[Cu(NH3)4]2+ is a coordination complex with a Cu2+ center bonded to four ammonia ligands. In Intro to Chemistry, it shows how ligands donate lone pairs to a metal ion.
[Cu(NH3)4]2+ is a copper(II) coordination complex in Intro to Chemistry, made when one Cu2+ ion binds four ammonia (NH3) ligands. The copper is the central metal, and each ammonia acts as a ligand by donating a lone pair of electrons into a coordinate covalent bond.
The charge on the whole complex is 2+, because the copper ion starts as Cu2+ and the ammonia ligands are neutral. That is a common pattern in coordination chemistry: the ligands can change the shape and behavior of the metal without changing the ligand charge itself. If you are tracking oxidation state, the copper stays at +2 in this complex.
In a basic chemistry class, this complex usually comes up when you are learning how transition metals form coordination compounds and how ligands attach to them. The notation in brackets tells you the complex stays together as a unit. The subscript 4 tells you there are four ammonia ligands around the copper center.
The geometry of [Cu(NH3)4]2+ is often described as square planar in intro-level chemistry. That means the four ammonia ligands sit in one plane around the copper, instead of spreading out in a tetrahedral shape. Geometry matters because it affects the complex’s color, stability, and reactivity, which is why these compounds are so noticeable in lab and in reaction examples.
You may also see this complex in reactions where ammonia is added to a copper(II) solution. The solution can shift as ammonia replaces water molecules around Cu2+, forming a deep blue coordination complex. That color change is one of the easiest ways to recognize that a metal-ligand complex has formed.
[Cu(NH3)4]2+ gives you a concrete example of how coordination chemistry works instead of just describing it in theory. It connects three ideas you see early in Intro to Chemistry: oxidation state, bonding, and molecular geometry. Once you can read this formula, you can start unpacking a lot of other coordination compounds the same way.
This complex also shows why transition metals behave differently from many main-group elements. Copper can accept electron pairs from ligands, and ammonia can act as a Lewis base by donating its lone pair. That donor-acceptor relationship is a big part of why metal complexes form in the first place.
It also helps with lab observations. If your class adds ammonia to a copper(II) solution, the color shift is not random, it is evidence that a new complex has formed. Being able to connect a visible change to the structure behind it is a core chemistry skill, especially in labs and problem sets.
Finally, [Cu(NH3)4]2+ is a useful model for reading coordination formulas correctly. You can identify the central metal, count ligands, track charge, and connect the formula to geometry. That same process shows up again and again with other complexes, including ones with different ligands and different shapes.
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Visual cheatsheet
view galleryCoordination Complex
This is the bigger category that [Cu(NH3)4]2+ belongs to. A coordination complex always has a central metal ion or atom bonded to surrounding ligands, and the formula in brackets shows that whole unit. When you read this term, you are learning one specific example of the broader coordination-compound pattern.
Ligand
Ammonia is the ligand in [Cu(NH3)4]2+, and it is doing the electron-pair donation that makes the complex possible. Looking at the ligand helps you predict charge, bonding, and sometimes geometry. Different ligands can make the same metal form very different complexes.
Oxidation State
The copper in [Cu(NH3)4]2+ stays at +2, which is how you track the metal’s charge bookkeeping in the complex. Since ammonia is neutral, it does not change the oxidation state. This is the move you use when you separate ligand charge from metal charge.
Coordination Number
The coordination number here is 4, because there are four ligands attached directly to the copper center. That number helps you think about shape and bonding around the metal. In many intro problems, counting ligands is the first step before naming the geometry.
A quiz or problem-set question may ask you to identify the metal, ligands, charge, or oxidation state in [Cu(NH3)4]2+. You might also be asked to describe the bonding as coordinate covalent, explain why NH3 qualifies as a ligand, or connect the formula to square planar geometry. In a lab question, you could see a copper(II) solution turning deep blue after ammonia is added and need to explain that a coordination complex formed. If you are given several complexes, you may need to compare which one has the higher coordination number or which ligand is neutral. The fastest strategy is to parse the brackets first, then separate the central metal from the ligands, then check charge and geometry.
[Cu(NH3)4]2+ and [Fe(CN)6]4- are both coordination complexes, but they are not built the same way. Copper here is bonded to neutral ammonia ligands, while the iron complex uses cyanide ligands and has a negative overall charge. The metal, ligand type, charge, and geometry can all differ, so you cannot treat every complex formula the same way.
[Cu(NH3)4]2+ is a copper(II) coordination complex with four ammonia ligands attached to one central metal ion.
The ammonia ligands are neutral, so the complex keeps the +2 charge from the Cu2+ ion.
Each NH3 ligand donates a lone pair to copper, which is why the bond is described as coordinate covalent.
In intro chemistry, this formula is a model for reading coordination compounds, finding oxidation state, and counting coordination number.
The complex is often linked to the deep blue color seen when ammonia reacts with copper(II) solutions.
It is a coordination complex made of one copper(II) ion bonded to four ammonia ligands. In Intro to Chemistry, it is a standard example of how transition metals bind ligands through coordinate covalent bonds.
The copper is +2. The ammonia ligands are neutral, so they do not change the oxidation state of the metal ion in the complex.
No. It is a coordination complex, which means the metal and ligands are bonded in a specific structure that acts as one unit. The bonding and geometry matter, not just the charges.
That color change usually signals that a new copper-ammonia complex has formed in solution. In intro chemistry labs, the deep blue color is a visual clue that ligands have attached to Cu2+.