Editing Exploring the Full Potential of Photocatalytic Carbon Dioxide Reduction Using a Dinuclear Re2Cl2 Complex Assisted by Various Photosensitizers

{{BaseTemplate}}
[[Category:Photocatalytic CO2 conversion to CO]]
{{DOI|doi=10.1002/cptc.202100034}}{{FaultyMolecule}}

===Abstract===

==== Summary ====
A photochemical reduction of CO<sub>2</sub> to CO was shown using the dirhenium complex {{#moleculelink:|link=RNNNRBGABJVOGO-UHFFFAOYSA-L|image=false|width=300|height=200}} in combination with the ruthenium and copper photosensitizers {{#moleculelink:|link=GJHHESUUYZNNGV-UHFFFAOYSA-N|image=false|width=300|height=200}} and {{#moleculelink:|link=RLYPDFWLVSLBDF-UHFFFAOYSA-N|image=false|width=300|height=200}}. Turnover numbers (TONs) of up to 270 were reached after 4 h of irradiation (λ > 400 nm) in DMF.

==== Advances and special progress ====
One of very few studies where a dinuclear catalytic system able to activate CO<sub>2</sub> is used in combination with photosensitizers.

==== Additional remarks ====
The experiments were preformed using the rhenium complex (50 μM in DMF) as the catalyst in combination with different loadings of the sensitizers and sacrificial electron donors under 4 h of irradiation with λ > 400 nm.

===Content of the published article in detail===
The article contains results of a detailed study on the influence of additional photosensitizers on the catalytic performance of the dinuclear rhenium catalyst {{#moleculelink:|link=RNNNRBGABJVOGO-UHFFFAOYSA-L|image=false|width=300|height=200}} for the reduction of CO<sub>2</sub> to CO. The catalytic system performs best (referring to the TON of CO production) for the combination of the above mentioned catalyst with the iridium complex {{#moleculelink:|link=GJHHESUUYZNNGV-UHFFFAOYSA-N|image=false|width=300|height=200}} as the photosensitizer in the presence of BIH/TEA as sacrificial electron donors.

==== Catalyst ====
<chemform smiles="C(C)(C)1C2C=C(C(C)(C)C)C=C(C3C=N4[Re+]([C-]#[O+])([C-]#[O+])([Cl-])([C-]#[O+])N5=CC=CC=C5C4=CC=3)C=2OC2C(C3C=CC4C5C=CC=CN=5[Re+]([C-]#[O+])([C-]#[O+])([C-]#[O+])([Cl-])N=4C=3)=CC(C(C)(C)C)=CC1=2" inchi="1S/C43H42N4O.6CO.2ClH.2Re/c1-41(2,3)29-21-31(27-15-17-37(46-25-27)35-13-9-11-19-44-35)39-33(23-29)43(7,8)34-24-30(42(4,5)6)22-32(40(34)48-39)28-16-18-38(47-26-28)36-14-10-12-20-45-36;6*1-2;;;;/h9-26H,1-8H3;;;;;;;2*1H;;/q;;;;;;;;;2*+1/p-2" inchikey="RNNNRBGABJVOGO-UHFFFAOYSA-L" height="200px" width="300px" float="none">
  -INDIGO-01112411252D

  0  0  0  0  0  0  0  0  0  0  0 V3000
M  V30 BEGIN CTAB
M  V30 COUNTS 64 72 0 0 0
M  V30 BEGIN ATOM
M  V30 1 C 2.55001 -5.94999 0.0 0
M  V30 2 C 3.05001 -6.81603 0.0 0
M  V30 3 C 4.05001 -6.81604 0.0 0
M  V30 4 O 4.54999 -5.95001 0.0 0
M  V30 5 C 4.04999 -5.08397 0.0 0
M  V30 6 C 3.04999 -5.08396 0.0 0
M  V30 7 C 2.5521 -4.22028 0.0 0
M  V30 8 C 3.05197 -3.35393 0.0 0
M  V30 9 C 4.55186 -4.21416 0.0 0
M  V30 10 C 4.04694 -3.35174 0.0 0
M  V30 11 C 4.5479 -7.67972 0.0 0
M  V30 12 C 4.04803 -8.54607 0.0 0
M  V30 13 C 2.54814 -7.68584 0.0 0
M  V30 14 C 3.05306 -8.54826 0.0 0
M  V30 15 C 1.68398 -5.44999 0.0 0
M  V30 16 C 1.68398 -6.44999 0.0 0
M  V30 17 C 5.55185 -4.21098 0.0 0
M  V30 18 C 5.5479 -7.67991 0.0 0
M  V30 19 C 2.5509 -2.48852 0.0 0
M  V30 20 C 3.04983 -1.62188 0.0 0
M  V30 21 C 1.5509 -2.48976 0.0 0
M  V30 22 C 2.0509 -1.62249 0.0 0
M  V30 23 C 2.55665 -9.41635 0.0 0
M  V30 24 C 1.55665 -9.42048 0.0 0
M  V30 25 C 3.06022 -10.2803 0.0 0
M  V30 26 C 2.05665 -10.2824 0.0 0
M  V30 27 N 7.04951 -3.34441 0.0 0
M  V30 28 C 6.05188 -3.34415 0.0 0
M  V30 29 C 7.55057 -4.21092 0.0 0
M  V30 30 C 6.05491 -5.08096 0.0 0
M  V30 31 C 7.05496 -5.07449 0.0 0
M  V30 32 C 8.55056 -4.20928 0.0 0
M  V30 33 C 10.0468 -3.34026 0.0 0
M  V30 34 N 9.04917 -3.34163 0.0 0
M  V30 35 C 10.5493 -4.20595 0.0 0
M  V30 36 C 9.05504 -5.07843 0.0 0
M  V30 37 C 10.0551 -5.07034 0.0 0
M  V30 38 C 7.04556 -6.81333 0.0 0
M  V30 39 C 6.04792 -6.81307 0.0 0
M  V30 40 C 7.54661 -7.67984 0.0 0
M  V30 41 C 6.05096 -8.54988 0.0 0
M  V30 42 N 7.05101 -8.54342 0.0 0
M  V30 43 C 8.54661 -7.67821 0.0 0
M  V30 44 C 10.0429 -6.80919 0.0 0
M  V30 45 C 9.04522 -6.81056 0.0 0
M  V30 46 C 10.5453 -7.67488 0.0 0
M  V30 47 N 9.05109 -8.54736 0.0 0
M  V30 48 C 10.0511 -8.53926 0.0 0
M  V30 49 Re 8.00662 -2.4123 0.0 0 CHG=1
M  V30 50 Re 8.02601 -9.43444 0.0 0 CHG=1
M  V30 51 Cl 6.48162 -2.4373 0.0 0 CHG=-1
M  V30 52 C 9.40662 -2.3873 0.0 0 CHG=-1
M  V30 53 C 6.97451 -1.3802 0.0 0 CHG=-1
M  V30 54 C 9.06373 -1.3552 0.0 0 CHG=-1
M  V30 55 C 9.72601 -9.43444 0.0 0 CHG=-1
M  V30 56 Cl 6.55101 -9.45944 0.0 0 CHG=-1
M  V30 57 C 6.8939 -10.6666 0.0 0 CHG=-1
M  V30 58 C 9.03312 -10.5666 0.0 0 CHG=-1
M  V30 59 O 6.26741 -0.673089 0.0 0 CHG=1
M  V30 60 O 9.77083 -0.648089 0.0 0 CHG=1
M  V30 61 O 10.4066 -2.3873 0.0 0 CHG=1
M  V30 62 O 6.1868 -11.3737 0.0 0 CHG=1
M  V30 63 O 9.74022 -11.2737 0.0 0 CHG=1
M  V30 64 O 10.726 -9.43444 0.0 0 CHG=1
M  V30 END ATOM
M  V30 BEGIN BOND
M  V30 1 1 1 6
M  V30 2 1 1 2
M  V30 3 2 2 3
M  V30 4 1 3 4
M  V30 5 1 4 5
M  V30 6 2 5 6
M  V30 7 2 8 7
M  V30 8 1 5 9
M  V30 9 1 7 6
M  V30 10 2 9 10
M  V30 11 1 10 8
M  V30 12 2 12 11
M  V30 13 1 2 13
M  V30 14 1 11 3
M  V30 15 2 13 14
M  V30 16 1 14 12
M  V30 17 1 1 15
M  V30 18 1 1 16
M  V30 19 1 9 17
M  V30 20 1 11 18
M  V30 21 1 8 19
M  V30 22 1 19 20
M  V30 23 1 19 21
M  V30 24 1 19 22
M  V30 25 1 14 23
M  V30 26 1 23 24
M  V30 27 1 23 25
M  V30 28 1 23 26
M  V30 29 2 28 17
M  V30 30 2 29 27
M  V30 31 1 17 30
M  V30 32 1 27 28
M  V30 33 2 30 31
M  V30 34 1 31 29
M  V30 35 1 29 32
M  V30 36 2 34 32
M  V30 37 2 35 33
M  V30 38 1 32 36
M  V30 39 1 33 34
M  V30 40 2 36 37
M  V30 41 1 37 35
M  V30 42 2 39 18
M  V30 43 2 40 38
M  V30 44 1 18 41
M  V30 45 1 38 39
M  V30 46 2 41 42
M  V30 47 1 42 40
M  V30 48 1 40 43
M  V30 49 2 45 43
M  V30 50 2 46 44
M  V30 51 1 43 47
M  V30 52 1 44 45
M  V30 53 2 47 48
M  V30 54 1 48 46
M  V30 55 10 27 49
M  V30 56 10 49 34
M  V30 57 10 42 50
M  V30 58 10 50 47
M  V30 59 10 49 51
M  V30 60 10 49 52
M  V30 61 10 49 53
M  V30 62 10 49 54
M  V30 63 10 50 55
M  V30 64 10 50 56
M  V30 65 10 50 57
M  V30 66 10 50 58
M  V30 67 3 53 59
M  V30 68 3 54 60
M  V30 69 3 52 61
M  V30 70 3 57 62
M  V30 71 3 58 63
M  V30 72 3 55 64
M  V30 END BOND
M  V30 END CTAB
M  END
</chemform>

==== Photosensitizer ====
<chemform smiles="C(F)1C2C3C=CC=CN=3[Ir+3]3(N4C=CC=CC=4C4=[C-]3C=C(F)C=C4F)3(N4C=CC=CC=4C4=[C-]3C=C(F)C=C4F)[C-]=2C=C(F)C=1" inchi="1S/3C11H6F2N.Ir/c3*12-8-4-5-9(10(13)7-8)11-3-1-2-6-14-11;/h3*1-4,6-7H;/q3*-1;+3" inchikey="GJHHESUUYZNNGV-UHFFFAOYSA-N" height="200px" width="300px" float="none">
  -INDIGO-11272314332D

  0  0  0  0  0  0  0  0  0  0  0 V3000
M  V30 BEGIN CTAB
M  V30 COUNTS 43 51 0 0 0
M  V30 BEGIN ATOM
M  V30 1 C 6.33485 -0.200074 0.0 0
M  V30 2 C 8.06515 -0.199589 0.0 0
M  V30 3 C 7.20164 0.300033 0.0 0
M  V30 4 C 8.06515 -1.20053 0.0 0
M  V30 5 C 6.33485 -1.20502 0.0 0
M  V30 6 C 7.20382 -1.70003 0.0 0 CHG=-1
M  V30 7 C 5.46882 -1.70502 0.0 0
M  V30 8 C 4.6051 -3.20433 0.0 0
M  V30 9 N 5.46921 -2.70573 0.0 0
M  V30 10 C 3.73792 -2.70444 0.0 0
M  V30 11 C 4.59818 -1.20313 0.0 0
M  V30 12 C 3.73534 -1.70875 0.0 0
M  V30 13 F 5.4689 0.30005 0.0 0
M  V30 14 F 8.93141 0.300008 0.0 0
M  V30 15 C 10.7482 -4.56624 0.0 0
M  V30 16 C 9.88344 -6.06497 0.0 0
M  V30 17 C 10.7479 -5.56696 0.0 0
M  V30 18 C 9.0166 -5.5645 0.0 0
M  V30 19 C 9.87787 -4.06377 0.0 0
M  V30 20 C 9.01469 -4.56881 0.0 0 CHG=-1
M  V30 21 C 9.87787 -3.06377 0.0 0
M  V30 22 C 9.01129 -1.56611 0.0 0
M  V30 23 N 9.01103 -2.56374 0.0 0
M  V30 24 C 9.8778 -1.06505 0.0 0
M  V30 25 C 10.7478 -2.56071 0.0 0
M  V30 26 C 10.7414 -1.56066 0.0 0
M  V30 27 F 11.6143 -4.06637 0.0 0
M  V30 28 F 9.88298 -7.06497 0.0 0
M  V30 29 C 4.66173 -6.18724 0.0 0
M  V30 30 C 3.79616 -4.689 0.0 0
M  V30 31 C 3.79523 -5.68664 0.0 0
M  V30 32 C 4.663 -4.18853 0.0 0
M  V30 33 C 5.53204 -5.68477 0.0 0
M  V30 34 C 5.52625 -4.68471 0.0 0 CHG=-1
M  V30 35 C 6.39806 -6.18477 0.0 0
M  V30 36 C 8.12836 -6.18312 0.0 0
M  V30 37 N 7.26452 -5.68408 0.0 0
M  V30 38 C 8.12903 -7.18407 0.0 0
M  V30 39 C 6.39874 -7.18971 0.0 0
M  V30 40 C 7.26804 -7.68414 0.0 0
M  V30 41 F 4.66158 -7.18724 0.0 0
M  V30 42 F 2.93037 -4.1886 0.0 0
M  V30 43 Ir 7.21023 -3.58073 0.0 0 CHG=3
M  V30 END ATOM
M  V30 BEGIN BOND
M  V30 1 2 3 1
M  V30 2 2 4 2
M  V30 3 1 1 5
M  V30 4 1 2 3
M  V30 5 2 5 6
M  V30 6 1 6 4
M  V30 7 1 5 7
M  V30 8 2 9 7
M  V30 9 2 10 8
M  V30 10 1 7 11
M  V30 11 1 8 9
M  V30 12 2 11 12
M  V30 13 1 12 10
M  V30 14 1 1 13
M  V30 15 1 2 14
M  V30 16 2 17 15
M  V30 17 2 18 16
M  V30 18 1 15 19
M  V30 19 1 16 17
M  V30 20 2 19 20
M  V30 21 1 20 18
M  V30 22 1 19 21
M  V30 23 2 23 21
M  V30 24 2 24 22
M  V30 25 1 21 25
M  V30 26 1 22 23
M  V30 27 2 25 26
M  V30 28 1 26 24
M  V30 29 1 15 27
M  V30 30 1 16 28
M  V30 31 2 31 29
M  V30 32 2 32 30
M  V30 33 1 29 33
M  V30 34 1 30 31
M  V30 35 2 33 34
M  V30 36 1 34 32
M  V30 37 1 33 35
M  V30 38 2 37 35
M  V30 39 2 38 36
M  V30 40 1 35 39
M  V30 41 1 36 37
M  V30 42 2 39 40
M  V30 43 1 40 38
M  V30 44 1 29 41
M  V30 45 1 30 42
M  V30 46 10 9 43
M  V30 47 10 6 43
M  V30 48 10 43 34
M  V30 49 10 43 37
M  V30 50 10 43 20
M  V30 51 10 43 23
M  V30 END BOND
M  V30 END CTAB
M  END
</chemform><chemform smiles="C1C=C2C(C3C=CC=CC=3)=CC=N3[Cu+]4(P(C5C=CC=CC=5)(C5C=CC=CC=5)C5C6OC7C(P4(C4C=CC=CC=4)C4C=CC=CC=4)=CC=CC=7C(C)(C)C=6C=CC=5)N4=CC=C(C5C=CC=CC=5)C=1C4=C23.[P-](F)(F)(F)(F)(F)F" inchi="1S/C39H32OP2.C24H16N2.Cu.F6P/c1-39(2)33-25-15-27-35(41(29-17-7-3-8-18-29)30-19-9-4-10-20-30)37(33)40-38-34(39)26-16-28-36(38)42(31-21-11-5-12-22-31)32-23-13-6-14-24-32;1-3-7-17(8-4-1)19-13-15-25-23-21(19)11-12-22-20(14-16-26-24(22)23)18-9-5-2-6-10-18;;1-7(2,3,4,5)6/h3-28H,1-2H3;1-16H;;/q;;+1;-1" inchikey="RLYPDFWLVSLBDF-UHFFFAOYSA-N" height="200px" width="300px" float="none">
  -INDIGO-11272314442D

  0  0  0  0  0  0  0  0  0  0  0 V3000
M  V30 BEGIN CTAB
M  V30 COUNTS 76 88 0 0 0
M  V30 BEGIN ATOM
M  V30 1 C 4.75985 -5.47507 0.0 0
M  V30 2 C 6.49015 -5.47459 0.0 0
M  V30 3 C 5.62664 -4.97497 0.0 0
M  V30 4 C 6.49015 -6.47553 0.0 0
M  V30 5 C 4.75985 -6.48002 0.0 0
M  V30 6 C 5.62882 -6.97503 0.0 0
M  V30 7 C 5.6282 -3.9804 0.0 0
M  V30 8 C 6.4927 -3.48202 0.0 0
M  V30 9 N 7.3581 -4.97422 0.0 0
M  V30 10 C 7.35297 -3.97724 0.0 0
M  V30 11 N 7.35042 -6.97074 0.0 0
M  V30 12 C 7.35263 -7.96665 0.0 0
M  V30 13 C 5.63103 -7.97493 0.0 0
M  V30 14 C 6.49673 -8.46554 0.0 0
M  V30 15 C 4.76217 -3.4804 0.0 0
M  V30 16 C 3.03187 -3.48205 0.0 0
M  V30 17 C 3.89572 -3.98109 0.0 0
M  V30 18 C 3.0312 -2.4811 0.0 0
M  V30 19 C 4.7615 -2.47545 0.0 0
M  V30 20 C 3.8922 -1.98102 0.0 0
M  V30 21 C 4.765 -8.47493 0.0 0
M  V30 22 C 3.90128 -9.97424 0.0 0
M  V30 23 C 4.76539 -9.47564 0.0 0
M  V30 24 C 3.0341 -9.47435 0.0 0
M  V30 25 C 3.89436 -7.97304 0.0 0
M  V30 26 C 3.03152 -8.47866 0.0 0
M  V30 27 C 13.925 -6.05001 0.0 0
M  V30 28 C 13.425 -5.18397 0.0 0
M  V30 29 C 12.425 -5.18396 0.0 0
M  V30 30 O 11.925 -6.04999 0.0 0
M  V30 31 C 12.425 -6.91603 0.0 0
M  V30 32 C 13.425 -6.91604 0.0 0
M  V30 33 C 11.9271 -4.32028 0.0 0
M  V30 34 C 12.427 -3.45393 0.0 0
M  V30 35 C 13.9269 -4.31416 0.0 0
M  V30 36 C 13.4219 -3.45174 0.0 0
M  V30 37 C 13.9229 -7.77972 0.0 0
M  V30 38 C 13.423 -8.64607 0.0 0
M  V30 39 C 11.9231 -7.78584 0.0 0
M  V30 40 C 12.4281 -8.64826 0.0 0
M  V30 41 P 10.9271 -4.32009 0.0 0
M  V30 42 P 10.9231 -7.78902 0.0 0
M  V30 43 C 11.1859 -3.35416 0.0 0
M  V30 44 C 10.7365 -1.68325 0.0 0
M  V30 45 C 10.478 -2.64682 0.0 0
M  V30 46 C 11.7032 -1.42354 0.0 0
M  V30 47 C 12.1564 -3.09341 0.0 0
M  V30 48 C 12.409 -2.12576 0.0 0
M  V30 49 C 10.0611 -3.82009 0.0 0
M  V30 50 C 8.33077 -3.82174 0.0 0
M  V30 51 C 9.19462 -4.32078 0.0 0
M  V30 52 C 8.3301 -2.82079 0.0 0
M  V30 53 C 10.0604 -2.81514 0.0 0
M  V30 54 C 9.1911 -2.32071 0.0 0
M  V30 55 C 11.182 -8.75494 0.0 0
M  V30 56 C 10.0571 -8.28902 0.0 0
M  V30 57 C 12.4066 -9.9773 0.0 0
M  V30 58 C 12.1487 -9.01358 0.0 0
M  V30 59 C 11.6993 -10.6855 0.0 0
M  V30 60 C 10.4718 -9.46602 0.0 0
M  V30 61 C 10.7369 -10.4303 0.0 0
M  V30 62 C 9.1934 -9.78832 0.0 0
M  V30 63 C 10.0575 -9.28973 0.0 0
M  V30 64 C 8.32622 -9.28843 0.0 0
M  V30 65 C 9.18648 -7.78713 0.0 0
M  V30 66 C 8.32364 -8.29275 0.0 0
M  V30 67 C 14.6321 -5.3429 0.0 0
M  V30 68 C 14.6321 -6.75712 0.0 0
M  V30 69 Cu 8.52413 -5.87422 0.0 0 CHG=1
M  V30 70 P 15.625 -2.175 0.0 0 CHG=-1
M  V30 71 F 15.625 -1.175 0.0 0
M  V30 72 F 14.759 -2.675 0.0 0
M  V30 73 F 16.491 -2.675 0.0 0
M  V30 74 F 16.491 -1.675 0.0 0
M  V30 75 F 15.625 -3.175 0.0 0
M  V30 76 F 14.759 -1.675 0.0 0
M  V30 END ATOM
M  V30 BEGIN BOND
M  V30 1 2 3 1
M  V30 2 2 4 2
M  V30 3 1 1 5
M  V30 4 1 2 3
M  V30 5 2 5 6
M  V30 6 1 6 4
M  V30 7 2 8 7
M  V30 8 1 2 9
M  V30 9 1 7 3
M  V30 10 2 9 10
M  V30 11 1 10 8
M  V30 12 2 12 11
M  V30 13 1 6 13
M  V30 14 1 11 4
M  V30 15 2 13 14
M  V30 16 1 14 12
M  V30 17 1 7 15
M  V30 18 2 17 15
M  V30 19 2 18 16
M  V30 20 1 15 19
M  V30 21 1 16 17
M  V30 22 2 19 20
M  V30 23 1 20 18
M  V30 24 1 13 21
M  V30 25 2 23 21
M  V30 26 2 24 22
M  V30 27 1 21 25
M  V30 28 1 22 23
M  V30 29 2 25 26
M  V30 30 1 26 24
M  V30 31 1 27 32
M  V30 32 1 27 28
M  V30 33 2 28 29
M  V30 34 1 29 30
M  V30 35 1 30 31
M  V30 36 2 31 32
M  V30 37 2 34 33
M  V30 38 1 28 35
M  V30 39 1 33 29
M  V30 40 2 35 36
M  V30 41 1 36 34
M  V30 42 2 38 37
M  V30 43 1 31 39
M  V30 44 1 37 32
M  V30 45 2 39 40
M  V30 46 1 40 38
M  V30 47 1 33 41
M  V30 48 1 39 42
M  V30 49 1 41 43
M  V30 50 2 45 43
M  V30 51 2 46 44
M  V30 52 1 43 47
M  V30 53 1 44 45
M  V30 54 2 47 48
M  V30 55 1 48 46
M  V30 56 1 41 49
M  V30 57 2 51 49
M  V30 58 2 52 50
M  V30 59 1 49 53
M  V30 60 1 50 51
M  V30 61 2 53 54
M  V30 62 1 54 52
M  V30 63 1 42 55
M  V30 64 1 42 56
M  V30 65 2 58 55
M  V30 66 2 59 57
M  V30 67 1 55 60
M  V30 68 1 57 58
M  V30 69 2 60 61
M  V30 70 1 61 59
M  V30 71 2 63 56
M  V30 72 2 64 62
M  V30 73 1 56 65
M  V30 74 1 62 63
M  V30 75 2 65 66
M  V30 76 1 66 64
M  V30 77 1 27 67
M  V30 78 1 27 68
M  V30 79 10 9 69
M  V30 80 10 11 69
M  V30 81 10 69 42
M  V30 82 10 69 41
M  V30 83 1 70 71
M  V30 84 1 70 72
M  V30 85 1 70 73
M  V30 86 1 70 74
M  V30 87 1 70 75
M  V30 88 1 70 76
M  V30 END BOND
M  V30 END CTAB
M  END
</chemform>

==== Investigation ====
{{#experimentlist: |form=Photocatalytic_CO2_conversion_experiments|name=Optimizations of the conditions}}

==== Sacrificial electron donor ====
In this study, TEA ({{#moleculelink:|link=ZMANZCXQSJIPKH-UHFFFAOYSA-N|image=false|width=300|height=200}}) and BIH ({{#moleculelink:|link=VDFIVJSRRJXMAU-UHFFFAOYSA-N|image=false|width=300|height=200}}) were used as sacrificial electron donors.