How are metal carbonyls classified depending on the number of metal atoms?

Explanation

The structures of the binuclear metal carbonyls involve either metal-metal bonds or bridging CO groups , or both .The carbonyl ligands that are attached to only one metal atom are referred to as terminal carbonyl groups. Whereas those attached to two metal atoms simultaneously are called bridging carbonyls. Depending upon the structures metal carbonyls are classified as follows.
Non -bridged metal carbonyls:
These metal carbonyls do not contain any bridging carbonyl ligands .They may be of two types
(i) Non-bridged metal carbonyls which contain only terminal carbonyls . Examples: `[Ni(CO)_4], [Fe(CO)_5]and [Cr(CO)_6]`
Non-bridged metal carbonyls which contains terminal carbonyls as well as metal-Metal bonds ,For examples The structure of ` Mn_2(CO)_(10) ` actually involve only a metal -metal bond so the formula is more correctly represented as ` (CO)_5 Mn-Mn(CO)_5` Other examples of this type are ` T_(C_2) )CO)_(10 ) ` and `Re_2(CO)_(10 ) `
` (##SUR_CHE_XII_V01_C05_E12_011_S01.png" width="80%">