Crystal structure of hydrazine iron(III) phosphate, the first transition metal phosphate containing hydrazine

The title compound, poly[(μ₂-hydrazine)(μ₄-phosphato)iron(III)], [Fe(PO₄)(N₂H₄)]_n, was prepared under hydro­thermal conditions. Its asymmetric unit contains one Fe^III atom located on an inversion centre, one P atom located on a twofold rotation axis, and two O, one N and two H atoms located on general positions. The Fe^III atom is bound to four O atoms of symmetry-related PO₄ tetra­hedra and to two N atoms of two symmetry-related hydrazine ligands, resulting in a slightly distorted FeO₄N₂ octa­hedron. The crystal structure consists of a three-dimensional hydrazine/iron phoshate framework whereby each PO₄ tetra­hedron bridges four Fe^III atoms and each hydrazine ligand bridges two Fe^III atoms. The H atoms of the hydrazine ligands are also involved in moderate N—H⋯O hydrogen bonding with phosphate O atoms. The crystal structure is isotypic with the sulfates [Co(SO₄)(N₂H₄)] and [Mn(SO₄)(N₂H₄)].

1. Chemical context

During the last century, transition metal phosphates have been studied intensively not only for their rich crystal- and magneto-chemistry (Kabbour et al., 2012), but also for their various potential applications. For example, NH₄M^IIPO₄·H₂O phases, where M is a transition metal, are used as pigments for protective paint finishes on metals, as fire retardants in paints and plastics but may also be applied as catalysts, fertilizers and magnetic devices (Erskine et al., 1944; Bridger et al., 1962; Barros et al., 2006; Ramajo et al., 2009). More recently, it was demonstrated by Goodenough and co-workers that in electrodes the presence of PO₄ groups results in higher positive potentials (Padhi et al., 1997), leading to an intensive research on LiFePO₄, one of the most promising materials for the new generation of Li batteries (Ouvrard et al., 2013).

2. Structural commentary

The structure of the title compound, [Fe(PO₄)(N₂H₄)], is isotypic with the sulfates [Co(SO₄)(N₂H₄)] and [Mn(SO₄)(N₂H₄)] (Jia et al., 2011). The Fe^III atom is bound to four PO₄ tetra­hedra and to two N atoms of hydrazine ligands, resulting in a slightly distorted FeO₄N₂ octa­hedron (Fig. 1). The crystal structure consists of a three-dimensional network made up of Fe^III atoms which are inter­connected through neutral hydrazine (N₂H₄) ligands and phosphate (PO₄³⁻) anions (Fig. 2). If the phosphate and sulfate structures are isotypic, the presence of phosphate implies an oxidation state of +III for the transition metal compared to +II for the sulfate analogues. The replacement of sulfate for phosphate leads to a change in the coordination sphere of the metal. These differences are mainly associated with the metal–oxygen bond lengths. The average Fe^III—O bond length is 1.97 Å for [Fe(PO₄)(N₂H₄)] and the average Co^II—O bond length is 2.12 Å for [Co(SO₄)(N₂H₄)], whereas the average M—N bond lengths involving the N atom of the hydrazine ligand are similar, with values of 2.17 and 2.12 Å, respectively. As a consequence, the FeN₂O₄ octa­hedron is more distorted, appearing like an FeO₄ square additionally bound by two trans hydrazine ligands in axial positions.

Figure 1 The coordination environment of the Fe^III atom in the structure of [Fe(PO4)(N2H4)]. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) x, y, z; (ii) 0.5-x, 0.5-y; (iii) −x, y + 0.5, 0.5-z; (iv) x + 0.5, −y, 0.5-z; (v) −x, −y, −z; (vi) x + 0.5, y + 0.5, −z; (vii) x, 0.5-y, z + 0.5; (viii) 0.5-x, y, z + 0.5.]

Figure 2 The crystal structure of [Fe(PO4)(N2H4)] in a projection along [001].

It should be noted that it seems rather surprising to stabilize Fe^III with hydrazine, since the latter is a powerful reducing agent. Efforts are currently underway to obtain the title compound as a pure phase to perform magnetic measurements. It could be a way, by comparison with the results reported for [Co(SO₄)(N₂H₄)] (Jia et al., 2011), to study the ability of hydrazine to transmit magnetic coupling.

3. Supra­molecular features

The three-dimensional framework structure of [Fe(PO₄)(N₂H₄)] is consolidated by N—H⋯O inter­actions between the hydrazine ligands and phosphate O atoms (Fig. 3). One of the two hydrogen bonds is bifurcated. Considering the N⋯O distances and the values of the N—H⋯angles (Table 1), this type of hydrogen bonding can be considered as moderately strong.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N—H1⋯O1^i	0.85 (3)	2.36 (2)	3.086 (2)	144 (2)
N—H1⋯O2^ii	0.85 (3)	2.27 (3)	2.974 (2)	141 (2)
N—H2⋯O1^iii	0.85 (3)	2.19 (3)	2.873 (2)	137 (2)
Symmetry codes: (i) ; (ii) ; (iii) .

Figure 3 The crystal structure of [Fe(PO4)(N2H4)] in a projection along [100], emphasizing the hydrogen bonding between the components (black dotted lines). P atoms have been omitted for clarity.

4. Synthesis and crystallization

Iron(II) chloride tetra­hydrate (>99.0%, Sigma–Aldrich), hydrazine monohydrate (99+%) and KH₂PO₄ (both VWR Inter­national) were used as received without further purification. Iron(II) chloride tetra­hydrate (2 g) was dissolved in water (20 ml) before adding hydrazine monohydrate (2 ml). The obtained solution was stirred for 5 min. Then, KH₂PO₄ (11.5 g) was added. After 10 min of stirring for homogenization, the obtained solution (15 ml) was incorporated in a 23 ml autoclave. The autoclave was then heated at 433 K for 10 h before being cooled to room temperature at a rate of 10 K h⁻¹. The obtained mixture, consiting of orange crystals of the title phase and yellow crystals of an additional phase, was washed with water. The obtained crystals were very small (around 20 µm) and well isolated from the others. Details of the composition and structure of the yellow crystals will be described in a forthcoming article.

5. Refinement details

Crystal data, data collection and structure refinements are summarized in Table 2. All H atoms were located in a difference Fourier map and were refined freely with isotropic displacement parameters.

Table 2
Experimental details

Crystal data
Chemical formula	[Fe(PO4)(N2H4)]
Mr	182.87
Crystal system, space group	Orthorhombic, Pccn
Temperature (K)	293
a, b, c (Å)	6.3114 (13), 7.6680 (15), 8.6485 (18)
V (Å^3)	418.55 (15)
Z	4
Radiation type	Mo Kα
μ (mm^−1)	3.89
Crystal size (mm)	0.05 × 0.03 × 0.03
Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2013)
Tmin, Tmax	0.668, 0.746
No. of measured, independent and observed [I > 3σ(I)] reflections	13820, 601, 457
Rint	0.065
(sin θ/λ)max (Å^−1)	0.717
Refinement
R[F^2 > 3σ(F^2)], wR(F^2), S	0.020, 0.027, 1.46
No. of reflections	601
No. of parameters	47
H-atom treatment	All H-atom parameters refined
Δρmax, Δρmin (e Å^−3)	0.40, −0.33
Computer programs: APEX2and SAINT (Bruker, 2013), SUPERFLIP (Palatinus & Chapuis, 2007), JANA2006 (Petříček et al., 2014) and DIAMOND (Brandenburg & Putz, 2010).

Supporting information

Computing details

Data collection: APEX2 (Bruker, 2013); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007); program(s) used to refine structure: JANA2006 (Petrićek et al., 2014); molecular graphics: DIAMOND (Brandenburg & Putz, 2010); software used to prepare material for publication: JANA2006 (Petrićek et al., 2014).

Poly[(µ₂-hydrazine)(µ₄-phosphato)iron(III)]

Crystal data

[Fe(PO4)(N2H4)]	F(000) = 364
Mr = 182.87	Dx = 2.902 Mg m^−3
Orthorhombic, Pccn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ab 2ac	Cell parameters from 2128 reflections
a = 6.3114 (13) Å	θ = 4.2–26.9°
b = 7.6680 (15) Å	µ = 3.89 mm^−1
c = 8.6485 (18) Å	T = 293 K
V = 418.55 (15) Å^3	Parallelepiped, orange
Z = 4	0.05 × 0.03 × 0.03 mm

Data collection

Bruker APEXII CCD diffractometer	457 reflections with I > 3σ(I)
Radiation source: X-ray tube	Rint = 0.065
phi scan	θmax = 30.6°, θmin = 4.2°
Absorption correction: multi-scan (SADABS; Bruker, 2013)	h = −9→8
Tmin = 0.668, Tmax = 0.746	k = −10→10
13820 measured reflections	l = −12→12
601 independent reflections

Refinement

Refinement on F	0 constraints
R[F > 3σ(F)] = 0.020	All H-atom parameters refined
wR(F) = 0.027	Weighting scheme based on measured s.u.'s w = 1/(σ^2(F) + 0.0001F^2)
S = 1.46	(Δ/σ)max = 0.006
601 reflections	Δρmax = 0.40 e Å^−3
47 parameters	Δρmin = −0.33 e Å^−3
0 restraints

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

	x	y	z	Uiso*/Ueq
O1	−0.0604 (2)	0.30096 (17)	0.36016 (16)	0.0093 (4)
Fe	0	0	0	0.00652 (11)
P	−0.25	0.25	0.25868 (8)	0.00567 (17)
O2	−0.1898 (2)	0.09269 (19)	0.15978 (16)	0.0111 (4)
N	0.2656 (3)	0.1556 (2)	0.0781 (2)	0.0103 (5)
H1	0.306 (4)	0.132 (3)	0.169 (3)	0.024 (7)*
H2	0.364 (4)	0.139 (3)	0.012 (3)	0.020 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0089 (6)	0.0090 (7)	0.0099 (7)	0.0001 (5)	−0.0032 (5)	−0.0013 (5)
Fe	0.00692 (19)	0.0059 (2)	0.00678 (19)	−0.00013 (13)	0.00010 (16)	−0.00054 (16)
P	0.0059 (3)	0.0053 (3)	0.0057 (3)	−0.0001 (3)	0	0
O2	0.0135 (6)	0.0096 (7)	0.0101 (7)	0.0003 (5)	0.0030 (6)	−0.0033 (6)
N	0.0110 (8)	0.0074 (8)	0.0123 (9)	−0.0017 (7)	−0.0012 (8)	0.0010 (7)

Geometric parameters (Å, º)

O1—Fe^i	1.9843 (14)	P—O2^iii	1.5268 (15)
O1—P	1.5346 (15)	N—N^iv	1.461 (2)
Fe—O2	1.9621 (15)	N—H1	0.85 (3)
Fe—O2^ii	1.9621 (15)	N—H2	0.85 (3)
P—O2	1.5268 (15)
Fe^i—O1—P	133.97 (8)	O1—P—O2^iii	108.25 (7)
O1^v—Fe—O1^vi	180.0 (5)	O1^iii—P—O2	108.25 (7)
O1^v—Fe—O2	88.09 (6)	O1^iii—P—O2^iii	109.13 (7)
O1^v—Fe—O2^ii	91.91 (6)	O2—P—O2^iii	111.85 (9)
O1^vi—Fe—O2	91.91 (6)	Fe—O2—P	146.37 (9)
O1^vi—Fe—O2^ii	88.09 (6)	N^iv—N—H1	104.6 (18)
O2—Fe—O2^ii	180.0 (5)	N^iv—N—H2	104.2 (18)
O1—P—O1^iii	110.23 (8)	H1—N—H2	112 (2)
O1—P—O2	109.13 (7)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N—H1···O1^iv	0.85 (3)	2.36 (2)	3.086 (2)	144 (2)
N—H1···O2^vii	0.85 (3)	2.27 (3)	2.974 (2)	141 (2)
N—H2···O1^viii	0.85 (3)	2.19 (3)	2.873 (2)	137 (2)

Symmetry codes: (iv) −x+1/2, −y+1/2, z; (vii) x+1/2, −y, −z+1/2; (viii) −x+1/2, y, z−1/2.