Marijana Đaković

Coordination-driven self-assembly of thiocyanate complexes of Co(II), Ni(II) and Cu(II) with picolinamide: a structural and DFT study

The new heteroleptic complexes, [M(NCS)2(pia)2] M = Co(II) (1), Ni(II) (2), and [Cu(SCN)2(pia)2] (3), pia = pyridine-2-carboxamide, were synthesized and characterized. Their single crystal X-ray diffraction structures showed octahedral units, with the two thiocyanate ligands occupying cis-positions and binding through the nitrogen atom in Co(II) and Ni(II). In the Cu(II) complex, they were trans and S-bound. The crystal structures display a 2-d structure with NH⋯S hydrogen bonds for the Co(II) and Ni(II), forming tetrameric units, and are isomorphous with the Zn(II) complex, [Zn(NCS)2(pia)2], and a 2-d structure with NH⋯N for the Cu(II). DFT calculations were performed on the new complexes and the analogous polymorphs of [Zn(NCS)2(pia)2], including a second one containing dimeric motifs. The calculated vibrational modes of the thiocyanate ligands corroborate the experimental ones and reflect the coordination mode of the ligand. A comparison between the two Zn(II) polymorphs showed that the NH⋯S bond in the tetramer is stronger (−7.50 kcal mol−1 per metal) than the NH⋯O bond in the dimer (−4.01 kcal mol−1 per metal), indicating a preference for the formation of tetrameric units. The NH⋯N hydrogen bonds calculated in the Cu(II) crystal are stronger (−9.15 kcal mol−1 per metal) than the NH⋯S ones in Ni(II) and Zn(II).

Structural study of picolinamide complexes of Ni(II), Zn(II), Cd(II), and Hg(II) nitrates in solid state and solution

Three picolinamide complexes of nickel(II) (1), zinc(II) (2), and cadmium(II) (3) have been prepared and their solid state structures were determined by single-crystal X-ray diffraction analysis. Their structures in DMSO solutions as well as the structure of similar mercury(II) complex, [Hg(NO3)(pia)2](NO3) (4), have been elucidated by 1H and 13C NMR spectra. The picolinamide is bound through the N,O-donors in all four complexes in solid state, but only in 4 it is in solution state. In nickel (1), zinc (2), and cadmium (3) complexes the pia-N coordination in solution is suggested. The X-ray analysis revealed that isomorphous nickel (1) and zinc (2) crystal structures comprise the centrosymmetrical trans-[M(H2O)2(pia)2]2+ (M = Ni, Zn; pia = picolinamide) and nitrate. The crystal lattices also contain two non-coordinated H2O molecules. In 3, each cadmium(II) is N,O-chelated by two cis-oriented pia ligands, while remaining coordination sites of the capped pentagonal bipyramid are occupied by three oxygen atoms from two nitrates. Crystal structures are dominated by O/N/C–H···O hydrogen bonds. The carboxamide moieties in 1 and 2 do not form any head-to-head or catemeric supramolecular synthons, but participate in the formation of (12) motifs with solely the amide nitrogen atoms as double hydrogen bond donors. In 3, neighboring molecules are linked into head-to-head amide dimers. The biological effect of picolinamide and [Zn(pia)2(H2O)2](NO3)2 on ingestion and intracellular microbicidal capacities of human peripheral blood phagocytes was also assessed.

Can self-assembly of copper(II) picolinamide building blocks be controlled?

Four copper(II) derivatives with picolinamide (piaH), [Cu(N3)2(piaH)2] (1), [Cu(NCO)2(piaH)2] (2), [Cu(pia)2]·2H2O (3) and [Cu(pia)(piaH)(ClO4)]2 (4) are reported. 1 and 2 were isolated as powders shortly after precipitation, becoming crystalline (3) after prolonged standing in mother liquor. The single crystal X-ray analysis revealed the deprotonation of the amide nitrogen (pia) in both 3 (mononuclear square planar [Cu(pia-N,N)2] building blocks) and 4 (pia acting as a bridge between copper(II) ions within the dimer). MAGSUS χMT versus T curves suggest only weak magnetic interactions between the copper(II) species in 3 and 4, though 4 is dinuclear. The magnetic coupling was reproduced by DFT calculations on the experimentally determined structures. The mechanism of formation of compounds 3 and 4 was analyzed by DFT calculations. Models of 1 and 2 underwent transfer of two hydrogen atoms from the piaH ligands to the two axial ligands N3− or NCO− that were released yielding 3. In the reaction leading to 4, the perchlorate is a very weak base that cannot deprotonate the piaH ligand and after the first hydrogen transfer to acetate the dimer 4 is formed. This reactivity, favoring alternative pathways, may switch off an expected self-assembly process.

Impact of amide–amide hydrogen bonding on the stability of two nicotinamide complexes of silver(I)

The nicotinamide (pyridine-3-carboxamide, nia) complexes of silver(I), [Ag(nia)2(NO3)]·H2O (1), [Ag(nia)2(NO3)] (2), and {K[Ag(nia)2](NO3)2}n (3), were prepared and characterised by IR spectroscopy and TG/DTA thermal methods. The solid state structures of 2 and 3 were determined by single-crystal X-ray diffraction analysis. In both complexes two nicotinamide ligands are coordinated to silver(I) through the nitrogen atom of the pyridine ring in a near-linear fashion. In 2, additional coordination by two oxygen atoms of one nitrate group leads to the distorted tetrahedral coordination environment of silver(I). In 3, nitrate ions bridge potassium cations giving rise to a 2D coordination network which is further stabilised by cross-bridging of each two potassium atoms in [1 0 0] direction by complex cations, [Ag(nia)2]+. Despite different aggregation of 2 and 3 in the solid state, both complexes demonstrate quite similar thermal stability. The amide self-complementary hydrogen bonds appear to be the main driving force for establishing the crystal structures of both 2 and 3.

Building inorganic supramolecular architectures using principles adopted from the organic solid state

The possibility of converting crystal engineering principles that originate in the organic solid state into productive strategies for the effective supramolecular assembly of coordination complexes has been established through a range of complementary techniques. Calculated molecular electrostatic potentials, in conjunction with a systematic structural study, demonstrate that the existence and structural importance of the key hydrogen-bond interactions are not disrupted by the presence of metal cations and charge-balancing anions.

Competition between hydrogen bonds and halogen bonds: a structural study

The competition and balance between intermolecular hydrogen bonds (HBs) and halogen bonds (XBs) were explored by co-crystallizing tetra-functionalized (2 × HB (–OH) and 2 × XB (–CC–I)) molecules, trans-1,4-bis(iodoethynyl)cyclohexane-1,4-diol (D1) and cis-1,4-bis(iodoethynyl)cyclohexane-1,4-diol (D2), with six ditopic nitrogen based acceptor molecules. The crystal structures of both D1 and D2 showed non-covalent interactions between HB/XB donors and available acceptor sites (oxygen/triple bond/negative region of iodine). In three co-crystals of D1 the HB and XB donors act in similar ways as both activated iodine and hydroxyl hydrogen bind to the nitrogen acceptors in the solid state. In contrast, in a co-crystal of D2, a geometric isomer of D1, there were only hydrogen bonds to the co-former and the halogen-bond donor interacted with the hydroxyl oxygen atoms of D2. A stronger tendency for linear XB interactions (as well as greater van der Waals radii reduction) was observed with nitrogen atoms as acceptors (average reduction = 21%) compared to those involving an oxygen atom as an acceptor (average reduction = 16%). A control molecule, trans-1,4-diethynylcyclohexane-1,4-diol (D3), which has only HB donors (–OH and –CC–H) was also examined to get a better understanding of the balance between XB and HB intercations. The ethynyl hydrogen atom did not form hydrogen bonds to the nitrogen atoms in acceptors, and only O–H⋯N and –CC–H⋯O hydrogen bonds were observed in these structures.

Testing the limits of halogen bonding in coordination chemistry

In order to link coordination complexes via halogen bonds and to test the limit of halogen-bond interactions in metal-containing crystalline solids, a series of thirteen new acac complexes of CoII and NiII with small halogen-bearing aromatic ligands, namely 3-halopyridines, 2-halopirazines and 5-halopyrimidine were prepared. Ligands having a single aromatic ring were used to limit the influence of π–π stacking on the resulting crystal structure, while fine-tuning of the electron density at the halogen atom σ-hole was achieved via two routes: (i) by changing the position of the additional nitrogen heteroatom on the aromatic ring, and (ii) by utilizing different transition metal ions. The moderate ‘activation’ of the halogen atom produced the desired halogen interaction in a limited number of supramolecular events. Two supramolecular links, C–X⋯O and C–H⋯O, were shown to have a larger influence on the overall supramolecular assembly, and their role could be explained on the basis of calculated molecular electrostatic potential values. Slight electronic changes introduced by metal–cation exchange revealed an additional handle for achieving a switch between different supramolecular interactions and architectures.

6-Iodo-2-methyl-1,3-benzothia-zole.

The title compound, C8H6INS, is essentially planar, the largest deviation from the mean plane being for the I atom [0.075 (3) Å]. The crystal structure is mainly stabilized by intermolecular C—I⋯N halogen bonds, forming zigzag supramolecular chains in [10]. Relatively short off-set π–π contacts [centroid–centroid distance = 3.758 (2) Å] between the thiazole rings of inversion-related molecules link neighbouring chains and provide the secondary interactions for building the crystal structure.

Croatian Meeting of Chemists and Chemical Engineers

• Prof Wayne Carter, Nottingham University, UK • Prof. Dr. Gerrit Schüürmann, Head HCER,UFZ, Germany • Dr. D. Ramaiah, Director, CSIR-NEIST, Jorhat, Assam • Dr. Rao V. Jayathirtha, IICT,Hyderabad • Dr. Mohan S. Venkat, IICT, Hyderabad • Prof. S. Gourinath, JNU, New Delhi • Dr. Madava Sharma, IICT, Hyderbad, • Dr. M. Chandraseharan, IICT, Hyderabad • Prof. P. K. Joshi, JNU, New Delhi • Prof. D. E. Babu, Andhra University, Visakhapatnam • Prof. G. R. Naidu, SVU, Tirupathi • Prof. Vibha Tandon, JNU, NEW Delhi • Prof. A. L. Ramanathan, JNU, New Delhi • Prof. P. Rajendra Prasad, Andhra University, Visakhapatnam • Dr. G. Parthasarathi, NGRI, Hyderabad • Dr. I. Gurappa, DMRL, Hyderabad • Prof. K. Sreeramulu, Gulberga University, Gulberga • Dr. Surender Singh, Scientist, IARI, New Delhi • Dr. Suresth Yadav, Scientist, ICMR, Ahmedabad • Prof. M. Pandurangappa, Bangalore University, Bengaluru • Prof. Rajendra, Former VC, SVU, Tirupathi • Prof. S. V. Krishna Murthy, Kuvepu University • Dr. T. N. V. Rao, CEO, Aquamark, Bengaluru • Dr. K. N. Rao Aurigene, Reddy Laborataries, Bengaluru

A new tecton with parallel halogen-bond donors : a path to supramolecular rectangles

A new tecton, 1,8-diiodoethynylanthracene, with two halogen-bond donor sites was synthesized and characterized. This tecton is capable of forming two parallel halogen bonds at once, which makes it a useful building block for the construction of a variety of supramolecular squares and rectangles.