Crystal structure of a new hybrid compound based on an iodido-plumbate(II) anionic motif.

Crystals of the one-dimensional organic-inorganic lead iodide-based compound catena-poly[bis-(piperazine-1,4-diium) [[tetra-iodido-plumbate(II)]-μ-iodido] iodide monohydrate], (C4N2H12)2[PbI5]I·H2O, were obtained by slow evaporation at room temperature of a solution containing lead iodide and piperazine in a 1:2 molar ratio. Inorganic lead iodide chains, organic (C4N2H12)(2+) cations, water mol-ecules of crystallization and isolated I(-) anions are connected through N-H⋯·I, N-H⋯OW and OW-H⋯I hydrogen-bond inter-actions. Zigzag chains of corner-sharing [PbI6](4-) octa-hedra with composition [PbI4/1I2/2](3-) running parallel to the a axis are present in the structure packing.

Chemical context

Organic–inorganic hybrid materials offer the opportunity to combine the desirable properties of the organic moiety such as processability, toughness and impact strength with the typical properties of the inorganic part such as high temperature stability and durability. The opto-electronic characteristics of hybrid materials are closely related to the metal cluster size. In recent years, a significant number of organic–inorganic hybrid materials based on lead halide units have been prepared and studied (Billing & Lemmerer, 2006 ▸; Rayner & Billing, 2010 ▸), in particular with self-organized low-dimensional families of lead iodide-based crystals where the [PbI6] octa­hedra form one-, two- or three-dimensional networks (Elleuch et al., 2007 ▸; Trigui et al., 2011 ▸). In one-dimensional lead halide hybrid compounds, the inorganic chains may be formed by one, two or three bridging halides, referred to as corner-, edge- and face-sharing polyhedra, respectively. Thanks to their anti­cipated electroluminescence, photoluminescence and non-linear optical properties, these compounds are the most desired ones (Lemmerer & Billing, 2006 ▸). Lead iodide-based hybrid materials are studied extensively for their excitonic and magneto-optical properties. In this work we report the synthesis and crystal structure determination of a new lead iodide hybrid, (C4N2H12)2[PbI5]·I·H2O, (I).

Structural commentary

The structural units of (I) consist of one piperazine mol­ecule, one water mol­ecule, one isolated iodine and one [PbI6] unit (Fig. 1 ▸). The electrical neutrality is ensured by two organic mol­ecules of doubly protonated piperazine.

Figure 1

Structural units of the title compound, showing the atom-numbering scheme. Atomic displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radius. [Symmetry codes: (i) x,  − y, z; (ii) − + x,  − y,  − z.]

The main part of the inorganic moiety is composed by the lead Pb2+ cation which adopts a distorted octa­hedral coordin­ation. The angles between cis-related I− ions range from 85.022 (12) to 96.89 (3)° at most, whereas the trans angles deviate from 180° by 12.95 (3)° (Table 1 ▸). Two adjacent corners connect the [PbI6] octa­hedron to its neighbours, leading to zigzag chains running parallel to the a axis (Fig. 2 ▸). This one-dimensional anionic network leaves empty spaces in which the organic cations are located. The [PbI6] octa­hedra establish two strong hydrogen bonds (Table 2 ▸), N2—H4N⋯I3 and N2i—H4N i⋯I3, via the I3 corners [symmetry code: (i) x,  − y, z] as illustrated in Fig. 3 ▸.

Table 1

Selected geometric parameters (Å, °)

Pb—I2	3.0689 (9)	Pb—I4	3.2396 (9)
Pb—I3	3.1511 (9)	Pb—I4ii	3.3535 (9)
Pb—I1	3.2173 (8)	I4—Pbiii	3.3535 (9)
Pb—I1i	3.2173 (8)	OW—HW2	0.86 (2)
I2—Pb—I3	96.06 (3)	I1—Pb—I4	87.185 (13)
I2—Pb—I1	85.021 (12)	I1i—Pb—I4	87.185 (13)
I3—Pb—I1	93.943 (13)	I2—Pb—I4ii	179.99 (3)
I2—Pb—I1i	85.022 (12)	I3—Pb—I4ii	83.95 (3)
I3—Pb—I1i	93.944 (13)	I1—Pb—I4ii	94.978 (12)
I1—Pb—I1i	167.89 (2)	I1i—Pb—I4ii	94.977 (12)
I2—Pb—I4	96.89 (3)	I4—Pb—I4ii	83.105 (14)
I3—Pb—I4	167.05 (3)	Pb—I4—Pbiii	178.91 (3)

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

Figure 2

The [PbI4/1I2/2]3− chain of (I) running parallel to the a-axis direction and exhibiting a zigzag conformation.

Table 2

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1N⋯OW iv	0.90	2.05	2.874 (5)	155
N1—H2N⋯I5v	0.90	2.69	3.543 (4)	160
N2—H4N⋯I3	0.90	2.85	3.656 (4)	151
OW—HW1⋯I5vi	0.86	2.74	3.477 (5)	145

Symmetry codes: (iv) ; (v) ; (vi) .

Figure 3

Linkage around one [PbI6] octa­hedron formed by two similar octa­hedra and two protonated piperazine cations. Hydrogen bonds are drawn as dashed green lines. [Symmetry codes: (i) x,  − y, z; (ii) − + x,  − y,  − z.]

The second part of the inorganic moiety contains a water mol­ecule and the iodide anion I5 linked by a strong hydrogen-bond inter­action (Table 2 ▸). Both are located in the same layers in which the [PbI6] octa­hedra are located. As shown in Fig. 4 ▸, the anion I5 is linked to one water mol­ecule by I5⋯HW1i–OW i [symmetry code: (i) 1 − x,  + y, 1 − z] and two organic cations via I5⋯H2N i—N1ii and I5⋯H2N iii—N1iii [symmetry codes: (ii)  + x,  − y,  − z; (iii)  + x, y,  − z]. On the other hand, the water mol­ecule is associated to one iodine (I5) via OW—HW1⋯I5iii [symmetry code: (iii) 1 − x, − + y, 1 − z) and to two piperazinium cations via OW⋯H1N ii—N1ii and OW⋯H1N i—N1i (Fig. 5 ▸). In this configuration, no acceptor was found for HW2 and H3N.

Figure 4

Hydrogen-bonding inter­actions with isolated iodide in (I). [Symmetry codes: (i) 1 − x,  + y, 1 − z; (ii)  + x,  − y,  − z; (iii)  + x, y,  − z.]

Figure 5

Water mol­ecule hydrogen bonding inter­actions in (I). [Symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) 1 − x, − + y, 1 − z.]

The six-membered piperazinium cation ring adopts a chair conformation. It inter­acts with the inorganic chain via strong N2—H4N⋯I3 hydrogen bonds with a 2.85 Å bond length (Table 2 ▸ and Fig. 6 ▸). In the crystal structure, the piperazinium cations are also linked to the water mol­ecule by an N1—H1N⋯OW iii hydrogen bond and to the iodine anion by N1—H2N⋯I5iii hydrogen bonds.

Figure 6

The hydrogen bonding environment of the cation of the title compound. [Symmetry codes: (i) − + x,  − y,  − z; (ii) − + x,  − y,  − z; (iii) 1 − x,  + y, 1 − z.]

Compared to its homologous hybrids, the structure of the title compound exhibits an original arrangement of the inorganic layers. It is composed by two parts: the first are the [PbI6] octa­hedra sharing adjacent corners and so assembling into chains running along the [100] direction. The second original feature is the structural cohesion by water mol­ecules and isolated iodide anions. This structural arrangement will probably have an impact on the dielectric behavior of the material. Luminescence and UV–visible spectroscopy measurements of this compound, coupled to theoritical calculation of the Highest Occupied Mol­ecular Orbital (HOMO) and Lowest Unoccupied Mol­ecular Orbital (LUMO) electronic transitions are in progress.

As shown in Fig. 7 ▸, the structure of (I) is self-assembled into alternating organic and inorganic layers parallel to the ac plane. The organic part is made up of (C4H12N2)2+ cations located in the voids around the corner-sharing [PbI6]4− octa­hedra. The iodine anions and the water mol­ecules connect the organic and inorganic sheets by strong hydrogen-bond inter­actions.

Figure 7

A packing diagram of (I), viewed along the a axis showing the alternating organic and inorganic layers. Hydrogen bonds are omitted for clarity.

Database survey

Using the piperazine-1,4-diium cation scheme in the similarity option of the WEBCSD inter­face (Groom & Allen, 2014 ▸), more than 90 records are found in the CCDC database. Only 24 are inorganic–organic hybrid compounds with several metals Cu, Zn, Co, Bi, Cd, Sb, Au etc. The closest chemical composition found is a bis­muth-based compound (II): (C4N2H12)2[BiCl6]·Cl·H2O (Gao et al., 2011 ▸). In spite of the chemical formula similarity, it seems that the ortho­rhom­bic (Pnma) title structure is much more regular than the monoclinic (P21/c) compound (II) with approximately the same cell volume, where the small difference is probably due to the chlorine/iodine substitution. In contrast to the structure of (I), the anionic network in the structure of (II) is 0-D, built up by isolated [BiCl6] octa­hedra. The water mol­ecule and the isolated halogen play, in both cases, the same crucial role in the structural cohesion, linking the anionic part to the organic moieties.

Synthesis and crystallization

Crystals of the title compound were prepared by slow evaporation at room temperature by mixing 1,4-di­aza­cyclo­hexane (C4H10N2) (2 mol) with a solution of lead iodide PbI2 (1 mol) in an equimolar mixture of ethanol and DMF. After several weeks, the obtained crystals were isolated and dried.

Refinement

Data collection and structure refinement details are summarized in Table 3 ▸. Hydrogen atoms were placed using geometrical constraints using adequate HFIX instructions (SHELXL) and refined with AFIX instructions. Water hydrogen atoms were found in Fourier difference maps and O—H distances were restrained using DFIX (0.86 Å) and DANG instructions.

Table 3

Experimental details

Crystal data
Chemical formula	(C4H12N2)2[PbI5]I·H2O
M r	1162.92
Crystal system, space group	Orthorhombic, P n m a
Temperature (K)	298
a, b, c (Å)	8.7477 (10), 13.488 (2), 20.336 (3)
V (Å3)	2399.4 (6)
Z	4
Radiation type	Mo Kα
μ (mm−1)	14.75
Crystal size (mm)	0.45 × 0.14 × 0.10
Data collection
Diffractometer	Enfar–Nonius CAD-4
Absorption correction	ψ scan (North et al., 1968 ▸)
T min, T max	0.622, 0.999
No. of measured, independent and observed [I > 2σ(I)] reflections	3601, 2729, 1941
R int	0.034
(sin θ/λ)max (Å−1)	0.638
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.037, 0.086, 1.05
No. of reflections	2729
No. of parameters	105
No. of restraints	3
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	2.00, −1.28

Computer programs: CAD-4 EXPRESS (Enraf–Nonius, 1994 ▸), XCAD4 (Harms & Wocadlo, 1995 ▸), SHELXS97 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸), DIAMOND (Brandenburg, 2006 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989015023786/vn2104sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015023786/vn2104Isup2.hkl

CCDC reference: 1429047

Additional supporting information: crystallographic information; 3D view; checkCIF report

(C4H12N2)2[PbI5]I·H2O	Dx = 3.219 Mg m−3
Mr = 1162.92	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pnma	Cell parameters from 25 reflections
a = 8.7477 (10) Å	θ = 13.7–14.7°
b = 13.488 (2) Å	µ = 14.75 mm−1
c = 20.336 (3) Å	T = 298 K
V = 2399.4 (6) Å3	Prism, yellow
Z = 4	0.45 × 0.14 × 0.10 mm
F(000) = 2040

Enfar–Nonius CAD-4 diffractometer	Rint = 0.034
Radiation source: fine-focus sealed tube	θmax = 27.0°, θmin = 2.0°
ω/2τ scans	h = −11→2
Absorption correction: ψ scan (North et al., 1968)	k = −1→17
Tmin = 0.622, Tmax = 0.999	l = −1→25
3601 measured reflections	2 standard reflections every 120 min
2729 independent reflections	intensity decay: −1%
1941 reflections with I > 2σ(I)

Refinement on F2	Primary atom site location: heavy-atom method
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.086	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ2(Fo2) + (0.0358P)2 + 1.6589P] where P = (Fo2 + 2Fc2)/3
2729 reflections	(Δ/σ)max < 0.001
105 parameters	Δρmax = 2.00 e Å−3
3 restraints	Δρmin = −1.28 e Å−3

Experimental. Number of psi-scan sets used was 4 Theta correction was applied. Averaged transmission function was used. No Fourier smoothing was applied.

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.

	x	y	z	Uiso*/Ueq
Pb	0.70782 (5)	0.2500	0.37128 (2)	0.02909 (13)
I1	0.74558 (6)	0.48720 (5)	0.37511 (3)	0.03537 (16)
I2	0.94306 (9)	0.2500	0.48324 (4)	0.0367 (2)
I3	0.41658 (9)	0.2500	0.46247 (4)	0.0410 (2)
I4	0.95081 (10)	0.2500	0.25107 (4)	0.0421 (2)
I5	0.54190 (11)	0.7500	0.19255 (5)	0.0489 (3)
N1	0.3401 (9)	0.5979 (6)	0.3685 (3)	0.0430 (19)
H1N	0.2673	0.6433	0.3635	0.052*
H2N	0.4301	0.6287	0.3680	0.052*
N2	0.1611 (9)	0.4232 (6)	0.3784 (3)	0.0407 (19)
H3N	0.0691	0.3951	0.3792	0.049*
H4N	0.2305	0.3754	0.3828	0.049*
C1	0.3329 (10)	0.5257 (8)	0.3131 (4)	0.039 (2)
H1A	0.3455	0.5604	0.2716	0.046*
H1B	0.4151	0.4779	0.3172	0.046*
C2	0.1836 (9)	0.4737 (7)	0.3138 (4)	0.035 (2)
H2A	0.1805	0.4252	0.2787	0.042*
H2B	0.1019	0.5210	0.3066	0.042*
C3	0.3199 (10)	0.5469 (8)	0.4320 (4)	0.041 (2)
H3A	0.4040	0.5012	0.4389	0.050*
H3B	0.3214	0.5953	0.4672	0.050*
C4	0.1744 (10)	0.4919 (8)	0.4337 (4)	0.046 (3)
H4A	0.1677	0.4552	0.4746	0.055*
H4B	0.0900	0.5386	0.4325	0.055*
OW	0.4301 (11)	0.2500	0.6369 (5)	0.051 (3)
HW1	0.393 (13)	0.2500	0.676 (2)	0.080*
HW2	0.352 (9)	0.2500	0.612 (4)	0.059*

	U11	U22	U33	U12	U13	U23
Pb	0.0224 (2)	0.0364 (3)	0.0284 (2)	0.000	0.00002 (19)	0.000
I1	0.0287 (3)	0.0386 (4)	0.0388 (3)	0.0019 (2)	−0.0011 (2)	0.0008 (3)
I2	0.0322 (4)	0.0408 (6)	0.0372 (4)	0.000	−0.0079 (4)	0.000
I3	0.0296 (4)	0.0498 (6)	0.0435 (4)	0.000	0.0088 (4)	0.000
I4	0.0353 (4)	0.0420 (5)	0.0491 (5)	0.000	0.0180 (4)	0.000
I5	0.0525 (5)	0.0392 (6)	0.0550 (5)	0.000	0.0114 (5)	0.000
N1	0.030 (4)	0.042 (5)	0.058 (5)	−0.007 (4)	−0.009 (4)	0.002 (4)
N2	0.044 (4)	0.032 (4)	0.046 (4)	−0.009 (4)	−0.008 (4)	0.006 (4)
C1	0.039 (5)	0.051 (6)	0.025 (4)	−0.002 (5)	−0.001 (4)	0.005 (4)
C2	0.031 (4)	0.035 (5)	0.040 (5)	0.002 (4)	−0.004 (4)	−0.005 (4)
C3	0.035 (5)	0.046 (6)	0.043 (5)	0.000 (5)	0.001 (4)	−0.015 (5)
C4	0.029 (5)	0.067 (8)	0.041 (5)	−0.009 (5)	0.008 (4)	−0.012 (5)
OW	0.046 (6)	0.038 (6)	0.068 (6)	0.000	−0.003 (5)	0.000

Pb—I2	3.0689 (9)	N2—H4N	0.8900
Pb—I3	3.1511 (9)	C1—C2	1.483 (11)
Pb—I1	3.2173 (8)	C1—H1A	0.9700
Pb—I1i	3.2173 (8)	C1—H1B	0.9700
Pb—I4	3.2396 (9)	C2—H2A	0.9700
Pb—I4ii	3.3535 (9)	C2—H2B	0.9700
I4—Pbiii	3.3535 (9)	C3—C4	1.473 (12)
N1—C1	1.490 (11)	C3—H3A	0.9700
N1—C3	1.474 (11)	C3—H3B	0.9700
N1—H1N	0.8900	C4—H4A	0.9700
N1—H2N	0.8900	C4—H4B	0.9700
N2—C4	1.462 (11)	OW—HW1	0.86 (2)
N2—C2	1.493 (10)	OW—HW2	0.86 (2)
N2—H3N	0.8900
I2—Pb—I3	96.06 (3)	H3N—N2—H4N	107.9
I2—Pb—I1	85.021 (12)	C2—C1—N1	109.8 (7)
I3—Pb—I1	93.943 (13)	C2—C1—H1A	109.7
I2—Pb—I1i	85.022 (12)	N1—C1—H1A	109.7
I3—Pb—I1i	93.944 (13)	C2—C1—H1B	109.7
I1—Pb—I1i	167.89 (2)	N1—C1—H1B	109.7
I2—Pb—I4	96.89 (3)	H1A—C1—H1B	108.2
I3—Pb—I4	167.05 (3)	C1—C2—N2	110.0 (7)
I1—Pb—I4	87.185 (13)	C1—C2—H2A	109.7
I1i—Pb—I4	87.185 (13)	N2—C2—H2A	109.7
I2—Pb—I4ii	179.99 (3)	C1—C2—H2B	109.7
I3—Pb—I4ii	83.95 (3)	N2—C2—H2B	109.7
I1—Pb—I4ii	94.978 (12)	H2A—C2—H2B	108.2
I1i—Pb—I4ii	94.977 (12)	C4—C3—N1	111.1 (7)
I4—Pb—I4ii	83.105 (14)	C4—C3—H3A	109.4
Pb—I4—Pbiii	178.91 (3)	N1—C3—H3A	109.4
C1—N1—C3	110.7 (7)	C4—C3—H3B	109.4
C1—N1—H1N	109.5	N1—C3—H3B	109.4
C3—N1—H1N	109.5	H3A—C3—H3B	108.0
C1—N1—H2N	109.5	N2—C4—C3	111.6 (7)
C3—N1—H2N	109.5	N2—C4—H4A	109.3
H1N—N1—H2N	108.1	C3—C4—H4A	109.3
C4—N2—C2	112.1 (7)	N2—C4—H4B	109.3
C4—N2—H3N	109.2	C3—C4—H4B	109.3
C2—N2—H3N	109.2	H4A—C4—H4B	108.0
C4—N2—H4N	109.2	HW1—OW—HW2	104 (3)
C2—N2—H4N	109.2

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1N···OWiv	0.90	2.05	2.874 (5)	155
N1—H2N···I5v	0.90	2.69	3.543 (4)	160
N2—H4N···I3	0.90	2.85	3.656 (4)	151
OW—HW1···I5vi	0.86	2.74	3.477 (5)	145