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. 2015 May 13;16(5):10767–10796. doi: 10.3390/ijms160510767

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© 2015 by the authors; licensee MDPI, Basel, Switzerland.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/).

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The structures of the tetrahydrates of the s-trans species 5 and 10 and the s-cis species 8 and 15 as optimized in continuum water solvent at the IEF-PCM/B97D/aug-cc-pvtz level. The hydrogen bond parameters (from left to right) in Figure 1 are as follow. 5 tA: OCCN = 180°, the O=C, O…H_w11 (198 pm), and O…H_w21 (201 pm) bonds are coplanar, bond angles: O_w1H_w11…O = 177°, O_w2H_w21…O = 178°. The C=N, N–H and the N…H_w31 (187 pm) bonds are coplanar, H…O_w4 = 208 pm. The N…H_w31O_w3 bond angle is 177°, N–H…O_w4 = 173°. 10 tAA: NCCN = 179.9°, the N=C, N–H, and N…H_w21 (187 pm) bonds are coplanar, H…O_w1 = 209 pm. Bond angles: O_w1…H–N = 173°, O_w2H_w21…N = 177°. The C=N, N–H and the N…H_w31 (187 pm) bonds are coplanar, H…O_w4 = 208 pm. The N…H_w31O_w3 bond angle is 177°, N–H…O_w4 = 173°. 8 cA: OCCN = 23.7°, only one water—carbonyl hydrogen bond: O…H_w11 (194 pm), O_w1H_w11…O = 161°. Waters 1 and 2 form a solvent-solvent hydrogen bond with O_w1…H_w21 distance of 194 pm and O_w1…H_w21O_w2 angle of 177°. Water 2 and water 3 are also linked by a solvent-solvent hydrogen bond: H_w22…O_w3 = 187 pm and O_w2H_w22…O_w3 = 177°. The C=N, N–H and the N…H_w31 (186 pm) bonds are almost coplanar (the sum of the bond angles is 359°), H…O_w4 = 201 pm. The N…H_w31O_w3 bond angle is 178°, N–H…O_w4 = 176°. 15 cAA: NCCN = 30.5°, the N=C, N–H, and N…H_w21 (182 pm) bonds are coplanar, H…O_w1 = 207 pm. Bond angles: O_w1…H–N = 176°, O_w2H_w21…N = 177°. Water 2 and water 3 form a solvent–solvent hydrogen bond: O_w2…H_w32 = 193 pm and O_w2…H_w32O_w3 = 161°. The C=N, N–H and the N…H_w31 (190 pm) bonds are coplanar, H…O_w4 = 210 pm. The N…H_w31O_w3 bond angle is 175°, N–H…O_w4 = 172°.