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Complex compounds in so-called acid form contain hydrogen atoms that are liberated as protons on dissolution. Different cases of localization of such mobile H atoms can be observed in crystals. It is not infrequent that crystallization water molecules undergo protonation to give oxonium ion, either individual or associated with different number of water molecules. Such compounds include crystals with complex anionsand [ Co ( Cdta )] -[1-4]. Protonation of coordinated acetate ion takes place in the [ Co ( en ) 2 ( CH 3 CO 2 )( CH 3 CO 2 H )]( ClO 4 ) 2 · H 2 O crystals: the acetate ions of two complex cations are bonded by a short hydrogen bond [5]. A similar situation is observed in the [Co ( H 3 Cdta )( CN ) 2 ] complexes [6] with coordinated acetate groups and in the [ Co ( Dtmp )( HAla )] HgCl 4 crystals with propionate groups of both ligands [7]. In crystals of [Co(HEddda)] · 2 H 2 O [8] and [ Co ( H 2 Eddp )( HEddp )] Br 2 · 4 H 2 O [9], the carboxylate group of one of the coordinated propionate chains is also protonated, but is bound by a short hydrogen bond with water molecule. 1 Some complexes were supposed to have protonated crystallization water molecules, rather than pro-1 The above-indicated ligands (written in abbreviated form as Gly, Ala, Dtmp, Ida, Edda, Eddp, Eddda, Cdta) are anions of amiacids, respectively; en is ethylenediamine. Another abbreviated forms used in the text will be interpreted further on.tonated carboxyl groups of six-membered cycles [10][11][12].The validity of such a supposition will be discussed below.In continuation of our previous X-ray diffraction studies of the acid Co(III) complexes with aminopropionate six-membered cycles [7-9], we investigated the structures of a complex with S -proline-N -mono-3-propionic acid ( H 2 Promp ). The structures of only two metal complexes (copper(II)) with this ligand have been reported recently [13,14].In all the above cases, protonated carboxyl group remains coordinated by the metal atom. However, as a result of protonation of the Co(III) complex with hexadentate ethylenediaminetetraacetic acid ( H 4 Edta ), one of the acetate branches of the ligand does not participate in coordination [15]. This fact is explained by sufficient strains in the [ Co ( Edta )] -ion arising due to involvement of the ligand atoms in five conjugated fivemembered metal cycles [16,17]. In this case, the greatest distortions are exhibited by aminoacetate cycles of G type, which are almost coplanar to the ethylenediamine cycle. It is exactly one of these cycles that is cleaved on protonation and on coordination of additional monodentate ligands. Therefore, it was of interest to study the mode of protonation of the [Co(Edta)X] complexes, which are less strained, since one acetate group is noncoordinated. For this purpose we selected a complex with cyanide ion as the additional X ligand stable toward aquation. Abstract -Crystal structures of [Co(Promp)(Hpromp)] · H 2 O ( I ) (where Promp and Hpromp are deprotonated and monoprotonated anions of S -proline-N -mono-3-pro...

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so than amplitudes determine the form of electron density maps. Vector (Patterson) maps contain images related by the the twin law. There appear to be no circumstances where least-squares refinements should be made with detwinned data, since the process of detwinning unavoidably introduces considerable noise into what might have been an excellent data set. Various examples will be used to illustrate strategies for the identification of twinning (preand post-data collection), de1ivation of the twin law. and solution and optimal refinement of structures.