Supplementary information

Fig 1. Liquid -assisted grinding in the system 5 (anhydrous L-serine+andydrous oxalic acid+water drop). Amount of liquid water varied according with η-criterion (η=0.05, 0.1, 0.25, and 1).1 The formation of [L-serH]2[ox]▪2H2O form II was detected (trace amount along with initial reactants) at η=0.05. The mixtures of [L-serH]2[ox]▪2H2O polymorphs were observed at η=0.1. The LAG at η=0.25 gave only [L-serH]2[ox]▪2H2O form I with significant amount of L-serine monohydrate. Finally, almost total transformation of initial components to [L-serH]2[ox]▪2H2O form I was obtained at η=1. LS - L-serine, LSM – L-serine monohydrate, OA – oxalic acid (alpha-form), OAD – oxalic acid dihydrate

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Fig 2. Dehydration of L-serine monohydrate (LSM) on storage. The complete loss of water and formation of L-serine (LS) was observed after 3 hours. Calculated XRPD patterns of LSM and LS shown black and orange respectively

Fig 3. FTIR ATR spectra of [L-serH]2[ox]▪2H2O: a) form I, b) form II. The fundamental vibrations corresponding to NH3

+, COO- and OH-groups are shown by arrows (and pointed out in a table 1-ESI): 1 – OH stretching; 2 – NH3+

stretching; 3 – COO- asymmetric stretching; 4 - COO- symmetric stretching. An assignment for all the modes is shown in the Table 1-ESI

Table 1. Tentative assignment of vibration modes for two forms of [L-serH]2[ox]▪2H2O in FTIR ATR spectra

Assignment of vibrationsForm I Form II3423; 3342 3448,3407 OH stretching3266 32972973; 2881 29541733 1746; 17221589 16151548; 1514 15291464 14621408 14321367 1379 CH bending, CC stretching1309 12811233 12371160; 1122 1145 COH bending1093 1092 CO stretching1033; 1028 1057; 1047985; 979 999; 986898; 886 916830 860 CC stretching790 767756 737; 717629 658; 606

Frequencies in wavenumber (cm -1)

NH3+ stretching

CH2, CH stretchingNH3

+ bendingNH3

+ bendingCOO- asymmetric stretchingCH2 bendingCOO- symmetric stretching

CH2 waggingCH2 twisting

NH3+ rocking

NH3+ rocking, CC stretching

CH2 rocking

COO- twistingCOO- waggingCOO- rocking

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Table 2. Graph sets for [L-serH]2[ox]▪2H2O I form. D – finite discrete motif, C – infinite chain motif, R – ring motif. Superscript and subscript correspond to the number of proton acceptors and donors, respectively. When no subscript and superscript are given, one donor and one acceptor are implied. The size or degree of a pattern, based on the number of atoms in a hydrogen-bonded ring, for example, is shown in parentheses following the graph set descriptor2,3

Table 3. Graph sets for [L-serH]2[ox]▪2H2O II form. D – finite discrete motif, C – infinite chain motif, R – ring motif. Superscript and subscript correspond to the number of proton acceptors and donors, respectively. When no subscript and superscript are given, one donor and one acceptor are implied. The size or degree of a pattern, based on the number of atoms in a hydrogen-bonded ring, for example, is shown in parentheses following the graph set descriptor2,3

Fig 4. The only second level chain motif in the structure of [L-serH]2[ox]▪2H2O II form

Type of H-bond a b c d e f g h iabcd De Df – Dg – Dh – – – – – Di – D

C22(10)

R22(10) C1

2(4)D2

2(8) D22(5) D2

2(5)C2

2(11) C22(9) C2

2(9) D22(6)

D22(5) D2

2(6) D22(6) D2

2(6)D2

2(5) D22(6) D2

2(6) D22(6) C1

2(7)D2

2(6) D22(5)

D12(3) D2

2(6) D22(6) D2

2(6) C22(10) C2

2(9) D22(6)

Type of H-bond a b c d ea Db Dc Dd – De – D

D22(5)

D22(8) R1

2(7)D2

2(6) D22(6)

D22(6) D2

2(6) C12(7)

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Fig 5. All second level chain motifs in the structure of [L-serH]2[ox]▪2H2O I form. Interestingly, all chains expand along the same axis corresponding to the direction normal to the plane of Fig. 8 (see the main text of the article)

References

1. T. Friscic, S. L. Childs, S. A. A. Rizvi and W. Jones, CrystEngComm, 2009, 11, 418.

2. M. C. Etter, J. C. MacDonald and J. Bernshtein, Acta Cryst., 1990, B46, 256.

3. M. C. Etter, J. Phys. Chem., 1991, 95, 4601.

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