[Fe(CN)6]^{4-} is the hexacyanoferrate(II) ion, also called ferrocyanide. In Inorganic Chemistry II, it is a classic octahedral coordination complex used to identify Fe(II), cyanide as a strong-field ligand, and 6-coordinate geometry.
[Fe(CN)6]^{4-} is the ferrocyanide ion, a coordination complex with one iron center surrounded by six cyanide ligands. In Inorganic Chemistry II, you will meet it as a standard example of how ligands, oxidation state, and geometry work together in one clean formula.
The metal here is iron in the +2 oxidation state, so the complex is named hexacyanoferrate(II). The six CN- ligands each donate a lone pair to Fe, giving the complex a coordination number of 6. That number almost always points you toward an octahedral arrangement unless the problem gives a special reason to expect something else.
Cyanide is a strong-field ligand, which matters a lot in coordination chemistry. Because CN- creates a large crystal-field splitting, the d electrons on Fe(II) are arranged differently than they would be with weak-field ligands. That affects magnetic behavior, color, and sometimes the stability of the complex. For this ion, the strong ligand field is one reason it behaves so differently from simple iron salts.
The formula also tells you something about charge balance. Six cyanide ligands contribute a total charge of -6. Since the whole complex is 4-, the iron must be +2. That kind of charge bookkeeping shows up constantly in naming and formula-writing problems, especially when you need to move between the name hexacyanoferrate(II) and the formula [Fe(CN)6]^{4-}.
A common misconception is to treat CN- as just another anionic ligand with no special behavior. In reality, cyanide is both a strong sigma donor and a pi acceptor, so it changes the metal's electronic structure more than many other ligands do. That is why [Fe(CN)6]^{4-} shows up so often when a course wants to illustrate strong-field ligand effects without adding extra structural complications.
[Fe(CN)6]^{4-} shows up whenever a course wants a compact example of coordination chemistry that still carries real structural and electronic information. It lets you practice the exact moves you need in Inorganic Chemistry II: find oxidation state, count coordination number, identify ligand type, and predict geometry from the formula.
It also gives you a reference point for ligand field ideas. Once you know that cyanide is strong-field, you can compare this complex with weak-field cases and see why d-electron splitting, magnetism, and color change from one ligand set to another. That comparison comes up again in spectra, bonding questions, and problem sets about high-spin versus low-spin behavior.
The ion is also useful because the name and formula each tell part of the story. If you can read hexacyanoferrate(II), you can reconstruct [Fe(CN)6]^{4-} and know that the metal is Fe(II), not Fe(III). That naming skill transfers directly to other coordination compounds, especially ones with multiple ligand types or charged complexes.
Keep studying Inorganic Chemistry II Unit 1
Visual cheatsheet
view galleryOxidation State
You use oxidation state to get from the formula to the metal charge. For [Fe(CN)6]^{4-}, each cyanide is -1, so six ligands give -6 total and iron must be +2 to make the complex 4-. That same charge counting shows up in naming and in redox questions about whether the metal center is Fe(II) or Fe(III).
Coordination Number
This complex has coordination number 6 because six ligands are attached to the central iron atom. In Inorganic Chemistry II, that number is a fast clue for geometry, and 6 usually means octahedral. When you see a coordination number in a problem, you are not just counting atoms, you are predicting arrangement and bonding patterns.
Cyano
Cyano is the ligand identity inside [Fe(CN)6]^{4-}. The CN- ligand is strong-field, so it changes the electronic structure of the metal more strongly than many common ligands. If your course asks why a complex is low-spin, colored a certain way, or especially stable, cyano is often the reason.
Anionic Ligands
Cyanide is an anionic ligand, so it gets named with the ending -o in coordination nomenclature. That matters when you compare this compound with neutral ligands, because naming rules change depending on ligand charge. Seeing cyano in the formula helps you practice how anionic ligands affect both naming and total complex charge.
A quiz or problem set may give you [Fe(CN)6]^{4-} and ask you to name it, find the oxidation state, or predict the geometry. The move is straightforward: count the six CN- ligands, total their charge, and solve for Fe as +2. Then identify the coordination number as 6 and connect that to an octahedral structure.
You might also be asked about ligand field strength. In that case, cyanide is your clue that the complex is strong-field, so you should think about larger d-orbital splitting and the possibility of low-spin behavior depending on the electron count. If your instructor uses spectra or magnetism examples, this ion is a good one to label as a strong-field coordination complex rather than a simple ionic salt.
[Fe(CN)6]^{4-} is the Fe(II) member of the hexacyanoferrate pair, while [Fe(CN)6]^{3-} contains Fe(III) and is ferricyanide. The ligands are the same, but the metal oxidation state and overall charge are different, which changes electron count and some physical properties. If you mix them up, check the charge first.
[Fe(CN)6]^{4-} is the ferrocyanide ion, a hexacyanoferrate(II) complex with iron in the +2 oxidation state.
The complex has coordination number 6, so it is octahedral in the usual coordination-chemistry picture.
Cyanide is a strong-field ligand, which makes this ion useful for discussing d-orbital splitting, spin state, and magnetic behavior.
You can get the iron oxidation state by adding the six -1 ligand charges and matching the overall 4- charge.
This ion is a standard naming and formula-writing example because the ligand name, metal oxidation state, and complex charge all have to line up.
It is the ferrocyanide ion, a coordination complex with Fe(II) in the center and six cyanide ligands around it. The formula shows an octahedral 6-coordinate complex, and the charge balance tells you the metal is iron in the +2 oxidation state.
It is octahedral. The coordination number is 6, and six-coordinate complexes are usually octahedral unless the problem gives a special structural reason otherwise. Square planar is more typical for certain 4-coordinate complexes, not this one.
Cyanide creates a relatively large splitting between the metal d orbitals, so it is called strong-field. That changes how Fe(II) electrons fill the orbitals and can affect magnetism and color. In problems, cyanide is a signal that ligand field effects matter.
The name is hexacyanoferrate(II). The prefix hexa- tells you there are six cyanide ligands, and the (II) tells you iron is in the +2 oxidation state. If you see the 3- analogue instead, that is hexacyanoferrate(III).