Prasenjit Bag

Synthesis, structure, and two-photon absorption studies of a phosphorus-based tris hydrazone ligand (S)P[N(Me)N=CH-C6H3-2-OH-4-N(CH2CH3)2]3 and its metal complexes.

A phosphorus-supported multidentate ligand (S)P[N(Me)N=CH-C(6)H(3)-2-OH-4-N(CH (2)CH(3))(2)](3) (1) has been used to prepare mononuclear complexes LM [M = Fe (2) Co (3)] and trinuclear complexes L(2)M(3) [M = Mn (4), Ni (5), Zn (6), Mg (7), Cd (8)]. In both 2 and 3 the ligand binds the metal ion in a facial coordination mode utilizing three imino nitrogen (3N) and three phenolic oxygen (3O) atoms. The molecular structures of L(2)Mn(3), L(2)Ni(3), L(2)Zn(3), L(2)Mg(3), and L(2)Cd(3) (4-8) are similar; two trihydrazone ligands are involved in coordination to hold the three metal ions in a linear fashion. Each of the trishydrazone ligands behaves as a trianionic hexadentate ligand providing three imino and three phenolic oxygen atoms for coordination to the metal ions. The coordination environment around the two terminal metal ions is similar (3N, 3O) while the central metal ion has a 6O coordination environment. Third-order non-linear optical properties of these compounds as measured by their two-photon absorption (TPA) cross section reveals that while 1 does not possess obvious TPA activity, complexes 2 (3213 GM) and 4 (3516 GM) possess a large TPA cross section at 770 nm.

Molecular iron(III) phosphonates: synthesis, structure, magnetism, and Mössbauer studies.

The reaction of Fe(ClO4)2·6H2O with t-BuPO3H2 or Cl3CPO3H2 in the presence of an ancillary pyrazole phenolate as a coligand, H2phpzH [H2phpzH = 3(5)-(2-hydroxyphenyl)pyrazole], afforded tetra- and pentanuclear Fe(III) phosphonate complexes [Fe4(t-BuPO3)4(HphpzH)4]·5CH3CN·5CH2Cl2 (1) and [HNEt3]2[Fe5(μ3-O)(μ-OH)2 (Cl3CPO3)3(HphpzH)5(μ-phpzH]·3CH3CN·2H2O (2). Single-crystal X-ray structural analysis reveals that 1 possesses a cubic double-4-ring (D4R) core similar to what is found in zeolites. The molecular structure of 2 reveals it to be pentanuclear. It crystallizes in the chiral P1 space group. Magnetic studies on 1 and 2 have also been carried out, which reveal that the bridging phosphonate ligands mediate weak antiferromagnetic interactions between the Fe(III) ions. Magnetization dynamics of 1 and 2 have been corroborated by a Mössbauer spectroscopy analysis.

Windmill-shaped octanuclear ZnII4/LnIII4 (LnIII = Dy, Tb, Ho) heterometallic ensembles supported by a tetraferrocene scaffold

Utilizing a new ferrocene-based compartmental ligand, H4L (1), a series of novel heterometallic complexes [{LZn(μ-OAc)Dy}4(μ4-H2O)] (2), [{LZn(μ-OAc)Tb}4(μ4-H2O)] (3), [{LZn(μ-OAc)Ho}4(μ4-H2O)] (4), [L = Fe[(C5H4){-C(Me)[double bond, length as m-dash]N-N[double bond, length as m-dash]C6H3-(o-O)(m-O)}]2] were synthesized and characterized. 2 and 3 crystallize in the monoclinic crystal system in the I2/m space group, whereas 4 crystallizes in the tetragonal crystal system in the I4/m space group. The tetra deprotonated ligand L4- has two distinct coordination compartments: one pocket (2N, 2O) suitable for the transition metal (3d) ions and another pocket (4O) suitable for lanthanide (4f) metal ions. Additionally, the terminal phenoxo group can be utilized for cluster expansion. In all the complexes, the ZnII ion is in a perfect square pyramidal (2N, 3O) geometry whereas the lanthanide ion has a coordination number of eight (8O) in a distorted biaugmented trigonal-prism geometry. The electrochemical properties of 2 and 3 along with ligand H4L (1) were studied by cyclic voltammetry (CV). All the complexes display a similar type of electrochemical behavior viz., one quasi-reversible oxidation typical of a ferrocene/ferrocenium motif. The magnetic properties of all the complexes have also been investigated.