The effect of core geometry constraints of hydrogenase H-cluster analogues on reduction chemistry have been explored by a combination of structural, electrochemical and IR spectroelectrochemical (IR-SEC) studies. A series of phosphido-bridged diiron hexacarbonyl complexes, Fe 2 (µ 2 -PPh 2 (CH 2 ) x PPh 2 )(CO) 6 , x = 2 (2P) and 4 (4P) and previously reported with x = 3 (3P) and the unlinked bis-diphenylphosphido (DP) analogues were investigated. The X-ray structures of the neutral complexes demonstrate the effect of the linking group on the Fe2P2 core geometry with P-Fe-Fe-P torsion angles of 95 (2P), 101 (3P), 108 (4P) and 109° (DP) and a twisting of the Fe(CO) 3 fragments from an eclipsed geometry (2P, 3P and DP) for 4P. For all four compounds the primary reduction process involves two close-spaced one-electron reactions (E 1 and E 2 ) with a systematic trend to more negative reduction potentials with a shorter link between the bridging phosphorus atoms. This reflects the greater constraint that the bridging group places on the adoption of a planar 2Fe2P geometry. The sensitivity of the core geometry is greater for E 2 than E 1 and this impacts the stability of the monoanion with respect to disproportion (K disp (298 K) = 0.02 (2P), 2.4 (3P) and 3540 (4P and DP)). 4P has a stable dianion and gives reversible cyclic voltammetry at 298 K and is quasi-reversible at 253 K, whereas the response of 2P is irreversible at 298 K, with two distinct daughter products, but becomes quasi-reversible at 253 K. IR-SEC measurements enabled elucidation of the spectra and time evolution of the reduction products. These results are consistent with a bimolecular reaction giving a distinct reduced product modelled as a dimeric, 4Fe species. The sensitivity of the reduction chemistry of the bridged diiron compounds underpins their utility as catalytic proton reduction catalysts and the systematic trends delineated in this investigation provide the framework for charting the path of their redox-coupled chemical reactions.

One of the critical issues of using chlorophyll (Mg-Chl) as a dye photosensitizer in DSSC is related to a rapid decay of this material. Changing the alkali metal using transition metal ions could theoretically increase the stability of chlorophyll. In this research, the substitution of Mg2+ with Mnn+ ions (n = 2 and 4) in chlorophyll structure isolated from Gliricidia sepium leaves had been carried out. The column chromatography technique was chosen to separate the chlorophyll followed by modifying the metal centre using two different compounds containing manganese, namely MnCl2 and MnO2. The results show that there are differences in Rf values after substitutions, [0.90 (Mg-Chl), 0.81 (Mn2+-Chl), and 0.96 (Mn4+-Chl)]. The Soret bands experience a redshift from 330 to 338 nm for Mn2+-Chl and a blue shift from 411 to 401 nm for Mn4+-Chl while the Q band has a redshift from 665 to 668 nm for Mn2+-Chl but a blue shift from 665 to 526 nm for Mn4+-Chl. The obtained products have similar IR absorption patterns to Mg-Chl but differ only in its transmittance with slightly higher wavenumbers shifts. Shifting of UV-Visible and Infra-red characteristics indicate different molecular electronic nature of the obtained compounds. This implies successful substitution for the metal centre without damaging the structure of the chlorophyll.

The aims of this research are to determine the adsorbent properties, the effect of flow rate and ratio of adsorbent in lowering COD, turbidity, pH levels, and to determine the effect of flow rate interaction and adsorbent ratio in decreasing COD, turbidity and pH levels. This research was conducted with Completed Random Design (CRD) 23 consisting of 2 independent variables namely flow rate (0.2; 0.5; and 0,7 mL/s) and ratio of adsorbent (w/w) of clay : coral (1:1; 1:2; and 2:1) with 3 times replications. The result of the test of the adsorbent properties showed that the clay has hihger acidity and surface area then coral reef, and the coral content of coral reefs is 38.65 %. The flow rate and the ratio of adsorbent based on results of the study also reinforced by the ANOVA test give effect on the levels of COD and turbidity while the interaction of this two variables have an effect on the COD content. The best treatment based on Duncan Multiple Range Test (DMRT) was at 0.7 mL/s flow rate with a 1:1 adsorbent ratio. The multiple regression model for this study is Y =160.3 – 171.17X1 -188.83X2 + 31.67X1X2 + 146.67X12 + 66.67X22.

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