Supporting Information  Copyright Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, 2012

Boronate Ligands in Materials: Determining Their Local Environment By Using a Combination of IR/Solid-State NMR Spectroscopies and DFT Calculations Saad Sene,[a] Marc Reinholdt,[a] Guillaume Renaudin,[b] Dorothe Berthomieu,[a] Claudio M. Zicovich-Wilson,[c] Christel Gervais,[d] Philippe Gaveau,[a] Christian Bonhomme,[d] Yaroslav Filinchuk,[e] Mark E. Smith,[f] Jean-Marie Nedelec,[b] Sylvie Bgu,[a] P. Hubert Mutin,[a] and Danielle Laurencin*[a] chem_201203560_sm_miscellaneous_information.pdf

SUPPLEMENTARY TABLES

Table S1:

Experimental 11B NMR parameters determined for Ca(C4H9-B(OH)3)2 and Ca(C6H5-B(OH)3)2.

Table S2:

Interatomic distances (in Å) in the butylboronate ligands for the experimental structure, and the different DFT relaxed models.

Table S3:

Experimental vs calculated 11B NMR parameters of Ca(C4H9-B(OH)3)2.

Table S4:

Experimental vs calculated 13C NMR isotropic chemical shifts of Ca(C4H9-B(OH)3)2.

Table S5:

Experimental vs calculated 43Ca NMR parameters for Ca(C4H9-B(OH)3)2.

Table S6:

Calculated anharmonic OH vibration frequencies and 1H chemical shifts of the hydroxyl groups in Ca(C4H9-B(OH)3)2 and Ca(C6H5-B(OH)3)2.

Table S7:

Refined atomic positional and displacement parameters for Ca(C4H9-B(OH)3)2.

Table S8:

Explicit coefficients of the TZP 6211111/331111/31 basis set used for Ca in the calculations.

SUPPLEMENTARY FIGURES Figure S1:

Comparison of the TGA of Ca(C4H9-B(OH)3)2 and Ca(C6H5-B(OH)3)2.

Figure S2:

Comparison of the connection modes between boronate ligands and Ca2+ in Ca(C4H9-B(OH)3)2 and Ca(C6H5-B(OH)3)2.

Figure S3:

Comparison of 11B MAS NMR spectra of Ca(C4H9-B(OH)3)2 before or after physical dilution of the powder in SiO2.

Figure S4:

Analysis of the influence of the recycle delay and power of the excitation pulse on the 11B MAS NMR lineshape of Ca(C4H9-B(OH)3)2.

Figure S5:

3QMAS 11B NMR spectrum of Ca(C4H9-B(OH)3)2 recorded at 9.4 T, and simulation of the quadrupolar lineshapes for the 2 extracted sites.

Figure S6:

Schematic representation of the 13C{11B} REDOR NMR pulse sequence.

Figure S7:

Solution 13C NMR spectrum of (C4H9-B(OH)3)‒.

Figure S8:

43

Ca MAS NMR spectra of Ca(C4H9-B(OH)3)2 recorded at 9.4 and 14.1 T.

Figure S9:

Comparison of the 1H MAS NMR spectra of Ca(C4H9-B(OH)3)2, recorded by fast MAS or using the DUMBO sequence.

Figure S10:

Comparison of the complete IR spectra of Ca(C4H9-B(OH)3)2 and Ca(C6H5-B(OH)3)2.

Figure S11:

Illustration of the linear regression extrapolation of δiso(13C) as a function of temperature.

Figure S12:

Differences in the modes of interaction of boronate ligands in Ca(C4H9-B(OH)3)2 and Ca(C6H5-B(OH)3)2.

Figure S13 & S14:

Environment SEM analyses of crystallites of Ca(C4H9-B(OH)3)2.

Figure S15:

SEM analysis of the structure of crystallites of Ca(C4H9-B(OH)3)2, synthesized under diluted conditions.

SUPPLEMENTARY TABLES

Table S1. Experimental B(OH)3)2.

11

B NMR parameters determined for Ca(C4H9-B(OH)3)2 and Ca(C6H5Ca(C6H5-B(OH)3)2 a

Ca(C4H9-B(OH)3)2 Site 1 δiso = 4.78 ± 0.03 ppm CQ = 1.46 ± 0.02 MHz ηQ = 0.28 ± 0.03

a

Site 2 δiso = 4.54 ± 0.04 ppm CQ = 1.47 ± 0.03 MHz ηQ = 0.13 ± 0.02

M. Reinholdt et al, Inorg. Chem. 2011, 50, 7802.

Site 1 δiso = 3.8 ± 0.3 ppm CQ = 1.4 ± 0.2 MHz ηQ = 0.4 ± 0.2

Site 2 δiso = 4.0 ± 0.2 ppm CQ = 1.3 ± 0.1 MHz ηQ = 0.2 ± 0.1

---------------------------------------------------

Table S2. Interatomic distances (in Å) in the butylboronate ligands for the experimental structure of Ca(C4H9-B(OH)3)2, and the different DFT relaxed models. structure

B-C1

Average B-O

C1-C2

C2-C3

C3-C4

Average Ca-O

XRD (Exp-R1)a

1.629 (B1) 1.632 (B2)

1.501 1.506

1.523 1.531

1.564 1.563

1.591 1.559

2.506

H relaxed

1.629 1.632

1.501 1.506

1.523 1.531

1.564 1.563

1.591 1.559

2.506

C,H relaxed

1.609 1.605

1.501 1.506

1.536 1.537

1.535 1.536

1.531 1.531

2.506

C,H relaxed No dispersionb

1.608 1.603

1.501 1.506

1.533 1.535

1.531 1.532

1.528 1.528

2.506

C,H,O,B relaxed

1.620 1.610

1.508 1.509

1.536 1.538

1.536 1.536

1.532 1.531

2.497

All relaxed

1.610 1.620

1.509 1. 508

1.538 1.536

1.536 1.536

1.531 1.532

2.495

XRD (Exp-R2)c

1.620 1.618

1.508 1.506

1.538 1.540

1.546 1.545

1.531 1.531

2.503

a

Initial refinement of the experimental XRD powder pattern (see experimental section for details). The Grimme correction was not included in these calculations. c New refinement of the experimental data following the DFT calculations, leading to the .cif file now published. b

Table S3. Experimental vs calculated 11B NMR parameters of Ca(C4H9-B(OH)3)2. site

NMR parameter

B1

δiso (ppm) CQ (MHz) ηQ Ω(ppm) κ δiso (ppm) CQ (MHz) ηQ Ω(ppm) κ

B2

Exp (23°C) 4.78 ± 0.03 1.46 ± 0.02* 0.28 ± 0.03 4.54 ± 0.04 1.47 ± 0.03* 0.13 ± 0.02

H relaxed 3.8 ‒1.60 0.21 11.6 0.33 4.0 ‒1.51 0.26 7.5 0.15

C, H relaxed 3.4 ‒1.61 0.20 11.5 0.36 3.7 ‒1.53 0.26 7.9 0.26

C, H, O, B relaxed 3.9 ‒1.54 0.33

All relaxed 3.9 ‒1.54 0.32 9.8 0.22 3.8 ‒1.51 0.07 7.4 0.56

3.7 ‒1.50 0.09

C, H relaxed No dispersion 3.4 ‒1.61 0.20 3.6 ‒1.53 0.26

* The sign of CQ is not measured experimentally.

--------------------------------------------------Table S4. Experimental vs calculated 13C NMR isotropic chemical shifts of Ca(C4H9-B(OH)3)2 (δiso, in ppm). site C1 C2 C3 C4 a

Experimental Data Exp Exp (23°C) (extrapolated at 0 K) ~27.6a ~27.6 a 30.9 31.2 30.2 29.9 29.9 30. 8 29.4 30.6 16.0 16.4 16.0 16.4

Site

H relaxed

C11 C21 C12 C22 C13 C23 C14 C24

27.6 28.4 30.3 29.9 36.3 36.0 15.3 15.4

Calculated Data C, H C, H, O, B relaxed relaxed 22.6 21.6 28.4 27.5 28.2 27.8 12.7 12.5

All relaxed

C, H relaxed No dispersion

24.9 22.8 28.6 27.3 27.9 28.0 12.3 12.2

22.4 21.7 28.4 27.4 28.0 28.0 12.6 12.2

24.7 22.8 28.7 27.3 27.9 28.0 12.4 12.3

The exact isotropic chemical shift cannot be determined for this peak (see Figure 2, and explanations in main text); thus, no extrapolation of the chemical shift at 0 K was calculated.

--------------------------------------------------Table S5. Experimental vs calculated 43Ca NMR parameters for Ca(C4H9-B(OH)3)2. NMR parameter δiso (ppm) CQ (MHz) ηQ

Exp (~23°C) 14.6 ± 2.0 1.50 ± 0.15* 0.60 ± 0.15

H relaxed 14.2 ‒1.51 0.74

* The sign of CQ is not measured experimentally.

C, H relaxed 15.4 ‒1.49 0.73

C, H, O, B relaxed 16.5 ‒1.80 0.99

All relaxed 17.9 ‒1.31 0.94

C, H relaxed No dispersion 15.5 ‒1.49 0.73

Table S6. Calculated anharmonic OH vibration frequencies and 1H chemical shifts of the OH groups. Ca(C4H9-B(OH)3)2 Calculated OH frequencies (in cm‒1)a

Calculated 1H chemical shifts (in ppm) b

a b

H relaxed 3693 3674 3634 3621 3561 3277 1.6 1.8 2.9 3.9 4.3 6.9

Ca(C6H5-B(OH)3)2

All relaxed 3675 3628 3615 3603 3559 3136 2.0 2.2 3.6 4.3 4.3 7.7

H relaxed 3729 3689 3651 3647 3419 3351 0.0 1.1 1.4 2.6 4.2 5.1

All relaxed 3724 3691 3657 3619 3341 3327 0.1 1.1 1.1 2.8 5.1 5.3

The frequencies are given here from the highest to the lowest. The 1H chemical shifts are given here from the lowest to the highest.

--------------------------------------------------Table S7. Refined atomic positional and displacement parameters for Ca(C4H9-B(OH)3)2

(P21/c space group, a = 16.4268 (9) Å, b = 8.3969 (4) Å, c = 9.8644 (6) Å, β = 90.462 (3)° and V = 1360.60 (13) Å3).

Site

x

y

z

Uiso (Å2)

Ca

4e

0.9898 (3)

0.4257 (5)

0.3179 (4)

0.030 (2)

B1

4e

0.1064 (2)

0.2433 (5)

0.1392 (4)

0.022 (2)

B2

4e

0.8606 (3)

0.2554 (5)

0.5774 (4)

= Uiso (B1)

O11

4e

0.0592 (6)

0.3889 (7)

0.0963 (8)

= Uiso (B1)

O12

4e

0.0832 (6)

0.1157 (9)

0.0380 (8)

= Uiso (B1)

O13

4e

0.0679 (6)

0.1914 (11)

0.2700 (6)

= Uiso (B1)

O21

4e

0.8914 (5)

0.3941 (7)

0.6602 (8)

= Uiso (B1)

O22

4e

0.8680 (6)

0.1115 (7)

0.6679 (8)

= Uiso (B1)

O23

4e

0.9234 (5)

0.2330 (10)

0.4689 (7)

= Uiso (B1)

C11

4e

0.2039 (3)

0.265 (2)

0.1565 (6)

0.019 (3)

C12

4e

0.2488 (4)

0.291 (2)

0.0221 (6)

= Uiso (C11)

C13

4e

0.3394 (3)

0.3319 (18)

0.0477 (6)

= Uiso (C11)

C14

4e

0.3856 (6)

0.357 (2)

-0.0848 (8)

= Uiso (C11)

C21

4e

0.7720 (3)

0.284 (2)

0.5089 (6)

= Uiso (C11)

C22

4e

0.7085 (3)

0.310 (2)

0.6207 (6)

= Uiso (C11)

C23

4e

0.6243 (3)

0.346 (2)

0.5568 (6)

= Uiso (C11)

C24

4e

0.5559 (5)

0.3530 (18)

0.6612 (10)

= Uiso (C11)

Table S8. Explicit coefficients of the TZP 6211111/331111/31 basis set used for Ca in the calculations. 20

15

0 0 6 2.0 1.00 202699.0000000 30382.5000000 6915.0800000 1959.0200000 640.9360000 233.9770000 0 0 2 2.0 1.00 92.2892000 37.2545000 0 0 1 2.0 1.00 9.1319800 0 0 1 2.0 1.00 3.8177900 0 0 1 0.0 1.00 1.0493500 0 0 1 0.0 1.00 0.4286600 0 0 1 0.0 1.00 0.0628226 0 2 3 6.0 1.00 1019.7600000 241.5960000 77.6370000 0 2 3 6.0 1.00 29.1154000 11.7626000 4.9228900 0 2 1 0.0 1.00 1.9064500 0 2 1 0.0 1.00 0.7369000 0 2 1 0.0 1.00 0.2764200 0 2 1 0.0 1.00 0.0602700 0 3 3 0.0 1.00 15.0800000 3.9260000 1.2330000 0 3 1 0.0 1.00 0.2600000

0.000222964 0.00172932 0.00900226 0.0366699 0.1194100 0.2918250 0.4044150 0.2963130 1.0000000 1.0000000 1.0000000 1.0000000 1.0000000 0.00205986 0.01665010 0.07776460 0.2418060 0.4325780 0.3673250 1.0000000 1.0000000 1.0000000 1.0000000 0.0368947 0.1778200 0.4255130 1.0000000

SUPPLEMENTARY FIGURES

Figure S1. Comparison of the thermogravimetric analyses (TGA) of Ca(C4H9-B(OH)3)2 (CaBBu, in green) and Ca(C6H5-B(OH)3)2 (CaBPh, in red). In the case of CaBBu, no clear weight loss occurs below ~130°C, temperature at which the organic chain starts to decompose. This suggests that there are no water molecules of crystallization in the structure. Measurement conditions: TGA measurements were performed on a Netzsch STA 409 PC instrument. About 40 mg of powder were heated in an alumina crucible from room temperature (RT) to 800 °C, under the flow of a 80/20 N2-O2 mixture (55 - 60 cm3.min‒1) and with a heating rate of 10 °C.min‒1. TG /% 100

90

CaBPh

80

CaBBu 70

60

50

40 100

200

300

400 T /°C

500

600

700

Figure S2. Comparison of the connection modes between boronates and Ca2+ in Ca(C4H9-B(OH)3)2 (CaBBu) and Ca(C6H5-B(OH)3)2 (CaBPh). Ca, B, C, O, and H atoms are shown in red, brown, grey, blue, and white, respectively.

CaBBu

CaBPh

B1

The 2 independent boronates have the same type of connectivity to Ca2+ in the crystal structure.

B2

Figure S3. Comparison of 11B MAS NMR spectra of Ca(C4H9-B(OH)3)2 (CaBBu) before or after physical dilution of the powder in SiO2. a/ Spectra were recorded spinning at 20 kHz. The lineshape observed for the as-prepared CaBBu powder (in green) cannot be simulated considering the experimental 11B NMR parameters of each site, especially towards the low-frequency part of the signal, where the intensity of the step is unexpectedly high (blue arrow). By physically diluting the sample in SiO2 (black spectrum), the height of the step can be decreased. Experimental conditions: 9.4 T, 3.2 mm probe, 20 kHz MAS, 45° solid pulse, 100 kHz spinal-64 1H decoupling. 9.4 T 20 kHz MAS

CaBBu CaBBu-diluted in SiO 2 30

20

10 11 B

0 -10 chemical shift (ppm)

-20

-30

b/ Spectra were recorded spinning at 10 kHz. The spectra in black were acquired when the sample first reached 10 kHz, while those in red were recorded after spinning the sample up to 20 kHz, and then spinning it back down to 10 kHz. The differences observed between the 2 spectra (shoulder on the right hand side of the peak – blue arrow) indicate that the orientations of the crystallites have varied inside the rotor, due to the fast spinning. However, the difference between the red and black spectra is much less pronounced after physical dilution in SiO2. Experimental conditions: 14.1 T, 3.2 mm probe, 10 kHz MAS, 45° solid pulse, 100 kHz spinal-64 1H decoupling. 14.1 T 10 kHz MAS

CaBBu

CaBBu diluted in SiO2

12

10

8

6 11 B

4 2 0 chemical shift (ppm)

-2

-4

-6

It should be noted that nother possibility to avoid the preferential orientation of the crystallites in the rotor would consist in embedding the powder in epoxy resin, shaving the epoxy, and then packing the rotor for the measurement.

Figure S4. Analysis of the influence of the recycle delay and power of the excitation pulse on the 11B MAS NMR lineshape of Ca(C4H9-B(OH)3)2. Experimental conditions: 9.4 T, 3.2 mm probe, 20 kHz MAS, 45° solid pulse, 100 kHz spinal-64 1H decoupling

D1 = 6s, softer pulse

D1 = 60s

D1 = 20s

D1 = 6s 40

30

20

10

0 δ(ppm)

-10

-20

-30

-40

Figure S5. 3QMAS 11B NMR spectrum of Ca(C4H9-B(OH)3)2 recorded at 9.4 T, and simulation of the quadrupolar lineshapes for the 2 extracted sites. Experimental conditions: The 11B 3Q-MAS (triple quantum-MAS) NMR spectrum of Ca(C4H9-B(OH)3)2 was acquired at 9.4 T on a 3.2 mm Varian T3 MAS probe spinning at 18.5 kHz, using a 3Q z-filter experiment. The 3Q excitation and conversion pulse widths were 2.1 and 0.9 ms respectively, with a precession rate of ~300 kHz on the solid; the selective π/2 pulse used a ~9 kHz precession rate on the solid. The spectral widths were 37 and 50 kHz for f1 and f2, respectively. 500 t1 increments were recorded, with a dwell time of 27 µs. A total of 48 transients were collected by the States method for each t1 increment, with a recycle delay of 2 s. Spectra were processed using standard shearing methods.

5 6 7 8 9 10 20

15

10

5 11B

0

-5

MAS shift (ppm)

-10

-15

-20

3QMAS isotropic shift (ppm)

4

δiso = 4.54 ± 0.04 ppm CQ = 1.47 ± 0.03 MHz ηQ = 0.13 ± 0.02

δiso = 4.78 ± 0.03 ppm CQ = 1.46 ± 0.02 MHz ηQ = 0.28 ± 0.03

11B

3QMAS 9.4 T 18.5 kHz

8

4 0 -4 B chemical shift (ppm)

11

Figure S6. Schematic representation of the 13C{11B} REDOR NMR pulse sequence.

π/2 1

H

tCP

dec

dec

dec

π 13

C

tCP

π

π

π

π

π

π

11

B n 0

n 2NTR

4NTR

The 13C{11B} REDOR NMR pulse sequence allows the study of 13C-11B through space proximities. With C{ B} REDOR, two 13C NMR spectra are acquired and compared: one corresponds to a normal “spin echo” 13C NMR spectrum, while the other has additional 11B recoupling π pulses. The series of rotor-synchronized π pulses on 11B allows reintroducing dipolar coupling to the nearest carbons, causing them to “dephase” and their signal to decrease in intensity. By comparison of spectra acquired with and without the 11B pulses, identification of carbon atoms that are closest to the boron is possible. The spatial range which is probed during the 13C{11B} dephasing is governed by the duration of the dephasing period. 13

11

Figure S7. Solution 13C NMR spectrum of (C4H9-B(OH)3)‒ (aqueous solution, with Na+ as a counterion). Experimental conditions: 600 MHz NMR magnet, D1 = 8 s, NS = 6144, solvent = D2O.

C4

C2

C3

C1 35

30

25 δ(ppm)

20

15

Figure S8. 43Ca MAS NMR spectra of Ca(C4H9-B(OH)3)2 recorded at 9.4 and 14.1 T (grey line), together with their simulation (dashed line).

δiso = 14.6 ± 1.1 ppm Cq = 1.52 ± 0.09 MHz η = 0.57 ± 0.09

14.1 T

9.4 T

50

40

30

20

10 δ(ppm)

0

-10

-20

-30

Figure S9. Comparison of the 1H MAS NMR spectra of Ca(C4H9-B(OH)3)2: a/ spectrum recorded at 16.45 T and 60 kHz MAS (single pulse excitation); b/ spectrum recorded at 14.1 T and 10 kHz MAS (DUMBO sequence). Experimental conditions for recording the fast-MAS spectrum The fast-MAS 1H NMR spectrum of Ca(C4H9-B(OH)3)2 was recorded on a Bruker Avance III 700 MHz (16.45 T) spectrometer at a frequency of 700.13 MHz, using a fast spinning 1.3 mm Bruker HX MAS probe. The as-prepared sample was directly characterized without dilution in SiO2. The single pulse experiments were performed with a 90° pulse of 1.8 µs and a recycle delay of 5 s. 16 transients were recorded at a spinning speed of 60 kHz. The experimental conditions for recording the DUMBO 1H NMR spectrum can be found in the experimental section of the article.

a/ 60 kHz MAS, 1pulse, 700 MHz

b/ 10 kHz MAS, DUMBO, 600 MHz 8

6

4

2

1 H chemical

0

shift (ppm)

-2

-4

Figure S10. Comparison of the IR spectra of Ca(C4H9-B(OH)3)2 (CaBBu) and Ca(C6H5-B(OH)3)2 (CaBPh).

CaBBu

CaBPh

3500

3000

2500

σ (cm-1)

2000

1500

1000

500

Figure S11. Illustration of the linear regression extrapolation of δiso(13C) as a function of temperature, for one of the C2 atoms, and for the C4 peak (which englobes the 2 non-equivalent C4 atoms).

C2

C4 30,98

16,12

δ (ppm)

30,97

δ (ppm)

16,1

30,96

16,08

30,95 30,94

16,06

30,93

16,04 30,92

16,02

30,91 30,9 -60

-50

-40

-30

-20

-10

16 0

10

20

T (°C)

30

-60

-50

-40

-30

-20

-10

0

10

20

T (°C)

30

Figure S12. Differences in the modes of interaction of the boronate ligands in Ca(C4H9-B(OH)3)2 and Ca(C6H5-B(OH)3)2.

CaBBu

CaBPh Coordination modes of the boronate ligands

(same type of coordination mode for the 2 independent boronates)

Total number of fairly strong OH…O hydrogen bonds (out of the 2 inequivalent boronate ligands) 1 H bond

2 H bonds

Schematic representation of the 3D organization of the structures Planes of Ca2+ interconnected with each other through boronate ligands, which then pile to form a 3D layered material

Chains of Ca2+ interconnected with each other through boronate ligands to form planes, which then pile to form a 3D layered material

Analysis of the surface defects in Ca(C4H9-B(OH)3)2 Scanning electron microscopy images show that the Ca-butylboronate precipitate is composed of microcrystalline platelets (see Figure 1C in the main text), which are ~10 µm long, and ~300 to 800 nm thick on average. Interestingly, holes and cracks are observed at the surface of the platelets. Attempts were made to try to understand their origin, because such holes had not been observed for phenylboronate phases.1 ------------------------------First, the SEM analysis conditions were looked into in more detail, in order to determine their possible influence on the surface aspect. When avoiding the metallization step prior to imaging, the holes are still observed at the surface of the crystallites. However, it is clear that when focusing the beam on the crystal surface, the holes become more pronounced.2 To avoid unwanted surface damage, which may be due to the combination of high vacuum (~10‒5 Pa), high beam voltages (2 to 5 kV) and local heating of the sample, environmental SEM (ESEM) analyses were thus carried out.3 As shown in Figures S13 and S14, even when working under a pressure of 100 Pa at 2°C (or 1.26 10‒3 Pa at 20°C), and with an acceleration voltage of 2 kV, the crystallites remain sensitive to the beam (movement of crystals and increase in the hole size). However, systematically, we observed defects at the surface of the crystallites, for the very first image made in a given region.4 This suggests that these defects are initially present at the crystal surface, and not just due to imaging artifacts. It should be noted that attempts were also made to use environmental SEM to image the crystallites formed during the precipitation, prior to the washing and drying steps. Despite the difficulties in focusing the beam, and additional crystallization of NaCl around the crystallites, SEM images also suggest that defects are present at the surface of the crystallites. 1

2

3

5 μm

5 μm

5 μm

5

4

5 μm

5 μm

Figure S13. Environmental SEM images of Ca(C4H9-B(OH)3)2, recorded at 100 Pa and 2°C (acceleration voltage of 2 kV): evidence of the movement of the crystallites under the beam. Only a few seconds separate the measurements for each image (for example 2 s between images # 4 and 5).

1

M. Reinholdt et al, Inorg. Chem. 2011, 50, 7802. Attempts to perform Transmission Electron Microscopy (TEM) analyses of the crystallites, coupled to XRD imaging, were unsuccessful, due to the destruction of the sample under the beam (voltage = 100 kV; vaccum = 10-8 to 10-9 Pa). 3 ESEM measurement conditions: Environmental Scanning Electron Microscopy (ESEM) experiments were performed using a FEI QUANTA 200F ESEM FEG microscope equipped with a cooling stage. The sample (or suspension) was directly placed in a 5 mm inner diameter aluminum crucible. Observations were performed under water vapour at operating pressures ranging from 7.3 10‒3 to 680 Pa, and a stage temperature between ‒5 and 20 °C. The acceleration voltage of the electrons ranged between 0.2 and 10 kV. 4 Lower acceleration voltages could not be used in the SEM analyses of surface features, as images of much lower quality are obtained in that case. 2

1

2

3

5 μm

4

5 μm

5 μm

5

6

5 μm

5 μm

5 μm

Figure S14. Environmental SEM images of Ca(C4H9-B(OH)3)2, recorded at 1.26.10‒3 Pa and 20°C (acceleration voltage of 2 kV): evidence of the appearance of holes at the surface of the crystallites. Only ~7 s separate the measurements for each image.

------------------------------Specific surface area measurements were carried out by N2 adsorption, revealing that CaBBu is non-porous, and has a very low BET surface (< 6 m2/g). This suggests that the holes correspond to large defects, and that they are most-likely localized mainly at the surface of the crystallites only. When varying the precipitation time (between 1 min and 2 days) or temperature (0 °C or room temperature), the holes are still observed at the surface of the crystallites. Similarly, when the filtration step is replaced by a centrifugation, or when the washing of the precipitate is avoided, or when the drying step is performed at room-temperature instead of 40°C, defects are still present at the surface. Several reaction solvents were tested, showing that if the {H2O/EtOH} 1/1 mixture is replaced by H2O only, or by a {CH3CN/H2O/EtOH} 1.5/1/1 mixture,5 the defects are still observed. This is also the case when the Ca precursor used is different (Ca-nitrate instead of Ca-chloride). By dilution of the reaction medium by a factor of 20, the platelets become more rectangular (Figure S15), but preserve the surface defects.6 Of all the experimental parameters we varied, it is the nature of the organic chain bound to the boron which seems to have the strongest influence on these surface defects. Indeed, as previously shown,1 in the case of phenylboronate precursors, no holes had been observed at the surface. In contrast, for precursors bearing long alkyl chains, as in 1,4-bis(hexyloxy)benzeneboronate, rougher surfaces are observed by SEM.7

60 μm

12 μm

Figure S15. SEM images of a Ca(C4H9-B(OH)3)2 phase, synthesized under higher dilution conditions. 5

It should be noted that using EtOH only in the syntheses leads to a dramatic loss in crystallinity, the platelet shapes of the crystallites not being observed in SEM anymore. In contrast, when using the CH3CN/EtOH/H2O mixture of solvents in the syntheses, more rectangular-shaped platelets were obtained, according to SEM. 6 We also found that another means of modifying the morphology of the platelets consists in adding to the reaction medium glycerol or ethylene glycol (at concentrations which are ~2 to 10% those of the butylboronate), although this has a much less pronounced effect on the platelet morphology. 7 C. L. Moy, R. Kaliappan, A. J. McNeil, J. Org. Chem. 2011, 76, 8501.