Potassium bis(ethylenediamine)­copper(II) ferricyanide

The title compound, potassium bis(ethylenediamine-N,N')copper(II) hexacyanoferrate(III), K[Cu(C₂H₈N₂)₂]-[Fe(CN)₆], contains [Cu(en)₂]²⁺ and [Fe(CN)₆]^3- complex ions, where en is ethylenediamine. The Fe^III and K⁺ ions lie on twofold axes and the Cu^II atom lies on an inversion center. The [Cu(en)₂]²⁺ ion has square-planar coordination with a mean Cu-N distance of 1.992 (2) Å and the [Fe(CN)₆]^3- ion has distorted octahedral coordination with a mean Fe-C distance of 1.947 (2) Å.

S1. Comment

The crystal engineering of two- and three-dimensional polymers is of current interest not only from the theoretical aspect related to the topologies of novel networks with inner cavities and channels (Hoskins & Robson, 1990; Carlucci et al., 1995; Yaghi & Li, 1995; Black et al., 1996), but also because of the potential applications of such complexes in catalysis (Fujita et al., 1994), host–guest chemistry (Yaghi et al., 1997) and molecular electronics (Fallah et al., 1996; Miyasaka et al., 1996). One of the most successful strategies leading to extended heterometallic supramolecular architecture is the use of metal cations such as Cu²⁺ or its coordinated ions to link relatively stable coordination anions such as [Fe(CN)₆]³⁻ containing potential bridging units (the cyanide groups). Such synthetic strategy has provided many complexes in the literature with extended networks possessing interesting photochemical, electrochemical and magnetic properties.

Cyanide is an ambidentate ligand capable of simultaneously bridging two metal centers in an asymmetric mode. Although the extended structure of Prussian blue with cyanide C-bonded to low-spin Fe^II and N-bonded to high-spin Fe^III has been known for a long time (Buser et al., 1977), the cyano-bridged polymeric materials have not received much attention until recently. Prussian blue analogues (Miyasaka et al., 1995; Ohba et al., 1994, 1995; Mallah et al., 1995) derived from the assembly of the anionic block [M(CN)₆]³⁻ (M = Cr, Fe, Mn etc.) and the cationic fragment (M'L_m)ⁿ⁺ (M' = Cu, Ni, Co, Fe etc.; L is a neutral terminal-N-containing ligand; m,n = 1, 2 or 3) having one to four unsaturated coordination sites, are potential molecular-based magnets, some of which are magnetically ordered at high temperature.

Due to the aforementioned interest, we have reacted [Cu(en)₂]²⁺ with [Fe(CN)₆]³⁻ (en is ethylenediamine). However, with a CuCl₂:Fe^III molar ratio of 1.5:1, in the presence of en, an ionic complex with discrete cations and anions was formed, instead of polymeric coordination complexes with extended networks such as formed with various ratios of CuBr₂:Fe^III (Zhang, 1999). It is possible that the larger Br⁻ ion assisted in the network formation. This ionic title complex, (I), contains [Cu(en)₂]²⁺ cations and [Fe(CN)₆]³⁻ anions with one K⁺ ion to balance the ionic charge and also template the crystal lattice (Fig. 1). The [Cu(en)₂]²⁺ cation is planar, with Cu²⁺ chelated by two en ligands with an average Cu—N distance of 1.992 (2) Å and an N—Cu—N bite angle of 84.97 (8)°. The [Fe(CN)₆]³⁻ anion is a slightly distorted octahedron with all Fe—C distances nearly equivalent [average 1.947 (2) Å]. However, only one of the trans-C—Fe—C angles is close to 180° [C4—Fe—C4(-x, y 1/2 − z) 179.48 (10)°], while the other two deviate by 6.55 (6)° from linearity (Fig. 2). \sch

Each Fe center in the anions is C-bonded to six cyanide ions, which are weakly bound to five different K⁺ ions at the N-ends [average K···N 2.84 (3) Å]. The K···N—C—Fe pathways are of two kinds, one is quasi-linear with an average K···N—C angle of 176.1° (Morpurgo et al., 1980, 1981), while the other is non-linear with an average K···N—C angle of 85.2° (Ibrahim et al., 1998). The [Cu(en)₂]²⁺ cations are thus located diagonally within the loose cubic cavities formed by six [Fe(CN)₆]³⁻ anions through weak N···K interactions, with a Cu···N(1 − x, y, 1/2 − z) distance of 2.8604 (8) Å.

S2. Experimental

To an aqueous solution (20 ml) containing K₃[Fe(CN)]₆ (0.281 g, 1.0 mmol) was added CuCl₂^.2H₂O (0.256 g, 1.5 mmol) with stirring at room temperature, followed by the addition of en (0.180 g, 3.0 mmol). After stirring for 10 min, the resulting dark solution was evaporated at room temperature for a week, giving crystalline plates of the title complex in 60% yield. Analysis calculated for C₁₀H₁₆CuFeKN₁₀: C 27.6, H 3.7, N 32.2%; found: C 27.7, H 3.7, N 32.3%.

S3. Refinement

The H atoms were located in difference maps, though they were later fixed in idealized geometries and allowed to ride. The C1 and C2 atoms are disordered over two positions and were refined with half occupancies.

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997a); molecular graphics: SHELXTL/PC (Sheldrick, 1997b); software used to prepare material for publication: SHELXTL/PC.

Figures

	Fig. 1. The molecular structure of K[Cu(en)2][Fe(CN)6], with displacement ellipsoids at the 30% probability level.
	Fig. 2. The packing of the cations and anions of the complex K[Cu(en)2][Fe(CN)6], showing the weak interactions between K and N, and between Cu and N.

Potassium Bis(ethylenediamine)copper(II) Ferricyanide

Crystal data

K[Cu(C2H8N2)2][FeC6N6]	F(000) = 880
Mr = 434.82	Dx = 1.733 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.428 (1) Å	Cell parameters from 31 reflections
b = 16.863 (1) Å	θ = 3.0–16.5°
c = 11.869 (1) Å	µ = 2.41 mm^−1
β = 98.86 (1)°	T = 295 K
V = 1666.7 (3) Å^3	Rectangular, black
Z = 4	0.40 × 0.32 × 0.30 mm

Data collection

Siemens P4 diffractometer	1856 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.013
Graphite monochromator	θmax = 29°, θmin = 3.0°
ω scans	h = −1→11
Absorption correction: ψ scan (North et al., 1968)	k = −1→22
Tmin = 0.813, Tmax = 0.921	l = −16→15
2601 measured reflections	3 standard reflections every 97 reflections
2206 independent reflections	intensity decay: 2.7%

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)] = 0.027	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.068	H-atom parameters constrained
S = 0.97	Calculated w = 1/[σ^2(Fo^2) + (0.0423P)^2] where P = (Fo^2 + 2Fc^2)/3
2206 reflections	(Δ/σ)max = 0.001
107 parameters	Δρmax = 0.46 e Å^−3
4 restraints	Δρmin = −0.55 e Å^−3

Special details

Experimental. The scan speed was variable in the range 4–60° min⁻¹ in ω. Background measurement used a stationary crystal and stationary counter at the beginning and end of the scan, each for 25% of the total scan time.

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)
Fe	0	0.384388 (19)	0.25	0.01833 (10)
Cu	0.5	0.5	0	0.03694 (12)
K	0	0.35976 (3)	−0.25	0.02618 (13)
N1	0.6159 (2)	0.41481 (11)	−0.07077 (15)	0.0383 (4)
H1A	0.5860	0.4151	−0.1469	0.046*
H1B	0.7224	0.4233	−0.0557	0.046*
N2	0.3797 (2)	0.41230 (11)	0.05942 (18)	0.0482 (5)
H2A	0.4139	0.4058	0.1345	0.058*
H2B	0.2743	0.4240	0.0496	0.058*
C1	0.5767 (8)	0.3370 (4)	−0.0236 (6)	0.0448 (17)	0.50
H1C	0.6478	0.3269	0.0473	0.054*	0.50
H1D	0.5913	0.2951	−0.0769	0.054*	0.50
C2	0.4058 (7)	0.3381 (3)	−0.0025 (5)	0.0424 (13)	0.50
H2C	0.3334	0.3361	−0.0744	0.051*	0.50
H2D	0.3849	0.2924	0.0426	0.051*	0.50
C1'	0.5356 (11)	0.3386 (4)	−0.0632 (6)	0.060 (3)	0.50
H1'1	0.6140	0.2961	−0.0572	0.072*	0.50
H1'2	0.4584	0.3300	−0.1316	0.072*	0.50
C2'	0.45228 (9)	0.33810 (4)	0.03847 (6)	0.060 (2)	0.50
H2'1	0.3699	0.2975	0.0283	0.072*	0.50
H2'2	0.5291	0.3240	0.1050	0.072*	0.50
N3	0.26267 (9)	0.25630 (4)	0.25372 (6)	0.0498 (5)
N4	−0.00596 (9)	0.38299 (4)	−0.01138 (6)	0.0389 (4)
N5	0.27505 (9)	0.50785 (4)	0.29361 (6)	0.0394 (4)
C3	0.16565 (9)	0.30319 (4)	0.25536 (6)	0.0287 (4)
C4	−0.00501 (9)	0.38372 (4)	0.08530 (6)	0.0253 (4)
C5	0.17078 (9)	0.46323 (4)	0.27407 (6)	0.0244 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe	0.01747 (18)	0.02081 (17)	0.01704 (17)	0.000	0.00366 (12)	0.000
Cu	0.0302 (2)	0.0345 (2)	0.0516 (2)	−0.00179 (14)	0.02375 (17)	−0.00465 (15)
K	0.0278 (3)	0.0280 (3)	0.0234 (3)	0.000	0.0059 (2)	0.000
N1	0.0316 (9)	0.0482 (10)	0.0372 (9)	0.0079 (8)	0.0121 (7)	0.0007 (8)
N2	0.0443 (11)	0.0513 (12)	0.0546 (12)	−0.0135 (9)	0.0251 (9)	−0.0101 (9)
C1	0.057 (4)	0.039 (3)	0.039 (4)	0.004 (3)	0.006 (3)	−0.007 (3)
C2	0.044 (3)	0.035 (3)	0.048 (3)	−0.008 (2)	0.004 (3)	−0.007 (2)
C1'	0.078 (6)	0.046 (4)	0.061 (5)	−0.017 (4)	0.028 (4)	−0.030 (4)
C2'	0.063 (5)	0.048 (3)	0.073 (5)	0.012 (3)	0.021 (4)	0.026 (3)
N3	0.0509 (13)	0.0523 (12)	0.0458 (12)	0.0251 (11)	0.0067 (10)	−0.0013 (10)
N4	0.0381 (11)	0.0557 (12)	0.0234 (9)	−0.0018 (8)	0.0057 (7)	−0.0013 (7)
N5	0.0347 (10)	0.0397 (10)	0.0446 (11)	−0.0113 (8)	0.0085 (8)	−0.0067 (8)
C3	0.0296 (10)	0.0319 (9)	0.0248 (9)	0.0048 (8)	0.0044 (8)	−0.0002 (7)
C4	0.0190 (8)	0.0310 (9)	0.0261 (9)	−0.0015 (7)	0.0040 (7)	0.0002 (7)
C5	0.0244 (9)	0.0263 (8)	0.0231 (8)	0.0008 (7)	0.0059 (7)	−0.0002 (6)

Geometric parameters (Å, º)

Fe—C3^i	1.9450 (17)	K—N5^vii	3.2002 (18)
Fe—C3	1.9450 (17)	K—C5^vi	3.3054 (17)
Fe—C5	1.9482 (17)	K—C5^vii	3.3054 (17)
Fe—C5^i	1.9482 (16)	N1—C1'	1.461 (6)
Fe—C4	1.9485 (16)	N1—C1	1.481 (6)
Fe—C4^i	1.9485 (16)	N2—C2	1.450 (5)
Cu—N2	1.9905 (17)	N2—C2'	1.478 (3)
Cu—N2^ii	1.9905 (17)	C1—C2	1.487 (7)
Cu—N1	1.9943 (15)	C1'—C2'	1.477 (7)
Cu—N1^ii	1.9943 (16)	N3—C3	1.140 (2)
K—N3^iii	2.8076 (16)	N3—K^iv	2.8076 (16)
K—N3^iv	2.8076 (16)	N4—C4	1.147 (2)
K—N4	2.8678 (14)	N5—C5	1.154 (2)
K—N4^v	2.8678 (14)	N5—K^vii	3.2002 (18)
K—N5^vi	3.2002 (18)	C5—K^vii	3.3054 (17)
C3^i—Fe—C3	90.93 (11)	N4^v—K—N5^vii	82.34 (5)
C3^i—Fe—C5	173.45 (6)	N5^vi—K—N5^vii	91.66 (6)
C3—Fe—C5	87.99 (7)	N3^iii—K—C5^vi	158.57 (5)
C3^i—Fe—C5^i	87.99 (7)	N3^iv—K—C5^vi	109.27 (5)
C3—Fe—C5^i	173.45 (6)	N4—K—C5^vi	82.17 (5)
C5—Fe—C5^i	93.80 (10)	N4^v—K—C5^vi	83.55 (5)
C3^i—Fe—C4	93.35 (7)	N5^vi—K—C5^vi	20.36 (4)
C3—Fe—C4	86.28 (7)	N5^vii—K—C5^vi	71.32 (4)
C5—Fe—C4	93.03 (7)	N3^iii—K—C5^vii	109.27 (5)
C5^i—Fe—C4	87.33 (7)	N3^iv—K—C5^vii	158.57 (5)
C3^i—Fe—C4^i	86.28 (7)	N4—K—C5^vii	83.55 (5)
C3—Fe—C4^i	93.35 (7)	N4^v—K—C5^vii	82.17 (5)
C5—Fe—C4^i	87.33 (7)	N5^vi—K—C5^vii	71.32 (4)
C5^i—Fe—C4^i	93.03 (7)	N5^vii—K—C5^vii	20.36 (4)
C4—Fe—C4^i	179.48 (10)	C5^vi—K—C5^vii	50.98 (6)
N2—Cu—N2^ii	180.0	C1'—N1—C1	20.8 (4)
N2—Cu—N1	84.97 (8)	C1'—N1—Cu	110.6 (4)
N2^ii—Cu—N1	95.03 (8)	C1—N1—Cu	108.9 (3)
N2—Cu—N1^ii	95.03 (8)	C2—N2—C2'	22.2 (3)
N2^ii—Cu—N1^ii	84.97 (8)	C2—N2—Cu	108.8 (3)
N1—Cu—N1^ii	180.0	C2'—N2—Cu	111.3 (3)
N3^iii—K—N3^iv	91.39 (8)	N1—C1—C2	108.3 (5)
N3^iii—K—N4	87.65 (5)	N2—C2—C1	109.3 (5)
N3^iv—K—N4	103.50 (5)	N1—C1'—C2'	112.4 (6)
N3^iii—K—N4^v	103.50 (5)	C1'—C2'—N2	111.0 (6)
N3^iv—K—N4^v	87.65 (5)	C3—N3—K^iv	179.67 (17)
N4—K—N4^v	164.17 (8)	C4—N4—K	172.55 (16)
N3^iii—K—N5^vi	169.85 (5)	C5—N5—K^vii	84.97 (13)
N3^iv—K—N5^vi	89.37 (5)	N3—C3—Fe	177.14 (16)
N4—K—N5^vi	82.34 (5)	N4—C4—Fe	179.02 (15)
N4^v—K—N5^vi	86.65 (5)	N5—C5—Fe	176.39 (16)
N3^iii—K—N5^vii	89.37 (5)	N5—C5—K^vii	74.68 (12)
N3^iv—K—N5^vii	169.85 (5)	Fe—C5—K^vii	107.61 (6)
N4—K—N5^vii	86.65 (5)
N2—Cu—N1—C1'	10.9 (4)	N5^vii—K—N4—C4	144.8 (10)
N2^ii—Cu—N1—C1'	−169.1 (4)	C5^vi—K—N4—C4	−143.6 (10)
N1^ii—Cu—N1—C1'	68 (100)	C5^vii—K—N4—C4	165.0 (10)
N2—Cu—N1—C1	−11.2 (3)	K^iv—N3—C3—Fe	−104 (23)
N2^ii—Cu—N1—C1	168.8 (3)	C3^i—Fe—C3—N3	100 (4)
N1^ii—Cu—N1—C1	46 (100)	C5—Fe—C3—N3	−86 (4)
N2^ii—Cu—N2—C2	−162 (100)	C5^i—Fe—C3—N3	20 (4)
N1—Cu—N2—C2	−15.4 (3)	C4—Fe—C3—N3	7 (4)
N1^ii—Cu—N2—C2	164.6 (3)	C4^i—Fe—C3—N3	−174 (4)
N2^ii—Cu—N2—C2'	−138 (100)	K—N4—C4—Fe	59 (9)
N1—Cu—N2—C2'	8.0 (3)	C3^i—Fe—C4—N4	−115 (9)
N1^ii—Cu—N2—C2'	−172.0 (3)	C3—Fe—C4—N4	−25 (9)
C1'—N1—C1—C2	−63.4 (16)	C5—Fe—C4—N4	63 (9)
Cu—N1—C1—C2	35.0 (5)	C5^i—Fe—C4—N4	157 (9)
C2'—N2—C2—C1	−61.3 (13)	C4^i—Fe—C4—N4	−70 (9)
Cu—N2—C2—C1	39.1 (5)	K^vii—N5—C5—Fe	−130 (2)
N1—C1—C2—N2	−49.2 (6)	C3^i—Fe—C5—N5	23 (3)
C1—N1—C1'—C2'	61.1 (14)	C3—Fe—C5—N5	−57 (2)
Cu—N1—C1'—C2'	−28.0 (8)	C5^i—Fe—C5—N5	129 (2)
N1—C1'—C2'—N2	35.0 (10)	C4—Fe—C5—N5	−144 (2)
C2—N2—C2'—C1'	62.5 (12)	C4^i—Fe—C5—N5	36 (2)
Cu—N2—C2'—C1'	−25.3 (8)	C3^i—Fe—C5—K^vii	−105.7 (6)
N3^iii—K—N4—C4	55.3 (10)	C3—Fe—C5—K^vii	173.69 (6)
N3^iv—K—N4—C4	−35.5 (11)	C5^i—Fe—C5—K^vii	0.0
N4^v—K—N4—C4	−169.3 (10)	C4—Fe—C5—K^vii	87.52 (6)
N5^vi—K—N4—C4	−123.0 (10)	C4^i—Fe—C5—K^vii	−92.86 (6)

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