Tetraaqua-1[kappa]⁴O-bis([epsilon]-caprolactam-1[kappa]O)-[mu]-cyano-1:2[kappa]²N:C-pentacyano-2[kappa]⁵C-iron(III)yttrium(III), a novel cyano-bridged dinuclear complex

Using caprolactam as a ligand, the novel title cyano-bridged yttrium(III)-ferricyanide complex, [Y(caprolactam)₂(H₂O)₄Fe(CN)₆] or [FeY(CN)₆(C₆H₁₁NO)₂(H₂O)₄], has been synthesized and structurally characterized. The Y atom is seven-coordinate and has approximately pentagonal-bipyramidal stereochemistry, with water mol­ecules occupying apical positions. Of the five ligands in equatorial positions, one is the N-bound bridging cyano group, and flanking this are two O-­bound caprolactam moieties, which are markedly inclined towards the bridged ferricyanide moiety such that they partially envelop it. Water mol­ecules occupy the remaining two equatorial positions. The Y-N-C-Fe-C-N sequence of atoms lies on a crystallographic twofold axis and is therefore perfectly linear, which has not been observed previously in cyano-bridged bimetallic complexes.

S1. Comment

Cyano-bridged Prussian Blue complexes have been widely studied in the past. Recently, a growing trend in this field has been to prepare lanthanoid-transition-metal complexes because of their fascinating applications as catalysts (Amer & Alper, 1989) and semi-permeable solid membranes to desalinate seawater (Mullica & Sappenfield, 1991), as well as precursors of electroceramic materials (Sadaoka et al., 1996), and chemical sensor materials and oxide fuel cells (Minh, 1993). The most attractive property of lanthanoid-transition-metal complexes is their magnetism. A series of cyano-bridged three-dimensional lanthanoid hexacyanometallates, [LnM(CN)₆].nH₂O (M is Fe^III or Cr^III, n = 4 or 5), were synthesized and ferrimagnetic ordering was observed in 1976 (Hulliger & Landolt, 1976). Very recently, many analogous Prussian Blue 4f-3 d complexes with interesting zero- and three-dimensional structures have been synthesized by incorporating betaine (Yan et al., 2001), 2,2'-bipyrimidine (Ma et al., 2001), 2,2'-dipyridyl-N,N'-dioxide (Gao et al., 1999), dimethylformamide (Kou et al., 1998; Kou, Gao & Jin, 2001; Kou, Gao, Sun & Zhang, 2001; Combs et al., 2000; Figuerola et al., 2001), dimethylsulfoxide (Yang et al., 2001), urea (Kou, Gao, Li et al., 2002) and pyrrolidone (Kou, Gao & Wang, 2002; Sun et al., 2002) as organic ligands.

Caprolactam (capro) has been shown to act as a useful ligand in the construction of 4f-3 d complexes, for example, one-dimensional [Ga(capro)₂(H₂O)₄Cr(CN)₆]·H₂O Should the first metal be Gd not Ga? (Kou, Gao, Li et al., 2002). Bearing in mind that the introduction of larger numbers of ligands always leads to lower-dimensional complexes, we tried to prepare an Y-capro-Fe complex with a molar ratio for Y:capro of 1:4. Unexpectedly, however, we obtained the title cyano-bridged bimetallic dimeric complex, (I). \sch

As shown in Fig. 1, the Y atom in (I) is seven-coordinate with approximately pentagonal-bipyramidal stereochemistry, with water molecules O3 and O3ⁱ [symmetry code: (i) -x, y, 1/2 - z] defining the apical positions. Of the five ligands in the equatorial positions, one is the N-bound µ-CN, and flanking this are two O-bound caprolactam moieties, which are markedly inclined towards the bridged ferricyanide moiety such that they partially envelop it. Water molecules occupy the other two equatorial positions. The two monodentate caprolactam molecules are in cis positions, with O1—Y—O1ⁱ 159.24 (10)°. The Y—N4—C4—Fe—C1—N1 sequence of atoms lies on a crystallographic twofold axis. To our knowledge, this perfectly linear cyano-bridging linkage has never previously been observed in other cyano-bridged complexes.

The Y—O_water bond lengths (Y—O2, Y—O3) are a little longer than that of Y—O_capro (Y—O1) (Table 1). The Y—N4 bond length is a little shorter than that of the Gd—N bonds in [Ga(capro)₂(H₂O)₄Cr(CN)₆]·H₂O Should the first metal be Gd not Ga? (2.505 and 2.501 Å; Kou, Gao, Li et al., 2002), which may be due to the difference in the radii of the two lanthanoid ions.

The geometry of the [Fe(CN)₆]^3- ion is approximately octahedral, with Fe—C bond distances in the range 1.930 (3)–1.937 (3) Å and C—Fe—C angles in the range 89.09 (8)–90.91 (8)°. The average C≡N bond length of 1.143 Å is in accord with the sum of the triple-bond radii of C and N atoms (0.603 and 0.55 Å, respectively; Reference?). The Fe—C—N bonds are almost linear and range from 178.1 (3) to 180.0° Please clarify - only two values in the CIF, the second of which is 179.2 (2)°.

S2. Experimental

Since K₃[Fe(CN)₆] has a tendency to decompose on heating and irradiation, the synthesis was performed at room temperature and crystallization in the dark. A solution of K₃[Fe(CN)₆] (65.8 mg, 0.2 mmol) in water (5 ml) was added to an aqueous solution (5 ml) of YCl₃·6H₂O (60.7 mg, 0.2 mmol) and caprolactam (90.4 mg, 0.8 mmol). The mixture was filtered and slowly evaporated to generate yellow single crystals of (I) (yield 30%).

S3. Refinement

The coordinates of the H atoms of the water molecules were found from difference Fourier maps and normalized to have an O—H distance of 0.85 Å. H atoms bound to C and N atoms were also visible in difference maps, and were placed using the HFIX commands in SHELXL97 (Sheldrick, 1997) and refined as riding atoms, with C—H distances of 0.96–0.97 Å and N—H distances of 0.86 Å. During the refinement, there was a high peak (2.0 e ų) in the vicinity of C5 (1.2 Å), indicating the presence of a degree of disorder about the C atom. A treatment of disorder was applied, and the refinement gave occupancies for C5 and C5' of 0.82 and 0.18, respectively.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2002); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. A view of (I) with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. The suffix A denotes atoms at (?) Please provide missing symmetry code.

Tetraaqua-1κ⁴O-bis(ε-caprolactam-1κO)-µ-cyano-1:2κ²N:C-pentacyano- 2κ⁵C-iron(III)yttrium(III)

Crystal data

[FeY(C6H11NO)2(CN)6(H2O)4]	F(000) = 1228
Mr = 599.26	Dx = 1.508 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 4518 reflections
a = 14.006 (3) Å	θ = 2.4–32.0°
b = 12.951 (3) Å	µ = 2.78 mm^−1
c = 15.011 (3) Å	T = 293 K
β = 104.15 (3)°	Block, yellow
V = 2640.3 (10) Å^3	0.30 × 0.26 × 0.18 mm
Z = 4

Data collection

Make Model CCD area-detector diffractometer	4853 independent reflections
Radiation source: fine-focus sealed tube	3691 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
Detector resolution: 15 × 15 microns pixels mm^-1	θmax = 33.5°, θmin = 2.2°
φ and ω scans	h = −19→20
Absorption correction: multi-scan (SADABS; Bruker, 2000)	k = −16→19
Tmin = 0.445, Tmax = 0.606	l = −22→13
12364 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)] = 0.044	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.087	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0132P)^2 + 5.7178P] where P = (Fo^2 + 2Fc^2)/3
4853 reflections	(Δ/σ)max = 0.002
161 parameters	Δρmax = 0.81 e Å^−3
4 restraints	Δρmin = −0.55 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	Occ. (<1)
Y	0.0000	0.77158 (2)	0.2500	0.02047 (8)
Fe	0.0000	1.19406 (3)	0.2500	0.01897 (10)
O1	0.12658 (14)	0.80234 (15)	0.36757 (14)	0.0413 (5)
O2	0.09388 (15)	0.62302 (15)	0.24751 (18)	0.0571 (7)
H21	0.1527	0.6183	0.2419	0.069*
H20	0.0822	0.5597	0.2553	0.069*
O3	−0.09493 (15)	0.80271 (17)	0.35407 (14)	0.0463 (5)
H30	−0.1511	0.7738	0.3407	0.056*
H31	−0.0658	0.8119	0.4103	0.056*
N1	0.0000	1.4318 (2)	0.2500	0.0479 (9)
N2	0.0225 (2)	1.1874 (2)	0.45933 (18)	0.0539 (7)
N3	0.22582 (18)	1.1919 (2)	0.2837 (2)	0.0479 (6)
N4	0.0000	0.9570 (2)	0.2500	0.0425 (8)
N5	0.1558 (2)	0.9120 (2)	0.4853 (2)	0.0605 (8)
H5A	0.0943	0.9075	0.4840	0.073*
C1	0.0000	1.3433 (3)	0.2500	0.0306 (7)
C2	0.01371 (18)	1.1917 (2)	0.38158 (19)	0.0314 (5)
C3	0.14200 (18)	1.19343 (18)	0.27128 (18)	0.0285 (5)
C4	0.0000	1.0450 (3)	0.2500	0.0295 (7)
C5	0.2920 (3)	0.8568 (3)	0.4244 (3)	0.0507 (13)	0.824 (10)
H5B	0.3263	0.8257	0.4813	0.061*	0.824 (10)
H5C	0.3006	0.8128	0.3755	0.061*	0.824 (10)
C5'	0.2475 (9)	0.9120 (14)	0.3679 (8)	0.0507 (13)	0.176 (10)
H5'A	0.2660	0.8580	0.3316	0.061*	0.176 (10)
H5'B	0.2093	0.9609	0.3258	0.061*	0.176 (10)
C6	0.3386 (3)	0.9559 (4)	0.4163 (4)	0.0925 (16)
H6A	0.3594	0.9929	0.3690	0.111*	0.176 (10)
H6B	0.3855	0.9012	0.4346	0.111*	0.176 (10)
H6C	0.2956	0.9922	0.3655	0.111*	0.824 (10)
H6D	0.3999	0.9430	0.3991	0.111*	0.824 (10)
C7	0.3590 (3)	1.0280 (3)	0.4956 (3)	0.0793 (13)
H7A	0.3888	1.0900	0.4781	0.095*
H7B	0.4070	0.9961	0.5457	0.095*
C8	0.2714 (4)	1.0590 (4)	0.5303 (4)	0.0952 (17)
H8A	0.2940	1.1043	0.5827	0.114*
H8B	0.2275	1.0989	0.4827	0.114*
C9	0.2150 (3)	0.9768 (4)	0.5574 (3)	0.0839 (14)
H9A	0.1714	1.0073	0.5913	0.101*
H9B	0.2604	0.9323	0.5997	0.101*
C10	0.1851 (2)	0.8600 (2)	0.4224 (2)	0.0444 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Y	0.02200 (14)	0.01577 (14)	0.02371 (15)	0.000	0.00572 (11)	0.000
Fe	0.0189 (2)	0.0149 (2)	0.0240 (2)	0.000	0.00688 (17)	0.000
O1	0.0365 (11)	0.0409 (11)	0.0392 (11)	−0.0055 (8)	−0.0044 (9)	−0.0054 (8)
O2	0.0365 (11)	0.0215 (9)	0.124 (2)	0.0016 (8)	0.0396 (13)	−0.0001 (11)
O3	0.0361 (11)	0.0717 (15)	0.0348 (11)	−0.0177 (10)	0.0158 (9)	−0.0194 (10)
N1	0.061 (2)	0.0219 (16)	0.062 (3)	0.000	0.0188 (19)	0.000
N2	0.0506 (16)	0.082 (2)	0.0309 (13)	−0.0053 (14)	0.0141 (12)	−0.0024 (13)
N3	0.0271 (12)	0.0602 (16)	0.0576 (17)	0.0007 (11)	0.0127 (11)	0.0081 (13)
N4	0.053 (2)	0.0181 (14)	0.056 (2)	0.000	0.0123 (17)	0.000
N5	0.0412 (15)	0.082 (2)	0.0624 (19)	−0.0184 (14)	0.0215 (13)	−0.0323 (16)
C1	0.0330 (18)	0.0220 (16)	0.039 (2)	0.000	0.0126 (15)	0.000
C2	0.0266 (12)	0.0360 (13)	0.0327 (14)	−0.0019 (10)	0.0092 (10)	−0.0021 (11)
C3	0.0260 (12)	0.0266 (11)	0.0338 (13)	−0.0014 (9)	0.0094 (10)	0.0017 (10)
C4	0.0320 (18)	0.0219 (15)	0.0346 (19)	0.000	0.0079 (14)	0.000
C5	0.037 (2)	0.055 (3)	0.061 (3)	−0.0021 (16)	0.0136 (18)	−0.0164 (19)
C5'	0.037 (2)	0.055 (3)	0.061 (3)	−0.0021 (16)	0.0136 (18)	−0.0164 (19)
C6	0.075 (3)	0.104 (4)	0.117 (4)	−0.036 (3)	0.058 (3)	−0.033 (3)
C7	0.058 (2)	0.070 (3)	0.111 (4)	−0.028 (2)	0.022 (2)	−0.025 (3)
C8	0.085 (3)	0.083 (3)	0.120 (4)	−0.021 (3)	0.028 (3)	−0.055 (3)
C9	0.087 (3)	0.103 (3)	0.071 (3)	−0.028 (3)	0.038 (2)	−0.052 (3)
C10	0.0351 (15)	0.0492 (18)	0.0472 (18)	−0.0095 (12)	0.0069 (13)	−0.0121 (14)

Geometric parameters (Å, º)

Y—O1^i	2.211 (2)	N5—C9	1.458 (4)
Y—O1	2.211 (2)	N5—H5A	0.8600
Y—O2	2.3359 (19)	C5—C6	1.458 (5)
Y—O3	2.321 (2)	C5—C10	1.491 (4)
Y—O3^i	2.321 (2)	C5—H5B	0.9600
Y—O2^i	2.3359 (19)	C5—H5C	0.9599
Y—N4	2.401 (3)	C5'—C6	1.422 (9)
Fe—C1	1.933 (3)	C5'—C10	1.496 (9)
Fe—C2	1.937 (3)	C5'—H5'A	0.9599
Fe—C3^i	1.936 (2)	C5'—H5'B	0.9600
Fe—C3	1.936 (2)	C6—C7	1.484 (6)
Fe—C4	1.930 (3)	C6—H6A	0.9600
Fe—C2^i	1.937 (3)	C6—H6B	0.9600
O1—C10	1.256 (3)	C6—H6C	0.9700
O2—H21	0.8500	C6—H6D	0.9700
O2—H20	0.8499	C7—C8	1.501 (6)
O3—H30	0.8495	C7—H7A	0.9700
O3—H31	0.8512	C7—H7B	0.9700
N1—C1	1.146 (4)	C8—C9	1.442 (6)
N2—C2	1.145 (4)	C8—H8A	0.9700
N3—C3	1.143 (3)	C8—H8B	0.9700
N4—C4	1.140 (5)	C9—H9A	0.9700
N5—C10	1.304 (4)	C9—H9B	0.9700
O1^i—Y—O1	159.24 (10)	C6—C5—C10	116.2 (3)
O1^i—Y—O3	91.52 (8)	C6—C5—H5B	107.9
O1—Y—O2	79.43 (8)	C10—C5—H5B	108.1
O1—Y—O3	84.89 (8)	C6—C5—H5C	108.4
O3—Y—O2	124.84 (8)	C10—C5—H5C	108.3
O1—Y—O2^i	118.71 (8)	H5B—C5—H5C	107.6
O1—Y—O3^i	91.52 (8)	C6—C5'—C10	118.1 (8)
O3—Y—O2^i	73.44 (8)	C6—C5'—H5'A	104.4
O2^i—Y—O2	69.09 (10)	C10—C5'—H5'A	104.9
O3^i—Y—O3	159.99 (11)	C6—C5'—H5'B	111.0
O1^i—Y—O2	118.71 (8)	C10—C5'—H5'B	110.5
O3^i—Y—O2	73.44 (8)	H5'A—C5'—H5'B	106.9
O1^i—Y—O3^i	84.89 (8)	C5'—C6—C7	129.4 (8)
O1^i—Y—O2^i	79.43 (8)	C5—C6—C7	119.3 (4)
O3^i—Y—O2^i	124.84 (8)	C5'—C6—H6A	102.6
O1^i—Y—N4	79.62 (5)	C7—C6—H6A	104.2
O1—Y—N4	79.62 (5)	C5'—C6—H6B	108.5
O2—Y—N4	145.46 (5)	C7—C6—H6B	104.5
O3—Y—N4	80.00 (5)	H6A—C6—H6B	105.6
O3^i—Y—N4	80.00 (5)	C5—C6—H6C	106.7
O2^i—Y—N4	145.46 (5)	C7—C6—H6C	106.7
C1—Fe—C2	90.91 (8)	C5—C6—H6D	108.3
C1—Fe—C3	90.24 (7)	C7—C6—H6D	108.2
C3—Fe—C2	89.43 (11)	H6C—C6—H6D	107.0
C4—Fe—C2	89.09 (8)	C6—C7—C8	115.6 (3)
C4—Fe—C3	89.76 (7)	C6—C7—H7A	108.4
C2^i—Fe—C2	178.17 (16)	C8—C7—H7A	108.4
C3^i—Fe—C3	179.52 (14)	C6—C7—H7B	108.4
C4—Fe—C3^i	89.76 (7)	C8—C7—H7B	108.4
C1—Fe—C3^i	90.24 (7)	H7A—C7—H7B	107.4
C4—Fe—C2^i	89.09 (8)	C9—C8—C7	116.8 (4)
C1—Fe—C2^i	90.91 (8)	C9—C8—H8A	108.1
C3^i—Fe—C2^i	89.43 (11)	C7—C8—H8A	108.1
C3—Fe—C2^i	90.57 (11)	C9—C8—H8B	108.1
C3^i—Fe—C2	90.57 (11)	C7—C8—H8B	108.1
C10—O1—Y	153.9 (2)	H8A—C8—H8B	107.3
Y—O2—H21	128.5	C8—C9—N5	117.8 (4)
Y—O2—H20	131.6	C8—C9—H9A	107.9
H21—O2—H20	99.7	N5—C9—H9A	107.9
Y—O3—H30	114.5	C8—C9—H9B	107.9
Y—O3—H31	118.5	N5—C9—H9B	107.9
H30—O3—H31	119.1	H9A—C9—H9B	107.2
C10—N5—C9	127.8 (3)	O1—C10—N5	120.8 (3)
C10—N5—H5A	116.1	O1—C10—C5	119.2 (3)
C9—N5—H5A	116.1	N5—C10—C5	119.4 (3)
N2—C2—Fe	178.1 (3)	O1—C10—C5'	106.5 (5)
N3—C3—Fe	179.2 (2)	N5—C10—C5'	119.5 (7)

Symmetry code: (i) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H21···N3^ii	0.85	2.07	2.823 (3)	148
O2—H20···N1^iii	0.85	2.01	2.809 (3)	157
O3—H30···N3^iv	0.85	2.03	2.861 (3)	167
O3—H31···N2^v	0.85	1.90	2.739 (3)	168
N5—H5A···N2^v	0.86	2.36	3.098 (4)	144

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