Photophysical and Electrochemical Studies of Multinuclear Complexes of Iron(II) with Acetate and Extended Conjugated N‐Donor Ligands

Abstract

A dimeric iron(II) complex, trans-[Fe2(CH3COO)4(L1)2] (1), and a trinuclear iron(II) complex, [Fe3(CH3COO)4(H2O)4(L2)] (2), were studied as potential dye-sensitised solar cell materials. The structures of both complexes were deduced by a combination of instrumental analyses and molecular modelling. Variable-temperature magnetic susceptibility data suggested that 1 was made up of 56.8% high-spin (HS) and 43.2% low-spin (LS) Fe(II) atoms at 294 K and has a moderate antiferromagnetic interaction (J = −81.2 cm−1) between the two Fe(II) centres, while 2 was made up of 27.7% HS and 72.3% LS Fe(II) atoms at 300 K. The optical band gaps (E o) for 1 were 1.9 eV (from absorption spectrum) and 2.2 eV (from fluorescence spectrum), electrochemical bandgap (E e) was 0.83 eV, excited state lifetime (τ) was 0.67 ns, and formal redox potential (E′(FeIII/FeII)) was +0.63 V. The corresponding values for 2 were 3.5 eV (from absorption spectrum), 1.8 eV (from fluorescence spectrum), 0.69 eV, 2.8 ns, and +0.41 V.

Magnetic, thermal, mesomorphic and thermoelectric properties of mononuclear, dimeric and polymeric iron(ii) complexes with conjugated ligands

“…1). The structure of 1 was reported previously, 26 while those of 2 and 3 were in accord with combined instrumental data (Table 1). The elemental analyses for C, H, and N (Experimental) for 2 and 3 were in good agreement with their chemical formulas.…”

“…General Ligand L1 and complex 1 were synthesized and characterised as previously reported. 26 Other chemicals were commercially available and used as received.…”

“…The E o value was 1.9 eV, which was the same as 1. 26 The c M T value was 1.0 cm 3 K mol À1 , indicating 33% HS and 67% LS Fe(II) atoms at 25 C (since the expected value for a mononuclear HS Fe(II) complex is 3.01 cm 3 K mol À1 , 1 while a LS Fe(II) complex is diamagnetic). The higher percentage of LS Fe(II) atom in 2 compared to 1 (Table 1) is consistent with a stronger ligand eld (shorter Fe-N bonds) in the former complex (FeN 6 chromophore) compared to the latter (FeN 2 O 4 chromophore).…”

“…The ligand L1 was a N 2 -donor with extended conjugated bonds and appended with four linear 14-carbon alkyloxy chains at the aromatic rings. It reacted with [Fe(CH 3 COO) 2 ] (mole ratio ¼ 1 : 1) to form a dimeric neutral complex, [Fe 2 (CH 3 COO) 4 (L1) 2 ] (1), 26 and with Fe(BF 4 ) 2 $6H 2 O (mole ratio ¼ 3 : 1) to form a mononuclear ionic complex, [Fe(L1) 3 ](BF 4 ) 2 $4H 2 O (2). On the other hand, the ligand L2 was a conjugated polymeric amide with N,S-donors.…”

“…This paper is an extension of our study on [Fe 2 (CH 3 COO) 4 (L1) 2 ] (1), where L1 was a p-conjugated N 2 -donor ligand. 26 It reports the syntheses, structural deduction and magnetic properties of [Fe(L1) 3 ](BF 4 ) 2 $4H 2 O (2) and {[Fe 2 (CH 3 COO) 4 (L2)]$2H 2 O} n (3), where L2 was a conjugated N,S-donor ligand. This is followed by thermal, mesomorphic and thermoelectric properties of 1-3.…”