Synthesis, Characterization, and Nanomaterials Generated from 6,6′-(((2-Hydroxyethyl)azanediyl)bis(methylene))bis(2,4-di- tert-butylphenol) Modified Group 4 Metal Alkoxides

Article abstract of DOI:10.1021/acs.inorgchem.8b01907

The impact on the morphology nanoceramic materials generated from group 4 metal alkoxides ([M(OR)₄]) and the same precursors modified by 6,6′-(((2-hydroxyethyl)azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) (referred to as H₃-

Full text of DOI:10.1021/acs.inorgchem.8b01907

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Synthesis, Characterization, and Nanomaterials Generated from
6,6′-(((2-Hydroxyethyl)azanediyl)bis(methylene))bis(2,4-di-tert-
butylphenol) Modified Group 4 Metal Alkoxides
Timothy J. Boyle,*,‡ Joshua Farrell,† Daniel T. Yonemoto,‡,# Jeremiah M. Sears,‡ Jessica M. Rimsza,§
Diana Perales,‡ Nelson S. Bell,‡ Roger E. Cramer,∥ LaRico J. Treadwell,‡ Peter Renehan,†
Casey J. Adams,‡,⊥ Michael T. Bender,‡,∇ and William Crowley†
‡Advanced Materials Laboratory, Sandia National Laboratories, 1001 University Boulevard, SE, Albuquerque, New Mexico 87106,
United States
†Department of Chemistry, College of the Holy Cross, Box C, 1 College Street, Worcester, Massachusetts 01610, United States
§Geochemistry Department, Sandia National Laboratories, PO Box 5800, MS 0754, Albuquerque, New Mexico 87185-0754, United
States
∥Department of Chemistry, University of Hawaii - Manoa, 2545 McCarthy Mall, Honolulu, Hawaii 96822-2275, United States
S
* Supporting Information
ABSTRACT: The impact on the morphology nanoceramic materials
generated from group 4 metal alkoxides ([M(OR)4]) and the same
precursors modified by 6,6′-(((2-hydroxyethyl)azanediyl)bis-
(methylene))bis(2,4-di-tert-butylphenol) (referred to as H3-AM-DBP2
(1)) was explored. The products isolated from the 1:1 stoichiometric
reaction of a series of [M(OR)4] where M = Ti, Zr, or Hf; OR =
OCH(CH3)2(OPri); OC(CH3)3(OBut); OCH2C(CH3)3(ONep) with H3-
AM-DBP2 proved, by single crystal X-ray diffraction, to be [(ONep)Ti-
(k4(O,O′,O′′,N)-AM-DBP2)] (2), [(OR)M(μ(O)-k3(O′,O′′,N)-AM-
DBP2)]2 [M = Zr: OR = OPri, 3·tol; OBut, 4·tol; ONep, 5·tol; M = Hf:
OR = OBut, 6·tol; ONep, 7·tol]. The product from each system led to a tetradentate AM-DBP2 ligand and retention of a parent
alkoxide ligand. For the monomeric Ti derivative (2), the metal was solved in a trigonal bipyramidal geometry, whereas for the
Zr (3−5) and Hf (6, 7) derivatives a symmetric dinuclear complex was formed where the ethoxide moiety of the AM-DBP2
ligand bridges to the other metal center, generating an octahedral geometry. High quality density functional theory level gas-
phase electronic structure calculations on compounds 2−7 using Gaussian 09 were used for meaningful time dependent density
functional theory calculations in the interpretation of the UV−vis absorbance spectral data on 2−7. Nanoparticles generated
from the solvothermal treatment of the ONep/AM-DBP2 modified compounds (2, 5, 7) in comparison to their parent
[M(ONep)4] were larger and had improved regularity and dispersion of the final ceramic nanomaterials.
dielectric (k) nanomaterials for DW printed materials using the
group 4 metal oxides (MO2 where M = Ti, Zr, Hf). This report
discusses the first step in production of high quality N-inks,
with the development of precursors that will generate tailored
morphological ceramic nanoparticles.
Metal alkoxides ([M(OR)4]) are one of the most widely
used precursors to ceramic materials; however, due to
uncontrolled hydrolysis and condensation pathways for the
standard monodentate ligands, irregular nanoparticles are often
generated.19−22 Polydentate ligands are frequently used to
control the structure/decomposition of the [M(OR)4]
precursors.23−25 It was reasoned that multidentate ligands
might be useful for production of uniform MO2 NPs via
preferential/directed hydrolysis. Previously, we have inves-
INTRODUCTION
■
Group 4 ceramic nanoparticles (NP) are of interest for a
number of applications including orthopedic biomaterials,1
improved drug delivery,2 photocatalysts,3−5 jewelry, fire-
retardant materials,6−8 optical storage devices,9 light shutters,10
refractory material gate oxides in microelectronics,2,11−14 and
high dielectric materials in DRAM capacitors.2,13,15 For
electronic applications, controlled deposition of the ceramic
NPs in three-dimensional architectures is a growing demand
for industrial efforts.16,17 Direct-write (DW) methods are
considered to be a viable route to produce these complex
architectures.18 For these technologies, a computer controlled
stage follows a predesigned pattern, depositing layer upon layer
of ink to build the desired component. In order to have useful
DW printed components, it is critical to have high quality
nanoinks (N-inks), which necessitates controlled uniform
nanoparticles. It was, therefore, of interest to generate high
Received: July 9, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01907
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tigated tridentate ligands such as tris(hydroxymethyl)ethane
(H3-THME) and tris(hydroxymethyl)propane (H3-THMP).24
For the group 4 derivatives, these ligands formed complex
tetramers of the general formula [μ3-(O)(μ-(Ο′,Ο′′)-
THMR)2M4(OR)10].24
In an effort to generate less encumbered molecules to allow
for directionalized hydrolysis favoring more uniform nanoma-
terials production, ligands that are more flexible and chelate to
one metal were of interest. The 6,6′-(((2-hydroxyethyl)-
azanediyl)bis(methylene))bis(2,4-di-tert-butylphenol) ligand,
termed H3-AM-DBP2 (1, Figure 1), came to the forefront of
[M(OR)4] + H3 ‐AM‐DBP
2
→ [(OR)M(AM‐DBP )]n3H‐OR
(1)
2
The parent alkoxides [M(ONep)4]2 (M = Ti,28 Zr,29 and
Hf29) and the complementary AM-DBP2/ONep ligated
compounds 2, 5, and 7 were used to generate nanomaterials
under solvothermal (SOLVO; octadecene) conditions. A
comparison of the final materials was undertaken using
dynamic light scattering (DLS), transmission electron
microscopy (TEM), and powder X-ray diffraction (PXRD)
to determine the influence that the AM-DBP2 ligand has on
the thermal properties of the precursor and final materials’
properties.
EXPERIMENTAL SECTION
■
Organic Synthesis. All starting reagents were purchased from
commercial sources and used as received. NMR spectra were recorded
on an Oxford AS400 spectrometer and referenced to residual peaks in
the deuterated solvents.
H3-AM-DBP2 (1).30 Following established Mannich condensation-
like synthesis routes,26,27 ethanolamine (0.61 g, 10 mmol), 2,4 di-tert-
butylphenol (4.3 g, 21 mmol), and p-formaldehyde (0.63 g, 21 mmol)
were added to a 48 mL pressure flask equipped with a magnetic stir
bar. The flask was sealed, stirred, and heated to 90 °C for 18 h,
whereupon the reaction mixture liquefied and then solidified. After
cooling, methanol was added to the crude reaction mixture, followed
by sonication, filtration, and crystallization, which resulted in the
isolation of a pure white powder of 1. Additional product was
obtained from crystallization of the mother liquor. Yield 4.0 g, 81.0%.
1H NMR (CDCl3) δ 7.21 (2H, d, C6H2(C(CH3)3)2OH, JH−H = 2.4
Hz,), 6.90 (2H, d, C6H2(C(CH3)3)2OH JH−H = 2.4 Hz,), 3.88 (2H, t,
HOCH2CH2N, JH−H = 5.2 Hz,), 3.76 (4H, s, PhCH2N), 2.73 (2H, t,
HOCH2CH2N, J = 5.2 Hz), 1.39 (18 H, s, C6H2(C(CH3)3)2OH),
1.27 (18 H, s, C6H2(C(CH3)3)2OH). 13C (CDCl3) δ 152.75 (Ar−C),
141.20(Ar−C), 136.13 (Ar−C), 125.12 (Ar−C), 123.67 (Ar−C),
121.68 (Ar−C), 61.15 (NCH2CH2OH), 57.81 (ArCH2N), 53.56
(NCH2CH2OH), 35.03 (Ar-C(CH3)3), 34.26 (Ar-C(CH3)3), 31.80
(Ar−C(CH3)3), 29.75 (Ar−C(CH3)3). X-ray-quality crystals were
obtained by slow evaporation of a MeOH solution, resulting in the
formation of clear and colorless plates over the course of 4 days.
Inorganic Synthesis. All compounds and reactions described
below were handled with rigorous exclusion of air and water using
standard Schlenk line and argon filled glovebox techniques. All
solvents were stored under argon and used as received in (Aldrich)
Sure/Seal bottles, including hexane, toluene, tetrahydrofuran, pyridine
(solv). The following chemicals were used as received (Aldrich and
Alfa Aesar): titanium isopropoxide ([Ti(OPri)4]), titanium tert-
butoxide ([Ti(OBut)4]), zirconium isopropoxide complex ([Zr-
(OPri)4·HOPri]2), zirconium tert-butoxide ([Zr(OBut)4]), hafnium
tert-butoxide ([Hf(OBut)4]), and neo-pentanol (H-ONep). The
following compounds were prepared according to literature
procedures: [Ti(μ-ONep)(ONep)3]2,28 [M(μ-ONep)2(μ-OBut)-
(ONep)6]2 (M = Zr, Hf)29 (Note: these compounds are referred to
as [M(ONep)4] throughout the paper for simplicity). [(OR)Ti-
(k4(O,O′,O′′,N)-AM-DBP2)] was synthesized according to eq 1 using
H3-AM-DBP2 (1) and [Ti(OR)4] (where OR = OPri, OBut) and
concurrence of both the structure and analytical data with the
previously reported characterization data.31
Figure 1. Structure plot of 1. Thermal ellipsoids of heavy atoms
drawn at the 30% level with carbon atoms drawn as ball and stick, and
H-atoms are not shown for clarity. See Supporting Information Table
S1 for structural parameters.
our efforts due to the steric bulk of the ligand, the multidentate
properties, and the flexibility of the ethoxy moiety. The
synthesis of this ligand was undertaken following a Mannich
reaction pathway,26,27 and its coordination behavior with group
4 metals was investigated, according to eq 1. The products
isolated proved, by single crystal X-ray experiments, to be H3-
AM-DBP2 (1), [(ONep)Ti(k4(O,O′,O′′,N)-AM-DBP2)] (2),
[(OR)M(μ(O)-k3(O′,O′′,N)-AM-DBP2)]2 [M = Zr: OR =
OPri, 3·tol; OBut, 4·tol; ONep, 5·tol; M = Hf: OR = OBut, 6·
All analytical data were collected using dried crystalline material.
Fourier-transform infrared (FTIR) spectroscopic data were obtained
from a KBr pressed pellet of the sample using a Bruker Vector 22
Instrument under an atmosphere of flowing nitrogen. Elemental
analyses were performed on a PerkinElmer 2400 CHN-S/O elemental
analyzer.
General Synthesis. In an argon filled glovebox, the off-white
powder H3-AM-DBP2 was added to a vial that contained the
appropriate [M(OR)4] dissolved in toluene. After being stirred for 12
tol; ONep, 7·tol where OPri = OCH(CH3)2, OBut
=
OC(CH3)3, ONep = OCH2C(CH3)3]. Schematic structures
of the general coordination of these products are shown in
Scheme 1. The synthesis and characterization of 1−7 are
reported.
B
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Scheme 1. Schematic Representation of H3-AM-DBP2 (1) and Coordination Structures Isolated
h, the reaction mixture was allowed to sit with the cap removed until
X-ray quality crystals formed. The mother liquor was then removed,
some crystals were set aside for X-ray studies, and the remainder of
the powder were dried in vacuo for analytical evaluation. The final
yields were not optimized.
Elemental Analyses calc’d for C81H126N2O8Zr2 (MW = 1438.35; 5 ·
tol): 67.64%C; 8.83%H; 1.95%N; for C64H98N2O8Zr2 (MW =
1205.94; 5 - 2 CH2C(CH3)3): 63.74% C; 8.19% H; 2.32% N.
Found 63.47% C; 8.30% H; 1.90% N.
[(OBut)Hf(μ(O)-k3(O′,O′′,N)-AM-DBP2)]2 (6)·tol. Used [Hf-
(OBut)4] (0.500 g, 1.06 mmol) and H3-AM-DBP2 (0.528 g, 1.06
mmol) in tol (5 mL). Yield 61.5% (0.516g). FTIR (KBR, cm−1)
2954(s), 2902(s), 2869(s), 1604(m), 1560(w), 1479(s, br), 1415(s),
1389(m), 1360(s), 1309(s), 1267(s), 1243(s), 1197(s), 1171(s),
1132(m), 1087(m), 1027(s), 915(m), 875(m), 847(s), 813(m),
773(m), 753(m), 729(m), 694(m), 648(w), 624(w), 602(w),
545(m), 505(w), 481(w), 465(m). Elemental Analyses calc’d for
C79H122Hf2N2O8 (MW = 1584.83; 6·tol): 59.87% C; 7.76% H; 1.77%
N. Found 60.21% C; 7.90% H; 1.83% N.
[(ONep)Ti(k4(O,O′,O′′,N)-AM-DBP2)] (2). Used [Ti(ONep)4]
(0.500 g, 1.26 mmol) and H3-AM-DBP2 (0.628 g, 1.26 mmol) in
tol (5 mL) turned a pale orange-yellow color. Yield 98.0% (0.778g).
FTIR (KBR, cm−1) 2953(s), 2901(m), 2867(m), 1604(w), 1477(s),
1442(s), 1414(m), 1389(w), 1360(m), 1308(m), 1295(w), 1256(s),
1243(s), 1189(s), 1172(s), 1129(m), 1107(m), 1076(s), 1029(s),
916(m), 897(w), 877(m), 850(s), 812(w), 792(m), 759(s), 610(s),
596(s), 584(s), 494(m). Elemental Analyses calc’d for C37H59NO4Ti
(MW = 629.75, 2): 70.57% C; 9.44% H; 2.22% N. Found 70.49% C;
9.72% H; 2.22% N.
[(ONep)Hf(μ(O)-k3(O′,O′′,N)-AM-DBP2)]2 (7)·tol. Used [Hf-
(ONep)4] (0.500 g, 0.886 mmol) and H3-AM-DBP2 (0.441 g,
0.886 mmol) in tol (5 mL). Yield 75.6% (0.270g). FTIR (KBR, cm−1)
2952(s), 2903(m), 2866(m), 2706(w), 1479(s), 1443(w), 1415(w),
1394(w), 1361(m), 1267(w), 1243(w), 1203(w), 1171(m), 1128(s),
1024(m), 1008(m), 935(w), 915(w), 899(w), 875(w), 845(w),
752(w), 628(w), 585(w), 543(w), 465(w), 449(w). Elemental
Analyses calc’d for C37H59HfNO4 (MW = 760.37, 1/2 7): 58.45%
C; 7.82% H; 1.84% N. Found 58.15% C; 7.72% H; 1.76% N.
General X-ray Crystal Structure Information. Single crystals
were mounted onto a loop from a pool of Fluorolube or Parabar
10312 and immediately placed in a 100 K N2 vapor stream. X-ray
intensities were measured using a Bruker-D8 Venture dual-source
diffractometer (Cu Kα, λ = 1.5406 Å) and CMOS detector for 1 or a
Bruker APEX-II CCD diffractometer with Mo Kα radiation (λ =
0.71070 Å) for 2−7. Indexing, frame integration, and structure
solutions were performed using the BrukerSHELXTL32−34 software
package within Apex334 and/or OLEX235 suite of software. All final
CIF files were checked using the CheckCIF program (http://www.
iucr.org/). Additional information concerning the data collection and
final structural solutions can be found in the Supporting Information
or by accessing CIF files through the Cambridge Crystallographic
Data Base.36 Additional information concerning the data collection
and final structural solutions (Tables S1−S3) of these complexes can
be found in the Supporting Information or by accessing CIF files
through the Cambridge Crystallographic Data Base. The unit cell
parameters for the structurally characterized compounds 1−7 are
available in the Supporting Information (Figures S1−S7).
[(OPri)Zr(μ(O)-k3(O′,O′′,N)-AM-DBP2)]2 (3)·tol. Used [Zr(OPri)4·
HOPri]2 (0.155 g, 0.401 mmol) and H3-AM-DBP2 (0.200 g, 0.401
mmol) in tol (5 mL). Yield 87.5% (0.258 g). FTIR (KBR, cm−1)
2964(s), 2928(m), 2866(m), 2624(w), 1604(w), 1478(s), 1442(s),
1415(m), 1361(s), 1337(m), 1315(m), 1264(s), 1243(s), 1134(s,
br), 1055(m), 1008(s), 947(m), 915(w), 876(m), 844(s), 752(m),
729(w), 602(w), 551(m), 487(w), 462(m). Elemental Analyses calc’d
for C77H118N2O8Zr2 (MW = 1382.25, 3·tol): 66.91% C; 8.61% H;
2.03% N; C98H142N2O8Zr2 (MW = 1658.67, 3·4tol): 70.97% C;
8.63% H; 1.69% N. Found 70.26% C; 9.14% H; 2.07% N.
[(OBut)Zr(μ(O)-k3(O′,O′′,N)-AM-DBP2)]2 (4)·tol. Used [Zr(OBut)4]
(0.500 g, 1.30 mmol) and H3-AM-DBP2 (0.648 g, 1.30 mmol) in tol
(5 mL). Yield 83.7% (0.870g). FTIR (KBR, cm−1) 2962(s), 2903(s),
2868(m), 1604(w), 1478(s), 1443(s), 1414(m), 1389(w), 1360(m),
1309(m), 1265(s), 1242(s), 1193(s), 1171(m), 1132(m), 1090(w),
1048(m), 1019(s), 915(w), 875(m), 847(s), 754(m), 548(m),
501(w), 465(m). Elemental Analyses calc’d for C93H138N2O8Zr2
(MW = 1594.58; 4·3tol): 70.05% C; 8.72% H; 1.76% N;
C86H130N2O8Zr2 (MW = 1502.44; 4 · 2 tol): 68.75% C; 8.72% H;
1.86% N. Found 68.42% C; 8.35% H; 1.75% N.
[(ONep)Zr(μ(O)-k3(O′,O′′,N)-AM-DBP2)]2 (5)·tol. Used [Zr-
(ONep)4] (0.200 g, 0.419 mmol) and H3-AM-DBP2 (0.208 g,
0.419 mmol) in tol (∼3 mL). Yield 94.7% (0.286g). FTIR (KBR,
cm−1) 2955(s), 2902(s), 2867(s), 1604(w), 1477(s), 1443(s),
1414(m), 1391(w), 1362(m), 1304(m), 1264(s), 1243(s),
1204(m), 1171(m), 1133(m), 1107(m), 1076(m), 1055(w),
974(w), 916(w), 874(m), 843(m), 811(w), 753(m), 729(w),
694(w), 674(w), 637(m), 600(w), 545(m), 518(m), 465(m).
C
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Table 1. Metrical Data for [(OR)Ti(k4(O,O′,O′′,N)AM-
Ultraviolet−visible Absorbance Spectroscopy (UV−vis).
UV−vis absorbance spectroscopic data were obtained using a
Photonics CCD Array UV−vis spectrophotometer. Samples of H3-
AM-DBP2 and 2−7 were individually prepared in an argon filled
glovebox at a ∼0.2 M concentration in toluene. Scans ranged from
200 to 950 nm with a D2 source and W source with a crossover at 460
nm. See Supporting Information (Figure S8) for UV−vis absorbance
spectra of H3-AM-DBP2 and 2−7.
a
DBP2]31 (*) and 2−10
Thermogravimetric Analysis (TGA)/Differential Scanning
Calorimetry (DSC). The simultaneous TGA/DSC analysis was
obtained on a Mettler Toledo model TGA/DSC 1. All experiments
were conducted under an argon atmosphere at a heating rate of 10 °C
min−1 from room temperature to 1100 °C in an alumina crucible (see
Supporting Information Figure S9).
Nanoparticle Synthesis. Upon receipt of octadecene (Sigma-
Aldrich, 90% technical grade), the solvent was degassed and then
transferred to an argon filled glovebox. Under an inert atmosphere,
individual 0.06 M solutions of compounds 2, 5, 7, [Ti(ONep)4],
[Zr(ONep)4], and [Hf(ONep)4] in octadecene were produced. A
sample of each solution (20 mL) was placed in individual Teflon
liners, sealed in a Parr Digestion Bomb, and transferred out of the
glovebox. The samples were then placed in a box oven and heated to
180 °C for 24 h, removed, and allowed to cool to room temperature.
After this time, the residual was isolated by centrifugation on the
benchtop and washed with hexanes (three times). The resulting
samples were used without further manipulation.
Dynamic Light Scattering (DLS). Measurement of particle size
distribution (PSD) was conducted using a Zetasizer Nano-ZS from
Malvern Instruments. Particles were prepared in dilute conditions, by
adding 50−100 mg of the nanoparticles to ∼5 mL of toluene. Under
an argon atmosphere, the samples were then pipetted into the glass
cuvettes and capped. Measured samples were of low solid
concentration (<10−4 wt %). Dispersion was promoted by treatment
of the suspension in an ultrasonic bath for 2 min (Branson
Ultrasonics). Ten measurements of each sample’s PSD were
performed and examined for particle sedimentation or drift in
response with time. The PSD is presented as the average of the 10
measurements (see Supporting Information, Figure S10).
Powder X-ray Diffraction (PXRD). PXRD patterns were
obtained using a PANalytical X’Pert Pro diffractometer (10−100°
two theta) employing CuKα radiation (1.5406 Å) and a RTMS
X’Celerator detector at a scan rate of 0.15°/s for the bulk powders or
at a scan rate of 0.15°/s using a zero-background holder. The PXRD
patterns were analyzed using JADE 9 software (Materials Data, Inc.,
Livermore CA) and indexed using The Powder Diffraction File PDF-
4+ 2013. Crystallite sizes were determined using Jade v9.6.0. All
samples were analyzed using a plastic holder.
Transmission Electron Microscopy (TEM). For TEM analyses,
the samples were individually dispersed in toluene and aliquots of the
solution placed onto a holey-carbon coated copper TEM grid and
allowed to dry prior to analysis. TEM images were obtained by
utilizing a JEOL 2100 LaB6 microscope operated at 200 keV (see
Supporting Information, Figure S11).
Computational Modeling. Gas-phase electronic structure
calculations were performed on 2−7 using Gaussian 0937 at the
density functional theory (DFT) level with the hybrid B3LYP
functional (Becke’s three parameter hybrid exchange functional with
Lee−Yang−Parr correlation function).38−40 The LANL2DZ effective
core potential basis set41,42 was used on the metals (Ti, Zr, and Hf);
all other atoms were described using the 6-31G basis set43−45 as part
of the complete basis set model described by Peterson et al.46 The
LANL2DZ basis set includes a scalar relativistic correction and has
been previously applied to Ti, Zr, and Hf-based molecules resulting in
agreement with experimental structures.47−50
a
Averaged metrical data are shown without error bars.
relaxations, time dependent density functional theory (TD-DFT)
calculations were also performed to identify the energies of the 50
lowest-energy electronic transitions.45,51,52 The UV−vis absorbance
spectra were then predicted from the calculated electronic transition
in the 200−800 nm portion of the spectra using the GaussSum
program.53 Plotted individual intensities and the Gaussian inter-
polations with a full-width-half-max (fwhm) value of 3000 1/cm are
included in Supporting Information (Figure S13). The three highest
contributions to the UV−vis absorbance spectra and the assigned
HOMO → LUMO transitions are included in Table 2.
Molecular structures were selected from solved crystal structures
and optimized in unrestricted calculations (included in Figure S12).
All atoms were allowed to relax during optimization. Reasonable
agreement in the metrical data between the crystal structures and
DFT optimized molecules (Table 1) validates the quality of the DFT
models and is discussed in the results. After the initial structural
RESULTS AND DISCUSSION
■
A search of structurally verified group 4 metals modified by the
AM-DBP2 ligand yielded two compounds: [(OR)Ti(k4-
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Table 2. Experimental and Calculated (TD-DFT) Adsorption Wavelength, λ (nm), with the Three Primary Contributions (1,
2, 3) and HOMO(H)-LUMO(L) Transitions Assignments
individual transitions (nm)
cmpds
exp’t, λ (nm)
calc’d, λ (nm)
first λ
assign.
second λ
assign.
third λ
assign.
a
a
2
282
330
298
270
341
299
291
351
307
H → L + 2
H → L
H-1 → L + 1
H → L
H-1 → L
H → L
264
343
293
H-4 → L + 1
H-1 → L + 1
H-2 → L
248
332
287
H-5 → L + 1
H-1 → L
H-2 → L
a
3
H-3 → L + 2
H-3 → L
H-3 → L + 2
4
5
294
294
303
302
310
311
289
294
H-2 → L
285
285
H-2 → (L, L + 1)
H-1 → L + 1
H → L
H-2 → (L, L + 3)
H-1 → L + 4
a
6
293
256
270
271
254
268
H-2 → L
250
255
H-1 → L + 1
H → L + 5
H-3 → L + 1
a
a
a
7
293
267
H-9 → L
H-9 → L
a
Contributes less than 50% of the transition.
(O,O′,O′′,N)AM-DBP2] where R = OPri, OBut.31 It is of note
that several other ligands with similar constructs as AM-DBP2
are available with a fur-2-ylmethyl54 or tetrahydrofur-2-yl55
moiety replacing the N-CH2CH2OH fragment or a meth-
oxide56 replacing the N-CH2CH2OH. The more complex
(ethylenedioxy)diethanamine-based tetraphenoxide ligands,
which possess two AM-DBP2 submoieties linked by -[N−
CH2CH2−O]2-, have also been used to modify group 4
compounds.57,58 The coordination of the metal in the
[(OR)Ti(k4(O,O′,O′′,N)AM-DBP2] family of compounds
were described as distorted trigonal bipyramidal (TBPY-5)
monomers, employing a tetradentate AM-DBP2 and one
parent alkoxide ligand. Similarly, when the 6,6′-(((2-
hydroxyethyl)azanediyl)bis(methylene))bis(2,4-dimethylphe-
nol) (H3-AM-DMP2), where Me groups replace the But
groups, was used, monomeric [(OR)Ti(k4(O,O′,O′′,N)AM-
DMP2] for OC6H3(R′)2-2,6 (where R′ = CH3,59 CH(CH3)2,60
C6H5,59) and dinuclear [(OR)Ti(μ-(O)(k3(O′,O′′,N)AM-
DMP2]2 for OR = OPri,31 OBut,31 OC6H4F-2,59 and
59
OC6H4F2-2,6, OC6F5 compounds were isolated. On the
basis of these structure types, it was evident that AM-R2 (R =
DMP or DBP) modified [M(OR)4] compounds might be
useful to induce controlled nanomaterial production. Since the
heavier group 4 congeners modified with AM-DBP2 ligand
have not been reported, we undertook their synthesis. Crystal
structure parameters and structure plots for 2−7 are available
in the Supporting Information. Representative structures are
shown in Figures 2, 3, and 4.
Figure 2. Structure plot of 2. Thermal ellipsoids of heavy atoms
drawn at the 30% level with carbon atoms drawn as ball and stick, and
H atoms are not shown for clarity. See Supporting Information Table
S1 for structural data collection parameters.
N was also noted: N(1)---H(1) = 2.583 Å; O(1)−H(1)---
N(1) = 128.2°; N(2)---H(5) = 2.664 Å; O(5)−H(5)---N(2) =
116.9°. Each N atom also strongly H-bonds to the remaining
OOAr atom (OOAr---H---N, N(1)---H(2) = 1.927 Å; N(2)---
Ligand Synthesis. The work by Padmanabhan et al.31
reported that the H3-AM-DBP2 ligand was synthesized
following the Siegl and Chattha30 synthesis. However, access
to the original report30 was limited, and the Padmanabhan
report31 indicated that a complicated crystallization and
column purification was necessary to isolate this ligand. To
simplify the synthesis of the ligand, the Mannich condensation
route was undertaken and found to readily produce H3-AM-
DBP2 (see Experimental Section). Once isolated, no additional
purification was necessary. Because of the limited analytical
data previously supplied, full characterization of this com-
pound is presented in the Experimental Section.
H(4) = 1.959 Å), which results in an elongation of the OOAr
−
H---OEtOH (O(1)−H(1)---O(3) = 156.984° and O(5)−
H(5)---O(6) = 157.933°) and OOAr−H---N (O(2)−H(2)---
N(1) = 146.9°; O(4)−H(4)---N(2) = 147.8°). There does not
appear to be an intermolecular interaction. Full data collection
parameters are available in the Supporting Information.
1
Additionally, H and 13C NMR spectra were collected on 1,
and the resulting spectral data were in full agreement with the
proposed and crystal structure obtained.
1:1 Metal Alkoxide/AM-DBP2 Compounds. With this
well characterized ligand in hand, the initial experiments
undertaken were to generate the previously isolated 1:1
[(OR)Ti(AM-DBP2)] compounds31 where OR = OPri, OBut
for use as a precursor for nanoceramic materials. Upon mixing
of the white ligand with the clear [Ti(OR)4], the reaction
mixture turned an orange-yellow color. No precipitates were
A single crystal of 1 was isolated where the two molecules
per unit cell clearly show the proposed connectivity. Strong H-
bonding was observed in each molecule between one of the
phenol and ethanol oxygen atoms (OOAr---H---OOEt-H: O(6)---
H(5) = 1.999 Å; O(3)---H(1) = 2.040 Å). An additional weak
H-bond interaction of H(1) and H(5) atoms with their parent
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It was expected that the larger Zr cation would yield
alternative species (i.e., solvates or dinuclear complexes). Upon
mixing of the H3-AM-DBP2 ligand with the different
[Zr(OR)4] derivatives in a 1:1 stoichiometry, no color change
or precipitate was noted after stirring for 12 h. Crystals were
grown by slow evaporation from toluene, and the product
proved to be a dinuclear species with each AM-DBP2 ligand
binding to the Zr atoms in a tetradentate manner (O,
O′,O′′,N). For these species, the oxygen atom of the ethoxide
moiety acts as a bridge between the two metals. The Zr metal
finishes its distorted-octahedral (OC-6) geometry by retaining
the parent OR ligand (OPri (3); see Figure 3, OBut (4), ONep
(5)). Similar reactions were undertaken for [Hf(OR)4] species.
Again, no color change was noted upon complexation of the
AM-DBP2. The Hf derivatives [OBut (6) and ONep (7; Figure
4)] were found to adopt similar structures as noted for Zr
complexes 3−5. The general arrangement of 3−7 are in
agreement with [(OR)Ti(μ-(O)(k3(O′,O′′,N)AM-
DMP2]2.31,59 All attempts to produce the simple monomeric
species with the larger metals56 were not successful. Scheme 1
shows the two general structure types noted from eq 1.
Figure 3. Structure plot of 3·tol. Thermal ellipsoids of heavy atoms
drawn at the 30% level with carbon atoms drawn as ball and stick, and
H atoms are not shown for clarity. See Supporting Information Table
S1 for structural data collection parameters.
Metrical Data. Select averaged distance and angles of 2−7
were tabulated in Table 1. In contrast to what was reported for
the [(OR)Ti(k4(O,O′,O′′,N))AM-DBP2] where R = OPri or
31
OBut compounds, the angles around the Ti of 2 proved to
adopt a fairly regular TBPY-5 geometry (τ = 0.981). The bond
distances of 2 were found to be in general agreement with the
other similarly constructed species.31,54−60
Since no AM-DBP2 or AM-DMP2 of Zr or Hf complexes
have been previously reported, alternative structural models
needed to be used for metrical comparison. While the general
constructs of the AM-DBP2 ligand bound to a Zr were
available, none of the ligands possessed the three OH groups
but instead had either a (i) fur-2-ylmethyl ((N,N-bis(3,5-di-t-
butyl-2-oxybenzyl)-N-((tetrahydrofur-2-yl)methyl)amine-
N,O,O′,O′′)),54 (ii) tetrahydrofur-2-yl ((N-(fur-2-ylmethyl)-
N,N-bis(3,5-di-t-butyl-2-oxybenzyl)amine-N,O,O′,O′′)),55 or
(iii) methoxy (N,N-bis(3,5-di-t-butyl-2-oxybenzyl)-2-methox-
yethylamine-N,O,O′,O′′)57 group replacing the ethanol tail
forming [(L)Zr(CH2Ph)2] complexes. Only the methoxy
derivative (N,N-bis(3,5-di-t-butyl-2-oxybenzyl)-2-methoxye-
57
thylamine-N,O,O′,O′′)Hf(CH2Ph)2 was available for the Hf
metrical model. These were used for comparison, along with
Figure 4. Structure plot of 7·tol. Thermal ellipsoids of heavy atoms
drawn at the 30% level with carbon atoms drawn as ball and stick, and
H atoms are not shown for clarity. See Supporting Information Table
S1 for structural data collection parameters.
the dinuclear Ti complex, [(OR)Ti(μ-(O)(k3(O′,O′′,N)AM-
31,59
DMP2]2
whose metrical data was adjusted for the cation
size.61 Initial comparisons between 3 and 7 found the metrical
data to be fairly regular, which is expected as Zr and Hf have
similar cation sizes in the 4+ oxidation state (see Table 1): M---
M from 3.56−3.61 Å; M---N from 2.39−2.54 Å; M---O from
1.99−2.00 Å; and M-OR from 1.91−1.93 Å. As can be noted
in Table 1, the angles around the metal clearly show the
distortion from rigorous OC-6 geometry.
observed when the solution sat overnight. Crystals were grown
by slow evaporation, and single crystal X-ray experiments were
undertaken. In agreement with the literature structure reports,
a distorted TBPY-5 monomer was solved as [(OBut)Ti-
(k3(O′,O′′,N)AM-DBP2)] where OR = OPri and OBut.31 Since
altering the pendant chains on the aryloxide ring from tert-
butyl to methyl groups led to the formation of the dinuculear
[(OR)Ti(μ-(O)(k3(O′,O′′,N)AM-DMP2]2,31,59 it was of inter-
est to determine if the OR ligand could be used to tune the
structure as well. This was investigated by introducing the
ONep ligand; however, the isolation of 2 (see Figure 2)
resulted in the same TBPY-5 monomeric species, which
indicates the parent OR has little impact on the overall
structure. The N(1) of the AM-DBP2 and the O(4) of the
ONep ligand were located in the axial position of the Ti metal
centers coordination.
The structures from the DFT simulations were compared
with the experimental data of 2−7 (see Table 1). All
coordination structures around M noted in the experimental
results were found to be stable in the DFT simulations. For the
M−O and M−N bonds, the DFT simulations slightly
underestimate the bond length by ∼1−2% (or 0.02−0.05 Å),
which is most notable in the M−OR and M−N bonds. The
M---M interactions can be difficult to model, but surprisingly
these interatomic distances were only 0.03−0.07 Å shorter
than in the crystal structures and similar to the variance
observed in previous studies of metal oxide clusters.62
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Interatomic angles experienced similar variances (∼1% or less).
In general, the regularity in the metrical data between the
experimental and simulation data indicates the low energy
stable molecular structures developed would be useful for
additional calculations (vide infra).
Bulk Powder Characterization. In an effort to determine if
the bulk materials were consistent with the single crystal
structures, additional analytical studies were performed. These
included FTIR spectroscopy, UV−vis absorbance spectrosco-
py, and elemental analysis.
methylene resonances were broad, “missing”, or the integration
on the observed peaks proved to be inconsistent with the
structural properties. This was believed to be due to fluxional
and/or monomer−dimer exchange in solution 2−7 in CDCl3.
Therefore, variable temperature 1H NMR studies were
undertaken to further clarify the behavior of these compounds
in solution. Initial efforts to lock out a single structure by low
temperature NMR experiments failed due to preferential
crystallization of the precursors out of solution. Alternatively,
high temperature spectra in CDCl3 were collected with the
expectation that monomeric species would be favored at
elevated temperatures. The high temperature variable temper-
ature NMR studies are shown in the Supporting Information.
While there were significant changes noted, in the general
spectra of 2−7, a mixture of monomers and dimers was still
present for each sample. Unfortunately, the higher temper-
atures necessary to force complete conversion to the
monomeric form was not possible as the CDCl3 temperature
limit had been reached. Additional experiments to elucidate
the solution behavior of 2−7 were not undertaken.
Since some of the M-(AM-DBP2) derivatives were highly
colored, UV−vis absorbance spectroscopic analyses were
undertaken to further assist in characterizing 2−7. The H3-
AM-DBP2 ligand was found to have a strong absorbance at 293
nm, which was preliminarily assigned to a π → π* transition. A
similar absorbance was noted for the various derivatives with
λmax for [(OBut)Ti(AM-DBP2)] at 285; 2, 290; 3, 298; 4, 294;
5, 294; 6, 293; 7, 293 nm. In addition, another peak was
readily observed for the Ti derivatives (λmax = 330 nm for
OBut, and 340 nm for 2). There is a minor λmax noted for the
Zr (3, 352; 4, 384; and 5, 354 nm) and the Hf (6, 373 and 7,
355 nm) compounds. On the basis of the quality of the DFT
models, TD-DFT UV−vis absorbance calculations were
undertaken to assist in assigning the absorbances noted
experimentally. In the Ti derivative 2, the calculated spectrum
revealed a major absorbance at 270 nm with a significant
shoulder at 341 nm. This is consistent with the two
absorbances noted in the experimental spectrum of 2. The
shoulder at 341 nm in the UV−vis absorbance spectrum of 2 is
attributed to a mixed π → π* and ligand to metal charge
transfer (LMCT) transitions (from visualization of the
molecular orbitals shown in Figure S15). The LMCT
transition is largely in the AM-DBP2 phenyl ring and Ti−O
and the π → π* in the C−C π bonds (HOMO and HOMO-1
molecular orbitals) which transition to π* bonds (LUMO and
LUMO+1 molecular orbitals). The shoulder in 3 develops
from a LMCT transition between the AM-DBP2 and the
associated Ti atom and ligand linkages. Structurally, the Ti-
based molecule 2 has a shorter M−OAM‑DBP2, M−OAm‑EtO, and
M−μ−OR interatomic distance (Table 1) than 3, 4, 5, 6, and
7. A strong Ti−O interaction may be playing a role in the
development of the intense shoulder in the UV−vis
absorbance spectra.
FTIR spectroscopy is often a useful means of determining
the completion of the alcoholysis reaction through loss of the
HO- stretch (3392 cm−1) coupled with the ingrowth of the
alkyl groups of the AM-DBP2 ligand. For 2−7, there was no
HO-stretch recorded in the FTIR spectra. Additionally, the
stretches assigned to the But (2954 cm−1) of the H3-AM-DBP2
were present (2, 2953; 3, 2964; 4, 2962; 5, 2955; 6, 2954; 7,
2952 cm−1) along with other H3-AM-DBP2 alkyl stretches
(1481 cm−1: 2, 1478; 3, 1477; 4, 1479; 5, 1479; 6, 1477; 7,
1479 cm−1). The bands observed for 2−7 were much broader
than the free ligand with a shoulder peak around 1442 cm−1,
which was attributed to the binding of the AM-DBP2 ligand to
the various metal centers. Because of the multiple bends and
stretches present in the remainder of the spectra, identification
of other stretches associated with the AM-DBP2 ligand is
difficult; however, for each sample, a new M−O stretch was
observed for Ti−O ([(OBut)Ti(AM-DBP2)]31 and 2 at 610
cm−1), Zr−O (3, 551; 4, 548; 5, 545 cm−1), and Hf−O (6,
545; 7, 543 cm−1).63 These data indicate that the general
features of the AM-DBP2, pendant OR, and M−O bonds are
present.
Elemental analyses of the majority of compounds were
found to be in agreement with the solid-state structures, in
terms of the percent composition. For 5 and 7, the %C was too
low but may be a reflection of the ONep ligand, which is often
reported to not have reproducible thermal elemental
analyses.28,29 For 5, when the −CH2C(CH3)3 moieties are
removed from consideration, the calculated values of 5 are in
agreement with experimental values. Attempts at employing
mass spectral analysis were not informative in terms of
identifying the parent ions. In particular, the main peaks found
were not associated with any aspect of the observed structures.
This may be due to the sensitivity of the remaining alkoxide
ligand reacting with ambient atmospheric water, prior to
analysis.
As noted, the solid-state structures of 2−7 were determined
by single crystal X-ray diffraction studies as both monomeric
and dimeric complexes. If the solid state symmetry was
retained upon dissolution, the 1H NMR spectra of these
compounds were expected to yield the following resonances:
two singlets for the aromatic protons, two resonances for the t-
butyl aryl (OAr-But2) substituents, the appropriate resonances
for the alkoxides (singlet for But; two singlets for ONep), and
three methylene resonances (benzyl hydrogens, O−CH2 and
CH2−N). A variety of solvent systems were explored (toluene-
d8, THF-d8, pyridine-d8) in an attempt to determine the
solution behavior of 2−7. Unfortunately, these spectra were
dominated by numerous, overlapping, broad resonances that
Between compounds 2−7, the variance in λmax values arise
from shifts in the HOMO → LUMO, HOMO−1 → LUMO
+1, and HOMO−1 → LUMO transitions (Table 2). The
model spectra for the Zr compounds (3, 4, and 5) identified a
primary peak for each, which was within 10 nm of the value of
the single peak experimentally observed. The λmax noted for the
Hf-based molecules’ spectra (6, 7) revealed a consistent blue-
shift of 30−40 nm from the experimental values. This variation
was assumed to be a function of the selected DFT methods
and complications with modeling the f-electrons. The
1
could not be meaningfully interpreted. In contrast, H NMR
spectra collected for 2−7 in CDCl3 (Sigma-Aldrich, 99.8 atom
% D; see the Supporting Information for the full spectra
obtained in CDCl3) revealed the appropriate resonances for
the OAr-But2 and the parent OR; however, the various
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absorbance maxima for 3−6 were determined to arise primarily
from HOMO → LUMO, HOMO−1 → LUMO+1, and
HOMO−1 → LUMO transitions, as shown in Table 2.
Overall, the transitions in the Ti-based molecule 2 was found
to be shifted to much higher wavelengths than in the Zr- and
Hf-based molecules. This may be a reflection of the final
structure types.
Nanomaterials. In order to determine the influence, the
AM-DBP2 had on the final nanomaterials generated, a series of
SOLVO reactions were undertaken using both the parent
alkoxides [M(ONep)4]2 (M = Ti, Zr, and Hf) and compounds
2, 5, and 7 under similar conditions. The latter compounds
were selected since they had the ONep ligand and the AM-
DBP2 modifier, which allows for a meaningful comparison of
the final materials.
The TGA spectra (see Supporting Information) were
collected for the parent alkoxide and 2, 5, and 7 to determine
if they would be acceptable for nanomaterial production by
solution routes. The parent alkoxides all showed early low
temperature decomposition, with final weight losses completed
by 300 °C. In contrast, the spectra for the AM-DBP2 species
had much higher final weight loss temperatures, 500 °C with
the initiation of these weight losses below 300 °C. Therefore,
the decomposition pathways of the AM-DBP2 derivatives
versus the parent alkoxides were expected to vary significantly
upon processing.
Of the solution routes available, SOLVO processing was
selected using octadecene due to the high boiling point, non-
coordinating nature, low toxicity, and low water content. The
reactions and powder isolated were run under inert
atmospheres, as described in the Experimental Section, to
eliminate potential hydrolysis products. After this, a compar-
ison of the materials generated was undertaken using PXRD,
TEM (Figure 5), and DLS (Figure 6). For each sample
isolated, an amorphous material was generated, as confirmed
by PXRD analyses. A subset of these samples was fired (650
°C; 1/2 h) to crystallize the powders. Samples were analyzed
by PXRD and proved to be the MO2 (TiO2: PDF 99-000-3236
(rutile)/98-000-0081(anatase) (2); ZrO2: PDF 01-072-2742
(3), 01-075-9645 (4), 01-072-2742 (5); HfO2: PDF 00-043-
1017(6), 00-053-0560 (7)). The spectra for all of the samples
are shown in the Supporting Information.
Figure 5. TEM images for column (i) [M(ONep)4] and column (ii)
[(AM-DBP2)M(ONep)]n where M = (a) Ti and 2, (b) Zr and 5, and
(c) Hf and 7.
TEM images were collected on all of the samples and are
shown in Figure 5. For the [Ti(ONep)4], there are flat round
plate-shaped particles on the order of 30−40 nm in size
(Figure 5a,i) but also smaller species distributed throughout
the sample. For 2, the particles were also identified as flat
plates (Figure 5a,ii) but appear to be smaller in size ranging
from 10−20 nm in size, with little evidence of smaller
particulates present. The [Zr(ONep)4] generated powders
were found to be small particulates (Figure 5b,i), ∼1 nm in
size. In contrast, the particles isolated from 5 reveal larger
particles formed in the range of 5−20 nm; however, it is of
note that a number of the smaller particles were present
(Figure 5b,ii). The Hf system (Figure 5c) shows a similar
trend with small particles observed for the parent [Hf-
(ONep)4] but much larger particles (20−40 nm) for 7.
Combined, these data demonstrate that the AM-DBP2 plays a
role in altering the particulate size, most likely by introducing
controlled hydrolysis regions.
Figure 6. DLS data for nanomaterials generated from [M(ONep)4]
and [(AM-DBP2)M(ONep)]n where M = (a) Ti and 2, (b) Zr and 5,
and (c) Hf and 7.
Figure 6. The ceramic material generated from the parent
[Ti(ONep)4] was found to possess a bimodal distribution,
with peaks centered at 713 (84%) and 91 nm (15%). In
contrast, the particles generated from 2 were monomodal with
a cluster size of 834 nm (99%). For [Zr(ONep)4], there was
also a bimodal distribution, with peaks at 862 (98%) and 34
nm (2%), but 5 had a primary peak at 641 nm (99%) with a
Additional classification of the particulate size was under-
taken to verify the trends identified in the TEM images. The
PSD results determined form the DLS analyses are shown in
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very small secondary cluster (less than 1%). For [Hf(ONep)4],
a very broad PSD was recorded, with the main peak at 497 nm
(81%), and additional peaks noted at 732 (14%) and 1353 nm
(1.2%). In contrast, compound 7 has a much tighter
distribution at 697 (97%) nm with a small fraction of
nanomaterials at 46 nm (3%). These results indicate the
colloidal stability of the product and their aggregation into
larger polycrystals. The DLS data also show the peak locations
(i.e., size) and intensity value (i.e., particle frequency/number/
volume) for the generated particle distribution. The distribu-
tion of particle sizes relates to the precursor decomposition in
solution, as well as their state of agglomeration during the
SOLVO process. Since the SOLVO experiments were
conducted without stirring, there is an inherent inhomogeneity
in the reaction mixture due to sedimentation and cluster
growth, which makes interpretation of the data difficult.
Nonetheless, a generalized understanding can be drawn from
the location and width of the measured peaks. Sol−gel reaction
theory describes how the decomposition of the precursor leads
to polymerize or crystallize the metal oxide, which is then
followed by particulate growth. Consequently, the rapid
decomposition of a precursor leads to numerous discrete
growth nuclei, yielding small particles, whereas slow decom-
position leads to deliberate nucleation and growth processes
that result in particle aggregation and larger, broader particle
populations. The size (nm) of the predominant DLS peak is
therefore a proxy for the rate of reaction - rapid reaction
forming nanomaterials and slow precursor decomposition
followed by growth or aggregation giving a broad peak
distribution.
For the parent [M(ONep)4] precursors’ SOLVO products,
there is a general trend toward bimodal or multimodal
distributions. Each sample reveals the presence of a broad
predominant peak in the submicron range along with
measurable amounts of nanomaterials. This type of distribu-
tion may result if the initial particles that form are large and
subsequently precipitate. The remaining soluble precursors
continue to decompose but under diluted conditions,
providing the source of the nanoparticles. This suggests that
the cluster formation occurs via particle agglomeration, and the
nanoparticles form by dilute nucleation over time. The TEM
images in Figure 5 confirm the heterogeneous nucleation
growth, revealing polycrystalline products or polycrystalline
materials in an amorphous matrix. The major size populations
were fit with Gaussian peaks in each case, whereas the
nanoparticle presence is very small. With larger size as a proxy
for slower reactivity, the ONep compounds indicate that the
rate of nucleation from [M(ONep)4] is Zr > Ti > Hf. While
the particle distribution of the AM-DBP2 precursors 2 and 7
has a bimodal character, the most intense peak in size is larger
than that of the respective [M(OR)4]. For each of these
samples, there is an additional shoulder in the distribution,
above the major peak, which suggests that the decomposition
reaction of the compound is slowed kinetically compared to
the [M(OR)4]. This change is attributed to the stability
induced by the tetradentate AM-DBP2 modifier. This is
consistent with the TGA/DSC curves and the larger particles
noted in the TEM data. However, for compound 5 the PSD
shows formation of a lower particle size entirely and no
shoulder at higher peak size. The TEM images indicate that a
very diverse set of materials were generated, which complicates
the understanding of the precursor/material relationship. It is
of note that while more studies are necessary to fully elucidate
the growth mechanism of these particles and how the stabilized
AM-DBP2 compounds impact this process and the morphol-
ogy of the final nanomaterials produced.
SUMMARY AND CONCLUSIONS
■
The modification of group 4 metal alkoxides with the AM-
DBP2 ligand was found to produce two types of structures
depending on the cation, which were identified as [(OR)Ti-
(k4(O,O′,O′′,N))-AM-DBP2)] (2) and [(OR)M(μ(O)-
k3(O′,O′′,N)-AM-DBP2)]2 (3−7). In all instances, the bonding
mode of the AM-DBP2 ligand was found by single crystal X-ray
diffraction experiments to adopt a tetradentate binding mode,
using the three O atoms and the N to chelate to the metal. The
introduction of this ligand substantially increased the thermal
stability in comparison to the parent alkoxides as determined
by TGA analyses. DFT calculations were found to generate
useful metrical models which were applied to elucidate the
various UV−vis absorbance spectra. The thermal stability led
to larger and more uniform particles of the AM-DBP2
precursors in comparison to their parent alkoxides when
SOLVO routes were employed. The changes wrought by the
AM-DBP2 precursors are anticipated to allow for better N-ink
formulations due to the slightly larger size and uniformity of
sample. Further attempts to tailor the size of the nanomaterials
for N-ink applications using different processing and solution
preparations are underway.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01907.
Data collection parameters for 1−7; structure plots of
1−7; UV−vis absorbance spectra of 2−7, and H3-AM-
DBP2; TGA/DSC, and DLS data: parent alkoxides, 2, 5,
and 7 (PDF)
Accession Codes
CCDC 1854168−1854174 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tjboyle@Sandia.gov. Phone: (505)272-7625. Fax:
(505)272-7336.
■
ORCID
Timothy J. Boyle: 0000-0002-1251-5592
Present Addresses
#(D.T.Y.) North Carolina State University, Department of
Chemistry, 2620 Yarbrough Drive, Raleigh, NC 27695-8204.
⊥(C.J.A.) Northwestern University, Department of Chemistry,
2504 Silverman Hall, 2170 Campus Dr., Evanston, IL 60208.
∇(M.T.B.) University of Wisconsin−Madison, Department of
Chemistry, 1101 University Avenue, Madison, Wisconsin
53706.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This work was supported by the NSF REU program at UNM
(Grant Number CBET-1560058 and DMR 1263387), as well
as the Laboratory Directed Research and Development
program at Sandia National Laboratories. Sandia National
Laboratories is a multimission laboratory managed and
operated by National Technology and Engineering Solutions
of Sandia, LLC., a wholly owned subsidiary of Honeywell
International, Inc., for the U.S. Department of Energy’s
National Nuclear Security Administration under contract
DE-NA0003525.
(22) Nikonova, O. A.; Nedelec, J. M.; Kessler, V. G.; Seisenbaeva, G.
A. Precursor-directed assembly of complex oxide nanobeads: The role
of strongly coordinated inorganic anions. Langmuir 2011, 27, 11622−
11628.
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