Five new zinc phosphite structures: Tertiary building blocks in the construction of hybrid materials

Article abstract of DOI:10.1021/ic048204u

The syntheses and structures of five new zinc phosphites [Zn(HPO ₃)(C₄H₆N₂)] (1), [Zn ₂(HPO₃)₂(C₁₀H₁₀N ₂)₂]₂ (2), [Zn(HPO₃)(C ₁₄H₁₄N₄)O_0.5] (3), [Zn ₂(HPO₃)₂(C₁₄H₁₄N ₄)]·0.4H₂O (4), and [Zn₂(HPO ₃)₂(C₁₄H₁₄N₄)] (5) are reported. In compounds 1-3, the zinc atoms are ligated by 1-methylimidazole, 1-benzylimidazole, and 1,4-bis(imidazol-1-ylmethyl)-benzene, respectively, while compounds 4 and 5 are synthesized in the presence of the same bifunctional ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. The inorganic framework of compound 1 is composed of vertex-shared ZnO₃N and HPO₃ tetrahedra that form 4-rings, which, in turn, are linked to generate a one-dimensional ladder structure. In 2, the inorganic framework is composed of 4-rings and 8-rings to form the well-known 4.8² 2D network. This is connected via C-H...π interactions between 1-benzylimidazole ligand to generate a pseudo-pillared-layer structure. In 3, the inorganic framework again has the 4.8² topology pillared by the bis(imidazole) ligand, 1,3-bis(imidazol-1-ylmethyl)benzene. In 4, a new layer pattern is observed. Specifically, three edge-sharing 4-rings form triple-fused 4-rings. These tertiary building units are further connected to form 12-rings. The alternating triple 4-rings and 12-rings form a previously unknown 2D inorganic sheet. The sheets are joined together by the bis(imidazole) ligand, 1,3-bis(imidazol-1- ylmethyl)benzene, to generate a 3D pillared-layer structure. In 4, benzene rings and imidazole rings stack in a zigzag pattern in the interlayer space. A significant role for the triple 4-ring tertiary building unit in the formation of hybrid inorganic/organic metal phosphite structures is proposed for 4 and 5. In 5, the triple 4-rings fuse to give a 1D stair-step structure. Calculations show that the triple 4-ring pattern observed in the linear ladder structure of 1 is more stable than that in the stair step pattern of 5.

Full text of DOI:10.1021/ic048204u

Inorg. Chem. 2005, 44, 2719−2727
Five New Zinc Phosphite Structures: Tertiary Building Blocks in the
Construction of Hybrid Materials
Jian Fan,† Carla Slebodnick,† Diego Troya,† Ross Angel,‡ and Brian E. Hanson*,†
Department of Chemistry, Virginia Polytechnic Institute and State UniVersity,
Blacksburg, Virginia 24061, and Department of Geosciences, Virginia Polytechnic Institute and
State UniVersity, Blacksburg, Virginia 24061
Received December 20, 2004
The syntheses and structures of five new zinc phosphites [Zn(HPO3)(C4H6N2)] (1), [Zn2(HPO3)2(C10H10N2)2]2 (2),
[Zn(HPO3)(C14H14N4)0.5] (3), [Zn2(HPO3)2(C14H14N4)] 0.4H2O (4), and [Zn2(HPO3)2(C14H14N4)] (5) are reported. In
compounds 1 3, the zinc atoms are ligated by 1-methylimidazole, 1-benzylimidazole, and 1,4-bis(imidazol-1-ylmethyl)-
‚
−
benzene, respectively, while compounds 4 and 5 are synthesized in the presence of the same bifunctional ligand,
1,3-bis(imidazol-1-ylmethyl)benzene. The inorganic framework of compound 1 is composed of vertex-shared ZnO3N
and HPO3 tetrahedra that form 4-rings, which, in turn, are linked to generate a one-dimensional ladder structure.
In 2, the inorganic framework is composed of 4-rings and 8-rings to form the well-known 4.82 2D network. This is
connected via C−H‚‚‚π interactions between 1-benzylimidazole ligand to generate a pseudo-pillared-layer structure.
In 3, the inorganic framework again has the 4.82 topology pillared by the bis(imidazole) ligand, 1,3-bis(imidazol-
1-ylmethyl)benzene. In 4, a new layer pattern is observed. Specifically, three edge-sharing 4-rings form triple-fused
4-rings. These tertiary building units are further connected to form 12-rings. The alternating triple 4-rings and
12-rings form a previously unknown 2D inorganic sheet. The sheets are joined together by the bis(imidazole)
ligand, 1,3-bis(imidazol-1-ylmethyl)benzene, to generate a 3D pillared-layer structure. In 4, benzene rings and imidazole
rings stack in a zigzag pattern in the interlayer space. A significant role for the triple 4-ring tertiary building unit in
the formation of hybrid inorganic/organic metal phosphite structures is proposed for 4 and 5. In 5, the triple 4-rings
fuse to give a 1D stair-step structure. Calculations show that the triple 4-ring pattern observed in the linear ladder
structure of 1 is more stable than that in the stair step pattern of 5.
Introduction
are depicted in Scheme 1. Isolated 6-rings may also be
considered as an SBU in the formation of 63 nets,8 and other
SBUs are possible. The formation of the 4-ring SBU under
hydrothermal conditions is implied by the many observed
structures that have this motif. Common themes include
The concept of secondary building units, SBUs, in the
construction of hybrid inorganic/organic zinc phosphates and
zinc phosphites is critical to the understanding of structure
of these materials.1 The primary building units, PBUs,
namely zinc and phosphorus tetrahedra, may be linked in a
remarkable variety of patterns. One common motif is the
zinc phosphate/phosphite 4-ring, which is recognized as a
secondary building unit or SBU.2-7 These building blocks
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* Author to whom correspondence should be addressed. E-mail:
hanson@vt.edu.
† Department of Chemistry.
‡ Department of Geosciences.
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A. Acc. Chem. Res. 2001, 34, 80. (b) Cheetham, A. K.; Fe´rey. G.;
Loiseau, T. Angew. Chem., Int. Ed. 1999, 38, 3268. (c) Murugavel.
R.; Walawalkar, Dan, M.; Roesky, H. W.; Rao, C. N. R. Acc. Chem.
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10.1021/ic048204u CCC: $30.25
Published on Web 03/23/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 8, 2005 2719

Fan et al.
Scheme 1. Drawings of PBUs, SBUs, and TBUs
during synthesis, it may be possible to devise rational
syntheses of specific hybrid inorganic/organic structures.7b
Here, we suggest that the triple-fused 4-ring may be
considered as a tertiary building unit in two new zinc
phosphite/imidazolyl hybrid compounds. The triple 4-ring
has been observed in related structures in the literature.9
The construction of higher dimensional structure in zinc
phosphate/phosphite may be viewed as the self-assembly of
building units, PBUs, SBUs, and TBUs.6f The synthesis of
hybrid inorganic/organic materials with novel topologies is
accomplished with organic ligand to interfere in this aufbau
process,1a by means of connecting or separating the building
units. To date only a few examples of the hybrid inorganic/
organic zinc phosphites have been reported.1d,5f,10 In this
work, 1-methylimidazole, 1-benzylimidazole, 1,4-bis(imi-
dazol-1-ylmethyl)benzene, and 1,3-bis(imidazol-1-ylmethyl)-
benzene are used as ancillary ligands, and five new zinc
phosphites [Zn(HPO3)(C4H6N2)] (1), [Zn2(HPO3)2(C10H10N2)2]2
(2), [Zn(HPO3)(C14H14N4)0.5] (3), [Zn2(HPO3)2(C14H14N4)]‚
0.4H2O (4), and [Zn2(HPO3)2(C14H14N4)] (5) are synthesized
and structurally characterized.
isolated 4-rings in molecular compounds,2 chains of 4-rings
in ladder structures,3 and sheets of 4-rings linked through
corners to make alternating 4- and larger number-ring
structures in two dimensions.4 The SBU concept implies that
the 4-rings exist in solution and that the final structure is
dictated, in part, by the manner in which these are modified
by the added organic template or ligand.3a,4f,6 Alternatively,
the observed structure could form directly from the self-
assembly of primary building units or from tertiary building
units, TBUs. A building unit may be considered tertiary if it
can be derived from two or more SBUs. There is value in
identifying tertiary patterns in hybrid inorganic/organic
materials as a visualization tool and as a hint to possible
synthesis mechanisms. If tertiary patterns can be controlled
Experimental Section
Materials and Measurements. All commercially available
chemicals are of reagent grade and used as received without further
purification. The ligands 1,4-bis(imidazol-1-ylmethyl)benzene11a and
1,3-bis(imidazol-1-ylmethyl)benzene11b were synthesized by the
reaction of imidazole with R,R′-dibromo-p-xylene and R,R′-
dibromo-m-xylene, respectively, by the same procedures reported
for the preparation of 1,3-bis(1-imidazolyl)-5-(imidazol-1-ylmethyl)-
benzene.12 Elemental analyses of C, H, and N were performed by
Galbraith Laboratories, Inc. Thermogravimetric measurements were
performed on a TGA Q500 thermal analyzer in the following N2
with the heating rate of 10 °C min-1. Calculations were performed
using the PM3 semiempirical Hamiltonian,13 as in the GAMESS
suite of programs.14
General Synthesis Conditions. All hydrothermal syntheses were
done in heavy-wall glass tubes constructed in the Chemistry Glass
Shop. The tubes, 15 mm × 15 cm (after sealing) with a wall
thickness of 2 mm, were filled with materials to approximately 40%
of available volume and sealed under vacuum. The sealed tubes
were placed in an oven in an isolated room that was preheated to
the desired reaction temperature. Table 1 gives the initial molar
concentrations of imidazole nitrogen (R-Im), zinc acetate, phos-
phorous acid, and NaOH. After addition, the relevant species,
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Jakobsen, H. J. Inorg. Chem. 2005, in press. (j) Norquist, A. J.; O’Hare,
D. J. Am. Chem. Soc. 2004, 126, 6673. (k) Mandal, S.; Natarajan. S.
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2720 Inorganic Chemistry, Vol. 44, No. 8, 2005

Zinc Phosphite Structures
Table 1. Initial Molar Concentrations for Syntheses
compd
R-Im (M)
Zn(OAc)2 (M)
HPO3H2 (M)
NaOH (M)
temp (°C)/time (d)
yield (%)
1
2
3
4
5
0.5
0.17
0.1
0.1
0.15
0.17
0.083
0.1
0.1
0.1
0.33
0.17
0.1
0.1
0.1
0
0
130/10
125/9
125/10
125/10
125/10
84
15
14
25
77
0.083
0.083
0.083
Table 2. Crystal Data and Structure Refinement Parameters for 1-5a
struct param
1
2
3
4
5
empirical formula
fw
T/K
C4H7N2O3PZn
227.46
100
C40H44N8O12P4Zn4
1214.19
100
C7H8N2O3PZn
264.49
100
C14H16N4O6P2Zn2
528.99
100
C14H16N4O6P2Zn2
528.99
100
space group
a/Å
b/Å
P212121
5.2488(5)
9.6411(8)
14.5214(13)
90
P1h
P21/c
P21/n
P21/n
9.6190(6)
9.6847(6)
26.2565(16)
100.260(5)
100.104(5)
90.091(3)
2368.2(3)
2
11.2732(13)
8.8605(9)
9.9607(11)
90.00
110.166(10)
90.00
933.94(18)
4
1.881
10.8713(9)
10.1001(7)
18.2501(11)
90
90.285(6)
90
2003.9(2)
4
1.753
7.6613(5)
16.3179(11)
14.5275(10)
90
92.866(6)
90
1813.9(2)
4
1.937
c/Å
R/deg
â/deg
γ/deg
V/Å3
Z
90
90
734.84(11)
4
2.056
3.515
0.0282
0.0667
D
calc/g cm-3
1.703
2.205
0.0603
0.1610
µ/mm-1
2.781
0.0641
0.1675
2.592
0.0424
0.0909
2.863
0.0255
0.0633
R1a [I > 2σ(I)]
wR2b [I > 2σ(I)]
2
2
2
a R1 ) Σ|Fo| - |Fc|/Σ|Fo|. b wR2 ) {Σ[w(Fo - Fc )2]/Σ[w(Fo )2]}1/2, where w ) 1/[σ2(Fo)2 + (aP)2 + bP] and P ) [(Fo)2 + 2(Fc)2]/3.
R-ImH+ and HPO3H-, and acetic acid have pKas in the range 4.7-
6.9. The initial pH, as determined by paper indicator, for each
reaction was in the range 6-8 as expected from the compositions.
After the reaction the pH values were found to be in the 6-8 range.
The reactions appear to be effectively buffered by the presence of
the ligand and all other reaction components.
(49.2 mg, 0.6 mmol), sodium hydroxide (20.0 mg, 0.5 mmol), 1,3-
bis(imidazol-1-ylmethyl)benzene (71.4 mg, 0.3 mmol), and distilled
water (6 mL) for 10 days at 125 °C yields a plate crystalline product
and a block crystalline material, compound 5, as evidenced by X-ray
powder diffraction. Yield: about 25% on the basis of zinc source.
FT-IR (cm-1): 3125 (m), 2353 (m), 1523 (m), 1448 (w), 1400 (w),
1274 (w), 1235 (m), 1148 (s), 1086 (s), 1028 (s), 1004 (s), 949 (s),
894 (w), 834 (m), 820 (m), 772 (m), 752 (m), 742 (m), 722 (s),
677 (w). Anal. Calcd for C14H16.8N4O6.4P2Zn2: C, 31.36; H, 3.16;
N, 10.45. Found: C, 31.13; H, 3.30; N, 10.16. To confirm the
noncoordinated water content, thermogravimetric measurements
using a TGA Q500 thermal analyzer were performed on a crystalline
product of 3 in the following N2 with the heating rate of 10 °C
min-1. The weight loss (32 to ∼160 °C) corresponds to the loss of
noncoordinated water molecules (obsd 1.6%, 0.44 H2O; calcd
1.5%). This compound is stable up to 300 °C as shown in the TGA
curve.
[Zn2(HPO3)2(C14H14N4)] (5). Hydrothermal treatment of zinc
acetate dihydrate (65.9 mg, 0.3 mmol), phosphorous acid (49.2 mg,
0.6 mmol), sodium hydroxide (20.0 mg, 0.5 mmol), 1,3-bis-
(imidazol-1-ylmethyl)benzene (107.1 mg, 0.45 mmol), and distilled
water (6 mL) for 10 days at 125 °C yields a block crystalline
product. Yield: 77% on the basis of zinc source. FT-IR (cm-1):
3122 (w), 2358 (m), 1534 (m), 1516 (m), 1438 (w), 1277 (w), 1231
(w), 1189 (s), 1135 (s), 1109 (s), 1082 (s), 1022 (s), 1007 (s), 952
(m), 847 (m), 826 (m), 817 (m), 767 (m), 747 (m), 715 (m), 670
(w). Anal. Calcd for C14H16N4O6P2Zn2: C, 31.79; H, 3.05; N, 10.59.
Found: C, 31.89; H, 3.33; N, 10.35.
[Zn(HPO3)(C4H6N2)] (1). Hydrothermal treatment of zinc acetate
dihydrate (219.5 mg, 1.0 mmol), phosphorous acid (164.0 mg, 2.0
mmol), 1-methylimidazole (246.1 mg, 3.0 mmol), and distilled
water (6 mL) for 10 days at 130 °C yields a colorless crystalline
product. Yield: 84% on the basis of zinc source. FT-IR (cm-1):
3122 (w), 2368 (m), 1542 (m), 1527 (m), 1289 (w), 1239 (w), 1145
(s), 1110 (s), 1084 (s), 1044 (s), 1030 (s), 1007 (s), 953 (s), 866
(w), 835 (s), 778 (s), 675 (w). Anal. Calcd for C4H7N2O3PZn: C,
21.12; H, 3.10; N, 12.32. Found: C, 21.03; H, 3.42; N, 11.76.
[Zn2(HPO3)2(C10H10N2)2]2 (2). Hydrothermal treatment of zinc
acetate dihydrate (109.8 mg, 0.5 mmol), phosphorous acid (82.0
mg, 1.0 mmol), 1-benzylimidazole (158.2 mg, 1.0 mmol), and
distilled water (6 mL) for 9 days at 125 °C yields a colorless
crystalline product. Yield: 15% on the basis of zinc source. FT-IR
(cm-1): 3105 (w), 2356 (m), 1528 (m), 1444 (w), 1358 (w), 1284
(m), 1244 (m), 1155 (m), 1100 (s), 1028 (s), 1008 (s), 950 (m),
873 (m), 860 (m), 825 (m), 782 (w), 738 (m), 711 (s), 692 (m).
Anal. Calcd for C40H44N8O12P4Zn4: C, 39.57; H, 3.65; N, 9.23.
Found: C, 39.73; H, 3.98; N, 9.20.
[Zn(HPO3)(C14H14N4)0.5] (3). Hydrothermal treatment of zinc
acetate dihydrate (131.8 mg, 0.6 mmol), phosphorous acid (49.2
mg, 0.6 mmol), sodium hydroxide (20.0 mg, 0.5 mmol), 1,4-bis-
(imidazol-1-ylmethyl)benzene (71.4 mg, 0.3 mmol), and distilled
water (6 mL) for 10 days at 125 °C yields a block crystalline
product, accompanied by an unknown powder product. Yield: 14%
on the basis of zinc source. FT-IR (cm-1): 3107 (m), 2381 (m),
1530 (m), 1454 (w), 1355 (w), 1285 (w), 1245 (m), 1168 (w), 1147
(s), 1115 (s), 1095 (s), 1082 (s), 1029 (s), 1006 (s), 950 (m), 879
(m), 864 (m), 739 (m), 718 (m). Anal. Calcd for C7H8N2O3PZn:
C, 31.79; H, 3.05; N, 10.59. Found: C, 30.91; H, 3.13; N, 10.20.
[Zn2(HPO3)2(C14H14N4)]‚0.4H2O (4). Hydrothermal treatment
of zinc acetate dihydrate (65.9 mg, 0.3 mmol), phosphorous acid
Crystallographic Analyses. Low-temperature (100 K) single-
crystal X-ray diffraction measurements for compounds 1-5 were
collected on a Oxford Diffraction Xcalibur2 diffractometer equipped
with the Enhance X-ray source and a Sapphire 2 CCD detector.
The data collection routine, unit cell refinement, and data processing
were carried out with the program CrysAlis.15 The structures were
solved by SHELXS-97 and refined by full-matrix least squares.
The final refinements involved an anisotropic model for all non-
(15) CrysAlis V1.171; Oxford Diffraction: Wroclaw, Poland, 2004.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2721

Fan et al.
hydrogen atoms.16 The refinement of the Flack absolute parameter
in 1 to -0.001(10) indicated that the absolute structure is well
defined. A noncoordinated water oxygen with a site occupancy
factor of 0.44 was found in the structural channel of 4. The hydrogen
atom bonded to this oxygen atom was not located. In 1-5, the
hydrogen atoms attached to the phosphorus group were located from
the residual e- density map and refined independently, and the
hydrogen atoms attached to the organic ligand were added by the
expected geometry. The crystal parameters, data collection param-
eters, and refinement results for compounds 1-5 are summarized
in Table 2. Selected bond length and angles are listed in Table 3.
Further details are provided in the Supporting Information.
Table 3. Selected Bond Distances (Å) and Angles (deg) for 1-5a
Compound 1
Zn1-N1
2.0153(19)
1.9357(16)
109.71(7)
113.96(7)
109.97(7)
134.20(10)
128.14(10)
Zn1-O1
1.9389(17)
1.9371(16)
113.72(7)
107.08(8)
101.88(7)
129.64(10)
Zn1-O2#1
Zn1-O3#2
O2#1-Zn1-O3#2
O3#2-Zn1-O1
O3#2-Zn1-N1
P1-O1-Zn1
P1-O3-Zn1#1
O2#1-Zn1-O1
O2#1-Zn1-N1
O1-Zn1-N1
P1-O2-Zn1#2
Compound 2
Zn1-O3
1.929(3)
1.949(3)
1.914(3)
1.944(3)
1.916(3)
1.946(3)
1.948(3)
Zn1-O4
1.936(3)
2.002(4)
1.934(3)
1.990(4)
1.932(3)
1.984(4)
1.928(3)
1.989(4)
Zn1-O6#3
Zn1-N1
Zn2-O5
Zn2-O2#4
Zn2-O1#5
Zn2-N3
Zn3-O8#6
Zn3-O12#7
Results and Discussion
Zn3-O11
Zn3-N5
Zn4-O7#8
Zn4-O10
Description of the Crystal Structures. [Zn(HPO3)-
(C4H6N2)] (1) and [Zn2(HPO3)2(C10H10N2)2]2 (2). The
asymmetric unit of compound 1 contains one zinc atom, one
phosphite, and one 1-methylimidazole as shown in Figure
1a. Each zinc atom in compound 1 is coordinated by three
oxygen atoms from three different phosphite groups and one
nitrogen atom from 1-methylimidazole to complete its
tetrahedral coordination environment. Compound 1 is closely
related to C4N2O3H8‚ZnHPO33a (C4N2O3H8 ) L-asparagine),
which crystallizes in the same space group P212121 and has
a similar 1D ladder structure but with the tetrahedral
coordination geometry of the zinc atom defined by four
oxygen atoms. The zinc coordination mode in compound 1
has typical geometrical parameters: (Zn-O)av ) 1.94 Å, and
O-Zn-O bond angles are in the range of 109.7-114.0° with
an average value of 112.5°. The O-Zn-N bond angles are
in the range 101.9-110.0° with an average value of 106.3°.
The phosphorus atom bonds to three oxygen atoms [dav(P-
O) ) 1.52 Å] with the fourth tetrahedral vertex occupied by
a hydrogen atom. The three bridging O atoms have an
average Zn-O-P bond angle of 130.7°.
The ZnO3N and HPO3 groups are connected to form an
edge-shared ladder structure of 4-rings that propagates along
the [100] direction (Figure 1b). The 1-methylimidazole
ligands are attached to the zinc atoms and extend to each
side of the ladder structure. The neutral chains in compound
1 are held together by van der Waals forces. A packing
diagram is included in the Supporting Information.
The asymmetric unit of compound 2 contains two crys-
tallographically independent motifs. Each motif contains two
zinc atoms, two phosphite units, and two 1-benzylimidazole
groups (Figure 2a). Each zinc atom is tetrahedrally coordi-
nated by three oxygen atoms from three different phosphite
groups and one nitrogen atom from one 1-benzylimidazole.
In 2, the O-Zn-O bond angles are in the range of 101.0-
110.9°, and O-Zn-N bond angles are in the range 109.1-
116.0°. Each phosphite group in compound 2 bridges three
zinc atoms with the Zn-O distance ranging from 1.914(3)
to 1.949(3) Å.
Zn4-O9
1.947(3)
Zn4-N7
O3-Zn1-O4
O4-Zn1-O6#3
O4-Zn1-N1
O5-Zn2-O2#4
O2#4-Zn2-O1#5
O2#4-Zn2-N3
O8#6-Zn3-O12#7
O12#7-Zn3-O11
O12#7-Zn3-N5
O10-Zn4-O9
O9-Zn4-N7
O9-Zn4-O7#8
P2-O4-Zn1
P2-O5-Zn2
P4-O11-Zn3
101.96(14)
106.05(13)
116.00(14)
105.62(16)
107.50(16)
110.40(15)
105.33(15)
106.08(14)
113.57(14)
101.02(14)
115.59(14)
107.61(13)
131.42(19)
144.1(2)
O3-Zn1-O6#3
O3-Zn1-N1
O6#3-Zn1-N1
O5-Zn2-O1#5
O5-Zn2-N3
O1#5-Zn2-N3
O8#6-Zn3-O11
O8#6-Zn3-N5
O11-Zn3-N5
O10-Zn4-N7
O10-Zn4-O7#8
O7#8-Zn4-N7
P1-O3-Zn1
P3-O9-Zn4
P4-O10-Zn4
110.89(15)
112.47(15)
109.14(15)
103.31(15)
115.47(15)
113.86(15)
105.51(15)
115.56(15)
110.05(15)
112.44(15)
110.07(14)
109.70(15)
143.1(2)
130.81(19)
143.6(2)
134.5(2)
Compound 3
Zn1-O2
Zn1-O1
1.918(3)
1.943(3)
Zn1-O3
Zn1-N1
1.928(3)
1.999(4)
O2-Zn1-O3
O3-Zn1-O1
O3-Zn1-N1
P1-O3-Zn1
P1#10-O1-Zn1
101.96(13)
109.36(13)
114.66(15)
127.63(18)
129.51(17)
O2-Zn1-O1
O2-Zn1-N1
O1-Zn1-N1
P1#9-O2-Zn1
112.10(13)
111.49(14)
107.31(14)
140.3(2)
Compound 4
Zn1-O6
1.920(3)
1.948(3)
Zn1-O1#11
1.940(2)
1.998(3)
1.937(3)
Zn1-O3
Zn1-N31#12
Zn2-O4
Zn2-O2
1.937(3)
1.943(3)
Zn2-O5#13
Zn2-N11
1.987(3)
O6-Zn1-O1#11
O1#11-Zn1-O3
O1-Zn1-N31#12
O4-Zn2-O5#13
O5#13-Zn2-O2
O5#13-Zn2-N11
P2-O4-Zn2
P1-O2-Zn2
106.78(12)
98.21(10)
108.20(12)
112.93(11)
104.58(11)
107.39(12)
135.69(16)
121.74(15)
O6-Zn1-O3
O6-Zn1-N31#12
O3-Zn1-N31#12
O4-Zn2-O2
O4-Zn2-N11
O2-Zn2-N11
P2-O6-Zn1
P1-O3-Zn1
115.07(12)
113.77(13)
113.18(13)
110.32(11)
110.94(12)
110.47(12)
138.03(17)
121.30(15)
Compound 5
Zn1-O1
1.9163(13) Zn1-O6
2.0009(15) Zn1-N31#14
1.9335(13) Zn2-O3#15
1.9527(13) Zn2-O4
1.9449(13)
2.0074(15)
1.9410(13)
1.9290(13)
105.95(6)
Zn1-N11
Zn2-O2
Zn2-O5#16
O1-Zn1-O6
O6-Zn1-N11
111.26(6)
112.46(6)
O1-Zn1-N11
O1-Zn1-N31#14
113.92(6)
O6-Zn1-N31#14 100.48(6)
N11-Zn1-N31#14 112.94(6)
O4-Zn2-O2
O2-Zn2-O3#15
O2-Zn2-O5#16
P2-O4-Zn2
P1-O2-Zn2
116.62(6)
116.65(6)
104.25(6)
135.79(8)
141.69(9)
O4-Zn2-O3#15
O4-Zn2-O5#16
O3-Zn2-O5#16
P2-O6-Zn1
108.11(6)
109.98(6)
99.66(6)
119.94(7)
141.07(9)
P1-O1-Zn1
Unlike the chain structure in compound 1, the ZnO3N and
HPO3 groups in 2 are connected to form a 2D sheet, as
a
Symmetry transformations used to generate equivalent atoms: #1, x
+ 1/2, -y + 7/2, -z; #2, x - 1/2, -y + 7/2, -z; #3, -x + 2, -y, -z; #4,
-x + 2, -y + 1, -z; #5, x + 1, y, z; #6, -x + 1, -y + 2, -z + 1; #7, -x
+ 1, -y + 1, -z + 1; #8, -x, -y + 2, -z + 1; #9, x, -y + 3/2, z + 1/
2; #10, -x + 1, -y + 1, -z; #11, -x - 1, y + 1/2, -z + 3/2; #12, -x,
-y + 1, -z + 1; #13, -x - 1, -y + 1, -z + 1; #14, -x + 3/2, y + 1/2,
-z + 3/2; #15, -x + 2, -y + 1, -z + 1; #16, -x + 1, -y + 1, -z + 1.
(16) (a) Sheldrick, G. M. SHELXS97, Program for Crystal Structure
Determination; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(b) Sheldrick, G. M. SHELXL97, Program for Crystal Structural
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
2722 Inorganic Chemistry, Vol. 44, No. 8, 2005

Zinc Phosphite Structures
Figure 1. (a) ORTEP plot of the asymmetric unit of compound 1 showing the atom-labeling scheme. The ellipsoids are drawn at the 50% probability level.
Two additional symmetry-related atoms are indicated by O2A and O3A. (b) Ladder structure of compound 1: (left) connectivity of the HPO3 (yellow) and
ZnO3N (blue) tetrahedra; (right) zigzag arrangement of 4-rings with Zn-O-P linkage drawn by a single line.
illustrated in Figure 2b. Zinc tetrahedra and phosphorus
tetrahedra are connected to form 4-rings and 8-rings. Each
4-ring is surrounded by four 8-rings, and each 8-ring is
surrounded by four 4-rings. Thus, the 2D network has a 4.82
topology.2f,12 Recently, a 2-fold interpenetrated zinc phosphite
framework connected by ethylenediamine was reported, in
which the inorganic sheets are of the same 4.82 topology
and the ethylenediamine groups pass through the 8-rings to
connect alternating sheets.10c In the case of 2, the 1-ben-
zylimidazole ligands that coordinate zinc and extend to each
side of the sheet with the benzene ring nearly perpendicular
to the inorganic sheet. The opening of the 8-ring is about
6.7 × 5.8 Å, which is too small to allow the benzene rings
to pass through. Within each 2D sheet of compound 2, the
4-rings are not parallel to each other (Figure 2b) and a helical
chain can be extracted from this layer structure as reported
previously for 4.82 rings.10d The layer that contains Zn(1)
and Zn(2) atoms forms an independent sheet, A, and the layer
that contains Zn(3) and Zn(4) atoms forms an adjacent sheet,
B. The two kinds of sheets are packed in an ABAB mode,
and the topology of each sheet is identical.
in 84% yield. The addition of a benzene ring to methylimi-
dazolyl to form benzylimidazole apparently is not readily
accommodated by a ladder structure. It is likely that the
C-H‚‚‚π interactions18 drive the formation of a layer
structure in 2 and that the layered structure observed
maximizes benzene-benzene interactions. The C-H-X (X
refers to the centroid of the benzene ring) angles range from
145.2 to 171.7°, and the H‚‚‚X distances range from 2.64 to
3.21 Å. A figure illustrating the C-H‚‚‚π interaction between
benzene rings is included in the Supporting Information.
Further, if each pair of benzene rings involved in
C-H‚‚‚π interactions is taken as a single unit, then the 3D
structure of compound 2 can be regarded as a pillared layer
structure. Namely, the inorganic sheets are supported by a
pseudo-bis(imidazole) ligands. To further elaborate the role
of bis(imidazole) ligands in the formation of the hybrid
inorganic/organic zinc phosphite materials, we investigated
the reactions of 1,4-bis(imidazol-1-ylmethyl)benzene and 1,3-
bis(imidazol-1-ylmethyl)benzene with zinc phosphites. Three
new compounds with unique architectures are formed. In 3
and 4, inorganic zinc phosphite sheets are pillared by the
Both 1 and 2 are built from monodentate imidazole
ligands, 1-methylimidazole and 1-benzylimidazole, respec-
tively. Thus, it is interesting to note the role of the benzene
ring in defining the structure of 2. The ladder structure is
commonly observed with monodendate and bridging ligands
and appears to be a stable structure under hydrothermal
synthesis conditions.6a,17 Compound 1, for example, is formed
(17) Fan, J.; Slebodnick, C.; Angel. R.; Hanson, B. E. Inorg. Chem. 2005,
in press.
(18) (a) Choudhury, A. R.; Islam, K.; Kirchner, M. T.; Mehta, G.; Row,
T. N. G. J. Am. Chem. Soc. 2004, 126, 12274. (b) Caradoc-Davies, P.
L.; Gregory, D. H.; Hanton, L. R.; Turnbull, J. M. J. Chem. Soc.,
Dalton Trans. 2002, 1574. (c) Jitsukawa, K.; Iwai, K.; Masuda, H.;
Ogoshi, H.; Einaga, H. J. Chem. Soc., Dalton Trans. 1997, 3691. (d)
Zhu, H. F.; Kong, L. Y.; Okamura, T.-a.; Fan, J.; Sun, W. Y.; Ueyama,
N. Eur. J. Inorg. Chem. 2004, 1465.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2723

Fan et al.
Figure 3. (a) ORTEP plot of the asymmetric unit of compound 3 showing
the atom-labeling scheme. The ellipsoids are drawn at the 50% probability
level. Symmetry-related atoms are indicated by O1A, etc. (b) Crystal packing
diagram for compound 3.
a trans-conformation. In 3, the organic ligands are held
together via weak C-H‚‚‚π interactions. A packing diagram
is included with the Supporting Information. The C-H-X
(X refers to the centroid of the benzene ring) angle is 128.7°,
and the H‚‚‚X distance is 3.02 Å. Recently, Feng and co-
workers reported two 3D zinc phosphites, [C6H4(CH2NH3)2]‚
[Zn3(HPO3)4] and [CH3CH2CH2NH3]2‚[Zn3(HPO3)4], in which
the inorganic layers with similar topology as in 3 are
connected by inorganic chains and not by organic groups as
in 3.5f
The asymmetric unit of 4 contains two zinc atoms, two
phosphite units, one 1,3-bis(imidazol-1-ylmethyl)benzene,
and one partially occupied noncoordinated water molecule.
As shown in Figure 4a, each zinc atom in 4 has the same
coordination environment as observed in 1-3, namely
tetrahedrally coordinated by three oxygen atoms and one
nitrogen atom.
In 4, the ZnO3N and HPO3 groups are connected to form
a triple fused 4-rings, and four triple fused 4-rings are held
together to generate a 12-ring (Figure 4b). Within one 12-
ring, the shortest distance between the diagonal zinc atoms
is 7.44 Å. The free space within the 12-ring is greatly reduced
because the Zn-N bonds attached to these two zinc atoms
extend toward the center of the 12-ring. The alternating triple-
fused 4-rings and 12-rings form an unusual 2D inorganic
sheet. The most common ring patterns in zinc phosphites
are 4-rings and 8-rings,2f,10,11 and although 12-rings are
known in framework structures,2d,4c,20 the 12-ring pattern of
4 has not previously been observed. In 4, the two imidazole
groups of the ligand extend to the same side of the benzene
ring, with a dihedral angle between these two rings of 57.7°.
Thus the bis(imidazole) ligand in 4 adopts a cis-conformation
Figure 2. (a) ORTEP plot of the asymmetric unit of compound 2 showing
the atom-labeling scheme. The ellipsoids are drawn at the 50% probability
level. Symmetry-related atoms are indicated by O1A, etc. (b) 2D structure
of compound 2: (left) connectivity of HPO3 (yellow) and ZnO3N (blue)
tetrahedra to 4-ring and 8-ring loops; (right) schematic drawing of the 2D
4.82 network. (c) Crystal packing diagram for compound 2 with the C-H‚
‚‚π interactions indicated by dashed lines.
bis(imidazole) ligand to form a 3D structure, and in 5,
inorganic zinc phosphite chains are linked by the ligand to
generate a 3D structure.
Compounds [Zn(HPO3)(C14H14N4)0.5] (3), [Zn2(HPO3)2-
(C14H14N4)]‚0.4H2O (4), and [Zn2(HPO3)2(C14H14N4)] (5).
The asymmetric unit of 3 contains one zinc atom, one
phosphite unit, and a half 1,4-bis(imidazol-1-ylmethyl)-
benzene ligand (Figure 3a). The zinc atoms in 3 are
tetrahedrally coordinated by three oxygen atoms and one
nitrogen atom as in 2. It is interesting to note that the ZnO3N
and HPO3 groups are connected to form the same topology,
namely 4.82, as in 2. Furthermore, the layer structure is
connected by the organic ligand to form a pillared structure
as shown in Figure 3b. In 3, the two imidazole groups of
the ligand extend to both sides of the benzene ring, with a
dihedral angle between the benzene ring and the imidazole
plane of 74.3°. Thus, the bis(imidazole) ligand in 3 adopts
2724 Inorganic Chemistry, Vol. 44, No. 8, 2005

Zinc Phosphite Structures
of 2.81 Å. The distance between the benzene ring and the
neighboring imidazole ring is 4.09 Å with the dihedral angle
of 14.8°. This implies the occurrence of weak π‚‚‚π
interactions, and the organic ligands are connected to form
a 1D zigzag chain along the c axis.21
Interestingly, compound 5 is synthesized under reaction
conditions similar to those of compound 4, i.e., the same
ligand, reaction temperature, and time, but with a different
ligand-to-zinc ratio (see Experimental Section). The struc-
tures of 4 and 5, however, are quite different. Due to its
flexibility, the bis(imidazole) ligand can adopt subtly different
conformations to meet the geometrical requirement of metal
ions, leading to the formation of 4 and 5. Additionally, the
triple 4-ring pattern shows different degree of distortion in
the two compounds (see below).
The asymmetric unit of compound 5 contains two zinc
atoms, phosphite units, and one 1,3-bis(imidazol-1-ylmethyl)-
benzene, which repeat to form the framework (Figure 5a).
In 5, Zn2 atom is coordinated by four oxygen atoms from
four different phosphite groups, ZnO4 [dav(Zn-O) ) 1.94
Å], and Zn1 is coordinated by two oxygen atoms from two
different phosphite groups [dav(Zn-O) ) 1.93 Å] and two
nitrogen atoms from two different ligands [dav(Zn-N) ) 2.00
Å].
In 5, the ZnO3N and HPO3 groups are connected to form
a triple-fused 4-rings (A-C loops), which are held together
to generate a 1D chain via Zn-O-P linkages (Figure 5b).
A visual way of describing the 1D chain is that it consists
of triple-fused 4-rings, which are held together in a stair-
step pattern. A similar stair step structure is formed in a
related compound [(C6N4H22)0.5]2+[Zn2(HPO4)]2-;4c the stair
steps in this structure are further linked by Zn-O-P linkages
to form 2D sheets that contain 12-rings. In 5, however each
1D chain is connected to four neighboring chains by the
organic ligand to form the 3D structure. The chains propagate
along the a axis. The ligand in 5 adopts a cis conformation
as in 4, with the dihedral angle between the two imidazole
rings of 107.7°. A packing diagram is included in the
Supporting Information.
In compounds 4 and 5, the two terminal 4-rings of the
triple fused 4-rings extend to the each side of the central
4-ring. Thus, the triple 4-rings adopt a trans conformation
(Figure 6). In 4, the four T (T ) Zn, P) atoms of the central
4-ring are coplanar while the T atoms of the terminal rings
are not. The terminal rings adopt a butterfly structure with
dihedral angles of 127.1 and 123.3°, respectively, between
the trigonal planes, and the dihedral angles between the
central ring and its neighboring trigonal planes are 109.1
and 146.2°, respectively (Figure 6a). In 5, the corresponding
dihedral angles are 164.7, 165.7, 107.6, and 96.9°, respec-
tively (Figure 6b). That is, the triple 4-rings in 5 are less
distorted than in 4. The relationship between the triple 4-rings
in the chain structure of 5 and the triple 4-rings in the sheet
structure of 4 is depicted in Scheme 2. Starting from 4, (I)
the two connected triple 4-rings units may be cleaved into
two independent units, (II) one triple 4-ring is rotated and
Figure 4. (a) ORTEP plot of the asymmetric unit of compound 4 showing
the atom-labeling scheme. The ellipsoids are drawn at the 50% probability
level. Three additional symmetry-related atoms are indicated by N31A, O5A,
and O1A. (b) 2D inorganic framework of compound 4: (left) connectivity
of the HPO3 (yellow) and ZnO3N (blue) tetrahedra to the triple fused 4-rings
and 12-ring loops; (right) schematic drawing of the 2D network. (c) Crystal
packing diagram for compound 4 with the hydrogen bond indicted by dashed
lines.
and connects adjacent sheets to form the pillared layer
structure (Figure 4c). The benzene ring of the ligand is
essentially perpendicular to the inorganic layer as in 2, which
results in a large interlayer spacing of 11.47 Å. Noncoordi-
nated water molecules are located within the structural
channels, which are hydrogen bonded to a phosphite oxygen
atom as indicated by the O1w‚‚‚O5 (x + 1, y - 1, z) distance
(19) (a) Phillips, M. L. F.; Nenoff, T. M.; Thompson, C. T.; Harrison, W.
T. A. J. Solid State Chem. 2002, 167, 337. (b) Dong, W.; Li, G.; Shi,
Z.; Fu, W.; Zhang, D.; Chen, X.; Dai, Z.; Wang, L.; Feng, S. Inorg.
Chem. Chem. 2003, 6, 776. (c) Gordon, L. E.; Harrison, W. T. A.
Acta Crystallogr. 2004, C60, m637.
(20) (a) Jensen, T. R.; Hazell, R. F. J. Chem. Soc., Dalton Trans. 2000,
2831. (b) Ayi, A. A.; Choudhury, A.; Natarajan, S.; Rao, C. N. R. J.
Mater. Chem. 2000, 10, 2606. (c) Harrison, W. T. A.; Phillips, M. L.
F.; Nenoff, T. M. J. Chem. Soc., Dalton Trans. 2001, 2459. (d)
Harrison, W. T. A.; Bircsak, Z.; Hannooman, L.; Zhang, Z. J. Solid
State Chem. 1998, 136, 93. (e) Harrison, W. T. A.; Phillips, M. L. F.
Chem. Mater. 1997, 9, 1837. (f) Wang, Y.; Yu, J.; Guo, M.; Xu, R.
Angew. Chem., Int. Ed. 2003, 42, 4089. (g) Cui, A.; Yao, Y. Chem.
Lett. 2001, 1148. (h) Chidambaram, D.; Neeraj, S.; Natarajan, S.; Rao,
C. N. R. J. Solid State Chem. 1999, 147, 154. (i) Kongshaug, K. O.;
Fjellvag, H.; Lillerud, K. P. Microporous Mesporous Mater. 2000,
39, 341. (j) Fu, W.; Shi, Z.; Zhang, D.; Li, G.; Dai, Z.; Chen, X.;
Feng, S. J. Solid State Chem. 2003, 174, 11. (k) Zhang, P.; Wang, Y.;
Zhu, G.; Shi, Z.; Liu, Y.; Yuan, H.; Pang, W. J. Solid State Chem.
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(21) Hunter, C. A.; Sanders, J, K. M. J. Am. Chem. Soc. 1990, 112, 5525.
Inorganic Chemistry, Vol. 44, No. 8, 2005 2725

Fan et al.
Figure 5. (a) ORTEP plot of the asymmetric unit of compound 5 showing the atom-labeling scheme. The ellipsoids are drawn at the 50% probability level.
Three additional symmetry-related atoms are indicated by N31A, O5A, and O3A. (b) 1D inorganic framework of 5: (left) connectivity of the HPO3 (yellow)
and ZnO2N2/ZnO4 (blue) tetrahedra to the triple fused 4-rings; (right) schematic drawing of the 1D network.
triple-fused 4-rings. In each case, a portion of the structure
that included five fused 4-rings served as the starting point,
and coordination sites that are left dangling were filled with
hydroxide or imidazole groups consistent with the crystal
structure. A similar procedure was not readily available for
structure 4 since the triple 4-rings in this structure are
connected to form 12-rings and the calculation could not be
equivalently truncated. The structures of the five fused
4-rings were then optimized using quantum-mechanical
methods. The PM3 semiempirical Hamiltonian,13 as imple-
Figure 6. Schematic drawing of the triple fused 4-rings in 4 (a) and 5 (b)
with the numbers indicating the dihedral angles between these edge-sharing
planes.
mented in the GAMESS suite of programs,14 was used in
all calculations. The first and last rings of each chain is
distorted upon minimization due to the finite size of our
Scheme 2. Possible Mechanism for the Formation of the
One-Dimensional Chain in 5 from the Triple Fused 4-Rings in 4
clusters. However, the core triple 4-rings are expected to be
a genuine representation of the fused rings in the extended
structures. In fact, the geometries of the optimized structures
concur with the crystal structure data.
The goal of our calculations is to establish the relative
strain energies of the inorganic triple 4-ring patterns alone,
in the absence of ligands. Thus, although we optimized the
motifs including all of the corresponding ligands and an
additional ring at each side of the triple 4-ring structures,
we neglect the contributions of the ligands and terminal rings
in the calculation of the relative stability of the triple 4-ring
moves closer to another unit, (III) these two units are
reconnected by double Zn-O-P linkages to generate a new
4-ring, and (IV) the pattern repeats to form a 1D stair step.
structures. In this manner, we find that the triple 4-ring within
the ladder structure is 17 kcal mol-1 more stable than the
triple 4-ring pattern of the stair step pattern. The minimized
structures for 1 and 5 with five rings and pendant groups
are shown in Figure 7. The portion of the each structure
within the box is the basis for determining the relative energy
of the triple 4-rings. The observation that the triple 4-ring
in 1 is more stable is consistent with the common occurrence
of ladders among zinc phosphates/phosphites1a,3a,6a,f,17 and the
rare occurrence of the stair step pattern observed in 5.4c
Although we could not estimate the relative energy of the
Calculations
Calculations are emerging as an important tool in evaluat-
ing substructures in silicate and metal phosphate composi-
tions.22 Here we evaluate the relative stability of the triple
4-rings contained within the ladder structure of 1 and the
stair step structure of 5. In both cases the crystallographic
coordinates were used as starting points for the calculation
of the optimized geometries and relative energetics of the
(22) Catlow, C. R.; Coombes, D. S.; Lewis, D. W.; Pereira, J. C. Chem.
Mater. 1998, 10, 3249.
2726 Inorganic Chemistry, Vol. 44, No. 8, 2005

Zinc Phosphite Structures
Figure 7. Results of the PM3 calculations shown graphically for the ladder structure, A, on the left, and the stair step structure, B, on the right. The
calculated energies of the core triple 4-rings shown in the boxes establish that the triple 4-ring within ladder motif, A, is 17 kcal mol-1 more stable than the
triple 4-ring in the stair step structure, B.
triple 4-ring in 4 in a similar fashion, it is likely that it also
is less stable than the ladder pattern of 1. It is only by the
presence of ligands that these distorted ring patterns can be
stabilized.
reported here it appears that the inorganic portion of the
structure adopts a pattern that maximizes metal-ligand
bonding and ligand-ligand interactions. Growth of the
inorganic phase is modified accordingly. In consideration
of structures 4 and 5, we come to the conclusion that zinc
phosphite/phosphate structures may be more predictable if
rigid ligands are used to connect zinc phosphate/phosphite
phases. We are currently investigating several rigid bifunc-
tional ligands for the construction of novel inorganic/organic
zinc phosphite/phosphate materials.
Conclusion
Five new zinc phosphites have been synthesized in the
presence of 1-methylimidazole, 1-benzylimidazole, 1,4-bis-
(imidazol-1-ylmethyl)benzene, and 1,3-bis(imidazol-1-yl-
methyl)benzene. In compound 1, the mono(imidazole)
ligands simply decorate the ladder structure. In 2 and 3, the
zinc and phosphorus tetrahedra form 4.82 inorganic sheets
which are pillared in the former by C-H‚‚‚π interactions
between 1-benzylimidazole ligands and by 1,4-bis(imidazol-
1-ylmethyl)benzene in the latter to form similar 3D layered
structures. Compounds 4 and 5 are synthesized with the same
ligand, and in both structures a tertiary building united
comprised of a triple fused 4-ring is identified. The triple
4-ring is also seen in the ladder structure, 1, and has been
noted previously in the literature.4c Calculations show that,
in the absence of ligands, the triple 4-ring in the ladder
structure of 1 is 17 kcal mol-1 more stable than the triple
4-ring in 5. Clearly the bonding requirement of the ligand
plays the dominant role in determining the observed struc-
tures. This suggests that the key to hybrid materials synthesis
and structure is ligand design. In each of the structures
Acknowledgment. We thank R. J. Reynolds for support
of this work through a McNair Postdoctoral Fellowship to
J.F. We thank the NSF (Grant CHE-0131128) for funding
the purchase of the Oxford Diffraction Xcalibur2 single-
crystal diffractometer.
Supporting Information Available: Figure S1, showing the
packing diagram of 1, Figure S2, showing the helix motif in 2,
Figure S3, showing the arrangement of benzene rings in 2, Figure
S4, showing the arrangement of ligands in 3, Figure S5, showing
the arrangement of ligands in 4, Figure S6, showing the stair-step
connection mode of the 1D chain in 5, Figure S7, showing the
packing diagram of 5, and X-ray crystallographic files in CIF
format. This material is available free of charge via Internet at
http://pubs.acs.org.
IC048204U
Inorganic Chemistry, Vol. 44, No. 8, 2005 2727