Synthesis of new heteroleptic strontium complexes

Article abstract of DOI:10.1039/c4dt00689e

A series of heteroleptic strontium complexes (1-9) using a combination of different aminoalkoxides and 2,2,6,6-tetramethyl-3,5-heptanedionate (tmhd) were prepared to examine the effect of the bulkiness and coordination ability of the aminoalkoxide ligand in these complexes as well as potential strontium precursors. All complexes were characterized by FT-IR, FT-NMR, elemental analyses, and thermo-gravimetric (TG) analyses. The crystal structure analyses of 1, 2, 4, and 5 demonstrate their stability in the dimer form and the unwillingness of the strontium atom to form more than six coordination bonds in these complexes. The complex 5 shows an unusual picture: the existence of one hexa-coordinated and one penta-coordinated strontium atom side by side in its dimer structure. The introduction of ether groups as coordination sites in complexes 6-9 led to a decrease in steric hindrance which resulted in the formation of the complex 7 as a tetramer. The complex 7 shows a unique Sr₄O₄cubane core where oxygen atoms undergo μ₃-bridging between strontium atoms. The TG analyses show that the complexes exhibit a step-wise decomposition character, with the major mass losses in the region 150-400 °C.

Full text of DOI:10.1039/c4dt00689e

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Synthesis of new heteroleptic strontium
complexes†
Cite this: Dalton Trans., 2014, 43,
14461
Sheby Mary George,a Hyo-Suk Kim,a Myoung Soo Lah,b Bo Keun Park,a
Chang Gyoun Kim*a and Taek-Mo Chung*a
A series of heteroleptic strontium complexes (1–9) using a combination of different aminoalkoxides and
2,2,6,6-tetramethyl-3,5-heptanedionate (tmhd) were prepared to examine the effect of the bulkiness and
coordination ability of the aminoalkoxide ligand in these complexes as well as potential strontium precur-
sors. All complexes were characterized by FT-IR, FT-NMR, elemental analyses, and thermo-gravimetric
(TG) analyses. The crystal structure analyses of 1, 2, 4, and 5 demonstrate their stability in the dimer form
and the unwillingness of the strontium atom to form more than six coordination bonds in these com-
plexes. The complex 5 shows an unusual picture: the existence of one hexa-coordinated and one penta-
coordinated strontium atom side by side in its dimer structure. The introduction of ether groups as
coordination sites in complexes 6–9 led to a decrease in steric hindrance which resulted in the formation
of the complex 7 as a tetramer. The complex 7 shows a unique Sr4O4 cubane core where oxygen atoms
undergo µ3-bridging between strontium atoms. The TG analyses show that the complexes exhibit a step-
wise decomposition character, with the major mass losses in the region 150–400 °C.
Received 7th March 2014,
Accepted 3rd June 2014
DOI: 10.1039/c4dt00689e
www.rsc.org/dalton
extremely difficult. It is well established that the kinetic stabi-
lity of many complexes depends on a delicate balance between
Introduction
The interest in the chemistry of group 2 metals, and especially steric effects, metal size, ligand basicity, and solubility equili-
in strontium, is due to their applications such as insulators for bria. Therefore, the ligands introduced should be of large size
dynamic random access memories,1 ferroelectrics for compu- and possess multiple coordination sites to saturate the metal
ter memory,2 high-Tc superconductors,3 electroluminescent center as well as to form a strong bond with the metal such
films,4 ionic conductors for fuel cell electrolytes,5 and mixed- that the complex remains stable at high temperatures.
electronic ionic conductors for fuel cell cathodes.6 All of these
The commonly used strontium precursors are developed
applications have required the fabrication of strontium-con- using sterically bulky 2,2,6,6-tetramethyl-3,5-heptanedionate
taining oxide thin films through atomic layer deposition (ALD) (tmhd)7 or substituted cyclopentadienyl derivatives.8 The intro-
or chemical vapor deposition (CVD). For the deposition of thin duction of functionalities into the ligands of a known precur-
films using these techniques, strontium precursors with good sor has been the usual way to achieve a given requirement in
stability and volatility are essential.
the case of homoleptic strontium precursors. However, owing
The development of strontium precursors has often been a to the uniformity of the ligands, it is difficult for a homoleptic
challenge because of the formation of oligomeric compounds metal precursor to adopt the desired reactivity and stability.
with low solubility and poor volatility as a result of the large The recent development in heteroleptic precursor chemistry9
size of heavier group 2 ions which makes ligand selection of various metals shows the advantage of having two different
ligands in a metal complex which gives an interesting alterna-
tive with high volatility, good stability, and the desired reac-
tivity. The careful selection of ligands according to the
requirement may lead to a suitable precursor with the desired
properties in heteroleptic complexes. The previously reported
heteroleptic strontium precursor10 justified the above by exhi-
biting enhanced volatility and stability compared to the
respective homoleptic complexes.
Our recently reported group 2 metal precursors with 1-((2-
(dimethylamino)ethyl)(methyl)amino)-2-methylpropan-2-olate
(demamp) and tmhd as coordinating ligands10 exhibit good
aThin Film Materials Research Group, Korea Research Institute of Chemical
Technology, P.O. Box 107, 141 Gajeong-Ro, Yuseong-Gu, Daejeon 305-600, Republic
of Korea. E-mail: cgkim@krict.re.kr, tmchung@krict.re.kr; Fax: (+82)42–861-4151
bInterdisciplinary School of Green Energy, Ulsan National University of Science and
Technology, UNIST-gil 50, Ulsan 689-798, Republic of Korea
†Electronic supplementary information (ESI) available: The TGA plot of com-
plexes 4–9. A summary of the crystal and some crystallography data is given in
Table S1. ORTEP diagrams of compounds 1, 2, and 4 are given with the observed
disorders in their crystal structures. The ORTEP diagram of the cubane core in 7
is given. CCDC 973486–973489, 1004596. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c4dt00689e
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 14461–14469 | 14461

View Article Online
Paper
Dalton Transactions
physical properties compared to their respective homoleptic mampH)
for
1,
1-(bis(2-(diethylamino)ethyl)amino)-
parent compounds, especially in the case of the strontium 2-methylpropan-2-ol (bdeaeampH) for 2, 1-(bis(3-(dimethyl-
metal. In this paper, we extend our work on heteroleptic stron- amino)propyl)amino)-2-methylpropan-2-ol (bdmapampH) for
tium precursors using 2,2,6,6-tetramethyl-3,5-heptanedione 3, 1,7-bis(dimethylamino)-4-(2-(dimethylamino)ethyl)heptan-4-
(tmhdH) in combination with various aminoalcohols.
ol (bdmadmaehH) for 4, 1,7-bis(dimethylamino)-4-(3-(di-
methylamino)propyl)heptan-4-ol (bdmadmaphH) for 5, 1-(2-
(dimethylamino)ethoxy)-2-methylpropan-2-ol
(dmaempH)
for 6, 1-(3-(dimethylamino)propoxy)-2-methylpropan-2-ol
Results and discussion
(dmapmpH) for 7, 1-((1-(dimethylamino)propan-2-yl)oxy)-
2-methylpropan-2-ol (dmamempH) for 8, and 1-(2-(2-(dimethyl-
amino)ethoxy)ethoxy)-2-methylpropan-2-ol (dmaeempH) for 9.
Among these, dmaemampH, dmaempH, dmapmpH, and dma-
mempH are tridentate ligands while bdeaeampH, bdma-
pampH, bdmadmaehH, bdmadmaphH, and dmaeempH are
tetradentate ligands.
The recently reported volatile heteroleptic complex
10
Sr(demamp)(tmhd)]2 shows a dimeric structure in which the
strontium atoms are held together by oxygen atoms from two
demamp groups through μ2-bridging. The volatility of the com-
pounds is inversely related to their molecular weights and
thus to the oligomerization. To overcome the dimerization of
this type of compound, we employed several aminoalcohol
ligands with larger alkyl groups attached to the alkoxy carbon
atom and introduced more coordination sites within the
ligand to saturate the strontium ion. The aminoalcohols we
used (Table 1) in combination with tmhdH are 3-(((2-(di-
methylamino)ethyl)(methyl)amino) methyl)pentan-3-ol (dmae-
The crystal structure analyses of 1, 2, 4, and 5 revealed that
all these complexes were crystallized in the monoclinic crystal
system and as dimers where the strontium atoms were held
together through the oxygen atoms of aminoalkoxide ligands
by μ2-bridging. Even though the ligands were bulky and had
higher coordination sites, the formation of dimers revealed
the stability possessed by these dimeric structures, which are
unaffected by the introduction of a variety of aminoalkoxide
ligands. From the available crystal data, it is clear that irrespec-
tive of their coordination ability, all the ligands remained tri-
coordinated, sometimes even bi-coordinated (in 5) with the
strontium metal, and the rest of the coordination sites
remained uncoordinated in their complexes. There were
several thermal disorders in the crystal structures of these
complexes especially in the aminoalkoxide part, detailed struc-
tures with disorders are given in the ESI (Fig. S1 and S2†). But
the introduction of less steric ether groups as coordination
sites at the expense of amine groups in complexes 6–9 has an
effect on complex structures. The complex 7 formed as a tetra-
mer with a Sr4O4 cubane core. The alkoxide oxygen atoms in 7
undergo µ3-bridging between three strontium atoms whereas
the ether oxygen coordinated to individual strontium atoms
and the terminal amine group remained uncoordinated. The
formation of a high nuclearity complex might be due to the
less steric effects associated with ether groups compared to
the tertiary amine groups which provide more flexibility to the
ligands in the formation of the complex.
Table 1 Aminoalkoxide ligands used in complexes 1–9
Compound
Ligand used
Ligand structure
1
dmaemampH
2
bdeaeampH
3
4
bdmapampH
bdmadmaehH
The complexes were prepared through a procedure slightly
modified from that in previously published work.10 The Sr[N-
(SiMe3)2]2·2DME solution in toluene was first treated with the
corresponding aminoalcohol in an equivalent ratio followed by
the addition of tmhdH (as shown in Scheme 1 for the complex
1), and the resulting reaction mixture was stirred overnight at
room temperature to afford the respective complexes 1–9. The
X-ray quality crystals of complexes 1, 2, 4, 5, and 7 were grown
from a saturated hexane solution of the corresponding com-
plexes at −30 °C.
5
bdmadmaphH
6
7
dmaempH
dmapmpH
8
9
dmamempH
dmaeempH
The complex 1 crystallized in the P21/n space group (Fig. 1),
in which one 3-(((2-(dimethylamino)ethyl)(methyl)amino)-
methyl)pentan-3-olate anion, one 2,2,6,6-tetramethyl-3,5-heptane-
dionato anion and one strontium atom are observed as an
14462 | Dalton Trans., 2014, 43, 14461–14469
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Scheme 1 Synthesis of complexes 1 and 7.
asymmetric unit. In 1, the metal centers appeared to be in a
highly distorted octahedral structure, where the alkoxide
oxygen bridged two strontium atoms, exactly as reported pre-
viously for [Sr(demamp)(tmhd)]2.10 The introduction of the
ethyl group (in dmaemamp) into the alkoxide carbon atom
compared to methyl groups (in demamp) had little impact on
the bonding nature or the overall structure of the complex.
The complex 2 (Fig. S1†), which has two 1-(bis(2-(diethyl-
amino)ethyl)amino)-2-methylpropan-2-olate anions, two 2,2,6,6-
tetramethyl-3,5-heptanedionato anions and two strontium
atoms in its asymmetric unit, crystallized in the monoclinic
space group Pc. The introduction of an extra coordination site,
using a tetradentate bdeaeamp ligand turned out to be less
useful as 2 remains in the dimer form, making use of only
three coordination sites from the bdeaeamp ligand and
leaving one amine side chain as a free site. The use of other
tetradentate ligands, that is, bdmadmaeh in 4 and bdmad-
maph in 5, had a similar effect: only three coordination sites
were used to form the dimer complexes and one of the amine
side chains remained as a free site. In 5 the Sr(2) appeared as
penta-coordinated leaving two of the amine side chains as free
sites. The complex 4 crystallized in the P21/n space group
(Fig. S2†), in which one 1,7-bis(dimethylamino)-4-(2-(dimethyl-
amino)ethyl)heptan-4-olate anion, one 2,2,6,6-tetramethyl-3,5-
heptanedionato anion, and one strontium atom are observed
as an asymmetric unit, whereas in 5 (Fig. 1) two strontium
atoms,
two
1,7-bis(dimethylamino)-4-(3-(dimethylamino)-
propyl)heptan-4-olate anions, and two 2,2,6,6-tetramethyl-3,5-
heptanedionato anions are observed as an asymmetric unit. In
complexes 4 and 5, apart from the bridging of the strontium
atoms with alkoxide μ2-oxygens, the amine side chains play an
important role in dimer formation by holding together both
the strontium atoms with coordinate bonds (N(1) bonding to
Sr(1), N(2) bonding to Sr(1i), and N(3) remaining free in 4; and
N(4) bonding to Sr(1), N(5) bonding to Sr(2), and N(6) remain-
Fig. 1 Crystal structure of complexes 1 (above) & 5 (below) (disorders
were avoided for clarity).
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 14461–14469 | 14463

View Article Online
Paper
Dalton Transactions
10
ing free in 5). Considering the bonding pattern in other stron- observed for the [Sr(demamp)(tmhd)]2 complex (3.7119(6)),
tium complexes of the same category, this type of cross brid- but shorter than those of other reported oxygen bridged com-
ging is quite unusual. In 5 Sr(2) remained penta-coordinated, plexes of strontium, such as the dinuclear complexes
going against the common trend in these complexes to acquire [Sr2(tmhd)4(HOCH2CH2OMe)2],11 and [Sr2(tmhd)4(dmaeH)2
a distorted octahedron (like Sr(1) in the same molecule). This (μ2-dmaeH)2],12 where the distance between the metal centres
is because of the unusual tilting of the tmhd group attached to is 4.039(2) and 4.435(2) Å, respectively. The average distances
Sr(2) by about 80.47(11)°, which creates significant hindrance between the strontium metal and the μ2-bridging alkoxide
to possible amine coordination with Sr(2) (the two planes that oxygen atoms are 2.4178(18) Å in 1, 2.426(2) Å in 2, 2.4265(3) Å
hold the two tmhd groups in these dimer complexes appear in in 4, and 2.448 (2) Å in 5, which are in the range seen for [Sr-
parallel to each other with angles between the planes of 0° in (demamp)(tmhd)]2 (2.416(2) Å), but shorter than the Sr–O
1, 4, and in [Sr(demamp)(tmhd)]2 but 9.62(23)° in 2). The Sr(2) bonds (2.728(6) and 2.796(6)) in [Sr2(tmhd)4(dmaeH)2(μ2-
atom in 5 shows a distorted square-pyramidal structure where dmaeH)2].12 The bridging angles (∠M–O–M) observed in these
the amine occupies the top of the pyramid. The distance complexes (98.59(6)° in 1, 103.52(8)° in 2, 100.39(9)° in 4, and
between the two metal centers in the dimeric structures was 100.85(8)° in 5) are comparable to that observed in
3.6659(12), 3.8128(10), 3.7287(10), and 3.7412(7) Å for 1, 2, 4, [Sr(demamp)(tmhd)]2 (104.58(5)°). Many attempts to produce
and 5, respectively (Table 2), which are within the range X-ray quality crystals of 3 were unsuccessful. However, with the
Table 2 Selected bond lengths (Å) and bond angles (°) of 1, 2, 4, and 5
[Sr(dmaemamp)(tmhd)]2 (1)
[Sr(bdeaeamp)(tmhd)]2 (2)
[Sr(bdmadmaeh)(tmhd)]2 (4)
[Sr(bdmadmaph)(tmhd)]2 (5)
Bond lengths (Å)
Sr(1)–O(3)i
Sr(1)–O(3)
Sr(1)–O(2)
Sr(1)–O(1)
Sr(1)–N(2)
Sr(1)–N(1)
2.3902(17)
Sr(1)–O(6)
Sr(1)–O(2)
Sr(1)–O(3)
Sr(1)–O(1)
Sr(1)–N(2)
Sr(1)–N(1)
Sr(2)–O(3)
Sr(2)–O(4)
Sr(2)–O(6)
Sr(2)–O(5)
Sr(2)–N(5)
Sr(2)–N(4)
Sr(1)⋯Sr(2)
2.399(2)
Sr(1)–O(3)i
Sr(1)–O(1)
Sr(1)–O(2)
Sr(1)–O(3)
Sr(1)–N(2)i
Sr(1)–N(1)
2.390(3)
2.445(3)
2.457(3)
2.463(3)
2.771(4)
2.787(4)
Sr(1)–O(4)
Sr(1)–O(3)
Sr(1)–O(1)
Sr(1)–O(2)
Sr(1)–N(1)
Sr(1)–N(4)
Sr(2)–O(1)
Sr(2)–O(4)
Sr(2)–O(6)
Sr(2)–O(5)
Sr(2)–N(51)
2.443(2)
2.451(2)
2.453(2)
2.479(2)
2.706(3)
2.712(3)
2.389(2)
2.411(2)
2.418(2)
2.421(2)
2.704(3)
2.4454(19)
2.4460(18)
2.452(2)
2.693(3)
2.754(3)
2.433(3)
2.453(2)
2.480(3)
2.747(3)
2.866(3)
2.402(2)
2.428(3)
2.455(2)
2.475(3)
2.761(3)
2.845(3)
3.8128(10)
Sr(1)⋯Sr(1)i
3.6659(12)
Sr(1)⋯Sr(1)i
3.7287(10)
Sr(1)⋯Sr(2)
3.7412(7)
Bond angles (°)
O(3)i–Sr(1)–O(3)
O(3)i–Sr(1)–O(2)
O(3)–Sr(1)–O(2)
O(3)i–Sr(1)–O(1)
O(2)–Sr(1)–O(1)
O(3)i–Sr(1)–N(2)
O(3)–Sr(1)–N(2)
O(2)–Sr(1)–N(2)
O(1)–Sr(1)–N(2)
O(3)i–Sr(1)–N(1)
O(3)–Sr(1)–N(1)
O(1)–Sr(1)–N(1)
N(2)–Sr(1)–N(1)
Sr(1)i–O(3)–Sr(1)
81.41(6)
113.30(6)
98.41(6)
121.33(7)
70.94(6)
141.51(8)
66.75(7)
92.99(7)
92.96(8)
96.89(7)
96.20(8)
84.81(8)
67.14(8)
98.59(6)
O(6)–Sr(1)–O(2)
O(6)–Sr(1)–O(3)
O(2)–Sr(1)–O(3)
O(6)–Sr(1)–O(1)
O(2)–Sr(1)–O(1)
O(3)–Sr(1)–O(1)
O(6)–Sr(1)–N(2)
O(3)–Sr(1)–N(2)
O(1)–Sr(1)–N(2)
O(2)–Sr(1)–N(1)
O(3)–Sr(1)–N(1)
O(1)–Sr(1)–N(1)
N(2)–Sr(1)–N(1)
Sr(2)–O(3)–Sr(1)
Sr(1)–O(6)–Sr(2)
O(3)–Sr(2)–O(4)
O(3)–Sr(2)–O(6)
O(4)–Sr(2)–O(6)
O(3)–Sr(2)–O(5)
O(4)–Sr(2)–O(5)
O(6)–Sr(2)–O(5)
O(3)–Sr(2)–N(5)
O(6)–Sr(2)–N(5)
O(5)–Sr(2)–N(5)
O(4)–Sr(2)–N(4)
O(6)–Sr(2)–N(4)
O(5)–Sr(2)–N(4)
N(5)–Sr(2)–N(4)
102.99(9)
76.52(8)
113.94(8)
101.27(8)
69.90(8)
175.83(8)
114.02(9)
95.13(9)
82.49(9)
95.75(9)
66.39(8)
115.48(9)
67.19(9)
103.52(8)
103.53(8)
103.26(9)
76.43(8)
111.59(9)
105.75(9)
69.78(9)
177.22(8)
114.26(9)
94.65(9)
82.89(9)
93.14(9)
66.65(8)
111.06(9)
67.60(9)
O(3)i–Sr(1)–O(1)
O(3)i–Sr(1)–O(2)
O(1)–Sr(1)–O(2)
O(3)i–Sr(1)–O(3)
O(1)–Sr(1)–O(3)
O(2)–Sr(1)–O(3)
O(3)i–Sr(1)–N(2)i
O(1)–Sr(1)–N(2)i
O(2)–Sr(1)–N(2)i
O(3)i–Sr(1)–N(1)
O(1)–Sr(1)–N(1)
O(3)–Sr(1)–N(1)
N(2)i–Sr(1)–N(1)
Sr(1)i–O(3)–Sr(1)
166.60(10)
103.26(9)
70.97(9)
79.61(9)
112.95(9)
99.36(9)
81.01(12)
86.61(12)
87.78(11)
101.70(11)
84.73(11)
84.57(11)
96.67(12)
100.39(9)
O(4)–Sr(1)–O(3)
O(4)–Sr(1)–O(1)
O(3)–Sr(1)–O(1)
O(3)–Sr(1)–O(2)
O(1)–Sr(1)–O(2)
O(4)–Sr(1)–N(1)
O(3)–Sr(1)–N(1)
O(1)–Sr(1)–N(1)
O(2)–Sr(1)–N(1)
O(4)–Sr(1)–N(4)
O(3)–Sr(1)–N(4)
O(1)–Sr(1)–N(4)
O(2)–Sr(1)–N(4)
Sr(2)–O(4)–Sr(1)
Sr(2)–O(1)–Sr(1)
O(1)–Sr(2)–O(4)
O(1)–Sr(2)–O(6)
O(4)–Sr(2)–O(6)
O(1)–Sr(2)–O(5)
O(4)–Sr(2)–O(5)
O(6)–Sr(2)–O(5)
O(1)–Sr(2)–N(51)
O(4)–Sr(2)–N(51)
O(6)–Sr(2)–N(51)
O(5)–Sr(2)–N(51)
105.32(8)
77.14(7)
173.17(8)
70.42(7)
108.33(7)
105.98(9)
86.92(8)
86.28(8)
84.47(9)
85.60(9)
87.41(9)
99.18(8)
83.79(8)
100.85(8)
101.18(8)
78.98(7)
115.36(8)
165.32(8)
122.26(9)
98.81(8)
71.35(8)
114.46(9)
89.49(8)
87.18(9)
123.24(10)
14464 | Dalton Trans., 2014, 43, 14461–14469
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
Table 3 Selected bond lengths (Å) and bond angles (°) of 7
(7)
Bond lengths (Å)
Sr(1)–O(1)
Sr(1)–O(2)
Sr(1)–O(3)i
Sr(1)–O(3)ii
Sr(1)–O(3)
2.432(2)
2.440(2)
2.509(2)
2.546(2)
2.554(2)
2.557(2)
2.510(2)
2.547(2)
3.8389(8)
3.8979(7)
3.8980(7)
Sr(1)–O(4)
O(3)–Sr(1)ii
O(3)–Sr(1)i
Sr(1)⋯Sr(1)iii
Sr(1)⋯Sr(1)i
Sr(1)⋯Sr(1)ii
Bond angles (°)
O(1)–Sr(1)–O(2)
O(1)–Sr(1)–O(3)i
O(2)–Sr(1)–O(3)i
O(1)–Sr(1)–O(3)ii
O(2)–Sr(1)–O(3)ii
O(3)i–Sr(1)–O(3)ii
O(1)–Sr(1)–O(3)
O(2)–Sr(1)–O(3)
O(3)i–Sr(1)–O(3)
O(3)ii–Sr(1)–O(3)
O(1)–Sr(1)–O(4)
O(2)–Sr(1)–O(4)
O(3)i–Sr(1)–O(4)
O(3)ii–Sr(1)–O(4)
O(3)–Sr(1)–O(4)
Sr(1)ii–O(3)–Sr(1)i
Sr(1)ii–O(3)–Sr(1)
Sr(1)i–O(3)–Sr(1)
70.61(8)
123.94(8)
96.92(8)
98.41(8)
164.54(8)
79.97(8)
155.98(8)
115.82(8)
79.38(8)
78.70(8)
92.80(8)
82.98(8)
141.20(7)
109.01(8)
66.32(7)
98.80(7)
100.67(8)
99.68(8)
Fig. 2 Crystal structure of the complex 7.
support of all identified structures of this class of compounds,
we expect that the overall structure of the complex 3 might be
similar to others.
The complex 7 crystallized in the I41/a space group (Fig. 2),
in which one 1-(3-(dimethylamino) propoxy)-2-methylpropan-
2-olate (dmapmp) anion, one 2,2,6,6-tetramethyl-3,5-heptane-
dionato anion and one strontium atom are observed as an
asymmetric unit. The introduction of ether oxygen as a coordi- the coordinating nitrogen atoms (detailed assignments of
nation site in 7 compared to the amine nitrogen atoms of com- identified individual protons are given in the Experimental
plexes 1–5 resulted in formation of a tetrameric complex. The section). The chemical shifts observed for the ligand protons
µ3-bridging of alkoxide oxygen atoms between three strontium in the complexes, and the absence of any –OH peak, con-
metal atoms afforded the Sr4O4 cubane core for the complex firmed the successful coordination of the corresponding
which is observed for the first time in strontium complexes aminoalkoxide and tmhd ligands to the strontium metal. The
although this type of metal–oxygen cubane structural motif tmhd protons display comparatively sharper peaks. The two
was reported for other metals.13 The ether oxygen atoms of tmhd tertiary butyl groups from complexes 1–9 resonate as
four dmapmp ligands were coordinated to single strontium singlets at δ = 1.33, 1.38, 1.34, 1.34, 1.33, 1.33, 1.35, 1.33, and
atoms each and the terminal amine groups were left uncoordi- 1.35 ppm, respectively, while the β-CH resonate at δ = 5.84,
nated. The coordination of two oxygen atoms from the tmhd 5.87, 5.88, 5.84, 5.84, 5.85, 5.90, 5.86, and 5.85 ppm according
ligands to each of the strontium atoms completes the coordi- to the order. Broad NMR peaks were reported in this work and
nation sphere, where the strontium atoms are in the hexaco- other aminoalkoxide strontium complexes10,14 may be due to
ordinated state with a distorted octahedral structure (Table 3). the slow site exchange in solution on the NMR time scale. To
The introduction of the ether group as a coordination site in examine possible structural changes in solution compound 1
complexes 6–9 compared to the amine groups in 1–5 has a dra- was studied through VT-NMR experiments in which tmhd
matic effect on complex formation. The low steric hindrance peaks remained as singlets and did not provide any proof of
exerted by the ether group allowed the formation of a high dissociation of the complex 1 in solution.
nuclearity complex for 7, whereas in 1–5 all complexes remained
In the literature the tmhd complexes and alkoxide com-
as dimers. There may be a similar effect in other complexes plexes of strontium displayed structural changes and solvent
(6, 8, and 9) where the ether group is present as a coordination coordination with the polar solvents used.15 So we repeated
site, but we were unsuccessful in obtaining quality crystals for the synthesis of complexes 1 and 7 in polar solvents like THF,
those complexes to conclude its structure.
diethyl ether, and DME to examine the stability of these com-
The NMR spectra of the complexes were recorded using plexes in different solvents. To our surprise none of the polar
C6D6 as the solvent and standard at room temperature. The 1H solvents coordinated to the metal and the complexes 1 and 7
NMR spectra of all the complexes exhibit broadness in the were obtained in pure form from those polar solvents. The pro-
aminoalkoxide protons, especially for those that are closer to ducts were isolated and characterized by NMR, IR and elemen-
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 14461–14469 | 14465

View Article Online
Paper
Dalton Transactions
is in agreement with the above assumption. The study of the
volatile character for the compounds at reduced pressure
(0.5 Torr) resulted in decomposition of complexes 6–9 at
150 °C, whereas complexes 1–5 display a stable character
throughout the experiment.
Experimental
General remarks
NMR spectra were recorded on a Bruker 300 MHz spectrometer
with C6D6 as the solvent and standard. IR spectra were
obtained with a Nicolet Nexus FT-IR spectrophotometer.
Elemental analyses were carried out on a ThermoScientific
OEA Flash 2000 Analyzer. Thermo-gravimetric analyses were
conducted on a SETARAM 92-18 TG-DTA instrument with a
constant flow of nitrogen throughout the experiment.
Fig. 3 TGA plots of [Sr(dmaemamp)(tmhd)]2 (1) (black), [Sr(bdeaeamp)-
(tmhd)]2 (2) (red), and [Sr(bdmapamp)(tmhd)]2 (3) (blue).
Sr[N(SiMe2)2]2·2DME,16
and
the
aminoalcohols,
bdeaeampH,14b bdmapampH,14b dmapmpH,17 dmaeempH,17
dmaempH,17 dmamempH,17 and 2,2-diethyloxirane18 were
prepared according to the literature methods. All reactions
were carried out under inert dry conditions using standard
Schlenk techniques or in an argon filled-glove box. Hexane
and toluene were purified with an Innovative Technology
PS-MD-4 solvent purification system. All other chemicals were
purchased from Aldrich and used as received.
tal analysis to confirm the results. This result shows the stabi-
lity of [Sr(aminoalkoxide)(tmhd)]x complexes which are
unaffected by the presence of coordinating polar solvents.
Thermo-gravimetric analyses of products 1–9 were con-
ducted from room temperature to 900 °C (Fig. 3, S4 and S5†).
Prior to the analyses, sampling was carried out in an argon
filled glove box, and data collection was performed under a
constant flow of nitrogen to avoid any air contact. The TGA
plot of compound 1 displays 5% loss in mass from 100 to
250 °C, followed by 71% loss up to 400 °C and further 4% up
to 500 °C. The first step may be due to the evaporation of any
trapped solvent in the complex, whereas the major weight loss
at 250–400 °C might be due to the evaporation of a part of the
compound and possible decomposition of the product and the
third mass loss should be attributed to the evaporation of a
portion of the decomposition products. Compounds 2–5 show
a step like character in their TG curves, with mass losses of
26% (150–300 °C), 40% (300–400 °C), and 6% (400–500 °C) for
2, 31% (120–325 °C), 54% (325–400 °C), and 4.4%
(400–500 °C) for 3, 33% (150–275 °C), 42% (275–380 °C), and
5% (380–500 °C) for 4, and 40% (150–330 °C), 36%
(330–400 °C), and 3% (400–500 °C) for 5. Compounds 6–9
exhibit a similar pattern in their respective TGA plots, in
which a considerable loss of mass can be seen from room
temperature to 300 °C, that is, 4%, 6%, 16%, and 11%,
respectively, followed by a major mass loss of 56%, 60%, 61%,
and 59%, respectively, in the region of 300–400 °C. Further
mass losses were observed in these complexes up to 500 °C as
7%, 4%, 3%, and 5%, respectively. The stepwise decompo-
sition pattern displayed by the complexes in the TG analyses
and relatively high amount of residues (except for 3) indicate
the self-decomposition of the complexes during the TG analy-
sis, which reflects the temperature instability of the complexes.
As all possibilities of contact with air and oxygen were avoided,
the residue is thought to be a mixture of strontium oxide and
non-volatile fractions as a result of ligand decomposition. The
calculation based on the molecular weights of the compounds
Syntheses
3-(((2-(Dimethylamino)ethyl)(methyl)amino)methyl)pentan-
3-ol (dmaemampH). 2,2-Diethyloxirane (10.0 g, 0.10 mol) was
added dropwise at 0 °C with constant stirring to a 40% water
solution of trimethylethane-1,2-diamine (10.2 g, 0.10 mol)
taken in a three-necked flask fitted with a reflux condenser.
After the addition, the reaction mixture was allowed to warm
up to room temperature and stirring was continued for
another six hours. Then, the product was extracted three times
with ether (50 mL × 3) and the combined organic layer was
washed with brine. The solvent was removed, and the residue
was distilled (60 °C/0.5 Torr) to obtain the pure product as a
colorless liquid. Yield 14.2 g (70%). FTIR (νmax/cm−1) 3375
(OH). Found: C, 65.28; H, 12.92; N, 13.86. Calc. for C9H22N2O:
C, 65.30; H, 12.95%; N, 13.84. δH (300 MHz; C6D6; TMS) 0.97
(6 H, t, OC(CH2CH3)2), 1.57 (4 H, m, OC(CH2CH3)2), 2.02 (6 H,
s, N(CH3)2), 2.10 (2 H, t, (CH3)2NCH2), 2.21 (3 H, s, N(CH3)),
2.24 (2 H, s, N(CH3)CH2), 2.32 (2 H, t, (CH3)2NCH2CH2), 5.25
(1 H, s, OH).
1,7-Bis(dimethylamino)-4-(2-(dimethylamino)ethyl)heptan-4-ol
(bdmadmaehH). Methyl 3-(dimethylamino)propanoate (5.07 g,
0.040 mol) in 200 mL anhydrous benzene was added dropwise
under nitrogen to a stirred solution of 3-dimethylaminopropyl-
magnesium chloride prepared from dry magnesium turnings
(2.94 g, 0.12 mol) and 3-dimethylaminopropyl chloride (14.1 g,
0.11 mol) in anhydrous THF (100 mL). The reaction mixture
was heated at reflux for 10 h and then cooled in an ice bath
and hydrolyzed by adding a saturated solution of ammonium
chloride (50 mL). The organic layer was separated and the
14466 | Dalton Trans., 2014, 43, 14461–14469
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
aqueous solution was extracted with diisopropyl ether (10 × 2.30–2.90 (18 H, br), 5.87 (1 H, s, β-CH). EI-MS: m/z calc. for
50 mL). The organic solutions were combined and dried over [Sr(bdeaeamp)(tmhd)]2: 1086.65 [M]+; found 725 [Sr2(tmhd)3]+,
Na2SO4. The solvent was evaporated to give the crude product. 271 [Sr(tmhd)]+.
The purified product was collected by distillation (125 °C/0.02
Torr) as a colorless liquid. Yield 5.00 g (47%). FTIR (νmax/cm−1
[Sr(bdmapamp)(tmhd)]x (3). Sr(btsa)2·2DME (0.590 g,
1.0 mmol), 1-(bis(3-(dimethylamino)propyl)amino)-2-methyl-
)
3254 (OH). Found: C, 65.83; H, 12.90; N, 15.39. Calc. for propan-2-ol (bdmapampH) (0.260 g, 1.0 mmol) and 2,2,6,6-tetra-
C9H22N2O: C, 65.88; H, 12.90; N, 15.37%. δH (300 MHz; C6D6; methyl-3,5-heptanedione (tmhdH) (0.184 g, 1.0 mmol) were
TMS) 1.52–1.65 (10 H, m, (CH2CH2CH2)2C(OH)CH2CH2), 1.98 used. Yield 0.490 g (93%). FTIR (νmax/cm−1) 2950s, 2862w,
(6 H, s, CH2CH2N(CH3)2), 2.11 (12 H, s, 2 (CH2CH2CH2N- 2814w, 2783w, 1592s, 1577m, 1534w, 1504m, 1457m, 1417vs,
(CH3)2), 2.22 (4 H, t, 2 (CH2CH2CH2N(CH3)2), 2.33 (2 H, t, 1388m, 1358m, 1224w, 1183w, 1128w, 1041w, 864w, 791w,
CH2CH2N(CH3)2), 5.87 (1 H, s, OH).
755w, 473w. Found: C, 56.40; H, 9.62; N, 8.06. Calc. for
1,7-Bis(dimethylamino)-4-(3-(dimethylamino)propyl) heptan- C50H102N4O6Sr2: C, 56.73; H, 9.71; N, 7.94%. δH (300 MHz;
4-ol (bdmadmaphH). A similar procedure was followed to that C6D6; TMS) 1.34 (18 H, br s, C(CH3)3), 1.61 (10 H, br s, C(CH3)2
described above, but using methyl 4-(dimethylamino) butano- and CH2CH2CH2), 2.11 (16 H, s + m, N(CH3)2 and CH2CH2CH2),
ate (5.80 g, 0.040 mol). The purified product was collected by 2.23 (4 H, t, CH2CH2CH2), 2.61 (2 H, br s, CH2C-(CH3)2), 5.88
distillation (130 °C/0.02 Torr) as a colorless liquid. Yield 2.80 g (1 H, s, β-CH). EI-MS: m/z calc. for [Sr(bdmapamp)(tmhd)]2:
(25%). FTIR (νmax/cm−1) 3196 (OH). Found: C, 66.53; H, 12.95; 1030.59 [M]+; found 725 [Sr2(tmhd)3]+, 271 [Sr(tmhd)]+.
N, 14.65. Calc. for C9H22N2O: C, 66.85; H, 12.97%; N, 14.62. δH
[Sr(bdmadmaeh)(tmhd)]2 (4). Sr(btsa)2·2DME (0.590 g,
(300 MHz; C6D6; TMS) 1.53–1.65 (12 H, m, (CH2CH2CH2)3C- 1.0 mmol), 1,7-bis(dimethylamino)-4-(2-(dimethylamino)ethyl)
(OH)), 2.08 (18 H, s, 3 (N(CH3)2), 2.18 (6 H, t, (CH2CH2CH2)3C- heptan-4-ol (bdmadmaehH) (0.274 g, 1.0 mmol) and 2,2,6,6-
(OH)), 5.79 (1 H, s, OH).
tetramethyl-3,5-heptanedione (tmhdH) (0.184 g, 1.0 mmol)
were used. Yield 0.480 g (88%). FTIR (νmax/cm−1) 2949s, 2862w,
2813w, 2782w, 1590s, 1576m, 1533w, 1504m, 1452m, 1415vs,
General procedure for [Sr(aminoalkoxide)(tmhd)]2 complexes
The aminoalcohol in toluene (5 mL) was added dropwise at 1387m, 1356m, 1223w, 1183w, 1128w, 1041w, 864w, 789w,
room temperature to a solution of Sr(btsa)2·2DME in toluene 752w, 471w. Found: C, 57.31; H, 9.81; N, 7.68. Calc. for
(15 mL) under stirring. After stirring for 5 h at room tempera- C52H106N6O6Sr2: C, 57.47; H, 9.83; N, 7.73%. δH (300 MHz;
ture, 2,2,6,6-tetramethyl-3,5-heptanedione (tmhdH) was added C6D6; TMS) 1.34 (18 H, s, C(CH3)3), 1.50 (10 H, br m,
to the reaction mixture, which was then stirred for another (CH2CH2CH2)2C(OH)CH2CH2), 2.06 (6 H, s, CH2CH2N(CH3)2),
15 h at room temperature. Then, the solvent was evaporated 2.27 (16 H, br s, CH2CH2CH2N(CH3)2 and CH2CH2N(CH3)2),
and the residue was extracted with hexane, filtered, and dried 2.75 (2 H, br s, CH2CH2CH2N(CH3)2), 5.84 (1 H, s, β-CH).
to obtain the product. X-ray quality crystals were grown from EI-MS: m/z calc. for [Sr(bdmadmaeh)(tmhd)]2: 1086.63 [M]+;
concentrated hexane solutions upon cooling.
found 725 [Sr2(tmhd)3]+, 271 [Sr(tmhd)]+.
[Sr(dmaemamp)(tmhd)]2 (1). Sr(btsa)2·2DME (0.590 g,
[Sr(bdmadmaph)(tmhd)]2 (5). Sr(btsa)2·2DME (0.590 g,
1.0
mmol),
3-(((2-(dimethylamino)ethyl)(methyl)amino)- 1.0 mmol), 1,7-bis(dimethylamino)-4-(3-(dimethylamino)-
methyl) pentan-3-ol (dmaemampH) (0.202 g, 1.0 mmol), and propyl) heptan-4-ol (bdmadmaphH) (0.288 g, 1.0 mmol) and
2,2,6,6-tetramethyl-3,5-heptanedione (tmhdH) (0.184 g, 2,2,6,6-tetramethyl-3,5-heptanedione (tmhdH) (0.184 g,
1.0 mmol) were used. Yield 0.420 g (89%). FTIR (νmax/cm−1
)
1.0 mmol) were used. Yield 0.500 g (90%). FTIR (νmax/cm−1
)
2961s, 2864w, 1590vs, 1576m, 1534w, 1504m, 1456m, 1420vs, 2947s, 2863w, 2814w, 2778w, 1591s, 1577m, 1534w, 1503m,
1354w, 1224w, 1186w, 1126w, 1038w, 863w, 789(w), 751w, 1451m, 1417vs, 1388m, 1358m, 1272w, 1183w, 1128w, 1040w,
470w. Found: C, 54.76; H, 9.12; N, 5.70. Calc. for 864w, 790w, 755w, 472w. Found: C, 57.95; H, 9.94; N, 7.45.
C44H88N4O6Sr2: C, 55.96; H, 9.39; N, 5.93%. δH (300 MHz; Calc. for C54H110N6O6Sr2: C, 58.18; H, 9.95; N, 7.54%. δH
C6D6; TMS) 0.91 (6 H, br m, OC(CH2CH3)2), 1.33 (18 H, s, (300 MHz; C6D6; TMS) 1.33 (18 H, s, C(CH3)3), 1.54 (6 H, br m,
C(CH3)3), 1.2–1.8 (4 H, br m, OC(CH2CH3)2), 2.0–2.4 (11 H, br CH2CH2CH2N(CH3)2), 1.67 (6 H, br m, CH2CH2CH2N(CH3)2),
m), 2.50 (4 H, br s), 5.84 (1 H, s, β-CH). EI-MS: m/z calc. for 2.18 (18 H, s, (CH3)2N), 2.40 (6 H, br m, CH2CH2CH2N(CH3)2),
[Sr(dmaemamp)(tmhd)]2: 944.48 [M]+; found 725 [Sr2(tmhd)3]+, 5.84 (1 H, s, β-CH). EI-MS: m/z calc. for [Sr(bdmadmaph)-
271 [Sr(tmhd)]+.
[Sr(bdeaeamp)(tmhd)]2 (2). Sr(btsa)2·2DME (0.590 g, [Sr(tmhd)]+.
1.0 mmol), 1-(bis(2-(diethylamino)ethyl)amino)-2-methyl- [Sr(dmaemp)(tmhd)]x
(tmhd)]2: 1114.66 [M]+; found 725 [Sr2(tmhd)3]+, 271
(6). Sr(btsa)2·2DME
(0.590
g,
propan-2-ol (bdeaeampH) (0.288 g, 1.0 mmol) and 2,2,6,6- 1.0 mmol), 1-(2-(dimethylamino)ethoxy)-2-methylpropan-2-ol
tetramethyl-3,5-heptanedione (tmhdH) (0.184 g, 1.0 mmol) (dmaempH) (0.161 g, 1.0 mmol) and 2,2,6,6-tetramethyl-3,5-
were used. Yield 0.510 g (92%). FTIR (νmax/cm−1) 2967s, 2814w, heptanedione (tmhdH) (0.184 g, 1.0 mmol) were used. Yield
1591s, 1576m, 1534w, 1503m, 1455m, 1417vs, 1387m, 1356m, 0.370 g (86%). FTIR (νmax/cm−1) 2952s, 2899m, 2866m, 2821w,
1220w, 1181w, 1129w, 1058w, 976w, 863w, 789w, 731w, 468w. 2781w, 1596s, 1576m, 1534w, 1503m, 1456s, 1419vs, 1388m,
Found: C, 58.07; H, 9.89; N, 7.40. Calc. for C54H110N4O6Sr2: C, 1358m, 1271w, 1225m, 1184m, 1109m, 1043w, 982w, 945w,
58.18; H, 9.95; N, 7.54%. δH (300 MHz; C6D6; TMS) 1.04 (12 H, 863w, 790w, 752w, 472w. Found: C, 52.41; H, 8.71; N, 3.18.
t, N(CH2CH3)2), 1.38 (18 H, s, C(CH3)3), 1.44 (6 H, s, C(CH3)2O), Calc. for C38H74N2O8Sr2: C, 52.93; H, 8.65; N, 3.25%. δH
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 14461–14469 | 14467

View Article Online
Paper
Dalton Transactions
(300 MHz; C6D6; TMS) 1.33 (18 H, s, C(CH3)3), 1.53 (6 H, br s, beam monochromator. The RapidAuto software19 was used for
C(CH3)2), 2.08 (8 H, br s, (CH3)2N and OCH2CH2), 3.24 (2 H, br data collection and processing. The crystal structures were
s, C(CH3)2OCH2O), 3.46 (2 H, br s, CH2OCH2), 5.85 (1 H, s, solved by the direct method with SIR-97 of the WINGX soft-
β-CH). EI-MS: m/z calc. for [Sr(dmaemp)(tmhd)]2: 862.36 [M]+; ware package20 and refined by full-matrix least-squares calcu-
found 725 [Sr2(tmhd)3]+, 271 [Sr(tmhd)]+.
[Sr(dmapmp)(tmhd)]4 (7). Sr(btsa)2·2DME
lations with the SHELXTL software package.21
One 3-(((2-(dimethylamino)ethyl)(methyl)amino)methyl)-
(0.590
g,
1.0 mmol), 1-(3-(dimethylamino)propoxy)-2-methylpropan-2-ol pentan-3-olate anion, one 2,2,6,6-tetramethyl-3,5-heptanedio-
(dmapmpH) (0.175 g, 1.0 mmol) and 2,2,6,6-tetramethyl-3,5- nato anion and one strontium atom were observed as an asym-
heptanedione (tmhdH) (0.184 g, 1.0 mmol) were used. Yield metric unit for 1, two 1-(bis(2-(diethylamino)ethyl)amino)-2-
0.390 g (88%). FTIR (νmax/cm−1) 2952s, 2865w, 2815w, 2765w, methylpropan-2-olate anions, two 2,2,6,6-tetramethyl-3,5-
1588s, 1577s, 1535w, 1504m, 1455m, 1413vs, 1388m, 1357m, heptanedionato anions and two strontium atoms were
1271w, 1183w, 1130w, 1077m, 940w, 864w, 791w, 755w, 471w. observed as an asymmetric unit in 2, one 1,7-bis(dimethyl-
Found: C, 53.34; H, 8.92; N, 3.29. Calc. for C40H78N2O8Sr2: C, amino)-4-(2-(dimethylamino)ethyl)heptan-4-olate anion, one
53.96; H, 8.83; N, 3.15%. δH (300 MHz; C6D6; TMS) 1.35 (18 H, 2,2,6,6-tetramethyl-3,5-heptanedionato anion and one stron-
s, C(CH3)3), 1.65 (6 H, s, C(CH3)2), 1.77 (2 H, m, tium atom were observed as an asymmetric unit in 4, two
(CH3)2NCH2CH2CH2), 2.09 (6 H, s, (CH3)2N), 2.21 (2 H, t, strontium atoms, two 1,7-bis(dimethylamino)-4-(3-(dimethyl-
(CH3)2NCH2CH2CH2), 3.70 (4 H, m, (CH3)2NCH2CH2CH2 and amino)propyl)heptan-4-olate anions, and two 2,2,6,6-tetra-
C(CH3)2OCH2), 5.90 (1 H, s, β-CH). EI-MS: m/z calc. for methyl-3,5-heptanedionato anions were observed as an
[Sr(dmapmp)(tmhd)]2: 890.39 [M]+; found 725 [Sr2(tmhd)3]+, asymmetric unit in 5, and one 1-(3-(dimethylamino) propoxy)-
271 [Sr(tmhd)]+.
2-methylpropan-2-olate (dmapmp) anion, one 2,2,6,6-tetra-
[Sr(dmamemp)(tmhd)]x (8). Sr(btsa)2·2DME (0.590 g, methyl-3,5-heptanedionato anion and one strontium atom are
1.0 mmol), 1-((1-(dimethylamino)propan-2-yl)oxy)-2-methyl- observed as an asymmetric unit in 7. All non-hydrogen atoms
propan-2-ol (dmamempH) (0.175 g, 1.0 mmol) and 2,2,6,6- are refined anisotropically; the hydrogen atoms were assigned
tetramethyl-3,5-heptanedione (tmhdH) (0.184 g, 1.0 mmol) isotropic displacement coefficients U(H) = 1.2U (C) and 1.5U
were used. Yield 0.380 g (85%). FTIR (νmax/cm−1) 2952vs, (Cmethyl), and their coordinates were allowed to ride on their
2865s, 2829w, 2781w, 1595vs, 1577s, 1534w, 1504m, 1456s, respective atoms. In 1, the least-squares refinement of the
1418vs, 1388m, 1359m, 1272w, 1224w, 1184w, 1128w, 1082w, structural model was performed under geometry restraint
1051w, 989w, 950w, 863w, 790w, 755w, 472w. Found: C, 52.56; DFIX for the disordered part of a 3-(((2-(dimethylamino)ethyl)-
H, 9.02; N, 3.01. Calc. for C40H78N2O8Sr2: C, 53.96; H, 8.83; N, (methyl)amino)methyl)-pentan-3-olate anion. Refinement of
3.15%. δH (300 MHz; C6D6; TMS) 1.23 (3 H, br s, CH(CH3)), the structure converged at a final R1 = 0.0422 and wR2 = 0.0820
1.33 (18 H, s, C(CH3)3), 1.54 (6 H, br s, C(CH3)2), 2.12 (6 H, br for 4152 reflections with I > 2σ(I); R1 = 0.0770 and wR2 = 0.0905
s, (CH3)2N), 2.66 (1 H, br s, N(CH3)2CH2), 3.34 (1 H, br s, for all 5953 reflections. The largest difference peak and hole
CH(CH3)OCH2), 3.55 (2H, br s, CH(CH3)OCH2), 5.86 (1H, s, were 0.346 and −0.520 e Å−3, respectively. In 2 the least-
β-CH). EI-MS: m/z calc. for [Sr(dmamemp)(tmhd)]2: squares refinement of the structural model was performed
890.39 [M]+; found 725 [Sr2(tmhd)3]+, 271 [Sr(tmhd)]+.
[Sr(dmaeemp)(tmhd)]x (9). Sr(btsa)2·2DME (0.590
under geometry restraint DFIX and displacement parameter
g, restraint ISOR for the disordered part of a 1-(bis(2-(diethyl-
1.0 mmol), 1-(2-(2-(dimethylamino)ethoxy)ethoxy)-2-methyl amino)ethyl)amino)-2-methylpropan-2-olate anion. Refine-
propan-2-ol (dmaeempH) (0.205 g, 1.0 mmol) and 2,2,6,6-tetra- ment of the structure converged at a final R1 = 0.0383 and
methyl-3,5-heptanedione (tmhdH) (0.184 g, 1.0 mmol) were wR2 = 0.0809 for 10 590 reflections with I > 2σ(I); R1 = 0.0573
used. Yield 0.410 g (86%). FTIR (νmax/cm−1) 2950s, 2820w, and wR2 = 0.0919 for all 13 398 reflections. The largest differ-
2771w, 1593s, 1576m, 1533w, 1504m, 1455s, 1420vs, 1387m, ence peak and hole were 0.536 and −0.586 e Å−3, respectively.
1357m, 1270w, 1224w, 1184w, 1126m, 1090w, 1052w, 950w, In 4, structural refinement converged to a final value of R1 =
863w, 789w, 472w. Found: C, 52.34; H, 9.01; N, 2.92. Calc. for 0.0434, wR2 = 0.0933 for all 4609 reflections with I > 2σ(I); R1 =
C42H82N2O10Sr2: C, 53.08; H, 8.70; N, 2.95%. δH (300 MHz; 0.0882, wR2 = 0.1429 for all 6938 reflections. The largest differ-
C6D6; TMS) 1.35 (18 H, s, C(CH3)3), 1.56 (6 H, br s, C(CH3)2), ence peak and hole were 0.966 and −1.219 e Å−3, respectively.
2.12 (6 H, br s, (CH3)2N), 2.37 (2 H, br m, (CH3)2NCH2), 3.52 In 5, refinement of the structure converged at a final R1
=
(8 H, br m), 5.85 (1 H, s, β-CH). EI-MS: m/z calc. for 0.0540, wR2 = 0.0984 for 9012 reflections with I > 2σ(I); R1
=
[Sr(dmaeemp)(tmhd)]2: 950.41 [M]+; found 725 [Sr2(tmhd)3]+, 0.1068, wR2 = 0.1165 for all 14 403 reflections. The largest
271 [Sr(tmhd)]+.
difference peak and hole were 0.725 and −0.499 e Å−3, respect-
ively. In 7, refinement of the structure converged at a final R1 =
0.0508, wR2 = 0.1035 for 3608 reflections with I > 2σ(I); R1
0.0904, wR2 = 0.1205 for all 5378 reflections. The largest differ-
Crystallographic data collection and refinement of the
structure
=
Crystals of complexes 1, 2, 4, 5, and 7 were coated with para- ence peak and hole were 0.622 and −0.772 e Å−3, respectively.
tone oil and the diffraction data were measured at 173 K with CCDC-973486 (1), 973487 (2), 973488 (4), 973489 (5), and
Mo Kα radiation on an X-ray diffraction camera system using 1004596 (7) contain the supplementary crystallographic data
an imaging plate equipped with a graphite crystal incident for this paper.
14468 | Dalton Trans., 2014, 43, 14461–14469
This journal is © The Royal Society of Chemistry 2014

View Article Online
Dalton Transactions
Paper
(b) R. A. Gardiner, D. C. Gordon, G. T. Stauf and
B. A. Vaartstra, Chem. Mater., 1994, 6, 1967; (c) S. R. Drake,
S. A. S. Miller and D. J. Williams, Inorg. Chem., 1993, 32, 3227.
8 (a) T. Hatanpää, M. Vehkamäki, I. Mutikainen, J. Kansikas,
M. Ritala and M. Leskelä, J. Chem. Soc., Dalton Trans., 2004,
1181; (b) M. Vehkamäki, T. Hatanpää, T. Hanninen,
M. Ritala and M. Leskelä, Electrochem. Solid-State Lett.,
1999, 2, 504; (c) T. Hatanpää, M. Ritala and M. Leskelä,
J. Organomet. Chem., 2007, 692, 5256.
9 (a) J. P. Lee, M. H. Park, T.-M. Chung, Y. Kim and
M. M. Sung, Bull. Korean Chem. Soc., 2004, 25, 475;
(b) S. W. Lee, O. S. Kwon, J. H. Han and C. S. Hwang, Appl.
Phys. Lett., 2008, 92, 222903; (c) T. Blanquart, J. Niinistö,
M. Gavagnin, V. Longo, V. R. Pallem, C. Dussarrat,
M. Ritala and M. Leskela, Chem. Mater., 2012, 24, 3420;
(d) J. Niinistö, K. Kukli, M. Kariniemi, M. Ritala,
M. Leskelä, N. Blasco, A. Pinchart, C. Lachaud,
N. Laaroussi, Z. Wang and C. Dussarrat, J. Mater. Chem.,
2008, 18, 5243; (e) S. M. George, B. K. Park, C. G. Kim and
T.-M. Chung, Bull. Korean Chem. Soc., 2013, 34, 967.
Conclusions
Attempts to synthesize several heteroleptic complexes of stron-
tium with different aminoalkoxide and tmhd ligands were suc-
cessful. Although the introduction of various aminoalkoxide
ligands with increased coordination ability and bulkiness was
not successful in making monomeric structures, various struc-
turally interesting strontium complexes were prepared. The
strontium atoms in complexes 1–5 used only five or six coordi-
nation sites from the several available to form stable dimer
structures. The tendency of strontium atoms to form strong μ2-
oxygen bridging with an alkoxy group appeared to be the setback
in our attempts to produce efficient monomer complexes. The
crystal structures of 4 and 5 show an interesting bonding
nature of amine side chains in which one unit of bdmadmaeh
and bdmadmaph forms coordination bonds to both the stron-
tium atoms in their respective dimers. Whereas in complexes
6–9 the introduction of ether groups in place of amine groups
as coordination sites resulted in formation of high nuclearity
compounds due to the less steric hindrance in those ligands.
The complex 7 formed as a tetramer and the alkoxide oxygen 10 S. M. George, B. K. Park, C. G. Kim and T.-M. Chung,
underwent μ3-bridging in the complex which resulted in a Eur. J. Inorg. Chem., 2014, 2002.
unique Sr4O4 cubane core for the complex. The TG analyses of 11 H. Guillon, L. G. Hubert-Pfalzgraf and J. Vaisserman, Main
the complexes show a major weight loss in the region of Group Metal Chem., 1997, 20, 633.
250–300 °C for 1 and two-step losses at 150–400 °C for com- 12 H. O. Davies, J. J. Brooks, A. C. Jones, T. J. Leedham,
plexes 2–5, whereas in complexes 6–9 a major loss occurred at
300–400 °C. Studies are in progress on the application of these
J. F. Bickley, A. Steiner, P. O’Brien, A. J. P. White and
D. J. Williams, Polyhedron, 2001, 20, 2397.
heteroleptic strontium complexes as possible precursors for 13 (a) M. H. Chisholm, S. R. Drake, A. A. Naiini and
the growth of thin films of SrTiO3 (STO) and Ba0.5Sr0.5TiO3
(BSTO). The high solubility of these complexes makes the syn-
thesis of STO nanoparticles in the solution phase feasible.
W. E. Streib, Polyhedron, 1991, 10, 337; (b) H. Lehmkuhl,
K. Mehler, R. Benn, A. Rufinska and C. Kriiger, Chem. Ber.,
1986, 119, 1054; (c) V.-C. Arunasalam, I. Baxter, S. R. Drake,
M. B. Hursthouse, K. M. A. Malik and D. J. Otway, Inorg.
Chem., 1995, 34, 5295.
Acknowledgements
14 (a) T.-M. Chung, C. G. Kim, S. S. Lee, J. C. Won and
M.-J. Park, Korean Pat., 10-1039442, 2010; (b) T.-M. Chung,
C. G. Kim, S. S. Lee, J. C. Won and M.-J. Park, Korean Pat.,
10-1052359, 2010; (c) Y. Chi, S. Ranjan, T.-Y. Chou,
C.-S. Liu, S.-M. Peng and G.-H. Lee, J. Chem. Soc., Dalton
Trans., 2001, 2462.
This research was supported by the Converging Research
Center Program through the Ministry of Education, Science
and Technology (2013K000153).
15 (a) W. Paw, T. H. Baum, K.-C. Lam and A. L. Rheingold, Inorg.
Chem., 2000, 39, 2011; (b) W. D. Buchanan, M. A. Guino-o
and K. Ruhlandt-Senge, Inorg. Chem., 2010, 49, 144.
16 M. Westerhausen, Inorg. Chem., 1991, 30, 96.
Notes and references
1 S. Ezhilvalavan and T. Y. Tseng, Mater. Chem. Phys., 2000,
65, 227.
2 A. C. Jones and P. R. Chalker, J. Phys. D: Appl. Phys., 2003, 17 M. Kim, H. S. Jang, T.-M. Chung, C. G. Kim, Y. Kim and
36, R80.
B. R. Cho, Bull. Korean Chem. Soc., 2005, 26, 829.
18 J. Adams, L. Hoffman Jr. and B. M. Trost, J. Org. Chem.,
1970, 35, 1600.
19 Rapid Auto software, R-Axis series, Cat. no. 9220B101,
Rigaku Corporation.
3 Z. X. Shen and D. S. Dessau, Phys. Rep., 1995, 253, 1–162.
4 H. Heikkinen, L. S. Johansson, E. Nykanen and L. Niinisto,
Appl. Surf. Sci., 1998, 133, 205.
5 K. D. Kreuer, Annu. Rev. Mater. Res., 2003, 33, 333.
6 M. Mogensen and S. Skaarup, Solid State Ion. Diffus. React., 20 L. J. Farregia, WINGX program (Version 1. 70. 01), J. Appl.
1996, 86–88, 1151. Crystallogr., 1999, 32, 837.
7 (a) O. S. Kwon, S. K. Kim, M. Cho, C. S. Hwang and 21 G. M. Sheldrick, SHELX program, Acta Crystallogr., Sect. A:
J. Jeong, J. Electrochem. Soc., 2005, 152, C229;
Fundam. Crystallogr., 2008, 64, 112.
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 14461–14469 | 14469