Metal binding pattern of acyclovir in ternary copper(II) complexes having an S-thioether or S-disulfide NO^sub 2^S-tripodal tetradentate chelator

Synthesis and crystal structures of two novel ternary copper(II) complexes with a NO2S-tripodal tetradentate chelator and acyclovir (acv) are reported, providing new insights into the metal binding pattern (MBP) of this synthetic purine nucleoside. N,N-bis(carboxymethyl)-S-benzylcysteaminate(2-) (BCBC) and N,N,N′,N′,-tetrakis(carboxymethyl)cysteaminate(4-) (TCC) chelators supply S-thioether or S-disulfide donor atoms, respectively. In [Cu(BCBC)(acv)]·2.5MeOH·0.5H2O and [Cu2(TCC)(acv)2]·6H2O the copper(II) atom exhibits an asymmetrical elongated octahedral coordination (type 4+1+1*, where (*) indicates a very weak coordination bond, ~3 Å), and acv displays the rather uncommon N7,O6-chelating mode, (early reported by Turel for trans-[Cu(acv)2(H2O)2](NO3)2 (with a Cu–O6(acv) bond distance of ~2.7 Å). The weakness of the (acv)O6⋯Cu interaction is related to the shortness of the Cu-S(thioether or disulfide) apical/distal bonds. A ‘molecular form’ of the binary parent-complex [Cu2(TCC)(H2O)2] (4) is also reported and features a relevant intra-molecular stabilization by two symmetry related (aqua)O–H⋯O(carboxylate) interactions (2.722(1) Å, 169.0°) linking together both halves of the complex molecule. The structure of H2BCBC and its hemi-acetone solvate H2BCBC·0.5C3H6O shows distinct intra-molecular H-bonding stabilizations in their H2BCBC± zwitterions.