Spin-only magnetic moment: mu = sqrt(n(n+2)) BM, where n = number of unpaired electrons. Values: n=1: 1.73 BM, n=2: 2.83 BM, n=3: 3.87 BM, n=4: 4.90 BM, n=5: 5.92 BM. Experimental magnetic moment helps determine spin state. If [Mn(CN)6]3- has mu = 2.83 BM, it has 2 unpaired electrons — confirming low spin d4 ($t2g^3$ $eg^1$ would give 4, but $t2g^4$ gives 2 for low spin — wait, low spin d4: $t2g^4$ $eg^0$ = 2 unpaired). Diamagnetic (mu = 0): all electrons paired. Examples: [Fe(CN)6]4- (low spin d6), [Ni(CO)4] (d10), [Zn(NH3)4]2+ (d10).