Certain physical properties associated with certain space groups or point groups
Piezoelectricity is the property of a crystal to develop an electric charge when subjected to pressure or tension in certain directions and is observed in crystals with polar axes. o Applications of piezoelectricity include (but are not limited to) quartz timepieces and microphones; triboluminescence….later Optical activity refers to the ability of crystals to rotate plane-polarized light. Pyroelectricity is the property of a crystal to develop electrical polarization when the temperature is changed and can only occur in non-centrosymmetric crystal systems. Ferroelectricity (important in electro-ceramics) also shows polarization for a temperature change but has the additional feature of changing the direction of polarization in an electric field. See Table below for a listing of the point groups that exhibit the above-mentioned properties
Point Group Properties
Crystal System Point Groups Enantio-
morphism Optical Activity
Piezo-electricity
Pyro-electricity
C1 Triclinic Ci
C2 Cs
Monoclinic
C2h D2 C2v
Orthorhombic
D2h C4 S4 C4h D4 C4v D2d
Tetragonal
D4h C3 C3i D3 C3v
Trigonal
D3d C6 C3h C6h D6 C6v D3h
Hexagonal
D6h T Th O Td
Cubic
Oh
Literature case studies
1. TRIBOLUMINESCENCE: • Non-centric space groups
2. Conducting materials• Segregated 1-D stacks
3. Magnetic materials• Integrated 1-D stacks
4. Photoluminescent materials• Packing by closed-shell metal-metal
interactions
A Structural Study of Triboluminescence (TL)
• General
– Almost exclusively seen in crystalline samples
– Luminescent species• the surrounding gas (N2)• the compound itself • a combination of both
TL spectrum of sucrose
11 eV
ground state
3u
3g
Energy level of N2
excitation emission
piezoelectricity Noncentrosymmetric space group
• Zink’s “golden rule” : only noncentrosymmetric crystals could be
triboluminescent. See ABSTRACT & TABLE 1 IN
HANDOUT: B. P. Chandra, J. I. Zink, Inorg. Chem., 1980,
19, 3098.
Some other papers by Professor Zink about triboluminescence:
• Zink, J.; Hardy, G. E.; Sutton, J. E., J. Phys. Chem., 1976, 80, No.3, 248.
• G. E. Hardy; J. I. Zink, Inorg. Chem., 1976, 15, 3061.
• B. P. Chandra, J. I. Zink, J. Phys. Chem., 1982, 86, 4138
Zink’s Rule is Valid for 11 Tetrahedral Mn(II) Complexes
Compound TriboluminescentSpace Group Known Previously
Space Group Determined in This Work
(PyH)2MnCl4 No P1
(Me3PhP)2MnCl4 Yes P213 (noncentro)
(Me4N)2MnCl4 No P21/n
(Et4N)2MnBr4 Yes P421m (noncentro)
(Bu4N)2MnI4 No
(Ph3PO)2MnCl2 Yes (80K) Fdd2 (noncentro)
(Ph3PO)2MnBr2 Yes P1 (noncentro)
(Ph3PO)2MnI2 Yes P1 (noncentro)
(Ph3AsO)2MnCl2 No P21/n
(Ph3AsO)2MnBr2 Yes (80K) Pca21 (noncentro)
(Ph3AsO)2MnI2 No P 1
Cotton, F. A.; Daniels, L. M.; Huang, P. Inorg. Chem. 2001, 40, 3576.
SECOND HANDOUT Refutation of a Claimed Exception to Zink’s Rule: (TEA)[Eu(DBM)4]
I2/a Z = 4
R(F) = 0.0749R(wF) = 0.0817
Ia Z = 4
R1 = 0.0581wR2 = 0.0952 Flack x = 0.00(2)
redetermine
Sweeting, L. M.; Rheingold, A. L. J. Am. Chem. Soc., 1987, 109, 2652.
Cotton, F. A.; Daniels, L. M.; Huang, P. Inorg. Chem. Comm., 2001, 4, 319.
Three Genuine Exceptions to Zink’s Rule: Structural Redeterminations
[TbCl2(H2O)6]Cl
P2/n Z = 2
R1 = 0.0147wR2 = 0.0317
(piperidinium)[Eu(BA)4]
P21/n Z = 4
R1 = 0.0253WR2 = 0.0601
[Tb(antipyrine)6]I3
R Z = 3 3
R1 = 0.0573WR2 = 0.0887
Rheingold, A. L.; King, W., Inorg. Chem., 1989, 28, 1715.
Not Every Noncentrosymmetric Eu(III) Complexes Are Observably Triboluminescent
O
O
O
O O
Eu O
O
O
O
O
O
O
O
O
O
. 3Na+ . 8H2O
3 -
O O O O
O O O O
Eu Eu
O
O
N
N
O
O
N
N
. 2H2O
Na3[Eu(ODA)3]•8H2O Eu2(phen)2(C8H7O2)6 ]•2H2O
Cc Z = 4
R1 = 0.0255WR2 = 0.0699
Cc Z = 4
R1 = 0.0547 WR2 = 0.1214
Albin, M.; Whittle, R. R.; Horrocks, W. D. Inorg. Chem. 1985, 24, 4591.
Jin, L.-P.; Wang, R.-F. Chem. J. Chin. Univ. 1993, 14, 1195.
Not Triboluminescent