Zoran D. Tomić

Stacking vs. CH–π interactions between chelate and aryl rings in crystal structures of square-planar transition metal complexes

The crystal structures of square-planar transition-metal complexes from the Cambridge Structural Database (CSD) with close contacts between planar chelate rings and aryl rings containing six carbon atoms (C6-aryl) were analyzed. Most of the chelate rings in these structures are fused with aromatic or other π-delocalized chelate rings. The results show that planar chelate rings can be involved in stacking and CH–π interactions with organic aryl rings. However, the number of stacking interactions is a few times larger than the number of CH–π interactions. The analysis also shows that in almost all cases CH–π interactions are formed only when stacking interactions are prevented by voluminous substituents. Hence, between planar chelate rings and C6-aryl rings stacking interactions are preferred to CH–π interactions.

Synthesis and biological evaluation of new pyrazole- and tetrazole-related C-nucleosides with modified sugar moieties

Abstract 3(5)-Carboxamido-4-(β- d -ribofuranosyl)pyrazoles bearing 2′-benzamido ( 15 ) and 3′-mesyloxy ( 29 ) isosteric groups, as well as the tetrazole C -nucleosides with 2-benzamido-2-deoxy-β- d -ribofuranose ( 19 ) and 3-azido-3-deoxy-β- d -xylofuranose ( 36 ) as sugar segments, have been synthesized starting from d -glucose, by utilizing the 2,5-anhydro- d -glucose ethylene acetal derivatives 1 and 20 as divergent intermediates. The C -nucleosides 15 and 36 were shown to be moderate inhibitors of the in vitro growth of both N2a and BHK 21 tumour cell lines, whereas 29 showed a selective, although not potent cytotoxic activity against N2a cells. Compound 29 also showed a moderate in vitro antiviral activity towards the rabies virus.

Influence of metal and ligand types on stacking interactions of phenyl rings with square-planar transition metal complexes

In order to find out whether metal type influences the stacking interactions of phenyl rings in square-planar complexes, geometrical parameters for Cu, Ni, Pd and Pt complexes, with and without chelate rings, were analyzed and compared. By searching the Cambridge Structural Database, 220 structures with Cu complexes, 211 with Ni complexes, 285 with Pd complexes, and 220 with Pt complexes were found. The results show that the chelate ring has a tendency to make the stacking interaction with the phenyl ring independent of metal type in the chelate ring. However, there are some differences among metals for complexes without a chelate ring. There are a number of structures containing Pd and Pt complexes, without chelate rings, that have short carbon-metal distances and parallel orientations of the phenyl ring with respect to the coordination plane. It was found that some of these complexes have a common fragment, CN, as a part of the ligands. This indicates that the CN supports stacking interactions of square planar complexes with the phenyl ring.

Structural, spectroscopic and computational studies of the HgL2Cl2 complex (L = 3,5-dimethyl-1-thiocarboxamide pyrazole) and the crystal structure of L

In the present paper we report the synthesis as well as the structural and vibrational characterisation of the HgL2Cl2 complex (L = 3,5-dimethyl-1-thiocarboxamide). The crystal and molecular structures of both L and the HgL2Cl2 complex were determined by single-crystal X-ray diffraction. The coordination propensity of L to HgCl2 was explored by quantum chemical calculations. We found the preference of the monodentate coordination of L to HgCl2 through the sulfur atom (instead of the “pyridine” nitrogen) to be in agreement with Pearson’s acid–base character of the atoms involved and the steric effects. The vibrational properties of HgL2Cl2 were evaluated by a joint FT-IR and quantum chemical analysis. In addition, the thermal decomposition of the complex and ligand is reported.

Parallel stacking interactions in square‐planar transition‐metal complexes containing fused chelate and C6‐aromatic rings

Stacking interactions in the crystal structures of square-planar transition metal complexes from the Cambridge Structural Database with five- and six-membered chelate rings fused with C(6-arom) rings (arom = aromatic) were analyzed. The distribution of distances between the closest C(6-arom)-C(6-arom) and C(6-arom)-chelate contacts shows that in a large fraction of the intermolecular interactions the C(6-arom) ring of one molecule is closer to the chelate than to the C(6-arom) ring of the other molecule. These results indicate a possible preference of the C(6-arom) ring to form stacking contacts with the chelate rings. The preference is ubiquitous and does not depend on the metal type.

Preparation and molecular structure of the trans(O6) isomer of dihydrogen (1,3-propanediamine-N,N′-diacetato-N,N′-di-3-propionato)copper(II) complex. The stereochemistry of copper(II)-edta-type complexes in relation to the structure of the ligand

Abstract The hexadentate complex [Cu(H21,3-pddadp)] · 1.5H20 (1,3-pddadp = 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate ion) has been prepared and isolated and its molecular structure determined by the single crystal X-ray diffraction technique. The complex is a trans(O6) isomer, in which the copper(II) ion is surrounded octahedrally by two nitrogen and four oxygen atoms of 1,3-pddadp with two protonated β-alaninate rings in trans positions. The copper atom environment is a tetragonally elongated octahedron with tetragonality (T) 0.798. A comparison of structures of the copper(II)-edta-type complexes shows an expected variation in their stereochemistry, depending on the structure of the ligand. The 1,3-pddadp ligand encircles the CuII ion more favourably than the edta ligand, which is capable of forming five-membered chelate rings only. Some properties of the complex are also given.

Transition metal complexes with pyrazole-derived ligands. X. [Zn(CH3COO)2L2].2MeOH (L = 3-amino-5-phenylpyrazole)

Monocrystals of the title complex, bis(acetato-O)bis(3-amino-5-phenylpyrazole-N 2 )zinc(II) dimethanol solvate, [Zn(C 2 H 3 O 2 ) 2 (C 9 H 9 N 3 ) 2 ].2CH 4 O, were obtained by crystallization from a methanolic solution of Zn(OAc) 2 .-2H 2 O and 3-amino-5-phenylpyrazole (L) (1:2 molar ratio). The two pyridine-N atoms from the pyrazole derivative and two O atoms from the acetate groups are coordinated to the Zn atom in a distorted tetrahedral arrangement. The phenyl and aminopyrazole rings in both ligand molecules are planar within experimental accuracy. As a consequence of the arrangement of the molecules in the unit cell, the dihedral angles between the phenyl and aminopyrazole ring planes in the two ligand molecules are 5.6 (2) and 27.4 (2)°.

Anion-/cation-directed reaction routes to polymorphic forms of a pyrazole-type ligand and its coordination compounds with zinc. Key structural differences between polymorphs’

Abstract Synthetic paths toward the two polymorphs of a monohydrate, one anhydrous polymorph of 1-carboxamidino-5-hydroxy-3-methylpyrazole (hcmp) and two polymorphs of zinc complexes containing hcmp ligand are presented. By choosing ions which are not part of the final product, it is possible to direct the synthesis toward the particular polymorph. In all three modifications of hcmp, the same hydrogen bonding motif appears, leading to formation of similar molecular chains. Differences arise due to different modes of chain aggregation and the presence of solvent water. Analysis of the crystal packing and the energetic features of hcmp polymorphs is made using the PIXEL model. The thermal decomposition processes are examined using differential scanning calorimetry and thermogravimetry. Analysis of crystal packing in the two polymorphs of zinc complex suggests the key role of the hydrogen bonding capacity of the aqua ligand for the appearance of the two polymorphic forms. In both polymorphs of zinc complex, stacking interactions have an important role. However, the enhanced hydrogen bonding capacity of the aqua ligand influences the formation of multistacking arrangement.

Transition metal complexes with ­thiosemicarbazide‐based ligands. XLIII.

In the title compound, [ZnCl(C(2)H(7)N(3)S)(2)]Cl, the Zn(II) ion is five-coordinated in a distorted trigonal-bipyramidal arrangement, with the hydrazine N atoms located in the apical positions. The structure is stabilized by N[bond]H...Cl hydrogen bonds, which involve both the Cl atoms and all the hydrogen donors, except for one of the two thioamide N atoms. A comparison of the geometry of thiosemicarbazide and S-methylisothiosemicarbazide complexes with Zn(II), Cu(II) and Ni(II) shows the pronounced influence of the hydrogen-bond network on the coordination geometry of Zn(II) compounds.

Tris(3,5-dimethyl-1H-pyrazole-1-thiocarboxamidato-kappa(2)N(2),N)cobalt(III).

In the crystal structure of the title complex, [Co(C(6)H(8)N(3)S)(3)], the Co(III) atom is octahedrally coordinated by three monodeprotonated bidentate 3,5-dimethyl-1H-pyrazole-1-thiocarboxamide ligands with two thiocarboxamide N atoms in axial positions. The asymmetric unit contains two molecules (A and B) and these molecules are arranged in chains in an alternating fashion connected by N-H...S interactions.