I hope you can help. I'm interested in finding a diamagnetic non-toxic gas which has a large amplitude (volume) magnetic susceptibility. I expect this to be difficult to achieve (as gases are inherently low density), but I wondered if there's a molecule out there which has an electron configuration which results in sufficient magnetization to overcome the low density of gases. The best gas I've found so far is butane, with a molar susceptibility of -5.7x10^-5 cm^3/mol.
If this is difficult, I'd be very happy if people posted list of useful resources.