The complexes: [Co(BAE)(PEt 3 )]ClO 4 . H 2 O(BAE 5 bis(acetylacetone)ethylenediimine) and [Co(BBE)(PR 3 )]ClO 4 . H 2 O, (BBE 5 bis(benzoylacetone)ethylenediimine and R 5 Et, Bu),were synthesized and characterized. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically for 1 : 1 adduct formation of [Co(chel)L]ClO 4 . H 2 O, (where chel 5 BAE, BBE and L 5 PBu 3 , PEt 3 and PMe 2 Ph) as acceptors and P(OR) 3 (R 5 Me, Et and Ipr) as donors, in acetonitrile in constant ionic strength (I 5 0.01M Et 4 NClO 4 ) and at various temperatures T 5 293 to 313 K. The trend of the equilibrium constants of five coordinate cobalt(III) Schiff base complexes toward a given phosphite donor according to the axial ligand is as follows: PMe 2 Ph > PBu 3 % PEt 3 . Also, the trend of the equilibrium constants of the donors (phosphite) toward a given cobalt(III) Schiff base complex is as follows: P(OEt) 3 > P(OIpr) 3 > P(OMe) 3 . The trend of the equilibrium constants of cobalt(III) Schiff base complexes with respect to the Schiff bases used in this research is as follows: BBE > BAE.

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A novel Wells-Dawson heteropolyacid-based magnetic Inorganic-organic nanohybrid, Fe 3 O 4 @SiO 2 @ADMPT/H 6 P 2 W 18 O 62 , was fabricated and used as a green, efficient, eco-friendly, and highly recyclable catalyst for the one-pot and multi-component synthesis of 1,4-Dihydopyridine (1,4-DHP) derivatives from the reaction of various aromatic aldehydes with ethyl acetoacetate and ammonium acetate with good to excellent yields and in a short span of time. The nanohybrid catalyst was prepared by the chemical anchoring of Wells-Dawson heteropolyacid H 6 P 2 W 18 O 62 onto the surface of functionalized Fe 3 O 4 nanoparticles with 2,4-bis(3,5dimethylpyrazol)-triazine (ADMPT) linker. These nanocatalysts were identified by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and vibrating sample magnetometer (VSM). This protocol is developed as a safe, cost-effective and convenient alternate method for the synthesis of 1,4-DHP derivatives utilizing an eco-friendly, and a highly reusable catalyst.

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