S = 1 Tetraazacyclophane Diradical Dication with Robust Stability: a Case of Low Temperature One-Dimensional Antiferromagnetic Chain

Transcription

1 Supporting Information for S = 1 Tetraazacyclophane Diradical Dication with Robust Stability: a Case of Low Temperature One-Dimensional Antiferromagnetic Chain Wenqing Wang, Chao Chen, Chan Shu, Suchada Rajca, Xinping Wang,*, Andrzej Rajca*, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing , China; Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588, USA. xpwang@nju.edu.cn, arajca1@unl.edu S1

2 Table of contents Table S1. Crystal data and structure refinement for [Al(OR Me ) 4 ] at 123 and 90 K. 3 Table S2. Selected intermolecular distances for [Al(OR Me ) 4 ] at 123 and 90 K. 3 Figure S1. Crystal packing of [Al(OR Me ) 4 ]..4 Figure S2. Demonstration of the inter-chain interaction in the crystal packing of [Al(OR Me ) 4 ]..5 Magnetic Studies 6 Figure S3. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 500 Oe (0.05 Tesla) in the warming mode 8 Figure S4. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 5000 Oe (0.5 Tesla) in the warming mode 9 Figure S5. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 5000 Oe (0.5 Tesla) in the cooling mode 10 Figure S6. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 30,000 Oe (3 Tesla) in the warming mode..11 TGA, IR and EPR spectroscopy.12 Figure S7. EPR spectrum (with simulation) of diradical dication salt [Al(OR Me ) 4 ] in DBP at 117 K. 12 Figure S8. TGA with and without IR spectroscopy..13 Figure S9. Representative IR spectra of the head space during the TGA 14 Figure S10. 3 rd TGA run up to 190 C with IR spectroscopy, followed by EPR spectrum of the residue..15 Figure S11. Overlay of the IR spectrum, obtained during the TGA run, with the IR spectra of hexafluoroacetone and 1,1,1-trifluoroacetone Figure S12. EPR spectrum of [Al(OR Me ) 4 ] in DBP at 117 K following annealing of solid sample at C on air DFT computations...18 Table S3. Computed Total Energy (and S 2 in Parentheses) in Atomic Units for Diradical Dication and Its Dimer from Single Point Calculations at the X-ray Structure Geometry Using 6-31G(d) and G(d,p) Basis Sets. Computed Values of J and J (in Kelvin) Using Equations S4 S Table S4. Computed Spin Densities for - Interactions in Quintet States of Dimers A and B at the X-ray Geometries.20 Table S5. Mulliken spin densities for the optimized geometry of triplet state of (UB3LYP/6-31G(d)) 21 Coordinates for optimized geometries 22 Supporting references..47 S2

3 Table S1. Crystal Data and Structure Refinement for [Al(OR Me ) 4 ] at 123 and 90 K. 123 K 90 K formula Mr [g mol -1 ] crystal system C84H68Al2F48N4O Triclinic Triclinic space group P-1 P-1 Z 2 2 Temp. (K) 123(2) 90(2) μ (mm -1 ) a (Å) (10) (15) b (Å) (11) (15) c (Å) (15) (2) α ( ) (16) (2) β ( ) (17) (2) γ ( ) (18) (2) V [Å 3 ] (6) (8) R1 (I>2σ(I)) wr2 (all data) C84H68Al2F48N4O8 Table S2. Selected intermolecular distances for [Al(OR Me ) 4 ] at 123 and 90 K. Dimer A Dimer B Dimer B C39-C39 [Å] para-para C39'-C41' [Å] para-ortho C40'-C41'[Å] meta-ortho 123 K K Change of distance S3

4 Figure S1. Crystal packing of [Al(OR Me ) 4 ]. S4

5 Figure S2. Demonstration of the inter-chain interaction (circled) in the crystal packing of [Al(OR Me ) 4 ]. S5

6 Magnetic Studies 1. SQUID Magnetic Studies. Magnetic studies were carried out on polycrystalline samples of diradical dication salt [Al(OR Me ) 4 ] - using Quantum Design SQUID VSM magnetometer with fields of 30000, 5000 and 500 Oe (T = K). The sample (e.g., m sample = mg) was mounted in a holder and wrapped with a polyethylene film. Correction for diamagnetism was implemented by strict point-by-point background subtraction; background M vs T data at H = 500, 5000, and Oe were obtained for film (M film ), neutral diamine (M diamine ) and lithium salt of the counterion (M ion ), using identical sequences of temperatures. First, the data for the sample (M sample ) were corrected for diamagnetism of the film: M cor = M sample M film (m samplefilm /m film ) where m samplefilm (e.g., 8.75 mg) is the mass of the film wrapping the sample of [Al(OR Me ) 4 ] - and M film is the magnetization of the film sample with mass of m film (e.g., mg) Subsequently, the M cor, M diamine, and M ion were converted to corresponding molar magnetic susceptibilities, as illustrated for M cor : cor = M cor /(H*n molsample ), where, H is the applied magnetic field in Oe and n molsample is the number of moles of the sample of [Al(OR Me ) 4 ] -. ( diamine and ion are obtained in a similar way but by using the number of moles of diamine or Li-salt of counterion.) Then, the final magnetic susceptibility for the sample of [Al(OR Me ) 4 ] -, m (in emu mol -1 ), is: m = cor diamine (2* ion ) We note that this procedure overestimates the correction for diamagnetism because of two additional Li + and two hydrogen atoms are included. However, given the large molecular mass of [Al(OR Me ) 4 ] - (M w = ) this overestimate is expected to have a negligible effect on m, especially in view of presence of small amounts of magnetic impurities. 2. Selected Models for Numerical Fitting of Magnetic Data for Diradical Dication Salt [Al(OR Me ) 4 ] -. Diradical Model. This model is used to fit T vs T data at elevated temperatures, in order to obtain the singlet-triplet energy gap (2J/k in Kelvin or E ST in kcal mol -1 ). Impurities and inaccuracies in the mass balance are accounted for by the mass factor, N (eq. 1, main text); relatively weak inter-molecular interactions between diradical dication molecules may be described by mean-field parameter. This model accounts for paramagnetic saturation. S = 1 Dimer Model. In this model, it is assumed that all S = 1 diradical dications are involved in only one dominant pairwise intra-dimer antiferromagnetic exchange coupling (J/k). Energy eigenvalues for Heisenberg Hamiltonian ( 2 i,j J i,j S i S j ) are obtained by vector decoupling technique. S1,S2 Equations for the temperature dependence of magnetic susceptibility ( vs. T or T vs. T) are provided (eq. S1a and eq. S1b). Also, impurities and inaccuracies in the mass balance are accounted for by the mass factor, N (eqs. S1a and S1b). Both equations account for paramagnetic saturation. Relatively weak inter-dimer interactions may be accounted by using the mean-field parameter. = (1.118/H)N[NOM/DEN] (S1a) T = (1.118T/H)N[NOM/DEN] (S1b) NOM = sinh(a) + 2sinh(2a) + [(sinh(a))exp(( 4J/k)/T)] DEN = 1 + 2cosh(a) + 2cosh(2a) + [(cosh(a))exp(( 4J/k)/T)] + exp(( 6J/k)/T) a = 1.345(H/(T )) 3. Details of numerical fitting of SQUID magnetic data. The magnetic data at high temperature (T > 80 K) were fit with 3-parameter diradical model. Three variable parameters were: J intramolecular exchange coupling constant (in Kelvin); note that 2J = singlet-triplet energy gap (in Kelvin); N mass factor (N = 1.00 for perfectly pure S = 1 diradical S6

7 dication), and the mean-field parameter to account for relatively weak inter-molecular interactions between diradicals. Fit to the data at H = Oe in the warming mode, gives 2J/k 240 K (or E ST 0.5 kcal mol -1 ), which is most likely close to the upper limit, because of the presence of small amounts of magnetic contaminants (see: SQUID Magnetic Studies section). The magnetic data at low temperatures (T < 60 K) were fit using either 3-parameter or 2-parameter models. In the three-parameter models, three variable parameters were: J intra-chain or intra-dimer antiferromagnetic exchange coupling constant (in Kelvin), N the mass factor (N = 1.00 for perfectly pure S = 1 diradical dication), and - the mean-field parameter to account for relatively weak interchain or inter-dimer exchange couplings (in Kelvin). In the two-parameter models, two variable parameters were J and N ( was set to zero). The SigmaPlot for Windows software package was used for numerical curve fitting of the magnetic data. Standard error (SE) for each variable parameter is provided. The reliability of a fit is measured by the parameter dependence (DEP), which is defined for each variable parameter as follows: DEP = 1 ((variance of the parameter, other parameters constant)/(variance of the parameter, other parameters changing)). Values close to 1 indicate an overparametrized fit. The quality of fits may be measured by a coefficient of determination (R 2 ), which is defined for nonlinear numerical fits of the magnetic data as follows (eq. S2): R 2 = 1 [( (y i Y i ) 2 )/( (y i <y>) 2 )] (S2) where y i, Y i, and <y> denote experimental values, fitted values, and the arithmetic mean of the experimental values. We list in figure captions values of R 2 that are statistically adjusted; values close to 1 indicate a fit of high quality. The quality of fits is more reliably measured by standard error of estimate (SEE), which is defined as follows (eq. S3): SEE = [SSE/(n 2)] 1/2 (S3) where, SSE is the sum of squared errors and n is the number of points. The perfect fit would imply SEE = Invariably, for low temperature data, the fits to one-dimensional (1D) chain of antiferromagnetically coupled S = 1 spins were found to be superior to the fits to antiferromagnetically coupled dimers of S = 1 spins. In three parameter fits, it was found that > 0, i.e., there is a small, inter-chain ferromagnetic exchange coupling with a typical +0.3 K. The values of tend to somewhat decrease for narrower temperature range of the fit to 1D chain, e.g., for fits to the H = 500 Oe data in the warming mode, = , , and ( SE) for T = , , K, respectively, but the decrease is small compared to standard error (SE), that is, +0.3 K for all temperature ranges. S7

8 Figure S3. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 500 Oe (0.05 Tesla) in the warming mode. Numerical fits using three variable parameters (left plots) and two variable parameters (right plots). Three variable parameters fits: 1D chain ( K), J /k = (SE = 0.07, DEP = 0.952), N = (SE = 0.011, DEP = 0.921), = (SE = 0.02, DEP = 0.807), R 2 = , SEE = ; 1D chain ( K), J /k = (SE = 0.08, DEP = 0.965), N = 1.00 (SE = 0.012, DEP = 0.946), = (SE = 0.02, DEP = 0.823), R 2 = , SEE = ; Dimer, J /k = (SE = 0.06, DEP = 0.951), N = (SE = 0.014, DEP = 0.837), = (SE = 0.02, DEP = 0.892), R 2 = , SEE = Two-variable parameters fits (set = 0): 1D chain, J /k = (SE = 0.08, DEP = 0.897), N = (SE = 0.017, DEP = 0.897), R 2 = , SEE = ; Dimer, J /k = (SE = 0.07, DEP = 0.774), N = (SE = 0.025, DEP = 0.774), R 2 = , SEE = S8

9 Figure S4. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 5000 Oe (0.5 Tesla) in the warming mode. Numerical fits using three variable parameters (left plots) and two variable parameters (right plots). Three variable parameters fits: 1D chain, J /k = (SE = 0.06, DEP = 0.952), N = (SE = 0.010, DEP = 0.920), = (SE = 0.02, DEP = 0.815), R 2 = , SEE = ; Dimer, J /k = (SE = 0.06, DEP = 0.948), N = (SE = 0.014, DEP = 0.839), = (SE = 0.02, DEP = 0.882), R 2 = , SEE = Two-variable parameters fits (set = 0): 1D chain, J /k = (SE = 0.08, DEP = 0.896), N = (SE = 0.016, DEP = 0.896), R 2 = , SEE = ; Dimer, J /k = (SE = 0.07, DEP = 0.774), N = (SE = 0.025, DEP = 0.774), R 2 = , SEE = S9

10 Figure S5. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 5000 Oe (0.5 Tesla) in the cooling mode. Numerical fits using three variable parameters (left plots) and two variable parameters (right plots). Three variable parameters fits: 1D chain, J /k = (SE = 0.06, DEP = 0.946), N = (SE = 0.009, DEP = 0.908), = (SE = 0.02, DEP = 0.807), R 2 = , SEE = ; Dimer, J /k = (SE = 0.06, DEP = 0.939), N = (SE = 0.014, DEP = 0.815), = (SE = 0.02, DEP = 0.864), R 2 = , SEE = Two-variable parameters fits (set = 0): 1D chain, J /k = (SE = 0.07, DEP = 0.888), N = (SE = 0.016, DEP = 0.888), R 2 = , SEE = ; Dimer, J /k = (SE = 0.07, DEP = 0.771), N = (SE = 0.025, DEP = 0.771), R 2 = , SEE = S10

11 Figure S6. SQUID magnetometry for polycrystalline diradical dication salt [Al(OR Me ) 4 ] - : vs T data, obtained at H = 30,000 Oe (3 Tesla) in the warming mode. Numerical fits using three variable parameters (left plots) and two variable parameters (right plots). Three variable parameters fits: 1D chain, J /k = (SE = 0.06, DEP = 0.947), N = (SE = 0.008, DEP = 0.910), = (SE = 0.02, DEP = 0.805), R 2 = , SEE = ; Dimer, J /k = (SE = 0.04, DEP = 0.966), N = (SE = 0.009, DEP = 0.881), = (SE = 0.02, DEP = 0.921), R 2 = , SEE = Two-variable parameters fits (set = 0): 1D chain, J /k = (SE = 0.08, DEP = 0.881), N = (SE = 0.016, DEP = 0.881), R 2 = , SEE = ; Dimer, J /k = (SE = 0.05, DEP = 0.777), N = (SE = 0.016, DEP = 0.777), R 2 = , SEE = S11

12 TGA, IR and EPR spectroscopy. In all experiments described in this section, a sample of [Al(OR Me ) 4 ] - from SQUID magnetometry was used. TGA instrument (TA Instruments TGA 550) was run either without or with IR attachment (Thermo NICOLET Is50 NIR). A sample of polycrystalline diradical dication salt [Al(OR Me ) 4 ] - (1.153 mg and mg) was placed in the TGA instrument; thermogravimetric analysis was carried out under N 2 with heating at 5 o C/min to 400 o C and maintained for 10 minutes at 400 o C (Figure S8). In the second identical TGA run, IR spectra were recorded (Figures S8 and S9). In the third TGA run, IR spectra were recorded and the sample was heated under N 2 at 5 o C/min to 190 o C and maintained for 10 minutes at ~190 o C, and then following the TGA run, EPR spectrum of the solid residue was obtained (Figure S10). CW X-band EPR spectra for radicals were acquired on Bruker EMX instrument, equipped with a frequency counter and nitrogen flow temperature control ( K). The spectra were obtained using a dual mode cavity, with an oscillating magnetic field perpendicular (TE 102 ) to the swept magnetic field; parallel mode (TE 012 ) was not used. Spin concentrations of radicals were measured at 117 K in dibutylphthalate (DBP) glass versus a 1.0 mm solution of a stable nitroxide radical (e.g., tempone in DBP) (Figure S7). Temperatures were verified using an independently calibrated thin wire thermocouple inserted into the EPR sample tube (containing the solvent) and positioned in the cavity at the same place as in the spin concentration studies. The samples were typically contained in 4-mm EPR sample tubes, equipped with high vacuum stopcocks (Kontes). To test the thermal stability on air, a 1.43-mg sample of [Al(OR Me ) 4 ] - was heated at o C inside the melting point apparatus; after 10 min, the melting point capillary was broken the solid was dissolved in degassed DBP (2.05 ml); EPR spectrum at 117 K showed only a small degree of decomposition (Figure S11). m s = experiment simulation mt Figure S7. X-band EPR ( = GHz, label: CS2-62R23) spectrum of 0.31 mm diradical dication salt [Al(OR Me ) 4 ] in DBP at 117 K; five (n = 5) measurements vs tempone reference gave T = emu K mol -1. Experiment (black line): m s = 1, center line corresponds to a small amount of monoradical impurity; microwave power = 0.02 mw (40 db), modulation amplitude = 1 Gauss, conversion = 41 ms, time constant = 10 ms, resolution = 1 k points; m s = 2, microwave power = 20 mw (10 db), modulation amplitude = 6 Gauss, conversion = 41 ms, time constant = 10 ms, resolution = 0.5 k points. Simulation (red line): S = 1, D/hc = cm -1, E/hc cm -1, A yy /hc cm -1, g x = , g y = , g z = ; Gaussian linewidths (mt): L x = 0.35, L y = 0.95, L z = 0.53; a small admixture of S = 1/2 (shown in Figure 6, main text), A yy /hc cm -1, g x = , g y = , g z = ; Gaussian linewidths (mt): L x = 0.25, L y = 0.55, L z = 0.4. S12

13 Weight/% mg, TGA-IR mg, TGA Temperature/ C Figure S8. TGA for polycrystalline [Al(OR Me ) 4 ] - under N 2 ; heating rate = 5 C min 1. S13

14 IR spectrum 100 %Transmittance min, 44.4 C min, C min, C min, C min, C Wavenumber (cm -1 ) Figure S9. IR spectra obtained during TGA (2 nd run) for polycrystalline [Al(OR Me ) 4 ] - under N 2 (label: CS2-60); heating rate = 5 C min 1. Top panel: summary of representative spectra; the spectrum at min, shown in dark green color, corresponds to an onset of decomposition: temperature of C, remaining mass of 99.2%. Bottom panel: the spectrum at min, corresponding to temperature of C, and remaining mass of 72.0%. S14

15 Weight/% Temperature/ C IR spectrum %Transmittance min, C min, C min, C min, C min, C min, C Wavenumbers (cm -1 ) mt Figure S10. Top plot: TGA (1.510 mg sample, 3 rd run) up to 190 C with temperature maintained at 190 C for 10 min for polycrystalline [Al(OR Me ) 4 ] - under N 2 (label: CS2-69); heating rate = 5 C min 1. Middle plot: IR spectra of the head space obtained during this TGA run. Bottom plot: EPR spectrum (label: CS2-69R3) of the solid residue after TGA (3 rd run), shown in the top plot; the spectrum is obtained in DBP at 117 K, using similar parameters to that in Figure S7 - spin concentration of monoradical is about 5% (computed vs mg sample) and the diradical is not detected. S15

16 Figure S11. Overlay of the TGA/IR spectrum (red line, see: Figure S9), obtained at min, C, 76.6 % remaining mass), with IR spectra for hexafluoroacetone (blue line, top plot) and 1,1,1- trifluoroacetone (blue line, bottom plot). The spectra were overlaid using software of the TGA/IR instrument. The reference spectra were from HR Nicolet Vapor Phase library, which was supplied with the TGA/IR instrument. S16

17 m s = 2 m s = mt Figure S12. EPR spectroscopic follow-up: thermal stability of [Al(OR Me ) 4 ] on air. X-band EPR ( = GHz) spectrum of diradical dication salt [Al(OR Me ) 4 ] in DBP at 117 K following heating solid sample at C for 10 min; two (n = 2) measurements vs tempone reference gave T 0.90 emu K mol -1. Center line corresponds to a small amount of monoradical impurity in the present sample this line is a bit larger compared that the original spectrum in Figure S7; both spectra in this Figure were acquired using identical parameters as for those in Figure S7. S17

18 DFT computations. DFT computations of intra-chain exchange coupling constant, J, were carried out for dimers A and dimers B at X-ray geometries of , obtained at 123 K or 90 K. All computations using 6-31G(d) basis set used int=(grid=ultrafine) and scf=tight commands in Gaussian 09. S3 Intramolecular coupling constant J for the monomers at the X-ray geometries was computed as well. Equations S4 S6 were used to extract values of J and J, S4 following Yamaguchi spin contamination correction. S5 Equation S4 refers to triplet (T) and broken symmetry singlet (BS) of the monomer Equations S5 and S6 refer to quintet (Q), broken symmetry triplet (BT), and broken symmetry singlet (BS) of the dimer of J = (E BS E T )/(<S 2 > T <S 2 > BS ) J + 2J = [(E BT E Q )*3.0000]/(<S 2 > Q <S 2 > BT ) 2J + 4J = [(E BS E Q )*4.0000]/(<S 2 > Q <S 2 > BS ) (S4) (S5) (S6) It was important to make sure that proper BT and BS states of dimers were obtained by verifying their spin density distributions: for the BT state of dimer, effectively a combination of triplet and BS states for monomer, and for the BS state of dimer, effectively a combination of two BS states for monomer. Proper convergence to the desired state was attained by using stable=opt command in Gaussian 09 and various scf convergence commands (e.g., scf = Fermi). Also, we analyzed spin densities for - interactions in dimers A and B using quintet (high spin) states at X-ray geometries (Table S4). S18

19 Table S3. Computed Total Energy (and S 2 in Parentheses) in Atomic Units for Diradical Dication and Its Dimer from Single Point Calculations at the X-ray Structure Geometry Using 6-31G(d) and G(d,p) as the Basis Set. Computed Values of J and J (in Kelvin) Using Equations S4 S6. UB3LYP/ 6-31G(d) 2S + 1 Monomer 3 1 Dimer A Dimer B UB3LYP/ G(d,p) 2S + 1 Monomer 3 1 Dimer A 5 3 Dimer B 5 UM06-2X/ G(d,p) a 2S Monomer 3 1 Dimer A 5 3 Dimer B 5 3 UPBE1PBE/ G(d,p) b 2S + 1 Monomer 3 1 Dimer A 5 3 Dimer B 5 3 Energy (<S 2 >) (2.0254) (1.0064) (6.0511) (3.0227) (1.9965) (6.0512) (3.0254) (1.9990) (2.0251) (1.0062) (6.0508) (3.0245) (6.0508) (3.0251) (2.0486) (1.0391) (6.0969) (3.0865) (6.0971) (3.0870) (2.0372) (1.0175) (6.0752) (3.0507) (6.0752) (3.0526) 123 K 90 K J J + 2J J Energy J or 2J + 4J [K] [K] [K] (<S 2 >) [K] (2.0254) (1.0064) (6.0512) (3.0276) (2.0021) (6.0511) (3.0272) (2.0025) (2.0251) (1.0076) (6.0507) (3.0272) (6.0508) (3.0271) (2.0487) (1.0398) (6.0970) (3.0872) (6.0972) (3.0878) (2.0372) (1.0188) (6.0751) (3.0526) (6.0753) (3.0541) J + 2J or 2J + 4J [K] J [K] a M06-2X functional of Zhao and Truhlar. S6 Note that Datta and coworkers obtained significantly better agreement between computed and experimental S2 values of J with the UB3LYP functional, compared to that for UM06-2X functional. S4 b The hybrid functional by Adamo and Barone, S8 based on the 1996 pure functional of Perdew, Burke and Ernzerhof; S7 the G09 keyword is PBE1PBE. This functional uses 25% exchange and 75% correlation weighting, and is known in the literature as PBE0. S19

20 Table S4. Computed Spin Densities for - Interactions in Quintet States of Dimers A and B at the X-ray Geometries. Temp. [K] Dimer Dist. Carbon UB3LYP UB3LYP UM06-2X UM06-2X PBE0 PBE0 type [Å] Atom /6-31G(d) / G(d,p) /6-31G(d) / G(d,p) /6-31G(d) / G(d,p) C39(p) A C39(p) C39'(p) B C41'(o) C41'(o) B C40'(meta) A C39 (p) C39 (p) B C39' (p) C41' (o) B C41' (o) C40'(meta) S20

21 Electron Spin Density Distribution of Triplet State of Table S5. Mulliken spin densities for the optimized geometry of triplet state of (UB3LYP/6-31G(d)). 1 C C H C H C C H C H C C H C C H C H C H C C H C H C C H C H C H H H C C H C H C C H C H C H H H C C H C H C C H C H C C H C C H C H C H C C H C H C C H C H C H H H C C H C H C C H C H C H H H N N N N S21

22 Coordinates for optimized geometries CS C C H C H C C H C H C C H C C H C H C H C C H C H C C H C H C H H H C C H C H C C H C H C H H H C C H C S22

23 H C C H C H C C H C C H C H C H C C H C H C C H C H C H H H C C H C H C C H C H C H H H N N N N OS C C H C H S23

24 C C H C H C C H C C H C H C H C C H C H C C H C H C H H H C C H C H C C H C H C H H H C C H C H C C H C H C C H S24

25 C C H C H C H C C H C H C C H C H C H H H C C H C H C C H C H C H H H N N N N T C C H C H C C H C H C C H C S25

26 C H C H C H C C H C H C C H C H C H H H C C H C H C C H C H C H H H C C H C H C C H C H C C H C C H C H C H C C S26

27 H C H C C H C H C H H H C C H C H C C H C H C H H H N N N N Coordinates for X-ray geometries 90K Dication monomer: C C C H C C C H H C H H H N H C C C C S27

28 C C C H H C H C C H C H H C N H N H C C C C C C C C C C C C H C C H H C C H H C C H C H H C H C H H C H H S28

29 C H C N H C C H C H H H H H H C C H C C H H C C H H H H Dimer A: C C H C H C C H C H C C H C C H C H C H C C S29

30 H C H C C H C H C H H C C H C H C C H C H C H H H C C H C H C C H C H C C H C C H C H C H C C H C H C C H S30

31 C H C H H H C C H C H C C H C H C H H N N N N H C C C H C C C H H C H H H N H C C C C C C C H H C H C C H S31

32 C H H C N H N H C C C C C C C C C C C C H C C H H C C H H C C H C H H C H C H H C H H C H C N H C C H C H S32

33 H H H H H C C H C C H H C C H H H H H Dimer B: C C H C H C C H C H C C H C C H C H C H C C H C H C C H C H S33