In the title salt,
catena-poly[[[aquacopper(II)]-μ-3-(2-pyridylmethyleneamino)propanoato-κ
4N,
N′,
O:
O′] perchlorate], {[Cu(C
9H
9N
2O
2)(H
2O)]ClO
4}
n, the monomeric unit contains a square-based pyramidal Cu
II centre. The four basal positions are occupied by a tridentate anionic Schiff base ligand which furnishes an NNO-donor set, with the fourth basal position being occupied by an O-donor atom from the carboxylate group of an adjacent Schiff base ligand. The coordination sphere is completed by a water molecule at the apical position. Interestingly, each carboxylate group in the ligand forms a
syn–anti-configured bridge between two Cu
II centres, leading to left-handed chiral helicity. The framework also exhibits O—H
O hydrogen bonds involving the water molecules and an O atom of the perchlorate anion.
Supporting information
CCDC reference: 746038
To a solution of β-alanine (0.080 g, 1.0 mmol) in methanol (10 ml) containing
KOH (0.050 g, 1.0 mmol) was added 2-pyridinecarboxaldehyde (0.100 g, 1.0 mmol)
in methanol (10 ml). The solution was refluxed with stirring for 2 h. To the
cold, filtered solution was added a solution of copper(II) perchlorate (0.350 g, 1.0 mmol) in DMF [N,N-dimethylformamide?] (5 ml) and the mixture
stirred
for
2 h.
After
filtration, the filtrate was left to stand at room temperature for one month
and blue block-like crystals of the title salt appeared in a yield of 0.11 g
(22%).
The water H atoms were located in a difference Fourier map and refined with
O–H distances restrained to 0.85 (1) Å and Uiso(H)
=1.5Ueq(O). Other H atoms were placed at geometrically calculated
positions (C—H = 0.93 Å or 0.97 Å) and refined as riding, with
Uiso(H) = 1.2Ueq(C).
Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg & Berndt, 2005); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
catena-poly[[[aquacopper(II)]-µ-3-(2-pyridylmethyleneamino)propanoato-
κ4N,
N',
O:
O'] perchlorate]
top
Crystal data top
[Cu(C9H9N2O2)(H2O)]ClO4 | F(000) = 724 |
Mr = 358.19 | Dx = 1.823 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 1230 reflections |
a = 7.9552 (13) Å | θ = 2.3–22.3° |
b = 11.6740 (19) Å | µ = 1.91 mm−1 |
c = 14.050 (2) Å | T = 295 K |
V = 1304.8 (4) Å3 | Block, blue |
Z = 4 | 0.14 × 0.12 × 0.10 mm |
Data collection top
Bruker SMART APEX CCD area-detector diffractometer | 2457 independent reflections |
Radiation source: sealed tube | 2092 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.034 |
ϕ and ω scans | θmax = 26.0°, θmin = 2.3° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −9→8 |
Tmin = 0.776, Tmax = 0.832 | k = −14→14 |
5173 measured reflections | l = −5→17 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.054 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.129 | w = 1/[σ2(Fo2) + (0.0694P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.01 | (Δ/σ)max < 0.001 |
2457 reflections | Δρmax = 0.48 e Å−3 |
182 parameters | Δρmin = −0.34 e Å−3 |
0 restraints | Absolute structure: Flack (1983) |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: −0.02 (3) |
Crystal data top
[Cu(C9H9N2O2)(H2O)]ClO4 | V = 1304.8 (4) Å3 |
Mr = 358.19 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 7.9552 (13) Å | µ = 1.91 mm−1 |
b = 11.6740 (19) Å | T = 295 K |
c = 14.050 (2) Å | 0.14 × 0.12 × 0.10 mm |
Data collection top
Bruker SMART APEX CCD area-detector diffractometer | 2457 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 2092 reflections with I > 2σ(I) |
Tmin = 0.776, Tmax = 0.832 | Rint = 0.034 |
5173 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.054 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.129 | Δρmax = 0.48 e Å−3 |
S = 1.01 | Δρmin = −0.34 e Å−3 |
2457 reflections | Absolute structure: Flack (1983) |
182 parameters | Absolute structure parameter: −0.02 (3) |
0 restraints | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Cu1 | 0.80083 (9) | 0.64574 (5) | 0.94224 (5) | 0.0439 (2) | |
O1 | 1.0294 (5) | 0.6929 (3) | 0.9762 (3) | 0.0483 (14) | |
O1W | 0.7201 (6) | 0.6400 (4) | 1.1065 (3) | 0.0657 (16) | |
O2 | 1.2467 (5) | 0.6917 (3) | 1.0726 (3) | 0.0493 (14) | |
N1 | 0.5962 (7) | 0.5794 (4) | 0.8811 (3) | 0.0483 (17) | |
N2 | 0.8664 (6) | 0.4825 (4) | 0.9459 (4) | 0.0507 (16) | |
C1 | 0.6040 (9) | 0.4641 (6) | 0.8758 (4) | 0.0517 (19) | |
C2 | 0.4783 (10) | 0.4004 (6) | 0.8334 (4) | 0.063 (3) | |
C3 | 0.3409 (11) | 0.4559 (8) | 0.7964 (5) | 0.073 (3) | |
C4 | 0.3310 (9) | 0.5737 (7) | 0.8026 (4) | 0.065 (3) | |
C5 | 0.4637 (8) | 0.6324 (7) | 0.8454 (4) | 0.058 (2) | |
C6 | 0.7563 (8) | 0.4143 (5) | 0.9142 (4) | 0.053 (2) | |
C7 | 1.0267 (8) | 0.4425 (5) | 0.9810 (5) | 0.059 (2) | |
C8 | 1.0949 (8) | 0.5176 (5) | 1.0593 (5) | 0.054 (2) | |
C9 | 1.1272 (7) | 0.6422 (5) | 1.0337 (4) | 0.0407 (17) | |
Cl1 | 0.5922 (2) | 0.34785 (15) | 1.17237 (12) | 0.0586 (5) | |
O3 | 0.5761 (11) | 0.4523 (6) | 1.2184 (5) | 0.131 (3) | |
O4 | 0.7570 (9) | 0.3329 (8) | 1.1422 (6) | 0.139 (4) | |
O5 | 0.4878 (11) | 0.3482 (7) | 1.0954 (6) | 0.136 (3) | |
O6 | 0.5478 (11) | 0.2652 (7) | 1.2362 (7) | 0.158 (4) | |
H1WB | 0.63220 | 0.68030 | 1.11430 | 0.0990* | |
H2 | 0.48650 | 0.32100 | 0.83000 | 0.0760* | |
H1WA | 0.70010 | 0.57130 | 1.12290 | 0.0990* | |
H3 | 0.25530 | 0.41450 | 0.76730 | 0.0870* | |
H4 | 0.23830 | 0.61290 | 0.77880 | 0.0780* | |
H5 | 0.45870 | 0.71190 | 0.84890 | 0.0690* | |
H6 | 0.77250 | 0.33540 | 0.91550 | 0.0640* | |
H7A | 1.10660 | 0.44070 | 0.92890 | 0.0710* | |
H7B | 1.01410 | 0.36490 | 1.00470 | 0.0710* | |
H8A | 1.19960 | 0.48450 | 1.08160 | 0.0650* | |
H8B | 1.01630 | 0.51560 | 1.11210 | 0.0650* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cu1 | 0.0351 (4) | 0.0385 (3) | 0.0581 (4) | −0.0027 (3) | 0.0004 (4) | −0.0005 (4) |
O1 | 0.036 (2) | 0.044 (2) | 0.065 (3) | −0.0028 (19) | −0.003 (2) | 0.0063 (19) |
O1W | 0.065 (3) | 0.055 (2) | 0.077 (3) | 0.013 (3) | 0.020 (2) | 0.011 (2) |
O2 | 0.039 (2) | 0.0418 (19) | 0.067 (3) | 0.0003 (18) | −0.005 (2) | 0.003 (2) |
N1 | 0.048 (3) | 0.053 (3) | 0.044 (3) | −0.011 (3) | 0.007 (3) | −0.005 (2) |
N2 | 0.045 (3) | 0.045 (2) | 0.062 (3) | −0.001 (2) | 0.011 (3) | −0.011 (3) |
C1 | 0.056 (4) | 0.058 (3) | 0.041 (3) | −0.016 (3) | 0.010 (3) | −0.006 (3) |
C2 | 0.068 (5) | 0.067 (4) | 0.055 (4) | −0.023 (4) | 0.008 (4) | −0.012 (3) |
C3 | 0.070 (6) | 0.096 (6) | 0.052 (4) | −0.029 (5) | 0.004 (4) | −0.013 (4) |
C4 | 0.043 (4) | 0.097 (6) | 0.055 (4) | −0.015 (4) | −0.006 (3) | −0.005 (4) |
C5 | 0.046 (4) | 0.074 (4) | 0.053 (3) | −0.007 (4) | −0.007 (3) | −0.005 (4) |
C6 | 0.050 (4) | 0.044 (3) | 0.065 (4) | −0.012 (3) | 0.011 (3) | −0.007 (3) |
C7 | 0.047 (4) | 0.044 (3) | 0.086 (5) | −0.001 (3) | 0.009 (4) | −0.001 (3) |
C8 | 0.049 (4) | 0.045 (3) | 0.067 (4) | 0.006 (3) | −0.001 (4) | 0.007 (3) |
C9 | 0.037 (3) | 0.041 (3) | 0.044 (3) | 0.005 (3) | 0.007 (2) | 0.005 (3) |
Cl1 | 0.0587 (10) | 0.0531 (9) | 0.0653 (9) | 0.0075 (9) | 0.0086 (8) | 0.0059 (9) |
O3 | 0.158 (7) | 0.100 (5) | 0.135 (5) | −0.024 (5) | 0.042 (6) | −0.046 (5) |
O4 | 0.084 (5) | 0.183 (8) | 0.154 (6) | 0.047 (5) | 0.052 (4) | 0.055 (6) |
O5 | 0.140 (6) | 0.138 (6) | 0.134 (6) | −0.018 (5) | −0.054 (5) | −0.012 (5) |
O6 | 0.144 (7) | 0.127 (6) | 0.204 (8) | 0.049 (6) | 0.092 (6) | 0.100 (6) |
Geometric parameters (Å, º) top
Cu1—O1 | 1.959 (4) | C1—C6 | 1.448 (9) |
Cu1—O2i | 1.957 (4) | C1—C2 | 1.381 (10) |
Cu1—O1W | 2.397 (4) | C2—C3 | 1.373 (11) |
Cu1—N1 | 1.997 (5) | C3—C4 | 1.380 (12) |
Cu1—N2 | 1.976 (5) | C4—C5 | 1.395 (10) |
Cl1—O4 | 1.390 (8) | C7—C8 | 1.508 (9) |
Cl1—O5 | 1.369 (9) | C8—C9 | 1.520 (8) |
Cl1—O3 | 1.387 (7) | C2—H2 | 0.9300 |
Cl1—O6 | 1.364 (9) | C3—H3 | 0.9300 |
O1—C9 | 1.268 (7) | C4—H4 | 0.9300 |
O2—C9 | 1.240 (7) | C5—H5 | 0.9300 |
O1W—H1WB | 0.8500 | C6—H6 | 0.9300 |
O1W—H1WA | 0.8500 | C7—H7A | 0.9700 |
N1—C1 | 1.350 (8) | C7—H7B | 0.9700 |
N1—C5 | 1.321 (8) | C8—H8B | 0.9700 |
N2—C6 | 1.265 (8) | C8—H8A | 0.9700 |
N2—C7 | 1.445 (8) | | |
| | | |
O1—Cu1—O1W | 91.26 (17) | C1—C2—C3 | 119.1 (7) |
O1—Cu1—N1 | 166.05 (18) | C2—C3—C4 | 119.5 (7) |
O1—Cu1—N2 | 91.13 (18) | C3—C4—C5 | 118.3 (7) |
O1—Cu1—O2i | 87.57 (16) | N1—C5—C4 | 122.5 (7) |
O1W—Cu1—N1 | 100.66 (17) | N2—C6—C1 | 117.3 (6) |
O1W—Cu1—N2 | 91.1 (2) | C9—C8—C7 | 116.4 (5) |
O1W—Cu1—O2i | 94.06 (17) | O2—C9—C8 | 118.1 (5) |
N1—Cu1—N2 | 81.5 (2) | O1—C9—C8 | 119.6 (5) |
O2i—Cu1—N1 | 98.68 (18) | O1—C9—O2 | 122.3 (5) |
O2i—Cu1—N2 | 174.7 (2) | N2—C7—C8 | 112.3 (5) |
O3—Cl1—O6 | 107.2 (5) | C1—C2—H2 | 121.00 |
O4—Cl1—O5 | 109.1 (5) | C3—C2—H2 | 120.00 |
O4—Cl1—O6 | 110.8 (5) | C4—C3—H3 | 120.00 |
O5—Cl1—O6 | 111.6 (5) | C2—C3—H3 | 120.00 |
O3—Cl1—O5 | 108.1 (5) | C3—C4—H4 | 121.00 |
O3—Cl1—O4 | 110.1 (5) | C5—C4—H4 | 121.00 |
Cu1—O1—C9 | 126.4 (4) | N1—C5—H5 | 119.00 |
Cu1ii—O2—C9 | 125.0 (4) | C4—C5—H5 | 119.00 |
Cu1—O1W—H1WB | 109.00 | C1—C6—H6 | 121.00 |
Cu1—O1W—H1WA | 110.00 | N2—C6—H6 | 121.00 |
H1WB—O1W—H1WA | 109.00 | C7—C8—H8A | 108.00 |
C1—N1—C5 | 118.9 (6) | C9—C8—H8B | 108.00 |
Cu1—N1—C5 | 129.2 (5) | C9—C8—H8A | 108.00 |
Cu1—N1—C1 | 111.9 (4) | C7—C8—H8B | 108.00 |
Cu1—N2—C6 | 114.5 (4) | H7A—C7—H7B | 108.00 |
Cu1—N2—C7 | 123.6 (4) | H8A—C8—H8B | 107.00 |
C6—N2—C7 | 121.9 (5) | N2—C7—H7A | 109.00 |
C2—C1—C6 | 123.4 (6) | N2—C7—H7B | 109.00 |
N1—C1—C6 | 114.7 (6) | C8—C7—H7A | 109.00 |
N1—C1—C2 | 121.8 (6) | C8—C7—H7B | 109.00 |
| | | |
O1W—Cu1—O1—C9 | 53.8 (5) | Cu1ii—O2—C9—C8 | −175.1 (4) |
N2—Cu1—O1—C9 | −37.3 (5) | Cu1—N1—C1—C2 | −177.9 (5) |
O2i—Cu1—O1—C9 | 147.8 (5) | Cu1—N1—C1—C6 | −0.4 (6) |
O1W—Cu1—N1—C1 | −88.0 (4) | C5—N1—C1—C2 | 0.6 (9) |
O1W—Cu1—N1—C5 | 93.6 (5) | C5—N1—C1—C6 | 178.2 (5) |
N2—Cu1—N1—C1 | 1.5 (4) | Cu1—N1—C5—C4 | 178.5 (4) |
N2—Cu1—N1—C5 | −176.9 (5) | C1—N1—C5—C4 | 0.2 (8) |
O2i—Cu1—N1—C1 | 176.2 (4) | Cu1—N2—C6—C1 | 3.1 (7) |
O2i—Cu1—N1—C5 | −2.2 (5) | C7—N2—C6—C1 | −176.6 (6) |
O1—Cu1—N2—C6 | −170.6 (5) | Cu1—N2—C7—C8 | 31.6 (7) |
O1—Cu1—N2—C7 | 9.0 (5) | C6—N2—C7—C8 | −148.8 (6) |
O1W—Cu1—N2—C6 | 98.1 (5) | N1—C1—C2—C3 | −0.6 (9) |
O1W—Cu1—N2—C7 | −82.3 (5) | C6—C1—C2—C3 | −178.0 (6) |
N1—Cu1—N2—C6 | −2.5 (5) | N1—C1—C6—N2 | −1.8 (8) |
N1—Cu1—N2—C7 | 177.1 (5) | C2—C1—C6—N2 | 175.7 (6) |
O1—Cu1—O2i—C9i | −127.5 (5) | C1—C2—C3—C4 | −0.2 (10) |
O1W—Cu1—O2i—C9i | −36.4 (5) | C2—C3—C4—C5 | 1.0 (10) |
N1—Cu1—O2i—C9i | 65.1 (5) | C3—C4—C5—N1 | −1.0 (9) |
Cu1—O1—C9—O2 | −158.6 (4) | C7—C8—C9—O1 | 35.6 (8) |
Cu1—O1—C9—C8 | 19.2 (7) | C7—C8—C9—O2 | −146.6 (6) |
Cu1ii—O2—C9—O1 | 2.7 (8) | C9—C8—C7—N2 | −60.4 (7) |
Symmetry codes: (i) x−1/2, −y+3/2, −z+2; (ii) x+1/2, −y+3/2, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1WB···O1i | 0.85 | 2.12 | 2.730 (6) | 129 |
O1W—H1WA···O3 | 0.85 | 2.17 | 2.928 (9) | 149 |
Symmetry code: (i) x−1/2, −y+3/2, −z+2. |
Experimental details
Crystal data |
Chemical formula | [Cu(C9H9N2O2)(H2O)]ClO4 |
Mr | 358.19 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 295 |
a, b, c (Å) | 7.9552 (13), 11.6740 (19), 14.050 (2) |
V (Å3) | 1304.8 (4) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 1.91 |
Crystal size (mm) | 0.14 × 0.12 × 0.10 |
|
Data collection |
Diffractometer | Bruker SMART APEX CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.776, 0.832 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5173, 2457, 2092 |
Rint | 0.034 |
(sin θ/λ)max (Å−1) | 0.617 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.054, 0.129, 1.01 |
No. of reflections | 2457 |
No. of parameters | 182 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.48, −0.34 |
Absolute structure | Flack (1983) |
Absolute structure parameter | −0.02 (3) |
Selected geometric parameters (Å, º) topCu1—O1 | 1.959 (4) | O1—C9 | 1.268 (7) |
Cu1—O2i | 1.957 (4) | O2—C9 | 1.240 (7) |
Cu1—O1W | 2.397 (4) | N2—C6 | 1.265 (8) |
Cu1—N1 | 1.997 (5) | N2—C7 | 1.445 (8) |
Cu1—N2 | 1.976 (5) | | |
| | | |
O1—Cu1—O1W | 91.26 (17) | O1W—Cu1—N2 | 91.1 (2) |
O1—Cu1—N1 | 166.05 (18) | O1W—Cu1—O2i | 94.06 (17) |
O1—Cu1—N2 | 91.13 (18) | N1—Cu1—N2 | 81.5 (2) |
O1—Cu1—O2i | 87.57 (16) | O2i—Cu1—N1 | 98.68 (18) |
O1W—Cu1—N1 | 100.66 (17) | O2i—Cu1—N2 | 174.7 (2) |
Symmetry code: (i) x−1/2, −y+3/2, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O1W—H1WB···O1i | 0.85 | 2.12 | 2.730 (6) | 129 |
O1W—H1WA···O3 | 0.85 | 2.17 | 2.928 (9) | 149 |
Symmetry code: (i) x−1/2, −y+3/2, −z+2. |
Well defined chiral metal complexes and metal-containing helical species have attracted much interest in coordination chemistry and materials science (Albrecht, 2001; Erxleben, 2001; Ezuhara et al., 1999), due to their importance in biological systems, asymmetric catalysis, enantioselective separation and nonlinear optical material. The design and synthesis of chiral helical structure are challenging because the chirality must be achieved in the extended crystal structure (Coronado et al., 2003; Imai et al., 2004). In most cases, self-assembly of metal ions and multidentate ligands results in the formation of covalently bonded single-, double-, triple- and even quadruple-stranded metal helicates (Lehn, 1995; Piguet et al., 1997; Williams, 1997), in which left-handed and right-handed helical chains alternate in the lattices, resulting in optically inactive racemic crystals. However, metal-containing chiral helical complexes derived from achiral ligands have received less attention (Biradha et al., 1999; Colacio et al., 1992; Studer et al., 1989). Here we report the preparation of a novel, chiral, single-stranded helical CuII coordination polymer, (I), using a tridentate Schiff base carboxylate-containing ligand derived from the condensation of 2-pyridinecarboxaldehyde with β-alanine.
The structure of (I) consists of helical chains of {[Cu(C9H9N2O2)(H2O)]n+ and of ClO4- anions as shown in Fig. 1. The copper(II) complex exhibits a CuN2O3 square-based-pyramidal coordination environment, with the three donor atoms of the ligand and one O atom belonging to the carboxylate group of an adjacent molecule occupying the four basal positions, while an O atom from a water molecule coordinates in the apical position. The Cu atom is displaced by 0.149 (2) Å from the mean basal plane towards the axial donor. Each carboxylate group bridges two CuII ions in a syn-anti fashion: the intrachain Cu···Cu distance is 4.938 (1) Å, and left-handed chiral helices run parallel to the crystallographic a axis (Fig. 2). While the Cu1—O1 distance of 1.959 (4) Å is comparable to the commonly observed bond lengths between bridging carboxylate O and CuII (Colacio et al., 2000; Studer et al., 1989), the Cu1—O1W distance is somewhat longer. The shortest Cu···O distance between CuII ions and ClO4- anions [Cu1···O6 = 3.305 (2) Å] indicates that such contacts are not significant. One water H atom (H1WB) participates in an intrachain O—H···O hydrogen bond with the carboxylate O1 atom [O1W···O1 2.730 (6) Å, H1WB···O1 2.12 Å, and O1W—H1WB···O1 129°], but there are no significant hydrogen-bonding contacts between the helical chains due to the nearest interchain separation of 2.85 Å [H8B—C3i, (i) = -x + 3/2, -y + 1, z + 1/2] being somewhat longer. However, there are O–H···O hydrogen bonds between the water molecules and the O3 atoms of the perchlorate anions (Table 2, Fig. 1).
Treatment of copper(II) perchlorate with an equimolar amount of the same ligand as (I) in methanol/H2O (3:1 v/v), yields blue crystals of poly[[µ -N-(2-pyridylmethylene)-2-carboxyethylamine)-aqua-copper(II)] perchlorate dihydrate], (II), (Colacio et al., 2000), which has a similar structure to (I). Both complexes exhibit approximately square-based-pyramidal CuII ions which are bridged by syn-anti carboxylate groups to form helical chains. In the lattice of (II), however, left-handed and right-handed helical chains alternate, resulting in optically inactive racemic crystals. The structural differences between (I) and (II) suggest that the solvent molecules exert an influence on the spontaneous resolution of left- and right-handed helices; this opens up the possibility of controlling the formation of the chiral helical structures by varying the nature of the solvent used.