Comparison of density functionals for the study of the high spin low spin gap in Fe(III) spin crossover complexes. Issue 9 (25th February 2017)

• Record Type: Journal Article
• Authors: Sirirak, Jitnapa; Sertphon, Darunee; Phonsri, Wasinee; Harding, Phimphaka; Harding, David J.
• Is Part Of: International journal of quantum chemistry. Volume 117:Issue 9(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-02-25
• Subjects: basis sets -- DFT calculations -- functionals -- iron(III) complexes -- spin crossover; Quantum chemistry -- Periodicals; 541.28
• DOI: 10.1002/qua.25362
• Languages: English
• ISSNs: 0020-7608

Abstract

Abstract: A detailed investigation of the accuracy of different quantum mechanical methods for the study of iron(III) spin crossover complexes is presented. The energy spin state gap between the high and low spin states; Δ E (HS‐LS) of nine iron(III) quinolylsalicylaldiminate complexes were calculated with nine different DFT functionals, then compared. DFT functionals: B3LYP, B3LYP‐D3, B3LYP*, BH&HLYP, BP86, OLYP, OPBE, M06L, and TPSSh were tested with six basis sets: 3‐21G*, dgdzvp, 6‐31G**, cc‐pVDZ, Def2TZVP, and cc‐pVTZ. The cations from the X‐ray crystal structures of [Fe(qsal‐OMe)2 ]Cl·MeCN·H2 O, [Fe(qsal‐OMe)2 ]Cl·2MeOH·0.5H2 O, [Fe(qsal‐OMe)2 ]BF4 ·MeOH, [Fe(qsal‐OMe)2 ]NCS·CH2 Cl2, [Fe(qsal‐F)2 ]NCS, [Fe(qsal‐Cl)2 ]NCS·MeOH, [Fe(qsal‐Br)2 ]NCS·MeOH, [Fe(qsal‐I)2 ]OTf·MeOH, and [Fe(qsal)2 ]NCS⋅CH2 Cl2 were used as starting structures. The results show that B3LYP, B3LYP‐D3, OLYP, and OPBE with a 6‐31G**, Def2TZVP, and cc‐pVTZ basis set give reasonable results of Δ E (HS‐LS) compared with the experimental data. The enthalpy of [Fe(qsal‐I)2 ] + calculated with an OLYP functional and cc‐pVTZ basis set (1.48 kcal/mol) most closely matches the experimental data (1.34 kcal/mol). B3LYP* yields an enthalpy of 5.92 kcal/mol suggesting it may be unsuitable for these Fe(III) complexes, mirroring recent results by Kepp ( Inorg . Chem ., 2016, 55, 2717–2727). Abstract : Spin crossover complexes represent a challenging computational problem with spin states close in energy. Here, DFT calculations are used to explore the impact of the functional and basis set on the spin state splitting, Δ E (HS‐LS) in a series of Fe(III) compounds. The results show that a careful choice of basis set and functional are required to accurately predict Δ E (HS‐LS). B3LYP*, commonly used in Fe(II) spin crossover systems, is found to be unsuitable for these Fe(III) complexes.