Bis{μ-[6-(hydroxy­methyl)-2-pyridyl]­methano­lato-κ³N,O:O}bis{[2,6-bis­(hydroxy­methyl)­pyridine-κ³O,N,O′]copper(II)} di­acetate

The title dinuclear Cu^II complex, [Cu₂(C₇H₈NO₂)₂(C₇H₉NO₂)₂](CH₃COO)₂, has been synthesized by the reaction of Cu(CH₃COO)₂·H₂O with pdmH₂ (pdmH₂ is pyridine-2,6-diyldi­methanol) in the presence of tetra­butyl­ammonium hydro­xide. The title complex contains a centrosymmetric Cu₂O₂ core and each Cu^II atom has distorted octahedral geometry. Molecular [Cu₂(pdmH)₂(pdmH₂)]²⁺ cations are connected by hydrogen bonds involving the CH₃COO⁻ anions, forming one-dimensional chains along the a axis.

S1. Comment

The 2,6-pyridyldimethanolate ligand functions as a bridge through its two O atoms to afford polynuclear metal complexes (Boskovic et al., 2002; Yoo et al., 2000). Our main strategy is to synthesize polynuclear copper complexes using N,O-donor hydroxyalkylpyridyl ligands, because these cluster complexes act as model complexes for active centers of many metalloenzymes (Agnus, 1988) and as supramolecular building blocks for promising magnetic materials (Del Sesto et al., 2000). Less attention has been given to copper complexes based on N,O-donor hydroxyalkylpyridyl ligands. Few mononuclear (Andac et al., 2002; Koman et al., 2000) and dinunclear complexes (Cheng et al., 2002) have been reported. Herein, we report the synthesis and X-ray structure of a new dinuclear Cu^II complex, [Cu₂(pdmH)₂(pdmH₂)₂](CH₃COO)₂, (I), from the reaction of Cu(acetate)₂·H₂O and pdmH₂ (pdmH₂ is pyridine-2.6-diyldimethanol) in the presence of tetrabutylammonium hydroxide.

The complex cation of the title compound comprises a [Cu^II₂(µ₂-O)₂] core, in which the two µ₂-O atoms belong to the bridging pdmH⁻ ligand. As shown in Fig. 1, each Cu^II atom is coordinated by neutral pdmH₂ as a terminal tridentate ligand and anionic pdmH⁻ as a bridging bidentate ligand. The crystallographic inversion center is located in the middle of the [Cu₂O₂] rhombus. In the planar [Cu₂O₂] unit, the Cu—Cu separation and Cu—O—Cu angle are comparable with other known alkoxo-bridged [Cu₂O₂] complexes (Berti et al., 2003; Cheng et al., 2002; Graham et al., 2001). Each Cu atom has a highly distorted octahedral geometry (see Table 1), with acute µ-O—Cu—µ-O and N—Cu—O angles in the [Cu(pdmH₂)] unit, which are similar to those found in other known distorted-octahedral CuO₄N₂ cores containing the pdmH₂ ligand (Andac et al., 2002; Koman et al., 2000). The axial Cu1—O1 [2.358 (2) Å] and Cu1—O2 [2.360 (2) Å] distances are substantially longer than the equatorial Cu—O and Cu—N distances [1.909 (2)–2.094 (2) Å], which indicates severe Jahn–Teller distortion, despite the presumably restraining effects of the chelate rings. The equatorial distances are similar to the corresponding distances in the tetragonally elongated octahedral complex [Cu(C₅H₅NO)₆](NO₃)₂·2H₂O (Wood et al., 1984), while the axial Cu—O bond distances are shorter than the bond lengths of 2.478 (2) Å found in [Cu(C₅H₅NO)₆](NO₃)₂·2H₂O and 2.548 Å found in [Cu(3,2,3-tet)(ClO₄)]_n [3,2,3-tet is N,N'-bis(3-aminopropyl)ethylenediamine; Kwak et al., 2001], in which axial coordination ligands have no geometrical constraints. The O1—Cu1—O1' angle [147.54 (8) °] is significantly reduced from 180°.

It is hard to estimate quantitatively the elongation of the axial Cu—O bond that results from the Jahn–Teller effect and from geometrical restraints of the chelate ring. However, it is certain that there is conflict between stabilization from the Jahn–Teller effect and the chelate geometrical requirements, because the nature of the chelate ring tends to restrict the distortion of a complex (Huheey, 1983). Bond parameters of (I) are not different from those of various CuL₂ compounds with the CuO₄N₂ chromophore (L = chelate ligand; Koman et al., 2000) and Cu^II compounds containing the pdmH fragment (Atkinson et al., 2000), whereas [Cu(pdmH₂)₂]²⁺ exhibits a Jahn–Teller contraction effect (Andac et al., 2002).

The adjacent dinuclear copper complex units are associated via hydrogen bonds between the hydroxide groups of the 2,6-pyridinedimethanol ligands and the acetate anions, as illustrated in Fig. 2 and Table 2. There is one carboxylate anion in the asymmetric unit. Carboxylate atom O5 interacts with two hydroxide H atoms of adjacent pdmH₂ ligands, while atom O6 interacts with the H atom on the hydroxide O4 atom of pdmH⁻, resulting in one-dimensional linear chains running parallel to the a axis.

S2. Experimental

To a green solution of Cu(CH₃COO)₂·H₂O (0.3254 g, 1.63 mmol) in acetonitrile (30 ml), pdmH₂ (0.56 g, 4 mmol) was added. The reaction mixture was stirred continuously, and then a solution of n-Bu₄NOH (0.4 ml, 1.0 mol) in methanol was added dropwise, causing the color of the solution to change to bright blue. The solution was stirred for 4 h, then filtered and concentrated under reduced pressure. The resulting green solution was treated with hexane to afford a crystalline solid. Recrystallization from dichloromethane–hexane solution gave single crystals suitable for X-ray analysis. Analysis found: C 48.7, H 5.09, N 7.14%; C₃₂H₄₀Cu₂N₄O₁₂ requires: C 48.1, H 5.04, N 7.00%.

S3. Refinement

All H atoms were introduced at calculated positions as riding atoms, with bond lengths of 0.93 (CH), 0.96 (CH₃) and 0.82 Å (OH) and displacement parameters equal to 1.2 (CH and OH) or 1.5 (CH₃) times that of the parent atom.

Computing details

Data collection: MACH3 (Nonius, 1996); cell refinement: CELDIM (Nonius, 1996); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. An ORTEP diagram of (I), with the atomic numbering scheme. Displacement ellipsoids shown at the 50% probability level.
	Fig. 2. The crystal packing of (I), showing the linear chain structure formed by (dashed) hydrogen bonds.

(I)

Crystal data

[Cu2(C7H8NO2)2(C7H9NO2)2](C2H3O2)2	F(000) = 828
Mr = 799.76	Dx = 1.590 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 10.252 (1) Å	θ = 19.9–31.3°
b = 12.1310 (7) Å	µ = 1.34 mm^−1
c = 14.2226 (8) Å	T = 296 K
β = 109.150 (5)°	Plate, green
V = 1671.0 (2) Å^3	0.25 × 0.20 × 0.11 mm
Z = 2

Data collection

Enraf–Nonius CAD4 diffractometer	2427 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.045
Graphite monochromator	θmax = 25.0°, θmin = 2.2°
θ/2θ scans	h = −12→11
Absorption correction: ϕ-scan (PSISCANS; North et al., 1968)	k = 0→14
Tmin = 0.761, Tmax = 0.883	l = 0→16
3061 measured reflections	3 standard reflections every 200 reflections
2938 independent reflections	intensity decay: none

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)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.096	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0497P)^2 + 1.3695P] where P = (Fo^2 + 2Fc^2)/3
2938 reflections	(Δ/σ)max < 0.001
227 parameters	Δρmax = 0.34 e Å^−3
0 restraints	Δρmin = −0.39 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
Cu1	0.12725 (4)	0.06953 (3)	0.01222 (2)	0.03014 (13)
N1	0.2848 (2)	0.1092 (2)	0.13593 (17)	0.0301 (5)
N2	0.1721 (2)	0.1286 (2)	−0.11208 (17)	0.0317 (5)
O1	0.2989 (3)	−0.06113 (19)	0.01535 (17)	0.0479 (6)
H51	0.2726	−0.1254	0.0103	0.058*
O2	0.0749 (2)	0.2476 (2)	0.05630 (16)	0.0435 (6)
H52	−0.0068	0.2633	0.0440	0.052*
O3	−0.0311 (2)	0.0142 (2)	−0.08976 (14)	0.0412 (5)
O4	0.3993 (3)	0.3664 (2)	−0.0467 (2)	0.0552 (7)
H54	0.4584	0.3571	−0.0733	0.066*
C1	0.3950 (3)	0.0425 (3)	0.1678 (2)	0.0356 (7)
C2	0.4949 (4)	0.0578 (3)	0.2603 (3)	0.0483 (9)
H2	0.5707	0.0109	0.2815	0.058*
C3	0.4809 (4)	0.1428 (3)	0.3202 (2)	0.0498 (9)
H3	0.5462	0.1531	0.3827	0.060*
C4	0.3698 (3)	0.2121 (3)	0.2868 (2)	0.0410 (8)
H4	0.3598	0.2712	0.3256	0.049*
C5	0.2722 (3)	0.1928 (2)	0.1939 (2)	0.0325 (6)
C6	0.4126 (4)	−0.0490 (3)	0.1018 (3)	0.0485 (9)
H6A	0.4941	−0.0345	0.0834	0.058*
H6B	0.4276	−0.1176	0.1388	0.058*
C7	0.1464 (3)	0.2655 (3)	0.1581 (2)	0.0410 (8)
H7A	0.0856	0.2500	0.1963	0.049*
H7B	0.1742	0.3421	0.1685	0.049*
C8	0.0922 (3)	0.0758 (3)	−0.1937 (2)	0.0379 (7)
C9	0.0992 (4)	0.0977 (3)	−0.2883 (2)	0.0518 (9)
H9	0.0433	0.0601	−0.3440	0.062*
C10	0.1909 (4)	0.1763 (4)	−0.2969 (3)	0.0586 (10)
H10	0.1977	0.1927	−0.3590	0.070*
C11	0.2719 (4)	0.2304 (3)	−0.2145 (3)	0.0489 (9)
H11	0.3334	0.2842	−0.2204	0.059*
C12	0.2624 (3)	0.2051 (3)	−0.1220 (2)	0.0347 (7)
C13	−0.0081 (4)	−0.0065 (3)	−0.1791 (2)	0.0473 (9)
H13A	−0.0945	−0.0017	−0.2337	0.057*
H13B	0.0285	−0.0804	−0.1783	0.057*
C14	0.3485 (3)	0.2634 (3)	−0.0290 (2)	0.0423 (8)
H14A	0.2932	0.2740	0.0141	0.051*
H14B	0.4260	0.2166	0.0061	0.051*
C15	0.7356 (3)	0.3387 (3)	−0.0439 (2)	0.0391 (7)
C16	0.7937 (4)	0.4523 (3)	−0.0255 (3)	0.0593 (10)
H16A	0.7842	0.4873	−0.0880	0.089*
H16B	0.8897	0.4485	0.0137	0.089*
H16C	0.7448	0.4941	0.0095	0.089*
O5	0.8080 (2)	0.2609 (2)	0.00571 (18)	0.0466 (6)
O6	0.6187 (2)	0.3253 (2)	−0.10525 (19)	0.0561 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0313 (2)	0.0350 (2)	0.02149 (19)	−0.00561 (16)	0.00519 (14)	−0.00086 (15)
N1	0.0312 (13)	0.0322 (13)	0.0257 (12)	−0.0046 (11)	0.0075 (10)	−0.0001 (10)
N2	0.0329 (13)	0.0358 (14)	0.0274 (12)	0.0047 (11)	0.0110 (10)	0.0024 (11)
O1	0.0580 (15)	0.0382 (13)	0.0407 (13)	0.0062 (11)	0.0066 (11)	−0.0033 (10)
O2	0.0386 (12)	0.0558 (15)	0.0341 (12)	0.0096 (11)	0.0093 (10)	−0.0002 (10)
O3	0.0449 (12)	0.0550 (14)	0.0211 (10)	−0.0175 (11)	0.0073 (9)	−0.0028 (10)
O4	0.0607 (16)	0.0444 (14)	0.0710 (17)	−0.0090 (12)	0.0360 (14)	−0.0033 (13)
C1	0.0311 (15)	0.0391 (17)	0.0330 (16)	−0.0044 (13)	0.0056 (12)	0.0042 (13)
C2	0.0373 (18)	0.058 (2)	0.0408 (19)	−0.0013 (16)	0.0003 (14)	0.0059 (17)
C3	0.0435 (19)	0.064 (2)	0.0312 (17)	−0.0178 (18)	−0.0024 (14)	0.0030 (17)
C4	0.0477 (19)	0.0468 (19)	0.0266 (15)	−0.0151 (16)	0.0096 (14)	−0.0061 (14)
C5	0.0359 (16)	0.0333 (16)	0.0296 (15)	−0.0099 (13)	0.0128 (12)	−0.0002 (12)
C6	0.0406 (18)	0.046 (2)	0.050 (2)	0.0051 (15)	0.0029 (15)	−0.0026 (16)
C7	0.0488 (19)	0.0374 (18)	0.0333 (16)	−0.0034 (15)	0.0085 (14)	−0.0079 (14)
C8	0.0461 (18)	0.0413 (18)	0.0279 (15)	0.0023 (15)	0.0144 (13)	−0.0007 (13)
C9	0.064 (2)	0.068 (3)	0.0259 (16)	−0.0087 (19)	0.0174 (16)	−0.0037 (16)
C10	0.070 (3)	0.078 (3)	0.038 (2)	0.000 (2)	0.0322 (19)	0.0087 (19)
C11	0.051 (2)	0.059 (2)	0.0446 (19)	−0.0023 (18)	0.0263 (16)	0.0084 (17)
C12	0.0338 (15)	0.0385 (17)	0.0346 (16)	0.0053 (13)	0.0150 (13)	0.0050 (13)
C13	0.059 (2)	0.055 (2)	0.0287 (16)	−0.0155 (18)	0.0148 (15)	−0.0080 (15)
C14	0.0389 (18)	0.0459 (19)	0.0447 (19)	−0.0055 (15)	0.0172 (15)	0.0030 (15)
C15	0.0348 (17)	0.050 (2)	0.0370 (17)	0.0079 (15)	0.0185 (14)	−0.0022 (15)
C16	0.063 (3)	0.045 (2)	0.065 (3)	−0.0003 (18)	0.016 (2)	−0.0053 (18)
O5	0.0427 (13)	0.0450 (14)	0.0505 (14)	0.0032 (11)	0.0128 (11)	0.0034 (11)
O6	0.0366 (13)	0.0680 (18)	0.0581 (16)	0.0016 (12)	0.0078 (12)	−0.0018 (13)

Geometric parameters (Å, º)

Cu1—O3	1.909 (2)	C4—C5	1.391 (4)
Cu1—O3^i	1.983 (2)	C4—H4	0.9300
Cu1—N1	2.018 (2)	C5—C7	1.506 (4)
Cu1—N2	2.094 (2)	C6—H6A	0.9700
Cu1—O1	2.358 (2)	C6—H6B	0.9700
Cu1—O2	2.360 (2)	C7—H7A	0.9700
Cu1—Cu1^i	3.0298 (7)	C7—H7B	0.9700
N1—C5	1.340 (4)	C8—C9	1.396 (4)
N1—C1	1.341 (4)	C8—C13	1.496 (5)
N2—C8	1.343 (4)	C9—C10	1.372 (5)
N2—C12	1.351 (4)	C9—H9	0.9300
O1—C6	1.397 (4)	C10—C11	1.361 (5)
O1—O5^ii	2.636 (3)	C10—H10	0.9300
O1—H51	0.8200	C11—C12	1.385 (5)
O2—C7	1.408 (4)	C11—H11	0.9300
O2—O5^iii	2.596 (3)	C12—C14	1.504 (4)
O2—H52	0.8200	C13—H13A	0.9700
O3—C13	1.389 (4)	C13—H13B	0.9700
O3—Cu1^i	1.983 (2)	C14—H14A	0.9700
O4—C14	1.408 (4)	C14—H14B	0.9700
O4—O6	2.689 (4)	C15—O6	1.240 (4)
O4—H54	0.8200	C15—O5	1.264 (4)
C1—C2	1.390 (4)	C15—C16	1.489 (5)
C1—C6	1.502 (5)	C16—H16A	0.9600
C2—C3	1.375 (5)	C16—H16B	0.9600
C2—H2	0.9300	C16—H16C	0.9600
C3—C4	1.369 (5)	O6—H54	1.8839
C3—H3	0.9300
O3—Cu1—O3^i	77.79 (9)	C5—C4—H4	120.5
O3—Cu1—N1	169.80 (9)	N1—C5—C4	121.8 (3)
O3^i—Cu1—N1	92.23 (9)	N1—C5—C7	118.7 (3)
O3—Cu1—N2	81.17 (9)	C4—C5—C7	119.5 (3)
O3^i—Cu1—N2	158.71 (9)	O1—C6—C1	113.0 (3)
N1—Cu1—N2	108.7 (1)	O1—C6—H6A	109.0
O3—Cu1—O1	102.8 (1)	C1—C6—H6A	109.0
O3^i—Cu1—O1	98.6 (1)	O1—C6—H6B	109.0
N1—Cu1—O1	76.39 (9)	C1—C6—H6B	109.0
N2—Cu1—O1	82.91 (9)	H6A—C6—H6B	107.8
O3—Cu1—O2	108.24 (9)	O2—C7—C5	110.9 (3)
O3^i—Cu1—O2	97.08 (9)	O2—C7—H7A	109.5
N1—Cu1—O2	74.75 (9)	C5—C7—H7A	109.5
N2—Cu1—O2	92.48 (9)	O2—C7—H7B	109.5
O1—Cu1—O2	147.54 (8)	C5—C7—H7B	109.5
O3—Cu1—Cu1^i	39.77 (6)	H7A—C7—H7B	108.0
O3^i—Cu1—Cu1^i	38.02 (6)	N2—C8—C9	122.2 (3)
N1—Cu1—Cu1^i	130.22 (7)	N2—C8—C13	116.7 (3)
N2—Cu1—Cu1^i	120.87 (7)	C9—C8—C13	121.1 (3)
O1—Cu1—Cu1^i	103.72 (6)	C10—C9—C8	118.1 (3)
O2—Cu1—Cu1^i	106.13 (6)	C10—C9—H9	121.0
C5—N1—C1	119.3 (3)	C8—C9—H9	121.0
C5—N1—Cu1	120.4 (2)	C11—C10—C9	120.1 (3)
C1—N1—Cu1	119.7 (2)	C11—C10—H10	120.0
C8—N2—C12	118.8 (3)	C9—C10—H10	120.0
C8—N2—Cu1	109.1 (2)	C10—C11—C12	119.8 (3)
C12—N2—Cu1	132.2 (2)	C10—C11—H11	120.1
C6—O1—Cu1	110.35 (19)	C12—C11—H11	120.1
C6—O1—O5^ii	113.1 (2)	N2—C12—C11	121.0 (3)
Cu1—O1—O5^ii	109.62 (11)	N2—C12—C14	117.1 (3)
C6—O1—H51	109.5	C11—C12—C14	121.9 (3)
Cu1—O1—H51	114.5	O3—C13—C8	109.7 (3)
O5^ii—O1—H51	5.0	O3—C13—H13A	109.7
C7—O2—Cu1	109.09 (18)	C8—C13—H13A	109.7
C7—O2—O5^iii	114.9 (2)	O3—C13—H13B	109.7
Cu1—O2—O5^iii	107.11 (10)	C8—C13—H13B	109.7
C7—O2—H52	109.5	H13A—C13—H13B	108.2
Cu1—O2—H52	117.5	O4—C14—C12	113.8 (3)
O5^iii—O2—H52	10.4	O4—C14—H14A	108.8
C13—O3—Cu1	113.64 (19)	C12—C14—H14A	108.8
C13—O3—Cu1^i	132.9 (2)	O4—C14—H14B	108.8
Cu1—O3—Cu1^i	102.21 (9)	C12—C14—H14B	108.8
C14—O4—O6	106.7 (2)	H14A—C14—H14B	107.7
C14—O4—H54	109.5	O6—C15—O5	123.4 (3)
O6—O4—H54	9.0	O6—C15—C16	118.9 (3)
N1—C1—C2	121.1 (3)	O5—C15—C16	117.7 (3)
N1—C1—C6	119.7 (3)	C15—C16—H16A	109.5
C2—C1—C6	119.2 (3)	C15—C16—H16B	109.5
C3—C2—C1	119.5 (3)	H16A—C16—H16B	109.5
C3—C2—H2	120.2	C15—C16—H16C	109.5
C1—C2—H2	120.2	H16A—C16—H16C	109.5
C4—C3—C2	119.3 (3)	H16B—C16—H16C	109.5
C4—C3—H3	120.3	C15—O6—H54	121.4
C2—C3—H3	120.3	C15—O6—O4	118.1 (2)
C3—C4—C5	118.9 (3)	H54—O6—O4	3.9
C3—C4—H4	120.5

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H51···O5^ii	0.82	1.82	2.636 (4)	173
O2—H52···O5^iii	0.82	1.80	2.596 (4)	165
O4—H54···O6	0.82	1.88	2.689 (4)	167

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