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