Preparation and Study of Some New Complexes that Can Be Used as Dental Restoration Materials

8 
Chapter One 
Introduction 
 
1-Complex Ions          
 
        
One of the most important chemical properties of d-block 
elements is their ability to form complex ions. This ability is not 
confined to d-block elements.  Aluminum and boron, for example, 
also form complex. 
A complex ion is formed when one or more molecules or 
negatively charged ions become attached to a central atom.  The 
molecular negative ion that becomes attached is called a ligand.  They 
are normally attached to the central atom by means of coordinate 
bond.  The compounds formed are thus called coordination 
compounds and the number of ligands attached to the central atom is 
called the coordinate on number. 
Simple ligand such as H
2
O, NH
3
, CN
-
 and Cl
-
 are called 
monodentate ligands since they can only use one coordinate bond. 
Monodentate means “one teeth”.  Bidentate ligands have “two teeth”. 
In other words they form two coordinate bonds with the central atom. 
Ligands that form three coordinate bonds are called tridentate. 
Complex formed by d-block elements may be neutral, positive or 
negative. 
The charge on an ion is delocalised over the whole ion.  The 
charge is the algebraic sum of charges on the central ion and on the 
ligands. 
Some ligands are able to form ring structure with central atoms. 
This property is known as chelation and the resulting compounds are 
known as chelato compounds 
(1)
.
9 
1-2. Dental chemistry 
 Chemistry is important in several aspects of dentistry.  Foremost is 
the structure of tooth enamel, the chemical reactions of breakdown and 
reformation of the enamel, and the role of fluoride in prevention of decay. 
Chemistry is also involved when the dentist enters the picture 
(2)
. 
 
1-3.1. Dental Cement 
Dental cements are materials of comparatively low strength, but they 
are used extensively in dentistry when strength is not a prime 
consideration.  With two possible exceptions, they are not truly adhesive 
to enamel and dentin.  Except for the resin cement they dissolve and 
erode in oral fluids.  Such defects are likely to make them impermanent.   
However, regardless of certain inferior properties, they posses so many 
desirable characteristic that they are used in 40 to 60 per cent of all 
restoration.  They are employed as (1) cementing (referred to as luting) 
agents for fixed cast restorations or orthodontic bands, (2) as thermal 
insulators under metallic restorations, (3) for temporary or permanent 
restorations, (4) as root canal sealant, and (5) as pulp capping agents.  It 
should be reemphasized that as a group their chemical and physical 
properties leave much to be desired, and the manipulative techniques be 
designed to provide the optimal behavior 
(3)
.
10 
Chapter Two 
Literature Review 
 
2-1. Introduction to complexes 
The chemistry of transition elements is very largely concerned with 
the chemistry of co-ordination compounds.  Co-ordination compounds or, 
complexes as they are perhaps more usually called, complexes play a 
very important part in our lives today, and studying them has contributed 
greatly to our understanding of the chemical bond and inorganic 
chemistry as a whole.  The number of possible co-ordination compounds 
in chemistry is almost infinite.  For many years complexes were regarded 
as of interest to the theoretical and inorganic chemist only, but now they 
are playing vital roles in analytical chemistry, in the synthesis of organic 
chemicals, in polymerization processes, and in our understanding of 
biological processes.  Perhaps the most important are the naturally 
occurring complexes such as chlorophyll, the magnesium complex that is 
important in plant photosynthesis, and iron complex that is a carrier of 
oxygen in blood 
(4)
. 
There are many compounds, which can be used as ligands, but the 
following compounds were of particular interest to our aim. 
 
2-2.  The Aromatic Ligands 
 
2-2.1. EUGENOL
11 
Eugenol is 4-allyl-2-methoxyphenol, and may be seperated by 
shaking clove oil with an excess of a solution of sodium hydroxide, 
separating the resulting solution of sodium eugenolate, and decomposing 
it with dilute sulphuric acid.  It is a colorless or pale yellow liquid with a 
characteristic odor and a pungent spicy taste. It has boiling point of 
254°C and it darkens in color with age or on exposure to air. 
Action and uses: Eugenol is carminative. Applied externally, it is 
rubefacient, counter-irritant and slightly analgesic. 
   Eugenol is used to flavor dentifrice. It is a useful local analgesic for 
hypersensitive dentine, carious cavities, or exposed tooth pulp.  Mixed 
with zinc oxide, clove oil is used as a temporary filling, though eugenol is 
often preferred for this purpose. It has useful preservative properties 
(5)
.   
Eugenol is protoplasmic poisons, cussing precipitation of cellular protein.       
Eugenol is highly irritating to vital tissue and precipitates an 
inflammatory response in tissue that it contacts 
(10)
. 
   
 
 
2-2.2. Salicylic Acid 
        
 
 
Salicylic acid is o-hydroxy benzoic acid, and may be prepared by 
treating sodium phenoxide with carbon dioxide, and acidifying the 
solution of the sodium salicylate obtained. It occurs as colorless, almost 
odorless crystals or light feathery crystalline powder, with sweetish acrid 
taste.  It has a melting point of 158°C to 161°C. A solution in water is 
acid to methyl red.
 
 
Action and uses: Salicylic acid is a bacteriostatic and fungicide 
(Kills tissue containing fungus) disinfectants.  It is used externally in
12 
dusting powders, lotions or ointments for the treatment of chronic ulcers, 
dandruff, and parasitic skin diseases such as ringworm.  In the form of 
paint in collodion base or as a plaster, it is employed to destroy warts or 
corns
 (5)
. 
 
2-2.2. Vanillin  
  
 
  
 
 
Vanillin is 4-hydroxy-3-methoxybenzaldehyde, and may be obtained 
from vanilla planifolia Andrews, or other species of vanilla (fam. 
Orchidaceae), or prepared synthetically. 
Uses: Vanillin is used as a flavoring agent and in perfumery
  (5)
. 
 
2-2.4.  Methyl salicylate  
 
 
 
 
Methyl salicylate is methyl o-hydroxybenzoate, and may be prepared 
by dissolving salicylic acid in methyl alcohol, gradually adding sulphuric 
acid, warming for about twenty-four hours, and distilling in a current of 
steam.  It is a colorless or pale yellow liquid with a characteristic 
aromatic odor and a sweet warm aromatic taste.  It has a weight per ml. at 
20°C of 1.180 g. to 1.184 g. 
Methyl salicylate contains not less than 99.0 per cent w/w of 
C
8
H
8
O
3
.
13 
Action and uses: Methyl salicylate has the actions of salicylates, and it 
has antipyretic and analgesic actions. When given by mouth, it is 
absorbed mainly through the intestine and is rapidly excreted; frequent 
does are therefore required to maintain a satisfactory concentration in the 
blood.  It is a gastric irritant, and sodium bicarbonate is often given with 
it to reduce this effect: however, the bicarbonate also increases the rate of 
excretion, and thus lowers the concentration of salicylate in the blood to 
less effective levels.  Sodium salicylate causes dilatation of the skin 
vessels and some perspiration, and the increased loss of heat results in a 
fall in the temperature. 
The principle use of sodium salicylate is in the treatment of acute 
rheumatic fever.  Metylsalicylate is seldom given by the mouth and it is 
readily absorbed through the skin and is applied in liniments and 
ointments for the relief of pain in lumbago, sciatica and rheumatic 
conditions.  Also it is used in perfumery; for flavoring candies, 
mouthwash etc.
 (5)
.  
 
2-2.5.  Cresol 
                     CH
3
                         CH
3                       
 CH
3 
   
 
 
 
                   para                     meta                  ortho 
 
Cresol is a mixture of o-, m- and p-cresol, CH
3
.C
6
H
4
.OH, in which 
the meta-isomer predominates, and of other phenols obtained from coal 
tar.  It is an almost colorless to pale brownish-yellow liquid, which 
becomes darker on keeping or an exposure to light.  It has a characteristic 
phenolic odor, and an a pungent taste. 
OH 
OH 
   OH
14 
O-Cresol is a colorless deliquescent solid with a characteristic odor; it 
becomes yellow on keeping, melts at about 30°C and boils at about 
191°C. 
m-Cresol is a colorless or yellowish liquid, slightly soluble in water and 
readily soluble in organic solvents; it melts at about 10°C and boils at 
about 202°C. P-Cresol is a crystalline solid, slightly soluble in water and 
readily soluble in alcohol and in ether; it melts at about 36°C and boils at 
about 201°C. 
Action and uses: Cresol has an action similar to phenol, but it is less 
caustic and less poisonous than is phenol. Most pathogens are killed in a 
ten- minute exposure to solutions containing 0.3 to 0.6 per cent of cresol, 
but spores require higher concentrations and longer exposure times. 
Cresol may be used in place of phenol in lotions and ointments.  It is most 
frequently used as cresol and soap solution as a general antiseptic; when 
used on skin the solution may be irritating unless well diluted 
(6)
.   
 
2-2.6.  Guaiacol  
 
 
 
 
 2-Methoxyphenol; methylcatechol; o-hydroxyanisol; 1-hydroxy- 
Anastil. C
7
H
8
O
2
. 
Guaiacol white or slightly yellow crystals mass or colorless to 
yellowish, very refractive liquid; characteristic odor. Darkens on 
exposure to air and light.  
Action and uses: Cough syrups, expectorants 
(5)
.
15 
2-2.7. Thymol   
 
 
 
 
 
 
Thymol 5-methyl-2-isopropyl-1-phenol; 1-methyl-3-hydroxy-4-iso-
propylbenzene; 3-p-cymenol; 3-hydroxy-p-cymene; thyme. C
10
H
14
O;    
Crystals, appreciably volatile at 100°c; volatilizes in water vapors. 
Characteristic odor; pungent, somewhat caustic taste.  
Action and use: For destroying mold; preserving documents, art objects 
and urine.  Stabilizer (antioxidant) for trichloroethylene, halothane.  Also 
used in mouthwash and toothpaste; effective against hookworm
 (5)
. 
 
2-3. The aliphatic ligand 
2-3.1. Menthol       
                                                  OH 
              CH
3
                                         
                   CH                                 CH
3
        
         CH
3
                                                     
 
Menthol, p-menthan-3-ol, is natural or synthetic (levo)-menthol, or 
synthetic (±)-menthol.  Natural (-)-menthol may be obtained from the 
volatile oils of various species of Mentha (Fam. Labiatae); it is separated 
from the oils by freezing.  Synthetic menthol may be obtained by the 
catalytic hydrogenation of thymol.  Menthol occurs as colorless acicular 
or prismatic crystals with a penetrating odor similar to that of peppermint
16 
oil and a warm aromatic taste followed by a sensation of cold.  A 5.0 % 
solution in alcohol in neutral to litmus. 
Action and uses: Menthol is used to relieve the symptoms of bronchitis 
and sinusitis.  For this purpose it is used, frequently mixed with camphor 
and eucalyptus oil, in pastilles, inhalations and ointments.  Also it is used 
in liqueurs, confectionery, perfumery, cigarettes, cough drops, nasal 
inhalers and in toothpaste
(7)
.  Recently, menthol is used as a cooling 
compound and in the thirst, the drive to breath and arousal 
(8,9)
.             
 
2-4.  The ligand and stability of complexes:  
In order to be effective as a ligand a substance must be or have within 
its structure one or more highly electronegative atoms capable of acting 
as electron pair donors.  Thus all ligands are or include nonmetals. The 
most effective in this respect are P, C, S, Cl, N, O, and F. A ligand may 
be an anion or it may be a neutral molecule.  The halide and halogenoids, 
(pseudo halogens) the best-known anionic ligands, are in order of 
coordination strength CN
-
>CNO
-
>SCN
-
>F
-
>Cl
-
>Br
-
>I
-
. Other anions, 
including complex anions, are equally capable of acting as ligands. The 
hydroxyl ion falls between chloride and fluoride in this scale. The ability 
of a complex anion to act as ligand falls off rapidly with increasing 
charge of a very small central unit and the compactness of its “ligand” 
electron cloud. Thus perchlorate  is considered to be incapable of acting 
as a ligand and is for that reason used as the anion of choice in solution 
intended for study of free uncomplexed cations 
(10)
.