The structure of the title compound, C42H56N2O2, comprises a centrosymmetric molecule, with only half of the molecule in the asymmetric unit and with an inversion centre in the middle of the squarate ring. The squaraine moiety is planar and extensively delocalized, with the dihedral angle between the squarate and indoline planes being 3.9 (2)°.
Supporting information
CCDC reference: 197482
Key indicators
- Single-crystal X-ray study
- T = 150 K
- Mean (C-C) = 0.004 Å
- R factor = 0.070
- wR factor = 0.208
- Data-to-parameter ratio = 19.2
checkCIF results
No syntax errors found
ADDSYM reports no extra symmetry
Alert Level C:
RINTA_01 Alert C The value of Rint is greater than 0.10
Rint given 0.125
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check
The title compound was prepared according to the literature procedures described by Lynch & Byriel (1999), and crystals were grown from a chloroform solution.
All H atoms were included in the refinement at calculated positions as riding models, with C—H set to 0.95 (Ar—H), 0.99 (CH2) and 0.98 Å (CH3). The high Rint value of 0.125 is the result of weak high-angle data.
Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON97 (Spek, 1997); software used to prepare material for publication: SHELXL97.
2,4-Bis(3,3-dimethyl-1-octylindolin-2-ylidenemethyl)cyclobutenediylio-1,3- diolate
top
Crystal data top
C42H56N2O2 | F(000) = 676 |
Mr = 620.89 | Dx = 1.154 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 9.2547 (4) Å | Cell parameters from 7704 reflections |
b = 16.2169 (8) Å | θ = 2.9–27.5° |
c = 12.2437 (7) Å | µ = 0.07 mm−1 |
β = 103.569 (2)° | T = 150 K |
V = 1786.28 (16) Å3 | Plate, blue |
Z = 2 | 0.20 × 0.07 × 0.02 mm |
Data collection top
Bruker Nonius KappaCCD area-detector diffractometer | 4051 independent reflections |
Radiation source: Bruker Nonius FR591 rotating-anode | 1951 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.125 |
Detector resolution: 9.091 pixels mm-1 | θmax = 27.5°, θmin = 3.0° |
ϕ and ω scans | h = −11→11 |
Absorption correction: multi-scan (SORTAV; Blessing, 1995) | k = −17→21 |
Tmin = 0.986, Tmax = 0.999 | l = −15→15 |
16116 measured reflections | |
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)] = 0.070 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.208 | H-atom parameters constrained |
S = 0.98 | w = 1/[σ2(Fo2) + (0.1015P)2] where P = (Fo2 + 2Fc2)/3 |
4051 reflections | (Δ/σ)max < 0.001 |
211 parameters | Δρmax = 0.39 e Å−3 |
0 restraints | Δρmin = −0.33 e Å−3 |
Crystal data top
C42H56N2O2 | V = 1786.28 (16) Å3 |
Mr = 620.89 | Z = 2 |
Monoclinic, P21/n | Mo Kα radiation |
a = 9.2547 (4) Å | µ = 0.07 mm−1 |
b = 16.2169 (8) Å | T = 150 K |
c = 12.2437 (7) Å | 0.20 × 0.07 × 0.02 mm |
β = 103.569 (2)° | |
Data collection top
Bruker Nonius KappaCCD area-detector diffractometer | 4051 independent reflections |
Absorption correction: multi-scan (SORTAV; Blessing, 1995) | 1951 reflections with I > 2σ(I) |
Tmin = 0.986, Tmax = 0.999 | Rint = 0.125 |
16116 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.070 | 0 restraints |
wR(F2) = 0.208 | H-atom parameters constrained |
S = 0.98 | Δρmax = 0.39 e Å−3 |
4051 reflections | Δρmin = −0.33 e Å−3 |
211 parameters | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
O1 | 0.73301 (18) | 0.05283 (12) | 0.54000 (17) | 0.0354 (5) | |
N1 | 0.3602 (2) | 0.19835 (14) | 0.74619 (18) | 0.0249 (6) | |
C1 | 0.6064 (3) | 0.02261 (17) | 0.5168 (2) | 0.0257 (6) | |
C2 | 0.4719 (3) | 0.04398 (17) | 0.5540 (2) | 0.0232 (6) | |
C3 | 0.4603 (3) | 0.10813 (17) | 0.6279 (2) | 0.0241 (6) | |
H3 | 0.5480 | 0.1404 | 0.6500 | 0.030* | |
C4 | 0.3462 (3) | 0.13357 (16) | 0.6749 (2) | 0.0218 (6) | |
C5 | 0.1888 (3) | 0.09826 (16) | 0.6581 (2) | 0.0226 (6) | |
C6 | 0.1240 (3) | 0.15398 (17) | 0.7339 (2) | 0.0239 (6) | |
C7 | −0.0145 (3) | 0.15433 (18) | 0.7562 (2) | 0.0305 (7) | |
H7 | −0.0879 | 0.1155 | 0.7217 | 0.038* | |
C8 | −0.0448 (3) | 0.2133 (2) | 0.8309 (3) | 0.0371 (8) | |
H8 | −0.1399 | 0.2140 | 0.8478 | 0.046* | |
C9 | 0.0604 (3) | 0.27039 (18) | 0.8807 (2) | 0.0335 (7) | |
H9 | 0.0367 | 0.3097 | 0.9313 | 0.042* | |
C10 | 0.2007 (3) | 0.27128 (18) | 0.8578 (2) | 0.0300 (7) | |
H10 | 0.2737 | 0.3107 | 0.8911 | 0.037* | |
C11 | 0.2290 (3) | 0.21187 (17) | 0.7840 (2) | 0.0236 (6) | |
C12 | 0.4870 (3) | 0.25518 (17) | 0.7725 (2) | 0.0285 (7) | |
H121 | 0.5803 | 0.2233 | 0.7821 | 0.036* | |
H122 | 0.4884 | 0.2834 | 0.8444 | 0.036* | |
C13 | 0.4804 (3) | 0.31896 (19) | 0.6817 (3) | 0.0352 (8) | |
H131 | 0.3914 | 0.3540 | 0.6764 | 0.044* | |
H132 | 0.4707 | 0.2908 | 0.6085 | 0.044* | |
C14 | 0.6186 (3) | 0.37325 (19) | 0.7050 (3) | 0.0376 (8) | |
H141 | 0.7069 | 0.3385 | 0.7063 | 0.047* | |
H142 | 0.6312 | 0.3988 | 0.7801 | 0.047* | |
C15 | 0.6098 (3) | 0.44087 (19) | 0.6174 (3) | 0.0419 (8) | |
H151 | 0.5208 | 0.4751 | 0.6157 | 0.052* | |
H152 | 0.5977 | 0.4151 | 0.5425 | 0.052* | |
C16 | 0.7467 (3) | 0.4964 (2) | 0.6397 (3) | 0.0463 (9) | |
H161 | 0.7324 | 0.5388 | 0.5798 | 0.058* | |
H162 | 0.7533 | 0.5255 | 0.7118 | 0.058* | |
C17 | 0.8917 (3) | 0.4533 (2) | 0.6448 (3) | 0.0450 (9) | |
H171 | 0.9129 | 0.4165 | 0.7111 | 0.056* | |
H172 | 0.9717 | 0.4952 | 0.6561 | 0.056* | |
C18 | 0.8968 (4) | 0.4029 (2) | 0.5416 (3) | 0.0500 (9) | |
H181 | 0.8200 | 0.3592 | 0.5319 | 0.063* | |
H182 | 0.8722 | 0.4390 | 0.4747 | 0.063* | |
C19 | 1.0461 (4) | 0.3633 (2) | 0.5480 (3) | 0.0527 (9) | |
H191 | 1.1235 | 0.4058 | 0.5613 | 0.066* | |
H192 | 1.0448 | 0.3350 | 0.4770 | 0.066* | |
H193 | 1.0669 | 0.3233 | 0.6097 | 0.066* | |
C20 | 0.1036 (3) | 0.10860 (18) | 0.5353 (2) | 0.0288 (7) | |
H201 | −0.0014 | 0.0952 | 0.5283 | 0.036* | |
H202 | 0.1455 | 0.0715 | 0.4876 | 0.036* | |
H203 | 0.1124 | 0.1658 | 0.5117 | 0.036* | |
C21 | 0.1891 (3) | 0.00806 (17) | 0.6958 (2) | 0.0283 (7) | |
H211 | 0.2452 | 0.0032 | 0.7740 | 0.035* | |
H212 | 0.2356 | −0.0264 | 0.6478 | 0.035* | |
H213 | 0.0866 | −0.0103 | 0.6895 | 0.035* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
O1 | 0.0257 (10) | 0.0377 (13) | 0.0443 (13) | −0.0092 (9) | 0.0114 (9) | −0.0154 (10) |
N1 | 0.0242 (12) | 0.0251 (14) | 0.0266 (13) | −0.0055 (9) | 0.0083 (10) | −0.0028 (11) |
C1 | 0.0277 (14) | 0.0249 (17) | 0.0252 (16) | −0.0005 (12) | 0.0073 (12) | −0.0024 (13) |
C2 | 0.0219 (13) | 0.0232 (16) | 0.0250 (16) | −0.0006 (11) | 0.0064 (11) | −0.0002 (12) |
C3 | 0.0216 (13) | 0.0246 (16) | 0.0255 (16) | −0.0047 (11) | 0.0043 (11) | −0.0002 (13) |
C4 | 0.0260 (13) | 0.0194 (15) | 0.0193 (14) | −0.0021 (11) | 0.0036 (11) | −0.0019 (12) |
C5 | 0.0219 (13) | 0.0207 (16) | 0.0253 (15) | −0.0020 (11) | 0.0057 (11) | 0.0001 (12) |
C6 | 0.0259 (14) | 0.0233 (16) | 0.0230 (15) | 0.0012 (11) | 0.0067 (11) | 0.0033 (12) |
C7 | 0.0273 (15) | 0.0291 (18) | 0.0353 (18) | −0.0024 (12) | 0.0080 (13) | −0.0025 (14) |
C8 | 0.0317 (16) | 0.041 (2) | 0.043 (2) | 0.0029 (14) | 0.0171 (14) | −0.0019 (16) |
C9 | 0.0401 (17) | 0.0292 (18) | 0.0337 (18) | 0.0066 (13) | 0.0139 (13) | −0.0038 (14) |
C10 | 0.0348 (16) | 0.0259 (17) | 0.0290 (17) | −0.0040 (12) | 0.0071 (12) | −0.0025 (14) |
C11 | 0.0243 (14) | 0.0233 (16) | 0.0235 (15) | 0.0014 (11) | 0.0063 (11) | 0.0000 (12) |
C12 | 0.0286 (14) | 0.0284 (18) | 0.0279 (16) | −0.0084 (12) | 0.0055 (12) | −0.0109 (13) |
C13 | 0.0306 (15) | 0.0363 (19) | 0.0385 (19) | −0.0043 (13) | 0.0078 (13) | −0.0033 (15) |
C14 | 0.0356 (16) | 0.039 (2) | 0.0394 (19) | −0.0055 (13) | 0.0115 (14) | 0.0014 (16) |
C15 | 0.0384 (17) | 0.041 (2) | 0.048 (2) | −0.0036 (14) | 0.0128 (15) | 0.0047 (17) |
C16 | 0.0409 (17) | 0.043 (2) | 0.057 (2) | −0.0085 (15) | 0.0147 (16) | −0.0031 (18) |
C17 | 0.0401 (18) | 0.043 (2) | 0.054 (2) | −0.0095 (15) | 0.0150 (16) | −0.0083 (18) |
C18 | 0.056 (2) | 0.049 (2) | 0.045 (2) | −0.0064 (17) | 0.0114 (16) | −0.0077 (18) |
C19 | 0.066 (2) | 0.045 (2) | 0.048 (2) | 0.0041 (17) | 0.0155 (17) | −0.0033 (18) |
C20 | 0.0288 (14) | 0.0308 (17) | 0.0255 (16) | 0.0012 (12) | 0.0037 (12) | 0.0026 (14) |
C21 | 0.0314 (15) | 0.0212 (16) | 0.0335 (17) | −0.0022 (11) | 0.0102 (12) | −0.0021 (13) |
Geometric parameters (Å, º) top
O1—C1 | 1.240 (3) | C13—C14 | 1.523 (4) |
N1—C4 | 1.352 (3) | C13—H131 | 0.99 |
N1—C11 | 1.414 (3) | C13—H132 | 0.99 |
N1—C12 | 1.467 (3) | C14—C15 | 1.523 (4) |
C1—C2 | 1.464 (3) | C14—H141 | 0.99 |
C1—C2i | 1.466 (4) | C14—H142 | 0.99 |
C2—C3 | 1.399 (4) | C15—C16 | 1.526 (4) |
C2—C1i | 1.466 (4) | C15—H151 | 0.99 |
C3—C4 | 1.379 (3) | C15—H152 | 0.99 |
C3—H3 | 0.95 | C16—C17 | 1.502 (4) |
C4—C5 | 1.534 (3) | C16—H161 | 0.99 |
C5—C6 | 1.516 (4) | C16—H162 | 0.99 |
C5—C21 | 1.534 (4) | C17—C18 | 1.515 (4) |
C5—C20 | 1.534 (4) | C17—H171 | 0.99 |
C6—C7 | 1.372 (3) | C17—H172 | 0.99 |
C6—C11 | 1.387 (4) | C18—C19 | 1.509 (4) |
C7—C8 | 1.396 (4) | C18—H181 | 0.99 |
C7—H7 | 0.95 | C18—H182 | 0.99 |
C8—C9 | 1.378 (4) | C19—H191 | 0.98 |
C8—H8 | 0.95 | C19—H192 | 0.98 |
C9—C10 | 1.392 (4) | C19—H193 | 0.98 |
C9—H9 | 0.95 | C20—H201 | 0.98 |
C10—C11 | 1.387 (4) | C20—H202 | 0.98 |
C10—H10 | 0.95 | C20—H203 | 0.98 |
C12—C13 | 1.510 (4) | C21—H211 | 0.98 |
C12—H121 | 0.99 | C21—H212 | 0.98 |
C12—H122 | 0.99 | C21—H213 | 0.98 |
| | | |
C4—N1—C11 | 111.9 (2) | H131—C13—H132 | 107.9 |
C4—N1—C12 | 125.4 (2) | C13—C14—C15 | 112.3 (2) |
C11—N1—C12 | 122.3 (2) | C13—C14—H141 | 109.1 |
O1—C1—C2 | 131.5 (3) | C15—C14—H141 | 109.1 |
O1—C1—C2i | 137.4 (2) | C13—C14—H142 | 109.1 |
C2—C1—C2i | 91.2 (2) | C15—C14—H142 | 109.1 |
C3—C2—C1 | 125.2 (2) | H141—C14—H142 | 107.9 |
C3—C2—C1i | 145.9 (2) | C14—C15—C16 | 113.2 (3) |
C1—C2—C1i | 88.8 (2) | C14—C15—H151 | 108.9 |
C4—C3—C2 | 132.4 (2) | C16—C15—H151 | 108.9 |
C4—C3—H3 | 113.8 | C14—C15—H152 | 108.9 |
C2—C3—H3 | 113.8 | C16—C15—H152 | 108.9 |
N1—C4—C3 | 122.4 (2) | H151—C15—H152 | 107.7 |
N1—C4—C5 | 108.7 (2) | C17—C16—C15 | 115.4 (3) |
C3—C4—C5 | 128.9 (2) | C17—C16—H161 | 108.4 |
C6—C5—C21 | 111.0 (2) | C15—C16—H161 | 108.4 |
C6—C5—C20 | 110.4 (2) | C17—C16—H162 | 108.4 |
C21—C5—C20 | 111.3 (2) | C15—C16—H162 | 108.4 |
C6—C5—C4 | 101.3 (2) | H161—C16—H162 | 107.5 |
C21—C5—C4 | 112.4 (2) | C16—C17—C18 | 114.8 (3) |
C20—C5—C4 | 110.1 (2) | C16—C17—H171 | 108.6 |
C7—C6—C11 | 120.0 (3) | C18—C17—H171 | 108.6 |
C7—C6—C5 | 130.3 (3) | C16—C17—H172 | 108.6 |
C11—C6—C5 | 109.7 (2) | C18—C17—H172 | 108.6 |
C6—C7—C8 | 118.3 (3) | H171—C17—H172 | 107.6 |
C6—C7—H7 | 120.8 | C19—C18—C17 | 113.2 (3) |
C8—C7—H7 | 120.8 | C19—C18—H181 | 108.9 |
C9—C8—C7 | 121.3 (3) | C17—C18—H181 | 108.9 |
C9—C8—H8 | 119.3 | C19—C18—H182 | 108.9 |
C7—C8—H8 | 119.3 | C17—C18—H182 | 108.9 |
C8—C9—C10 | 120.9 (3) | H181—C18—H182 | 107.8 |
C8—C9—H9 | 119.5 | C18—C19—H191 | 109.5 |
C10—C9—H9 | 119.5 | C18—C19—H192 | 109.5 |
C11—C10—C9 | 116.9 (3) | H191—C19—H192 | 109.5 |
C11—C10—H10 | 121.6 | C18—C19—H193 | 109.5 |
C9—C10—H10 | 121.6 | H191—C19—H193 | 109.5 |
C6—C11—C10 | 122.6 (2) | H192—C19—H193 | 109.5 |
C6—C11—N1 | 108.5 (2) | C5—C20—H201 | 109.5 |
C10—C11—N1 | 129.0 (2) | C5—C20—H202 | 109.5 |
N1—C12—C13 | 112.1 (2) | H201—C20—H202 | 109.5 |
N1—C12—H121 | 109.2 | C5—C20—H203 | 109.5 |
C13—C12—H121 | 109.2 | H201—C20—H203 | 109.5 |
N1—C12—H122 | 109.2 | H202—C20—H203 | 109.5 |
C13—C12—H122 | 109.2 | C5—C21—H211 | 109.5 |
H121—C12—H122 | 107.9 | C5—C21—H212 | 109.5 |
C12—C13—C14 | 111.7 (2) | H211—C21—H212 | 109.5 |
C12—C13—H131 | 109.3 | C5—C21—H213 | 109.5 |
C14—C13—H131 | 109.3 | H211—C21—H213 | 109.5 |
C12—C13—H132 | 109.3 | H212—C21—H213 | 109.5 |
C14—C13—H132 | 109.3 | | |
| | | |
O1—C1—C2—C3 | 0.6 (5) | C11—C6—C7—C8 | −0.8 (4) |
C2i—C1—C2—C3 | −179.0 (3) | C5—C6—C7—C8 | 179.7 (3) |
O1—C1—C2—C1i | 179.6 (4) | C6—C7—C8—C9 | 0.6 (5) |
C2i—C1—C2—C1i | 0.0 | C7—C8—C9—C10 | 0.1 (5) |
C1—C2—C3—C4 | −176.4 (3) | C8—C9—C10—C11 | −0.6 (4) |
C1i—C2—C3—C4 | 5.4 (6) | C7—C6—C11—C10 | 0.3 (4) |
C11—N1—C4—C3 | −179.4 (2) | C5—C6—C11—C10 | 179.9 (2) |
C12—N1—C4—C3 | 7.6 (4) | C7—C6—C11—N1 | −179.5 (2) |
C11—N1—C4—C5 | 1.2 (3) | C5—C6—C11—N1 | 0.1 (3) |
C12—N1—C4—C5 | −171.8 (2) | C9—C10—C11—C6 | 0.4 (4) |
C2—C3—C4—N1 | 179.6 (3) | C9—C10—C11—N1 | −179.9 (3) |
C2—C3—C4—C5 | −1.1 (5) | C4—N1—C11—C6 | −0.9 (3) |
N1—C4—C5—C6 | −1.1 (3) | C12—N1—C11—C6 | 172.4 (2) |
C3—C4—C5—C6 | 179.6 (3) | C4—N1—C11—C10 | 179.4 (3) |
N1—C4—C5—C21 | −119.5 (2) | C12—N1—C11—C10 | −7.4 (4) |
C3—C4—C5—C21 | 61.1 (3) | C4—N1—C12—C13 | 79.1 (3) |
N1—C4—C5—C20 | 115.8 (2) | C11—N1—C12—C13 | −93.2 (3) |
C3—C4—C5—C20 | −63.6 (4) | N1—C12—C13—C14 | −175.4 (2) |
C21—C5—C6—C7 | −60.4 (4) | C12—C13—C14—C15 | −176.9 (2) |
C20—C5—C6—C7 | 63.4 (4) | C13—C14—C15—C16 | 179.6 (3) |
C4—C5—C6—C7 | −179.9 (3) | C14—C15—C16—C17 | 58.6 (4) |
C21—C5—C6—C11 | 120.1 (2) | C15—C16—C17—C18 | 55.8 (4) |
C20—C5—C6—C11 | −116.1 (2) | C16—C17—C18—C19 | 177.7 (3) |
C4—C5—C6—C11 | 0.6 (3) | | |
Symmetry code: (i) −x+1, −y, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C20—H201···O1ii | 0.98 | 2.59 | 3.561 (3) | 172 |
C20—H202···O1i | 0.98 | 2.37 | 3.263 (3) | 151 |
C21—H212···O1i | 0.98 | 2.42 | 3.287 (3) | 147 |
Symmetry codes: (i) −x+1, −y, −z+1; (ii) x−1, y, z. |
Experimental details
Crystal data |
Chemical formula | C42H56N2O2 |
Mr | 620.89 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 150 |
a, b, c (Å) | 9.2547 (4), 16.2169 (8), 12.2437 (7) |
β (°) | 103.569 (2) |
V (Å3) | 1786.28 (16) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.07 |
Crystal size (mm) | 0.20 × 0.07 × 0.02 |
|
Data collection |
Diffractometer | Bruker Nonius KappaCCD area-detector diffractometer |
Absorption correction | Multi-scan (SORTAV; Blessing, 1995) |
Tmin, Tmax | 0.986, 0.999 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 16116, 4051, 1951 |
Rint | 0.125 |
(sin θ/λ)max (Å−1) | 0.649 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.070, 0.208, 0.98 |
No. of reflections | 4051 |
No. of parameters | 211 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.39, −0.33 |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
C20—H201···O1i | 0.98 | 2.59 | 3.561 (3) | 172 |
C20—H202···O1ii | 0.98 | 2.37 | 3.263 (3) | 151 |
C21—H212···O1ii | 0.98 | 2.42 | 3.287 (3) | 147 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1, −y, −z+1. |
The 1-alkyl derivatives of 2,4-bis(3,3-dimethylindolin-2-ylidenemethyl)cyclobutenediylio-1,3-diolate (InSq) have been studied for a variety of photophysical effects (for example, Kuramoto et al., 1989; Dirk & Kuzyk, 1990; Terpetschnig et al., 1993; Zhang et al., 1997). In several other studies of squaraine dyes, the only known crystal structure of an InSq derivative, InSq1 (Kobayashi et al., 1986), was cited and a discussion of molecular behaviour based on the non-planar conformation of this structure given. In the structure of InSq1, one indolinyl ring is twisted by ca 25° away from the plane of the central ring, while the other ring is twisted by ca 8°. Certainly, before the structures of InSq2 (Natsukawa & Nakazumi, 1993), InSq3 (Tong & Bi-Xian, 1999), InSq4 and InSq5 (Lynch & Byriel, 1999) were published, the structure of InSq1 was the only guide as to the conformation of any InSq derivative. The significance of these latter InSq structures is that they are all planar across the bis(indolinylidene)squarate moiety, a characteristic of all other known squaraine structures (Lynch & Byriel, 1999).
As part of a series of studies on the structural aspects of squaraine dyes, the 1-octyl derivative of InSq, InSq6, was prepared and the structure determined (Fig. 1). Similar to InSq2–InSq5, InSq6 is planar, with the dihedral angle between the squarate and indoline planes being 3.9 (2)°. However, unlike InSq2 and InSq3, InSq6 is solvent-free and displays a similar packing mode to InSq4 and InSq5, with only half of the molecule in the asymmetric unit. The paper reporting the structures of InSq4 and InSq5 also reviewed the role of C—H···O close contacts in the packing of all known squaraine structures at that time. The results suggested that most solvent-free structures had the planar molecules stacked in rows of columns, with the individual molecules forming C—H···O close contacts with another molecule in either an adjacent column of a different row (of opposing direction) or the next column in the same row. InSq6 displays the same ribbon network arrangement as InSq5, through C—H···O close contacts, but InSq6 is not stacked. This rearrangement in the structure may be necessary to compensate for the extended alkyl chain, although no other N-octyl (or longer) squaraine analogue has been studied for comparison, so the obvious bulkiness of the alkyl chain may only be part of the reason for the difference in packing.
In conclusion, five of the six known structures of InSq derivatives are planar across the central ring system, suggesting that this is a more representative conformation than that of InSq1. This has a bearing on the discussion of the structure–property relationships of this squaraine analogue.