In situ generation of a family of substituted thioureas-Cadmium thiocyanate coordination polymers: a crystal engineering study for new topologies and properties.

(1)

In situ generation of a family of substituted

thioureas-Cadmium thiocyanate coordination polymers: a crystal

engineering study for new topologies and properties.

Emanuele Priola

1

, Elisabetta Bonometti

1

, Eliano Diana

1

University of Turin, Via Pietro Giuria 7, 10125, Italy,

e-mail: emanuele.priola@unito.it

Luminescent properties and interpretation of

transitions through TD-DFT

Computational model of the fragment Cd(tu)₂(SCN)₂(NCS)₂ and simulated spectrum. We used a TD-B3LYP functional on optimized structure, with 631gd set base for light atoms and ecp lan el for Cadmium. The model predicts very accurately the high energy adsorption electronic transitions common for all the family. It is quite interesting that in this case the Cadmium orbitals seem to have a great importance in electronic structure of the solid, different from what is usually said for Cadmium coordination polymers.

FREQUENCY (NM)

ORBITALS INVOLVED AND SYMMETRY OF TRANSITION ASSIGNMENT 280 HOMO-3 -> LUMO+1 1A u

Ligand (SCN-_{) to Ligand (tu) (LL)}

302 HOMO-3 -> LUMO / HOMO-1 ->LUMO

1_A u

Ligand (SCN-_{and tu) to a mixed}

state with the participation of s orbitals of Cadmium atom (LMCT)

313 HOMO-1 -> LUMO

1_A u

Ligand (SCN-_{) to mixed state with}

the participation of s orbitals of Cadmium atom (LMCT)

Introduction

The research in new materials through the rational design of weak interaction in the solid state is one of the main challenge in modern solid state chemistry and material science. We decided to develop the knowledge of the effects of weak interactions on coordination polymers of cadmium thiocyanate. This salt proved to be a good inorganic framework for coordination polymers [1], and with the choise of appropriate ancillary ligands it is possible to obtain different rational topologies and new materials with luminescence and NLO properties [2] . We decide to analize the effects of steric hindrance (more or less isotropic), hydrogen bond, pi-pi stacking and presence of halogens with the use of a very versatile family of organic ligands : N-substituted tioureas. We obtained five new compounds and we rationalize in this framework also three compounds yet reported in litterature: [Cd(SCN)₂(tu)₂]_n (1)[3], [Cd(SCN)₂(tu)]_n (2), [Cd(SCN)₂(tu)₂(H₂O)]_n (3)[4], [Cd(SCN)₂(N-metiltu)₂]_n (4), [Cd(SCN)₂(N-phenyltu)₂]_n (5), [Cd(SCN)₂(N-2,6-difluorophenyltu)₂]_n (6), [Cd(SCN)₂(N, N’-diphenyltu)₂(H₂O)₂]_n (7)[5], [Cd(SCN)₂(tu)₂(EtOH)₂]_n (8), The synthesis has been conduced with an heterogeneous approach, using ammonium and acethate as counter-ions that are lost in the atmosphere to obtain pure products. We characterize these compounds with single crystal X-ray diffraction, (raman and infrared) vibrational spectroscopy, and electronic adsorption and emission spectroscopy. This study allows also to rationalize the luminescent properties of this family and the effects of structural peculiarities, both in inorganic Cadmium thiocyanate framework and in organic ancillary ligands, to the emission properties with the help of computational models based on TD-DFT methods. [1] Zhang, H., Wang, X., Zhang, X., Teo, B.K.,Coord. Chem. Rev., 1999,183,157-195 [2]g, H.u, H., Xiao, W., Zhang, K., Teo, B.K., Inorg. Chem., 1999, 38, 886-892;Zhang, L.P., Lu, W.J., Mak, Chem. Comm., 2003, 2830-2831; Jia, H.L., Jia, M.J., Li, G.H., Wang, Y.N., Yu, J.H., Xu, J.Q., Dalton Trans., 2013, 42, 6429-6439 [3]Nardelli, M., Braibanti, A., Fava, G., Gazz. Chim. Ital., 1957, 87, 1209-1231 [4]Mietlarek-Kropidlowska, A., Chojnacki, J., Acta Cryst.,2012, E68, m1051-m1052 [5]Zhu, H.G., Yang, G., Chen, X.M., Ng, S.W., Acta Cryst., 2000, C56, e430-431

Conclusions and Discussion

From the structural analysis of this family of compounds emerge the importance of

different interactions:

1) The choice of the solvent is essential to direct the synthesis, and from weak difference

in hydrogen bonding capability and polarity very different topology can be obtained

2) Strong hydrogen bonds from N-H of thioureas are the main driving force of the

crystallization, and the disposition of substituents and the bridging capabilities of tu

and SCN is strongly correlated to the maximization of these interactions, eigter with

thiocyanate or with intercalated solvent molecules ( This is also clear from the

optimized computational model)

3) The pi-pi stacking has a strong influence in presence of aromatic substituents,

especially with halide substituents that maximize the quadrupole of the ring.

4) Bulky substituents has a more pronounced effect on topology, reducing the

possibilities to have multiple hydrogen bonds and isolating the inorganic framework.

The anisotropy of steric hindrance has weaker effects on structure than bulk.

This family of compounds shows great luminescent properties, that from computational

modeling seem to be strongly influenced by the presence of Cadmium, differently from

what is usually reported in literature.

Cd(Ac)

₂

+ 2 (NH

₄

)(SCN)+ x tu

H

₂

O

Ethanol

X=1

X=2

Effect of Solvent and hydrogen bonding on topology of

unsubstituted tiourea complexes

X=2

(1) (2)

(3)

Effect on the topology of coordination polymers of an asymmetric

N-substitution on tu

Cd(Ac)

₂

+ 2 (NH

₄

)(SCN)+ x N-Xtu

_X=phenyl

X=2,4-difluorophenyl

X=metyl

X=2 X=2 X=2 (4) (5) (6)

Effect on the topology of coordination polymers of a bulkier

symmetric substitution on tu and effect of solvent interaction

(2)

Twinning: structural peculiarities and opportunities in

coordination polymers

Emanuele Priola

1

University of Turin, Via Pietro Giuria 7, 10125, Italy,

e-mail: emanuele.priola@unito.it

And considering the properties of twinned solids?

WHADHAWAN

TENSORIAL

CLASSIFICATION

OF TWINS

T-twins: No difference in

tensor properties

B-twins: twins differ in

at least one tensor

properties, and no

prototype structure can

be defined

Aizu twins: twins differ

in at least one tensor

properties, and a

prototype structure can

be defined

THESE TWINS CHANGE THE TENSOR

PROPERTIES, THESE ARE THE GOAL FOR AN

IMPROVEMENT IN MATERIAL SCIENCE!!

Introduction

A twin is an oriented association of individual crystals of the same chemical and crystallographic species. The individuals in a twin are related by one or more geometrical laws (twin laws) expressed through the point symmetry of the twin versus the point symmetry of the individual. The twin element (twin center, twin axis, twin plane) is the geometric element about which twin operations (operations relating different individuals) are performed. These definitions allows the classifications of the different cases in the framework of Friedel’ s Reticular theory of twinning, extended in recent years by Nespolo and others [1]. A different, less group theory-based classification, is based on tensor properties of crystals subject of this phenomenon[2]. However, the first classification is important from an abstract definition of twins especially in the framework of polychromatic group theory [3], while the second is important for a more applicative study on this phenomenon. Tensor properties are fundamental for solid state physics: hyperpolarizability, electrical properties and mechanical properties are influenced by structural phenomena that change the components in the different directions. With a rational induction of twinning phenomenon, some peculiar properties in materials have been obtained, especially for metals, and a more comprehensive study in this directions can be significant. This abstract notions can be really important in the frameworks of the research on coordination polymers for more than one reason. At first, a deep knowledge of the group theory based approach to twin allows their recognition and classification when they are found in experimental work . This is essential, because often the unrecognition of this phenomenon cause a poor resolution in structural determination, or wrong space group assignation, or even the impossibility to resolve the structure. This is particularly significant in the case of Coordination polymers: the presence of weak non strongly directed interactions in certain specific directions is a favorable condition for the manifestation of twinning. On the other hand, the possibility to change the properties of solids with a rationally conducted growth of twins is a desirable and intriguing aim. This poster presents some of the instruments that the theory of Geminography give us for a better interpretation and rationalization of this phenomenon with possible developments.

[1]Grimmer, H., Nespolo, M., Z. Kristallogr., 2006, 221, 28-58 [2]Wadhawan, V.K., Acta Cryst., 1997, A53, 546-555

[3]Nespolo, M., Z. Kristallogr., 2004, 219, 57-71

D(L

_T

)

=

holohedral vector point group descrybing the point

symmetry of L

_T.

This is the twin lattice, the lattice common to

all the individuals of the twin

D(L

_ind

)

=

holohedral vector point group describing the point

symmetry of L

_ind

, that is the lattice of the individual

D(H)

=

holohedral supergroup of H

H

= intersection group of the oriented vector point groups of

individuals of twin

K

=

chromatic point group called

twin point group,

point group

that represent in the vector space the symmetry of the twin and

is a supergroup of H.

OBLIQUITY

:

lets indicate [u’,v’,w’] the direction

perpendicular to (hkl) and (h’,k’,l’) the plane perpendicular to

[uvw], where [uvw] and (hkl) are the lattice plane and the

lattice row that define the twin. The angle between [uvw] and

[u’v’w’] or (hkl) and (h’k’l’) is the obliquity.

cosω = (uh + vk + wl)/L(uvw)L(hkl)*

TWIN INDEX (molteplicity)

:

ratio of the volumes V

_t

and V

of primitive cells for L

_{T and}

L

_ind_.

NUMBER OF TWIN

INDIVIDUALS

Some little definitions…

ω

TWIN INDEX (n)

OBLIQUITY

(ω)

RELATIONS

AMONG

D(L

_T

),

D(L

_IND

), D(H)

AND H

Classification of crystal twins based on Friedel Lattice theory

n =1

n >1

ω =0

_{ω >0}

)

RETICULAR PSEUDOPOLYHOL OHEDRY

THE MOST FREQUENT IN COORDINATION

POLYMERS !!

But what is the group K? A deeper classification on the basis of polichromatic

symmetry (to kroma = the color)

.

Chromatic symmetry operation (twin law), that generate one individual from the other.

Chromatic point group , supergroup of the

intersection group with a left coset decomposition generated with the

chromatic symmetry operation .

Point group symmetry of individuals

Chromatic symmetry operation : symmetry operations that

exchange the colors of the squares.

Each individual is a different colored series of squares and maintain only the symmetry elements that doesn’t change the color

Chromatic point group is the group that formed by the “sum” of the symmetries that maintains the colors and of those that change the color with a comma to

distinguish them

{1120} Brazil Twin of alfa Quartz, a twin for syngonic merohedry