In the title polymeric compound, [Cu(C
9H
6O
4)(C
3H
4N
2)
2]
n, the copper(II) cation occupies an N
2O
3 coordination sphere defined by two 1
H-imidazole (imid) ligands in
trans positions and three carboxylate O atoms from three different 2-(carboxylatomethyl)benzoate (hpt
2−) dianions. The geometry is that of a square pyramid with one of the O atoms at the apex, bridging neighbouring metal centres into an [–ON
2CuO
2CuN
2O–] dinuclear unit. These units are in turn connected by hpt anions into a reticular mesh topologically characterized by two types of loops,
viz. a four-membered Cu
2O
2 diamond motif and a 32-membered Cu
4O
8C
20 ring. The imid groups do not take part in the formation of the two-dimensional structure, but take part in the N—H
O interactions. These arise only within individual planes, interplanar interactions being only of the van der Waals type.
Supporting information
CCDC reference: 855948
Complex (I) was synthesized by adding an aqueous solution (80 ml) of copper
acetate monohydrate (1 mmol) to an aqueous solution containing homophthalic
acid (0.5 mmol) and NaOH (1 mmol). The mixture was heated under reflux for 20 min. An ethanolic solution (30 ml) containing imidazole (0.5 mmol) was added
slowly and the final solution was maintained under reflux for 4 h. Single
crystals suitable for X-ray diffraction studies were obtained by slow
concentration of the solution.
All the H atoms were clearly seen in a difference Fourier map but they were
treated differently in the refinement. H atoms on C atoms were repositioned at
their expected locations and allowed to ride both with respect to their
coordinates (C—H = 0.93–0.97 Å) and their isotropic displacement
parameters [Uiso(H) = 1.2Ueq(C)]. H atoms attached to N
atoms were refined freely.
Data collection: SMART (Bruker, 2001); 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); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).
Poly[[µ
3-2-(carboxylatomethyl)benzoato-
κ3O1:
O2:
O2]-bis(1
H-imidazole-
κN3)copper(II)]
top
Crystal data top
[Cu(C9H6O4)(C3H4N2)2] | F(000) = 772 |
Mr = 377.84 | Dx = 1.532 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 5662 reflections |
a = 11.817 (3) Å | θ = 3.0–21.6° |
b = 9.871 (2) Å | µ = 1.36 mm−1 |
c = 14.106 (3) Å | T = 298 K |
β = 95.305 (4)° | Prisms, blue |
V = 1638.2 (6) Å3 | 0.37 × 0.16 × 0.12 mm |
Z = 4 | |
Data collection top
Bruker SMART CCD area-detector diffractometer | 3654 independent reflections |
Radiation source: fine-focus sealed tube | 2886 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.029 |
CCD rotation images, thin slices scans | θmax = 27.8°, θmin = 1.7° |
Absorption correction: multi-scan (SADABS in SAINT; Bruker, 2002) | h = −15→15 |
Tmin = 0.79, Tmax = 0.89 | k = −13→12 |
13360 measured reflections | l = −18→18 |
Refinement top
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)] = 0.042 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.109 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.06 | w = 1/[σ2(Fo2) + (0.0572P)2 + 0.267P] where P = (Fo2 + 2Fc2)/3 |
3654 reflections | (Δ/σ)max = 0.001 |
225 parameters | Δρmax = 0.66 e Å−3 |
0 restraints | Δρmin = −0.20 e Å−3 |
Crystal data top
[Cu(C9H6O4)(C3H4N2)2] | V = 1638.2 (6) Å3 |
Mr = 377.84 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 11.817 (3) Å | µ = 1.36 mm−1 |
b = 9.871 (2) Å | T = 298 K |
c = 14.106 (3) Å | 0.37 × 0.16 × 0.12 mm |
β = 95.305 (4)° | |
Data collection top
Bruker SMART CCD area-detector diffractometer | 3654 independent reflections |
Absorption correction: multi-scan (SADABS in SAINT; Bruker, 2002) | 2886 reflections with I > 2σ(I) |
Tmin = 0.79, Tmax = 0.89 | Rint = 0.029 |
13360 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.042 | 0 restraints |
wR(F2) = 0.109 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.06 | Δρmax = 0.66 e Å−3 |
3654 reflections | Δρmin = −0.20 e Å−3 |
225 parameters | |
Special details top
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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Cu1 | 1.05825 (2) | 0.59104 (3) | 0.40651 (2) | 0.03833 (13) | |
N11 | 0.96321 (18) | 0.7580 (2) | 0.41391 (15) | 0.0418 (5) | |
C21 | 0.9890 (3) | 0.8781 (3) | 0.3788 (2) | 0.0517 (7) | |
H21 | 1.0590 | 0.8988 | 0.3573 | 0.062* | |
N31 | 0.9034 (2) | 0.9647 (3) | 0.37823 (19) | 0.0596 (7) | |
H31 | 0.896 (3) | 1.041 (4) | 0.352 (3) | 0.076 (11)* | |
C41 | 0.8157 (3) | 0.8987 (3) | 0.4145 (3) | 0.0679 (9) | |
H41 | 0.7441 | 0.9336 | 0.4227 | 0.081* | |
C51 | 0.8535 (3) | 0.7724 (3) | 0.4360 (2) | 0.0570 (8) | |
H51 | 0.8111 | 0.7049 | 0.4621 | 0.068* | |
N12 | 1.15042 (19) | 0.4320 (2) | 0.37451 (15) | 0.0420 (5) | |
C22 | 1.1126 (2) | 0.3139 (3) | 0.33940 (19) | 0.0470 (6) | |
H22 | 1.0362 | 0.2918 | 0.3269 | 0.056* | |
N32 | 1.1981 (2) | 0.2314 (3) | 0.32436 (18) | 0.0544 (6) | |
H32 | 1.185 (3) | 0.151 (4) | 0.301 (3) | 0.087 (12)* | |
C42 | 1.2966 (3) | 0.2978 (3) | 0.3501 (2) | 0.0580 (8) | |
H42 | 1.3700 | 0.2650 | 0.3470 | 0.070* | |
C52 | 1.2672 (2) | 0.4207 (3) | 0.3811 (2) | 0.0499 (7) | |
H52 | 1.3179 | 0.4879 | 0.4036 | 0.060* | |
O13 | 0.80892 (15) | 0.20647 (18) | 0.10750 (13) | 0.0448 (4) | |
O23 | 0.84169 (16) | 0.19392 (19) | 0.26526 (14) | 0.0518 (5) | |
O33 | 0.87450 (15) | 0.50886 (18) | 0.27440 (12) | 0.0434 (4) | |
O43 | 0.92502 (15) | 0.47182 (18) | 0.42644 (12) | 0.0419 (4) | |
C13 | 0.6796 (2) | 0.3174 (3) | 0.19749 (18) | 0.0406 (6) | |
C23 | 0.6009 (2) | 0.3237 (3) | 0.1178 (2) | 0.0593 (8) | |
H23 | 0.6139 | 0.2740 | 0.0638 | 0.071* | |
C33 | 0.5048 (3) | 0.4014 (4) | 0.1169 (3) | 0.0785 (12) | |
H33 | 0.4530 | 0.4031 | 0.0632 | 0.094* | |
C43 | 0.4849 (3) | 0.4770 (4) | 0.1958 (3) | 0.0802 (11) | |
H43 | 0.4202 | 0.5307 | 0.1953 | 0.096* | |
C53 | 0.5620 (2) | 0.4722 (4) | 0.2756 (2) | 0.0627 (9) | |
H53 | 0.5482 | 0.5238 | 0.3285 | 0.075* | |
C63 | 0.6591 (2) | 0.3933 (3) | 0.2793 (2) | 0.0434 (6) | |
C73 | 0.7848 (2) | 0.2324 (2) | 0.19216 (19) | 0.0399 (6) | |
C83 | 0.7409 (2) | 0.3985 (3) | 0.36755 (19) | 0.0439 (6) | |
H83A | 0.7545 | 0.3069 | 0.3907 | 0.053* | |
H83B | 0.7058 | 0.4483 | 0.4163 | 0.053* | |
C93 | 0.8542 (2) | 0.4638 (2) | 0.35329 (17) | 0.0370 (5) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cu1 | 0.0382 (2) | 0.0381 (2) | 0.0385 (2) | −0.00455 (13) | 0.00284 (14) | 0.00193 (12) |
N11 | 0.0442 (12) | 0.0430 (12) | 0.0387 (12) | −0.0004 (10) | 0.0057 (9) | 0.0015 (9) |
C21 | 0.0555 (18) | 0.0453 (16) | 0.0558 (18) | 0.0002 (13) | 0.0131 (14) | 0.0052 (13) |
N31 | 0.0705 (18) | 0.0467 (15) | 0.0622 (17) | 0.0093 (14) | 0.0094 (14) | 0.0163 (13) |
C41 | 0.0527 (19) | 0.066 (2) | 0.085 (3) | 0.0152 (16) | 0.0101 (17) | 0.0169 (18) |
C51 | 0.0509 (17) | 0.0559 (18) | 0.065 (2) | 0.0012 (14) | 0.0092 (14) | 0.0158 (15) |
N12 | 0.0444 (13) | 0.0420 (12) | 0.0396 (12) | −0.0014 (10) | 0.0047 (10) | 0.0016 (9) |
C22 | 0.0504 (16) | 0.0464 (15) | 0.0433 (15) | −0.0050 (13) | −0.0008 (12) | −0.0001 (12) |
N32 | 0.0658 (17) | 0.0441 (14) | 0.0534 (15) | −0.0004 (12) | 0.0062 (12) | −0.0110 (12) |
C42 | 0.0519 (18) | 0.0572 (18) | 0.066 (2) | 0.0035 (15) | 0.0107 (15) | −0.0064 (15) |
C52 | 0.0434 (16) | 0.0510 (17) | 0.0553 (18) | −0.0041 (12) | 0.0058 (13) | −0.0054 (13) |
O13 | 0.0420 (10) | 0.0456 (10) | 0.0468 (11) | 0.0080 (8) | 0.0053 (8) | −0.0008 (8) |
O23 | 0.0532 (12) | 0.0471 (11) | 0.0527 (12) | 0.0113 (9) | −0.0077 (9) | 0.0033 (9) |
O33 | 0.0455 (10) | 0.0467 (11) | 0.0381 (10) | −0.0021 (8) | 0.0045 (8) | 0.0035 (8) |
O43 | 0.0407 (10) | 0.0485 (10) | 0.0355 (10) | −0.0078 (8) | −0.0020 (8) | 0.0035 (8) |
C13 | 0.0324 (12) | 0.0470 (15) | 0.0424 (14) | −0.0007 (11) | 0.0037 (11) | −0.0015 (11) |
C23 | 0.0437 (16) | 0.086 (2) | 0.0470 (17) | 0.0089 (15) | −0.0032 (13) | −0.0107 (16) |
C33 | 0.0441 (18) | 0.131 (4) | 0.057 (2) | 0.0293 (19) | −0.0109 (15) | −0.009 (2) |
C43 | 0.0455 (19) | 0.112 (3) | 0.082 (3) | 0.030 (2) | −0.0011 (18) | −0.011 (2) |
C53 | 0.0408 (16) | 0.083 (2) | 0.065 (2) | 0.0072 (16) | 0.0103 (15) | −0.0178 (18) |
C63 | 0.0342 (13) | 0.0527 (16) | 0.0434 (15) | −0.0044 (11) | 0.0047 (11) | −0.0020 (12) |
C73 | 0.0386 (13) | 0.0321 (12) | 0.0486 (16) | −0.0002 (10) | 0.0016 (12) | −0.0004 (11) |
C83 | 0.0377 (14) | 0.0567 (17) | 0.0378 (14) | −0.0074 (12) | 0.0069 (11) | −0.0040 (12) |
C93 | 0.0403 (14) | 0.0338 (12) | 0.0368 (14) | −0.0002 (10) | 0.0033 (11) | −0.0026 (10) |
Geometric parameters (Å, º) top
Cu1—O13i | 1.9643 (18) | C52—H52 | 0.9300 |
Cu1—N12 | 1.987 (2) | O13—C73 | 1.279 (3) |
Cu1—N11 | 2.003 (2) | O13—Cu1iii | 1.9643 (17) |
Cu1—O43 | 2.0060 (18) | O23—C73 | 1.237 (3) |
Cu1—O43ii | 2.4269 (17) | O33—C93 | 1.242 (3) |
N11—C21 | 1.331 (3) | O43—C93 | 1.269 (3) |
N11—C51 | 1.368 (4) | O43—Cu1ii | 2.4269 (17) |
C21—N31 | 1.324 (4) | C13—C23 | 1.393 (4) |
C21—H21 | 0.9300 | C13—C63 | 1.415 (4) |
N31—C41 | 1.363 (4) | C13—C73 | 1.507 (3) |
N31—H31 | 0.84 (4) | C23—C33 | 1.369 (4) |
C41—C51 | 1.349 (4) | C23—H23 | 0.9300 |
C41—H41 | 0.9300 | C33—C43 | 1.377 (5) |
C51—H51 | 0.9300 | C33—H33 | 0.9300 |
N12—C22 | 1.327 (3) | C43—C53 | 1.382 (5) |
N12—C52 | 1.379 (4) | C43—H43 | 0.9300 |
C22—N32 | 1.330 (4) | C53—C63 | 1.384 (4) |
C22—H22 | 0.9300 | C53—H53 | 0.9300 |
N32—C42 | 1.356 (4) | C63—C83 | 1.505 (4) |
N32—H32 | 0.87 (4) | C83—C93 | 1.516 (3) |
C42—C52 | 1.346 (4) | C83—H83A | 0.9700 |
C42—H42 | 0.9300 | C83—H83B | 0.9700 |
| | | |
O13i—Cu1—N12 | 88.60 (8) | C42—C52—N12 | 109.7 (3) |
O13i—Cu1—N11 | 89.15 (8) | C42—C52—H52 | 125.1 |
N12—Cu1—N11 | 169.82 (9) | N12—C52—H52 | 125.1 |
O13i—Cu1—O43 | 177.64 (7) | C73—O13—Cu1iii | 117.34 (16) |
N12—Cu1—O43 | 91.26 (8) | C93—O43—Cu1 | 112.92 (15) |
N11—Cu1—O43 | 91.39 (8) | C93—O43—Cu1ii | 139.61 (16) |
O13i—Cu1—O43ii | 104.59 (7) | Cu1—O43—Cu1ii | 106.95 (7) |
N12—Cu1—O43ii | 91.22 (7) | C23—C13—C63 | 118.8 (2) |
N11—Cu1—O43ii | 98.95 (7) | C23—C13—C73 | 118.5 (2) |
O43—Cu1—O43ii | 73.05 (7) | C63—C13—C73 | 122.7 (2) |
C21—N11—C51 | 104.3 (2) | C33—C23—C13 | 121.6 (3) |
C21—N11—Cu1 | 124.41 (19) | C33—C23—H23 | 119.2 |
C51—N11—Cu1 | 130.2 (2) | C13—C23—H23 | 119.2 |
N31—C21—N11 | 112.1 (3) | C23—C33—C43 | 120.0 (3) |
N31—C21—H21 | 123.9 | C23—C33—H33 | 120.0 |
N11—C21—H21 | 123.9 | C43—C33—H33 | 120.0 |
C21—N31—C41 | 107.2 (3) | C33—C43—C53 | 119.4 (3) |
C21—N31—H31 | 129 (2) | C33—C43—H43 | 120.3 |
C41—N31—H31 | 123 (3) | C53—C43—H43 | 120.3 |
C51—C41—N31 | 106.2 (3) | C43—C53—C63 | 122.1 (3) |
C51—C41—H41 | 126.9 | C43—C53—H53 | 118.9 |
N31—C41—H41 | 126.9 | C63—C53—H53 | 118.9 |
C41—C51—N11 | 110.2 (3) | C53—C63—C13 | 118.2 (3) |
C41—C51—H51 | 124.9 | C53—C63—C83 | 118.6 (3) |
N11—C51—H51 | 124.9 | C13—C63—C83 | 123.2 (2) |
C22—N12—C52 | 104.8 (2) | O23—C73—O13 | 124.4 (2) |
C22—N12—Cu1 | 127.28 (19) | O23—C73—C13 | 121.1 (2) |
C52—N12—Cu1 | 127.92 (19) | O13—C73—C13 | 114.5 (2) |
N12—C22—N32 | 111.2 (3) | C63—C83—C93 | 114.4 (2) |
N12—C22—H22 | 124.4 | C63—C83—H83A | 108.7 |
N32—C22—H22 | 124.4 | C93—C83—H83A | 108.7 |
C22—N32—C42 | 107.9 (2) | C63—C83—H83B | 108.7 |
C22—N32—H32 | 121 (3) | C93—C83—H83B | 108.7 |
C42—N32—H32 | 131 (3) | H83A—C83—H83B | 107.6 |
C52—C42—N32 | 106.3 (3) | O33—C93—O43 | 122.6 (2) |
C52—C42—H42 | 126.8 | O33—C93—C83 | 121.1 (2) |
N32—C42—H42 | 126.8 | O43—C93—C83 | 116.3 (2) |
Symmetry codes: (i) −x+2, y+1/2, −z+1/2; (ii) −x+2, −y+1, −z+1; (iii) −x+2, y−1/2, −z+1/2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N31—H31···O23iv | 0.84 (4) | 2.01 (4) | 2.824 (3) | 163 (4) |
N32—H32···O33iii | 0.87 (4) | 1.85 (4) | 2.699 (3) | 162 (4) |
C21—H21···O33i | 0.93 | 2.35 | 3.096 (4) | 137 |
C22—H22···O23 | 0.93 | 2.57 | 3.482 (3) | 167 |
C51—H51···Cg2ii | 0.93 | 2.66 | 3.294 (3) | 126 |
Symmetry codes: (i) −x+2, y+1/2, −z+1/2; (ii) −x+2, −y+1, −z+1; (iii) −x+2, y−1/2, −z+1/2; (iv) x, y+1, z. |
Experimental details
Crystal data |
Chemical formula | [Cu(C9H6O4)(C3H4N2)2] |
Mr | 377.84 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 298 |
a, b, c (Å) | 11.817 (3), 9.871 (2), 14.106 (3) |
β (°) | 95.305 (4) |
V (Å3) | 1638.2 (6) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 1.36 |
Crystal size (mm) | 0.37 × 0.16 × 0.12 |
|
Data collection |
Diffractometer | Bruker SMART CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS in SAINT; Bruker, 2002) |
Tmin, Tmax | 0.79, 0.89 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 13360, 3654, 2886 |
Rint | 0.029 |
(sin θ/λ)max (Å−1) | 0.657 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.042, 0.109, 1.06 |
No. of reflections | 3654 |
No. of parameters | 225 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.66, −0.20 |
Selected bond lengths (Å) topCu1—O13i | 1.9643 (18) | Cu1—O43 | 2.0060 (18) |
Cu1—N12 | 1.987 (2) | Cu1—O43ii | 2.4269 (17) |
Cu1—N11 | 2.003 (2) | | |
Symmetry codes: (i) −x+2, y+1/2, −z+1/2; (ii) −x+2, −y+1, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N31—H31···O23iii | 0.84 (4) | 2.01 (4) | 2.824 (3) | 163 (4) |
N32—H32···O33iv | 0.87 (4) | 1.85 (4) | 2.699 (3) | 162 (4) |
C21—H21···O33i | 0.93 | 2.35 | 3.096 (4) | 137 |
C22—H22···O23 | 0.93 | 2.57 | 3.482 (3) | 167 |
C51—H51···Cg2ii | 0.93 | 2.66 | 3.294 (3) | 126 |
Symmetry codes: (i) −x+2, y+1/2, −z+1/2; (ii) −x+2, −y+1, −z+1; (iii) x, y+1, z; (iv) −x+2, y−1/2, −z+1/2. |
The study of organic–inorganic hybrid coordination frameworks is a key point in [an important part of?] modern structural chemistry, mainly due to the potential properties [of these materials] with which many of these materials are adorned. In these `prediction, design, synthesis and structural analysis' exercises, the ligands usually preferred are those characterized by versatility, coordination capabilities and, eventually, a large number of possible coordination modes (Archer, 2001). Benzenecarboxylic acids of flexible structure, such as homophthalic acid (H2hpt), the ligand of interest to us, comply with many of these requisites and have largely proven to be useful in constructing complex frameworks with varied topology (He et al., 2006; Cavellec et al., 2003; Pan et al., 2003; Wan et al., 2003).
Interest in these types of materials, and in hpt-based materials, as representatives has been explosive in the last few years, as assessed by inspection of the distribution along the years of structural studies on hpt complexes [Cambridge Structural Database (CSD), Version 5.32; Allen, 2002]: the first report appeared in 2001 (Cotton et al., 2001) and in the following five years only two more followed (Burrows et al., 2003, 2004). But in the equivalent five-year-period following 2006, 18 new structures have appeared, confirming this fast-growing trend.
In these reported structures, the hpt ligand showed its varied binding capabilities by displaying nine different coordination modes. We refer the interested reader to Atria et al. (2011) for a comprehensive review of the ways in which the ligand has shown to bind to metal centres. In this same report, two new isomorphous hpt structures were presented, namely M[(Hdap)(hpt)(H2O)]2.4H2O (where dap is 2,6-diaminopurine and M is NiII or CoII); in these structures, the hpt anion displayed an unusual (and at the time unreported) µ-κ1O coordination mode.
In pursuit of our interest in the different architectures to which the hpt ligand can give rise, we present herein a new copper(II) complex poly[[µ3-2-(carboxylatomethyl)benzoato]bis(1H-imidazole)copper(II)], (I), incorporating a fully deprotonated 2-(carboxylatomethyl)benzoate (hpt2-) dianion and 1H-imidazole (imid) as an ancillary ligand. In this structure, again, a new bridging coordination mode for the hpt2- anion is found.
Fig. 1 presents an ellipsoid plot of the (extended) asymmetric unit of (I), showing the complete coordination environment of the copper(II) cation and the dimeric unit it gives rise to: two independent imid groups are in trans positions and three symmetry-related hpt2- anions complete a CuN2O2+O square-pyramidal arrangement, with a rather regular base [Cu—L distance range = 1.9643 (18)–2.0060 (18) Å and L—Cu—L cis angle range = 88.60 (8)–91.39 (8)°; L = basal N, O], and an apical bond tilted by 16.2 (2)° from the vertrical to the mean basal plane. The µ3κ2-O:O':O' mode displayed by hpt2- is novel and should be added to those listed in Atria et al. (2011). The imidazole ligands coordinate trans to each other [N—Cu—N = 169.82 (9)°] and only interact with the rest of the structure via nonbonding interactions (see below). The hpt2- anions, instead, play a leading role in the spatial arrangement: via the sharing of atom O43 with two different coordination polyhedra they define a dimeric substructure, linking adjacent moieties into dinuclear entities ("A" in Figs. 1 and 2), with a Cu1···Cu1ii distance of 3.5710 (8) Å [symmetry code: (ii) -x+2, -y+1, -z+1]. The resulting Cu2O2 loops, in turn, appear as the nodes of much larger macrocycles determined by the stretched out hpt2- carboxylato and methylcarboxylato arms, ending up in large Cu4O8C20 loops [or (CuO2C5)4, "B" in Fig. 2]. The final structure can be envisaged as the concatenation into a two-dimensional mesh of these two kinds of small and large loops. Even if imid ligands pend [bend?] outwards, with no direct intervention in the mesh formation, they collaborate [contribute?] to the mesh stability through two strong N—H···O hydrogen bonds described in Table 2 and shown in Fig 1. In these contacts, the donor atoms are the protonated imid N atoms, while the acceptors are the two carboxylate O atoms not involved in coordination. These contacts, as well as the remaining (though weaker) interactions of the C—H···O and C—H···π types shown in Table 2, are internal to the two-dimensional structures and do not mix adjacent planes, [for what] interplanar stability appears [to be] achieved through van der Waals forces only.
Fig. 3 shows two lateral views of these planes, depicting this lack of close contacts. The reader should note that the views in Fig. 3 might be deceptive in suggesting some kind of π–π interaction between benzene hpt2- groups; this is just a perspective artifact since the centroids of neighbouring hpt groups in contiguous planes lie more than 5.5 Å apart and the rings they belong to are far from parallel.
Large loops like the (CuO2C5)4 one herein, or, more generally, (M—L)4, with M being any transition metal and L being the `looping' ligand, are not uncommon in three-dimensional structures. Sometimes they appear embracing smaller, embedded loops and in this context the larger loops are not so relevant from a structural point of view. However, browsing through the CSD (Allen, 2002) we spotted a few cases presenting rings of a similar size as in (I) which also constituted primary building units in the crystal architecture. Surprisingly, in most of them, the L ligand was a close relative in the benzylcarboxylate family. Some examples, given in a sequence of the type [CSD refcode: M—L (reference)] are: ATORIK: Zn–isophthalohydrazide (He et al., 2004); FUDHOC, FUDHUI, FUHYAJ, FUHYAJ01, FUHYEN01, FUHYIR: Cu–trimesic acid (Ene et al., 2009); SOMLUC: Ni–pyrazole-3,5-dicarboxylate (Bai et al., 2008); TIGLAW: Co–pyrazole-3,5-dicarboxylate (Pan et al., 2001); TUHFIM: Co–5-tert-butylisophalate (Du et al., 2009).
Many of these examples display free open loops where solvents of different kinds and shapes (water or pyridylmethanol) reside. In the present case of (I), instead, the bulky hpt2- and imid groups lean towards the loop centre, thus limiting the hosting capability of the compound.