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Synthesis and crystal structures of two novel ternary copper(II) complexes with a NO 2 S-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·0.5H 2 O and [Cu 2 (TCC)(acv) 2 ]·6H 2 O 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 (H 2 O) 2 ](NO 3 ) 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 [Cu 2 (TCC)(H 2 O) 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 H 2 BCBC and its hemi-acetone solvate H 2 BCBC·0.5C 3 H 6 O shows distinct intra-molecular H-bonding stabilizations in their H 2 BCBC ± zwitterions. [ABSTRACT FROM AUTHOR]

Five novel ternary copper(II) complexes with the N,O 2 ,S-tripodal tetradentate chelators N,N-bis(carboxymethyl)-S-benzylcysteaminate(2-) ion (BCBC) or N,N,N′,N′-tetrakis(carboxymethyl)cystaminate(4-) ion (TCC) and adenine (Hade), 2,6-diaminopurine (Hdap), 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) as co-ligand were synthesized and characterized by X-ray diffraction and other physical methods: [Cu 2 (BCBC) 2 (μ 2 -N3,N7-H(N9)ade)(H 2 O) 2 ]·H 2 O ( 1 ), [Cu 2 (BCBC) 2 (μ 2 -N7,N9-H(N3)dap)(H 2 O) 2 ]·4H 2 O ( 2 ), [Cu 2 (μ 2 -TCC)(H(N9)ade) 2 (H 2 O) 2 ]·10H 2 O ( 3 ), [Cu 2 (μ 2 -TCC)(bpy) 2 ]·15H 2 O ( 4 ) and [Cu 2 (μ 2 -TCC)(phen) 2 ]·14H 2 O ( 5 ). The crystal structure of H 4 TCC·3H 2 O was also determined. All ternary Cu(II) complexes have molecular structures. The N-(2-mercaptoethyl)-iminodiacetate moieties of BCBC or TCC ligands play a NO 2 + S-tripodal tetradentate role, with the S-(thioether or disulfide) atom as the apical/distal donor of the copper(II) center. In 1 – 3 , the iminodiacetate moiety exhibits a mer-NO 2 conformation (two nearly coplanar chelate rings) while in 4 and 5 (with bpy or phen as coligand) it displays a fac-NO + O (apical/distal) conformation. We conclude that the formation of the Cu–S(thioether or disulfide) bonds is strongly favored by the N-branched topology of the S-ligands in the reported compounds. [ABSTRACT FROM AUTHOR]

Aqua(pyrazine-2-carboxamide)(iminodiacetato)copper(II) monohydrate, [Cu(IDA)(pza)(H2O)]·H2O, was synthesised and characterised by thermal, spectral, magnetic and X-ray diffraction methods. Its crystal structure was solved to a final R1=0.058. The Cu(II) atom exhibits a square base pyramidal coordination (type 4+1) with IDA ligand in mer-tridentate configuration [Cu–N(aliphatic) 1.986(7), Cu–O(carboxyl) 1.933(6) and 1.938(5) A˚], the Cu–N4(pza) bond [1.984(7) A˚] and Cu–O(apical aqua) bond [2.347(8) A˚]. The N4-monodentate ligand role of pza is in contrast with that of the N,O-bidentate pza-Cu(II) chelation in [Cu(pza)2(ClO4)2] or [Cu(acac)(pza)(ClO4)]·H2O. In the molecular recognition between Cu(IDA) chelate and pza the Cu–N4(pyridine-like) coordination mode is preferred because it enables the additional contribution of two weak intra-molecular inter-ligand C(aromatic)–H⋯O (IDA) interactions. [Copyright &y& Elsevier]

The synthetic nucleoside acyclovir is considered an outstanding model of the natural nucleoside guanosine. With the purpose of deepening on the influence and nature of non-covalent interactions regarding molecular recognition patterns, three novel Cu(II) complexes, involving acyclovir (acv) and the ligand receptor N-(2-hydroxyethyl)ethylenediamine (hen), have been synthesized and thoroughly characterized. The three novel compounds introduce none, one or two acyclovir molecules, respectively. Molecular recognition has been evaluated using single crystal X-ray diffraction. Furthermore, theoretical calculations and other physical methods such as thermogravimetric analysis, infrared and UV-Vis spectroscopy, electron paramagnetic resonance and magnetic measurements have been used. Theoretical calculations are in line with experimental results, supporting the relevance of the [metal-N7(acv) + H-bond] molecular recognition pattern. It was also shown that (hen)O-H group is used as preferred H-donor when it is found within the basal coordination plane, since the higher polarity of the terminal (hen)O-H versus the N-H group favours its implication. Otherwise, when (hen)O-H occupies the distal coordination site, (hen)N-H groups can take over. [ABSTRACT FROM AUTHOR]

Abstract: In contrast to the comprehensive structural information about metal complexes with adenine, the corresponding to its isomer 2-aminopurine (H2AP) is extremely poor. With the aim to rationalize the metal binding pattern of H2AP, we report the molecular and/or crystal structure of four novel compounds with various iminodiacetate-like (IDA-like) copper(II) chelates: [Cu(IDA)(H2AP)(H2O)]·H2O (1), [Cu(MIDA)(H2AP)(H2O)]·3H2O (2), {[Cu(NBzIDA)(H2AP)]·1.5H2O}n (3) and [Cu(MEBIDA)(H2AP)(H2O)]·3.5 H2O (4), where IDA, MIDA, NBzIDA and MEBIDA are R=H, CH3, benzyl- and p-tolyl- in R-N-(CH2-COO-)2 ligands, respectively. Synthesis strategies include direct reactions of copper(II) chelates with H2AP (alone, for 1 and 3) and/or with the base pairs H2AP:thymine (1–4) or H2AP:cytosine (3). Moreover, these compounds have been also investigated by spectral and thermal methods. Regardless of the N-derivative of the IDA chelator, molecular recognition between H2AP and the referred Cu(II)-chelates only displays the formation of the Cu–N7(purine-like) bond what is clearly in contrast to what was previously reported for adenine. The metal binding pattern of 2-aminopurine is discussed on the basis of the electronic effects and steric hindrance of the 2-amino exocyclic group. [Copyright &y& Elsevier]

N-(2-Pyridylmethyl)iminodiacetic acid hemi-hydrate (H2pmda·0.5H2O) was prepared and characterized by X-ray crystallography (final R1=0.042). The zwitterion H2pmda± is intra-stabilized by a trifurcated hydrogen bond. Intermolecular carboxylic-carboxylate hydrogen bonds and the parallel inter-ligand π,π-stacking (3.57(2) A˚) between pyridyl rings from pairs of adjacent zwitterions generate 2D frameworks (bi-layers with the carboxyl groups towards the external surfaces and py–pmda rings towards the inside). In the crystal, the bi-layered structures are connected by equivalent hydrogen bonds, which link each water molecule to two symmetry related O-carboxylate atoms from the adjacent external faces of two 2D frameworks. The compounds [Cu(pmda)(pca)]·3H2O (1) and [Cu(pmda)(Hpb)]·5H2O (2) were obtained by stoichiometric reaction of Cu2(CO3)(OH)2, H2pmda·0.5H2O and α-picolylamine (pca) or 2-(2′-pyridyl)benzimidazole (Hpb), respectively, and characterized by single crystal X-ray diffractometry. Compound 2 was also studied by TG analysis (with FTIR study of the evolved gasses in the pyrolysis), magnetic susceptibility at 80–300 K range, and FTIR, electronic, ESR spectra. In 1 and 2 the copper(II) atom exhibits a distorted octahedral coordination (type 4+1+1) and pmda acts as tripodal tetra-dentate ligand. However, pmda displays different coordination roles. The pmda supplies two N,O-meridional and two trans-apical N(py),O-donors in 1, whereas links the metal by three N,N(py),O-meridional and one O-apical atoms in 2. No π,π-stacking of pyridyl–(pmda) rings is observed in these complexes. The pyridyl–(pca) ring of 1 is not involved in ring–ring stacking interactions, but compound 2 recognizes itself by a roughly anti-parallel π,π-stacking of adjacent Hpb ligands (5.3°, 3.41(2) A˚) forming pairs of complex units. [Copyright &y& Elsevier]

Highlights: [•] The reasons of the extreme versatile behaviour of adenine are studied. [•] One N-heterocyclic donor atom per ring moiety, within adenine skeleton, is required. [•] Deaza-adenines, adenine isomers and aza-adenines are considered. [•] The structures of metal complexes with N-ligands related to adenine are discussed. [Copyright &y& Elsevier]

Mixed ligand MII-complexes (M Co Zn) with pyridine-2,6-dicarboxylate(2-) chelator (pdc) and adenine (Hade) have been synthesized and studied by X-ray diffraction and other spectral and thermal methods: [Cu(pdc)(H(N9)ade)(H2O)] (1), [Cu2(pdc)2(H2O)2(μ2-N3,N7-H(N9)ade)]·3H2O (2), trans-[M(pdc)(H(N9)ade)(H2O)2]·nH2O for M Co (3-L, 3-M, 3-H) or Zn (4-L, 4-H), where n is 0, 1 or 3 for the ‘lowest’ (L), ‘medium’ (M) and ‘highest’ (H) hydrated forms, and the salt trans-[Ni(pdc)(H2(N1,N9)ade)(H2O)2]Cl·2H2O (5). In all the nine compounds, both neutral and cationic adenine exist as their most stable tautomer and the molecular recognition pattern between the metal-pdc chelates and the adenine or adeninium(1+) ligands involves the M N7 bond in cooperation with an intra-molecular N6 H⋯O(coordinated carboxylate) interligand interaction. In addition the dinuclear copper(II) compound (2) has the Cu N3 bond and the N9 H⋯O(coord. carboxylate) interaction. The structures of mononuclear ternary complexes proved that the molecular recognition pattern is the same irrespective of (a) the coordination geometry of the complex molecule, (b) the different hydrated forms of crystals with Co or Zn, and (c) the neutral of cationic form of the adenine ligand. These features are related to the mer-NO2 chelating ligand conformation (imposed by the planar rigidity of pdc) as a driving force for the observed metal binding mode. [ABSTRACT FROM AUTHOR]

Abstract: In order to deepen on metal-binding patterns of acyclovir (acv), {[Cu(IDA)(acv)]·2MeOH}n (1) and [Cu(glygly)(acv)]·H2O (2) compounds have been synthesized and investigated by X-ray crystallography as well as spectral and thermal methods. These compounds have been chosen upon the assumption that iminodiacetate (IDA) and glycylglycinate (glygly) chelating ligands would bind copper(II) with mer-tridentate conformation, supplying two terminal H-acceptor carboxylate groups (IDA) or one H-acceptor carboxylate and one H-donor primary amino group (glygly). The main aim of this work was to clarify if the amino group of glygly can build an intra-molecular interligand H-bonding interaction to reinforce the Cu―N7(acv) bond. Our results are discussed in the context of an up-to-date critical look regarding the related structural information. From the viewpoint of molecular recognition, the structure of 1 shows that the chelate-nucleoside recognition only involves the Cu―N7(acv) coordination bond. In contrast, the molecular complex of 2 exhibits the Cu―N7(acv) coordination bond reinforced by an intra-molecular (glygly)N–H···O6(acv) interaction (2.961(3)Å, 140.5°). [Copyright &y& Elsevier]

Abstract: The available crystal structure information in the CSD database on ternary species prepared by the reaction of diverse copper(II) complexes (CuL) and purine, adenine and guanine or related purine derivatives is considered in order to deepen the intra-molecular interligand interactions affecting the molecular recognition patterns of the ‘metal complex+purine nucleobase’ and closely related systems. The degree of protonation and the possibilities of different tautomeric forms in the purine-like moieties are taken into account. The main conclusion is a general trend to form a Culike) coordination bond which can be reinforced by an intra-molecular interligand H-bonding interaction. N)⋯A (O or Cl acceptor) or Nigand L)⋯O6(oxo-purines) are commonly observed. In addition, selected examples revealed that the presence of a variety of non-coordinating groups in L or in the purine-like nucleobases can significantly influence the structurally observed molecular recognition pattern. Moreover, examples are known where binuclear cores of the types CuII 2(μ2-N3,N9-adeninate)4(aqua)2 or CuI 2(μ2-N3,N9-adeninate)2(aqua)2 recognise CuL chelates by means of the expectable pattern (Cunation bond+N6O(L) interaction). [Copyright &y& Elsevier]

Four ternary metal-complexes with Cu(II) or Zn(II), 2,6-pyridine-dicarboxylate (pdc) or glycyl-glycinate (GG) and the synthetic nucleoside 9-(2-hydroxyethyl)adenine (9heade) have been synthesized and studied by single-crystal X-ray diffraction and other physical methods. Relevant supramolecular assemblies found in the solid state structures have been further studied using density functional theory (DFT) calculations. In addition, the energetic features of the non-covalent interactions as well as the cooperativity effects have been calculated and characterized using the non-covalent interaction plot computational tool. Compounds trans -[Cu(pdc)(9heade)(H 2 O) 2 ·3H 2 O (1a) and [Cu(pdc)(9heade)(H 2 O)]·H 2 O (1b), trans -[Zn(pdc)(9heade)(H 2 O) 2 (2), share the same molecular recognition pattern consisting in the cooperation of the metal-N7(9heade) bond and an interligand (9heade)N6-H···O(pdc) interaction, regardless of the nature of the metal, the coordination environment and the water content. At a supramolecular level, these compounds exhibit pairs of complex molecules linked by H-bonds and interesting anion–π/π–π/π–anion assemblies (in 1a and 1b) or the unprecedented π-π interactions (in 2), involving the purine moieties or the exocyclic –6NH 2 purine groups, respectively. Compound 3 , {[Cu(GG)(9heade)(H 2 O)·Cu(GG)(μ 2 -9heade)]·8H 2 O} n , consists in asymmetric dinuclear complex units (Cu···Cu 7.83 Å) that connect with adjacent ones by pairs of very weak Cu-O(carboxylate) bonds (Cu···Cu 3.81 Å) building a polymeric chain. The supramolecular transition from a single molecule to dinuclear units and finally a polymeric chain is also observed in the electron paramagnetic resonance spectra and discussed from a structural point of view as well as by DFT calculations. The unprecedented N7 and μ-N7,O(ol) metal binding patterns of 9heade differs from that recently reported (μ-N1,N7) in a Cd(II) polymer. The molecular and supra-molecular recognition patterns in four Cu(II) or Zn(II) ternary complexes with two rigid-planar tridentate chelators and the nucleoside 9-(2-hydroxyethyl)adenine are discussed on the basis of crystallographic results and density functional theory calculations, providing a thorough evaluation of the contribution of interligand interactions. Unlabelled Image • Ternary complexes are studied by crystallographic and theoretical methods. • Rigid-planar tridentate chelators and an adenine synthetic nucleoside are involved. • The Zn(II) compound exhibits an unprecedented anti-parallel C···NH 2 π-interaction. • Interesting anti-parallel π-C·NH 2 or anion–π/π–π/π–anion interactions are reported. • The Cu-glycylglycinate-nucleoside forms dinuclear molecules that lead to a polymer. [ABSTRACT FROM AUTHOR]