Although tetrahedral configurations are by far the most common type of stereochemistry among organic compounds, they are not the only type to consider. Many other configurations exist, primarily among inorganic structures, and several of them are fairly common.

In the recommendations to follow, atom labels have been omitted from the structural diagrams at the ligand positions so that the orientation of the bonds may be seen most clearly. Traditionally, an unlabeled atom represents a carbon atom to organic chemists, but the unlabeled ligands here may represent any sort of structure, certainly including a carbon atom, but also potentially a hydrogen, a halogen, or any other element type. These recommendations are concerned only with the geometry of the central atom, generally labeled with an "M" below. They apply regardless of the types of ligands, and regardless of whether the ligands are discrete entities (chelating substituents, for example, would have one or more ligating atoms linked to each other, either directly or through other atoms).

The depictions in this section labeled as "preferred" have been selected in order to satisfy two primary goals: they must be recognizable to most chemists, and they must not be readily confused with any other conformation. Thus, a depiction of a square pyramidal configuration must clearly indicate the pyramidal arrangement of its four ligands, and at the same time it must not suggest that the ligands might be arranged in a planar or tetrahedral configuration instead. In consequence, the depictions here follow many of the general precepts regarding the use of perspective to represent configuration that are discussed more fully in ST-3.

In accordance with the IUPAC revision of the Nomenclature of Coordination Compounds (Draft March 2004), polyhedral symbols that are tied to the presence of lone pairs (e.g. TBPY-3, TBPY-4) are no longer recommended.

 

Linear

Polyhedral symbol: L-2

Number of ligands: 2

Linear configurations have two ligands diametrically opposite to each other, separated by exactly 180°. Although depiction styles are discussed here, for practical purposes the only important detail is that the ligands be drawn in a linear fashion, as implied by this configuration name.

Isolated linear systems should be drawn horizontally, vertically, or at a 30° angle rising or descending from left to right. Linear fragments that are part of larger compounds should be positioned according to the needs of the larger system.

PREFERRED	PREFERRED	PREFERRED	PREFERRED	PREFERRED	PREFERRED	PREFERRED

 

NOT ACCEPTABLE	NOT ACCEPTABLE

Because of their simplicity, linear systems can often be represented most succinctly using formulas rather than explicit atoms and bonds.

PREFERRED	PREFERRED	PREFERRED	PREFERRED	PREFERRED
HCCH	HCN	CO2	N3-	NNN-

 

Angular

Polyhedral symbol: A-2

Number of ligands: 2

Angular configurations have two ligands that are separated from each other by any amount other than 180°. Although depiction styles are discussed here, for practical purposes the only important detail is that the ligands not be drawn in a linear fashion, as implied by this configuration name.

Isolated angular systems should be drawn horizontally, with one bond extending upwards at a 30° angle rising from left to right, and the other bond extending downwards at the opposite angle. Angular fragments that are part of larger compounds should be positioned according to the needs of the larger system.

PREFERRED	PREFERRED	PREFERRED	PREFERRED

 

ACCEPTABLE	ACCEPTABLE	ACCEPTABLE	ACCEPTABLE	ACCEPTABLE

Because of their simplicity, Angular systems can often be represented most succinctly using formulas rather than explicit atoms and bonds.

PREFERRED	PREFERRED	PREFERRED	PREFERRED
H2O	H2S	NO2	O3

 

T-shaped

Polyhedral symbol: TS-3

Number of ligands: 3

T-shaped configurations have three ligands, so they must be clearly differentiated not only from trigonal pyramidal and trigonal planar configurations, but also from tetrahedral configurations that are drawn with an implicit hydrogen on the central atom. Although the T-shaped configuration does not technically need a depiction style of its own since all atoms are coplanar, it is useful to specify a recommended style to distinguish it from the other three-coordinate configurations. In other words, the recommended styles for a T-shaped configuration are not recommended for any of the other configurations.

Because they may also be mistakenly viewed as representing a tetrahedral configuration with one missing ligand, depictions of T-shaped configurations must clearly distinguish themselves tetrahedral depictions with, for example, an implicit hydrogen on the central atom. Accordingly, these configurations must never be drawn with implicit ligands. All three ligands must be drawn so that they are connected to the central atom by explicit bonds, and the central atom must clearly be labeled as a single atom (that is, as "Br" versus "BrCl", for example).

Furthermore, it is understood that the common organic elements carbon and nitrogen are virtually never found as the central atom in a T-shaped configuration. Even if a diagram is drawn in one of the recommended depiction styles below, it should not be considered to represent a T-shaped configuration if the central atom is a carbon or a nitrogen.

Because the recommended depiction style lacks any solid wedged or hashed wedged bonds, there is no way to distinguish visually a T-shaped structure of known configuration from one of unknown configuration. T-shaped structures of unknown axial/equatorial configuration should be described textually by using the (TS-3) prefix before the systematic name or formula, but no attempt should be made to draw them graphically.

In the recommended depictions, three plain bonds extend from the center exactly horizontally or exactly vertically.

PREFERRED	PREFERRED	PREFERRED	PREFERRED

The T-shaped configuration is inherently planar. Depictions that involve solid wedged or hashed wedged bonds, even though formally correct, are discouraged.

NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Sample depictions of some compounds known to exist in T-shaped configuration:

PREFERRED

 

Trigonal planar

Polyhedral symbol: TP-3

Number of ligands: 3

Trigonal planar configurations also have three ligands, and share many of the concerns seen with T-shaped configurations. They be clearly differentiated not only from T-shaped and trigonal pyramidal configurations, but also from tetrahedral configurations that are drawn with an implicit hydrogen on the central atom. Although this configuration does not technically need a depiction style of its own since all atoms are coplanar, it is useful to specify a recommended style to distinguish it from the other three-coordinate configurations. In other words, the recommended styles for a trigonal planar configuration are not recommended for any of the other configurations.

Because they may also be mistakenly viewed as representing a tetrahedral configuration with one missing ligand, depictions of trigonal planar configurations must clearly distinguish themselves from tetrahedral depictions with, for example, an implicit hydrogen on the central atom. Accordingly, these configurations must never be drawn with implicit ligands. All three ligands must be drawn so that they are connected to the central atom by explicit bonds, and the central atom must clearly be labeled as a single atom (that is, as "B" versus "BF", for example).

In the recommended depictions, three plain bonds extend from the center with equal angular spacing between them.

PREFERRED	PREFERRED	PREFERRED	PREFERRED

It is worth noting that sp² carbons are amongst the more common examples of trigonal planar configurations. In the case of an sp² carbon, the central atom does not need to be labeled. Further information about depiction of sp² carbons and related compounds may be found in the double-bond stereochemistry recommendations.

PREFERRED	PREFERRED	PREFERRED

Unfortunately, although the simplest and most accurate way to represent trigonal planar configurations is using three plain bonds as above, that leaves no way to distinguish a configuration that is explicitly known to be trigonal planar from an arbitrary three-coordinate center of unknown configuration, which might also be depicted with three plain bonds. When it is necessary to emphasize that a three-coordinate system definitely is in a trigonal planar configuration, it should be depicted with one plain bond, one solid wedged bond, and one hashed wedged bond. The solid wedged bond and the hashed wedged bond should be separated by an angle that is significantly less than 120°, and ideally close to 60° as shown here. The bisector of the angle between the solid wedged bond and the hashed wedged bond must be collinear with the plain bond. If the plain bond is oriented horizontally, the solid wedged bond should be positioned below the hashed wedged bond.

PREFERRED	ACCEPTABLE	ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Sample depiction of a compound known to exist in trigonal planar configuration:

PREFERRED

 

Trigonal pyramidal

Polyhedral symbol: TPY-3

Number of ligands: 3

Trigonal pyramidal configurations have three ligands, but are perhaps the most difficult configurations to depict unambiguously. Because they may also be viewed as representing a tetrahedral configuration with one missing ligand, depictions of trigonal pyramidal configurations must clearly distinguish themselves from tetrahedral depictions with, for example, an implicit hydrogen on the central atom. Accordingly, as with T-shaped configurations, trigonal pyramidal configurations must never be drawn with implicit ligands. All three ligands must be drawn so that they are connected to the central atom by explicit bonds, and the central atom must clearly be labeled as a single atom (that is, as "N" versus "NH", for example).

In the first recommended depiction, a plain bond and a hashed wedged bond form an angle between them of greater than 90 but less than 180°. The third bond is drawn as a solid wedged bond between the first two, but separated from the plain bond by greater than 90°.

PREFERRED	NOT ACCEPTABLE

In the second recommended depiction, two bonds are drawn as plain bonds, separated by an angle less than 180°. The third bond is drawn as a solid wedged bond or a hashed wedged bond, positioned at any angle. The third bond will traditionally bisect the angle formed by the plain bond, positioned either between them or opposite them, but such positioning is not mandatory.

This depiction style is very similar to depiction styles recommended for tetrahedral configurations. That is appropriate, since a trigonal pyramidal configuration does correspond to a tetrahedral configuration with one fewer ligand. This depiction style must therefore not be used in cases where the central atom might incorrectly be interpreted as having a fourth ligand.

PREFERRED	ACCEPTABLE	PREFERRED	ACCEPTABLE	ACCEPTABLE

A third depiction consists of one plain bond and two other bonds that are drawn both as solid wedged bonds or both as hashed wedged bonds, with each adjacent pair of atoms separated by less than 180°. This style, while formally correct, is discouraged because it has many stereobonds and may be confusing to the reader.

NOT ACCEPTABLE	NOT ACCEPTABLE

A related depiction consists of a plain bond, a solid wedged bond, and a hashed wedged bond, where the bisector of the angle formed by the solid and hashed wedged bonds is collinear with the plain bond. This should be avoided, as it actually describes a planar rather than a pyramidal configuration.

NOT ACCEPTABLE

A final depiction style consists of a three solid wedged bonds or three hashed wedged bonds. This style, while formally correct, is discouraged because it has so many stereobonds as to be confusing to the reader.

NOT ACCEPTABLE	NOT ACCEPTABLE

Trigonal pyramidal atoms should never be drawn with an explicit lone pair at the end of a bond because that bond could be misinterpreted as an additional methyl group.

PREFERRED	ACCEPTABLE	NOT ACCEPTABLE

 

PREFERRED	ACCEPTABLE	NOT ACCEPTABLE

In rare cases, a trigonal pyramidal atom with at least one double bond may be flanked by other stereocenters at the other ends of all of its single bonds. In such cases, one of the plain bonds should be changed to a wedged bond even though it joins two stereocenters. It is also acceptable to use a solid wedged or hashed wedged double bond, but that would not be preferred because wedged double bonds are so rarely seen in the literature

PREFERRED	ACCEPTABLE

Sample depictions of some compounds known to exist in trigonal pyramidal configuration:

PREFERRED	PREFERRED	PREFERRED

 

Square planar

Polyhedral symbol: SP-4

Number of ligands: 4

Square planar configurations have four ligands, the same as tetrahedral ones. One of the key issues in depicting these configurations is in making clear that a square planar configuration really is intended, and not a tetrahedral one. The recommended depictions are explicitly recommended not to be used for tetrahedral configurations.

The first recommended depiction should be drawn with two solid wedged bonds and two hashed wedged bonds. The two solid wedged bonds should be positioned below the central atom, while the two hashed wedged bonds should be positioned above. The angle between the solid wedged bonds should be equal to the angle between the hashed wedged bonds, and the bisectors of both angles should be coincident with the y-axis. Additionally, the angle between the solid wedged bonds should be greater than 90°, which implies that the angle between either solid wedged bond and its adjacent hashed wedged bond should be less than 90°.

PREFERRED	NOT ACCEPTABLE

It is also acceptable to draw similar structures with plain bonds. There are some cases where this drawing style would even be preferred, particularly when all four bonds are required to be in the plane of the paper by virtue of other aspects of the structural diagram (such as with the central atom of metalloporphyrins). When square planar configurations are drawn with plain bonds, it is preferable to have the angle between the bonds to be exactly 90°, and, as previously, the bisectors of angles formed by adjacent bonds should be coincident with the x- and y-axes. The similar depiction with the bonds themselves positioned along the axes is acceptable but should be avoided as it is extremely commonly used to represent tetrahedral centers, either if the tetrahedral configuration is achiral (carbon tetrachloride) or in Fischer projections.

PREFERRED	ACCEPTABLE	ACCEPTABLE

Four other depictions are formally correct, but are often used as (incorrect) depictions of tetrahedral configuration, particularly in bridged ring systems.

NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Sample depictions of some compounds known to exist in square planar configuration:

PREFERRED	PREFERRED

 

Square pyramidal

Polyhedral symbol: SPY-4

Number of ligands: 4

Square pyramidal configurations represent yet another type that has four ligands, the same as tetrahedral ones. Again, one of the key issues in depicting these configurations is in making clear that a square pyramidal configuration really is intended, and again the recommended depictions are explicitly recommended not to be used for tetrahedral configurations.

Furthermore, it is understood that the common organic element carbon is virtually never found in a square pyramidal configuration. Even if a diagram is drawn in one of the recommended depiction styles below, it should not be considered to represent a square pyramidal configuration if the central atom is isoelectronic with any member of the carbon group. Central atoms of that group are almost always found in tetrahedral configurations rather than square pyramidal configurations.

The first recommended depiction should be drawn with two solid wedged bonds and two hashed wedged bonds. The two solid wedged bonds should be positioned below the central atom, and the two hashed wedged bonds should also be positioned below the central atom. The angle between the solid wedged bonds should be less than to the angle between the hashed wedged bonds, and the bisectors of both angles should be coincident with the y-axis.

PREFERRED	NOT ACCEPTABLE

To further emphasize the perspective implied by the solid wedged and hashed wedged bonds, the two solid wedged bonds may be adjusted so that they are slightly longer than but less than 150% of the length of the hashed wedged bonds.

PREFERRED

It is also acceptable to draw similar structures with plain bonds.

PREFERRED

Sample depiction of compound known to exist in square pyramidal configuration:

PREFERRED

 

See-saw

Polyhedral symbol: SS-4

Number of ligands: 4

See-saw configurations, like square pyramidal ones, can be very difficult to distinguish from tetrahedral configurations. Yet again, one of the key issues in depicting these configurations is in making clear that a see-saw configuration really is intended, and again the recommended depictions are explicitly recommended not to be used for tetrahedral configurations.

Furthermore, it is understood that the common organic element carbon is virtually never found in a see-saw configuration. Even if a diagram is drawn in one of the recommended depiction styles below, it should not be considered to represent a see-saw configuration if the central atom is isoelectronic with any member of the carbon group. Central atoms of that group are almost always found in tetrahedral configurations rather than see-saw configurations.

The first recommended depiction should be drawn with two plain bonds extending exactly vertically above and below the center. A solid wedged bond should extend downward from the center, and a hashed wedged bond should similarly extend upward so that the bisector of the angle formed by the solid and hashed wedged bonds is coincident with the x-axis.

PREFERRED	PREFERRED	NOT ACCEPTABLE	NOT ACCEPTABLE

An acceptable variant on this preferred depiction would be to slant the plain bonds a small but equal amount from the vertical, so that they lean towards the solid and hashed wedged bonds. The plain bonds should remain closer to the y-axis than they are to the solid and hashed wedged bonds.

PREFERRED	PREFERRED

The third preferred depiction should be drawn with two plain bonds extending exactly horizontally to the left and the right of the center. A solid wedged bond and a hashed wedged bond should extend downward from the center so that the bisector of the angle formed by the solid and hashed wedged bonds is coincident with the y-axis.

PREFERRED	PREFERRED	PREFERRED	PREFERRED

An acceptable variant on this preferred depiction would be to slant the plain bonds a small but equal amount from the horizontal, so that they lean towards the solid and hashed wedged bonds. The plain bonds should remain closer to the x-axis than they are to the solid and hashed wedged bonds.

PREFERRED	PREFERRED	PREFERRED	PREFERRED

It is also acceptable to draw similar structures with plain bonds, particularly when at least one of the equatorial bonds is a double or triple bond. In this case, however, the axial bonds must be collinear, to distinguish this configuration from a square pyramidal one. Four plain bonds may be used only if the see-saw center is not itself chiral. Chiral see-saw configurations must be drawn with solid wedged bonds and hashed wedged bonds in order to confirm the specific chirality of the central atom.

PREFERRED	PREFERRED	PREFERRED	PREFERRED	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Six other depictions are formally correct, but are often used as depictions of tetrahedral configuration, and should be avoided as to reduce confusion.

NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Sample depictions of some compounds known to exist in see-saw configuration:

PREFERRED	PREFERRED	PREFERRED

 

Trigonal bipyramidal

Polyhedral symbol: TBPY-5

Number of ligands: 5

Trigonal bipyramidal configurations have five ligands, and offer fewer problems of interpretation than configurations with three or four ligands.

The preferred depiction views the bipyramid axis from the side. In this case, the two axial bonds are drawn as plain bonds oriented vertically and a third bond is also drawn as a plain bond, oriented exactly at right angles to the two axial bonds and extending to either the left or the right. The fourth bond is drawn as a solid wedged bond extending opposite the third bond and downward from the center, while the fifth bond is drawn as a hashed wedged bond opposite the third bond and extending upwards from the center. The bisector of the angle formed by the fourth and fifth bonds is coincident with the x-axis.

PREFERRED	PREFERRED	NOT ACCEPTABLE	NOT ACCEPTABLE

It is also acceptable to draw similar configurations with plain bonds if the trigonal bipyramidal center is not itself chiral. Chiral trigonal bipyramidal configurations must be drawn with solid wedged bonds and hashed wedged bonds in order to confirm the specific chirality of the central atom.

ACCEPTABLE	ACCEPTABLE

A third depiction shows the bipyramid axis viewed from above. In this case, the three equatorial bonds are drawn as plain bonds with equal separation. The fourth bond is drawn as a solid wedged bond extending downward from the center. The fifth bond is drawn as a hashed wedged bond that is collinear with the fourth bond, and hence extending upward. This depiction is acceptable but not preferred. It is used primarily in cases where it is useful to emphasize the coplanarity of the equatorial ligands.

ACCEPTABLE	ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

A fourth case, also viewed "from the side", is considered not acceptable. In this case, the third and fourth bonds are drawn as solid wedged bonds, both extending downward from the center, with the bisector of the angle formed by those bonds coincident with the y-axis. The fifth bond is drawn as a hashed wedged bond extending upwards from the center. A variation of this case has hashed wedged bonds drawn instead of solid wedged bonds and solid wedged bonds drawn instead of hashed wedged bonds; it is also considered not acceptable.

NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

A fifth case, also viewed "from the side" is also considered not acceptable. In this case, the third and fourth bonds are drawn as hashed wedged bonds, both extending upwards from the center, with the bisector of the angle formed by those bonds coincident with the y-axis. The fifth bond is drawn as a solid wedged bond extending downwards from the center. A variation of this case has hashed wedged bonds drawn instead of solid wedged bonds and solid wedged bonds drawn instead of hashed wedged bonds; it is also considered not acceptable.

NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Sample depictions of some compounds known to exist in trigonal bipyramidal configuration:

PREFERRED	PREFERRED

 

Square pyramidal

Polyhedral symbol: SPY-5

Number of ligands: 5

Square pyramidal configurations have five ligands, like trigonal bipyramidal configurations, but the configurations themselves are different enough that confusion is rare.

The first recommended depiction views the pyramid from the front. This depiction should be drawn with two solid wedged bonds and two hashed wedged bonds. The two solid wedged bonds should be positioned below the central atom, while the two hashed wedged bonds should also be positioned below, but above the two solid bonds. The bisectors of both angles should be coincident with the y-axis. The fifth bond is drawn as a plain bond extending exactly upwards from the center. This depiction emphasizes the noncoplanarity of the central atom with the four equatorial ligands and should not be used when it is known that the central atom is coplanar with them.

PREFERRED	NOT ACCEPTABLE

The second recommended depiction also views the pyramid from the front. This depiction should be drawn with two solid wedged bonds and two hashed wedged bonds. The two hashed wedged bonds should be positioned above the central atom, while the two solid wedged bonds should also be positioned above, but below the two solid bonds. The bisectors of both angles should be coincident with the y-axis. The fifth bond is drawn as a plain bond extending exactly downwards from the center. This depiction emphasizes the noncoplanarity of the central atom with the four equatorial ligands and should not be used when it is known that the central atom is coplanar with them.

PREFERRED	NOT ACCEPTABLE

The next two recommended depictions view the pyramid from the front. These depictions should be drawn with two solid wedged bonds and two hashed wedged bonds. The two solid wedged bonds should be positioned below the central atom, while the two hashed wedged bonds should be positioned above. The angle between the solid wedged bonds should be equal to the angle between the hashed wedged bonds, and the bisectors of both angles should be coincident with the y-axis. The fifth bond is drawn as a plain bond extending exactly upwards or exactly downwards from the center. These depictions (and all of the subsequent ones) emphasize the coplanarity of the central atom with the four equatorial ligands and should not be used when it is known that the central atom is not coplanar with them.

PREFERRED	PREFERRED	NOT ACCEPTABLE	NOT ACCEPTABLE

A fifth depiction views the pyramid from the top. Four bonds are drawn as plain bonds, with equal angular spacing between them. The fifth bond is drawn as a solid wedged bond that may be positioned at any angle. This depiction is acceptable but not preferred for most cases. It is used primarily in cases where it is useful to emphasize the coplanarity of the equatorial ligands, and would be preferred primarily when all four bonds are required to be in the plane of the paper by virtue of other aspects of the structural diagram (such as with the central atom of metalloporphyrins). When square pyramidal configurations are drawn in this configuration, it is preferable for the bisectors of angles formed by adjacent bonds to be coincident with the x- and y-axes. The similar depiction with the bonds themselves positioned along the axes is acceptable but should be avoided.

PREFERRED	ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

The sixth acceptable depiction views the pyramid from a corner. Two bonds are drawn as plain bonds, extending exactly horizontally in either direction from the center. The third bond is drawn as a solid wedged bond extending downward from the center. The fourth bond is drawn as a hashed wedged bond that is collinear with the third bond, and therefore extending upwards from the center. The fifth bond is drawn as a plain bond extending exactly vertically upwards or from the center. As in the previous depiction, this would most commonly be used when all the axial and two equatorial bonds are required to be in the plane of the paper by virtue of other aspects of the structural diagram (such as with the central atom of metalloporphyrins).

ACCEPTABLE	ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Sample depictions of some compounds known to exist in square pyramidal configuration:

PREFERRED	PREFERRED

 

Octahedral

Polyhedral symbol: OC-6

Number of ligands: 6

Octahedral configurations are by far the most common for six ligands.

The first recommended depiction should be drawn with two solid wedged bonds positioned below the central atom, while two hashed wedged bonds should be positioned above. The angle between the solid wedged bonds should be equal to the angle between the hashed wedged bonds, and the bisectors of both angles should be coincident with the y-axis. Finally, two plain bonds should extend exactly vertically, upwards and downwards from the center.

PREFERRED	NOT ACCEPTABLE

It is also acceptable to draw similar configurations with plain bonds if the octahedral center is not itself chiral. Chiral octahedral configurations must be drawn with solid wedged bonds and hashed wedged bonds in order to confirm the specific chirality of the central atom.

ACCEPTABLE

A third depiction is formally correct, but is not preferred because it has so many stereobonds as to be confusing to the reader. This depiction is used primarily to emphasize the C₃ symmetry of a configuration, or to emphasize that a configuration is explicitly not trigonal prismatic. In this configuration, three solid wedged bonds and three hashed wedged bonds are separated by equal angular spacing with the solid wedged bonds and hashed wedged bonds alternating.

ACCEPTABLE	ACCEPTABLE

A fourth depiction should be drawn with four plain bonds. Two of those should extend exactly vertically, one each above and below the center. Two others should extend exactly horizontally, one each to the left and to the right of the center. A fifth bond should be drawn as a solid wedged bond, extending downward from the center either to the left or the right. The sixth bond should be drawn as a hashed wedged bond, positioned collinear with the fifth, and therefore extending upwards from the center. The similar depiction with the bisectors of the plain bondspositioned along the axes is also acceptable. It is also acceptable for the plain bonds to be rotated 45°, so that the bisectors of angles formed by adjacent plain bonds are coincident with the x- and y-axes.

ACCEPTABLE	ACCEPTABLE	NOT ACCEPTABLE	NOT ACCEPTABLE

Sample depictions of some compounds known to exist in octahedral configuration:

PREFERRED	PREFERRED

 

Trigonal prismatic

Polyhedral symbol: TPR-6

Number of ligands: 6

Trigonal prismatic configurations are rather uncommon, and can be distinguished from octahedral configurations without much problem.

The recommended depiction should be drawn with two solid wedged bonds, two hashed wedged bonds, and two plain bonds. The two solid wedged bonds should be positioned to the right of the central atom, and the bisectors of the angle formed by these bonds should be coincident with the x-axis. The two hashed wedged bonds should be placed similarly, with the angle between them sufficiently larger or smaller than the angle between the solid wedged bonds so as to avoid overlap. The two plain bonds should be placed collinear with the two hashed or solid wedged bonds that form the smaller angle, and hence should extend to the left of the center. Similar depictions with the left and right sides reversed are also acceptable.

PREFERRED	ACCEPTABLE	PREFERRED	ACCEPTABLE

To further emphasize the perspective implied by the solid and hashed wedged bonds, the two solid wedged bonds may be adjusted so that they are slightly longer than but less than 150% of the length of the hashed wedged bonds.

PREFERRED	ACCEPTABLE	PREFERRED	ACCEPTABLE

Two other depictions are formally correct, but are discouraged because they have so many stereobonds as to be confusing to the reader.

NOT ACCEPTABLE	NOT ACCEPTABLE

The two depictions shown below should be strongly avoided because they imply that the central atom is coplanar with four of its ligands.

NOT ACCEPTABLE	NOT ACCEPTABLE

Additionally, this is the first configuration that is commonly depicted as the polyhedral solid, showing lines between ligands and not showing the central atom.

ACCEPTABLE