Crowding out: Ligand modifications and their structure directing effects on brucite-like {Mx(μ3-OH)y} (M = Co(ii), Ni(ii)) core growth within polymetallic cages

Article abstract of DOI:10.1039/c8dt04229b

Previous employment of the ligands 2-methoxy-6-[(methylimino)methyl]phenol (L₁H) and 2-methoxy-6-[(phenylimino)methyl]phenol (L₂H) has resulted in the self-assembly of pseudo metallocalix[6]arene complexes of general formulae: [M

Full text of DOI:10.1039/c8dt04229b

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Crowding out: ligand modifications and their
structure directing effects on brucite-like
{Mx(μ3-OH)y} (M = Co(II), Ni(II)) core growth
within polymetallic cages†
Cite this: DOI: 10.1039/c8dt04229b
Mari E. Slater-Parry,a James P. Durrant, a Joshua M. Howells,a Mateusz B. Pitak,b
c
Peter N. Horton,b Wim T. Klooster,b Simon J. Coles, b Helen M. O’Connor,
a
Euan K. Brechin, c Anne-Laure Barrad and Leigh F. Jones
*
Previous employment of the ligands 2-methoxy-6-[(methylimino)methyl]phenol (L1H) and 2-methoxy-6-
[(phenylimino)methyl]phenol (L2H) has resulted in the self-assembly of pseudo metallocalix[6]arene com-
plexes of general formulae: [M7(μ3-OH)6(Lx)6](NO3)y (M = Ni(II), x = 1, y = 2 (1) and Co(II/III), x = 2, y = 3 (2)).
Extrapolating upon this work, we report the coordination chemistry of ligands 2-methoxy-6-{[(2-
methoxyphenyl)imino]methyl}phenol (L3H), 2-[(benzylimino)methyl]-6-methoxyphenol (L4H), 2-[(benzyl-
amino)methyl]-6-methoxyphenol (L5H) and 2-[(benzylamino)methyl]-4-bromo-6-methoxyphenol (L6H),
whose structures are modifications of ligands L1–2H. These ligands are employed in the synthesis and
characterisation of the dimetallic complex [Ni(II)2(L3)3(H2O)](NO3)·2H2O·3MeOH (3); the monometallic
complexes [Ni(II)(L4)2] (4) and [Co(III)(L4)3]·H2O·MeOH (5a); and the tetranuclear pseudo metallocalix[4]arene
complexes: [(NO3)⊂Co(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O (6), [(NO3)⊂Ni(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O (7)
and [Ni(II)4(μ3-OH)2(L6)4(NO3)2]·MeCN (8). The tetrametallic ‘butterfly’ core topologies in 6–8 are
discussed with respect to their structural and topological relationship with their heptanuclear [M7]
(M = Co(II), Ni(II)) pseudo metallocalix[6]arene ancestors (1 and 2).
Received 23rd October 2018,
Accepted 20th December 2018
DOI: 10.1039/c8dt04229b
rsc.li/dalton
body-centred hexagonal arrays (Fig. 1), whereby each octa-
hedral metal centre is connected by µ3-bridging OH− ions.
Introduction
The ligands 2-methoxy-6-[(methylimino)methyl]phenol (L1H) Similar sheet-like {Mx(µ3-OH)y} topologies have been reported
and
2-methoxy-6-[(phenylimino)methyl]phenol
(L2H; for a variety of transition metal cages of numerous nucleari-
Scheme 1) have previously been employed for the formation of ties, such as [M4] (M = Mn,2 Fe,3 Co,4 Ni5 and Zn6), [Ni5],7
the pseudo metallocalix[6]arene complexes [M7(μ3-OH)6(Lx)6] [Ni6],8 [M7] (M = Mn,9,13 Fe,10 Co,1c,11 Ni1a,b,12 and Zn1b,13),
(NO3)y (M = Ni(II), x = 1, y = 2 (1) and Co(II/III) x = 2, y = 3 (2)) [Mn10],14 [Co12],15 [Fe17],16 [Ni18],17 [M19] (M = Mn,18 Fe16) and
(Fig. 1).1 Each of these compounds exhibit a double-bowl topo- [Co28].15
logy and in the solid state form molecular cavities that are able
‡
Moreover, the observation of such planar ‘Single Layer
to act as hosts for guests such as small organics and counter Double Hydroxide’ (SLDH) topologies is not surprising when
anions.1 The heptanuclear inorganic cores in 1 and 2 are best we consider their similarities to the sheet-like brucite (‘Layered
described as comprising six edge-sharing triangular {M3(μ3- Double Hydroxides’; LDH) topologies observed in minerals
19
OH)} (M = Ni(II)/Co(II/III)) units, resulting in planar sheet-like, such as the α- and β-polymorphs of Co(OH)2 and Ni(OH)2,20
as well as the familiar brucite structure of Mg(OH)2.
Interestingly, cobalt and nickel hydroxides hold significant
aSchool of Natural Sciences, Bangor University, Bangor, Wales, LL57 2DG, UK.
interest in the field of water splitting catalysis. More specifi-
E-mail: leigh.jones@bangor.ac.uk; Tel: +44(0)1248-38-2391
bUK National Crystallographic Service, Chemistry, Faculty of Natural and
Environmental Sciences, University of Southampton, England SO17 1BJ, UK
cEaStCHEM School of Chemistry, David Brewster Road, University of Edinburgh,
Edinburgh, Scotland, EH9 3FJ, UK
cally, in 2008 Nocera and co-workers devised an efficient Co
(OH)2/phosphate (Co-OEC) oxygen-evolving catalyst produced
dLNCMI-CNRS, Universite Grenoble-Alpes, Avenue des Martyrs, Grenoble, France
†Electronic supplementary information (ESI) available. CCDC 1874840–1874846.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c8dt04229b
‡CSD searches were limited to planar Mx(μ3-OH)y double hydroxide layered
sheets and any planar complexes with Mx(μ3-OR)y cores (where OR = aryloxide or
alkoxide) were omitted.
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electron transfer kinetics of their cobalt-phosphate (Co-OEC)
water splitting catalyst.23
Our aim in this work was to strategically modify the shape
and electronic nature of the [M7] metallocalix[6]arene-directing
ligands L1–2H (Scheme 1) and monitor any changes in resul-
tant complex nuclearity and topology (e.g. {Mx(OH)y} sheet
size) upon subsequent Co(II) and Ni(II) complexation. To this
end, we report here the successful synthesis of the novel
ligands 2-methoxy-6-{[(2-methoxyphenyl)imino]methyl}phenol
(L3H), 2-[(benzylimino)methyl]-6-methoxyphenol (L4H), 2-
[(benzylamino)methyl]-6-methoxyphenol (L5H) and 2-[(benzyl-
amino)methyl]-4-bromo-6-methoxyphenol (L6H) (Scheme 1).
We also present the first examples of transition metal
complexation of ligands L3–6H in the form of complexes:
[Ni(II)(L3)(H2O)](NO3)·2H2O·3MeOH (3), [Ni(II)(L4)2] (4) and
[Co(III)(L4)3]·H2O·MeOH (5a), along with the tetranuclear
compounds: [(NO3)⊂Co(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O (6),
[(NO3)⊂Ni(II)4(μ3-OH)2(L5)4](NO3)·H2O (7) and [Ni(II)4-
(μ3-OH)2(L6)4(NO3)2]· MeCN (8). Crystallographic data for com-
plexes 3–8 are given in Tables S1 and S2.†
Scheme 1 ChemDraw representation of the ligands 2-methoxy-6-
[(methylimino)methyl]phenol (L1H; a) and 2-methoxy-6-[(phenylimino)
methyl]phenol (in b when R = H; L2H), used previously in the formation
of [M7] (M = Co(II/III), Ni(II), Zn(II)) pseudo metallocalix[6]arenes (see main
text for details). ChemDraw representations of the ligands 2-methoxy-
6-{[(2-methoxyphenyl)imino]methyl}phenol (in b when R = OMe; L3H),
2-[(benzylimino)methyl]-6-methoxyphenol (L4H; c), 2-[(benzylamino)
methyl]-6-methoxyphenol (in d where R = H; L5H) and 2-[(benzylamino)
methyl]-4-bromo-6-methoxyphenol (in d where R = Br; L6H).
Results and discussion
We began our investigations by looking at the complexation of
2-methoxy-6-(((2-methoxyphenyl)imino)methyl)phenol (L3H)
and Ni(II), which gives rise to the dimetallic complex
[Ni(II)2(L3)3(H2O)](NO3)·2H2O·3MeOH (3) and crystallises in the
monoclinic P21/n space group (Fig. 2). The two Ni(II) ions (Ni1
and Ni2) are bridged by phenolic oxygens (O1 and O5) of two
−
L3 ligands exhibiting η1:η2:η1:η1 µ- and η2:η1 µ-bridging
motifs, to give the angles 101.86° (Ni1–O1–Ni2) and 96.10°
Fig. 1 Schematic depicting the coordination chemistry of ligands L1H
and L2H upon reaction with Ni(II) and Co(II/III) ions. Single crystal X-ray
data was used to produce the [Ni7] (1) and [Co(III)Co(II)6] (2) figures.1
Colour code (used throughout this work): green (Ni), purple (Co), red
−
(O), blue (N), grey (C). Hydrogen atoms omitted for clarity and NO3
counter anions represented in space-fill mode.
through electrode surface deposition that has been shown to
exhibit topological similarities with the sheet-like structures in
(for instance) β-Co(OH)2 and many Mx(µ3-OH)y transition
metal cages (vide supra).21 It should also be noted here that
Ni(OH)2-borate thin film electrocatalysts have recently been
produced by the same research group.22 Interestingly, and to
emphasise these similarities, the triflate analogues of our pre-
viously described homo- and heterovalent pseudo metallocalix
[6]arenes [Co(II)7(µ3-OH)6(L1)6](NO3)2 and [(NO3)⊂Co(II)6Co(III)
(µ3-OH)6(L2)6](NO3)2 (2),1c respectively, were employed by
Fig. 2 Crystal structure of [Ni(II)(L3)(H2O)](NO3)·2H2O·3MeOH (3) as
viewed off-set and parallel to the Ni–Ophen–Ni plane. Hydrogen atoms
Nocera and co-workers as models towards investigating the and counter anions have been omitted for clarity.
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−
(Ni1–O5–Ni2), respectively. The third L3 unit sits at approxi-
mately right angles to the Ni1–O1phen–Ni2 plane and chelates
(tridentate) at the Ni2 centre to complete its distorted octa-
hedral geometry. The η2:η1 µ-bridging ligand in 3 has a much
−
more contorted shape than the remaining two near planar L3
ligands, with its two aromatic rings twisted away from one
another through rotation of the Nimine–Carom (N2–C22) single
bond to give a torsion angle (C23–N2–C22–C21) of 118.67°
(Fig. 2). Interestingly, this twisting is also observed in all six
−
L2 ligands used in constructing the pseudo metallocalix[6]
arene [(NO3)⊂Co(II)6Co(III)(µ3-OH)6(L2)6](NO3)2 (2) (Fig. 1). The
introduction of the OMe group in L3H, along with the fact that
the remaining two L3− ligands in 3 remain almost planar plays
a decisive role in the resultant dimeric topology. The final
coordination site at Ni2 is taken by a single terminally bonded
H2O ligand (Ni1–O10 = 2.072(4) Å), whose protons partake in
intramolecular H-bonding interactions with juxtaposed ligand
Ophen (O10(H10A)⋯O8 = 2.02 Å) and OMe (O10(H10A)⋯O9 =
−
2.47 Å) oxygen donor atoms. The NO3 counter anions
Fig. 3 Crystal structure of [Ni(II)(L4)2] (4) as viewed perpendicular (a–c)
and parallel (d) to the equatorial plane. Majority of hydrogen atoms have
been omitted for clarity. Dashed lines are intramolecular H-bonds at dis-
tances: O1⋯H7B’(C7’) = 2.19 Å and O2⋯H5’(C5’) = 2.34 Å. The additional
‘ symbol in the atom labels indicates that these atoms are at equivalent
positions (1 − x, 1 − y, 1 − z).
(N4, O18–O20) in 3 act as molecular mortar in connecting the
individual {Ni(II)2} units through extensive H-bonding with
−
aromatic protons of neighbouring bridging L3 ligands
(C40(H40)⋯O18 = 2.58 Å, C36(H36)⋯O19 = 2.54 Å and
C34(H34)⋯O20 = 2.42 Å). These dimeric units in 3 arrange in
the common brickwork motif along the bc plane of the unit
cell, with the 2D sheets packing in superimposable rows along
the a unit cell direction (Fig. S4†).
The monometallic complex [Ni(II)(L4)2] (4) crystallises from agonal crystals which were found to be the complex [Co(II)7
ˉ
methanol in the triclinic P1 space group (Z = 1) after reaction (OMe)6(L4)6](NO3)2·0.5H2O·4MeOH (5b); whose structure is
of Ni(NO3)2·6H2O and L4H in the presence of NaOH. The core akin to the pseudo metallocalix[6]arenes of 1 and 2 (cf. Fig. 1
in 4 comprises a single Ni(II) centre (labelled Ni1 and lying on and Fig. 5). Interestingly, from
a synthetic view point,
an inversion centre) whose near perfect square planar geome- the deliberate oxidation of Co(II) using hydrogen peroxide
try (N1–Ni1–N1 = 180°; O1–Ni1–N1′ = 87.46° and O1–Ni1–N1 = efficiently promotes the sole crystallisation of [Co(III)(L4)3]·
92.54°) is templated by two chelating L4− ligands through their H2O·MeOH (5a), over the formation of [Co(II)7(OMe)6(L4)6]
Ophen (O1) and imine N atoms (N1) (Fig. 3). This topology is (NO3)2·0.5H2O·4MeOH (5b) (see Experimental section for
vastly different to the heptanuclear cores in 1–2 (Fig. 1 cf. details). However, despite numerous attempts using various
Fig. 3) and is attributed to the introduced methylene bridge reducing agents, our efforts in producing only 5b were
between the imine and lower rim phenyl group in L4H. Upon unsuccessful.
chelation the OMe and benzyl imine groups in the symmetry
The single Co(III) centre in 5a (Bond Valence Sum (BVS)
−
related L4 moieties in 4 significantly deviate from the plane score = 3.22; Table S3†) is enveloped by three singly deproto-
−
of their phenolic rings, resulting in N1–C7–C6 and C13–O2– nated L4 ligands that chelate the metal centre through their
C15 angles of 111.11° and 112.45°, respectively (Fig. 3). Nimine and Ophen atoms (bond length range: 1.882(2)–1.961(2)
Numerous intermolecular interactions stabilise and direct the Å; Fig. 4). As observed in [Ni(II)(L4)2] (4), the L4− phenyl groups
−
topology in 4. More specifically, the two symmetry equivalent L4
in 5a diverge from the plane of their phenolic rings to produce
ligands are involved in intramolecular H-bonding as shown as angles of 111.83° (N1–C9–C10), 113.60° (N2–C39–C40) and
dashed lines in Fig. 3 (O1⋯H7B′(C7′) = 2.19 Å, O2⋯(H5′(C5′) = 112.80° (N3–C24–C25), along with torsion angles of 87.77°
2.34 Å and the long contact: O2⋯H7B′(C7′) = 2.91 Å). (C8–N1–C9–C10), 46.26° (C38–N2–C39–C40) and 97.47° (C23–
Intermolecular H-bonding interactions between O atoms N3–C24–C25) (Fig. 4).
(O2 of the non-bonded –OMe group on L4−) and neighbouring
[Co(II)7(OMe)6(L4)6](NO3)2·0.5H2O·4MeOH (5b) crystallises
aromatic protons (H5) effectively link the {Ni1} units into in the monoclinic P21/c space group and there are two ‘half’
superimposable H-bonded rows along the c direction of the {Co(II)7} units in the asymmetric unit (labelled Co1–Co4 and
unit cell (O2⋯(H4′)C4′ = 2.65 Å) (Fig. S5†).
Co5–Co8, respectively; centres Co1 and Co5 lie on inversion
Reaction of L4H with Co(II)(NO3)2·6H2O gives rise to the co- centres). The inorganic core in 5b exhibits a planar body
crystallisation of the monometallic complex [Co(III) centred hexagonal array of Co(II) ions linked together with a
(L4)3]·H2O·MeOH (5a; purple needle-like crystals and predomi- combination of μ3-bridging −OMe and −OH ions (50 : 50 occu-
nant product), along with a much smaller quantity of red hex- pancy; see Crystallography section for details). The Co(II) oxi-
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(5b). The individual [Co(II)7] units arrange in superimposable
rows along the a unit cell direction and pack along the bc
plane in the space-efficient brickwork motif (Fig. S7†).
We speculated that by reducing the imine (CvN) bond in
L4H (to give ligand L5H) we could manipulate ligand shape
and allow multiple metal centre coordination and growth of a
more complex inorganic core. This proved to be the case when
Co(II)/Ni(II) metalation of L5H (and L6H) gave rise to the tetra-
nuclear
complexes:
[(NO3)⊂Co(II)4(μ3-OH)2(L5)4(H2O)2]
(NO3)·H2O (6), [(NO3)⊂Ni(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O (7)
and [Ni(II)4(μ3-OH)2(L6)4(NO3)2]·MeCN (8). The analogous com-
ˉ
plexes 6 and 7 crystallise in the triclinic P1 space group (Z = 1)
and each exhibits a butterfly-like [M4O2] core whereby the body
and wing-tip M(II) (M = Co, Ni) centres are connected by two
μ3-OH− ions (O1(H1) and s.e.). Inversion centres lie at the mid-
point of the Co2⋯Co2 and Ni2⋯Ni2 vertices in 6 and 7,
respectively. The Co(II) oxidation states in 6 were confirmed
using BVS calculations and charge balancing considerations
(Table S3†). In both 6 and 7, two of the four singly deproto-
Fig. 4 Crystal structure of [Co(III)(L4)3]·MeOH·H2O (5a). Hydrogen
atoms have been omitted for clarity.
nated L5 ligands exhibit η1:η2:η1 μ-bonding modes while the
−
remaining two demonstrate η1:η2 μ-bridging arrays whereby
their methoxy functional groups forge long contacts with
nearby Co(II) and Ni(II) centres (Co1⋯O3 = 2.58 Å and Ni1⋯O5
= 2.31 Å), respectively. The remaining metal centres are six
coordinate distorted octahedral sites (Fig. 6). Terminal water
ligands complete the coordination sphere at Co1 at a distance
of 2.02 Å (Co1–O6 and s.e.) and Ni1 at a distance of 2.04 Å
(Ni1–O6 and s.e.). The protons of these terminal waters also
−
participate in H-bonding with a neighbouring NO3 counter
anion lying at the periphery of the structures in 6 and 7. The
second nitrate ion in both analogues is situated above the
Fig. 5 Crystal
structure
observed
in
[Co(II)7(OMe)6(L4)6]
(NO3)2·H2O·3MeOH (5b) as viewed perpendicular (a) and parallel (b) to
the {Co(II)7} plane. Hydrogen atoms have been omitted for clarity.
dation states were assigned using BVS and charge balancing
considerations. The outer Co(II) ions (Co2–Co4 and Co6–Co8,
respectively) are further connected through η1:η2:η1 μ-bridging
−
L4 ligands that lie alternately above and below the planar
{Co(II)7} core in 5b, thus forming the double-bowl pseudo
metallocalix[6]arene as observed in our previous studies (com-
plexes 1 and 2; Fig. 1). As with complexes 4 and 5a, the phenyl
ligand groups in 5b twist away from their corresponding Ophen
aromatic rings. Interestingly, the torsion angles produced in
5b vary much more widely when compared with complexes 4
and 5a, with values including 5.69° (C23–N2–C24–C25), 21.56°
(C56–N4–C57–C58) and 89.19° (C86–N6–C87–C89). Thus the
ligand conformational flexibility in L4H, governed by free
rotation along the Nimine–CH2 bond, allows the feasible con-
Fig. 6 (Left) Crystal structures of [(NO3)⊂Co(II)4(μ3-OH)2(L5)4(H2O)2]
(NO3)·H2O (6; a) and [(NO3)⊂Ni(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O (7; c).
(Right) Space-fill representations of the disordered NO3 guests within
the molecular cavities formed by two {Co(II)4} metallocalix[4]arene units
in 6 (b) and three {Ni(II)4} units in 7 (d). Hydrogen atoms and waters of
−
struction of both low (4 and 5a) and high nuclearity complexes crystallisation have been omitted for clarity in all cases.
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Fig. 8 The “butterfly” inorganic {Co(II)4(μ3-OH)2}6+ and {Ni(II)4(μ3-
OH)2}6+ cores in 6 (a), 7 and 8 (b). The heptanuclear {Co(III)Co(II)6(μ3-
OH)6}9+ and {Ni(II)6(μ3-OH)6}8+ cores as observed in the original pseudo
metallocalix[6]arene complexes [(NO3)⊂Co(III)Co(II)6(μ3-OH)6(L2)6](NO3)2
(2, c) and [Ni(II)7(μ3-OH)6(L1)6](NO3)2 (1, d).1 Colour code: Co (purple),
Ni (green), O (red).
Fig. 7 Crystal structures of 6 and 7 as viewed perpendicular to the
−
{Co(II)4} plane (top) and {Ni(II)4} plane (bottom). Disordered NO3
counter anions are represented in space-fill mode. Hydrogen atoms and
waters of crystallisation have been omitted for clarity.
methoxyphenol ligand (L2H in Scheme 1). This overcrowding
and resultant nuclearity change is caused by the introduction
of the (distorted) trigonal pyramidal secondary amine group
along with the additional aliphatic carbon atom. The result is
planar {M(II)4} (M = Co, Ni) cores and are disordered over two a much more distorted ligand shape and although a planar
sites (50 : 50 occupation and related by a centre of inversion; {Mx(μ3-OH)y} (M = Co, Ni) core is achieved, its size has been
see crystallographic section for details) (Fig. 7).
limited accordingly.
The topologies in complexes 6 and 7 also share other struc-
The tetranuclear butterfly {Ni(II)4} core in 7 is once again
tural similarities to that of the heptanuclear metallocalix[6] observed upon construction of the complex [Ni(II)4(μ3-
arene [(NO3)⊂Co(III)Co(II)6(μ3-OH)6(L2)6](NO3)2 (2). More speci- OH)2(L6)4(NO3)2]·MeCN (8) (Fig. 9). Complex 8 was obtained
−
fically and as with the L2 ligands in 2 (Scheme 1b), the four from the reaction of Ni(NO3)2·6H2O and L6H (Br analogue of
−
singly deprotonated L5 ligands in 6 and 7 sit alternately L5H) in the presence of a suitable base (NaOH) using either
above and below their planar {M(II)4(μ3-OH)2}6+ (M = Co, Ni) MeOH or MeCN as solvent (see Experimental section for
ˉ
cores. This gives rise to pseudo metallocalix[4]arene topologies details). Complex 8 crystallises in the triclinic P1 space group
in both analogues, where one of the two previously described and comprises two half {Ni(II)4} units in the asymmetric unit,
−
NO3 counter anions occupies the molecular cavity formed by each of which exhibit an independent inversion centre located
two superimposed {M(II)4} (M = Co, Ni) units as they stack at the midpoint of the Ni2⋯Ni2 and Ni4⋯Ni4 vectors, respect-
along the a axis of the unit cells in both 6 and 7 (Fig. 6b and ively. Furthermore, a single MeCN solvent of crystallisation sits
d). These nitrate anions (labelled N3 and O7–9 and both cases) on a general position within the asymmetric unit in 8. Akin to
are held in position through H-bonding interactions with 6 and 7, the butterfly cores in 8 are connected by two μ3-brid-
protons of nearby μ3-bridging OH− ions (O1) and ligated ging OH− ions (O5 and s.e.; O105 and s.e.) and a combination
−
waters (O6) at distances of O1(H1)⋯O9 = 1.83 Å and O6(H6B) of η1:η2:η1 μ- and η1:η2 μ-bridging L6 ligands (Fig. 8 and 9).
−
⋯O7 = 1.82 Å in 6 and O1(H1)⋯O8 = 1.84 Å and O6(H6A)⋯O7 However, complex 8 does differ from 6 and 7 in that the NO3
= 1.85 Å in 7.
counter anions do not sit within the molecular cavities in 8,
Note that the planar inorganic cores in 6 and 7 may also be instead occupying the remaining ligation spots at the distorted
described as comprising half of a {M(II)7(μ3-OH)6}8+ (M = Co, octahedral metal centres (Ni1 and Ni3) through chelation. This
Ni) unit as exhibited in 1 (or {Co(III)Co(II)6(μ3-OH)6}9+ in 2), and significant difference gives rise to a different packing topology
highlighted in Fig. 8. Indeed, we can assume from these find- in 8 (cf. 6 and 7). Here, the individual {Ni(II)4} units are
ings that the employment of ligand L5H has sterically hindered connected to one another through H-bonding interactions
core growth, leading to the formation of the tetrametallic cores between their μ3-OH− protons and Br− groups of neighbouring
in 6 and 7 as opposed to the larger heptametallic core cages (e.g. O105(H105)⋯Br2 = 2.63 Å and O5(H5)⋯Br4 =
observed (for instance in 2) when using the 2-iminophenyl-6- 2.64 Å; Fig. S10†).
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Fig. 9 Crystal structure of one of the two [Ni(II)4(μ3-OH)2(L6)4](NO3)2
units observed in the a.s.u. of 8 as viewed perpendicular (top) and paral-
lel (bottom) to the {Ni4} plane. The solvents of crystallisation and the
majority of hydrogen atoms have been omitted for clarity. Dashed lines
represent intramolecular H-bonds at distances (Å): N1(H1)⋯O3’ = 2.192
and N2(H2)⋯O7’ = 2.229.
Intramolecular H-bonds are observed between the tertiary
amine protons and chelating NO3− counter anions (i.e. N2(H2)
⋯O7 = 2.162 Å and N102(H102)⋯O107 = 2.11 Å) and oxygen
atoms belonging to OMe groups on each L6− unit (N1(H1)⋯O3
= 2.14 Å and N101(H101)⋯O103 = 2.16 Å). Intermolecular
−
interactions also arise between aromatic L6 protons (i.e. H3
−
and H127) and chelating NO3 anions (i.e. O8) at distances of
(Å): 2.48 (C3(H3)⋯O8) and 2.60 (C127(H127)⋯O8). Weak inter-
molecular H-bonding also occurs between the protons of aro-
−
matic rings (i.e. H11) and OMe groups (H16A) of the L6
ligands with juxtaposed Br atoms also belonging to nearby
ligand units (C16(H16A)⋯Br1 = 3.03 Å and C11(H11)⋯Br1 =
2.98 Å). The individual {Ni(II)4} units in 8 pack in a brickwork
manner as shown in Fig. S11.†
Fig. 10 Top: Plot of χMT versus T for complexes 3, 6 and 8. Middle:
Reduced magnetisation data for complex 3. Bottom: Reduced magneti-
sation data for complex 8. The inset shows the exchange coupling
scheme used to fit the data; Ĥ = −2J1(Ŝ1·Ŝ2 + Ŝ2·Ŝ3 + Ŝ3·Ŝ4 + Ŝ4·Ŝ1) −
2J2(Ŝ2·Ŝ4). The solid lines represent a simultaneous best-fit of the experi-
mental susceptibility and magnetisation data as described in the main
text.
Magnetic studies
The dc (direct current) molar magnetic susceptibility, χM, of
polycrystalline samples of 3, 6 and 8 was measured in an
applied magnetic field, B, of 0.1 T, in the T = 2–300 K tempera-
ture range. The experimental results are shown in Fig. 10 in
the form of the χMT products, where χ = M/B, and M is the (2.40 cm3 mol−1 K) assuming gNi = 2.2, where gNi is the g-factor
magnetisation of the sample.
of Ni(II). Upon cooling, the value of χMT increases reaching a
For 3, the χMT product of 2.10 cm3 mol−1 K at T = 280 K is maximum of 2.93 cm3 mol−1 K at 13 K, before decreasing to
close to that expected for two non-interacting Ni(II) ions 1.76 cm3 mol−1 K at 2 K. This increase is indicative of weak
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intramolecular ferromagnetic exchange interactions between in 3 and that previously reported for Ni(II) ions in a distorted
the phenoxo-bridged Ni(II) ions, with the sharp decrease in the octahedral environment with similar donor atoms (Fig. 9).33
value of χMT at low temperature attributed to antiferro-
For 6 the value of χMT at 300 K is 8.84 cm3 mol−1
K
magnetic intermolecular interactions between neighbouring (Fig. 10), a value close to that expected for four non-interacting
dimers and/or zero-field splitting (zfs) effects. The suscepti- Co(II) ions (S = 3/2, gCo = 2.2, χMT = 9.07 cm3 mol−1 K). Upon
bility and magnetisation data (Fig. 10, middle) were fitted sim- cooling the value of χMT decreases, reaching a minimum of
ultaneously using the program PHI and a spin-Hamiltonian of 8.14 cm3 mol−1 K at 28 K, before increasing to a maximum
the form:24,25
value of 9.18 cm3 mol−1 K at 6 K, and then decreasing to
6.72 cm3 mol−1 K at 2 K. This behaviour is commonly observed
for complexes containing octahedral Co(II) ions: the initial
decrease in χMT is due to the orbital contribution of the Co(II)
ions, the increase to the maximum at T = 6 K due to the pres-
ence of some ferromagnetic interactions, with the decrease
below this temperature attributed to antiferromagnetic
n
n
X
X
ˆ
ˆ
ˆ
~
BgiSi
ˆ
H ¼ ꢀ 2
SiJijSj þ μB
i;j>i
i¼1
ð1Þ
n
X
ꢀ
ꢁ
2
ˆ
þ
D Sz;i ꢀ SiðSi þ 1Þ=3
i¼1
where Ŝ is a spin operator, J is the pairwise isotropic magnetic exchange interactions and/or zfs effects.34–37 Magnetisation
exchange interaction between constitutive N(II) centres, μB is data (Fig. S15†) is consistent with the presence of competing
~
the Bohr magneton, B the external static magnetic field, g the F/AF exchange and the presence of significant anisotropy. First
isotropic g-factor of Ni(II) (fixed to g = 2.2; see EPR section order spin orbit coupling effects associated with the octa-
below), the indices i and j refer to the two Ni ions (n = 2 for 3), hedral Co(II) ion preclude any simple quantitative analysis of
D is the second-order single-ion uniaxial anisotropy parameter the data. No out-of-phase ac signals were observed for 6, even
of Ni(II) and Ŝz,i2 is the Cartesian component of spin operator Ŝ in the presence of an applied dc field.
of the ith Ni(II) centre along the z-direction of the local coordi-
nate frame. The best-fit parameters obtained were 2J =
7.70 cm−1 and DNi = 7.42 cm−1 (Fig. S13† shows the corres-
ponding Zeeman energy diagram). These values are close to
that obtained from simulations of the EPR spectra (vide infra).
The fit of the susceptibility data can be improved marginally
through the addition of an intermolecular interaction, zJ′ =
−0.09 cm−1. Examples of ferromagnetically coupled phenoxo-
bridged Ni(II) dimers are rather rare,26,27 with most being
either heteroleptic,28,29 or homoleptic and possessing Ni–O–Ni
bridging angles less than 99°.30 Note that the asymmetric Ni–
O–Ni bridging angles in 3 are of 96.11° and 101.77°.
The susceptibility data for 6 and 8 are also given in Fig. 10.
The χMT value of 8 at 300 K is 4.85 cm3 mol−1 K which is in
excellent agreement with the expected high temperature value
for four S = 1 ions (gNi = 2.2, χMT = 4.84 cm3 mol−1 K). Upon
cooling, the value of χMT remains essentially constant until
approximately 60 K where it begins to decrease rapidly reach-
ing a minimum of 0.150 cm3 mol−1 K at 2 K. This behaviour is
indicative of weak antiferromagnetic exchange between the
metal ions, and/or zfs effects. The susceptibility and magneti-
sation data were fit simultaneously as described above using
the exchange coupling scheme depicted in the inset of Fig. 10
MF/HF EPR spectroscopy
In order to refine the values obtained from the fitting of the
magnetic measurements for complex 3, multi-frequency/high-
field EPR was employed on a powdered and pelletised sample.
Spectra were recorded at several frequencies ranging from 95
to 662 GHz and in the temperature range 5–25 K (Fig. 11 and
Fig. S16 and S17†). For all frequencies, only a few signals were
observed whose intensities change with temperature. At 331
and 442 GHz, besides the strong forbidden transition (at ∼2.55
and ∼3.88 T, respectively), small signals at higher fields (9 to
10 T at 331.2 GHz and 12 to 14 T at 442 GHz) were also
recorded. These permitted signals are attributed to the acces-
sing of successive energy levels from the lowest level group
(which would belong to the S = 2 multiplet in the strong coup-
ling limit) for the y orientation. For the frequency ranges
95–110 GHz and 220–255 GHz, we observe close to zero
signals, which are indicative of the existence of gaps in the
spin energy diagram, of approximately 3.3 and 7.3 cm−1
,
respectively. The structure of the spectra does not allow for a
simple analysis, as expected from the results of the magnetic
measurements, which suggest that |D1|, |D2| and |2J| are com-
parable (for comparative purposes see Fig. S18† for simu-
lations using a Giant spin description with a simple S = 2
model). Simulations of the spectra were thus performed in the
frame of the following Hamiltonian for a coupled Ni(II) dimer:
(bottom). The best-fit parameters obtained were 2J1
=
−5.68 cm−1, 2J2 = 35.70 cm−1 and DNi = 12.43 cm−1 (see
Fig. S14† for the corresponding Zeeman energy diagram for 8).
The coupling constants obtained are in line with those
derived for previously published, structurally analogous
[Ni(II)4] systems; the dominant structural parameter being
the average Ni–O–Ni angles in the butterfly.30 Ferromagnetic
exchange interactions would be expected for Ni–O–Ni angles
2
ˆ
ˆ
ˆ
ˆ
ˆ
H ¼ μBgB ꢁ ðS1 þ S2Þ ꢀ 2JS1 ꢁ S2 þ D1ðS1z ꢀ SðS þ 1Þ=3Þ
2
2
2
2
2
ˆ
ˆ
ˆ
ˆ
ˆ
þ E1ðS1x ꢀ S1y Þ þ D2ðS2z ꢀ SðS þ 1Þ=3Þ þ E2ðS2x ꢀ S2y
Þ
ð2Þ
<99° (Ni2–O–Ni4, ∼95°), with antiferromagnetic exchange where µB is the Bohr magneton, g is the single ion g-value, J is
interactions at Ni–O–Ni angles >99° (Ni1–O–Ni4 and Ni2–O– the magnetic exchange parameter, S is the spin quantum
Ni3, ∼99°; Ni1–O–Ni2 and Ni3–O–Ni4, ∼98–105°).31,32 The DNi number, and D and E are the ZFS axial and rhombic para-
value extracted from the fits is in the same range as that found meters, respectively. In order to avoid over parameterization,
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spectra clearly shows that the magnetic anisotropy of 3 is
rather rhombic (Ei/Di = 0.25) for both Ni(II) ions.
Conclusions
We have described the synthesis and characterisation of a
family ligands including 2-methoxy-6-{[(2-methoxyphenyl)
imino]methyl}phenol (L3H), 2-[(benzylimino)methyl]-6-meth-
oxyphenol (L4H), 2-[(benzylamino)methyl]-6-methoxyphenol
(L5H) and 2-[(benzylamino)methyl]-4-bromo-6-methoxyphenol
(L6H). Their subsequent complexation with Co(II) and Ni(II)
ions gave rise to the dimetallic complex [Ni(II)2(L3)3(H2O)]
(NO3)·2H2O·3MeOH (3); the monometallic [Ni(II)(L4)2] (4) and
[Co(III)(L4)3]·H2O·MeOH (5a) species along with the tetranuc-
lear siblings [(NO3)⊂Co(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O (6),
[(NO3)⊂Ni(II)4(μ3-OH)2(L5)4](NO3)·H2O (7) and [Ni(II)4(μ3-
OH)2(L6)4(NO3)2]·MeCN (8). Complexes 3–8 represent the first
examples of transition metal coordination of ligands L3–6H.
The inorganic planar cores in 6–8 ({M(II)4(μ3-OH)2}6+ (M = Co
and Ni)) may be viewed as fragments of the {M(II)7(μ3-OH)6}8+
(M = Co, Ni) and {Co(III)Co(II)6(μ3-OH)6}9+ cores observed
within our previously reported pseudo metallocalix[6]arenes,1
which were constructed using similar Schiff base ligands (L1H
and L2H in Scheme 1). Indeed, we have demonstrated here
that the combination of M(II)(NO3)2·6H2O (M = Co(II) and
Ni(II)) and NaOH promotes double hydroxide layer brucite-like
sheet formation whose growth/size is limited by the “cookie
cutter” Schiff base ligands employed in this work. Moreover,
we have highlighted that careful ligand selection can be used
Fig. 11 Experimental (top) and simulated (bottom) MF/HF-EPR spectra
obtained on
a polycrystalline pelletised sample of [Ni(II)2(L3)3(H2O)]
(NO3)·3MeOH·H2O (3) at frequencies of 331.2 and 441.6 GHz and temp-
eratures of 25 K (red line), 15 K (blue line) and 5 K (black line).
the description of the system is simplified significantly, due to to introduce more synthetic control in the production of
the reduced number of (independent) transitions detected in planar μ3-OH bridged Ni(II) and Co(II) polymetallic cages.
the experimental spectra. The assumption of the collinearity of
SQUID measurements on [Ni(II)2(L3)3(H2O)](NO3)·3MeOH·
both ZFS tensors is the most drastic. In addition, both g values H2O (3) reveal weak ferromagnetic exchange interactions
were taken as identical and the anisotropy of the g factors neg- between the two Ni(II) ions; a simultaneous fit of the suscepti-
lected. These last approximations are expected to affect the cal- bility and magnetisation data affording 2J = 7.70 cm−1 and
culated spectra much less, due to the masking effect of the DNi = 7.42 cm−1, in agreement with simulations of the
ZFS terms over variations of the Zeeman effect. Simulations of EPR data. Complex 3 is therefore a rather rare example of
the experimental spectra, for which the resonance positions
a
ferromagnetically coupled diphenoxo-bridged [Ni(II)2]
are rather well reproduced (Fig. 11), were obtained for the fol- complex, especially given the unusual Ni–O–Ni bridging
lowing set of parameters: D1 = 10(1) cm−1, E1 = 2.5(6) cm−1, D2 angles. Even if it has not been possible to obtain a fully
= 9(1) cm−1, E2 = 2.25(65) cm−1, g1 = g2 = g = 2.2(2) and 2J = 7.5 reliable set of parameters from the MF/HF EPR spectra of (3),
(1.5) cm−1. The Di (i = 1, 2) and 2J values obtained compare the analysis of the spectra does confirm the ferromagnetic
well with those obtained from the magnetic studies. The Ei character of the coupling. Indeed, the forbidden transition
values reported have been chosen, among the possible sets of evolves with a geff value close to 8 and more generally the
values, so that they lead to the same Ei/Di ratio. Indeed, the spectra exhibit similarities with the S = 2 spectra obtained for
three or four lowest energy levels of the system behave very the strong coupling limit of the single ion parameters. This is
similarly to changes on Ei if E1 + E2 is constant. One may because the signals observed come from the lowest energy
notice a discrepancy in the temperature behaviour of the levels, corresponding to the S = 2 levels in the strong coupling
signals associated to the y orientation at 331 and 442 GHz. limit. However, changing the J value modifies the resonance
This can be corrected through a change on Ei (i = 1, 2) values, positions.
at the expense of worsening the simulation of the low field
The best fit of the susceptibility and magnetisation data of
signals (observed at 110 and 220–255 GHz frequencies). [Ni(II)4(μ3-OH)2(L6)4(NO3)2]·MeCN (8), assuming a butterfly-like
Despite our best efforts, it has not been possible to find para- structure incorporating two different exchange interactions
meters fully satisfying all the identified signals, most prob- (wing–body and body–body) provided 2J1 = −5.68 cm−1, 2J2 =
ably as a result of the (over) simplified model used. Finally, the 35.70 cm−1 and DNi = 12.43 cm−1, values entirely consistent
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with previously published data on complexes with a similar All structures were refined and completed in-house by full
diamond-like arrangement of the metal ions. The tetrameric matrix least squares using SHELXL-1439 and refined with
[(NO3)⊂Co(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O
(6)
cluster OSCAIL packages.41
demonstrates competing anti- and ferromagnetic exchange
along with significant anisoptropy.
Collection and refinement details
Due to modelling difficulties, the residual electron densities
representing solvent entities within the solvent accessible
voids (total volume = 971 Å3) in 3 were removed from the struc-
Experimental
ture using the SQUEEZE program.42 The NO3 counter anion
−
Infra-red spectra for complexes 6–8 were recorded on a
PerkinElmer FT-IR Spectrum 100 spectrometer, while spectra
for 3–5 were obtained from a newly acquired Bruker Alpha
FT-IR Platinum ATR spectrometer (School of Natural Sciences,
Bangor University). Elemental analysis was carried out at OEA
Laboratories Ltd (Kelly Bray, Cornwall, UK). MALDI TOF-MS
measurements on complexes 6 and 8 were carried out at the
EPSRC UK National Mass Spectrometry Facility at Swansea
University. Powder XRD was carried out using a PANalytical
required the DFIX, DANG and FLAT restraints and remained
isotropic. All protons in 3 were assigned to calculated posi-
tions. All non hydrogen atoms were modelled as anisotropic in
4, while all hydrogen atoms were assigned to calculated posi-
tions. The SQUEEZE program was also employed in the treat-
ment of 5a, giving a total void volume of 551 Å3 and resulting
in the removal of 55 electrons from the structure. This electron
density has been assigned as representing 1 × MeOH and 1 ×
H2O solvent molecule per [Co1] molecule (Z = 2).
The μ3-bridging −OMe ions in 5b were best modelled as
sharing 50 : 50 occupancy with bridging −OH moieties. At two
of these positions, half occupancy waters of crystallisation
(labelled O50 and s.e.) lie above these bridging −OMe/−OH
ions and are presumed to partake in H-bonding with the −OH
moieties at distances of 2.84 Å (O18⋯O50). DFIX restraints
were employed on the O–CH3 distances of all bridging –OMe
functional groups in 5b. All non-hydrogen atoms in 5b apart
from the bridging −OMe carbons (labelled C46–C48 and
C94–96) were refined anisotropically and all protons were
assigned to calculated positions. Due to modelling difficulties
`
Philips XPert 3040/60 diffractometer at 45 kV and 35 mA
between 5 and 60° 2θ using Ni-Filtered Cu–Kα1 radiation (λ =
1.5405 Å) at the School of Natural Sciences, Bangor University.
Variable-temperature, solid-state direct current (dc) and
alternating current (ac) magnetic susceptibility data down to
2 K were collected on a Quantum Design MPMS-XL SQUID
magnetometer and a Quantum Design PPMS magnetometer
fitted with an ac measurement system, respectively.
Diamagnetic corrections were applied to the observed para-
magnetic susceptibilities using Pascal’s constants. All
measured complexes were set in eicosane to avoid torqueing of
the crystallites. All magnetic samples were collected as single-
crystalline products and analysed using microanalysis and IR
measurements prior to their magnetic assessment. Phase
purity between cross-batches were validated using unit cell
checks and IR measurements.
−
the residual electron densities representing NO3 counter
anions and solvent entities within the solvent accessible voids
(total volume ∼1911 Å3; ∼77 electrons per cage) in 5b were
modelled using the SQUEEZE program to give the final
formula [Co(II)7(OMe)6(L4)6](NO3)2·0.5H2O·4MeOH.42
MF/HF-EPR measurements were performed on a multi-fre-
quency spectrometer operating in a double-pass configuration.
A 110 GHz frequency source (Virginia Diodes Inc.) alone or with
multipliers up to the 6th harmonic), as well as 95 GHz and
115 GHz Gunn oscillators (Radiometer Physics GmbH) together
with a quadrupler or a quintupler were used. The measurements
were done on powdered samples pressed into pellets in order to
limit torqueing effects. Calculated spectra were obtained with
the SIM program from H. Weihe (Univ. of Copenhagen).
All non-hydrogen atoms in complexes 6 and 7 were mod-
elled as anisotropic. Both the NO3 counter anions in 6 were
−
restrained using the DFIX command. The −OH proton (H1)
and the terminal water protons (H6A and H6B) in 6 were
assigned to calculated positions, while the corresponding water
protons in 7 (H6A and H6B) were located in the difference
map. All other protons were assigned to calculated positions.
In complexes 6 and 7, both nitrates were found to be dis-
ordered over two sites (one of which lies at a special position
while the other shares space with a water of crystallisation
(labelled O7A in 6 and O13 in 7). Both were modelled at half
Crystallography
All complexes were collected on an Rigaku AFC12 goniometer occupancy. The selected single crystal in 8 contains light green
equipped with an enhanced sensitivity (HG) Saturn724+ detec- hexagonal plates. Most crystals within the sample looked
tor mounted at the window of an FR-E+ Super Bright molyb- twinned and gave multicomponent diffraction patterns. A
denum rotating anode generator with HF Varimax optics small clean fragment was selected for collection. Large
(100 m focus) (CCDC numbers: 1874840–1874846†). The cell residual electron density peaks observed were attributed to
determination and data collection of all complexes were small twin domains within the crystal, which contributed to
carried out using the CrystalClear-SM Expert package (Rigaku, the observed diffraction pattern.
2012). Each data reduction, cell refinement and absorption
Preparation of complexes
correction were carried out using CrysAlisPro software (Rigaku
OD, 2015),38 while all structures were initially solved and All reactions were performed under aerobic conditions and all
refined using SHELXT and SHELXL-201439 within OLEX-2.40 reagents and solvents were used as purchased. Caution:
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Although no problems were encountered in this work, care
Synthesis of [(NO3)⊂Co(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O
should be taken when manipulating the potentially explosive (6). Co(NO3)2·6H2O (0.25 g, 0.86 mmol), L5H (0.21 g,
nitrate salts.
0.86 mmol) and NaOH (0.034 g, 0.86 mmol) were dissolved in
MeCN and the solution stirred at room temperature for
4 hours. X-ray quality crystals of 6 were obtained in 20% yield
Synthetic procedures
Synthesis of [Ni(II)2(L3)3(H2O)](NO3)·2H2O·3MeOH (3). upon filtration and subsequent slow evaporation of the
Ni(NO3)2·6H2O (0.25 g, 0.85 mmol), L3H (0.22 g, 0.85 mmol) mother liquor. Elemental analysis (%) calculated (found) for
and NaOH (0.034 g, 0.85 mmol) were dissolved in methanol 6·2H2O (C60H76N6O21Co4): C 49.60 (48.95), H 5.27 (4.97),
(30 cm3) and stirred for 4 hours. The resultant lime green solu- N 5.78 (6.28). FT-IR (cm−1): 3577 (m), 3502 (m), 3274 (m), 3208
tion was filtered and X-ray quality crystals of 3 were obtained (vb), 3022 (m), 2926 (m), 2855 (m), 1639 (w), 1602 (m), 1579
upon slow evaporation in 30% yield after 3 weeks. Elemental (m), 1481 (s), 1389 (s), 1359 (s), 1330 (s), 1296 (m), 1255 (m),
analysis (%) calculated (found) for 3 (C48H58N4O17Ni2): C 53.36 1234 (m), 1207 (m), 1087 (m), 1066 (m), 1040 (m), 1028 (m),
(53.40), H 5.41 (4.81), N 5.19 (5.37). FT-IR (cm−1): 3368 (vb), 1003 (m), 922 (s), 854 (s), 740 (s), 699 (s), 633 (m), 610 (m), 560
3056 (w), 2942 (w), 2834 (w), 1611 (s), 1588 (s), 1541 (m), 1493 (w), 515 (w), 458 (w), 432 (w). MALDI-TOF MS (in DBTC-MeCN
(s), 1467 (s), 1441 (s), 1384 (s), 1336 (s), 1297 (s), 1228 (s), 1192 matrix) (%, m/z): 301 (5, [Co(II)(L4)]+), 364 (81, [{[Co(II)(L4)]
(s), 1173 (s), 1118 (m), 1078 (m), 1046 (m), 1011 (m), 974 (m), (NO3) + H+}], 637 (12, [Co(II)4(μ3-OH)2(L4)4(H2O)2]2+), 664 (100,
870 (w), 850 (w), 828 (w), 785 (m), 742 (s), 638 (m), 587 (m), [Co(II)4(μ3-OH)2(L4)4(H2O)5]2+), 755 (42, [Co(II)4(μ3-OH)2(L5)4
527 (m), 474 (w), 440 (w), 425 (w).
(H2O)6(MeCN)4]2+), 966 (22, {[Co(II)4(μ3-OH)4(L5*)4(H2O)2] +
Synthesis of [Ni(II)(L4)2] (4). Ni(NO3)2·6H2O (0.25 g, H+}), 1027 (6, {[Co(II)4(μ3-OH)2(L5*)4(H2O)2](NO3)}+), 1055
0.85 mmol), L4H (0.20 g, 0.85 mmol) and NaOH (0.034 g, (25, {[Co(II)4(μ3-OH)2(L5*)4](NO3)2 + H+}). Note: L5* = L5−-C6H5
0.85 mmol) were dissolved in methanol (30 cm3) and stirred (loss of pendant Ph group).
for 4 hours. The resultant lime green solution was filtered and
Synthesis of [(NO3)⊂Ni(II)4(μ3-OH)2(L5)4(H2O)2](NO3)·H2O
X-ray quality crystals of 4 were obtained upon slow evaporation (7). Ni(NO3)2·6H2O (0.25 g, 0.86 mmol), L5H (0.21 g,
in 25% yield after 2 weeks. Elemental analysis (%) calculated 0.86 mmol) and NaOH (0.034 g, 0.86 mmol) were dissolved in
(found) for 4 (C30H28N2O4Ni1): C 66.82 (66.56), H 5.23 (4.98), MeCN and the solution stirred at room temperature for
N 5.20 (5.12). FT-IR (cm−1): 3464 (b), 3055 (w), 3020 (w), 2928 4 hours. X-ray quality crystals of 7 were obtained in 12% yield
(w), 2903 (w), 2852 (w), 2828 (w), 1836 (w), 1615 (s), 1551 (m), upon filtration and subsequent slow evaporation of the
1495 (m), 1471 (s), 1452 (s), 1434 (s), 1399 (m), 1332(m), 1319 (m), mother liquor after 2 weeks. Elemental analysis (%) calculated
1241 (s), 1164 (m), 1115 (w), 1094 (w), 1056 (m), 1031 (m), 984 (w), (found) for 7·H2O (C60H74N6O20Ni4): C 50.25 (50.65), H 5.20
957 (m), 914 (w), 874 (m), 858 (w), 791 (w), 762 (m), 737 (s), (5.15), N 5.86 (6.19). FT-IR (cm−1): 3576 (w), 3537 (w), 3478 (w),
699 (s), 656 (m), 602 (w), 524 (w), 490 (m), 447 (m), 417 (m).
3268 (w), 3187 (w/vb), 3019 (w), 2841 (w), 1599 (w), 1577 (w),
Synthesis of [Co(III)(L4)3]·H2O·MeOH (5a) and [Co(II)7(OMe)6 1478 (s), 1442 (m), 1384 (m), 1360 (m), 1322 (m), 1298 (s), 1256
(L4)6](NO3)2·0.5H2O·4MeOH (5b) co-crystals. Co(NO3)2·6H2O (m), 1229 (s), 1210 (m), 1168 (w), 1112 (w), 1085 (m), 1072 (w),
(0.25 g, 0.85 mmol), L4H (0.20 g, 0.85 mmol) and NaOH 1042 (w), 1024 (w), 1001 (m), 921 (w), 880 (m), 851 (w), 817 (w),
(0.034 g, 0.85 mmol) were dissolved in methanol (30 cm3) and 778 (w), 768 (w), 739 (s), 697 (s), 643 (w), 633 (w), 614 (m), 555
stirred for 4 hours. The resultant purple solution was filtered (w), 540 (w), 519 (w), 493 (w), 460 (w), 433 (w), 416 (w).
and X-ray quality crystals of 5a (purple) and 5b (red) were
obtained upon slow evaporation of the mother liquor after 3 Ni(NO3)2·6H2O (0.25 g, 0.86 mmol), L6H (0.28 g, 0.86 mmol) and
weeks. NaOH (0.0344 g, 0.86 mmol) were dissolved in MeCN and the
Synthesis of [Ni(II)4(μ3-OH)2(L6)4(NO3)2]·MeCN (8). Method A:
Sole synthesis of [Co(III)(L4)3]·H2O·MeOH (5a). Co(NO3)2· solution stirred at room temperature for 4 hours. X-ray quality
6H2O (0.25 g, 0.86 mmol) was dissolved in methanol (30 cm3) crystals of 8 were obtained in 15% yield upon filtration and sub-
along with one equivalent of hydrogen peroxide (1 cm3, sequent slow evaporation of the mother liquor after 3 weeks.
0.86 mmol). The resultant purple solution was then intro- Method B: Ni(NO3)2·6H2O (0.25 g, 0.86 mmol), L6H (0.28 g,
duced to L4H (0.20 g, 0.85 mmol) and NaOH (0.034 g, 0.86 mmol) and NaOH (0.0344 g, 0.86 mmol) were dissolved in
0.85 mmol). X-ray quality crystal of 5a were obtained upon MeOH and the solution stirred at room temperature for 4 hours.
slow evaporation in 25% yield after 2 weeks. Elemental ana- The precipitous solution was then evaporated to dryness and re-
lysis (%) calculated (found) for 5a·H2O (C46H48N3O8Co1): C dissolved in MeCN. X-ray quality crystals of 8 were obtained in
65.17 (65.15), H 5.94 (5.58), N 4.96 (5.00). FT-IR (cm−1): 3650 18% yield upon filtration and subsequent slow evaporation of
(w), 3503 (w), 3325 (w), 2986 (m), 2910 (m), 2821 (w), 2361 (w), the mother liquor. Elemental analysis (%) calculated (found) for
2344 (w), 2028 (w), 1869 (w), 1845 (w), 1802 (w), 1624 (s), 1609 8 (C60H62N6O16Br4Ni4): C 42.96 (43.06), H 3.73 (3.76), N 5.01
(s), 1595 (s), 1559 (m), 1544 (m), 1508 (s), 1492 (s), 1470 (s), (4.95). FT-IR (cm−1): 3616 (s), 3268 (s), 3085 (w), 3062 (w), 3028
1437 (m), 1412 (m), 1394 (m), 1342 (s), 1316 (s), 1242 (s), 1221 (w), 3004 (w), 2959 (w), 2937 (w), 2861 (w), 1567 (m), 1484 (s),
(s), 1193 (m), 1167 (m), 1109 (m), 1075 (m), 1049 (m), 1035 1442 (sh), 1358 (m), 1331 (m), 1300 (m), 1247 (m), 1233 (s), 1207
(m), 1026 (m), 966 (m), 953 (m), 904 (m), 858 (m), 767 (s), 756 (m), 1095 (m), 1052 (m), 1035 (m), 1019 (m), 1009 (m), 929 (m),
(m), 730 (m), 694(m), 638 (m), 624 (m), 600 (m), 575 (m), 541 883 (m), 864 (m), 809 (w), 779 (s), 746 (s), 700 (s), 659 (w), 620
(m), 497 (w), 483 (w), 450 (w), 434 (w), 424 (w).
(m), 570 (w), 553 (w), 504 (w), 479 (w), 422 (w). MALDI-TOF MS
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(in DBTC-MeCN matrix) (%, m/z): 795 (100, [Ni(II)4(μ3-
OH)2(L6)4(H2O)2]2+), 820 (12, [Ni(II)4(μ3-OH)2(L6)4(MeCN)2]2+),
1632 (30, {[Ni(II)4(μ3-OH)2(L6)4(H2O)] + (NO3)}+).
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Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
LFJ would like to thank the School of Natural Sciences at
Bangor University for their support (MSP, JD and JH). We
would like to thank the EPSRC UK National Crystallographic
Service (University of Southampton) and EPSRC UK National
Mass Spectrometry Facility at Swansea University for their data
collection. EKB thanks the EPSRC for funding.
Notes and references
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