Thermal Monomerization Unlocks 3/2↔5/2 Spin Crossover in a Kinetically Trapped High Spin Fe(III) Dimer
Dey, Bijoy; Titis, Jan; Mehta, Sakshi; Mondal, Abhishake; Chandrasekhar, Vadapalli; Dalton Transactions  (2026) –; doi:10.1039/D5DT02175H

data_7720008
_publ_section_title
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 Thermal Monomerization Unlocks 3/2&#x2194;5/2 Spin Crossover in a
 Kinetically Trapped High Spin Fe(III) Dimer
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_journal_name_full               'Dalton Transactions'
_journal_paper_doi               10.1039/D5DT02175H
_journal_year                    2026
_chemical_formula_moiety         'C34 H38 Fe N4 O4, C N Se'
_chemical_formula_sum            'C35 H38 Fe N5 O4 Se'
_chemical_formula_weight         727.51
_space_group_crystal_system      monoclinic
_space_group_IT_number           14
_space_group_name_Hall           '-P 2ybc'
_space_group_name_H-M_alt        'P 1 21/c 1'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     iterative
_audit_creation_date             2025-10-16
_audit_creation_method
;
Olex2 1.5
(compiled 2023.03.06 svn.rbb2c1857 for OlexSys, GUI svn.r6748)
;
_audit_update_record
;
2025-10-17 deposited with the CCDC.	2025-12-10 downloaded from the CCDC.
;
_cell_angle_alpha                90
_cell_angle_beta                 90.486(4)
_cell_angle_gamma                90
_cell_formula_units_Z            4
_cell_length_a                   10.5373(11)
_cell_length_b                   10.8063(11)
_cell_length_c                   29.723(3)
_cell_measurement_reflns_used    9641
_cell_measurement_temperature    100(2)
_cell_measurement_theta_max      27.46
_cell_measurement_theta_min      2.33
_cell_volume                     3384.4(6)
_computing_cell_refinement       'SAINT V8.40B (?, 2016)'
_computing_data_reduction        'SAINT V8.40B (?, 2016)'
_computing_molecular_graphics    'Olex2 1.5 (Dolomanov et al., 2009)'
_computing_publication_material  'Olex2 1.5 (Dolomanov et al., 2009)'
_computing_structure_refinement  'SHELXL 2018/3 (Sheldrick, 2015)'
_computing_structure_solution    'olex2.solve 1.5 (Bourhis et al., 2015)'
_diffrn_ambient_temperature      100.0
_diffrn_measured_fraction_theta_full 0.980
_diffrn_measured_fraction_theta_max 0.977
_diffrn_measurement_device_type  'Bruker APEX-II CCD'
_diffrn_measurement_method       '\f and \w scans'
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0900
_diffrn_reflns_av_unetI/netI     0.0340
_diffrn_reflns_Laue_measured_fraction_full 0.980
_diffrn_reflns_Laue_measured_fraction_max 0.977
_diffrn_reflns_limit_h_max       13
_diffrn_reflns_limit_h_min       -13
_diffrn_reflns_limit_k_max       14
_diffrn_reflns_limit_k_min       -14
_diffrn_reflns_limit_l_max       38
_diffrn_reflns_limit_l_min       -38
_diffrn_reflns_number            114578
_diffrn_reflns_point_group_measured_fraction_full 0.980
_diffrn_reflns_point_group_measured_fraction_max 0.977
_diffrn_reflns_theta_full        25.242
_diffrn_reflns_theta_max         27.552
_diffrn_reflns_theta_min         1.933
_diffrn_standards_number         0
_exptl_absorpt_coefficient_mu    1.56
_exptl_absorpt_correction_T_max  0.7455
_exptl_absorpt_correction_T_min  0.4337
_exptl_absorpt_correction_type   multi-scan
_exptl_absorpt_process_details
;
SADABS-2016/2 (Bruker,2016/2) was used for absorption correction.
wR2(int) was 0.1545 before and 0.0891 after correction.
The Ratio of minimum to maximum transmission is 0.5818.
The \l/2 correction factor is Not present.
;
_exptl_crystal_colour            Black
_exptl_crystal_density_diffrn    1.43
_exptl_crystal_description       Block
_exptl_crystal_F_000             1500
_exptl_crystal_size_max          0.45
_exptl_crystal_size_mid          0.40
_exptl_crystal_size_min          0.35
_refine_diff_density_max         0.609
_refine_diff_density_min         -0.402
_refine_diff_density_rms         0.066
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   1.138
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     426
_refine_ls_number_reflns         7644
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.138
_refine_ls_R_factor_all          0.0927
_refine_ls_R_factor_gt           0.0750
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'w=1/[\s^2^(Fo^2^)+(0.0500P)^2^+5.4319P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.1524
_refine_ls_wR_factor_ref         0.1598
_reflns_Friedel_coverage         0.000
_reflns_number_gt                6147
_reflns_number_total             7644
_reflns_threshold_expression     'I > 2\s(I)'
_cod_data_source_file            d5dt02175h2.cif
_cod_data_source_block           Complex_1
_cod_database_code               7720008
_shelx_shelxl_version_number     2018/3
_olex2_refinement_description
;
1. Fixed Uiso
 At 1.2 times of:
  All C(H) groups, All C(H,H) groups, All N(H) groups
 At 1.5 times of:
  All C(H,H,H) groups
2. Others
 Fixed Sof: Se1(0.5) Se2(0.5)
3.a Ternary CH refined with riding coordinates:
 N2(H2), N4(H4)
3.b Secondary CH2 refined with riding coordinates:
 C27(H27A,H27B), C25(H25A,H25B), C9(H9A,H9B), C8(H8A,H8B), C10(H10A,H10B),
 C26(H26A,H26B)
3.c Aromatic/amide H refined with riding coordinates:
 C24(H24), C7(H7), C29(H29), C22(H22), C12(H12), C33(H33), C20(H20), C32(H32),
 C30(H30), C21(H21), C16(H16), C31(H31), C3(H3), C14(H14), C13(H13), C5(H5),
 C4(H4A), C15(H15)
3.d Idealised Me refined as rotating group:
 C34(H34A,H34B,H34C), C17(H17A,H17B,H17C)
;
_shelx_res_checksum              46434
_olex2_submission_special_instructions 'No special instructions were received'