogen bonds, as shown in Fig. 5. Thereby two O atoms (O10, O11, O12 and O13) are connected with an edge of an octahedron and the third O atom (O9 and O14)e/newcifs combines to different chains. The result is a three-dimensional network (Fig. 6).

Surprisingly, in Fe(NO₃)₃·4H₂O, the coordination number of iron(III) is enhanced to seven in the form of a pentagonal bipyramid (Fig. 7). Two bidentate coordinating nitrate ions and one water molecule (O2) are arranged nearly exactly in a pentagonal plane. The other two coordinated water molecules in axial positions are nearly perpendicular to this plane. The noncoordinated water molecule is hydrogen bonded to an axial water molecule of one complex and to the equatorial water of another complex, thus forming binary complex units with the equatorial water molecules directed to each other (Fig. 8). These double units are interconnected via hydrogen bonds by the noncoordinated nitrate ions. As illustrated in Fig. 9, every water molecule of the complex unit is connected to a nitrate ion. Thereby one O atom of the nitrate (O12) ion connects two complex units through their axial water molecules approximately in the direction of the b axis. The second O atom (O11) is connected with the equatorial water molecule of the complex. Altogether, a hydrogen-bond network arises with dominating bonds along the b and a axes, as shown in Fig. 10. The third O atom of the nitrate ions is not involved in hydrogen bonds, because its bond distance to the nearest H atom is greater than 2.3 Å.

There are examples in the literature of salts with tetranitratoferrate anions, [Fe(NO₃)₄]^-, where the nitrate groups coordinate in a bidentate fashion, resulting in a coordination number of eight for Fe^III (Addison & Chapman, 1965; Tikhomirov et al., 2002; Blackwell et al., 1975; Fedorova et al., 2002). However, the pentagonal–bipyramidal coordination of Fe^III has only been observed before for metal–organic Fe^III complexes (Andjelkovica et al., 2002; Bonardi et al., 1991). The reported structure for the iron(III) nitrate tetrahydrate represents the first simple iron(III) salt with such a coordination geometry.

Related literature

For related literature, see: Addison & Chapman (1965); Blackwell et al. (1975); Bonardi et al. (1991); Cameron & Robinson (1909); El Goundali & Kaddami (2006); Fedorova et al. (2002); Hair & Beattie (1977); Hathaway & Underhill (1960); Malquori (1929a,b); Rodenko & Panov (1994); Tikhomirov et al. (2002).

S2. Experimental

Iron(III) nitrate hexahydrate, (I), was prepared by recrystallizing Fe(NO₃)₃·5H₂O (2 g) in pure nitric acid (1 ml of 96.2% HNO₃) and concentrating the liquid by evaporation at reduced pressure. Colourless cubic crystals of 2–4 mm size were obtained after 14 d. The selected crystal was cut and embedded in perfluorinated ether for single-crystal diffraction experiments.

Iron(III) nitrate pentahydrate, (II), was prepared according to the method of Addison & Chapman (1965). Fe(NO₃)₃·9H₂O (10 g) reacted under vigorous stirring in an excess of liquid N₂O₄ (30 ml) for 3–5 d at room temperature to form a pale-yellow powder of the pentahydrate. To gain bigger crystals the N₂O₄ was removed under vacuum and the remaining mixture was recrystallized in sealed glass tubes by warming up and subsequent cooling to room temperature. A piece of the 1 mm-sized crystal was cut and embedded in perfluorether to prevent contact with the air humidity before being mounted on the single-crystal diffractometer.

Iron(III) nitrate tetrahydrate, (III), was prepared using a method analogous to that used for the hexahydrate using Fe(NO₃)₃·5H₂O (2 g) in pure nitric acid (1 ml of 96.2% HNO₃). Brown, needle-shaped crystals with a size of approximately 5 × 0.2 mm were obtained after 14 d. One piece of a crystal was cut and embedded in perfluorether before being mounted on the single-crystal diffractometer.

S3. Refinement

All water H atoms were initially located in difference Fourier maps and then their positions were refined with O—H and H···H distance restraints of 0.820 (5) and 1.30 (2) Å.

Computing details

For all compounds, data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: APEX2 (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. (a) The asymmetric unit and symmetry-related atoms of Fe(NO3)3·6H2O. Displacement ellipsoids are drawn at the 50% probability level and H atoms are not labelled. [Symmetry codes: (i) -y + 1, -z + 1, -x + 1; (ii) -z + 1, -x + 1, -y + 1; (iii) y, z, x; (iv) z, x, y; (v) -x + 1, -y + 1, -z + 1; (vi) x, -y + 1, -z + 1/2.] (b) The [Fe(H2O)6]3^+ octahedron with hydrogen bonds to NO3^- in iron(III) nitrate hexahydrate (black, dashed).
	Fig. 2. 2 × 2 × 2 unit cells of Fe(NO3)3·6H2O, viewed in the a-axis direction.
	Fig. 3. The asymmetric unit and symmetry-related atoms of Fe(NO3)3·5H2O. Displacement ellipsoids are drawn at the 50% probability level and H atoms are not labelled.
	Fig. 4. Chain structure in Fe(NO3)3·5H2O based on hydrogen bonds of the monodentate coordinating NO3^-.
	Fig. 5. Noncoordinated nitrate groups connecting chains via hydrogen bonds in Fe(NO3)3·5H2O. Atoms O10/O11 and O12/O13 are bound to water molecules of a ledge of an octahedron, and O9 and O14 join different chains at the corner.
	Fig. 6. Three-dimensional hydrogen-bond network in Fe(NO3)3·5H2O.
	Fig. 7. The asymmetric unit and symmetry-related atoms of Fe(NO3)3·4H2O. Displacement ellipsoids are drawn at the 50% probability level and H atoms are not labelled.
	Fig. 8. Noncoordinated water molecules in Fe(NO3)3·4H2O connecting two pentagonal–bipyramidal [Fe(NO3)2(H2O)3]^+ complexes via hydrogen bonds.
	Fig. 9. Interconnection of the structure units of Fe(NO3)3·4H2O illustrated in Fig. 8 by noncoordinated nitrate ions.
	Fig. 10. Hydrogen-bond network in Fe(NO3)3·4H2O, with dominating bonds along the b axis. For clarity, only the Fe—OH2 bonds (green thick lines) of the complex units are shown.

(I) hexaaquairon(III) trinitrate

Crystal data

[Fe(H2O)6](NO3)3	Melting point: 317.68 K
Mr = 349.98	Mo Kα radiation, λ = 0.71073 Å
Cubic, Ia3	Cell parameters from 692 reflections
Hall symbol: -I 2b 2c 3	θ = 1.8–27.5°
a = 13.7962 (2) Å	µ = 1.23 mm^−1
V = 2625.90 (7) Å^3	T = 190 K
Z = 8	Cuboid, colourless
F(000) = 1432	0.43 × 0.35 × 0.29 mm
Dx = 1.771 Mg m^−3

Data collection

Bruker X8 Kappa APEXII diffractometer	505 independent reflections
Radiation source: fine-focus sealed tube	432 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
ω and ϕ scans	θmax = 27.4°, θmin = 3.0°
Absorption correction: numerical (APEX2; Bruker, 2005)	h = −17→17
Tmin = 0.623, Tmax = 0.715	k = −17→17
9913 measured reflections	l = −17→17

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) = 0.081	All H-atom parameters refined
S = 1.09	w = 1/[σ^2(Fo^2) + (0.042P)^2 + 3.9345P] where P = (Fo^2 + 2Fc^2)/3
505 reflections	(Δ/σ)max < 0.001
39 parameters	Δρmax = 0.58 e Å^−3
3 restraints	Δρmin = −0.38 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
Fe1	0.5000	0.5000	0.5000	0.0153 (2)
N1	0.71342 (19)	0.5000	0.2500	0.0328 (6)
O1	0.62559 (9)	0.56088 (9)	0.46368 (9)	0.0219 (3)
O2	0.62608 (19)	0.5000	0.2500	0.0756 (11)
O3	0.75797 (11)	0.51865 (15)	0.32635 (12)	0.0472 (5)
H1	0.6352 (19)	0.6180 (6)	0.4750 (18)	0.050 (8)*
H2	0.6602 (16)	0.5431 (18)	0.4193 (14)	0.055 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.0153 (2)	0.0153 (2)	0.0153 (2)	−0.00036 (11)	−0.00036 (11)	−0.00036 (11)
N1	0.0236 (13)	0.0520 (16)	0.0228 (12)	0.000	0.000	−0.0045 (10)
O1	0.0201 (6)	0.0200 (6)	0.0256 (7)	−0.0039 (5)	0.0063 (5)	−0.0039 (5)
O2	0.0237 (12)	0.167 (4)	0.0363 (14)	0.000	0.000	−0.0196 (17)
O3	0.0278 (8)	0.0827 (14)	0.0311 (9)	0.0146 (7)	−0.0091 (6)	−0.0213 (8)

Geometric parameters (Å, º)

Fe1—O1^i	1.9896 (12)	Fe1—O1^v	1.9896 (12)
Fe1—O1	1.9896 (12)	N1—O2	1.205 (4)
Fe1—O1^ii	1.9896 (12)	N1—O3	1.246 (2)
Fe1—O1^iii	1.9896 (12)	N1—O3^vi	1.246 (2)
Fe1—O1^iv	1.9896 (12)
O1^i—Fe1—O1	87.60 (5)	O1^iii—Fe1—O1^iv	180.00 (6)
O1^i—Fe1—O1^ii	180.0	O1^i—Fe1—O1^v	92.40 (5)
O1—Fe1—O1^ii	92.40 (5)	O1—Fe1—O1^v	180.00 (6)
O1^i—Fe1—O1^iii	87.60 (5)	O1^ii—Fe1—O1^v	87.60 (5)
O1—Fe1—O1^iii	87.60 (5)	O1^iii—Fe1—O1^v	92.40 (5)
O1^ii—Fe1—O1^iii	92.40 (5)	O1^iv—Fe1—O1^v	87.60 (5)
O1^i—Fe1—O1^iv	92.40 (5)	O2—N1—O3	119.55 (13)
O1—Fe1—O1^iv	92.40 (5)	O2—N1—O3^vi	119.55 (13)
O1^ii—Fe1—O1^iv	87.60 (5)	O3—N1—O3^vi	120.9 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H2···O3	0.82 (1)	1.89 (1)	2.695 (2)	169 (3)
O1—H1···O3^vii	0.82 (1)	1.89 (1)	2.6946 (19)	169 (3)

Symmetry code: (vii) −z+1, −x+3/2, y.

(II) pentaaquanitratoiron dinitrate

Crystal data

[Fe(NO3)(H2O)5](NO3)2	Z = 2
Mr = 331.96	F(000) = 338
Triclinic, P1	Dx = 2.125 Mg m^−3
Hall symbol: -P 1	Melting point: 321.34 K
a = 6.7693 (4) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.0692 (4) Å	Cell parameters from 756 reflections
c = 11.6734 (6) Å	θ = 1.8–27.5°
α = 85.568 (2)°	µ = 1.55 mm^−1
β = 80.655 (1)°	T = 100 K
γ = 70.279 (2)°	Parallelepiped, yellow
V = 518.72 (5) Å^3	0.47 × 0.35 × 0.23 mm

Data collection

Bruker X8 Kappa APEXII diffractometer	2373 independent reflections
Radiation source: fine-focus sealed tube	2293 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.017
ω and ϕ scans	θmax = 27.5°, θmin = 1.8°
Absorption correction: multi-scan (SADABS; Bruker, 2006)	h = −8→8
Tmin = 0.528, Tmax = 0.716	k = −9→9
9108 measured reflections	l = −15→15

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)] = 0.019	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.059	All H-atom parameters refined
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0403P)^2 + 0.2256P] where P = (Fo^2 + 2Fc^2)/3
2373 reflections	(Δ/σ)max = 0.001
203 parameters	Δρmax = 0.46 e Å^−3
14 restraints	Δρmin = −0.30 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. Short inter D···A contact of 2.82 Angstroem for O7 and O9: Nitrate oxygen atoms O7 and O9 are not directly connected via hydrogen bond, but via water hydrogen atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Fe1	0.27910 (3)	0.72465 (2)	0.252494 (14)	0.00802 (7)
N1	0.64486 (17)	0.34386 (16)	0.22605 (9)	0.0095 (2)
N2	0.21421 (17)	0.28547 (16)	0.03571 (9)	0.0110 (2)
N3	0.26584 (18)	0.22095 (16)	0.46374 (9)	0.0104 (2)
O1	0.21908 (16)	0.79284 (14)	0.08948 (8)	0.01410 (19)
O2	0.06635 (16)	0.58186 (15)	0.28405 (9)	0.0159 (2)
O3	0.04208 (15)	0.97229 (13)	0.30303 (8)	0.01167 (18)
O4	0.50110 (15)	0.85616 (14)	0.22573 (8)	0.01217 (19)
O5	0.33240 (15)	0.69201 (15)	0.41828 (8)	0.01303 (19)
O6	0.46892 (14)	0.45797 (13)	0.19217 (8)	0.01159 (18)
O7	0.71829 (15)	0.39903 (14)	0.30153 (8)	0.01362 (19)
O8	0.73077 (15)	0.17968 (14)	0.17749 (8)	0.01314 (19)
O9	0.28024 (15)	0.31797 (15)	0.54734 (8)	0.0148 (2)
O10	0.08770 (15)	0.21098 (15)	0.45452 (8)	0.0151 (2)
O11	0.42580 (16)	0.14084 (15)	0.39382 (8)	0.0147 (2)
O12	0.23681 (16)	0.44044 (14)	−0.01346 (8)	0.0150 (2)
O13	0.14044 (16)	0.27776 (14)	0.14008 (8)	0.0151 (2)
O14	0.26678 (16)	0.12656 (14)	−0.02350 (8)	0.0154 (2)
H1	−0.0471 (18)	0.615 (3)	0.3272 (15)	0.030 (5)*
H2	0.070 (3)	0.497 (3)	0.2443 (17)	0.033 (6)*
H3	0.240 (3)	0.8862 (19)	0.0494 (14)	0.028 (5)*
H4	0.230 (4)	0.704 (2)	0.0456 (14)	0.037 (6)*
H5	−0.037 (2)	1.038 (2)	0.2578 (13)	0.025 (5)*
H6	0.055 (4)	1.052 (3)	0.3462 (15)	0.042 (6)*
H7	0.579 (3)	0.858 (3)	0.1647 (10)	0.030 (5)*
H8	0.487 (3)	0.9567 (19)	0.2603 (15)	0.031 (5)*
H9	0.4433 (17)	0.688 (3)	0.4387 (16)	0.032 (5)*
H10	0.248 (3)	0.674 (3)	0.4724 (12)	0.033 (6)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.00843 (11)	0.00710 (11)	0.00873 (11)	−0.00283 (8)	−0.00120 (7)	−0.00029 (7)
N1	0.0088 (5)	0.0093 (5)	0.0101 (5)	−0.0032 (4)	0.0000 (4)	−0.0005 (4)
N2	0.0100 (5)	0.0113 (5)	0.0122 (5)	−0.0040 (4)	−0.0017 (4)	−0.0011 (4)
N3	0.0134 (5)	0.0086 (5)	0.0096 (5)	−0.0040 (4)	−0.0018 (4)	0.0003 (4)
O1	0.0216 (5)	0.0107 (4)	0.0107 (4)	−0.0053 (4)	−0.0046 (4)	−0.0002 (3)
O2	0.0139 (5)	0.0143 (5)	0.0208 (5)	−0.0084 (4)	0.0056 (4)	−0.0080 (4)
O3	0.0129 (4)	0.0095 (4)	0.0115 (4)	−0.0010 (3)	−0.0041 (3)	−0.0013 (3)
O4	0.0150 (5)	0.0126 (4)	0.0108 (4)	−0.0083 (4)	0.0019 (4)	−0.0031 (3)
O5	0.0099 (4)	0.0184 (5)	0.0100 (4)	−0.0042 (4)	−0.0006 (3)	0.0014 (4)
O6	0.0093 (4)	0.0100 (4)	0.0142 (4)	−0.0005 (3)	−0.0034 (3)	−0.0015 (3)
O7	0.0134 (5)	0.0143 (4)	0.0145 (5)	−0.0045 (4)	−0.0041 (4)	−0.0048 (4)
O8	0.0131 (4)	0.0093 (4)	0.0152 (5)	−0.0004 (3)	−0.0022 (4)	−0.0048 (3)
O9	0.0151 (5)	0.0190 (5)	0.0118 (4)	−0.0067 (4)	−0.0006 (4)	−0.0074 (4)
O10	0.0124 (4)	0.0185 (5)	0.0158 (5)	−0.0060 (4)	−0.0018 (4)	−0.0052 (4)
O11	0.0150 (5)	0.0164 (5)	0.0121 (4)	−0.0061 (4)	0.0037 (4)	−0.0051 (4)
O12	0.0208 (5)	0.0118 (4)	0.0142 (5)	−0.0087 (4)	−0.0015 (4)	0.0014 (3)
O13	0.0200 (5)	0.0161 (5)	0.0103 (4)	−0.0091 (4)	0.0028 (4)	−0.0024 (4)
O14	0.0224 (5)	0.0116 (4)	0.0126 (5)	−0.0077 (4)	0.0028 (4)	−0.0041 (3)

Geometric parameters (Å, º)

Fe1—O3	1.9859 (9)	N1—O6	1.2965 (14)
Fe1—O4	1.9914 (9)	N2—O12	1.2411 (14)
Fe1—O6	1.9944 (9)	N2—O13	1.2439 (14)
Fe1—O2	1.9950 (9)	N2—O14	1.2793 (14)
Fe1—O1	1.9989 (9)	N3—O11	1.2369 (14)
Fe1—O5	2.0076 (9)	N3—O10	1.2536 (14)
N1—O7	1.2255 (14)	N3—O9	1.2695 (14)
N1—O8	1.2432 (14)
O3—Fe1—O4	95.20 (4)	O2—Fe1—O5	92.48 (4)
O3—Fe1—O6	167.88 (4)	O1—Fe1—O5	173.03 (4)
O4—Fe1—O6	95.73 (4)	O7—N1—O8	123.45 (11)
O3—Fe1—O2	86.72 (4)	O7—N1—O6	120.51 (10)
O4—Fe1—O2	177.06 (4)	O8—N1—O6	116.04 (10)
O6—Fe1—O2	82.57 (4)	O12—N2—O13	122.98 (11)
O3—Fe1—O1	88.65 (4)	O12—N2—O14	118.80 (10)
O4—Fe1—O1	90.62 (4)	O13—N2—O14	118.21 (10)
O6—Fe1—O1	86.01 (4)	O11—N3—O10	122.07 (10)
O2—Fe1—O1	91.66 (4)	O11—N3—O9	119.57 (11)
O3—Fe1—O5	85.99 (4)	O10—N3—O9	118.37 (10)
O4—Fe1—O5	85.44 (4)	N1—O6—Fe1	128.16 (8)
O6—Fe1—O5	100.08 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1···O9^i	0.82 (1)	1.93 (1)	2.7339 (14)	169 (2)
O2—H2···O13	0.78 (2)	1.93 (2)	2.6933 (14)	169 (2)
O1—H3···O14^ii	0.82 (1)	1.89 (1)	2.7027 (13)	171 (2)
O1—H4···O12	0.82 (1)	2.02 (1)	2.8069 (13)	161 (2)
O3—H5···O8^iii	0.82 (1)	1.90 (1)	2.7062 (13)	168 (2)
O3—H5···N1^iii	0.82 (1)	2.54 (1)	3.2543 (14)	147 (2)
O3—H5···O7^iii	0.82 (1)	2.57 (2)	3.0736 (13)	121 (2)
O3—H6···O10^ii	0.82 (1)	1.84 (1)	2.6571 (13)	174 (2)
O4—H7···O14^iv	0.82 (1)	1.82 (1)	2.6338 (13)	175 (2)
O4—H8···O11^ii	0.82 (1)	2.01 (1)	2.7844 (13)	159 (2)
O5—H9···O9^v	0.82 (1)	1.89 (1)	2.6934 (14)	168 (2)
O5—H10···O10^i	0.82 (1)	2.19 (1)	2.8691 (13)	142 (2)
O5—H10···O9	0.82 (1)	2.55 (2)	3.0377 (14)	120 (2)

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

(III) triaquadinitratoiron(III) nitrate monohydrate

Crystal data

[Fe(NO3)2(H2O)3]NO3·H2O	F(000) = 636
Mr = 313.94	Dx = 2.073 Mg m^−3
Monoclinic, P21/n	Melting point: 335.39 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71073 Å
a = 7.0696 (7) Å	Cell parameters from 1424 reflections
b = 15.1917 (16) Å	θ = 1.8–27.5°
c = 9.4264 (7) Å	µ = 1.58 mm^−1
β = 96.508 (3)°	T = 100 K
V = 1005.86 (16) Å^3	Prism, brown
Z = 4	0.5 × 0.4 × 0.3 mm

Data collection

Bruker X8 Kappa APEXII diffractometer	2303 independent reflections
Radiation source: fine-focus sealed tube	1985 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.031
ω and ϕ scans	θmax = 27.5°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Bruker, 2006)	h = −9→9
Tmin = 0.451, Tmax = 0.602	k = −19→19
11328 measured reflections	l = −12→12

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)] = 0.022	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.055	All H-atom parameters refined
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0258P)^2 + 0.2256P] where P = (Fo^2 + 2Fc^2)/3
2303 reflections	(Δ/σ)max = 0.001
186 parameters	Δρmax = 0.26 e Å^−3
12 restraints	Δρmin = −0.26 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. Short inter D···A contact of 2.82 Angstroem for O5 and O11: Nitrate oxygen atoms O5 and O11 are not directly connected via hydrogen bond, but via water hydrogen atoms.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Fe1	0.32508 (3)	0.404152 (14)	0.21984 (2)	0.01392 (7)
N1	0.01759 (19)	0.38468 (9)	0.32872 (15)	0.0208 (3)
N2	0.87740 (18)	0.61678 (9)	0.24763 (15)	0.0190 (3)
N3	0.49724 (19)	0.34257 (9)	0.01723 (14)	0.0194 (3)
O1	0.43710 (17)	0.30869 (7)	0.34377 (13)	0.0209 (2)
O2	0.49853 (16)	0.49024 (7)	0.33518 (13)	0.0200 (2)
O3	0.20267 (17)	0.49726 (8)	0.08999 (13)	0.0217 (2)
O4	0.39942 (17)	0.65649 (8)	0.39764 (13)	0.0218 (3)
O5	0.56613 (16)	0.40451 (7)	0.09934 (12)	0.0225 (3)
O6	0.33141 (15)	0.31698 (7)	0.04514 (12)	0.0208 (2)
O7	0.57804 (18)	0.31173 (8)	−0.07625 (13)	0.0295 (3)
O8	0.14734 (16)	0.44070 (8)	0.37318 (12)	0.0224 (3)
O9	0.05611 (16)	0.34221 (8)	0.21746 (12)	0.0223 (3)
O10	−0.12433 (17)	0.37336 (9)	0.38499 (15)	0.0327 (3)
O11	0.80194 (16)	0.54484 (8)	0.20639 (13)	0.0247 (3)
O12	1.04023 (15)	0.63524 (7)	0.20676 (13)	0.0228 (3)
O13	0.80185 (18)	0.66812 (9)	0.32247 (14)	0.0326 (3)
H1	0.443 (3)	0.2564 (5)	0.326 (2)	0.048 (7)*
H2	0.496 (3)	0.3181 (13)	0.4217 (11)	0.037 (6)*
H3	0.210 (3)	0.4992 (14)	0.0045 (7)	0.047 (7)*
H4	0.153 (3)	0.5409 (8)	0.1197 (19)	0.035 (6)*
H5	0.454 (3)	0.5354 (8)	0.365 (2)	0.038 (6)*
H6	0.5966 (19)	0.5046 (14)	0.303 (2)	0.054 (8)*
H7	0.452 (3)	0.6857 (13)	0.3409 (19)	0.046 (7)*
H8	0.2855 (10)	0.6669 (16)	0.382 (3)	0.069 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.01516 (12)	0.01231 (11)	0.01506 (12)	−0.00097 (8)	0.00511 (8)	−0.00068 (8)
N1	0.0182 (6)	0.0203 (7)	0.0253 (8)	0.0029 (5)	0.0087 (6)	0.0070 (6)
N2	0.0169 (6)	0.0183 (7)	0.0221 (7)	−0.0016 (5)	0.0029 (5)	0.0024 (6)
N3	0.0229 (7)	0.0176 (7)	0.0188 (7)	−0.0007 (5)	0.0069 (6)	−0.0012 (6)
O1	0.0285 (6)	0.0136 (6)	0.0195 (6)	0.0014 (5)	−0.0018 (5)	−0.0015 (5)
O2	0.0199 (6)	0.0176 (6)	0.0236 (6)	−0.0030 (5)	0.0076 (5)	−0.0070 (5)
O3	0.0277 (6)	0.0195 (6)	0.0188 (6)	0.0055 (5)	0.0068 (5)	0.0044 (5)
O4	0.0217 (6)	0.0219 (6)	0.0219 (6)	0.0024 (5)	0.0036 (5)	0.0024 (5)
O5	0.0222 (6)	0.0221 (6)	0.0247 (6)	−0.0076 (5)	0.0090 (5)	−0.0096 (5)
O6	0.0207 (6)	0.0196 (6)	0.0235 (6)	−0.0052 (5)	0.0078 (5)	−0.0041 (5)
O7	0.0350 (7)	0.0308 (7)	0.0257 (7)	−0.0019 (6)	0.0166 (5)	−0.0109 (5)
O8	0.0230 (6)	0.0206 (6)	0.0254 (6)	−0.0008 (5)	0.0107 (5)	−0.0027 (5)
O9	0.0209 (6)	0.0230 (6)	0.0237 (6)	−0.0032 (5)	0.0063 (5)	0.0001 (5)
O10	0.0228 (6)	0.0366 (7)	0.0421 (8)	0.0013 (5)	0.0188 (6)	0.0102 (6)
O11	0.0246 (6)	0.0203 (6)	0.0303 (7)	−0.0088 (5)	0.0074 (5)	−0.0039 (5)
O12	0.0167 (5)	0.0165 (6)	0.0362 (7)	−0.0025 (4)	0.0077 (5)	0.0013 (5)
O13	0.0316 (7)	0.0305 (7)	0.0381 (8)	−0.0020 (5)	0.0148 (6)	−0.0122 (6)

Geometric parameters (Å, º)

Fe1—O1	1.9711 (12)	N1—O8	1.2862 (18)
Fe1—O3	2.0019 (12)	N1—O9	1.2865 (17)
Fe1—O2	2.0233 (11)	N2—O13	1.2153 (18)
Fe1—O8	2.0949 (11)	N2—O11	1.2582 (18)
Fe1—O6	2.1176 (11)	N2—O12	1.2855 (17)
Fe1—O9	2.1194 (11)	N3—O7	1.1986 (17)
Fe1—O5	2.1524 (11)	N3—O5	1.2791 (17)
N1—O10	1.1992 (17)	N3—O6	1.2902 (17)
O1—Fe1—O3	177.43 (5)	O2—Fe1—O5	79.29 (4)
O1—Fe1—O2	88.79 (5)	O8—Fe1—O5	159.42 (4)
O3—Fe1—O2	93.75 (5)	O6—Fe1—O5	60.23 (4)
O1—Fe1—O8	91.04 (5)	O9—Fe1—O5	139.34 (4)
O3—Fe1—O8	89.03 (5)	O10—N1—O8	123.52 (14)
O2—Fe1—O8	80.35 (5)	O10—N1—O9	123.62 (15)
O1—Fe1—O6	87.61 (5)	O8—N1—O9	112.85 (12)
O3—Fe1—O6	90.70 (5)	O13—N2—O11	122.54 (13)
O2—Fe1—O6	139.22 (4)	O13—N2—O12	120.09 (13)
O8—Fe1—O6	140.31 (4)	O11—N2—O12	117.36 (13)
O1—Fe1—O9	88.81 (5)	O7—N3—O5	123.50 (14)
O3—Fe1—O9	88.97 (5)	O7—N3—O6	123.49 (14)
O2—Fe1—O9	141.35 (5)	O5—N3—O6	113.00 (12)
O8—Fe1—O9	61.14 (4)	N3—O5—Fe1	92.72 (8)
O6—Fe1—O9	79.17 (4)	N3—O6—Fe1	94.00 (8)
O1—Fe1—O5	91.47 (5)	N1—O8—Fe1	93.51 (8)
O3—Fe1—O5	89.36 (5)	N1—O9—Fe1	92.37 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O12^i	0.82 (1)	1.87 (1)	2.6858 (16)	177 (2)
O1—H2···O4^ii	0.81 (1)	1.82 (1)	2.6304 (17)	173 (2)
O3—H3···O11^iii	0.81 (1)	2.09 (1)	2.8627 (17)	158 (2)
O3—H3···O5^iii	0.81 (1)	2.44 (2)	2.9572 (16)	122 (2)
O3—H4···O12^iv	0.82 (1)	1.87 (1)	2.6852 (17)	174 (2)
O2—H5···O4	0.82 (1)	1.91 (1)	2.7036 (16)	163 (2)
O2—H6···O11	0.82 (1)	1.90 (1)	2.7117 (16)	172 (2)
O4—H7···O9^v	0.82 (1)	2.44 (2)	3.0518 (17)	133 (2)
O4—H7···O7^iii	0.82 (1)	2.48 (2)	3.0896 (17)	132 (2)
O4—H7···O13	0.82 (1)	2.51 (2)	3.0140 (17)	121 (2)
O4—H8···O12^iv	0.82 (1)	2.31 (2)	2.9587 (17)	137 (2)
O4—H8···O6^v	0.82 (1)	2.55 (2)	3.0163 (16)	118 (2)

Symmetry codes: (i) −x+3/2, y−1/2, −z+1/2; (ii) −x+1, −y+1, −z+1; (iii) −x+1, −y+1, −z; (iv) x−1, y, z; (v) −x+1/2, y+1/2, −z+1/2.