Donor Atom Set and Spin State of Iron(II). Bis(ligand)iron(II) and Bis(ligand)nickel(II) Complexes of 2,2′-Bipyridine-6-carbothioamide and 2,2′-Bipyridine-6-carboxamide

Abstract

2,2′-Bipyridine-6-carbothioamide (bpytm) and 2,2′-bipyridine-6-carboxamide (bpyam) are NNS and NNO donors, respectively, in their cationic bis(ligand)iron(II) and bis(ligand)nickel(II) complexes. The former ligand provides the stronger field and salts of [Fe(bpytm)₂]²⁺ have a singlet ground state, while those of [Fe(bpyam)₂]²⁺ have a quintet ground state. The magnetism and the electronic and Mössbauer spectra of salts of these cations have been measured. The low-temperature Mössbauer spectra of iron(II) complex salts of the carboxamide indicate, for the perchlorate and triflate salts, but not for the fluoroborate salt, a partial transition to singlet-state species. The mode of coordination of the ligands is indicated by infrared spectral data and has been confirmed by determination of the structures of [Ni(bpytm)₂] Cl₂.4H₂O, [Ni(bpyam)₂] [BF₄]₂.H₂O and [Fe(bpyam)₂] [BF₄]₂. In addition, the structures of the free ligands have been determined. Hydrogen bonding is present in the free ligands and their complexes. 2,2′-Bipyridine-6-carbothioamide: monoclinic, space group P2₁/c, a 8·265(3), b 11·175(2), c 11·114(4) Å, β 94·47(2)°, Z 4. 2,2′-Bipyridine-6-carboxamide: monoclinic, space group P2₁/c, a 13·581(2), b 9·926(1), c 16·824(3) Å, β 116·481(7)°, Z 8. [Ni(bpytm)₂] Cl₂.4H₂O: triclinic, space group P^-1, a 9·291(5), b 12·426(7), c 13·425(7) Å, α 113·54(3), β 95·63(3), γ 94·43(3)°, Z 2. [Ni(bpyam)₂][BF₄]₂.H₂O: triclinic, space group P^-1, a 10·663(5), b 10·861(6), c 12·799(6) Å, α 68·70(4), β 77·84(4), γ 78·47(4)°, Z 2. [Fe(bpyam)₂] [BF₄]₂: orthorhombic, space group P bcn, a 12¡317(6), B 12¡609(4), c 16·644(8) Å, Z 4.