2-(2′-Pyridyl)benzimidazole (pybzim = LH) coordinates to iron(II) as a bidentate and forms the tris-ligated complex, [Fe(pybzim)₃]²⁺ as isolated in the solid. Titration of [Fe(pybzim)₃]²⁺ with base demonstrates the successive deprotonation of the imino hydrogens of the coordinated ligands. Protonation constants for the free ligand, pybzim (Iog₁₀ K ^H = 11.33) and the complex, [Fe(pybzim)₃]²⁺ (log₁₀ K ^H ₁ = 9.58, log₁₀ K ^H ₂ = 8.13 and log₁₀ K ^H ₃ = 6.97) were measured in 30% (v/v) H₂O/EtOH. Results show that coordination to iron(II) increases the acidity of the imino hydrogen of the ligand. Spin-crossover behaviour of the complex were studied in different solvents ME, AC, AN, NM, NB, DMF, DMSO and ANL. The complex shows strong spin-crossover behaviour which is solvent dependent. Values of the spin-equilibrium constant (K _sc) and the associated thermodynamic parameters (ΔH _sc = 18.1–21.3 kJ mol⁻¹ and δS _sc = 69.6–84.4JK⁻¹ mol⁻¹) were calculated. An increase of the enthalpy is observed with increasing donor number (DN) of the solvent.

The Dhaleswari river is considered as one of the most important rivers of Bangladesh due to its geographical location and ecological services. The present study attempts to evaluate the degree of heavy metal pollution, contamination, and accumulative behavior in the sediment of the Dhaleswari river. The sediment samples were collected from fifteen different locations of the Dhaleswari river. Heavy metals were analyzed using the Flame Atomic Spectrophotometer (FAAS). The mean concentrations of Zn, Cu, Cr, Pb and Cd were 131.9, 48.89, 43.16, 33.23 and 0.37 mgkg^-1, respectively. According to the United States Environmental Protection Agency (USEPA) Sediment Quality Guideline, the sediment of most of the locations were not polluted for Pb and Cd. But S-11 location for Cd (0.8 mg kg^-1) was highly polluted. For Cr, Cu and Zn, maximum locations were moderately polluted. Although the geo-accumulation index (Igeo) values of Dhaleswari river sediments showed almost no severe contamination for most of the sampling locations, the pollution load index (PLI) values showed that most of the sampling sites were contaminated for all heavy metals tested. Moreover, for all measured heavy metals, the mean Contamination Factor (CF) values indicated moderate pollution, except for Cr, which suggested low pollution. The Pearson’s correlation coefficient matrix among the selected heavy metals of Dhaleswari river sediment showed no significant correlation among each other. Therefore, regular monitoring of the heavy metal concentration of the Dhaleshwari river sediment from different location is necessary to identify the sources of pollution so that proper initiative could be taken to prevent heavy metal pollution.

This study reports the effects of weeding on physical and chemical properties of soil from two different hill sites with rigorous plantation. Soil samples were collected from top, middle and bottom hill positions, having plot size of 0.5m × 0.5m. This study analyzed for five soil physical variables including moisture content, maximum water holding capacity, field capacity, bulk density and particle density; and seven soil chemical variables including organic matter, organic carbon, total nitrogen, pH, Carbon nitrogen ration, available potassium and available calcium. Top hill position captures significantly lower Organic matter, Organic carbon, pH, available Ca and K having with lower soil physical variables of Moisture content, Field capacity and Maximum water holding capacity in both sites irrespective of presence and absence of weed. In this study, we found that all studied soil physical and chemical variables were higher in the presence of weed in both sites except bulk density and particle density. This study concluded that weeding practice in artificial hill forest showed adverse impact on soil physical and chemical properties. Moreover, undisturbed ground vegetation will provide continuous organic matter flow after decomposition and helps to improve the soil properties. For plantation in hilly areas it is more crucial as the hill top found significantly lower physico-chemical soil properties.