RESUMO
Pyrazole (pz)-derived ligands can, besides exhibiting a strong coordination ability toward different metal ions, exhibit a great diversity in their coordination geometry and nuclearity, which can be achieved by varying the type and position of the pz substituents. The present study reports the synthesis and crystal structure of two binuclear complexes, namely bis(µ-4-nitro-1H-imidazol-1-ide-5-carboxylato)-κ3N1,O:N2;κ3N2:N1,O-bis[aqua(dimethylformamide-κO)copper(II)], [Cu2(C4HN3O4)2(C3H7NO)2(H2O)2], (II), and bis(µ-4-nitro-1H-imidazol-1-ide-5-carboxylato)-κ2N1,O:N2;κ2N2:N1,O-bis[triaquacobalt(II)] dihydrate, [Co2(C4HN3O4)2(H2O)6]·2H2O, (III). These compounds represent rare examples of metal complexes comprising 3,4-substituted pz derivatives as a bridging ligand and also the first crystal structures of transition-metal complexes with ligands derived from 4-nitropyrazole-3-carboxylic acid. Recently, the crystal structures of the same ligand in the neutral and mixed neutral/anionic forms have been reported. We present here the third form of this ligand, where it is present in a fully deprotonated anionic form within a salt, i.e. ammonium 4-nitropyrazole-3-carboxylate, NH4+·C4H2N3O4-, (I). Single-crystal X-ray diffraction revealed that in the present complexes, the CuII and CoII centres adopt distorted square-pyramidal and octahedral geometries, respectively. In both cases, the N,N',O-coordinated pz ligand shows simultaneously chelating and bridging coordination modes, leading to the formation of a nearly planar six-membered M2N4 metallocycle. In all three crystal structures, the supramolecular arrangement is controlled by strong hydrogen bonds which primarily engage the carboxylate O atoms as acceptors, while the nitro group adopts the role of an acceptor only in structures with an increased number of donors, as is the case with CoII complex (III). The electrostatic potential, as a descriptor of reactivity, was also calculated in order to examine the changes in ligand electrostatic preferences upon coordination to metal ions.
RESUMO
Macrophytes react to changes in the quality of the environment in which they live (water/sediment), and they are good bioindicators of surface water conditions. In the present study, the content of the metals cobalt (Co) and nickel (Ni) was determined in the sediment, the water, and different organs of macrophytes from six localities around Lake Skadar, across four different seasons of year. The aquatic macrophytes that have been used as bioindicator species in this study are Phragmites australis (an emerged species), Ceratophyllum demersum (a submerged species), and Lemna minor (a floating species). The aim of this study was to determine the distribution of metals in macrophyte tissues and also to discover the degree of bioaccumulation of the investigated metals, depending both on the location and on the season. The content of Co and Ni in the examined parts of the macrophytes was in the range of 0.04-8.78 and 0.30-28.5 ppm, respectively. The greatest content of the investigated metal in the organs of P. australis and C. demersum was recorded at the beginning of and during the growing season. Greater concentrations of metals in the tissue of L. minor were observed at the end of the growing season.
