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_7720009
_publ_section_title
;
 Thermal Monomerization Unlocks 3/2&#x2194;5/2 Spin Crossover in a
 Kinetically Trapped High Spin Fe(III) Dimer
;
_journal_name_full               'Dalton Transactions'
_journal_paper_doi               10.1039/D5DT02175H
_journal_year                    2026
_chemical_formula_moiety         'C38 H44 Fe2 N6 O6 Se2, C H4 O'
_chemical_formula_sum            'C39 H48 Fe2 N6 O7 Se2'
_chemical_formula_weight         982.45
_space_group_crystal_system      triclinic
_space_group_IT_number           2
_space_group_name_Hall           '-P 1'
_space_group_name_H-M_alt        'P -1'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     dual
_audit_creation_date             2025-03-28
_audit_creation_method
;
Olex2 1.5
(compiled 2023.03.06 svn.rbb2c1857 for OlexSys, GUI svn.r6748)
;
_audit_update_record
;
2025-08-18 deposited with the CCDC.	2025-12-10 downloaded from the CCDC.
;
_cell_angle_alpha                73.820(4)
_cell_angle_beta                 74.571(4)
_cell_angle_gamma                63.611(5)
_cell_formula_units_Z            2
_cell_length_a                   11.0509(6)
_cell_length_b                   11.3802(6)
_cell_length_c                   19.4658(7)
_cell_measurement_reflns_used    13984
_cell_measurement_temperature    100(10)
_cell_measurement_theta_max      28.2020
_cell_measurement_theta_min      2.7700
_cell_volume                     2077.1(2)
_computing_cell_refinement       'CrysAlisPro 1.171.39.29d (Rigaku OD, 2017)'
_computing_data_collection       'CrysAlisPro 1.171.39.29d (Rigaku OD, 2017)'
_computing_data_reduction        'CrysAlisPro 1.171.39.29d (Rigaku OD, 2017)'
_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    'SHELXT 2018/2 (Sheldrick, 2018)'
_diffrn_ambient_environment      N~2~
_diffrn_ambient_temperature      100(10)
_diffrn_detector                 'CCD plate'
_diffrn_measured_fraction_theta_full 0.998
_diffrn_measured_fraction_theta_max 0.879
_diffrn_measurement_details
;
List of Runs (angles in degrees, time in seconds):

  # Type    Start    End  Width  t~exp~   \w     \q     \k     \f   Frames
  1  \w      4.00  29.00   0.50   30.00    --    7.10  32.00 -83.00   50
  2  \w    -63.00 -37.00   0.50   30.00    --    7.10 -32.00 117.00   52
  3  \w     51.00  77.00   0.50   30.00    --   -7.50  32.00 -83.00   52
  4  \w    -45.00  22.00   0.50   30.00    --   -7.50 -32.00 117.00  134
  5  \w     50.00  96.00   0.50   30.00    --    7.10  77.00 150.00   92
  6  \w     50.00  94.00   0.50   30.00    --    7.10  77.00-150.00   88
  7  \w     50.00  96.00   0.50   30.00    --    7.10  77.00-120.00   92
  8  \w     59.00  95.00   0.50   30.00    --    7.10  77.00 -90.00   72
  9  \w    -96.00  -4.00   0.50   30.00    --   -7.50 -38.00 -60.00  184
 10  \w      5.00  30.00   0.50   30.00    --   -7.50 -38.00 -60.00   50
 11  \w    -51.00  27.00   0.50   30.00    --   -7.50 -77.00 150.00  156
 12  \w    -54.00  35.00   0.50   30.00    --   -7.50 -82.00  60.00  178
 13  \w    -60.00  31.00   0.50   30.00    --   -7.50 -82.00 -30.00  182
;
_diffrn_measurement_device       'four-circle diffractometer'
_diffrn_measurement_device_type  'XtaLAB AFC12 (RINC): Kappa single'
_diffrn_measurement_method       '\w scans'
_diffrn_orient_matrix_type
'CrysAlisPro convention (1999,Acta A55,543-557)'
_diffrn_orient_matrix_UB_11      -0.0185829000
_diffrn_orient_matrix_UB_12      -0.0552302000
_diffrn_orient_matrix_UB_13      0.0150323000
_diffrn_orient_matrix_UB_21      0.0686258000
_diffrn_orient_matrix_UB_22      -0.0416430000
_diffrn_orient_matrix_UB_23      0.0049718000
_diffrn_orient_matrix_UB_31      -0.0149390000
_diffrn_orient_matrix_UB_32      0.0151517000
_diffrn_orient_matrix_UB_33      0.0350608000
_diffrn_radiation_monochromator  graphite
_diffrn_radiation_probe          x-ray
_diffrn_radiation_type           'Mo K\a'
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0397
_diffrn_reflns_av_unetI/netI     0.0420
_diffrn_reflns_Laue_measured_fraction_full 0.998
_diffrn_reflns_Laue_measured_fraction_max 0.879
_diffrn_reflns_limit_h_max       14
_diffrn_reflns_limit_h_min       -14
_diffrn_reflns_limit_k_max       14
_diffrn_reflns_limit_k_min       -15
_diffrn_reflns_limit_l_max       20
_diffrn_reflns_limit_l_min       -25
_diffrn_reflns_number            40336
_diffrn_reflns_point_group_measured_fraction_full 0.998
_diffrn_reflns_point_group_measured_fraction_max 0.879
_diffrn_reflns_theta_full        25.242
_diffrn_reflns_theta_max         28.908
_diffrn_reflns_theta_min         2.604
_diffrn_source                   'fine-focus sealed X-ray tube'
_diffrn_source_type              'Enhance (Mo) X-ray Source'
_exptl_absorpt_coefficient_mu    2.5
_exptl_absorpt_correction_T_max  1.00000
_exptl_absorpt_correction_T_min  0.45932
_exptl_absorpt_correction_type   multi-scan
_exptl_absorpt_process_details
;
CrysAlisPro 1.171.39.29d (Rigaku Oxford Diffraction, 2017)
Empirical absorption correction using spherical harmonics,
 implemented in SCALE3 ABSPACK scaling algorithm.
;
_exptl_crystal_colour            Black
_exptl_crystal_density_diffrn    1.57
_exptl_crystal_description       Plate
_exptl_crystal_F_000             1000
_exptl_crystal_size_max          0.35
_exptl_crystal_size_mid          0.3
_exptl_crystal_size_min          0.27
_refine_diff_density_max         0.974
_refine_diff_density_min         -0.440
_refine_diff_density_rms         0.075
_refine_ls_extinction_method     none
_refine_ls_goodness_of_fit_ref   0.969
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     511
_refine_ls_number_reflns         9608
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      0.969
_refine_ls_R_factor_all          0.0721
_refine_ls_R_factor_gt           0.0459
_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^)+(0.1000P)^2^] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.1279
_refine_ls_wR_factor_ref         0.1415
_reflns_Friedel_coverage         0.000
_reflns_number_gt                7067
_reflns_number_total             9608
_reflns_threshold_expression     'I > 2\s(I)'
_cod_data_source_file            d5dt02175h2.cif
_cod_data_source_block           Complex_2
_cod_database_code               7720009
_shelx_shelxl_version_number     2018/3
_chemical_oxdiff_formula         'C H N O Fe Se'
_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, All O(H) groups
2.a Ternary CH refined with riding coordinates:
 N5(H5), N2(H2)
2.b Secondary CH2 refined with riding coordinates:
 C9(H9A,H9B), C27(H27A,H27B), C8(H8A,H8B), C28(H28A,H28B), C29(H29A,H29B),
 C10(H10A,H10B)
2.c Aromatic/amide H refined with riding coordinates:
 C26(H26), C7(H7), C5(H5A), C3(H3), C4(H4), C24(H24), C22(H22), C12(H12),
 C16(H16), C35(H35), C23(H23), C14(H14), C31(H31), C13(H13), C32(H32), C15(H15),
  C33(H33), C34(H34)
2.d Idealised Me refined as rotating group:
 C38(H38A,H38B,H38C), C19(H19A,H19B,H19C), C36(H36A,H36B,H36C), C17(H17A,H17B,
 H17C), C39(H39A,H39B,H39C)
2.e Idealised tetrahedral OH refined as rotating group:
 O7(H7A)
;
_shelx_res_checksum              865
_olex2_submission_special_instructions 'No special instructions were received'
_oxdiff_exptl_absorpt_empirical_details
;
Empirical correction (ABSPACK) includes:
- Absorption correction using spherical harmonics
- Frame scaling
;
_oxdiff_exptl_absorpt_empirical_full_max 1.609
_oxdiff_exptl_absorpt_empirical_full_min 0.616