The most common coordination numbers are 2, 4 and 6. However, several examples of coordination compounds which have coordination numbers of 3, 5 and 7 are well known.
The trichloromercurate (II) complex ion is an example of CN 3 coordination complex and has a trigonal planar structure.
(bipy)(terpy)ruthenium (II), CN 5, has a square pyramidal structure. Three N atoms from the terpy molecule and one N atom from the bipy are bonded to the Ru atom at the corners of the equitorial square and the other N atom of the bipy molecule is bonded to the metal above the plane of the square.
For this coordinate complex, the CN 5 results in a trigonal bipyramidal structure. Three carbon monoxide molecules are bonded to the Fe atom at the corners of an equilateral triangle and the other two CO molecules are bonded to the metal above and below the plane of the triangle.
Iodine heptafluoride contains only main-group elements. CN 7 results is pentagonal bipyramidal structure. Note that five F ions are bonded to the I atom at the corners of a pentagon while the other two fluoride ions are bonded axially above and below the plane of the pentagon.
The CN 7 for hexaflurooxoniobate (III) results in a capped octahedron - triangular face structure. AS shown six F ions are bonded to the Nb atom in an octahedral arrangement. The O atom is bonded to the Nb atom at one of the triangular faces of the octahedron, thus capping the octahedron.