1. Determination Of Magnetic Moments In Metal-Metal Bonded Complexes
Daniel Villanueva1
1The Johns Hopkins University
Department Of Chemistry
Baltimore, MD

2. Background Information / Introduction
The idea that metal atoms could individually bond to other metal atoms was one that arose comparatively late in the development of inorganic chemistry
It was not until 1913 that a compound was discovered to have a metal-metal bond
Compounds are currently known containing not only metal-metal single bonds, but also double, triple, and even quadruple bonds

3. Problem / Hypothesis
Rhodium(II) acetate ethanolate and copper(II) acetate monohydrate were synthesized and characterized using Infrared Spectroscopy (IR) and Nuclear Magnetic Resonance (NMR), to determine specific bonding and their magnetic moments respectively. These magnetic moments were used to determine if a metal-metal bond exists.

4. Experimental Procedure
Part A: Rhodium(II) Acetate Ethanolate
50mg of rhodium(III) chloride hydrate, 100mg of sodium acetate trihydrate, 1mL of glacial acetic acid, & 1mL of absolute ethanol were refluxed for 1 hour
Part B: Copper(II) Acetate Monohydrate
160mg of copper(II) sulfate, 1mL of ammonia, & 80mg of sodium hydroxide flakes were stirred and heated for 25 minutes
IR & NMR spectra were collected
Coaxial NMR tube (See Figure 3) → Inner Tube: sample + DMSO; Outer Tube: only DMSO
Figure 3: Coaxial NMR Tube

5. Results Rhodium(II) Acetate Ethanolate Copper(II) Acetate Monohydrate
Blue-green crystals
IR Spectrum: C-H bond (2904cm-1), O-C-O bond (1720cm-1)
Copper(II) Acetate Monohydrate
Deep blue crystals
IR Spectrum: C-H bond (2950cm-1), O=C (1736cm-1), C-O bond (1260cm-1)
Figure 1: Structure of rhodium(II) acetate alcoholate [L = ethanol]
Figure 2: Structure of copper(II) acetate monohydrate

6. Results NMR Spectrum Of Rhodium(II) Acetate Ethanolate
Signal of solvent protons in outer tube
NMR Spectrum Of Rhodium(II) Acetate Ethanolate
Signal of solvent protons in inner tube
NMR Spectrum Of Copper(II) Acetate Monohydrate
Signal of solvent protons in outer tube
Signal of solvent protons in inner tube

7. Discussion Of Results
The nuclei of the NMR solvent in the two compartments are shielded differently due to the different volume susceptibility
Resulting shift difference of the absorption signals is related to the magnetic moment, μ, of the paramagnetic substance in the inner tube
μ = a√(T∆ν/c) *a = constant (2522x10-4 mol1/2K-1/2ml-1/2cps-1/2; T = absolute
temperature; ∆ν = shift difference (in cps) [1ppm = 10cps]; c =
concentration of solute
Rhodium(II) acetate ethanolate:
T = 293.8K; ∆ν = 8.35cps; c = x10-5mol/ml
μ = Bohr magnetons
Rh-Rh bond exists because the magnetic moment is small
Copper(II) Acetate Monohydrate
T = 293.8K; ∆ν = 11.45cps; c = x10-5mol/ml
μ = Bohr magnetons
Cu-Cu bond is absent because the magnetic moment is large

8. Conclusion Rhodium(II) acetate ethanolate contains a metal-metal bond
The unpaired electrons of rhodium(II) (d7) are strongly coupled and the complex is diamagnetic
Copper(II) acetate monohydrate does NOT contain a Cu-Cu bond
The unpaired electrons of copper(II) (d9) are weakly coupled and the highly populated low energy excited state is paramagnetic