Nickel, copper, and zinc dinuclear helicates: how do bulky groups influence their architecture?

Dal on
T ansac ions
PAPER
Ci e his: Dal on T ans., 2024, 53,
5676
Recei ed 30 h Janua y 2024,
Accep ed 26 h Feb ua y 2024
DOI: 10.1039/d4d 00279b
sc.li/dal on
Nickel, coppe , and zinc dinuclea helica es: how
do bulky g oups influence hei a chi ec u e?†
Sand a Fe nández-Fa iña,
b
Ma celino Manei o,
b
Guille mo Za agoza,
c
José M. Seco,
d
Rosa Ped ido *
a
and Ana M. González-Noya *
a
The ligand design ac o s ha may influence he isola ion o me allosup amolecula helica es o meso-
ca es s ill dese e o be in es iga ed. In his sense, dinuclea nickel(II), coppe (II) and zinc(II) compounds
we e ob ained by elec ochemical syn hesis using a amily o fi e Schiffbase ligands, H
2
L
n
(n=1–5),
de i ed om bisphenylme hane and unc ionalized wi h bulky e -bu yl g oups in he pe iphe y and e hyl
g oups in he space . Six o he new complexes we e cha ac e ized by X- ay c ys allog aphy, hus demon-
s a ing ha he helica e s uc u e is p edominan in he solid s a e.
1
H NMR s udies we e pe o med o
he zinc complexes o analyze i he helical a chi ec u e o he me al complexes is e ained in solu ion.
These s udies e eal ha he p esence o a e -bu yl g oup in he o ho posi ion wi h espec o he OH
g oup is an essen ial ac o iden ified o he exis ence o a helica e con o ma ion in solu ion.
In oduc ion
The knowledge and unde s anding o how diffe en elemen s
and molecules combine h ough di e se sel -assembly p o-
cesses has led o he eme gence o a new ield called sup amo-
lecula chemis y.
1
Sup amolecula chemis y is ocused on
he design and s udy o hose sys ems o med by he spon-
aneous union o wo o mo e componen s h ough he in e -
ac ion o non-co alen bonds, o ins ance, hyd ogen bonds,
an de Waals o ces o π–πin e ac ions.
2–4
These in e ac ions
a e o en ound in na u e, such as in p o eins o DNA, and a e
essen ial o he de elopmen o hei main unc ions.
5
Me al–ligand in e ac ions a e also impo an ools wi hin
he sup amolecula chemis y ield. Depending on he o ien-
a ion o he pa en ligand, a wide a ie y o me allosup a-
molecula a chi ec u es showing in e es ing p ope ies and
applica ions
5–7
can be ob ained. Among hem, helica es and
mesoca es ha e eme ged as wo o he mos p omising unc-
ional me allosup amolecula a chi ec u es. Helica es a e
o med by one o mo e o ganic ligands helically w apped
a ound a se ies o me al ions de ining he axis o he
helix.
1,8–10
In con as , mesoca es a e o med by wo o mo e
ligands coo dina ed o me al ions wi hou c ossing each
o he .
11
Cu en ly, in con as o mesoca es, helica es ha e
been ex ensi ely s udied. In his sense, a ew e iews on heli-
ca es can be ound in he li e a u e.
10,12–15
Al hough he p epa-
a ion o helica e/mesoca e a chi ec u es is ela i ely simple, a
single con olled ou e o achie ing helica e e sus mesoca e has
no ye been es ablished. In ecen yea s, some o he ac o s
ha go e n he sel -assembly p ocesses o helica es and/o
mesoca es ha e been iden i ied: he coo dina i e p e e ences o
he me al ion, i s size
16
and ha d o so cha ac e is ic,
17
he
inne design o he o ganic ligand,
3,16,18–23
he empe a u e and
he p esence o anions.
24
I should be highligh ed ha unde -
s anding and con olling hese ac o s a e c ucial because heli-
ca e/mesoca e isome s may exhibi diffe en biological beha-
iou s.
25
Addi ionally, i has been ound ha he isola ion o
helicoidal o meso-helicoidal a chi ec u es can be con olled by
in a- and in e molecula in e ac ions ha occu be ween he
ligands.
26,27
In he li e a u e he e is a la ge a ie y o examples
o helicoidal a chi ec u es de i ed om ligands whose o -
ma ion is a ou ed by he exis ence o weak non-co alen π–πo
CH⋯πin e ac ions.
28–31
Along his line, i was ound ha he
exis ence o non-co alen CH⋯πin e ac ions a ou ed he heli-
ca e- ype s uc u e, con a y o expec a ions, since inc easing
he dis ance be ween he linking domains o he ligand should
a ou he mesoca e con o ma ion.
32
†Elec onic supplemen a y in o ma ion (ESI) a ailable: De ailed expe imen al
p ocedu es, compound cha ac e iza ion and syn he ic and c ys allog aphic da a;
Fig. S1–S14 and Tables S1–S8. CCDC 2321087–2321094. Fo ESI and c ys allo-
g aphic da a in CIF o o he elec onic o ma see DOI: h ps://doi.o g/10.1039/
d4d 00279b
a
Depa amen o de Química Ino gánica, Facul ade de Química, Campus Vida,
Uni e sidade de San iago de Compos ela, San iago de Compos ela, Galicia, E-15782,
Spain. E-mail: [email p o ec ed], ana.gonza[email p o ec ed]
b
Depa amen o de Química Ino gánica, Facul ade de Ciencias, Campus Te a,
Uni e sidade de San iago de Compos ela, E-27002 Lugo, Spain
c
Unidade de Di acción de Raios X, Edi icio CACTUS, Uni e sidade de San iago de
Compos ela, Campus Su , San iago de Compos ela, Galicia, E-15782, Spain
d
Depa amen o de Química O gánica Facul ade de Química, Campus Vida,
Uni e sidade de San iago de Compos ela, San iago de Compos ela, Galicia, E-15782,
Spain
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Wi h his in mind, we ha e decided o del e deepe in o he
ac o s ha in luence bo h he me al ions and he ligand
design o ob aining helical o meso-helical compounds. To
achie e ha , he coo dina ion chemis y o a amily o bisphe-
nylme hane-de i ed Schiffbase ligands (H
2
L
n
, Fig. 1) has been
explo ed owa ds nickel(II), coppe (II) and zinc(II) me al ions.
Schiffbase ligands
33
cons i u e one o he mos used
app oaches o syn hesizing helica es and mesoca es, as hey
equi e cheap o easy- o-p epa e s a ing ma e ials and sho
p epa a ion imes.
15,19,34
The long and semi- igid bisphenylme hane-de i ed space s
we e success ully employed by Hannon and co-wo ke s in he
pa en ligands o p epa e helica es and/o mesoca es.
28,35–37
In
ac , hese pionee ing wo ks es ablished ha unc ionaliza ion
wi h e hyl g oups in he a oma ic ings o he space could
o eseeably a ou he o ma ion o helicoidal species ins ead
o mesoca es.
37
In addi ion, diffe en bisphenylme hane-
de i ed ligands leading o helical- ype species a e ound in he
li e a u e.
31,38–40
Besides, he Schiffbase b anches in ou se ies H
2
L
n
(Fig. 1)
ha e been unc ionalized wi h e -bu yl g oups in he salicy-
loyl g oups (Fig. 1). We will modi y he posi ion o he e -
bu yl g oup wi h espec o he hyd oxy g oup (pa a o H
2
L
1
and H
2
L
4
, and o ho o H
2
L
2
and H
2
L
5
) and in oduce a
second e -bu yl g oup (H
2
L
3
) o de e mine whe he he posi-
ion and numbe o bulky g oups p e en and/o de e mine
he o ma ion o helica es o mesoca es. The p esence o he
alkyl g oups in he skele on o hese ligands could also
imp o e he solubili y o he species o med in apola sol en s
and hus a ou hei c ys alliza ion.
Expe imen al sec ion
Ma e ials and me hods
All sol en s, p- oluenesul onic acid, 4,4′-me hylenedianiline,
4,4′-me hylenebis(2,6-die hylaniline), 3- e -bu yl-2-hyd oxy-
benzaldehyde, 5- e -bu yl-2-hyd oxybenzaldehyde, 3,5-di- e -
bu yl-2-hyd oxybenzaldehyde and nickel, coppe and zinc
pla es we e pu chased om comme cial sou ces and we e used
wi hou pu i ica ion. Mel ing poin s we e de e mined using a
Buchi 560 ins umen . Elemen al analysis o compounds (C, N
and H) was ca ied ou on a Fisons EA model 1108 analyse .
In a ed spec a we e eco ded om 4000 o 500 cm
−1
on a
B uke FT-MIR spec opho ome e model VERTEX 70V in he
solid s a e using KB pelle s. Mass spec a we e ob ained using
B uke Mic o o spec ome e s o he ESI
+
echnique (elec o-
sp ay ioniza ion in posi i e mode) and B uke Au o lex o he
MALDI echnique (ma ix assis ed lase deso p ion/ioniza ion),
bo h coupled o a ime-o - ligh (TOF) analyse . Room- emp-
e a u e magne ic suscep ibili ies we e measu ed using a
digi al measu emen sys em MSB-MKI ib a ing magne -
ome e . Te akis(iso hiocyana o)cobal a e(II) was employed as a
suscep ibili y s anda d. A Va ian Ino a 400 spec ome e was
employed o eco d he
1
H NMR spec a ope a ing a oom
empe a u e using ace one-d
6
as a deu e a ed sol en .
Chemical shi s a e epo ed as δ(in ppm).
Syn hesis and cha ac e iza ion o he Schiffbase ligands H
2
L
n
The Schiffbase ligands H
2
L
n
(n=1–5) ha e been p epa ed by a
condensa ion eac ion be ween wo equi alen s o he co es-
ponding hyd oxyl-benzaldehyde unc ionalized wi h e -bu yl
g oups and one equi alen o he amine compound
(Fig. S13†), ollowing he same p ocedu e p e iously epo ed
o H
2
L
1
1and H
2
L
2
2ligands.
41
All he ligands ha e been ully
cha ac e ized by mel ing poin de e mina ion, elemen al ana-
lysis, in a ed spec oscopy, mass spec ome y and
1
H NMR
spec oscopy echniques, as well as by X- ay diff ac ion in he
cases whe e i was possible o ob ain quali y c ys als.
H
2
L
3
3. Yield: 1.38 g (87%); m.p.: 190–195 °C; elemen al ana-
lysis: % heo e ical (C
43
H
54
N
2
O
2
) C, 81.9; N, 4.4; H, 8.6; expe i-
men alC,81.3;N,4.4;H,9.2;IR(cm
−1
)ν:3435s(O–H), 2958 s.
(C–H), 1618 s. (C N), 1250 m (C–O), 820 w (CH
2
); MALDI-TOF
(m/z)631.1[H
2
L
3
+H]
+
;
1
H-NMR (400 MHz, ace one-d
6
,δ(m, nH,
Hx, J)): 13.88 (s, 2H, H
1
), 8.90 (s, 2H, H
2
), 7.50 (bs, J= 2.3 Hz, 2H,
H
3
), 7.46 (bs, J=2.3Hz,2H,H
4
), 7.31 (bs, 8H, H
5
+H
6
), 4.08 (s,
2H, H
7
), 1.47 (s, 18H, H
8
), 1.33 (s, 18H, H
9
).
H
2
L
4
4. Yield: 0.405 g (81%); m.p.: 165–170 °C; elemen al
analysis: % heo e ical (C
43
H
54
N
2
O
2
) C, 81.9; N, 4.4; H, 8.6;
expe imen al C, 80.7; N, 4.3; H, 8.4; IR (cm
−1
)ν: 3395 w (O–
H), 2963 s (C–H), 1628 s. (C N), 1265 s (C–O), 824 m (CH
2
);
ESI
+
(m/z) 631.4 [H
2
L
4
+H]
+
;
1
H-NMR (400 MHz, ace one-d
6
,δ
(m, nH, Hx, J)): 12.79 (s, 2H, H
1
), 8.56 (s, 2H, H
2
), 7.61 (d, J=
2.2 Hz, 2H, H
3
), 7.52 (dd, J= 8.7, 2.4 Hz, 2H, H
4
), 7.09 (s, 4H,
Fig. 1 Syn hesized Schiffbase ligands H
2
L
n
.
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H
5
), 6.94 (d, J= 8.7 Hz, 2H, H
6
), 3.94 (s, 2H, H
7
), 2.53 (q, J= 7.5
Hz, 8H, H
8
), 1.47 (s, 18H, H
9
); 1.12 ( , J= 7.5 Hz, 12H, H
10
). By
slow e apo a ion o he mo he liquo du ing he syn hesis o
he ligand in e hanol, colou less p isms sui able o X- ay diff -
ac ion s udies we e ob ained H
2
L
4
4*.
H
2
L
5
5. Yield: 0.431 g (86%); m.p.: 110–115 °C; elemen al
analysis: % heo e ical (C
43
H
54
N
2
O
2
) C, 81.9; N, 4.4; H, 8.6;
expe imen al C, 79.8; N, 4.5; H, 8.9; IR (cm
−1
)ν: 3433 w (O–
H), 2964 s (C–H), 1618 s. (C N), 1190 s (C–O), 750 m (CH
2
);
ESI
+
(m/z) 631.4 [H
2
L
5
+H]
+
;
1
H-NMR (400 MHz, ace one-d
6
,δ
(m, nH, Hx, J)): 13.82 (s, 2H, H
1
), 8.54 (s, 2H, H
2
), 7.45 (dd, J=
7.8, 1.2 Hz, 2H, H
3
), 7.41 (dd, J= 7.8, 1.5 Hz, 2H, H
4
), 7.11 (s,
4H, H
5
), 6.93 ( , J= 7.8 Hz, 2H, H
6
), 3.95 (s, 2H, H
7
), 2.54 (c, J=
7.5 Hz, 8H, H
8
), 1.47 (s, 18H, H
9
); 1.13 ( , J= 7.5 Hz, 12H, H
10
).
By slow e apo a ion o he mo he liquo du ing he syn hesis
o he ligand in e hanol, colou less p isms sui able o X- ay
diff ac ion s udies we e ob ained H
2
L
5
5*.
Syn hesis and cha ac e iza ion o helica es
The elec ochemical syn hesis o nickel, coppe , and zinc
neu al helica es was pe o med using an elec ochemical cell
and a powe supply o egula e he in ensi y (10 mA) and he
po en ial (10–15 V) o he eac ion.
41
The cell con ains a solu-
ion o he Schiffbase ligand in ace oni ile, along wi h a
small quan i y o e ae hylammonium pe chlo a e (10 mg) o
ac as a conduc i e elec oly e. The elec ochemical eac ion
in ol es educ ion o he ligand a he pla inum ca hode and
oxida ion o he me al anode. The elec ochemical cell is
depic ed as ollows:
P ðÞjH2Lnþace oni ilejMðþÞ
The p oposed mechanism o he o ma ion o he neu al
helica es [M
2
(L)
2
] in ol es wo elec ons pe ligand, as shown
below.
Ca hode :2H2Lnþ4e!2ðLnÞ2þ2H2ðgÞ
Anode :2M !2M2þþ4e
Global :2ðLnÞ2þ2M2þ!½M2ðLnÞ2
The main analy ical and cha ac e iza ion da a o he com-
plexes a e gi en below.
[Ni
2
(L
1
)
2
]·H
2
O6.Yellow solid. Yield: 0.071 g (59%); m.p.: >
300 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
70
H
74
N
4
O
5
Ni
2
) C, 72.0; N, 4.8; H, 6.4; expe imen al C, 70.9;
N, 4.7; H, 6.1; IR (cm
−1
)ν: 3435 s (O–H); 2958 m (C–H); 1620
s. (C N); 1261 m (C–O); 833 m (CH
2
); MALDI-TOF (m/z):
1151.3 [Ni
2
(L
1
)
2
+H]
+
, 1726.5 [Ni
3
(L
1
)
3
+H]
+
;μ
eff
= 3.1 B.M.
[Ni
2
(L
2
)
2
]·H
2
O7.O ange solid. Yield: 0.069 g (58%); m.p.: >
300 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
70
H
74
N
4
O
5
Ni
2
) C, 72.0; N, 4.8; H, 6.4; expe imen al C, 71.3;
N, 4.7; H, 6.4; IR (cm
−1
)ν: 3433 s. (O–H); 2957 m (C–H); 1607
s. (C N); 1271 w (C–O); 752 m (CH
2
); MALDI-TOF (m/z):
1151.5 [Ni
2
(L
2
)
2
+H]
+
;μ
eff
= 3.0 B.M. By slow e apo a ion o he
mo he liquo du ing he syn hesis, b own c ys als sui able o
X- ay diff ac ion s udies we e ob ained [Ni
2
(L
2
)
2
]·CH
3
CN 7*.
[Ni
2
(L
3
)
2
]8.O ange solid. Yield: 0.064 g (59%); m.p.: decom-
poses a 230 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e-
ical (C
86
H
104
N
4
O
4
Ni
2
) C, 75.1; N, 4.1; H, 7.6; expe imen al C,
73.0; N, 3.9; H, 7.8; IR (cm
−1
)ν: 2956 s (C–H); 1614 s (C N);
1255 m (C–O); 837 w (CH
2
); MALDI-TOF (m/z): 688.7 [Ni(L
3
)+
H]
+
;μ
eff
= 3.4 B. Rec ys alliza ion in dichlo ome hane yielded
yellow p isms sui able o X- ay diff ac ion s udies
[Ni
2
(L
3
)
2
]·2CH
2
Cl
2
8*.
[Ni
2
(L
4
)
2
]·H
2
O9.G een solid. Yield: 0.062 g (54%); m.p.:
255 °C; E
= 0.6 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
106
N
4
O
5
Ni
2
) C, 74.1; N, 4.0; H, 7.7; expe imen al C, 72.6;
N, 3.9; H, 7.5; IR (cm
−1
)ν: 3442 m (O–H); 2963 s (C–H); 1618
s. (C N); 1267 m (C–O); 831 w (CH
2
); MALDI-TOF (m/z):
1375.8 [Ni
2
(L
4
)
2
+H]
+
;μ
eff
= 3.2 B.M.
[Ni
2
(L
5
)
2
] 10. B own solid. Yield: 0.065 g (59%); m.p.: 225 °C;
E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
104
N
4
O
8
Ni
2
) C, 75.1; N, 4.1; H, 7.6; expe imen al C, 74.3;
N, 3.9; H, 7.3; IR (cm
−1
)ν: 2967 s (C–H); 1605 s (C N); 1269 w
(C–O); 853 w (CH
2
); MALDI-TOF (m/z): 1375.7 [Ni
2
(L
5
)
2
+H]
+
;
μ
eff
= 3.3 B.M.
[Cu
2
(L
3
)
2
]·H
2
O 11. B own solid. Yield: 0.075 g (65%); m.p.:
200 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
106
N
4
O
5
Cu
2
) C, 73.6; N, 4.0; H, 7.6; expe imen al C, 74.3;
N, 3.9; H, 7.4; IR (KB , cm
−1
): ν=(O–H) 3444 (d), (C–H) 2954
( ), (C N) 1614 ( ), (C–O) 1255 (m), (CH
2
) 833 (d); MALDI-TOF
(m/z) 694.5 [Cu(L
3
)+H]
+
, 1386.9 [Cu
2
(L
3
)
2
+H]
+
;μ
eff
= 1.7 B.M.
By slow e apo a ion o he mo he liquo du ing he syn hesis,
b own c ys als sui able o X- ay diff ac ion s udies we e
ob ained [Cu
2
(L
3
)
2
]·2CH
3
CN 11*.
[Cu
2
(L
4
)
2
] 12. B own solid. Yield: 0.059 g (51%); m.p.:
260 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
104
N
4
O
4
Cu
2
) C, 71.4; N, 3.9; H, 7.8; expe imen al C, 68.8;
N, 3.7; H, 7.5; IR (KB , cm
−1
): ν=(C–H) 2963 (m), (C N) 1618
(m), (C–O) 1267 (d), (CH
2
) 835 (d); MALDI-TOF (m/z) 691.5 [Cu
(L
4
)+H]
+
, 1386.9 [Cu
2
(L
4
)
2
+H]
+
;μ
eff
= 1.9 B.M.
[Cu
2
(L
5
)
2
]·H
2
O 13. B own solid. Yield: 0.074 g (67%); m.p.:
220 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
104
N
4
O
4
Cu
2
) C, 71.4; N, 3.9; H, 7.8; expe imen al C, 72.3;
N, 3.9; H, 7.3; IR (KB , cm
−1
): ν=(C–H) 2963 (m), (C N) 1603
(m ), (C–O) 1184 (m), (CH
2
) 750 (d); MALDI-TOF (m/z) 691.3
[Cu(L
5
)+H]
+
, 1386.6 [Cu
2
(L
5
)
2
+H]
+
.μ
eff
= 1.8 B.M. By slow
e apo a ion o he mo he liquo du ing he syn hesis, b own
c ys als sui able o X- ay diff ac ion s udies we e ob ained
[Cu
2
(L
5
)
2
]·2CH
3
CN 13*.
[Zn
2
(L
1
)
2
] 14. Yellow solid. Yield: 0.071 g (59%); m.p.: >
300 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
70
H
72
N
4
O
4
Zn
2
) C, 72.2; N, 4.8; H, 6.2; expe imen al C, 70.1;
N, 4.5; H, 6.6; IR (cm
−1
)ν: 3435 s (O–H); 2959 m (C–H); 1618 s
(C N); 1263 m (C–O); 833 m (CH
2
); MALDI-TOF (m/z): 581.9
[Zn(L
1
)−H]
+
, 1165.3 [Zn
2
(L
1
)
2
+H]
+
, 1745.4 [Zn
3
(L
1
)
3
+H]
+
;
1
H-NMR (400 MHz, ace one-d
6
)δ/ppm: 8.63 (s
b
, 2H, H
2
), 7.50
(s
b
, 2H, H
A
), 7.39 (s
b
, 2H, H
A
), 6.94 (s
b
, 8H, H
A
), 6.84 (s
b
, 2H,
H
A
), 3.87 (s, H
8
), 1.32 (s
b
, 18H, H
9
). Rec ys alliza ion in a
mix u e o dichlo ome hane : me hanol (1 : 1) yielded yellow
p isms sui able o X- ay diff ac ion s udies
[Zn
2
(L
1
)
2
]·2.8CH
3
OH 14*.
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[Zn
2
(L
2
)
2
] 15. Yellow solid. Yield: 0.065 g (58%); m.p.: >
300 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
70
H
72
N
4
O
4
Zn
2
) C, 72.2; N, 4.8; H, 6.2; expe imen al C, 69.1;
N, 5.0; H, 6.0; IR (cm
−1
)ν: 2955 w (C–H); 1614 w (C N); 1292
w (C–O); 752 w (CH
2
); MALDI-TOF (m/z): 581.9 [Zn(L
2
)−H]
+
,
1165.3 [Zn
2
(L
2
)
2
+H]
+
, 1745.4 [Zn
3
(L
2
)
3
+H]
+
;
1
H-NMR
(400 MHz, ace one-d
6
)δ/ppm: 8.59 (s, 2H, H
2
), 7.42 (m, H
A
),
7.28 (d, 2H, H
A
), 6.94 (s, 8H, H
5
+H
6
), 6.63 ( , 2H, H
7
), 3.87 (s,
H
8
), 1.48 (s, 18H, H
9
).
[Zn
2
(L
3
)
2
] 16. Yellow solid. Yield: 0.071 g (72%); m.p.:
270 °C; E
= 0.5 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
112
N
4
O
8
Zn
2
) C, 70.7; N, 3.8; H, 7.7; expe imen al C, 68.6;
N, 3.6; H, 7.3; IR (cm
−1
)ν: 3442 m (O–H); 2958 m (C–H); 1616
s(C N); 1253 m (C–O); 789 w (CH
2
); MALDI-TOF (m/z): 1389.0
[Zn
2
(L
3
)
2
+H]
+
;
1
H-NMR (400 MHz, ace one-d
6
)δ/ppm: 8.60 (s,
2H, H
2
), 7.56 (s
a
, 2H, H
3
), 7.26 (s
a
, 2H, H
4
), 6.94 (s
a
, 8H, H
A
),
3.87 (s, H
5
), 1.50 (s, 18H, H
6
), 1.33 (s, 18H, H
7
).
[Zn
2
(L
4
)
2
] 17. Yellow solid. Yield: 0.060 g (54%); m.p.:
265 °C; E
= 0.6 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
104
N
4
O
4
Zn
2
) C, 74.4; N, 4.0; H, 7.5; expe imen al C, 73.1;
N, 3.9; H, 7.3; IR (cm
−1
)ν: 2963 s (C–H); 1622 s. (C N);
1260 m (C–O); 833 w (CH
2
); MALDI-TOF (m/z): 1389.6 [Zn
2
(L
4
)
2
+H]
+
;
1
H-NMR (400 MHz, ace one-d
6
)δ/ppm: 8.25 (s, 2H, H
2
),
7.61–6.66 (m, 10H, H
A
), 3.99 (s, H
7
), 2.53 (c, 8H, H
8
), 1.27 (m,
18H, H
9
), 0.77 ( , 12H, H
10
).
[Zn
2
(L
5
)
2
]·H
2
O 18. Yellow solid. Yield: 0.052 g (46%); m.p.:
225 °C; E
= 0.7 mol F
−1
; elemen al analysis: % heo e ical
(C
86
H
106
N
4
O
5
Zn
2
) C, 73.4; N, 4.0; H, 7.6; expe imen al C, 73.1;
N, 3.8; H, 7.4; IR (cm
−1
)ν: 3442 m (O–H); 2965 s (C–H); 1607
s. (C N); 1180 m (C–O); 750 m (CH
2
); MALDI-TOF (m/z):
1388.6 [Zn
2
(L
5
)
2
+H]
+
;
1
H-NMR (400 MHz, ace one-d
6
)δ/ppm:
8.22 (s, 2H, H
2
), 7.46–7.36 (m, H
A
), 7.20 (d, H
A
), 7.15–7.13 (m,
H
A
), 6.69 (s
a
,H
A
), 6.55 ( , 2H, H
6
), 4.01 (s, H
7
), 2.54 (c, H
8
),
1.44 (s, H
9
), 0.84 ( , H
10
). By slow e apo a ion o he mo he
liquo du ing he syn hesis, b own c ys als sui able o X- ay
diff ac ion s udies we e ob ained [Zn
2
(L
5
)
2
]·2CH
3
CN 18*.
C ys allog aphic da a collec ion
C ys allog aphic da a o ligands H
2
L
4
4* and H
2
L
5
5* and
compounds 7*,8*,11*,13*,14* and 18* we e collec ed a
100 K on a B uke D8 VENTURE diff ac ome e equipped wi h
a CCD de ec o , using a MoK(α) g aphi e monoch oma o (λ=
0.71073 Å). The da a we e ea ed using APPEX3 2018.7-2 so -
wa e o all compounds, excep o complex 8* and 11*, which
we e ea ed using APPEX2 (B uke AXS). In all cases, an
abso p ion co ec ion (SADABS)
42
was applied o he measu ed
e lec ions. The H
2
L
5
s uc u e was sol ed using SHELXT 2014/
5,
43
while he emaining s uc u es we e sol ed wi h
SHELXT2018/2.2. All s uc u es we e e ined using
SHELXL2018/3,
44
wi h he excep ion o he 11* s uc u e,
which was e ined using SHELXL2016/6.
43
Hyd ogen a oms
we e included in he model a geome ically calcula ed and
e ined posi ions. The images included in his chap e we e
p epa ed using Me cu y.
45
CCDC 2321087–2321094†con ain
he supplemen a y c ys allog aphic da a o he compounds.
Resul s and discussion
Schiffbase ligands H
2
L
n
The amily o Schiffbase ligands named H
2
L
n
(n=1–5, Fig. 1)
is po en ially dianionic wi h wo biden a e [NO] domains sep-
a a ed by a semi- igid a oma ic space . The ligands we e ully
cha ac e ized using a wide a ie y o echniques, as de ailed in
he Expe imen al sec ion and in Fig. S1–S3 and Tables S1 and
S2, (ESI).†
The s udy o he ligand c ys al s uc u es is ele an since i
allows us o explo e he con o ma ional changes ha should
be unde gone o coo dina e o he me al ions. P e ious s udies
showed ha he p esence o a la ge space de e mined ha
each o he [NO] linke domains o he ligand coo dina ed o
diffe en me al ions, gi ing ise o dinuclea helicoidal o
meso-helicoidal s uc u es.
46
Quali y c ys als alid o X- ay diff ac ion s udies o ligands
H
2
L
4
4* (Fig. 2) and H
2
L
5
5* (Fig. 3) we e ob ained by slow
e apo a ion o he e hanol mo he liquo s du ing he syn-
hesis. Due o he simila i y o hei s uc u es, bo h will be
discussed oge he below.
The s uc u es show disc e e molecules c ys allizing in he
iclinic P1
ˉsys em. In bo h ligands he wo b anches exhibi
an Econ igu a ion wi h espec o he imine bonds and a syn-
ype con o ma ion, wi h espec o he space , wi h he wo
ligand b anches o ien ed owa d he same side. This con o -
ma ion is achie ed by he es ablishmen o s ong in a-
molecula hyd ogen bonds
47
in ol ing he imine ni ogen o
each ligand b anch and he phenol g oup (H
2
L
4
4*:O2–
H20⋯N2 2.574 Å, O1–H10⋯N1 2.615 Å and H
2
L
5
5*:O2–
H20⋯N1 2.586 Å, O1–H10⋯N2 2.565 Å). These in e ac ions
a e diffe en in he wo ligands due o he opposi e o ien a ion
adop ed by he phenol ing as a consequence o he posi ion
o he e -bu yl g oup (o ho o pa a). In he case o an o ho
Fig. 2 S ick ep esen a ion o he ligand H
2
L
4
4* showing he syn
configu a ion o i s b anches and he in amolecula hyd ogen bonds.
Fig. 3 S ick ep esen a ion o he ligand H
2
L
5
5* showing he syn
configu a ion o i s b anches and he in amolecula hyd ogen bonds.
Dal on T ansac ions Pape
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subs i u ion a o a ion a ound he C N bond is equi ed o
a oid un a ou able s e ic hind ance. The imine and phenol
dis ances a e in he usual ange ound in Schiffbase
ligands.
48,49
Assembly o nickel(II), coppe (II) and zinc(II) complexes
The nex s ep was he p epa a ion o he nickel, coppe and
zinc de i ed complexes wi h he ligands o he se ies H
2
L
n
.I
is well known ha me al ions would ha e hei own coo dina-
i e p e e ences and diffe en affini ies o dono a oms, so he
use o me al ions wi h diffe en elec onic con igu a ions
could lead o dis inc me allosup amolecula s uc u es.
The Cu
2+
me al ion is a d
9
sys em ha could exhibi
diffe en coo dina ion geome ies: squa e-plana o e ahed al
( ou -coo dina e), squa e py amidal o igonal bipy amidal
( i e-coo dina e) o oc ahed al (six-coo dina e). I is impo an
o men ion ha he Cu(II) complexes de i ed om he ligands
H
2
L
1
and H
2
L
2
we e p e iously epo ed by us.
41
Bo h com-
plexes we e ound o be simila e acoo dina ed helica es
[Cu
2
(L
1|2
)
2
]·xCH
3
CN showing a dis o ed e ahed al en i on-
men . In ha wo k we obse ed ha he posi ion o he bulky
-bu yl g oups in luenced he in e molecula Cu–Cu dis ance
in he ex ended s uc u es and hei magne ic beha iou .
Ou s udy was comple ed wi h Ni
2+
, whose elec onic con-
igu a ion is d
8
. The p e e en ial coo dina ion sphe es o Ni
2+
a e six-coo dina e (oc ahed al geome y)
19,50
o ou -coo dina e
complexes wi h plana -squa e i he ligand- ield is s ong.
51
Howe e , he e a e also some examples o e ahed al geome-
ies.
52
We ha e also chosen he so e acid Zn
2+
ion, a d
10
sys em whose geome ical p e e ences a e mo e a iable: oc a-
hed al (six-coo dina e),
53
pen acoo dina e wi h a squa e-based
py amidal geome y,
54,55
o he mos common ype, he e a-
hed al geome y ( ou -coo dina e).
16,54
The neu al nickel, coppe and zinc complexes de i ed om
he Schiffbase ligand se ies H
2
L
n
we e p epa ed using an
elec ochemical me hodology.
41
The isola ed complexes a e
powde y solids s able o ligh and ai . Bo h analy ical and spec-
oscopic da a allow us o p opose dinuclea s oichiome y
[M
2
(L
n
)
2
] o he complexes, wi h he ligands being bound o
he me al ions in hei dianionic [L
n
]
2−
o m. The IR spec a o
he complexes exhibi some shi ing in he ν(C N) and ν(C–O)
bands, hus indica ing ha he ligand coo dina es o he me al
ion ia he imine ni ogen and phenolic oxygen a oms. The
dinuclea na u e o hese complexes was addi ionally con-
i med by MALDI-TOF (+) mass spec ome y expe imen s as
peaks co esponding o he dinuclea agmen s [M
2
(L
n
)
2
+H]
+
we e obse ed (Fig. S4–S8†).
X- ay diff ac ion s udies
The X- ay diff ac ion echnique allowed us o analyse whe he
he numbe and posi ion o he bulky g oups o he ligands
and he na u e and coo dina i e p e e ences o he me al ion
in luence he inal a chi ec u e o he complexes. Slow e apo -
a ion o he mo he liquo s du ing he syn hesis o 7,11,13
and 18, and ec ys alliza ion in dichlo ome hane (solid 8)o
dichlo ome hane : me hanol (solid 14) allowed us o ob ain
alid c ys als o X- ay diff ac ion s udies.
All he s uc u es show ou -coo dina e dinuclea neu al
helica e- ype a chi ec u e (Fig. 4) o med by wo s ands o he
dianionic ligand [L
n
]
2−
, which c oss-coo dina e a ound he wo
M(II) ions [M = Ni, Cu, and Zn].
Speci ically, he s uc u es e ealed he o ma ion o dinuc-
lea neu al helica es [Ni
2
(L
2
)
2
]·CH
3
CN 7* (Fig. 5),
[Ni
2
(L
3
)
2
]·2CH
2
Cl
2
8* (Fig. 6), [Cu
2
(L
3
)
2
]·2CH
3
CN 11* (Fig. 7),
[Cu
2
(L
5
)
2
]·3CH
3
CN 13* (Fig. 8), [Zn
2
(L
1
)
2
]·2.8CH
3
OH 14*
(Fig. 9) and [Zn
2
(L
5
)
2
]·2CH
3
CN 18* (Fig. 10). Tables S3–S8†
summa ize he mos ele an dis ances and angles.
The six c ys al s uc u es a e simila so, in o de o a oid
epe i i e desc ip ions, we will only desc ibe in de ail he zinc
complex [Zn
2
(L
1
)
2
]·2.8CH
3
OH 14* (Fig. 9), highligh ing only
some s uc u al ac s ha could be a ibu ed o he subs i-
u ion in he emaining complexes.
The molecula s uc u e o 14* (Fig. 9) shows a non-cen o-
symme ic dinuclea neu al Zn
2+
complex. The wo H
2
L
1
ligands a e helically a anged a ound he wo Zn
2+
ions, so
hese me al cen es ha e he same absolu e con igu a ion. The
wo enan iome s a e p esen in he c ys al cell as a acema e.
The Schiffbase ligands ac in such a way ha each o hei
biden a e [NO] b anches coo dina e o a diffe en me al ion
Fig. 4 Spacefill ep esen a ion o he [Ni
2
(L
2
)
2
]·CH
3
CN 7* complex,
showing he helicoidal s uc u e common o all he complexes s udied
by X- ay diff ac ion.
Fig. 5 C ys al s uc u e o he nickel(II) helica e [Ni
2
(L
2
)
2
]·CH
3
CN 7*.
Sol en molecules and hyd ogen a oms ha e been omi ed o cla i y.
Pape Dal on T ansac ions
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gi ing ise o a dis o ed e ahed al geome y [≠109.5
0
]. The
O–M–N bond angles clea ly show he dis o ion o he e a-
hed al geome y (Table S7†). The main bond dis ances Zn–O
and Zn–N a e in he expec ed anges o complexes de i ed
om Schiffbase ligands wi h phenol g oups
56
wi h he Zn–O
dis ance being sligh ly sho e han Zn–N dis ance (Table S7†).
The in e me allic dis ance Zn⋯·Zn (11.639 Å) is simila o he
dis ance be ween he zinc ions in dinuclea helicoidal com-
pounds and does no dese e u he commen s.
56
On he o he hand, hyd ogen bonds a e es ablished
be ween he O3 and O4 phenolic oxygens o he helica e
ligands and wo me hanol molecules. In line wi h his, one o
he sol en molecules o ms a hyd ogen bond wi h an adjacen
me hanol molecule [O6–H6⋯O3 2.74 Å, O5–H5⋯O4 2.76 Å
and O6–H6⋯O7 2.74 Å] (Fig. S9†). Addi ionally, he exis ence
o eigh a oma ic ings in each helica e makes i necessa y o
explo e a oma ic π–πo CH⋯·πs acking in e ac ions. Thus,
he e a e weak π–πin e ac ions be ween he a oma ic ings o
he wo ligands ha con ibu e o he s abiliza ion o he heli-
coidal s uc u e [ he dis ance be ween cen oids: 4.48 Å and
4.63 Å] (Fig. S9†).
In he case o he c ys al la ice o [Zn
2
(L
1
)
2
]·2.8CH
3
OH 14*
(Fig. 11), in e molecula π–πin e ac ions a e obse ed be ween
he a oma ic ings o he space o adjacen helica es (a cen-
oid–cen oid dis ance o 3.95 Å), wi h hese in e ac ions
being s onge han he in amolecula ones (cen oid o cen-
oid dis ances: 4.2 and 4.6 Å).
57
Addi ionally, hese in e -
Fig. 7 C ys al s uc u e o he coppe (II) helica e [Cu
2
(L
3
)
2
]·2CH
3
CN 11*.
Sol en molecules and hyd ogen a oms ha e been omi ed o cla i y.
Fig. 8 C ys al s uc u e o he coppe (II) helica e [Cu
2
(L
5
)
2
]·3CH
3
CN
13*. Sol en molecules and hyd ogen a oms ha e been omi ed o
cla i y.
Fig. 10 C ys al s uc u e o he zinc(II) helica e [Zn
2
(L
5
)
2
]·2CH
3
CN 18*.
Sol en molecules and hyd ogen a oms ha e been omi ed o cla i y.
Fig. 6 C ys al s uc u e o he nickel(II) helica e [Ni
2
(L
3
)
2
]·2CH
2
Cl
2
8*.
Sol en molecules and hyd ogen a oms ha e been omi ed o cla i y.
Fig. 9 C ys al s uc u e o he zinc(II) helica e [Zn
2
(L
1
)
2
]·2.8CH
3
OH 14*.
Sol en molecules and hyd ogen a oms ha e been omi ed o cla i y.
Dal on T ansac ions Pape
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ac ions a e obse ed be ween one o he phenyl ings o he
space and he a oma ic ing o a linke domain (cen oid–cen-
oid dis ances o 3.59 and 3.44 Å).
In addi ion, CH⋯πin e ac ions be ween he a oma ic ing
o one o he ligand b anches and one o he e -bu yl subs i-
uen s o he adjacen helica e can be obse ed in he c ys al-
line packing o [Zn
2
(L
1
)
2
]·2.8CH
3
OH 14*, (Fig. S10†).
I should be no ed ha he six helicoidal s uc u es s udied
exhibi simila packing pa e ns o he 14* helica e, excep in
he case o he [Zn
2
(L
5
)
2
]·2CH
3
CN 18* helica e (Fig. 10), whe e
he s acking dis ances a e much longe .
Addi ionally, as can be seen in Fig. S11–S14†, hecomplexes
wi h e -bu yl g oups in he o ho posi ion o he phenol g oups
(7*,8*,11*,13*,and18*) exhibi hyd ogen bonds be ween he
CH
3
o he e -bu yl g oups and he phenolic oxygens.
Addi ionally, he c ys al s uc u e de i ed om he H
2
L
5
ligand
unc ionalized wi h e hyl g oups on he space exhibi s CH⋯π
in e ac ions be ween he e hyl g oups and he a oma ic ings o
he adjacen ligand space (Fig. S13 and S14†).
The ob ainmen o dinuclea helica es in all hese cases
shows ha he posi ion and/o he numbe o bulky g oups in
he ligands does no affec he ype o s uc u e isola ed, bu i
does affec he mic os uc u e o he helica es.
Ou esul s demons a ed ha he unc ionaliza ion o he
ligands wi h e hyl subs i uen s in he space (H
2
L4 and H
2
L
5
)
gene a es new in amolecula non-co alen CH⋯πin e ac ions
be ween he CH
2
o he e hyl g oups and he a oma ic ings o
he space o he adjacen ligand, which could addi ionally
a ou he helicoidal con o ma ion in he compounds.
Fu he mo e, he esul s demons a e ha he use o me al
ions wi h diffe en na u es (Cu
2+
,Ni
2+
and Zn
2+
) does no
affec he a angemen o he ligands a ound he me al
cen es. In all cases, helica e a chi ec u es we e achie ed, indi-
ca ing ha he a ia ion om Cu
2+
o Ni
2+
o a simila -sized
me al ion Zn
2+
, wi h no ligand- ield s abiliza ion ene gy, does
no affec he mac os uc u e o he compounds.
I we check he coo dina ion ke nels in he wo pai s o Ni
(II), Cu(II) and Zn(II) helica es we can see ha he Zn(II) heli-
ca es show a dis o ed e ahed al geome y in bo h cases (14*:
τZn1 = 0.85, τZn2 = 0.76, Table S7;†18*:τZn1 = 0.82,
Table S8†), and he me al ions in he Cu(II) helica es exhibi
in e media e τ
4
alues (11*:τCu1 = 0.43; 13*:τCu1 = 0.58,
τCu2 = 0.42).
58
Howe e , in he case o he Ni(II) helica e
[Ni
2
(L
2
)
2
]·CH
3
CN 7*, his exhibi s a dis o ed e ahed al geo-
me y a ound one o he nickel ions (Ni1) and a dis o ed
squa e-plana geome y a ound he second me al ion
(Table S3,†τNi1 = 0.76; τNi2 = 0.30) whe eas a dis o ed
squa e-plana en i onmen a ound bo h Ni
2+
me al ions was
ound in he case o [Ni
2
(L
3
)
2
]·2CH
2
Cl
2
8* (Table S4,†τNi1 =
0.28). In his case, he p esence o one (H
2
L
2
) o wo e -bu yl
g oups (H
2
L
3
) in he pe iphe y o he ligands does affec he
mic os uc u e o he nickel complexes ob ained.
1
H NMR s udies
Hannon and co-wo ke s
37
ha e a wide expe ience in he p epa-
a ion o helica e/mesoca e complexes wi h bisphenylme hane
de i ed ligands. In hese s udies, hey s a ed ha a ca e ul ana-
lysis o he
1
H NMR spec um in he alipha ic egion may be
indica i e o he exclusi e p esence o he mesoca e and heli-
ca e con o ma ions (Fig. 12) in solu ion, o he coexis ence o
bo h o ms.
In his sense, hey concluded ha i he ligand space is no
unc ionalised wi h alkyl subs i uen s in he phenyl ings, a
mix u e o helica e–mesoca e is shown, whe eas when adding
bulky g oups (e hyl and me hyl) o he ligand space , he
mesoca e a chi ec u e is p ecluded. This could be explained by
he ligand wis ing induced by he alkyl g oups and also by he
es ablishmen o new CH⋯πin e molecula in e ac ions
which a ou he helica e- ype a chi ec u e (dinuclea and i-
nuclea wi h Me, and dinuclea wi h E ).
Wha happens i we also in oduce bulky g oups in he
ligand b anches? T ying o go a s ep u he we s udied he ali-
pha ic me hylene egion o he se ies o he zinc complexes
14,15,16,17 and 18 in o de o explo e whe he he helical
s uc u e obse ed in he solid s a e is main ained in solu ion.
The zinc complex 14 [Zn
2
(L
1
)
2
] de i ed om he ligand wi h
he pa a e -bu yl g oup posi ion shows a cen al single signal
co esponding o he helica e- ype con o ma ion and ou
addi ional sa elli e signals ha could co espond o mesoca e
species (Fig. 13), hus con i ming ha bo h species co-exis in
solu ion. The e o e, he p esence o an ex e nal e -bu yl
g oup oge he wi h he non-subs i u ed space does no ip
Fig. 12 Helica e (le ) and mesoca e ( igh ) con o ma ions.
Fig. 11 In e molecula π-s acking in e ac ions in he c ys al la ice o
he complex [Zn
2
(L
1
)
2
]·2.8CH
3
OH 14*.
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he balance owa ds he mesoca e o helica e species ha co-
exis in solu ion.
In con as , he zinc complexes 15,16,17 and 18 show one
single , hus indica ing he exclusi e p esence o he helica e
species in solu ion only (Fig. 14). These expe imen al obse -
a ions indica e ha in he absence o bulky g oups in he
space , he equilib ium o helica e/mesoca e is displaced o
helica e a e unc ionaliza ion o he ex e nal ings wi h a e
bu yl g oup in he o ho posi ion o he phenol.
Likewise, in he case o he zinc complexes de i ed om
he ligands unc ionalised wi h he e hyl g oups in he space
ings, [Zn
2
(L
4
)
2
]17 and [Zn
2
(L
5
)
2
]18, he helica e- ype s uc-
u e is also con i med by he appea ance o ou signals co es-
ponding o dias e eo opic e hyl CH
2
p o ons (Fig. 15).
Thus, wo o he signals appea a low ield wi h espec o
he ee ligand and he emaining wo signals appea a high
Fig. 14
1
H NMR spec um o he CH
2
g oup alipha ic egion o
[Zn
2
(L
5
)
2
]18 (400 MHz, . ., ace one-d
6
).
Fig. 13
1
H NMR spec um o he CH
2
g oup alipha ic egion o
[Zn
2
(L
1
)
2
]14 (400 MHz, . ., ace one-d
6
).
Fig. 15
1
H NMR spec um o he alipha ic egion o [Zn
2
(L
5
)
2
]18 (400 MHz, . ., ace one-d
6
).
Table 1 Summa y o he deduced helix o he meso-helical na u e o
he Zn(II) compounds 14–18 om
1
H NMR spec oscopy
Complex Species Space ings Salicyloyl ings
14 Hel/Mes
15 Hel
16 Hel
17 Hel
18 Hel
Hel = Helica e; Mes = Mesoca e.
Dal on T ansac ions Pape
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ield. In addi ion, wo signals co esponding o he CH
3
o he
e hyl g oups a e obse ed, one o which appea s unshielded
wi h espec o he ee ligand due o he exis ence o
π-s acking in e ac ions along he c ys al la ice.
37
The e o e, he esul s o hese NMR s udies allow us o
deduce ha he d i ing ac o de e mining he exis ence in
solu ion o helica e o a helica e–mesoca e mix u e does no
eside exclusi ely in he space , as he in oduc ion o an o ho
bulky g oup on he ex e nal su ace o he helica e displaces
he equilib ium o helica e–mesoca e owa ds he helica e
(Fig. 14 and Table 1). Howe e , he in oduc ion o e hyl
g oups in he ligand space s ill s e ically a ou s he o -
ma ion o helica es, independen ly o he p esence o bulky
g oups in he pe iphe y o he complex (Fig. 15 and Table 1).
Conclusions
Dinuclea nickel(II), coppe (II) and zinc(II) complexes we e iso-
la ed using an elec ochemical me hodology om a amily o
i e Schiffbase ligands de i ed om bisphenylme hane and
unc ionalized wi h bulky e -bu yl g oups. The in oduc ion
o bulky g oups on bo h he space and ligand b anches
a ou s he o ma ion o dinuclea helica es. F om he six
c ys al s uc u es epo ed in his wo k, we can conclude ha
small modi ica ions o he ligands do no affec he mac o-
s uc u e o he compounds, all o hem being helica es.
Howe e , he mic os uc u e, e.g., he me al ion en i onmen ,
could be al e ed in some cases. Besides, he in oduc ion o
e hyl subs i uen s in he space p o ides new in amolecula
in e ac ions ha s abilize he helica e- ype a chi ec u e o he
compounds. Fu he mo e, he
1
H NMR s udy e eals ha he
p esence o he e -bu yl g oup in he o ho posi ion wi h
espec o he OH g oup is essen ial o he main enance o
he helica e con o ma ion in solu ion.
Au ho con ibu ions
The manusc ip was w i en h ough he con ibu ions o all
au ho s. All au ho s ha e gi en app o al o he inal e sion o
he manusc ip .
Conflic s o in e es
The e a e no con lic s o decla e.
Acknowledgemen s
This esea ch was unded by he ollowing FEDER co- unded
g an s: Conselle ía de Cul u a, Educación e O denación
Uni e si a ia, Xun a de Galicia GRC GI-1584 (ED431C 2023/
02), Me alBIONe wo k (ED431D2017/01), and Minis e io de
Ciencia e Inno ación, P ojec PID2021-127531NB-I00 (AEI/
10.13039/501100011033/FEDER/UE).
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Pape Dal on T ansac ions
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