The orientation of the bonds to the ligands about the central metal depends on the coordination number.
The table below shows that as expected from the principles of VSEPR,
The examples also show that complexes with a coordination number of 4 may be either tetrahedral or square planar.
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Complexes of period 4 (first row - blue) transition metals tend to be tetrahedral
Complexes of transition metals from period 5 and 6 (second and third row) and Groups 10 and 11 tend to be square planar.
The table below shows that as expected from the principles of VSEPR,
complexes with a coordination number of two are linear, and
complexes with coordination numbers of six are octahedral.
complexes with coordination numbers of six are octahedral.
| Coordination number | 2 least common |
| Geometry |  |
| Examples | [Ag(CN)2]– |
| 4 more common | 6 most common | |
 |  |  |
| [CoCl4]2– [CuCl4]2– | [PtCl2(NH3)2] | [Fe(OH2)6]3+ [Cu(NH3)4(OH2)2]2+ [CoF6]3– |
The examples also show that complexes with a coordination number of 4 may be either tetrahedral or square planar.
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| 1 | 2 | ||||||||||||||||
| 1H |  | 2He | |||||||||||||||
| 3Li | 4Be | 5B | 6C | 7N | 8O | 9F | 10Ne | ||||||||||
| 11Na | 12Mg | 13Al | 14Si | 15P | 16S | 17Cl | 18Ar | ||||||||||
| 19K | 20Ca | 21Sc | 22Ti | 23V | 24Cr | 25Mn | 26Fe | 27Co | 28Ni | 29Cu | 30Zn | 31Ga | 32Ge | 33As | 34Se | 35Br | 36Kr |
| 37Rb | 38Sr | 39Y | 40Zr | 41Nb | 42Mo | 43Tc | 44Ru | 45Rh | 46Pd | 47Ag | 48Cd | 49In | 50Sn | 51Sb | 52Te | 53I | 54Xe |
| 55Cs | 56Ba | 71Lu | 72Hf | 73Ta | 74W | 75Re | 76Os | 77Ir | 78Pt | 79Au | 80Hg | 81Tl | 82Pb | 83Bi | 84Po | 85At | |
Complexes of period 4 (first row - blue) transition metals tend to be tetrahedral
This is particularly so if the ligands coordinated to the metal are large and negatively charged (Cl–, Br–).
The reason for this is that the tetrahedral bond angle (109.5°) is larger than the square planar bond angle (90°).
The reason for this is that the tetrahedral bond angle (109.5°) is larger than the square planar bond angle (90°).
Complexes of transition metals from period 5 and 6 (second and third row) and Groups 10 and 11 tend to be square planar.
The square planar complexes of platinum(II) are famous because the one above is used to treat some forms of cancer.