Self-assembly of a one-dimensional iron(II) coordination polymer with p-phenyl­enebis(picolinaldimine)

catena-Poly[[[dichloridoiron(II)]-μ-N,N′-bis­(2-pyridylmethyl­ene)benzene-1,4-diamine] methanol disolvate], [FeCl₂(C₁₈H₁₄N₄)]·2CH₃OH, forms a one-dimensional coordination polymer. The polymeric chains run parallel to the c axis. O—H...Cl—Fe and C—H...O hydrogen-bonding inter­actions with meth­anol solvent mol­ecules stabilize the open supra­molecular framework. Each Fe^II atom adopts an octa­hedral geometry coordinated by four N atoms from two N,N′-bis­(2-pyridyl­methyl­ene)­benzene-1,4-diamine ligands and completed by two cis Cl atoms. The compound has C₂ (and C_i) mol­ecular symmetry, which is coincident with the crystallographic twofold symmetry at (0, y, ). The one-dimensional structure is propagated via the crystallographic inversion center located at the benzene ring centroid (0, , 0).

S1. Comment

A fundamental concept in inorganic supramolecular chemistry is the use of transition metal units (referred to as nodes) and polypyridyl molecules as bridging spacers to construct a vast array of multi-dimensional networks (Moulton & Zaworotko, 2001; Blake et al., 1999; Balzani & Juris, 2001). Exploiting the different coordination geometries that transition metal complexes can adopt and varying the spacer unit are two ways to influence which molecular or network architecture may be observed. Fine-tuning the stability and utility of these materials in applications such as molecular devices, sensors and catalysts can in part be accomplished through intra- and intermolecular interactions such as π–π stacking, halogen bonding and hydrogen bonding (for example, Beatty, 2001; Braga et al., 2005; Brammer, 2003).

The present work stems from our interest in developing complexes with interesting photophysical and photochemical properties. In one study, we investigated the binding properties of two pyridine-substituted ligands, namely 4,16-bis(picolinaldimine)-bis[2.2]paracyclophane (bppc) and p-phenylenebis(picolinaldimine) (pbp) (Ball et al., 2004). We describe here the self-assembly and structure of an iron(II) polypyridyl coordination polymer, (pbp)FeCl₂, (I), as a methanol disolvate.

The molecular subunit (Fig. 1) forms the basis of the one-dimensional polymer shown in Fig. 2(a). The compound has C₂ molecular symmetry, which is coincident with the crystallographic twofold symmetry (0, y, 1/4). The one-dimensional structure is propogated via the crystallographic inversion center located at the phenyl ring centroid (0, 1/2, 0). Each Fe^II atom adopts an octahedral geometry involving four coordinated N atoms from two pbp ligands and two cis Cl atoms. The pbp ligand is twisted; the mean plane of the pyridyl ring is at a 49.08 (10)° angle to that of the phenyl ring. Such twisting of the pbp backbone appears to be common (Shavaleev et al., 2003; Wu et al., 2006). The Fe—N_py bond [2.177 (2) Å] is shorter than the Fe—N_imino bond [2.257 (2) Å] consistent with related iron polypyridyl complexes (Small et al., 1998; Britovsek et al., 1999). Furthermore, the imino linkage, N2═ C6, maintains double-bond character with a distance of 1.278 (4) Å [the distance in pbp is 1.273 (2) Å (Ball et al., 2004)]. Similarly, [pbpZn(DMF)₂]_n](ClO₄)_2n.nDMF is a one-dimensional zigzag coordination polymer with a six-coordinate Zn^II center (Yoshida et al., 2000). The average Zn—N distances are 2.142 and 2.253 Å for the pyridyl and imine bonds, respectively. Self-assembly of AgClO₄ with pbp has been reported by Wu et al. (2006) to also form a one-dimensional polymeric array with Ag^I in a distorted tetrahedral environment. Although it appears that the pbp ligand promotes a polymeric extended bonding motif, this is not always the case. In the dinuclear complex [{η⁶-C₁₀H₁₄)RuCl}₂(µ-pbp)]BF₄, the `piano stool' Ru–arene units are trans-disposed with respect to the pbp ligand (Singh et al., 2004).

Little interaction between the neighboring zigzag chains in (I) is observed. The chains are parallel with a separation of 8.2276 (11) Å (between planes drawn through the Fe atoms in a chain). As a result, a relatively open framework is adopted, with cavity sizes suitable for small guest molecule incorporation (Moulton & Zaworotko, 2001). The estimated void space occupied by the disordered methanol molecule is 98 ų (Spek, 2003), with cavity dimensions of approximately 4.6 (1) × 8.7 (1) Å (between the ortho C atoms of the phenyl group which face the interior of the cavity). Hydrogen bonds within our one-dimensional architecture primarily involve the methanol molecule residing in the cavity (Fig. 2 b). The O—H···Cl—Fe interaction (see Table 2) is considered strong according to the classification of Aullón et al. (1998). A pair of C—H···O and C—H···Cl interactions lend stability to the overall extended structure.

Related literature

For related literature, see: Ball et al. (2004); Balzani & Juris (2001); Beatty (2001); Blake et al. (1999); Braga et al. (2005); Brammer (2003); Britovsek et al. (1999); Haga & Koizumi (1985); Moulton & Zaworotko (2001); Shavaleev et al. (2003); Singh et al. (2004); Small et al. (1998); Spek (2003); Wu et al. (2006); Yoshida et al. (2000).

S2. Experimental

The pbp ligand was prepared according to the method of Haga & Koizumi (1985). A bright-yellow solution of FeCl₃·6H₂O (0.0371 g, 0.14 mmol) in methanol (5 ml) was layered over a pale-yellow solution of pbp (0.0207 g, 0.072 mmol) in dichloromethane (5 ml) in a test tube. The test tube was covered with Parafilm. After approximately a week, dark-red microcrystals of (I), suitable for X-ray analysis, were formed.

S3. Refinement

The methanol solvent molecule is disordered at the O atom. The C—O distances (C10—O10A and C10—O10B) were restrained to be similar. The refined occupancy of the major conformer is 71 (1)%. The O atoms were refined isotropically with the displacement parameters restrained to be equivalent. Hydroxy atom H10 was located directly from a difference map and its position was held fixed (AFIX 1) in subsequent refinements. The remaining H atoms were palced in calculated positions and treated with a riding model (C_aromatic—H = 0.95 Å and C_methyl—H = 0.98 Å). The isotropic displacement parameters for all H atoms were defined as aU_eq of the adjacent atom (a = 1.5 for hydroxy and a = 1.2 for all other H atoms).

Computing details

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2003); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL and DIAMOND (Brandenburg, 2007); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. Structure of (I); atomic labelling scheme and 50% probability ellipsoids. The disordered methanol solvent is not shown. [symmetry code: (i) −x, y, 1/2 − z; (ii) −x, −y + 1, −z; (iii) x, −y + 1, −1/2 + z].
	Fig. 2. (a) The 1-D polymeric chain runs parallel to the c axis. (b) Methanol solvent (major conformer only, shown in yellow) fills the cavities; O—H···Cl—Fe interactions shown as dashed lines; only hydroxyl H-atom on methanol shown.

catena-Poly[[[dichloridoiron(II)]-µ-N,N'-bis(2-pyridylmethylene)benzene-1,4-diamine] methanol solvate]

Crystal data

[FeCl2(C18H14N4)]·2CH4O	F(000) = 984
Mr = 477.17	Dx = 1.542 Mg m^−3
Monoclinic, C2/c	Synchrotron radiation, λ = 0.77500 Å
Hall symbol: -C 2yc	Cell parameters from 3685 reflections
a = 20.646 (3) Å	θ = 2.7–30.8°
b = 9.3893 (13) Å	µ = 1.28 mm^−1
c = 13.4869 (19) Å	T = 173 K
β = 128.152 (3)°	Plate, dark red
V = 2055.9 (5) Å^3	0.04 × 0.03 × 0.01 mm
Z = 4

Data collection

Bruker Platinum 200 diffractometer	2546 independent reflections
Radiation source: synchrotron	2096 reflections with I > 2σ(I)
Si-<111> channel cut crystal monochromator	Rint = 0.060
Detector resolution: 0.75 pixels mm^-1	θmax = 31.1°, θmin = 2.7°
ω scans	h = −27→27
Absorption correction: multi-scan (SADABS; Blessing, 1995)	k = −12→12
Tmin = 0.957, Tmax = 0.987	l = −17→17
14014 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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.126	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0673P)^2 + 3.4071P] where P = (Fo^2 + 2Fc^2)/3
2546 reflections	(Δ/σ)max = 0.001
131 parameters	Δρmax = 0.46 e Å^−3
2 restraints	Δρmin = −0.77 e Å^−3

Special details

Experimental. A suitable crystal was mounted on a loop using paratone-N and immediately transferred to the goniostat bathed in a cold stream.

The final unit cell is obtained from the refinement of the XYZ weighted centroids of reflections above 20 σ(I).

Note that the absorption correction parameters Tmin and Tmax also reflect beam corrections, etc. As a result, the numerical values for Tmin and Tmax may differ from expected values based solely on absorption effects and crystal size.

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.

The methanol of crystallization is disordered at the oxygen atom. The C—O distances (C10—O10A and C10—O10B) were restrained to be similar. The refined occupancy of the major conformer is 71 (1)%. The O atoms were refined isotropically with the displacement parameters retrained to be equivalent. The hydroxyl hydrogen, H10, was located directly from the difference map and its position held fixed (AFIX 1) in subsequent refinements. The remaining H-atoms were calculated and treated with a riding model (C_aromatic—H = 0.95 Å, C_methyl—H = 0.98 Å). The isotropic displacement parameters for all hydrogen atoms were defined as a*U_eq of the adjacent atom (a = 1.5 for hydroxyl and 1.2 for all others).

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Fe1	0.0000	0.18136 (6)	0.2500	0.02424 (18)
Cl1	0.05342 (5)	0.01125 (8)	0.18386 (7)	0.0359 (2)
N1	0.11058 (14)	0.2288 (3)	0.4396 (2)	0.0256 (5)
N2	0.06189 (14)	0.3638 (3)	0.2290 (2)	0.0256 (5)
C1	0.13654 (18)	0.1586 (3)	0.5444 (3)	0.0317 (6)
H1	0.1060	0.0783	0.5376	0.038*
C2	0.2065 (2)	0.1986 (4)	0.6629 (3)	0.0384 (7)
H2	0.2236	0.1457	0.7355	0.046*
C3	0.2509 (2)	0.3155 (4)	0.6744 (3)	0.0390 (7)
H3	0.2989	0.3445	0.7547	0.047*
C4	0.22415 (18)	0.3903 (3)	0.5662 (3)	0.0335 (6)
H4	0.2533	0.4717	0.5711	0.040*
C5	0.15458 (17)	0.3440 (3)	0.4519 (3)	0.0270 (5)
C6	0.12394 (18)	0.4161 (3)	0.3333 (3)	0.0303 (6)
H6	0.1499	0.5002	0.3342	0.036*
C7	0.03157 (16)	0.4355 (3)	0.1139 (2)	0.0269 (5)
C8	0.01959 (18)	0.5820 (3)	0.1012 (3)	0.0299 (6)
H8	0.0326	0.6376	0.1703	0.036*
C9	−0.01138 (18)	0.6468 (3)	−0.0124 (3)	0.0298 (6)
H9	−0.0189	0.7471	−0.0211	0.036*
O10A	0.1566 (5)	−0.2242 (7)	0.3795 (6)	0.0837 (15)*	0.714 (11)
O10B	0.1192 (11)	−0.2584 (17)	0.3628 (12)	0.0837 (15)*	0.286 (11)
H10	0.1032	−0.2030	0.3089	0.126*
C10	0.1559 (3)	−0.2049 (5)	0.4795 (5)	0.0675 (12)
H10A	0.1488	−0.3051	0.4913	0.101*	0.71
H10B	0.1068	−0.1446	0.4379	0.101*	0.71
H10C	0.2106	−0.1632	0.5414	0.101*	0.71
H10D	0.1573	−0.2724	0.5362	0.101*	0.29
H10E	0.1247	−0.1283	0.4819	0.101*	0.29
H10F	0.2121	−0.1670	0.5321	0.101*	0.29

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.0293 (3)	0.0264 (3)	0.0177 (3)	0.000	0.0148 (2)	0.000
Cl1	0.0446 (4)	0.0359 (4)	0.0339 (4)	0.0047 (3)	0.0275 (3)	−0.0022 (3)
N1	0.0301 (11)	0.0286 (11)	0.0213 (10)	0.0000 (9)	0.0175 (9)	0.0003 (9)
N2	0.0315 (11)	0.0294 (12)	0.0202 (10)	0.0018 (9)	0.0181 (9)	0.0028 (9)
C1	0.0361 (14)	0.0342 (15)	0.0250 (13)	0.0001 (11)	0.0189 (12)	0.0037 (11)
C2	0.0430 (16)	0.0464 (18)	0.0218 (13)	0.0024 (14)	0.0179 (13)	0.0051 (12)
C3	0.0353 (15)	0.0479 (19)	0.0219 (13)	−0.0012 (13)	0.0116 (12)	−0.0025 (12)
C4	0.0350 (14)	0.0362 (16)	0.0271 (14)	−0.0037 (12)	0.0181 (12)	−0.0014 (12)
C5	0.0307 (13)	0.0285 (13)	0.0237 (12)	0.0019 (10)	0.0177 (11)	0.0003 (10)
C6	0.0346 (14)	0.0306 (14)	0.0289 (14)	−0.0020 (11)	0.0212 (12)	0.0022 (11)
C7	0.0307 (13)	0.0326 (14)	0.0216 (12)	−0.0018 (11)	0.0182 (11)	0.0040 (10)
C8	0.0404 (15)	0.0325 (15)	0.0226 (12)	−0.0018 (11)	0.0223 (12)	0.0000 (11)
C9	0.0399 (15)	0.0292 (14)	0.0257 (13)	0.0007 (11)	0.0230 (12)	0.0030 (11)
C10	0.078 (3)	0.066 (3)	0.065 (3)	0.002 (2)	0.047 (3)	0.003 (2)

Geometric parameters (Å, º)

Fe1—N1	2.177 (2)	C7—C8	1.390 (4)
Fe1—N2	2.257 (2)	C7—C9^i	1.393 (4)
Fe1—Cl1	2.4040 (8)	C8—C9	1.384 (4)
N1—C1	1.335 (3)	C8—H8	0.9500
N1—C5	1.355 (4)	C9—C7^i	1.393 (4)
N2—C6	1.278 (4)	C9—H9	0.9500
N2—C7	1.433 (3)	O10A—C10	1.370 (7)
C1—C2	1.390 (4)	O10A—H10	0.9306
C1—H1	0.9500	O10B—C10	1.353 (13)
C2—C3	1.375 (5)	O10B—H10	0.7827
C2—H2	0.9500	C10—H10A	0.9800
C3—C4	1.390 (4)	C10—H10B	0.9801
C3—H3	0.9500	C10—H10C	0.9801
C4—C5	1.376 (4)	C10—H10D	0.9800
C4—H4	0.9500	C10—H10E	0.9800
C5—C6	1.472 (4)	C10—H10F	0.9800
C6—H6	0.9500
N1^ii—Fe1—N1	156.38 (13)	N2—C6—H6	120.5
N1—Fe1—N2^ii	87.79 (8)	C5—C6—H6	120.5
N1—Fe1—N2	74.21 (8)	C8—C7—C9^i	120.3 (2)
N2^ii—Fe1—N2	81.25 (12)	C8—C7—N2	121.6 (2)
N1—Fe1—Cl1^ii	95.08 (6)	C9^i—C7—N2	118.0 (3)
N1—Fe1—Cl1	100.57 (6)	C9—C8—C7	119.8 (3)
N2^ii—Fe1—Cl1	167.39 (6)	C9—C8—H8	120.1
N2—Fe1—Cl1	91.87 (6)	C7—C8—H8	120.1
Cl1^ii—Fe1—Cl1	96.73 (4)	C8—C9—C7^i	119.8 (3)
C1—N1—C5	117.7 (2)	C8—C9—H9	120.1
C1—N1—Fe1	125.9 (2)	C7^i—C9—H9	120.1
C5—N1—Fe1	116.36 (17)	C10—O10A—H10	104.6
C6—N2—C7	118.8 (2)	C10—O10B—H10	116.5
C6—N2—Fe1	114.44 (18)	O10B—C10—H10A	78.4
C7—N2—Fe1	126.15 (17)	O10A—C10—H10A	97.2
N1—C1—C2	122.5 (3)	O10B—C10—H10B	84.9
N1—C1—H1	118.8	O10A—C10—H10B	98.6
C2—C1—H1	118.8	H10A—C10—H10B	116.3
C3—C2—C1	119.5 (3)	O10B—C10—H10C	131.4
C3—C2—H2	120.3	O10A—C10—H10C	100.6
C1—C2—H2	120.3	H10A—C10—H10C	117.0
C2—C3—C4	118.7 (3)	H10B—C10—H10C	119.8
C2—C3—H3	120.7	O10B—C10—H10D	113.2
C4—C3—H3	120.7	O10A—C10—H10D	132.1
C5—C4—C3	118.6 (3)	O10B—C10—H10E	113.8
C5—C4—H4	120.7	O10A—C10—H10E	122.5
C3—C4—H4	120.7	H10D—C10—H10E	98.7
N1—C5—C4	123.1 (3)	O10B—C10—H10F	122.6
N1—C5—C6	115.4 (2)	O10A—C10—H10F	91.8
C4—C5—C6	121.5 (3)	H10D—C10—H10F	102.7
N2—C6—C5	119.0 (3)	H10E—C10—H10F	102.7
N1^ii—Fe1—N1—C1	140.7 (2)	Cl1—Fe1—N2—C7	81.8 (2)
N2^ii—Fe1—N1—C1	100.9 (2)	C5—N1—C1—C2	−0.7 (4)
N2—Fe1—N1—C1	−177.6 (2)	Fe1—N1—C1—C2	−177.7 (2)
Cl1^ii—Fe1—N1—C1	9.2 (2)	N1—C1—C2—C3	0.6 (5)
Cl1—Fe1—N1—C1	−88.6 (2)	C1—C2—C3—C4	−0.1 (5)
Cl1—Fe1—N1—C1	−88.6 (2)	C2—C3—C4—C5	−0.3 (5)
N1^ii—Fe1—N1—C5	−36.28 (18)	C1—N1—C5—C4	0.3 (4)
N2^ii—Fe1—N1—C5	−76.1 (2)	Fe1—N1—C5—C4	177.6 (2)
N2—Fe1—N1—C5	5.42 (19)	C1—N1—C5—C6	179.2 (2)
Cl1^ii—Fe1—N1—C5	−167.80 (19)	Fe1—N1—C5—C6	−3.6 (3)
Cl1—Fe1—N1—C5	94.38 (19)	C3—C4—C5—N1	0.2 (5)
Cl1—Fe1—N1—C5	94.38 (19)	C3—C4—C5—C6	−178.6 (3)
N1^ii—Fe1—N2—C6	157.6 (2)	C7—N2—C6—C5	179.1 (2)
N1—Fe1—N2—C6	−7.0 (2)	Fe1—N2—C6—C5	7.6 (3)
N2^ii—Fe1—N2—C6	83.2 (2)	N1—C5—C6—N2	−2.9 (4)
Cl1^ii—Fe1—N2—C6	25.7 (4)	C4—C5—C6—N2	175.9 (3)
Cl1—Fe1—N2—C6	−107.4 (2)	C6—N2—C7—C8	−46.3 (4)
Cl1—Fe1—N2—C6	−107.4 (2)	Fe1—N2—C7—C8	124.2 (2)
N1^ii—Fe1—N2—C7	−13.3 (2)	C6—N2—C7—C9^i	136.0 (3)
N1—Fe1—N2—C7	−177.8 (2)	Fe1—N2—C7—C9^i	−53.6 (3)
N2^ii—Fe1—N2—C7	−87.6 (2)	C9^i—C7—C8—C9	−1.0 (5)
Cl1^ii—Fe1—N2—C7	−145.2 (2)	N2—C7—C8—C9	−178.7 (3)
Cl1—Fe1—N2—C7	81.8 (2)	C7—C8—C9—C7^i	1.0 (5)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O10A—H10···Cl1	0.93	2.41	3.073 (6)	128
O10B—H10···Cl1	0.78	2.41	3.167 (15)	163
C1—H1···Cl1^ii	0.95	2.83	3.443 (3)	123
C6—H6···O10B^iii	0.95	2.46	3.091 (16)	125

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