Iodine also adds a little to the bond length.
I asked a colleague and he said, what about about extending the lever (see law of the lever)? Indeed, it adds a little length.
His other thought was towards a BN triple bond. Not better than the CC triple bond in TBNBL I.
... and this is where I stop (again), because someone needs to beat my awesome DFT value of a super realistic molecule of 1441445 pm now (or 147.3 pm in "X-RAY length" if the ratio from Marko's comparison is applied).
... and this is where I stop, because someone needs to beat my awesome DFT value of a super realistic molecule of 144 pm now (or 147.3 pm in "X-RAY length" if the ratio from Marko's comparison is applied).
Iodine also adds a little to the bond length.
I asked a colleague and he said, what about about extending the lever (see law of the lever)? Indeed, it adds a little length.
His other thought was towards a BN triple bond. Not better than the CC triple bond in TBNBL I.
... and this is where I stop (again), because someone needs to beat my awesome DFT value of a super realistic molecule of 1445 pm now.
As Geoff and I were curious to see what happens, when Bromine is used instead of Chlorine, I did the calculations (only geometry optimization so far) and they indeed yield a slightly longer bond but nothing is dramatically changed.
$144.3$, $144.3$ and $\pu{144.4 pm}$.
As Geoff and I were curious to see what happens, when Bromine is used instead of Chlorine, I did the calculations (only geometry optimization so far) and they indeed yield a slightly longer bond but nothing is dramatically changed.
$144.3$, $144.3$ and $\pu{144.4 pm}$.
While the two other (so far) presented molecules look realistic (Martin) or are real (Marko), I couldn't find the constraint, that the molecules actually need to be realistic, so here we go.
This is Gaussian 16 Rev. A.03 using (again, why do we use this niveau?) B97D3/def2TZVPP with Opt=(VeryTight) and SCF=(VeryTight) on to-be-named-by-Loong I (TBNBL I) with some nice double (or so) bond length of $\pu{143.5 pm}$. (At least formally, it needs to be a double bond.)
E(RB97D3) = -692.564719674
C 0.00000000 0.71742600 0.00000100
C 0.00000000 -0.71742800 0.00000100
C -1.26096700 1.35299700 0.00000100
C 1.26096700 1.35299700 0.00000100
C -1.26096700 -1.35299900 0.00000100
C 1.26096700 -1.35299900 0.00000100
C -2.47714700 1.44346000 0.00000000
C -2.47714700 -1.44345900 0.00000100
C 2.47714700 -1.44345900 0.00000000
C 2.47714600 1.44345900 0.00000100
C -3.88898600 1.10111200 -0.00000100
C 3.88898600 1.10111300 0.00000000
C 4.18780000 0.00000100 -1.08412100
C 3.88898700 -1.10111100 -0.00000100
C 4.18780200 0.00000000 1.08411900
C -3.88898700 -1.10111100 0.00000000
C -4.18780000 0.00000000 -1.08412100
C -4.18780200 0.00000100 1.08411900
H -4.55239300 -1.97024400 -0.00000100
H -3.55876000 0.00000100 1.97407800
H -5.24617200 0.00000100 1.36283000
H -5.24617000 0.00000000 -1.36283300
H -3.55875700 0.00000000 -1.97407800
H -4.55239300 1.97024500 -0.00000100
H 4.55239300 -1.97024300 -0.00000100
H 5.24617000 0.00000100 -1.36283300
H 3.55875700 0.00000100 -1.97407800
H 5.24617200 0.00000000 1.36283000
H 3.55876000 0.00000000 1.97407800
H 4.55239300 1.97024500 -0.00000100
It has no negative frequencies and thus is a local minimum on its potential energy hypersurface. This holds true for every following molecule.
BDE according to [1] is 553 kJ/mol.
This led me to change the cyclobutyl rings into double bonds (TBNBL II), but that was not productive, as the bond length is reduced to $\pu{140.4 pm}$. BDE is $\pu{606 kJ/mol}$.
E(RB97D3) = -535.325912063
C 0.00000000 0.70224700 0.00000000
C 0.00000000 -0.70224700 0.00000000
C 1.29152400 1.32362500 0.00000000
C -1.29152400 1.32362500 0.00000000
C 1.29152400 -1.32362500 0.00000000
C -1.29152400 -1.32362500 0.00000000
C 2.51038500 1.30761800 0.00000000
C 2.51038500 -1.30761700 0.00000000
C -2.51038500 -1.30761700 0.00000000
C -2.51038500 1.30761700 0.00000000
C 3.80696800 0.68032900 0.00000000
C -3.80696800 0.68032900 0.00000000
C -3.80696800 -0.68032900 0.00000000
C 3.80696800 -0.68032900 0.00000000
H 4.73157700 -1.24777100 0.00000000
H 4.73157700 1.24777100 0.00000000
H -4.73157700 -1.24777100 0.00000000
H -4.73157700 1.24777100 0.00000000
Ok, if getting smaller does not help, maybe getting bigger again? What about changing the cyclobutyl* into cyclohexadiene*? We get larger again, but not larger as my first try. TBNBL III: $\pu{141.5 pm}$ with BDE of $\pu{587 kJ/mol}$.
E(RB97D3) = -844.915342833
C 0.00000 0.70775 0.00000
C -0.00000 -0.70775 0.00000
C 1.25608 1.36005 0.00000
C -1.25608 1.36005 -0.00000
C 1.25608 -1.36005 -0.00000
C -1.25608 -1.36005 0.00000
C 2.45242 1.57986 0.00000
C 2.45242 -1.57986 -0.00000
C -2.45242 -1.57986 0.00000
C -2.45242 1.57986 -0.00000
C -3.91584 1.44760 -0.00000
C -4.32828 0.66483 1.24739
C -4.32828 0.66483 -1.24739
C -4.32828 -0.66483 1.24739
H -4.57791 1.23705 2.13578
C -4.32828 -0.66483 -1.24739
H -4.57791 1.23705 -2.13578
C -3.91584 -1.44760 -0.00000
H -4.57791 -1.23705 2.13578
H -4.57791 -1.23705 -2.13578
H -4.39998 -2.43128 -0.00000
C 3.91584 1.44760 0.00000
C 4.32828 0.66483 -1.24739
C 4.32828 0.66483 1.24739
C 4.32828 -0.66483 -1.24739
H 4.57791 1.23705 -2.13578
C 4.32828 -0.66483 1.24739
H 4.57791 1.23705 2.13578
C 3.91584 -1.44760 -0.00000
H 4.57791 -1.23705 -2.13578
H 4.57791 -1.23705 2.13578
H 4.39998 -2.43128 0.00000
H 4.39998 2.43128 -0.00000
H -4.39998 2.43128 0.00000
There is also the cyclohexyl analogue (TBNBL IV) which has a little longer bond with $\pu{142.4 pm}$ and a BDE of $\pu{571 kJ/mol}$.
E(RB97D3) = -849.855064121
C 0.00000 -0.71210 0.00000
C -0.00000 0.71210 0.00000
C -1.25688 -1.35508 -0.01308
C 1.25688 -1.35508 0.01309
C -1.25688 1.35508 0.01309
C 1.25688 1.35508 -0.01308
C -2.46545 -1.49799 -0.06310
C -2.46545 1.49799 0.06310
C 2.46545 1.49799 -0.06310
C 2.46545 -1.49799 0.06310
C 3.90819 -1.43687 0.24464
C 4.25416 -0.48923 1.44910
C 4.64897 -0.93627 -1.02206
C 4.64897 0.93627 1.02206
H 5.08644 -0.93074 2.00793
H 3.39579 -0.45561 2.12315
C 4.25416 0.48923 -1.44910
H 5.72105 -0.97274 -0.79444
H 4.47838 -1.63040 -1.84994
C 3.90818 1.43687 -0.24464
H 5.72105 0.97275 0.79444
H 4.47838 1.63040 1.84994
H 3.39579 0.45561 -2.12315
H 5.08644 0.93074 -2.00793
H 4.28399 2.44120 -0.47664
C -3.90819 -1.43687 -0.24464
C -4.25416 -0.48923 -1.44910
C -4.64898 -0.93627 1.02206
C -4.64897 0.93627 -1.02206
H -5.08644 -0.93074 -2.00793
H -3.39579 -0.45561 -2.12314
C -4.25416 0.48923 1.44910
H -5.72105 -0.97274 0.79444
H -4.47838 -1.63040 1.84994
C -3.90819 1.43687 0.24464
H -5.72105 0.97275 -0.79444
H -4.47838 1.63040 -1.84994
H -3.39579 0.45561 2.12315
H -5.08644 0.93074 2.00793
H -4.28399 2.44120 0.47664
H -4.28399 -2.44120 -0.47665
H 4.28399 -2.44120 0.47664
So, this also did not help. Then I thought about going back to TBNBL I and modify it. Let's add Chlorine looking into the rings, which should push the triple bonds apart. That does not change anything with regard to the first molecule ... TBNBL V has $\pu{143.4 pm}$ with a BDE of $\pu{555 kJ/mol}$.
E(RB97D3) = -2531.12566838
C -0.00000 -0.00000 0.71686
C 0.00000 -0.00000 -0.71686
C -1.25995 0.00000 1.35010
C 1.25995 -0.00000 1.35010
C -1.25995 0.00000 -1.35010
C 1.25995 0.00000 -1.35010
C -2.47385 0.00000 1.43772
C -2.47385 0.00000 -1.43772
C 2.47385 0.00000 -1.43772
C 2.47385 -0.00000 1.43772
C -3.88167 0.00000 1.11523
C 3.88167 -0.00000 1.11523
C 4.23226 1.05834 0.00000
C 3.88167 0.00000 -1.11523
C 4.23226 -1.05834 -0.00000
C -3.88167 0.00000 -1.11523
C -4.23226 1.05834 -0.00000
C -4.23226 -1.05834 0.00000
H -4.54203 0.00000 -1.98574
H -5.30546 -1.25818 0.00000
H -5.30546 1.25818 0.00000
H -4.54203 0.00000 1.98574
H 4.54203 -0.00000 -1.98574
H 5.30546 1.25818 -0.00000
H 5.30546 -1.25818 0.00000
H 4.54203 0.00000 1.98574
Cl -3.41634 -2.62778 0.00000
Cl -3.41634 2.62778 0.00000
Cl 3.41634 2.62778 -0.00000
Cl 3.41634 -2.62778 0.00000
What about adding more chlorine atoms? Seems to work; TBNBL VI: $\pu{144.1 pm}$ with a BDE of $\pu{542 kJ/mol}$.
E(RB97D3) = -4369.66038511
C 0.00000 0.00000 0.72068
C 0.00000 0.00000 -0.72068
C -1.25395 0.00000 1.35718
C 1.25395 -0.00000 1.35718
C -1.25395 0.00000 -1.35718
C 1.25395 0.00000 -1.35718
C -2.46546 0.00000 1.48386
C -2.46546 0.00000 -1.48386
C 2.46546 0.00000 -1.48386
C 2.46546 -0.00000 1.48386
C -3.85845 0.00000 1.12299
C 3.85845 -0.00000 1.12299
C 4.13677 1.09997 0.00000
C 3.85845 0.00000 -1.12299
C 4.13677 -1.09997 -0.00000
C -3.85845 0.00000 -1.12299
C -4.13677 1.09997 -0.00000
C -4.13677 -1.09997 0.00000
H -4.57107 0.00000 -1.94770
H -4.57107 0.00000 1.94770
H 4.57107 -0.00000 -1.94770
H 4.57107 0.00000 1.94770
Cl -3.09602 -2.53375 0.00000
Cl -3.09602 2.53375 0.00000
Cl 3.09602 2.53375 0.00000
Cl 3.09602 -2.53375 0.00000
Cl -5.83899 1.64902 0.00000
Cl -5.83899 -1.64902 -0.00000
Cl 5.83899 -1.64902 0.00000
Cl 5.83899 1.64902 0.00000
... and this is where I stop, because someone needs to beat my awesome DFT value of a super realistic molecule of 144 pm now (or 147.3 pm in "X-RAY length" if the ratio from Marko's comparison is applied).
EXPERIMENTALISTS THINK SILICON IS REALLY FUN TO USE
ITS PLACE IN NOVEL COMPOUNDS IS CERTAIN TO AMUSE
THEY SIT ALL DAY IN LABORATORIES MAKING ALL THIS SLUDGE
"LOADED WITH THE SILICON THEY SAY", TO ME IT LOOKS LIKE FUDGE.
FOR HAPPY THOUGH THEY BE WITH CRUD, I'D LIKE TO KNOW A LITTLE
ABOUT THE PI BONDS ON THE EDGE AND SIGMAS IN THE MIDDLE.
SO LETS DERIVE A WAVEFUNCTION.....6-31G*
USE AN OPTIMAL GEOMETRY AND SEE WHERE ELECTRONS ARE.
BUT WHAT OF CORRELATION? ASKS THE WIRY LITTLE SKEPTIC.
WE'LL THROW IN PERTURBATION AS AN ELECTRON ANTISEPTIC.
AND WHEN THE PROGRAM GIVES US ANSWERS IN THEM WE CAN TRUST
SINCE NOBODY CAN MAKE THE STUFF, WE HAVE NO CHOICE, WE MUST.
SO THEORY GUYS HAVE GOT IT MADE, IN ROOMS FREE OF POLLUTION.
INSTEAD OF PROBLEMS WITH THE REFLUX, THEY HAVE ONLY SOLUTIONS.
AND WHEN THE FEDS ANNOUNCE THE LIST OF CARCINOGENIC TERRORS,
THE THEORISTS SIT SAFELY AT THEIR TERMINALS FIXING ERRORS.
IN OTHER WORDS, EXPERIMENTALISTS WILL LIKELY DIE OF CANCER
FROM WORKING HARD YET FRUITLESSLY...TILL THEORY GIVES THE ANSWER.
-- THOMAS A. HOLME, 1983
[1] Andreas A. Zavitsas, J. Phys. Chem. A, 2003, 107 (6), pp 897–898
[2] Images where created using CYLview, 1.0.564 BETA; Legault, C. Y., Université de Sherbrooke, 2009 (http://www.cylview.org)