Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105014538/ob1229sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270105014538/ob1229Isup2.hkl |
CCDC reference: 275513
The protonated ligand LH (C19H27N3O; Belmar et al., 2004, 2005; 0.1 g, 0.32 mmol) and Cu(O2CCH3)2·H2O (Quantity?) were dissolved in ethanol (10 ml) and heated to reflux for 1 h. The solution was then evaporated to a final volume of 5 ml and allowed to cool down to room temperature. The solid was filtered and crystallized by slow evaporation from a chloroform–hexane mixture (Ratio?) [yield 0.08 g, 73%; m.p. 396 (2) K].
H atoms were placed in their theoretical positions, with C—Haromatic = 0.93, C—H2 = 0.97 and C—H3 = 0.96 Å, and allowed to ride on their parent atoms, with Uiso(H) = 1.2Ueq(C) for the first two cases and 1.5Ueq(C) for the third. The methyl groups were also allowed to rotate around their C—C axis.
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL/PC (Sheldrick, 1994); software used to prepare material for publication: SHELXTL/PC.
[Cu(C19H26N3O)2] | Z = 1 |
Mr = 688.40 | F(000) = 367 |
Triclinic, P1 | Dx = 1.258 Mg m−3 |
Hall symbol: -P 1 | Melting point: 396(2) K |
a = 8.0366 (10) Å | Mo Kα radiation, λ = 0.71073 Å |
b = 8.8767 (11) Å | Cell parameters from 1870 reflections |
c = 14.3438 (17) Å | θ = 3.6–23.5° |
α = 94.121 (2)° | µ = 0.64 mm−1 |
β = 95.416 (2)° | T = 298 K |
γ = 115.946 (2)° | Prism, brown |
V = 908.67 (19) Å3 | 0.30 × 0.16 × 0.14 mm |
Bruker SMART CCD area-detector diffractometer | 3530 independent reflections |
Radiation source: fine-focus sealed tube | 2449 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.047 |
ϕ and ω scans | θmax = 26.0°, θmin = 2.6° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −9→9 |
Tmin = 0.86, Tmax = 0.91 | k = −10→10 |
7009 measured reflections | l = −17→17 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.066 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.139 | H-atom parameters constrained |
S = 1.02 | w = 1/[σ2(Fo2) + (0.0558P)2] where P = (Fo2 + 2Fc2)/3 |
3530 reflections | (Δ/σ)max = 0.003 |
217 parameters | Δρmax = 0.49 e Å−3 |
0 restraints | Δρmin = −0.31 e Å−3 |
[Cu(C19H26N3O)2] | γ = 115.946 (2)° |
Mr = 688.40 | V = 908.67 (19) Å3 |
Triclinic, P1 | Z = 1 |
a = 8.0366 (10) Å | Mo Kα radiation |
b = 8.8767 (11) Å | µ = 0.64 mm−1 |
c = 14.3438 (17) Å | T = 298 K |
α = 94.121 (2)° | 0.30 × 0.16 × 0.14 mm |
β = 95.416 (2)° |
Bruker SMART CCD area-detector diffractometer | 3530 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 2449 reflections with I > 2σ(I) |
Tmin = 0.86, Tmax = 0.91 | Rint = 0.047 |
7009 measured reflections |
R[F2 > 2σ(F2)] = 0.066 | 0 restraints |
wR(F2) = 0.139 | H-atom parameters constrained |
S = 1.02 | Δρmax = 0.49 e Å−3 |
3530 reflections | Δρmin = −0.31 e Å−3 |
217 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
Cu1 | 0.5000 | 0.5000 | 0.5000 | 0.0370 (2) | |
O1 | 0.5640 (4) | 0.4339 (3) | 0.38683 (16) | 0.0498 (7) | |
N1 | 0.7606 (4) | 0.3657 (4) | 0.3059 (2) | 0.0458 (8) | |
N2 | 0.8911 (4) | 0.3055 (4) | 0.3202 (2) | 0.0477 (8) | |
N3 | 0.6102 (4) | 0.3711 (3) | 0.57545 (19) | 0.0365 (7) | |
C1 | 0.6876 (5) | 0.3793 (4) | 0.3852 (3) | 0.0388 (9) | |
C2 | 0.7755 (5) | 0.3259 (4) | 0.4561 (2) | 0.0342 (8) | |
C3 | 0.9011 (5) | 0.2823 (4) | 0.4096 (3) | 0.0410 (9) | |
C4 | 1.0364 (5) | 0.2195 (5) | 0.4442 (3) | 0.0563 (11) | |
H4A | 1.1069 | 0.2137 | 0.3948 | 0.084* | |
H4B | 0.9699 | 0.1091 | 0.4626 | 0.084* | |
H4C | 1.1198 | 0.2952 | 0.4976 | 0.084* | |
C5 | 0.7292 (5) | 0.3166 (4) | 0.5493 (3) | 0.0372 (9) | |
C6 | 0.8135 (5) | 0.2364 (5) | 0.6155 (3) | 0.0498 (10) | |
H6A | 0.8165 | 0.2791 | 0.6801 | 0.060* | |
H6B | 0.9412 | 0.2675 | 0.6048 | 0.060* | |
C7 | 0.7035 (6) | 0.0449 (5) | 0.6019 (3) | 0.0643 (13) | |
H7A | 0.7672 | −0.0022 | 0.6412 | 0.096* | |
H7B | 0.6929 | 0.0028 | 0.5370 | 0.096* | |
H7C | 0.5810 | 0.0133 | 0.6189 | 0.096* | |
C8 | 0.5561 (5) | 0.3405 (5) | 0.6682 (3) | 0.0428 (9) | |
C9 | 0.3911 (6) | 0.2032 (5) | 0.6772 (3) | 0.0590 (12) | |
H9A | 0.3144 | 0.1333 | 0.6235 | 0.071* | |
C10 | 0.3390 (7) | 0.1688 (6) | 0.7648 (4) | 0.0719 (14) | |
H10A | 0.2287 | 0.0744 | 0.7699 | 0.086* | |
C11 | 0.4473 (8) | 0.2715 (7) | 0.8440 (4) | 0.0762 (15) | |
H11A | 0.4116 | 0.2474 | 0.9031 | 0.091* | |
C12 | 0.6092 (7) | 0.4108 (7) | 0.8359 (3) | 0.0692 (14) | |
H12A | 0.6830 | 0.4818 | 0.8899 | 0.083* | |
C13 | 0.6642 (6) | 0.4470 (5) | 0.7484 (3) | 0.0556 (11) | |
H13A | 0.7735 | 0.5426 | 0.7436 | 0.067* | |
C14 | 0.7233 (6) | 0.4135 (5) | 0.2151 (3) | 0.0560 (11) | |
H14A | 0.8412 | 0.4844 | 0.1943 | 0.067* | |
H14B | 0.6553 | 0.4800 | 0.2219 | 0.067* | |
C15 | 0.6118 (7) | 0.2645 (6) | 0.1400 (3) | 0.0678 (13) | |
H15A | 0.5973 | 0.3061 | 0.0806 | 0.081* | |
H15B | 0.6813 | 0.1997 | 0.1319 | 0.081* | |
C16 | 0.4214 (7) | 0.1497 (6) | 0.1628 (3) | 0.0738 (14) | |
H16A | 0.3544 | 0.2160 | 0.1740 | 0.089* | |
H16B | 0.4364 | 0.1042 | 0.2207 | 0.089* | |
C17 | 0.3049 (7) | 0.0050 (6) | 0.0865 (3) | 0.0758 (14) | |
H17A | 0.2868 | 0.0509 | 0.0292 | 0.091* | |
H17B | 0.3742 | −0.0586 | 0.0737 | 0.091* | |
C18 | 0.1176 (8) | −0.1137 (7) | 0.1092 (4) | 0.0977 (18) | |
H18A | 0.0481 | −0.0503 | 0.1218 | 0.117* | |
H18B | 0.1356 | −0.1597 | 0.1665 | 0.117* | |
C19 | 0.0025 (8) | −0.2575 (7) | 0.0330 (4) | 0.111 (2) | |
H19A | −0.1172 | −0.3245 | 0.0517 | 0.166* | |
H19B | 0.0656 | −0.3264 | 0.0232 | 0.166* | |
H19C | −0.0144 | −0.2137 | −0.0245 | 0.166* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Cu1 | 0.0349 (4) | 0.0432 (4) | 0.0360 (4) | 0.0203 (3) | 0.0049 (3) | 0.0056 (3) |
O1 | 0.0602 (18) | 0.0717 (19) | 0.0367 (15) | 0.0467 (16) | 0.0076 (13) | 0.0070 (14) |
N1 | 0.051 (2) | 0.053 (2) | 0.041 (2) | 0.0291 (17) | 0.0115 (16) | 0.0081 (16) |
N2 | 0.046 (2) | 0.051 (2) | 0.053 (2) | 0.0269 (17) | 0.0146 (17) | 0.0056 (17) |
N3 | 0.0362 (17) | 0.0400 (18) | 0.0348 (17) | 0.0173 (15) | 0.0080 (14) | 0.0090 (14) |
C1 | 0.040 (2) | 0.036 (2) | 0.042 (2) | 0.0182 (18) | 0.0094 (18) | 0.0028 (17) |
C2 | 0.033 (2) | 0.032 (2) | 0.041 (2) | 0.0163 (17) | 0.0090 (17) | 0.0062 (16) |
C3 | 0.035 (2) | 0.035 (2) | 0.051 (3) | 0.0134 (18) | 0.0072 (18) | 0.0051 (18) |
C4 | 0.052 (3) | 0.056 (3) | 0.072 (3) | 0.033 (2) | 0.017 (2) | 0.011 (2) |
C5 | 0.033 (2) | 0.031 (2) | 0.046 (2) | 0.0131 (17) | 0.0021 (17) | 0.0019 (17) |
C6 | 0.056 (3) | 0.057 (3) | 0.048 (3) | 0.035 (2) | 0.004 (2) | 0.009 (2) |
C7 | 0.083 (3) | 0.065 (3) | 0.063 (3) | 0.046 (3) | 0.017 (3) | 0.022 (2) |
C8 | 0.045 (2) | 0.047 (2) | 0.043 (2) | 0.026 (2) | 0.0067 (19) | 0.0100 (19) |
C9 | 0.059 (3) | 0.056 (3) | 0.054 (3) | 0.017 (2) | 0.013 (2) | 0.009 (2) |
C10 | 0.081 (4) | 0.068 (3) | 0.074 (4) | 0.031 (3) | 0.040 (3) | 0.027 (3) |
C11 | 0.106 (4) | 0.100 (4) | 0.050 (3) | 0.063 (4) | 0.030 (3) | 0.035 (3) |
C12 | 0.088 (4) | 0.096 (4) | 0.038 (3) | 0.057 (3) | −0.001 (3) | 0.005 (3) |
C13 | 0.058 (3) | 0.069 (3) | 0.043 (3) | 0.032 (2) | 0.002 (2) | 0.007 (2) |
C14 | 0.065 (3) | 0.065 (3) | 0.044 (3) | 0.032 (2) | 0.013 (2) | 0.013 (2) |
C15 | 0.082 (3) | 0.084 (3) | 0.040 (3) | 0.039 (3) | 0.010 (2) | 0.011 (2) |
C16 | 0.086 (4) | 0.076 (3) | 0.055 (3) | 0.032 (3) | 0.014 (3) | 0.009 (3) |
C17 | 0.084 (4) | 0.084 (4) | 0.058 (3) | 0.037 (3) | 0.005 (3) | 0.010 (3) |
C18 | 0.097 (4) | 0.089 (4) | 0.084 (4) | 0.019 (4) | 0.018 (3) | 0.013 (3) |
C19 | 0.093 (4) | 0.096 (4) | 0.107 (5) | 0.012 (4) | 0.002 (4) | 0.011 (4) |
Cu1—O1 | 1.879 (2) | C9—C10 | 1.374 (5) |
Cu1—O1i | 1.879 (2) | C9—H9A | 0.9300 |
Cu1—N3 | 2.036 (3) | C10—C11 | 1.360 (6) |
Cu1—N3i | 2.036 (3) | C10—H10A | 0.9300 |
O1—C1 | 1.282 (4) | C11—C12 | 1.370 (6) |
N1—C1 | 1.349 (4) | C11—H11A | 0.9300 |
N1—N2 | 1.375 (4) | C12—C13 | 1.383 (5) |
N1—C14 | 1.445 (5) | C12—H12A | 0.9300 |
N2—C3 | 1.314 (4) | C13—H13A | 0.9300 |
N3—C5 | 1.317 (4) | C14—C15 | 1.513 (5) |
N3—C8 | 1.446 (4) | C14—H14A | 0.9700 |
C1—C2 | 1.409 (5) | C14—H14B | 0.9700 |
C2—C5 | 1.420 (5) | C15—C16 | 1.505 (6) |
C2—C3 | 1.430 (5) | C15—H15A | 0.9700 |
C3—C4 | 1.486 (5) | C15—H15B | 0.9700 |
C4—H4A | 0.9600 | C16—C17 | 1.509 (6) |
C4—H4B | 0.9600 | C16—H16A | 0.9700 |
C4—H4C | 0.9600 | C16—H16B | 0.9700 |
C5—C6 | 1.506 (5) | C17—C18 | 1.495 (6) |
C6—C7 | 1.521 (5) | C17—H17A | 0.9700 |
C6—H6A | 0.9700 | C17—H17B | 0.9700 |
C6—H6B | 0.9700 | C18—C19 | 1.502 (6) |
C7—H7A | 0.9600 | C18—H18A | 0.9700 |
C7—H7B | 0.9600 | C18—H18B | 0.9700 |
C7—H7C | 0.9600 | C19—H19A | 0.9600 |
C8—C9 | 1.378 (5) | C19—H19B | 0.9600 |
C8—C13 | 1.381 (5) | C19—H19C | 0.9600 |
O1—Cu1—O1i | 180.00 (7) | C8—C9—H9A | 119.7 |
O1—Cu1—N3 | 92.24 (11) | C11—C10—C9 | 120.6 (5) |
O1i—Cu1—N3 | 87.76 (11) | C11—C10—H10A | 119.7 |
O1—Cu1—N3i | 87.76 (11) | C9—C10—H10A | 119.7 |
O1i—Cu1—N3i | 92.24 (11) | C10—C11—C12 | 119.4 (4) |
N3—Cu1—N3i | 180.00 (13) | C10—C11—H11A | 120.3 |
C1—O1—Cu1 | 122.5 (2) | C12—C11—H11A | 120.3 |
C1—N1—N2 | 112.1 (3) | C11—C12—C13 | 120.7 (4) |
C1—N1—C14 | 127.7 (3) | C11—C12—H12A | 119.6 |
N2—N1—C14 | 120.1 (3) | C13—C12—H12A | 119.6 |
C3—N2—N1 | 105.9 (3) | C8—C13—C12 | 119.7 (4) |
C5—N3—C8 | 116.8 (3) | C8—C13—H13A | 120.1 |
C5—N3—Cu1 | 126.6 (2) | C12—C13—H13A | 120.1 |
C8—N3—Cu1 | 116.6 (2) | N1—C14—C15 | 113.5 (3) |
O1—C1—N1 | 121.9 (3) | N1—C14—H14A | 108.9 |
O1—C1—C2 | 131.7 (3) | C15—C14—H14A | 108.9 |
N1—C1—C2 | 106.4 (3) | N1—C14—H14B | 108.9 |
C1—C2—C5 | 122.8 (3) | C15—C14—H14B | 108.9 |
C1—C2—C3 | 104.4 (3) | H14A—C14—H14B | 107.7 |
C5—C2—C3 | 132.8 (3) | C16—C15—C14 | 113.5 (4) |
N2—C3—C2 | 111.2 (3) | C16—C15—H15A | 108.9 |
N2—C3—C4 | 116.8 (3) | C14—C15—H15A | 108.9 |
C2—C3—C4 | 132.0 (4) | C16—C15—H15B | 108.9 |
C3—C4—H4A | 109.5 | C14—C15—H15B | 108.9 |
C3—C4—H4B | 109.5 | H15A—C15—H15B | 107.7 |
H4A—C4—H4B | 109.5 | C15—C16—C17 | 114.1 (4) |
C3—C4—H4C | 109.5 | C15—C16—H16A | 108.7 |
H4A—C4—H4C | 109.5 | C17—C16—H16A | 108.7 |
H4B—C4—H4C | 109.5 | C15—C16—H16B | 108.7 |
N3—C5—C2 | 120.6 (3) | C17—C16—H16B | 108.7 |
N3—C5—C6 | 121.3 (3) | H16A—C16—H16B | 107.6 |
C2—C5—C6 | 118.1 (3) | C18—C17—C16 | 114.9 (4) |
C5—C6—C7 | 111.9 (3) | C18—C17—H17A | 108.6 |
C5—C6—H6A | 109.2 | C16—C17—H17A | 108.6 |
C7—C6—H6A | 109.2 | C18—C17—H17B | 108.6 |
C5—C6—H6B | 109.2 | C16—C17—H17B | 108.6 |
C7—C6—H6B | 109.2 | H17A—C17—H17B | 107.5 |
H6A—C6—H6B | 107.9 | C17—C18—C19 | 114.6 (5) |
C6—C7—H7A | 109.5 | C17—C18—H18A | 108.6 |
C6—C7—H7B | 109.5 | C19—C18—H18A | 108.6 |
H7A—C7—H7B | 109.5 | C17—C18—H18B | 108.6 |
C6—C7—H7C | 109.5 | C19—C18—H18B | 108.6 |
H7A—C7—H7C | 109.5 | H18A—C18—H18B | 107.6 |
H7B—C7—H7C | 109.5 | C18—C19—H19A | 109.5 |
C9—C8—C13 | 118.8 (4) | C18—C19—H19B | 109.5 |
C9—C8—N3 | 119.5 (3) | H19A—C19—H19B | 109.5 |
C13—C8—N3 | 121.7 (3) | C18—C19—H19C | 109.5 |
C10—C9—C8 | 120.6 (4) | H19A—C19—H19C | 109.5 |
C10—C9—H9A | 119.7 | H19B—C19—H19C | 109.5 |
Symmetry code: (i) −x+1, −y+1, −z+1. |
Experimental details
Crystal data | |
Chemical formula | [Cu(C19H26N3O)2] |
Mr | 688.40 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 298 |
a, b, c (Å) | 8.0366 (10), 8.8767 (11), 14.3438 (17) |
α, β, γ (°) | 94.121 (2), 95.416 (2), 115.946 (2) |
V (Å3) | 908.67 (19) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 0.64 |
Crystal size (mm) | 0.30 × 0.16 × 0.14 |
Data collection | |
Diffractometer | Bruker SMART CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.86, 0.91 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 7009, 3530, 2449 |
Rint | 0.047 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.066, 0.139, 1.02 |
No. of reflections | 3530 |
No. of parameters | 217 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.49, −0.31 |
Computer programs: SMART (Bruker, 2001), SAINT (Bruker, 2000), SAINT, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL/PC (Sheldrick, 1994), SHELXTL/PC.
Cu1—O1 | 1.879 (2) | N3—C5 | 1.317 (4) |
Cu1—N3 | 2.036 (3) | N3—C8 | 1.446 (4) |
O1—C1 | 1.282 (4) | C1—C2 | 1.409 (5) |
N1—C1 | 1.349 (4) | C2—C5 | 1.420 (5) |
N1—N2 | 1.375 (4) | C2—C3 | 1.430 (5) |
N1—C14 | 1.445 (5) | C3—C4 | 1.486 (5) |
N2—C3 | 1.314 (4) | ||
O1—Cu1—N3 | 92.24 (11) |
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Pyrazolones constitute an important group of organic compounds (Elguero, 1996), for both theoretical and practical reasons. Their application fields include analgesic and anti-inflamatory drugs (Gürzov et al., 2000), dyes (Emeleus et al., 2001), extractants for several ions (Petinari et al., 2000), etc. Pyrazolones have attracted much attention because they exhibit prototropic tautomerism (Elguero et al., 1976; Uraev et al., 2000; Gilchrist, 2001) and they have been extensively studied both in solution and in the crystalline phase (Chmutova et al., 2001).
Pyrazolones have usually been obtained by the same synthetic procedure, a condensation between an acyl acetate and a hydrazine, for more than one century (Knorr, 1884). In spite of the many advantages of 1-alkylpyrazolone derivatives (viz. their greater solubility), most literature reports deal with 1-phenylpyrazolones or N1 unsubstituted pyrazolones. This situation may result from the fact that the few commercially available alkylhydrazines are very expensive. Furthermore, there are no convenient syntheses to obtain them. Emeleus et al. (2001) described the use of some alkylpyrazolones that were obtained following a different procedure (Butler & de Wald, 1971). However, alkylhydrazines were still one of the required reagents.
More recently, with the aim of studying the tautomerism involved, it was shown that pyrazolone could be easily alkylated at N1 with primary alkylhalides (Bartulin et al., 1992, 1994; Belmar et al., 1997, 1999). This procedure finally allowed the obtention of several enamines derived from 4-acyl-1-(n-hexyl)-3-methyl-5-pyrazolones (Belmar et al., 2004, 2005) and even some nitrido complexes using these ligands (Pérez et al., 2005). In addition to these reports, papers by Maurya et al. (1992) and Dey et al. (1999) described some complexes using 1-phenylpyrazolone-based imines. In this paper, we present the structure of the title compound, (I), Cu(L)2 (L is the C19H26N3O− anion), which is the first copper complex ever reported using a chelating 1-alkylpyrazolone-based enamine ligand.
Compound (I) is monomeric and consists of a tetracoordinated CuII atom lying on a symmetry centre, coordinated to two chelating (symmetry-related) bidentate L ligands (Fig. 1). The resulting CuO2N2 core is perfectly planar, due to the restraints imposed by symmetry. The coordination bond lengths do not depart significantly from average values taken from a selected subset of 80 structures with a similar coordination scheme found in the November 2004 release of the Cambridge Structural Database (CSD; Allen, 2002), viz. Cu—N 2.036 (3) and Cu—O 1.879 (2) Å in this work, compared with 2.001 (20) and 1.887 (21) Å, respectively, from the CSD. The ligand L does not twist appreciably because of chelation. Fig. 2 presents a superposition diagram of the free ligand (Belmar et al., 2004) and the ligand in (I); both cores overlap almost entirely, the larger departure being found in the phenyl ring [average discrepancies are 0.08 (8) Å for non-benzyl atoms and 1.8 (11) Å for benzyl atoms]. The free ligand forms an N—H···O intramolecular hydrogen bond, which rocks the conformation.
The pyrazine ring and its two substituents at C1 and C2 determine a planar group [mean deviation 0.01 (1) Å], which binds in a slightly slanted way through the outermost atoms O1 and N3 to the Cu coordination plane [dihedral angle 16.8 (1)°]. Thus, the six-membered ring O1/C1/C2/C5/N3/Cu1 presents an envelope conformation, with the Cu atom puckering 0.38 (1) Å away from the planar group defined by the remaining five atoms.
There are four lateral substituents attached to the planar main frame of (I), namely Me at C3, Et at C5, n-hexyl at N1 and Ph at N3. All of them, with the obvious exception of the methyl group, are almost perpendicular to the quasi-planar coordination core, the Ph group subtending an angle of 77.4 (1)° and the two aliphatic chains deviating from the vertical by 17 (1)°. The hexyl group presents a striking unperturbed almost planar zigzag conformation, with torsion angles in the range 177.1 (1)–179.2 (1)°. A survey of the CSD showed this to be a rather infrequent conformation: in 842 cases (89% out of a total of 947 hexyl groups reported), the aliphatic chain presented greater deviations from a perfect unperturbed zigzag state, as measured by the largest torsion angle deviation from an expected 180°. Incidentally, only one out of the 947 structures surveyed showed a symmetry-forced perfectly planar conformation.
This particular disposition of the sustituents in (I) introduces a strong steric limitation to the approach of planar groups from different molecules, and thus precludes the most noteworthy intermolecular interaction found in the structure of the free ligand (Belmar et al., 2004), viz. the π–π contact between aromatic rings.
Previously reported structural work on complexes derived from related ligands strongly suggests an `enamine-to-imine' shift of the character of the ligand upon coordination, viz. a nitridomanganese(V) complex with N,N'-bis{[1-(n-hexyl)-3-methyl-5-oxo-2-pyrazolin-4-yl]propyliden-1-yl}-ethylenediamine (Belmar et al., 2005). In those cases, however, the comparison of conformations `before' and `after' coordination could only be made through the use of similar (but not the same) ligands, as the present study is the first case where both structures (free ligand and a derived complex) are known from an X-ray analysis. A comparison of selected ligand bond distances for (I) and their homologues in the free moiety (taken from Belmar et al., 2004) is shown in Fig. 3. Although individual differences are subtle enough to be considered not relevant, the overall trend of the bond lengths changes in the N3—C5—C2—C1—O1 chain clearly points to an enamine-to-imine shift of the ligand character after complexation.