Bis­[μ-3{5}-(2-pyridyl)­pyrazolido]­bis­[(aceto­nitrile)copper(II)] diperchlorate

The title compound, [Cu₂(C₈H₆N₃)₂(C₂H₃N)₂](ClO₄)₂, con­tains a centrosymmetric dinuclear dication, with square-pyrami­dal Cu^II centres linked by two 1,2-pyrazolide bridging groups. There is a weak apical interaction between each Cu ion and a perchlorate O atom.

S1. Comment

Several polydentate ligands derived from 3-(2-pyridyl)pyrazol-1-yl moieties linked by a monoatomic spacer have been prepared by McCleverty and Ward (Ward et al., 2001). Of particular use have been the compounds R₂BH₂^- (Bardwell et al., 1997; Jones et al., 1997; Fleming, Psillakis, Couchman et al., 1998; Armaroli et al., 1999), R₂CH₂ (Mann et al., 1998), R₂PO₂^- (Psillakis et al., 1997) and R₂P{O}{S}^- (Fleming, Psillakis, Jeffrey et al., 1998), where R is 3-(2-pyridyl)pyrazol-1-yl. These ligands have afforded several luminescent lanthanide complexes (Bardwell et al., 1997; Armaroli et al., 1999), as well as a variety of high nuclearity coordination arrays (Jones et al., 1997; Psillakis et al., 1997). We have been employing bis(pyrazol-1-yl) ketone derivatives as organic synthetic intermediates, and so decided to investigate the complex chemistry of the new derivative bis[3-(2-pyridyl)pyrazol-1-yl] ketone (i.e. R₂C═O; L). Unfortunately, however, we have found that the sensitivity of the bis(pyrazol-1-yl) ketone moiety towards hydrolysis is increased upon coordination to transition ions, so that reaction of L with metal salts most often yields products containing 3{5}-(2-pyridyl)pyrazole (HL') as ligand. We report here the crystal structure of one such product, (I), which we isolated from the reaction of L with Cu(ClO₄)₂·6H₂O. Two other, tetrameric Cu^II complexes of L'^- have been reported previously (Jeffrey et al., 1997; Mann et al., 1999), while two dimeric complexes closely related to (I), containing methylated derivatives of L'^-, have also been structurally characterized (Singh et al., 1998; Satake et al., 2000).

The asymmetric unit of (I) contains half a dimeric dication lying across the crystallographic inversion centre and a perchlorate anion on a general position. The [Cu₂(µ-L')₂]²⁺ portion of the molecule is almost perfectly planar. The NCMe ligand is coordinated in an almost perfectly linear fashion [Cu—N1C—C2C = 176.0 (2)°], but is displaced by 19.38 (8)° out of the least-squares plane formed from the atoms of the [CuL']⁺ unit. This distortion is a consequence of the close intramolecular contacts N1C···H6B = 2.57 Å and N1C···H3Aⁱ = 2.63 Å [symmetry code: (i) 1 - x, 1 - y, 1 - z]. These values are slightly shorter than the sum of the van der Waals radii of H (1.2 Å) and N (1.5 Å; Pauling, 1960). There is a long apical interaction between Cu and O1A of the perchlorate anion, leading to a distorted square-pyramidal geometry at Cu. The τ index of Addison and Reedijk for (I) is 0.32, which is closer to the ideal value of 0 for a square pyramid than to the value of 1 expected for a trigonal bipyramid (Addison et al., 1984). The Cu···Cuⁱ distance is 3.9247 (6) Å.

The molecules in the crystal are arranged into stacks by translational symmetry parallel to the crystallographic a direction. Neighbouring molecules in the stacks are coplanar by symmetry, separated by 3.374 (6) Å, and aligned such that a pyridine ring of one molecule overlies a five-membered Cu—N—C—C—N chelate ring of its neighbour. The offset of the centroids of the two overlying L'^- ligands is 0.884 (9) Å, while the centroids of the pyridine rings of the two interacting ligands are offset by 2.775 (9) Å. This latter parameter, and the intermolecular spacing, are typical values for an attractive π–π interaction (Hunter & Sanders, 1990). There are no other noteworthy intermolecular contacts in the lattice.

S2. Experimental

Bis[3-(2-pyridyl)pyrazol-1-yl] ketone (L) was prepared as follows. A solution of 3{5}-(2-pyridyl)pyrazole (HL'; 5 g, 0.034 mol), phosgene (8.4 ml of a 2 M solution in toluene) and NEt₃ (3.4 g, 0.034 mol) in tetrahydrofuran (150 ml) was stirred under N₂ at 293 K for 1 h, affording a voluminous white precipitate. The solution was filtered and evaporated to dryness, leaving L as a white solid in >98% purity by NMR. This product was used for the complexation reaction without further purification. ¹H NMR (CDCl₃): δ 7.27 (d, 2.1 Hz), 7.32 (ddd, 7.8, 4.8, 0.8 Hz, 2H), 7.80 (ddd, 8.0, 7.8, 1.0 Hz, 2H), 8.20 (ddd, 8.0, 2.0, 0.8 Hz, 2H), 8.67 (ddd, 4.8, 2.0, 1.0 Hz, 2H), 8.82 (d, 2.1 Hz, 2H) p.p.m. IR (nujol): 1739 cm^-1. EI MS: m/z = 316 [M]⁺, 172 [M - L']⁺, 145 [L'H]⁺. A solution of L (0.25 g, 0.08 mmol) and Cu(ClO₄)₂·6H₂O (0.31 g, 0.08 mmol) in MeOH (30 ml) was stirred at 293 K for 30 min. The solution was filtered and evaporated to dryness. The blue solid residue was extracted with MeCN. Diffusion of Et₂O vapour into the resultant deep blue solution yielded deep blue crystals of (I), together with an unidentified sticky white residue.

S3. Refinement

All H atoms were placed in calculated positions and refined using a riding model, except for the acetonitrile H atoms, which were located in a Fourier map and refined as an idealized group based on these initial coordinates. The constraints employed for the final refinement were: C—H = 0.95 Å and U_iso = 1.2U_eq(C) for all sp² H atoms, and C—H = 0.98 Å and U_iso = 1.5U_eq(C) for the methyl H atoms.

Computing details

Data collection: COLLECT (Nonius, 1999); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEX (McArdle, 1995); software used to prepare material for publication: local program.

Figures

Fig. 1. The molecular structure of (I), showing 50% probability displacement ellipsoids and the atom-numbering scheme employed. H atoms have arbitrary radii and those referred to in the text are labelled. [Symmetry code: (i) 1 - x, 1 - y, 1 - z.]

Bis[µ-3{5}-(2-pyridyl)pyrazolido]bis[(acetonitrile)copper(II)] diperchlorate

Crystal data

[Cu2(C2H3N)2(C8H6N3)2](ClO4)2	F(000) = 700
Mr = 696.40	Dx = 1.811 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.9977 (3) Å	Cell parameters from 12294 reflections
b = 15.9230 (6) Å	θ = 2.9–27.5°
c = 12.1212 (4) Å	µ = 1.94 mm^−1
β = 124.194 (2)°	T = 150 K
V = 1276.77 (8) Å^3	Square prism, dark blue
Z = 2	0.21 × 0.20 × 0.16 mm

Data collection

Nonius KappaCCD diffractometer	2913 independent reflections
Radiation source: sealed tube	2563 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.052
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 2.9°
Area–detector scans	h = −10→10
Absorption correction: multi-scan (Blessing, 1995)	k = −20→19
Tmin = 0.686, Tmax = 0.747	l = −15→15
12294 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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.094	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.037P)^2 + 1.2569P] where P = (Fo^2 + 2Fc^2)/3
2913 reflections	(Δ/σ)max = 0.001
181 parameters	Δρmax = 0.49 e Å^−3
0 restraints	Δρmin = −0.63 e Å^−3

Special details

Experimental. Detector set at 30 mm from sample with different 2theta offsets 1 degree phi exposures for chi=0 degree settings 1 degree omega exposures for chi=90 degree settings

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. No disorder was detected during refinement. All non-H atoms were refined anisotropically and no restraints were applied.

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

	x	y	z	Uiso*/Ueq
Cu	0.46585 (5)	0.512659 (19)	0.64729 (3)	0.02755 (12)
N1A	0.3234 (3)	0.44685 (13)	0.4831 (2)	0.0286 (4)
N2A	0.3346 (3)	0.43544 (14)	0.3760 (2)	0.0301 (5)
C3A	0.1768 (4)	0.38578 (18)	0.2878 (3)	0.0340 (6)
H3A	0.1485	0.3682	0.2040	0.041*
C4A	0.0636 (4)	0.36451 (18)	0.3370 (3)	0.0341 (6)
H4A	−0.0543	0.3305	0.2960	0.041*
C5A	0.1612 (4)	0.40411 (16)	0.4603 (3)	0.0296 (5)
N1B	0.2562 (3)	0.45811 (14)	0.6689 (2)	0.0302 (5)
C2B	0.1256 (4)	0.40791 (16)	0.5660 (3)	0.0294 (5)
C3B	−0.0275 (4)	0.36447 (17)	0.5630 (3)	0.0364 (6)
H3B	−0.1177	0.3294	0.4897	0.044*
C4B	−0.0453 (5)	0.37361 (18)	0.6697 (3)	0.0397 (7)
H4B	−0.1492	0.3450	0.6701	0.048*
C5B	0.0889 (4)	0.42465 (18)	0.7755 (3)	0.0371 (6)
H5B	0.0788	0.4313	0.8495	0.045*
C6B	0.2375 (4)	0.46568 (18)	0.7721 (3)	0.0333 (6)
H6B	0.3301	0.5005	0.8451	0.040*
N1C	0.5188 (4)	0.59957 (15)	0.7831 (2)	0.0366 (5)
C2C	0.5434 (4)	0.65210 (18)	0.8540 (3)	0.0328 (6)
C3C	0.5767 (5)	0.71882 (19)	0.9459 (3)	0.0414 (7)
H3C1	0.5020	0.7064	0.9861	0.062*
H3C2	0.5293	0.7722	0.8975	0.062*
H3C3	0.7214	0.7229	1.0161	0.062*
Cl1	0.74626 (9)	0.36234 (4)	0.90364 (6)	0.03138 (16)
O1	0.6949 (4)	0.40986 (18)	0.7876 (3)	0.0633 (8)
O2	0.6157 (4)	0.29075 (16)	0.8613 (3)	0.0616 (7)
O3	0.9525 (3)	0.33450 (14)	0.9693 (2)	0.0438 (5)
O4	0.7192 (4)	0.41211 (17)	0.9904 (2)	0.0575 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.02961 (19)	0.02659 (18)	0.02772 (19)	−0.00017 (12)	0.01688 (15)	−0.00089 (12)
N1A	0.0321 (11)	0.0274 (11)	0.0292 (11)	0.0026 (9)	0.0189 (9)	0.0015 (9)
N2A	0.0328 (11)	0.0311 (11)	0.0258 (11)	0.0001 (9)	0.0162 (9)	−0.0017 (9)
C3A	0.0328 (13)	0.0363 (14)	0.0304 (14)	−0.0010 (11)	0.0162 (11)	−0.0045 (11)
C4A	0.0294 (13)	0.0344 (14)	0.0361 (15)	−0.0026 (11)	0.0169 (12)	−0.0033 (11)
C5A	0.0307 (13)	0.0261 (13)	0.0337 (13)	0.0029 (10)	0.0191 (11)	0.0025 (10)
N1B	0.0313 (11)	0.0281 (11)	0.0327 (12)	0.0027 (9)	0.0190 (10)	0.0018 (9)
C2B	0.0308 (13)	0.0259 (12)	0.0333 (13)	0.0055 (10)	0.0192 (11)	0.0033 (10)
C3B	0.0382 (15)	0.0295 (14)	0.0457 (16)	−0.0016 (11)	0.0261 (13)	−0.0021 (12)
C4B	0.0446 (16)	0.0338 (15)	0.0523 (18)	−0.0021 (12)	0.0343 (15)	0.0028 (13)
C5B	0.0451 (16)	0.0368 (14)	0.0425 (16)	0.0041 (12)	0.0326 (14)	0.0053 (12)
C6B	0.0381 (14)	0.0337 (14)	0.0329 (14)	0.0014 (11)	0.0229 (12)	−0.0006 (11)
N1C	0.0395 (13)	0.0358 (13)	0.0393 (13)	−0.0026 (10)	0.0251 (11)	−0.0020 (10)
C2C	0.0345 (14)	0.0334 (14)	0.0333 (14)	−0.0016 (11)	0.0208 (12)	0.0003 (11)
C3C	0.0500 (17)	0.0390 (16)	0.0388 (16)	−0.0050 (13)	0.0270 (14)	−0.0085 (12)
Cl1	0.0335 (3)	0.0335 (3)	0.0279 (3)	0.0029 (2)	0.0178 (3)	0.0026 (2)
O1	0.0560 (14)	0.0840 (18)	0.0649 (16)	0.0363 (13)	0.0432 (13)	0.0494 (14)
O2	0.0594 (15)	0.0506 (14)	0.0763 (18)	−0.0185 (12)	0.0390 (14)	−0.0204 (13)
O3	0.0346 (10)	0.0522 (13)	0.0399 (11)	0.0126 (9)	0.0182 (9)	0.0105 (10)
O4	0.0550 (14)	0.0708 (16)	0.0488 (13)	0.0030 (12)	0.0304 (12)	−0.0214 (12)

Geometric parameters (Å, º)

Cu—N1A	1.952 (2)	C3B—C4B	1.386 (4)
Cu—N2A^i	1.953 (2)	C3B—H3B	0.9500
Cu—N1B	2.031 (2)	C4B—C5B	1.382 (4)
Cu—N1C	2.005 (2)	C4B—H4B	0.9500
Cu—O1	2.330 (2)	C5B—C6B	1.378 (4)
N1A—C5A	1.349 (3)	C5B—H5B	0.9500
N1A—N2A	1.362 (3)	C6B—H6B	0.9500
N2A—C3A	1.358 (3)	N1C—C2C	1.135 (4)
C3A—C4A	1.378 (4)	C2C—C3C	1.451 (4)
C3A—H3A	0.9500	C3C—H3C1	0.9800
C4A—C5A	1.389 (4)	C3C—H3C2	0.9800
C4A—H4A	0.9500	C3C—H3C3	0.9800
C5A—C2B	1.462 (4)	Cl1—O1	1.438 (2)
N1B—C6B	1.346 (3)	Cl1—O2	1.432 (2)
N1B—C2B	1.349 (3)	Cl1—O3	1.441 (2)
C2B—C3B	1.389 (4)	Cl1—O4	1.427 (2)
N1A—Cu—N2A^i	97.80 (9)	N1B—C2B—C5A	113.8 (2)
N1A—Cu—N1C	160.18 (10)	C3B—C2B—C5A	124.0 (2)
N2A^i—Cu—N1C	90.80 (9)	C4B—C3B—C2B	118.3 (3)
N1A—Cu—N1B	81.43 (9)	C4B—C3B—H3B	120.8
N2A^i—Cu—N1B	179.21 (9)	C2B—C3B—H3B	120.8
N1C—Cu—N1B	89.89 (9)	C5B—C4B—C3B	119.6 (3)
N1A—Cu—O1	97.83 (10)	C5B—C4B—H4B	120.2
N2A^i—Cu—O1	91.82 (9)	C3B—C4B—H4B	120.2
N1C—Cu—O1	99.72 (10)	C6B—C5B—C4B	118.9 (3)
N1B—Cu—O1	88.44 (9)	C6B—C5B—H5B	120.5
C5A—N1A—N2A	107.9 (2)	C4B—C5B—H5B	120.5
C5A—N1A—Cu	114.99 (17)	N1B—C6B—C5B	122.3 (3)
N2A—N1A—Cu	136.90 (17)	N1B—C6B—H6B	118.9
C3A—N2A—N1A	107.3 (2)	C5B—C6B—H6B	118.9
C3A—N2A—Cu^i	127.29 (18)	C2C—N1C—Cu	176.0 (2)
N1A—N2A—Cu^i	125.28 (17)	N1C—C2C—C3C	179.4 (4)
N2A—C3A—C4A	110.4 (2)	C2C—C3C—H3C1	109.5
N2A—C3A—H3A	124.8	C2C—C3C—H3C2	109.5
C4A—C3A—H3A	124.8	H3C1—C3C—H3C2	109.5
C3A—C4A—C5A	104.2 (2)	C2C—C3C—H3C3	109.5
C3A—C4A—H4A	127.9	H3C1—C3C—H3C3	109.5
C5A—C4A—H4A	127.9	H3C2—C3C—H3C3	109.5
N1A—C5A—C4A	110.1 (2)	O4—Cl1—O2	108.91 (16)
N1A—C5A—C2B	116.0 (2)	O4—Cl1—O1	110.48 (16)
C4A—C5A—C2B	133.9 (2)	O2—Cl1—O1	108.57 (17)
C6B—N1B—C2B	118.6 (2)	O4—Cl1—O3	111.36 (14)
C6B—N1B—Cu	127.74 (19)	O2—Cl1—O3	109.32 (15)
C2B—N1B—Cu	113.63 (17)	O1—Cl1—O3	108.13 (13)
N1B—C2B—C3B	122.2 (2)	Cl1—O1—Cu	139.36 (14)

Symmetry code: (i) −x+1, −y+1, −z+1.