The one-dimensional structure of Cu(dmen)₂Pd(CN)₄ (dmen is N,N-di­methyl­ethyl­enedi­amine)

The title compound, catena-poly­[[μ-cyano-1:2κ²C:N-dicyano-1κ²C-bis(N,N-di­methyl­ethyl­enedi­amine-2κ²N,N′)­pallad­ium(II)­copper(II)]-μ-cyano-1:2′κ²C:N], [CuPd(CN)₄(C₄H₁₂N₂)₂]_n, consists of infinite quasi-linear chains with all metal positions on centers of symmetry. The paramagnetic [Cu(dmen)₂]²⁺ cations are linked by diamagnetic [Pd(CN)₄]²⁻ anions via bridging cyano groups, which occupy trans positions in both cation and anion, giving rise to 2,2-TT-type chains. The coordination polyhedron of the paramagnetic Cu atom is an octahedron exhibiting typical elongation due to the Jahn–Teller effect, with two longer Cu—N([triple bond]C) bonds in the axial positions [2.5528 (13) Å] and four shorter Cu—N_dmen bonds (dmen is N,N-dimethylethylenediamine) in the equatorial plane [1.9926 (11) and 2.1149 (12) Å]. The Cu—N[triple bond]C angle is 138.03 (12)°. Neighboring chains form weak N—H...NC hydrogen bonds.

S1. Comment

Low-temperature magnetic and thermodynamic studies of Cu(en)₂Ni(CN)₄ (CENC; en is ethylenediamine) indicate that this compound behaves as a two-dimensional magnet (Orendáč et al., 1995). From a structural point of view, this compound is one-dimensional: 2,2-TT chains [for the nomenclature see Černák et al. (2002)] are built up of [Cu(en)₂]²⁺ cations and [Ni(CN)₄]^2- anions linked by bridging cyano groups placed in both the cation and the anion in trans positions. Several studies indicate that hydrogen bonds can mediate magnetic exchange interactions (Goodson et al., 1994; Zhang et al., 1997; Kopinga et al., 1982). It is suggested that in the case of CENC, N—H···N hydrogen bonds may serve as paths of magnetic exchange interactions and thus may be responsible for enhanced magnetic dimensionality of this material. In order to modify the hydrogen-bonding scheme in CENC and thus obtain a better insight into the magnetostructural correlation in this class of compounds, Cu(L_n)₂Ni(CN)₄ (L_n is N, N-dimethylethylenediamine, N-methylethylenediamine and N,N'-dimethylethylenediamine) compounds were previously prepared and structurally characterized (Kuchár et al., 2003). Afterwards, the Ni^II atom was replaced by Pd^II in all of the above-mentioned compounds. The structure and magnetic properties of Cu(en)₂Pd(CN)₂ (CEPC) were described by (Černák et al., 2001), and the preparation, identification and crystal structure of Cu(dmen)₂Pd(CN)₄ (CDPC) are reported here.

The structure of CDPC has 2,2-TT-type chains of composition [–Cu(dmen)₂-NC—Pd(CN)₂—CN–]_n (Fig. 1), and thus this compound is isostructural with the parent CDNC compound and analogous to CENC. The Cu-atom coordination sphere displays the usual axial deformation due to the Jahn–Teller effect, with longer axial bonds. The dmen molecule is coordinated as a bidentate N-donor chelating ligand. Among the two independent Cu—N_dmen coordination bonds the Cu—N1 bond is significantly shorter than the Cu—N2 bond; this may be a consequence of the steric effect of the bulky methyl groups bonded to atom N2. The same effect? was observed in Cu(dmen)Cu(CN)₃ (Colacio et al., 2002) and the analogous CDNC compounds (Kuchár et al., 2003). The corresponding values in CENC are 1.998 (1) and 2.001 (1) Å, respectively (Seitz et al., 2001). The Ni atom in the anion lies on a symmetry center, so the NiC₄ chromophore is exactly planar. Among the four cyano groups, two in trans positions exhibit bridging character. The Cu—N4≡C6 angle is less bent than the corresponding angle in CENC [123.1 (1)°].

The title compound differes from CENC in that two H atoms are replaced with methyl groups, and therefore only two H atoms can be involved in hydrogen bonds. Atom H1A forms a weak hydrogen bond to atom N3 of the terminal cyano group of a neighboring chain (Fig. 2). The observed (N—)H···N distance (2.60 Å) is longer than the analogous distance in CENC (2.32 Å) and comparable to that in CDNC (2.57 Å), suggesting weaker hydrogen-bonding interactions in CDPC and CDNC than in CENC. The second H atom (H1B) is oriented almost perpendicularly (the N—H····A1 angle, where A1 is the midpoint of the cyano group, is 155.8°) to the bridging cyano group of the same neighboring chain at (1 - x, y, z), suggesting weak interaction with the π molecular orbital of the cyano group. This distance (2.67 Å) is at the limit of such interactions (Saenger & Jeffrey, 1991). The distance between the H atom and atom N4 at (1 - x, y, z) is 2.75 Å, but the N atom coordinates weakly to the Cu atom, and thus the C6/N4 cyano group can be considered to be a bridging ligand. The next? shortest distance is that between atom C5 and atom C3 at (1 + x, 1 - y, 1 + z) from a neighboring chain [3.572 (2) Å]; this contact may correspond only to a van der Waals interaction.

Table 2. Hydrogen bonding geometry (A1 is the middlepoint of the bridging cyano group of the neighbouring chain)

S2. Experimental

A solution formed by mixing a 0.1 M warm aqueous solution of CuSO₄ (10 ml, 1 mmol) and dmen (dmen is N,N-dimethylethylenediamine) solution in methanol (10 ml) and water (10 ml) (0.22 ml, 2 mmol), was mixed with a 0.1 M warm aqueous solution of K₂[Pd(CN)₄] (10 ml, 1 mmol). The resulting precipitate was dissolved by addition of a concentrated aqueous solution of ammonia (25%). Finally, the solution was filtered and left for crystallization at room temperature (291 K). The first single crystals appeared as blue plates after one day. IR ν(NH): 3337 (s), 3272 (versus); ν(CH): 2988, 2903 (w), 2851 (w); ν(CN): 2128 (versus); δ(NH₂): 1584 (s); δ(Pd—CN): 379 (s). Analysis found: C 32.42, H 5.43, N 25.08%; calculated: C 32.01, H 5.37, N 24.88%.

S3. Refinement

H atoms were placed in idealized positions and were treated as riding on their parent atoms, with C—H distances of 0.98–0.99 Å. The U_iso values were set at 1.2U_eq of the parent C atom.

Computing details

Data collection: SMART (Bruker 1998); cell refinement: SMART & SAINT (Bruker 1998); data reduction: SHELXTL (Bruker 1998); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Crystal Impact, 2001); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the 2,2-TT-type chain of CDPC, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A view of the structure of CDPC, displaying the hydrogen bonding system.

catena-poly[[µ-cyano-1:2κ²C:N-dicyano-1κ²C-bis(N,N- dimethylethylenediamine-2κ²N,N')palladium(II)copper(II)]-µ-cyano- 1:2'κ²C:N]

Crystal data

[CuPd(CN)4(C4H12N2)2]	F(000) = 454
Mr = 450.33	Dx = 1.778 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 53 reflections
a = 6.6940 (3) Å	θ = 2.0–28.0°
b = 13.8197 (7) Å	µ = 2.34 mm^−1
c = 9.1759 (5) Å	T = 173 K
β = 97.609 (1)°	Plates, blue
V = 841.38 (7) Å^3	0.32 × 0.24 × 0.02 mm
Z = 2

Data collection

Bruker SMART CCD area-detector diffractometer	1926 independent reflections
Radiation source: fine-focus sealed tube	1624 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
φ and ω scans	θmax = 27.5°, θmin = 2.7°
Absorption correction: integration based on measured indexed crystal faces (SHELXTL; Bruker, 1998)	h = −8→8
Tmin = 0.515, Tmax = 0.954	k = −17→17
7247 measured reflections	l = −11→11

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)] = 0.016	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.041	H-atom parameters constrained
S = 1.10	w = 1/[σ^2(Fo^2) + (0.013P)^2 + 0.2936P] where P = (Fo^2 + 2Fc^2)/3
1916 reflections	(Δ/σ)max < 0.001
105 parameters	Δρmax = 0.26 e Å^−3
0 restraints	Δρmin = −0.39 e Å^−3

Special details

Experimental. The IR spectrum was measured by FT—IR spectrometer (Thermo-Nicolet, AVATAR 330 F T—IR). CHN analysis (Carlo-Erba EA 1108 instrument).

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
Pd	0.0000	0.5000	0.0000	0.01787 (6)
Cu	0.5000	0.5000	0.5000	0.01756 (7)
N1	0.63719 (18)	0.46757 (9)	0.32635 (13)	0.0219 (2)
N2	0.42254 (18)	0.35162 (8)	0.49937 (12)	0.0203 (2)
N3	0.3815 (2)	0.37640 (11)	−0.04573 (15)	0.0344 (3)
N4	0.1684 (2)	0.52727 (10)	0.33305 (14)	0.0293 (3)
C1	0.6470 (2)	0.36163 (11)	0.30872 (16)	0.0270 (3)
C2	0.4550 (2)	0.31869 (11)	0.34982 (16)	0.0260 (3)
C3	0.5527 (2)	0.29564 (11)	0.61229 (16)	0.0276 (3)
C4	0.2108 (2)	0.33176 (12)	0.52021 (19)	0.0324 (4)
C5	0.2437 (2)	0.42186 (11)	−0.02776 (15)	0.0229 (3)
C6	0.1063 (2)	0.51843 (10)	0.21121 (16)	0.0219 (3)
H1A	0.5675	0.4946	0.2431	0.026*
H1B	0.7655	0.4929	0.3388	0.026*
H1C	0.7647	0.3353	0.3731	0.032*
H1D	0.6614	0.3452	0.2056	0.032*
H2A	0.3396	0.3389	0.2774	0.031*
H2B	0.4635	0.2472	0.3480	0.031*
H3A	0.5351	0.3197	0.7102	0.041*
H3B	0.6939	0.3030	0.5968	0.041*
H3C	0.5151	0.2271	0.6046	0.041*
H4A	0.1784	0.2641	0.4956	0.049*
H4B	0.1209	0.3742	0.4559	0.049*
H4C	0.1929	0.3439	0.6229	0.049*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0320 (8)	0.0278 (8)	0.0218 (7)	0.0066 (6)	0.0050 (6)	−0.0057 (6)
C2	0.0329 (8)	0.0221 (7)	0.0212 (7)	0.0003 (6)	−0.0023 (6)	−0.0041 (5)
C3	0.0347 (8)	0.0224 (8)	0.0242 (8)	0.0029 (6)	−0.0018 (6)	0.0031 (6)
C4	0.0261 (8)	0.0289 (8)	0.0423 (9)	−0.0048 (6)	0.0053 (7)	0.0082 (7)
C5	0.0264 (7)	0.0267 (8)	0.0155 (7)	−0.0002 (6)	0.0023 (5)	0.0039 (5)
C6	0.0207 (7)	0.0233 (7)	0.0219 (7)	0.0023 (5)	0.0033 (6)	0.0013 (5)
Cu	0.02165 (13)	0.01618 (13)	0.01596 (13)	−0.00046 (9)	0.00661 (9)	−0.00077 (8)
N1	0.0232 (6)	0.0252 (6)	0.0180 (6)	0.0015 (5)	0.0054 (5)	−0.0001 (5)
N2	0.0209 (6)	0.0192 (6)	0.0204 (6)	0.0005 (5)	0.0017 (4)	0.0011 (4)
N3	0.0350 (8)	0.0390 (8)	0.0300 (7)	0.0098 (6)	0.0077 (6)	0.0051 (6)
N4	0.0343 (7)	0.0305 (7)	0.0218 (7)	0.0022 (6)	−0.0010 (5)	0.0000 (5)
Pd	0.01862 (9)	0.02051 (9)	0.01421 (8)	0.00048 (6)	0.00113 (6)	0.00146 (5)

Geometric parameters (Å, º)

Pd—C6	1.9905 (15)	N1—H1B	0.9200
Pd—C6^i	1.9905 (15)	N4—C6	1.1465 (19)
Pd—C5^i	2.0008 (15)	C5—N3	1.1459 (19)
Pd—C5	2.0008 (15)	C1—C2	1.508 (2)
Cu—N1^ii	1.9926 (11)	C1—H1C	0.9900
Cu—N1	1.9926 (11)	C1—H1D	0.9900
Cu—N2^ii	2.1149 (12)	C2—H2A	0.9900
Cu—N2	2.1149 (12)	C2—H2B	0.9900
Cu—N4	2.5528 (13)	C4—H4A	0.9800
Cu—N4^ii	2.5528 (13)	C4—H4B	0.9800
N2—C3	1.4805 (18)	C4—H4C	0.9800
N2—C4	1.4809 (19)	C3—H3A	0.9800
N2—C2	1.4888 (18)	C3—H3B	0.9800
N1—C1	1.4755 (19)	C3—H3C	0.9800
N1—H1A	0.9200
C6—Pd—C6^i	180.00 (8)	C1—N1—H1B	109.7
C6—Pd—C5^i	89.97 (6)	Cu—N1—H1B	109.7
C6^i—Pd—C5^i	90.03 (6)	H1A—N1—H1B	108.2
C6—Pd—C5	90.03 (6)	C6—N4—Cu	138.03 (12)
C6^i—Pd—C5	89.97 (6)	N4—C6—Pd	178.74 (13)
C5^i—Pd—C5	180.00 (7)	N3—C5—Pd	178.83 (14)
N1^ii—Cu—N1	180.0	N1—C1—C2	108.14 (12)
N1^ii—Cu—N2^ii	85.33 (5)	N1—C1—H1C	110.1
N1—Cu—N2^ii	94.67 (5)	C2—C1—H1C	110.1
N1^ii—Cu—N2	94.67 (5)	N1—C1—H1D	110.1
N1—Cu—N2	85.33 (5)	C2—C1—H1D	110.1
N2^ii—Cu—N2	180.0	H1C—C1—H1D	108.4
N1^ii—Cu—N4	89.45 (5)	N2—C2—C1	110.09 (12)
N1—Cu—N4	90.55 (5)	N2—C2—H2A	109.6
N2^ii—Cu—N4	92.98 (4)	C1—C2—H2A	109.6
N2—Cu—N4	87.02 (4)	N2—C2—H2B	109.6
N1^ii—Cu—N4^ii	90.55 (5)	C1—C2—H2B	109.6
N1—Cu—N4^ii	89.45 (5)	H2A—C2—H2B	108.2
N2^ii—Cu—N4^ii	87.02 (4)	N2—C4—H4A	109.5
N2—Cu—N4^ii	92.98 (4)	N2—C4—H4B	109.5
N4—Cu—N4^ii	180.0	H4A—C4—H4B	109.5
C3—N2—C4	107.29 (12)	N2—C4—H4C	109.5
C3—N2—C2	109.95 (11)	H4A—C4—H4C	109.5
C4—N2—C2	108.75 (12)	H4B—C4—H4C	109.5
C3—N2—Cu	112.55 (9)	N2—C3—H3A	109.5
C4—N2—Cu	114.70 (9)	N2—C3—H3B	109.5
C2—N2—Cu	103.49 (8)	H3A—C3—H3B	109.5
C1—N1—Cu	110.04 (9)	N2—C3—H3C	109.5
C1—N1—H1A	109.7	H3A—C3—H3C	109.5
Cu—N1—H1A	109.7	H3B—C3—H3C	109.5
N1—Cu—N2—C3	101.45 (12)	N2^ii—Cu—N1—C1	169.37 (11)
N1^ii—Cu—N2—C3	−78.55 (12)	N4^ii—Cu—N1—C1	82.41 (12)
N4^ii—Cu—N2—C3	12.27 (11)	N4—Cu—N1—C1	−97.59 (12)
N4—Cu—N2—C3	−167.73 (11)	N1—Cu—N4—C6	5.9 (2)
N1—Cu—N2—C4	−135.55 (12)	N1^ii—Cu—N4—C6	−174.1 (2)
N1^ii—Cu—N2—C4	44.45 (12)	N2—Cu—N4—C6	−79.3 (2)
N4^ii—Cu—N2—C4	135.27 (11)	N2^ii—Cu—N4—C6	100.7 (2)
N4—Cu—N2—C4	−44.73 (11)	Cu—N1—C1—C2	36.56 (16)
N1—Cu—N2—C2	−17.26 (10)	C3—N2—C2—C1	−78.38 (17)
N1^ii—Cu—N2—C2	162.74 (10)	C4—N2—C2—C1	164.49 (14)
N4^ii—Cu—N2—C2	−106.44 (10)	Cu—N2—C2—C1	42.10 (14)
N4—Cu—N2—C2	73.56 (10)	N1—C1—C2—N2	−53.88 (17)
N2—Cu—N1—C1	−10.63 (11)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···N3^iii	0.92	2.60	3.3482 (18)	139
N1—H1B···A1^iv	0.92	2.67	3.533 (1)	156

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